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                    PRINTED ON RECYCLED PAPER

















          MONITORING MARYLANDS CHESAPEAKE BAY OYSTERS
          A COMPREHENSIVE CHARACTERIZATION OF MODIFIED
                          FALL SURVEY RESULTS
                                 1990-1991


                      Gary F. Smith and Stephen J. Jordan

                   Maryland Department of Natural Resources
                Chesapeake Bay Research and Monitoring Division
                           Habitat Impacts Program
                         Cooperative Oxford Laboratory
                             904 S. Mortis Street
                           Oxford, Maryland 21654


                         Completed in cooperation with
                   Maryland Department of Natural Resources
                              Fisheries Division
                         Shelffish Propagation Program

                               September 1992








               Monitoring Marylands Oysters

                                                   EXECUTIVE SUMMARY
               This report presents two years of results           report is to stimulate suggestions from poten-
                                                                     al users as to possible survey modifications,
                                                                   ti
               (1'990-199 1) from a Maryland Chesapeake Bay        additional analysis to be performed, and report
               oyster monitoring program designed to charac-       format for future survey results.
               terize and assess the condition and trends of
               Maryland's oyster populations. The program          The approach of this monitoring program has
               was developed as a modification to the De-          been to assess the overall condition of the
               partment of Natural Resources, Division of          resource Baywide and dynamically over time.
               Fisheries, existing Fall Oyster Survey. The         The present Maryland oyster fishery is largely
               purpose of the modifications was to develop a       concentrated on a relatively few productive
               valid long-term oyster monitoring program           oyster bars, compared to Maryland's total
               from an existing survey which was geared to         oyster producing and growing bottom, upon
               providing qualitative information on a site-        which this survey concentrates. Although the
               specific basis, primarily for specific fishery      survey can provide direct answers to some
               management needs.                                   fishery management questions (e.g., spat
               The design of the modified survey is intended       density and disease prevalence in specific
               to provide annual estimates of Baywide and          areas are important in the repletion program),
               regional oyster spatfall intensity, mortality       it is designed primarily for broad scale assess-
               disease, and population size structure. Statis'     ment of the status of the resource and trends
                                                                   in response to natural and anthropogenic
               tical validity and consistency of data were         impacts.
               paramount considerations in the modified
               design. The aim was to assist oyster man-           Results suggest that parasitic infection by
               agement with a reliable and useful represen-        Perkinsus marinus (Dermo disease) was the
               tation of the resource, based upon a feasible       most significant factor affecting mortality and
               and cost-effective monitoring program con-          growth in oyster populations between 1990
               sistent with historical observations.               and 1991. Haplosporidium nelsoni (MSX
               The survey samples 64 "key", or regionall           disease), another parasite which recently has
                                                               y   been undetected in Maryland waters, also
               representative, oyster bars each year. Repli-       reappeared in 1990 and 1991. Although both
               cate samples provide information on spatfall,       diseases have been responsible for oyster
               population size structure, mortality, disease,      mortalities in Maryland waters since at least
               repletion history (i.e., the record of seed and     the 1950's, the current level of P. marinus
               shell placement), and physical characteristics.     disease is unprecedented.
               Data management and analysis are computer-
               automated, with mostly graphic output. The          Perkinsus disease levels at sampling sites
               objective of the data management system is to       correlated well with observed mortalities. In
               allow the data to speak to a variety of users.      1990, average estimated annual mortality on
               Numerical and statistical analyses are available    survey oyster bars was 17%. In 1991, this
               for specific needs. One objective of this initial   increased to 31     The highest percentage of

                                                                iii








                Monitoring Maryland's Oysters

                dying oysters was of a size range just below        0  Perkinsus marinus (Dermo disease) now
                that of a "market" or harvestable oyster. An           infects all surveyed oyster bars in Mary-
                additional effect of high P. marinus levels was        land.
                slow growth of affected populations.                0  The prevalence (percent of oysters infected)
                These high mortalities were responsible for a          of P. mafinus is higher than ever recorded
                noticeable Maryland Baywide decrease in                in Maryland, from records going back to
                relative oyster abundance between 1990 and             1960.
                1991. Actual quantification of this decrease is
                difficult due to the seeding of young oysters       0  Haplosporidium nelsoni (MSX disease)
                on some of the survey oyster bars.                     spread to a large percentage of surveyed
                                                                       oyster bars between 1991 and 1992.
                Spatfall relative to historical averages (Krantz
                1992) was poor to fair in 1990 and at histori-      0  Oyster mortalities in 1992 were higher than
                cal highs in 1991. Areas of highest spatfall           in 1991, reflecting the increased prevalence
                were also regions where P. marinus disease             and geographic distribution of both dis-
                was at its highest levels. The upper bay re-           eases.
                gions exhibited noticeably poor spatfall for
                both years.                                         0  Mortality of small (sub-market sized) oys-
                                                                       ters increased, very probably because of H.
                Although disease has been identified as a              nelsoni infections. This parasite, unlike P.
                major reason for the lack of marketable oys-           mafinus, generally kills oysters within the
                ters, the effects of harvest are also evident.         first year of infection.
                Analysis of the survey oyster bars which were
                harvested in both years (33% of total survey        The management implications of increased
                bars). estimated that 53% of market-sized           disease pressure and mortality will be dis-
                oysters were removed by harvest during a            cussed in the 1992 Population Status Report;
                given year. Seed repletion on many of these         however, the losses of both market and seed
                harvested oyster bars was vital to their re-        oysters in 1992 are expected to have severe
                maining productive.                                 impacts on the fishery beyond the 1992-1993
                                                                    season. Management options will be further
                Note added in proof                                 constrained by high mortalities of seed oys-
                During the period when this report was under-       ters, and the constriction of areas where
                going review and editing, the 1992 Modified         oysters can survive to market size in harvest-
                Fall Survey was completed. These results will       able densities.
                be reported in the annual Population Status
                Report for 1992, in draft as of March 22,
                1993. A few important findings are summa-
                rized below.






                                                                iv





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              Monitoring Maryland's Oysters


              ACKNOWLEDGEMENTS
              77se authors wish to express their gratitude to those whose contributions made the publication
              of this report possible.

              Thanks especial1y to SaUy Otto, Ron Klauda, and Mark Homer for scientific reviews and
              comments, as well as Jane Kellerfor editorial review. KeUy Greenhawk prepared many of the
              finalfigures and graphics for this report. Without the help of these people, this report would
              still be sitting on our desks.

              Funds for this pmject were provided in pail by a grant from the Maryland Coastal Zone
              Management Program.

              Survey Design                                     Pathology and Laboratory Services
                                                                Sara V Ott02
              C. Austin Farley'
              George E. Krantz2                                 C. Austin Farley
              Sara V. Otto                                      Lee Hamilton
              Roy Scot?                                         Donna Plutschak 2
                                                                Suzanne 7YIer'
              Field Data Collection                             Ben Straight2
              Roy Scott
              John Collier,                                     Data Entry
              Lee Daniels2                                      Margaret McGinty2
              Barbara Fetchk03                                  J. Eden Dunlop"
              John Hess'
                      y3
              Chris Jud
              George E. Krantz

              AFFILIA TIONS
              1 U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National
              Marine Fishefies Service, Cooperative Oxford Laboratory, Oxford, Maryland
              2Maryland Department of Natural Resources, Tidewater Administration, Chesapeake Bay
              Research and Monitoring Division, Cooperative Oxford Laboratory, Oxford, Maryland

              3Maryland Department of Natural Resources, Tidewater Administration, Fisheries Division,
              Annapolis, Maryland







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              Monitoring Maryland's Oysters
                                                           CONTENTS
                                                                                                           Page
              EXECVTIVE SUMMARY                                                                             iii


              ACKNOWLEDGEMENTS                                                                                v


              I. INTRODUCTION                                                                                 1


              II. METHODS                                                                                     3


                 Site Selection
                 Sampling Regime
                 Dredge Methodology
                 Laboratory Disease Analysis
                 Data Entry and Analysis

              III. RESULTS                                                                                   11

                 Spatfall and Recruitment to Fishery                                                         11
                      Spatfall
                      Recruitment of Spat into Fishery
                      Spatfall by Harvest Region
                      Replicate Spat Sampling
                      Recruitment of Spat into Year Class Population Structure
                 Population Structure and Mortality                                                          24
                      Mortality Statistics
                      Baywide Population Size Structure
                      Regional Population Age structures
                      Individual Site Age Structure
                 Disease                                                                                     40
                      Range and intensity of Perkinsus marinus (Dermo) infection
                      Baywide Changes in Perkinsus marinus, 1990 - 1991
                      Relationships Among Perkinsus marinus indicators
                      Association of 1991 Spat Densities with Perkinsus marinus
                      Association of Perkinsus marinus Intensity with Mortality
                      Reappearance of Haplosporidium nelsoni in Maryland
                 Harvest                                                                                     50
                      Harvested Oyster Bar Identification
                      Coparison of Harvested Oyster Bars to All MFS Bars
                      Estimation of Harvest Mortality

              IV. DISCUSSION                                                                                 63
                 Synopsis of Oyster Population Results                                                       63
                      Impact of Disease
                      Recruitment and Broodstock
                      Impact and Implications of Harvest
                      Potential for Management



                                                                 Vii









              Monitoring Maryland's Oysters

                The Modified Fall Oyster Survey - Design Considerations and Evaluation            68
                     Survey Design Criteria                                                       68
                             SITE SELECTION
                             SAMPLING REGIME
                             GEAR CONSIDERATIONS
                             SAMPLE SIZE
                     Improvements to Sampling Methodology                                         71
                             EFFECTS OF REPLETION (SEED AND SHELL)
                             SPAT MEASUREMENT
                             PHYSICAL DATA
                             DISEASE SUBSAMPLE
                             Box CLASSIFICATION
                             MANAGEMENT AND ANALYSIS OF SURVEY DATA
                             DATA DEVELOPMENT AND PRESENTATION FORMAT
                             SME-FREQUENCY ANALYSIS
                             SURVEY CALIBRATION NEEDS
                     Recommendations for Future Improvements to the Survey and for Uses of Data   75
                             INTERACTIVE STATISTICS
                             POTENTIAL FOR POPULATION MODELING
                             HimRicAL POPULATION AND DISEASE DATA


              V. LITERATURE CITED                                                                 77


              V1. APPENDICES                                                                      79

                A. Modified Fall Survey Data Storage Fields and Field Descriptions                79
                B. Spat Counts by Subsample and Total per Site (1.0 Bushel of Dredged Material)   84
                C. Mortality Data                                                                 88
                D. Disease and Condition Data by Site                                             91
























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              Monitoring Maryland's Oysters
                                                         :74BLES

                                                                                                          Page
              1. Modified Fall Survey sampling sites                                                          6

              2. Maryland Chesapeake bay oyster bars-geographic regions                                     11

              3. Maryland Chesapeake Bay harvest regions                                                    17

              4. Ratio of small oysters in fall 1991 to 1990 spat counts at three oyster bars               22

              5. Comparisons of mortality indices averaged over MFS sites                                   24

              6. Comparison of disease and condition indices, all sites 1990-1991                           45

              7. Sites exhibiting decreasing P. marinus intensity indices, 1990-1991                        46

              8. Modified Fall Survey oyster bars with presumed harvest activity, 1990-1991                 46

              9. Comparison of harvested and non-harvested oyster bars, 1990-1991                           55























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           Monitoring Maryland's Oysters
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             Monitoring Maryland's Oysters
                                                        fi@GURES
                                                                                                       Page
             1.   Modified Fall Survey sampling sites                                                      8
             2.   Modified Fall Survey sampling site codes                                                 9
             3.   Modified Fall Survey field data sheet                                                  10
             4.   Spatfall per bushel, 1990.                                                             12
             5.   Spatfall per bushel, 1991                                                              13
             6.   Spatfall averaged by region, 1990                                                      14
             7.   Spatfall averaged by region, 1991                                                      15
             8.   Oyster geographic regions, defined for aggregated site analysis                        16
             9.   Sites by spatfall range count, 1990 - 1991                                             18
             10.  Spatfall ranges averaged by region, 1990 - 1991                                        19
             11.  Baywide population structure by size class; a. 1990 ; b. 1991                          20
             12.  Oyster harvest regions                                                                 21
             13.  Spatfall per bushel averaged by region, 1990-1991                                      23
             14.  Replicate spat sampling confidence limits for three sites                              23
             15.  Comparison of 1990 spat count to 1991 Year I + age class                               25
             16.  Percent mortality by sampling site, 1990                                               26
             17.  Percent mortality by sampling site, 1991                                               27
             18.  Percent mortality by region, 1990                                                      28
             19.  Percent mortality by region, 1991                                                      29
             20.  Number of regions falling within designated mortality ranges, 1990-1991                31
             21.  Percent mortality by harvest region, 1990-1991                                         31
             22.  Average number of market sized oysters, 1990-1991                                      32
             23.  Average long-term and short-term mortality, 1990-1991                                  32
             24.  Baywide population structure by size class, 1990                                       33
             25.  Baywide population structure by size class, 1991                                       33
             26.  Total numbers of live and box oysters collected Baywide, 1990-1991                     33
             27.  Northern Bay-Chester River harvest region; a. 1990 ; b. 1991                           34
             28.  Choptank River-Little Choptank River harvest region; a. 1990 ; b. 1991                 34
             29.  Western Shore-Mid Eastern Shore harvest region; a. 1990 ; b. 1991                      34
             30.  Eastern Bay-Miles River harvest region; a. 1990     b. 1991                            35
             31.  Tangier Sound harvest region; a. 1990 ; b. 1991                                        35
             32.  Fishing Bay-Honga River harvest region; a. 1990      b. 1991                           35
             33.  Wicomico River-Nanticoke River harvest region; a. 1990 ; b. 1991                       36
             34.  Potomac River harvest region; a. 1990 ; b. 1991                                        36
             35.  Patuxent River harvest region; a. 1990 ; b. 1991                                       36
             36.  Choptank River-Tilghman Wharf (CRTW) oyster bar, 1991                                  37
             37.  Tangier Sound-Back Cove (TSBC) oyster bar, 1991                                        37
             38.  Holland Straights-Holland Straights oyster bar, 1991                                   37
             39.  Perkinsus marinus intensity index by site, 1990                                        41


                                                            xi








              Monitoring Maryland's Oysters

              40.  Perkinsus marinus intensity index by site, 1991                                      42
              41.  Perkinsus marinus intensity index by region, 1990                                    43
              42.  Perkinsus marinus intensity index by region, 1991                                    44
              43.  Number of regions falling within designated intensity index
                       ranges, 1990-1991                                                                47
              44.  Perkinsus marinus intensity index ranges expressed as
                       percentage of sites, 1990-1991                                                   47
              45.  Perkinsus matinus intensity index by harvest region, 1990-1991                       48
              46.  Perkinsus mafinus intensity index and severity index
                       vs. percent prevalence, 1991                                                     48
              47.  Perkinsus marinus intensity index, 1990                                              49
              48.  Perkinsus marinus intensity index vs. salinity, 1991                                 49
              49.  Perkinsus mafinus intensity index values at sites of
                       spat counts > 300 per bushel, 1991                                               51
              50.  Perkinsus marinus intensity index vs. long-term mortality                            52
              51.  Perkinsus marinus intensity index, percent prevalence, and
                       percent mortality, 1990-1991                                                     52
              52.  Haplospofidiwn nelsoni (MSX) intensity and prevalence, 1990                          53
              53.  Haplosporidium nelsoni (MSX) intensity and prevalence, 1991                          54
              54.  Mortality vs. Perkinsus matinus intensity index for harvested
                       and non-harvested oyster bars, 1991                                              58
              55.  Number of market oysters vs. Perkinsus marinus intensity index
                       for harvested and non-harvested oyster bars, 1991                                58
              56.  Baywide population structure of harvested oyster bars, 1990                          59
              57.  Baywide population structure of harvested oyster.bars,  1991                         59
              58.  Northern Bay, Chester River harvest region; a. 1990; b. 1991                         60
              59.  Mid-Eastem Shore, Choptank River harvest region; a. 1990; b. 1991                    60
              60.  Western Shore harvest region; a. 1990 ; b. 1991                                      60
              61.  Lower Eastern Shore harvest region; a. 1990 ; b. 1991                                61
              62.  Potomac River, Patuxent River harvest region; a. 1990    ; b. 1991                   61
              63.  Comparison of 1990 harvested bars population structure
                       to actual harvested bars, 1991                                                   62
              64.  Simulated harvest mortality on harvested oyster bars based
                       on grow-out of the 1990 live oyster population                                   62









                                                             xii








              Monitoring Maryland's Oysters


                                                     L INTRODUC77ON
              !-Vhe dramatic decline of the Maryland oyster       well as management strategies, stock enhance-
                                                                  ment methodologies, and research which could
              fishery over the past several years has been a      turn around the decline.
              matter of great concern to the industry, re-
              sponsible government agencies, and the public       For any of the above approaches to be suc-
              as a whole. Historically, the Chesapeake Bay        cessful, reliable information must be available
              had been the largest producer of oysters in the     from oyster monitoring programs. Such pro-
              United States. As recently as 1974, the Mary-       grams must be consistent from year to year
              land portion of Chesapeake Bay produced             and provide accurate and defensible data.
              2,800,000 million bushels of oysters annually.
              By the mid- 1980's, the harvest had declined to     Maryland historically has collected informa-
              approximately 1,000,000 million bushels (R.         tion on various aspects of its Baywide oyster
              Scott, MDNR, pers. comm.). By 1990, oyster          resource. Generally, these programs have
              yield had fallen to 418,000 bushels, and in         been designed to address specific and imme-
              1991, 322,000 bushels.                              diate management needs. The Maryland De-
              The effect of this decreasing harvest has been      partment of Natural Resources, Fisheries
              most dramatic in historically high producing        Division (and its predecessors) have been
              areas. The Tred Avon River, a small tributary       collecting oyster bar data from 1939 onward.
              of the Choptank River, produced 124,000             This annual survey has been referred to as the
              bushels of oysters in 1984. By 1991, harvest        Fall Survey. Spatfall, mortality, number of
              was reduced to 750 bushels. Eastern Bay             oysters, fouling, physical data, and many
              produced 900,000 bushels of oysters in 1973,        other variables have been recorded. Although
              but only 20,000 bushels in 1991. Only in the        these data have multiple uses, the primary
              Chester River has harvest maintained typicall       purpose was to provide information to assist
                                                              y   decisions about planting cultch (shell) and
              historical levels (-50,000 bushels; 1970's          moving spat.
              averages), due largely to extensive transfer
              and placement of oyster spat in this region         The Fisheries Division has also collected
              through the State's Repletion Program. Cur-         oyster harvest data based on regional landings.
              rently, this area, other northern Bay regions,      In addition to this harvest data, aerial surveys
              and upper reaches of some tributaries support       are periodically made to assess the geographic
              the remnant Maryland oyster harvest.                distribution and effort (boat counts by gear
              The historically low harvest of the 1991-1992       type) of the oyster fishery.
              oyster season has raised questions as to wheth-     Since the 1960's, oyster disease data have
              er the oyster industry in Maryland has a viable     been compiled by the Maryland Department of
              economic future. These concerns have not            Natural Resources in cooperation with the
              been ignored. Much effort has gone into             National Marine Fisheries Service. The preva-
              understanding the causes of this decline, as        lence and intensity of the oyster parasites

                                                               I








                 Monitoring Maryland's Oysters

                 Haplosporidium nelsoni (MSX) and Perkinsus             mation that can be recovered from the current
                 ma.rinus (Dermo) are the most important as-            survey.
                 pects of these data.
                                                                        The discussion has two parts. First is the
                 Modifications to the Fisheries Division Fall           development of an integrated interpretation of
                 Survey were made in 1990 and 1991; these               the four components of the results. Character-
                 were enhancements rather than a replacement            istics of Maryland's oyster populations are
                 of the existing survey. Historical data sheets         briefly reviewed in the context of a traditional
                 are completed as always. The modified design           population dynamics framework, accompanied
                 does not deviate from the historical survey in         by a simple model that attempts to estimate
                 a manner that would not allow direct com-              relative fishing mortality and the effects of
                 parison with historical data. The primary              seed on repopulating harvested oyster bars.
                 purposes of the modifications were to stan-            The second part of the discussion is a general
                 dardize sampling locations and protocols, and          review of the merits and limitations of the
                 to introduce replicate samples to allow statisti-      MFS, with recommendations for additional
                 cal inferences to be made for individual sam-          enhancements to this important monitoring
                 pling sites.                                           program-

                 This report presents results for the two years
                 that the Modified Fall Survey (MFS) has been
                 conducted (1991 and 1992). Although Fall
                 Survey data and oyster disease data have been
                 collected in a standard format from the 1960's
                 onward, comparison with this information is
                 not included within this report. Historical
                 analysis is a project objective, but will require
                 additional verification, calibration, and data
                 base integration. This work is now in progress
                 and will be described in another report.

                 Results have been organized into four major
                 population components: 1) recruitment; 2)
                 population structure and mortality; 3) disease;
                 4) harvest implications. The presentation is
                 mostly graphical. This report is not directed
                 toward hypothesis formulation and testing, but
                 rather a descriptive characterization. We hope
                 that this approach will provide a basis for
                 future analysis. Analysis of harvest activity
                 effects is limited to comparisons of the charac-
                 teristics of harvested oyster bars to those of
                 non-harvested oyster bars-the extent of infor-


                                                                    2








               Monitoring Maryland's Oysters

                                                         IL METHODS
               k
                   e Selection                                     C sampling locations on given oyster bars.
                  it                                               Because typical oyster bars cover a large area
               Sixty-four charted oyster bars distributed thr-     of bottom and vary greatly from point to point
               oughout the Maryland portion of Chesapeake          in character, sampling was done at the same
               Bay (Figures I and 2; Table 1) were chosen to       location on each oyster bar from year to year.
               provide geographical coverage of oyster
               regions of the State. These oyster bars were        Small inconsistencies between 1990 and 1991
               sampled for population variables consistently       sampling occurred due to oversights in coordi-
               from year to year to allow direct yearly com-       nation. In 1990, MADP (Manokin River-
               parisons. Samples from a subset of 43 of these      Drum Point) was omitted from the 64 moni-
               oyster bars were analyzed for P. marinus and        toring sites. Oyster bars selected for the
               H. nelsoni.                                         disease subsample also varied from the 42
               Site selection represented a consensus of           initially chosen. In 1991, one other oyster bar
               Cooperative Oxford Laboratory and Fisherie          CRRO (Choptank River-Royston) was ana-
               Division personnel, based on the followin        s  lyzed for disease. This additional site is now
               criteria:                                        9  considered as part of the disease monitoring
                                                                   subset.

               ï¿½ Full geographical coverage of historical
                  oyster-producing regions in the Maryland         These inconsistencies had little or no impact
                  Bay, not just current harvest producing          on the results reported here. The majority of
                  areas;                                           comparisons between years are represented as
                                                                   averages. Where summations were used in
               0  Greater coverage in Bay regions which            analysis, aggregrate differences between years
                  historically had been major oyster-produc-       greatly outweighed any variation due to single
                  ing regions (i.e. oyster bars were not ran-      sites.
                  domly selected Baywide);                         Sampling Regime
               ï¿½  Close correspondence with previously de-         All 1990 samples were collected between
                  fined "key bars" to maintain consistency         October 8 and November 16. In 1991, sam-
                  with historical spat count data (Krantz          ples were obtained between October 15 and
                  199 1);                                          November 18. The choice of fall for sampling
                                                                   is a compromise among three factors: 1) the
               ï¿½  Retain oyster bars which had been sampled        spring-summer spat set must grow to a size to
                  most frequently in the historical Fall Sur-      be visually identified; 2) P. mafinus and H.
                  vey, and those for which the most complete       nelsoni generally have exerted their effects on
                  records of disease existed.                      the population (mortality) during the preceding
                                                                   summer; 3) although the oyster harvest season
               Oyster bar latitudes and longitudes shown in        begins before the time of sampling, early fall
               Table I are those of the uncorrected LORAN          sampling minimizes the effects of harvest,
                                                                   given the other constraints on the survey.


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               Monitoring Maryland's Oysters

               Dredge Sampling Methodology                          5 A history of seed and shell placement on
               Oyster dredges had a 3 ft. (91.4cm) wide                the sampled portion of the oyster bar was
               opening with 12 teeth on the bottom trawl bar.          recorded by year of activity
               Tooth length varied between 2.5-3.25 in. (6.3-
               8.3cm). A chain bag constructed of 2 in.             6  Site identifications, salinity, temperature,
               (5. lcm) diameter steel rings extended back 20          and bottom depth
               in. (50.8cm) along the bottom -of the trawls.
               The remainder of the trawl bags were con-            7  At sites designated for disease samples, 30
               structed of 1.5 in. (3.8cm) square nylon mesh.          or more oysters greater than 50mm in
               A completely filled dredge holds approximate-           length were selected at random and retur-
               ly 2.0 bushels of material.                             ned to the Cooperative Oxford Laboratory
                                                                       for disease analysis. The minimum size
               Five independent dredge       tows were taken           restriction was due to laboratory processing
               from each of the 64 sites.    Tow distance was          limitations.
               based on filling the dredge bag with sufficient
               material to provide a complete sample. From          Laboratory Disease Analysis
               each of these five tows, 0.2 bushels of materi-      Diagnosis for P. marinus and H. nelsoni was
               al was extracted at random. Variables 1-3            conducted at the Cooperative Oxford Labora-
               below were recorded separately from each of          toTy. The standard technique employed for P.
               the five samples. Variables 4-6 were recorded        marinus analysis was rectal thioglycollate
               from the pooled full sample.                         culture (Ray 1952). Blood thioglycollate
                                                                    culture was also employed for most sites in
               1  Total spat count                                  1990 and a small number of sites in 1991.

               2  Measurement of each live oyster to 5mm            Analysis for H. nelsoni was conducted for
                  size classes                                      selected sites in both 1990 and 1991. Site
                                                                    selection was based on presence of high salini-
               3  Measurement of oyster boxes (dead oysters         ty in areas where resurgence of the disease
                  with two shell halves still attached). Each       was expected first to occur. Both blood histo-
                  box was categorized by relative time since        cytology and tissue histocytology methods
                  death: gaper (meat still intact); stage I         were employed for diagnosis, depending upon
                  (meat absent-inside of shell with light or        site and year.
                  absent fouling); stage 2 (inside of shell with
                  moderate fouling); stage 3 (inside of shell       Laboratory analysis determined individual
                  with heavy fouling).                              levels of infection for both A marinus and H.
                                                                    nelsoni for 30 oysters from a given oyster bar.
               4  Fouling of the sample (percent) was deter-        Stages ranged from 0 (no infection detected),
                  mined by category (mussels, MoIgula man-          to 7 (highest infection detectable). Three
                  hattensis, other). If there was sufficient        representive indices were calculated for each
                  fouling to affect sample volume significant-      oyster bar.
                  ly, fouling organisms were removed before
                  taking 0.2 bushel subsamples.


                                                                 4








             Monitoring Maryland's Oysters

             1 Percent prevalence of disease                    plantings with correct geographical designa-
                                100                             tions.
                                                                Appendix A details data storage file field
                                                                descriptions and statistical calculations used to
             2 Severity index                                   generate the summary statistics file.

                   DI+2D2+3D,+4D4+5D$+6DS+7D7       iD,

             3 Intensity index

                   DI+2D2+3D3+4D,+5DS+6D6+7D.       iD,
                                N                   N



                where Di = number of oysters at a given
                stage (i = 1-7) infected in the sample; I =
                number of oysters in the sample having
                infection (stage 1-7); N = total number of
                oysters in the sample (30).

             Data Entry and Analysis
             Data were entered into the computer directly
             from field sheets (Figure 3). Interactive entry
             programs prompt the user for study specific
             data. Data storage, entry, and analysis were
             primarily in dBase In+ format. All field data
             sheet infbrmation was entered and used in
             analysis.

             Present use of the data entry and analysis
             system has been for MFS data only. However,
             our computer sorting and filtering routines
             allow for entry and analysis of any oyster
             field data that follow the format of the MFS
             field sheet. Examples of such supplementary
             oyster data which could be analyzed are
             seasonal surveys, response surveys for critical
             needs, and seed and shell planting analyses.
             Files and program routines are on hand to
             identify known oyster bars and seed and shell



                                                              5








                    Monitoring Mary&nd's Oysters

                    Table 1. ModOW77all Survey sampling site*.-latitude and longitude we in degrees, minutes, and seconds. Cod" are those used
                    for computer storage at the Cooperative Oxford Laboratory. An "X' in the last column indicates that the she is sampled for
                    disease analysis.


                    code                 Anse                          ovellor Ber                    Ladbails  L=%ghude             Disease
                                                                                                                                     80100101"
                    BCDN                 Broad Creek                   Deep Nock                      384417    761433               X
                    BNMP                 Bay Bridge North              Mountain Point                 390509    762502
                    BNSP                                               Swan Point                     390827    761810               X
                    CHOR                 Chester River                 Buoy Rock                      365938    761242               X
                    CHOF                                               Old Field                      390448    760952               X
                    CRCP                 Choptank River                Cook* Point                    383909    761726               X
                    CRU                                                Lighthouse                     383927    761122               X
                    CROS                                               Oyster Shall Point             3WS18     760001               X
                    CRRO                                               Royston'                       384116    761430               X
                    CRSH                                               Sandy Hill                     383639    760700               X
                    CRTW`                                              Tilghman Wharf                 384247    761915               X
                    EBBU                 Eastern Bay                   Bugby                          385255    761320               X
                    EBHN                                               Hollicults N                   385114    762106               X
                    EBPI                                               Parsone Island                 385420    761602               X
                    EBWG                                               Wild Ground                    385339    761900
                    FBCI                 Fishing Bay                   Clay Island                    381422    755902
                    FBQC                                               Goo" Crook Addition            381702    760130               X
                    HCEP                 Harris Creek                  Eagle Point                    3B4345    761824
                    HOHO                 Holland Straka                Holland Straka                 3806"     760430               X
                    HRNO                 Honga River                   Normans                        301619    760815               X
                    HRWI                                               Windmill                       381659    760932
                    LCCA                 Little Choptank River         Cason                          3113159   761421               X
                    LCAP                                               Ragged Point                   383218    761760               X
                    MADP                 Manokin River                 Drum Point2                    380705    755216
                    MAGE                                               Georg" Ber                     380727    755124               X
                    MESR                 Mid-Eastern Shore             Stone Rock                     383920    762259               X
                    MRAS                 Miles River                   Ashcroft                       384741    761241
                    MRBI                                               Bruffs Island                  385129    761135               X
                    MRLP                                               Long Point                     384613    761032               X
                    MRTU                                               Turd* Back                     385119    761421               X
                    NRMG                 Nanticoke River               Middle Ground                  381345    766519
                    NRWE                                               Wotipiquin                     381959    756316
                    NRWS                                               Wilson Shoal                   381735    756518               X
                    POSH                 Poplar Island                 Shell Hill                     384523    762119
                    PROS                 Potomac River                 Blue Sow                       381404    764216
                    PRBW                                               Week Walnut                    381454    764105
                    PRCH                                               Cornfield Harbor               380253    762001               X
                    PRDC                                               Dukehart Channel               381315    764451
                    PRLC                                               Lower Codar Point              381959    766850               X
                    PRRP                                               Ragged Point                   380922    763633               X
                    PSGU                 Pocomoke Sound                Gunby                          375706    754626
                    PSMA                                               Marumeco                       376733    764409               X
                    P)(BA                Patuxent River                Back of Island                 381914    762739
                    PXBI                                               Broomes Island                 382428    763351               X
                    SMCC                 St. Marys River               Chickencock                    380723    762613               X
                    SMPA                                               Pagan                          381130    762636               X
                    TADM                 Trod Avon River               Double Mille                   384347    760825               X
                    TSBC                 Tangier Sound                 Back Cove                      380225    765939               X
                    TSQR                                               Great Rock                     375706    755506
                    TSOW                                               Old Womane Log                 375747    755823               X
                    TSPI                                               Piney Island                   380409    755734               X
                    TSSS                                               Sharkfin Shoal                 381256    755929               X




                                                                                        6








                    Monitoring Maryland's Oysters

                    Code               Ares                           oy Ber                      LaftWe    Lonsituds,          Disesse,
                                                                                                                                 S-Wim
                    TSTE               ITangler Sound)                Turtle Egg Island            380654    756928
                    UBBH               Upper Bay                      Brick House                  385620    762306
                    UBHA               Upper Bay                      Hacketts                     385869    762500              x
                    USTS                                              Three Voters I= Coots)       385138    762750
                    WRES               Wicomico River                 Evans Shoal                  381231    765341
                    WRIAV                                             Mt. Vernon Wharf             381515    754820
                    WSBU               Western Shore                  Butler
                                                                      (St. Mary@ Co. Shore]        380632    761937              x
                    WSFP                                              Flag Pond                    382606    762609              x
                    wSH`                                              Hog bland                    381854    762301              x
                    WSHP                                              Holland Point                38"07     763008              x
                    WWLA               Wicomico River lwoet)'         Lancaster                    381636    7649"               x
                    WWMW                                              MiNs West                    3B2009    765129              x


                    Not sampled in 1990 for disease.
                    Not sampled In 1990 for Fail Survey.
                    20womac River tributary.







                Monitoring Maryland's Oysters




                                                                                               it eA



















































              Figure 1. Northern Chesapeake gay with Modified Fall Survey sampling site* (hatched boxes). The subset of sites monitored for
              diseases are indicated by bold crosses. Geographical regions used in analysis are separated by lines.



                                                                            8






             Monitoring Marylands Oysters




                                                                            +








                                                                                   +






                                                                                  +
                                                               +  Eaf@     MTL,44+

                                                                                      +


                                                            + tW5W


                                                                                 +

                                                                     + *MEER + -CFCP



                                                                                          +           tCFM









                                                       +




                                +


                                                                                                          + 444S


                                                                                                                     4-W"
                                    Ib                                                               +i
                                           -FFUC                                                    +



                                                                          + -WmJ                              ++
                                                                                               I+ + *Tq-j
                                                                                                    +





                                                                                                    TSGW +           +






            Figure 2. Northam Chesapeake Bay with Modified Fall Survey site codes.





                                                                    9







                        Monitoring Maryland's Oysters

                                                                 (701117-rZDW SITP(DLDW&m0S LE6 C0LL.DATFjq[q& COLL.DY                                                         stir[". I
                                                                         L0IIC;.J!5&jWSAL.L 5 Twt,                               -t DrPTII 12- nrc. sy                       F?FC. VATF
                                                                                                           T _             _2j.S _                -                 -
                                                                 sun.'rypr: FALL-M I III -SEED-OTIIER (DESCRI13E_FALJ--                          DIS -       -REQ. ny-
                                                                 j 1 1. v E-01        each oyster w1th_;A-mp.1 t cam-efrom. I.E.11_1224445!i)

                                                                 972.@ 4

                                                                 3.0-1.4
                                                                    IH1-11 -
                                                                 i.O-@4@4_ U41 On 11                                                                                        RPAT COUNT
                                                                 4. 5 -
                                                                    Jill                                                                  UH Jul                    T
                                                                    "TI  I            111               1111                                                                                      RT
                                                                 5!5::               -lid- L -- ---.
                                                                                      w -IF1                                              LOW 11
                                                                    unow                                                                                            .2 itff ml m wr 114
                                                                 6.5-6 AM             IIII             J1w Wd H                                                     - Ila md 1wIw m               UK
                                                                 0--7


                                                                 11 5 7: S. 9_                                                                                        w ml 511 im fill
                                                                 2.0-i.4
                                                                 2--90 2-                                                                                             ILK Md un lilt-





                                                                 5-13.                                                                                         SAMPLE SIZE . zo
                                                                 14.0- 4.
                                                                 ji-S-1                                                                                             FOULING - It Voltime
                                                                                                                                                                      A@Alive D=Dead

                                                                                                                                                                    HUSS.

                                                                                                                                                                    MOLG.

                                                                                                                                                                    OTIIER.


                                                                 !jS_-qCXES: (gro !oL-a-JLL-9q-m                        PeC_j=__CJjJ                                                  31


                                                                 2.5-2.9
                                                                 iLgL- i:!c                                             - I                                         YR.        SEED/SIIELL
                                                                 ]-!5 =2


                                                                                                      33
                                                                 5.5 5.9
                                                                 6. Q-7;

                                                                 7.0-7.4


                                                                 9-5-71- 9                                                                                                  NOTES:
                                                                 9.0-q.4-
                                                                 L. s 9
                                                                 10.0-10.4                                                                                  In


                                                                 12. 0--


                                                                 i -5z 1.3@9


                                                                 15A) - 15. 4

                                                                 16-..4
                                                                 16. 5 -1.6. 9.-                                                         -





                    Figure 3. Modified Fall Survey field data shoot, as completed for TSOW in 1991 (reduced).
                                                                 2.




                                                                 i-.
                                                                 0 15





























                                                                 0-
                                                                 1.4M
                                                                 1.
                                                                 4

















                                                                                                                     10









                   Monitoring Maryland's Oysters

                                                                        III. RESULTS



                                                                                    analysis (i.e., Northern Bay Flats, Sassafras
                   Spatfall and Recruitment to Fishery
                   Spatfall                                                                 River, Northern Bay Neck, upper rivers and
                   Spatqfall counts in Maryland Chesapeake Bay                      upper mainstem). In 1990, the great majority
                   waters were very different between 1990 and                      of the Bay's oyster regions produced <20
                   1991. The mean spatfall for all MFS sites was                     spat per bushel. Only three regions had > 100
                   43 per bushel in 1990 and 215 in 1991. In                        spat per bushel. This pattern reversed in 1991,
                   comparison with historical data (1939 to                         with counts > 100 in more than half of the
                   present; see Krantz 1992), the 1990 spatfall                     Bay's oyster regions. In 1991, four of Mar-
                   was below the long-term average of 55 spat                       yland's oyster growing regions produced more
                   per bushel, whereas the 1991 set was far                         than 300 spat per bushel.
                   above average.
                                                                                    Table 2. Maryland Chesapeake Bay oyster bare-geographic
                                                                                    regions. Refer to Figure 8 for geographic boundaries. A = num-
                   Spatfall in both years was highly variable on                    ber of sites sampled for population data; B =number of sites
                   a bar by bar, as well as on a regional basis.                    sampled for disease data.
                   Gross regional trends were, however, very
                   apparent (Figures 4 and 5). Spat counts for                                          Geographic Region            A          B
                   individual oyster bars were tabulated in Ap-
                   pendix B.                                                        1.       Upper Bay mainstem                      3          1
                                                                                    2.        Chester River Region                   2          2
                                                                                    3.        Middle Rivers - Upper Bay              1          0
                   The 1990 set could be considered good only in                    4.        Lower Rivers - Upper Bay               1          1
                                                                                    5.        Eastern Bay                            4          3
                   the Tangier Sound region, portions of the                        6.        Miles-Wye Rivers                         4          3
                   lower Potomac River, and the Little Choptank                     7.        Mid-Bay mainstem                        4          3
                                                                                    S.        Lower Choptank River                   7          6
                   River. In 1991, spatfall was excellent in these                  9.        Upper Choptank River                    2          2
                   regions as well as the Choptank River, mid-                      lo.       Little Choptank River                  2          2
                   mainstem of the Bay, and Eastern Bay. In                         11-       Lower Bay maqinstem                     1          1
                                                                                    12.       Hongs River                            2          1
                   both 1990 and 1991, spatfall was poor or                           13.       Fishing Bay                            2          1
                   absent in the upper Bay and Chester River re-                    14.       Nanticoke-Wicomico Rivers              6          1
                                                                                    15.       Manokin-Big Annemessex Rivers           2          1
                   gions.                                                           16.       Pokomoke Sound                         2          1
                                                                                    17.       Tangier Sound                          7          5
                   Two-year changes in overall spatfall densities                   18.       Lower Potomac River                    3          3
                                                                                    19.       Mid-Potomac: River                     5          2
                   can be examined further as functions of the                      20.       Wicomico (Potomac) River               2          2
                   number of geographic regions falling within                      21.       Patuxent River                         3          2
                   six ranges of average spatfall (Figures 6 and                    In  1990, the mode of spat8qfall was in the 1-19
                   7). Refer to Table 2 for descriptions of the re-
                   gions and the numbers of monitoring sites in                     spat per bushel frequency class (approximately
                   each. Figure 8 shows the geographic locations                    45 % of the survey sites), whereas only 6 % of
                   of these regions. Four non-oyster producing                      the sites had over 200 spat per bushel. Spatfall
                   regions were removed from this and later                         in 1991 was bimodal, with peaks in the 20-99
                                                                                    (22%) and 300 spat per bushel (23%) ran

                                                                                11






           Monitoying Mary&nd's O@sters






                                                                     +



                                                     + *0         +
                                                    3* +
                                                        sw     +
                                                  +        k * ft.#++
                                                    +0 4,42          +2

                                                       ,4            +
                                                + *0    .&1

                                                                +
                                                       +     ++17+



                                                            +



                                                     #4
                                           ++3


                                                    +14. +7
                                                                     +@+Lc2 +5 412
                                                                      +             +tL@-*O
                                                                                      ++13
                                        +                                'A
                                                           +                              1+1


                                                                         LC39-0.+








          Figure 4. Spot derwity per busW of substrate by site, 1990.



                                                       12







              Monitoting Maryland's Oysters




                                                                            +


                                                                                       +.+
                                                                     #0            +
                                                                     +0


                                                                       L
                                                                   2054-+-        +
                                                                     +1          +
                                                                                         S-





                                                                   +33


                                                                                                             @+3


                                                                                                            +Y+20


                                                                          +                                   +
                                                                            +&7                        +       A'v I.
                                                                                            34,50t+








            Figure 5. Spat density per bushel of substrate by she, 1991.
                                                                                                61PI n
                                                                                                Wag.


                                                                    13



WIN






                Monitoring Maryland's Oysters


                M         300      to 2000 (0)
                W          HO      to       299        (3)
                W/'/         50    to          99      (2)
                XX          20     to          49      (3)
                          0.1      to          19     (11)
                               0                       (6)
























                                                                                           0o





             Figure 6. Average spat density ranges forgeographic regions, 1990. Shading does not reflect oyster growing bottom. Numbers
             in parentheses are the numbers of sites within each region.





                                                                         14







              Monitoring Maryland's Oysters


              M         300          to 2000           (4)
                        100          to       299      (7)
              V11,        50         1 o         99    (3)
              -,O<        20         t o         49    (3)
                            0A       to          19    (2)
                             0                         (6)







































              R uro 7. Average spot density ranges for geographic regions, 1991. Shading does not reflect oyster growing bottom. Numbers
              .9'*
              in parentheses are the numbers of ekes within each region.




                                                                          15







              Monitoring Maryland's Oysters





                                                                                    rtem





                                                       Upper v
                                                       U                              Sassafras River Region





                                                           U      Bay



                                                                             r          n


                                                  L4D

                                                                               Region




                                                                               e ver Region





                                                                                   River
                                                           Bay Stem                   PFr     tokin River Region

                                                                    Lit           River Region


                                     Patuxent       Reeo

                                                                            onga River Region
                           V        River Region

                                                                                            y    Cm



                                                                                                         moomico River Reizion

                                                                 Iower Bay Stem
                         bfid        Riverwon


                                                                                                             Aariememex Paver RegLOn

                                                                                      Tangier
                                                           to=C Riv Region                                        -nd Region

            Figure S. Geographic regions defined for aggregated analysis of oyster population data.





                                                                    16








                    Monitoring Maryland's O@sters

                    ges. Thirty-two percent of the sites had over                           strong positive influence on the aggregated
                    200 spat per bushel (Figure 9).                                         1991 spat counts.

                    Regional variation in spatfall between years
                    showed a similar pattern. In 19%, the great                             Table 3. Maryland Chesapeake Bay harvest regions. Aggregat-
                                                                                            d by site code prefixes. Refer to Figure 8 for geographic
                    majority of the Bay's oyster regions produced                           boundaries.
                    spatfall levels of <20 per bushel (Figure 10).
                                                                              >             Harvest                        Site* In             Sit" In
                    Only three regions had spat counts of                                   Region Sub-regions             Subregion             Region
                    per bushel. This situation reversed in 1991:
                    more than half of the regions had spat counts                           sN      BN - Bay North                  2                   7
                    > 100; four regions had > 300 spat per bush-                                    Us - Upper Bay                  3
                    el.                                                                             CH - Chester River              2
                                                                                            E8      EB - Eastern Bay                4                   a
                    Recruitwnt of Spat into Fishery                                                 MR - Milse River                4
                                                                                            CR      CR - Choptank River             6                11
                    A crude perspective on 19% and 1991 spatfall                                    I&C - Broad Creak               I
                    in terms of potential for the future fishery can                                HC - Harris Creak               1
                                                                                                    TA - Trod Avon River            1
                    be gained by comparing spat densities to                                        LC - L. Choptank R.             2
                    densities of the larger size classes (Figure 11).                       FS      FB - Fishing Bay                2                   4
                    Because surviving 1990 spat should appear                                       HR - Honga River                2
                    primarily in the 27-62mm size classes in                                WR      VVR - VVicomico River           2                   5
                    199 1, the 1990 year class will make only a                                     NR - Nanticoke River            3
                    small contribution to the future fishery. The                           Ts      TS - Tangier Sound              6                11
                    approximate five-fold increase in spat produc-                                  PS - Pocomake Sound             2
                                                                                                    MA - Manokin River              2
                    tion in 1991 would be expected to have a                                        HO - Holland Strait@            I
                    much greater impact on population structure in                          PR      PR - Potomac River              6                10
                    1992 and subsequent years, assuming equiva-                                     SM - St. Mary's River           2
                    lent survival.                                                                  WW - Wicomico R West            2

                                                                                            PX      PX - Patuxent River             2                   2
                    Spatfall by Harvest Region                                              WS      WS - Western Shore              4                   6
                    Spat data also can be represented within a                                      PO - Poplar Island              I
                    framework of harvest regions (Figure 12;                                        ME - Mid Eastern Shore          1
                    Table 3) as an alternative to the somewhat
                    arbitrary geographic segmentation employed
                    above. Except for the Northern Bay region
                    and the Potomac River, all harvest regions
                    showed substantial spatfall increases in 1991
                    over 1990 (Figure 13). The most marked
                    increases were in the Choptank River-Little
                    Choptank River (CR-LCR) and Fishing Bay-
                    Honga River regions (FB-HR). In this repre-
                    sentation, the inclusion of the Little Choptank
                    River in the Choptank fishery region had a


                                                                                      17








                 Monitoring Mary&nd's Oysters











                                    50-,

                                    45-                                 AVERAGE SPATFALL


                                    40-                                               1991-215
                                                                                                     199,
                                    35-'
                                65
                                LL  30-
                                0
                                w
                                    25-'

                                Z   20-
                                w

                                cc
                                w   15-


                                    10-1


                                      5-'


                                     0                                              9
                                                 0       1-19     20-99 100-199 200-299 300+
                                                          SPATFALL RANGE PER BUSHEL


                              Figure 9. Comparison of spot density range* by site for 1990 and 1991.
                                      Ll



                                                                  18








                Monitoring Maryland's Oysters






                         12-



                                                                                                  1990
                         10-1
                    CO                                                                            1991
                    z
                    0
                    0
                    w

                    LL
                    0
                    cc
                    w
                    CD
                    =M    4-'
                    z



                          2-'




                         0-
                                         0        0.1-19       20-49       50-99       100-2"     3006-2000
                                                            SPAT COUNT RANGES


                    Figure 10. Comparison of spat density ranges by geographic region for 1990 and 1991.
                                                                                                       IL



                                                                         19








                       Monitoring Marylands Oysters


                                  14-




                                  12-


                        cc
                        w         10-

                        0
                        LL        a-
                        0
                        cc
                        w


                        D
                        z
                        -i
                                  4-
                        0


                                  2-




                                  0-                . . .
                                               2 27 32 37 42 47 52 57 62167172'77182 87 92 97'102'107'112'117'122'127'132'137'142'147'132'157'102'167
                                                                                     SIZE CLASS (MM.)-


                      Figure I IA. Spot and older oyster denskies by she claw, 1990. AN spot were arbitrarily wWWwd to the 22mm eke class.

                               14-




                               12-




                               10-


                      0
                      LL       a-
                      0
                      cc
                      w        6

                      z
                      -i
                      @<-      4-
                      OR

                               2-


                               0-                                                                   0A 12'1 1A 22'1 2A 3A 37"142'1 4A 5A sil oil 67
                                            22 27 32 37 42 47 52 57 62 67       77 82 ST 92 97 1
                                                                                SIZE CLASS (MM.)
                      Figure 118. Spot and older oyster derwitles by size class, 1991. AN *pat were arbitrarily wsigmd to Ow 22mm size class.
                                              2


































                                                                                              20




           Monitoring Maryland's Oysters_




                                                                      Northern Bay - Chester River


                        Western &                                     Eastern Bay - Ifiles River
                        )hd Eastern

                         Shares


                                                                            Choptank & little Choptank Rivers


               Patuxent River



               Potomac River                            FIshing Bay   Honga Rive
                                                                                   Wimmica, & Nanticoke Rivers











                                                                                         Tangier Sound















          Figure 12. Oyster harvest regiom


                                                       21








                   Monitoring Maryland's Oysters

                                                                                  (MRAS; 1-19 spat per bushel); Poplar Island-
                                                                                  Shell Hill (POSH; 20-99), and Western Shore-
                   Table 4. Ratio of small oysters 1presurned 19ft yaw class      Hog Island (WSHI; @?_- 100). Subsample values
                   observed in fall 1991) to 1990 fall spat counts at three       were converted to a 1.0 bushel basis (x5)
                   selected oyster bers. TSBC = Tangier Sound Back Cave:
                   CRTW = Choptank River Tilghman Wharf: HOHO          Holland    prior to analysis.
                   Straits, Holland Straits Bar.
                   TorAL COUMS 0.0 MA*GLI                                         Confidence limits (95%) based upon the
                                                                                  standard error of the mean were calculated for
                   81"     Sm"       SW       Ro"                                 each site for various numbers of replicate
                   TSBC    127       159      0.80
                   CIFITW  139       101      1.38                                samples. Subsamples were removed at random
                   HOHO    115       '168     0.68                                to obtain confidence intervals for reduced
                   Coum Pa 0.2 Bumm stxmmKE                                       numbers of replicates.

                   TV=            CKM             HOHO                            At WSHI, use of five replicates produced
                   spa   ".     SW    SOL    SW     sm.
                   29    27     19    16     11     30                            confidence limits of 108-229 spat per bushel
                   36    21     28    26     28     30                            (figure 14). Thus, if any number of five
                   34    21     35    28     27     10                            replicate samples were taken at that site, 95 %
                   31    35     51    37     16     23
                   29    23     36    32     20     22                            of the time the average of these spat counts
                                                                                  would fall within these confidence limits.
                                                                                  With four subsamples, the 95% confidence
                   Replicate Spat Sampling                                        limits increased to 78-241. With three sub-
                   The MFS design included replicate sampling                     samples, the 95% confidence limits were 9-
                   for spat counts as well as for live and dead                   287.
                   (box) oyster counts. Five replicate dredge                     For the mid-range site (POSH), a similar
                   samples were taken; a subsample of 0.2 bush-                   increase in the confidence limits occurred as
                   el of material was removed from each (1.0                      subsamples were deleted: from 52-79 spat per
                   bushel total). Prior to 1990, the Fall Survey                  bushel with five subsamples, to <0-85 with
                   method used was one 0.5 bushel subsample,                      three subsamples. At the low spatfWI site
                   which was multiplied by 2 and reported as                      (MRAS), there was an apparent increase in
                   counts per 1.0 bushel on field sheets. Because                 precision with decreasing sample size. Two
                   heavy spatfaB in 1991 greatly increased on-                    factors were responsible for this anomaly: 1)
                   board processing time, we evaluated the                        random deletion of subsamples by chance
                   usefulness of counting five subsamples as                      removed the highest spat counts; 2) some
                   opposed to three or four.                                      remaining samples had spat counts of zero.
                                          I                                       These effects reduced both the range and
                   Three ranges of spatfall were subjected to                     mean and suggested that spat counts within
                   analysis: 1-19, 20-99, and @t 100 spat per                     this low range cannot be distinguished statisti-
                   bushel. The five subsamples were summed to                     cally from zero (for a single site), based upon
                   obtain units of spat per bushel (for historical                the current sampling protocols. The results
                   consistency). One sampling site that fell                      nevertheless showed that a meaningful in-
                   within each of the spatfall ranges was chosen                  crease in precision was provided by additional
                   at random for analysis: Miles River-Ashcraft

                                                                             22








                Monitoring Maryland's O@sters



                      600--


                      500-                                                                          ED
                  w                                                                                 1990


                                                                                                    1991
                  Cr  400--                                                                        -
                  w
                  CL

                  L<  300-
                  L


                  w   200-
                  cc
                  w

                      100-1




                        0
                                    BN      CR     WS      ES      TS      FB     WR      PR      PX
                                                               REGIONS


                1*" 13* Spa, donallise averaged by hwv"t reglons, 1990 and 1991,
                      250-
                                 -0*- RANGE


                                    -ft- MEAN
                      200-              95% CONF. UMIT

                  F-- 150-
                  z
                  D
                  0


                  IL  100-



                        50-      MRAS



                        0 -
                               3        4        5                  4                          4         5
                                                      NUMBER OF REPLICATES
                Figure 14. Influence of number of replicate spat counts on 95% confidence lingto for mean spat counts at three skee. 1991.
                MRAS = Milos River-Ashcraft; POSH = Poplar Island-Shell Hill; WSHI Western Shoro-Hog Island.




                                                                          23









                    Monitoring Maryland's Oysters

                    subsamples at the two sites averaging greater                      Population Structure and Mortality
                    than 20 spat per bushel.                                           Mortality Statistics
                                                                                       Mortality between 1990 and 1991 increased at
                    Recruitment of Spat into Year Class Popula-                        virtually every sampling site in the Maryland
                    tion Structure                                                     Bay (Figures 16 and 17). Overall, small and
                    Three sites were chosen for analysis to deter-                     market oyster mortality increased from 17%
                    mine the correlation between 1990 spatfall and                     in 1990 to 31 % in 1991 (Table 5). Mortality
                    recruitment into the I + year class (presump.-                     statistics on a site by site basis are presented
                    tive 1990 spat measured in 1991). Site selec-                      in Appendix C. In 1990, the majority of Bay
                    tion was based on the requirement of 1990                          regions showed mortalities of less than 30%
                    spatfall numbers sufficient to observe their                       with much of the upper Bay having low mor-
                    incorporation into 1991 size class structure.                      talities (Figure 18). This situation changed
                    Because 1990 spatfall was light, as well as                        greatly in 1991, with both increases in mortal-
                    limited in regional distribution, the choice of                    ity within most Bay regions as well higher
                    sites was quite limited. Within these limita-                      mortalities in the upper Bay region (Figure
                    tions, the three sites were chosen for geo-                        19).
                    graphic diversity.
                    Ratios of 1990 spat to 1991 small (< 3 in.,                        Table 5. Comparisons; of mortality Walla" everaiped (summed)
                                                                                       over 63 11990) or 64 (1991) MF8 ekes. Numbers without
                    I + year class) oysters for TSBC (Tangier                          Lwow we counts. Recent mortality - gapere + stage 1 box"
                    Sound-Back Cove) and HOHO (Holland                                 + stalp 2 boxes: markets we at 3 In. 176mm) In alhall hWgM:
                    Straits-Holland Straits) were reasonable, with                     smalle we < 3 In.
                    80 % and 68 % apparent survival of spat into
                    the second year (Table 4). Results for CRTW                        uv* oysters                 96160521        87(5541)
                    (Choptank River-Tilghman Wharf) were                               Boxeis                      200250)         3912523)
                                                                                       Smallmarket ratio                   2.9            2.9
                    anomalous, with 38 % more year 1 + oysters                         Market boxes                    9(538)      200279)
                                                                                       Small boxes                   11012)        19 112")
                    present in the 1991 sample than the 1990 spat                      Recent market boxes             21133)         21132)
                    sample count. Sites ISBC and HOHO, while                           Recent small boxes             412781          41261)
                    showing marked decreases in oyster numbers                         Total mortality M                   17             31
                                                                                       Market mortality                    20             38
                    between spat and year 1 + oysters, also exhib-                     small mortality m                   is             26
                    ited overlap of confidence limits (Figure 15).                     Recent modaft M                       6               7
                                                                                       Recent market entm aft 1%)            6               a
                    Thus, although ratios indicated decreases in                       Recent an," m,.ft (%,                 6               6
                    abundance, there was no clear statistical                          Mean length, recent boxes (mm)      64             63
                    discrimination between the two samples (at                         Mean length, all boxes Imm)         79             79
                    95 % confidence). Likewise, the apparently
                    counterintuitive trend at CRTW was not
                    persuasive given the large overlap of confi-
                    dence intervals.








                                                                                  24







            Monitoring Maryland's Oysters


                              300-       -00- RANGE

                                          - -GO- MEAN
                              250-        -qllL- 95% CONF. LIMIT

                              200-
                          D                                                                  CRTW
                          a)
                          cc
                          w


                          z   150-
                          Z)
                          0            F1



                              100-


                                         TSBC


                               50 -
                                      SPAT        YEAR 1       SPAT        YEAR 1        SPAT       YEAR 1
                                                                  YEAR CLASS


          FlIp" 15. Compmloon ol 1990 opet counw ito "mnw of 19,91 pr"ump,"vo yowling *"uro a, ft" aft"* TSCS   Tmmwr
          Sound-ftck Cove: WHO - HoNand Stroke-HoUand Stroke; CRTW = Choptank RIwr Ughman W.

































                                                                   25






               Monitoring Maryland's Oysters




                                                                                   +

                                                                           4-2                 +


                                                                                          + #4
                                                                           #2


                                                                                      +
                                                                     +                  + +

                                                                                             J


                                                                                              +
                                                                 ++3

                                                                                        +

                                                                            +       +       +













                                                            +

                                                                             +18                                      @+5
                                                                                               +                   +4+7
                                                                                                             #7
                                                                                                             17    +    +U


                                                                                + +3L

                                                                                  +18

                                                                                                                                + V+12




              Figure 16. Oyster mortality lpercent boxes) by sampling site, 1990.




                                                                               26






               Monitoring Maryland's O@sters






                                                                           +4

                                                                           +2-             +

                                                                     +                  + +


                                                                                              +
                                                                  ++14
                                                                            +           +    +
                                                                                    ++2            +           +2
                                                                                   +



                                                                          +34


                                                                              +rm                                     @05

                                                                                                                                4-6



                                                                                + 4w                             55f
                                                                                                                +4jm
                                                                                   +2B                            +Sa9l


                                                                                                                    +           +






              Figur* 17. Oystor moctality (parcont boxes) by sampling site, 1991.
                                                                                        +3 e\




                                                                              27






               Monitoring Maryland's Oysters


                         50     1 o     100        (0)
                         40     to       59
                V11,     30     1 o      39
                         20     to       29        (6)
                         10     10       19        (5)
                                to          9    (12)


                                                                         +











































                                                                                    01
                                                                                    10

                                                                                AO A-


                                                                                 00










              Figure, 18. Oyster mortality averaged by geographic regions, 1990.


                                                                              28






             Monitoring Maryland's Oysters


               M        50     t o     100     (4)
               0        40     t o      49     (2)
               V//,     30     to       39     (5)
               )@e,     20     t o      29     (4)
                        10     to       19     (2)
                           0   to          9   (8)





                                                                 +













































             Figure 19. Oyster mortality averaged by geographic r*giom, 1991


                                                                            29









                Monitoring Maryland's Oysters

                In 1990, the mode of mortality aggregated on          much reduced 1990 population which was
                a regional basis was in the 0-9 % range. in           centered at 75mm at the time of the 1990
                1991, the modal range of mortality was 30-            survey, and 2) the peak centered at approxi-
                39%. From 1990 to 1991, the number of                 mately  50mm incorporated 1990 spat as well
                regions with <30% mortality decreased,                as an undetermined number of seed oysters
                whereas the number with >30% mortality                transplanted to survey oyster bars.
                increased (Figure 20). There was a marked
                increase in the @!t50% mortality class; in            Overall natural mortality in 1990 was much
                1990, no Bay regions averaged > 50 % mortal-          lower than in 199 1. The most abundant size of
                ity, whereas in 1991 four regions fell within         *boxes was 60-90mm. The two-peaked size
                this category.                                        distribution in 1991 was also apparent with
                                                                      combined live oysters and boxes. Peak box
                Mean mortality estimates for six of the nine          counts were in the 50-100mm range.
                harvest regions were considerably greater in
                1991 than in 1990 (Figure 21). Three re-              There was substantial depletion of live oysters
                gions-Northern Bay-Chester River (NB-CR),             relative to the total sample within the span of
                Wicomico-Nanticoke Rivers (WR-NR), and                a year (Figure 26). No overall growth of the
                Potomac River (PR)-had only slight increases          population in terms of size increases between
                in mortality.                                         the time of the 1990 MFS survey and that of
                                                                      the 1991 MFS survey was observed.
                On a Baywide basis, the average number of
                live market oysters (@-3 in.) per bushel de-          Regional Population Age Structures
                creased between 1990 and 1991, while the              There was substantial variation in population
                number of market boxes increased (Figure              structure and relative oyster abundance be-
                22). The majority of the increased natural            tween harvest regions (Figures 27-35). Note
                mortality apparently occurred at least a month        that the vertical axes of these figures differ.
                before the survey (October-November), as the          Some distinctive characteristics within regions
                numbers of recently dead oysters remained             were observable and are discussed below.
                nearly constant between 1990 and 1991 (Fig-           Although year classes are identified as discrete
                ure 23).                                              entities, it should be realized that due to varia-
                                                                      tions in individual growth rates, oysters of
                Bayudde Population Size Structure                     different year classes may in fact be mixed
                Virtually all oysters sampled during both years       together. Due to this effect, year classes of
                of the survey fell between 30mm (1.2 in.) and         3 + or greater  are difficult to quantify accu-
                150mm (5.9 in.; Figures 24 and 25). Peak              rately.
                oyster size abundance (including boxes) was
                slightly less than 75mm (2.9 in.) in both                           ....... ....... .........
                years. In 1990, the distribution of live oyster
                lengths was symmetrical about this center of          Size frequency patterns were very different
                abundance. In 1991, two peaks of live oyster          between the two years (Figure 27). In 1990,
                abundance were observed: 1) the peak cen-             what appears by modal size to be a 2 + year
                tered at just over 80mm could reflect the             class dominated the population structure. What


                                                                  30









               Monitoring Mary&nd's Oysters


                     12-

                                                                                         ED
                     10-                                                                 1990
                                                                                         m
                                                                                         1991
                 z
                 0
                 F3
                 w
                 cc
                 LL
                 0    6-
                 cr
                 w
                 ca
                 :2   4-1
                 z


                      2-,




                                  0-9      10-19      20-29     30-39     40-59     50-100
                                             PERCENT MORTALITY RANGES


                 Roure 20. Rang" of mortality by geogrMphic regions.

                     50-


                     45--
                                                                         1990
                     40--                                                m
                                                                         1991

                     35--


                     30--
                 cc
                 0
                     25--

                 z
                 w   20--
                 cc
                 aw  15-

                     10-1


                      5-


                                BN CR WS             EB     TS     FIB WR        PR PX
                                                         REGION

                 Roure 21. Rang" of mortality by harvest regions.






                                                                        31








                    Monitoring Maryland's O@sters



                           60-                                                                           m
                                                                                                         NUMBER BOXES
                                                                                                         M
                           50-                                                                           NUMBER MARKETS
                        W
                        L
                        W
                        'r 40-'-
                        W
                        0-
                        cc
                        W
                        m
                        2  30-
                        0
                        z
                        W
                        (9
                        <  20-
                        cr
                        W


                           10-11




                             01'
                                                       1990             YEAR                1991

                    Figure 22. Baywide everages of nmwket-siz*d I k 76mm) ihm oysters and boxes.

                          40--



                          35-'              PERCENT SHORT TERM
                                           Im
                                            PERCENT LONG TERM
                          30-


                          25-

                      cc
                      0
                          20-

                      z
                      W
                      o   15-1
                      cl:
                      W
                      CL
                          10-@



                           5--'


                           0 V                       - -                .1
                                                    1990                                1991
                                                                     YEAR


                   Figure 23. Baywide averages of long-term lpercent of boxes estimated to be more than a few weeks past death), short-term,
                   and total mortality.





                                                                                  32








                   Monitoring Maryland's Oysters





                            WA              JL                   KM
                                                                 LK                                                                         Ua
                                           ;I-A






                                                          112   in    112                                                            a     in    In
                                                  Sm                                                                        SIN UJIM


                    Figure 24: Cumulative numbers of live and box oysters                      Figure 25. Cumulative number of live and box           oysters,
                    collected from all sites in Maryland Chesapeake Bay, 1990.                 collected from all sites in Maryland Chesapeake Bay, 1991.









                                                                                                91 L
                                                                                                   K

                                                                 440                            of KIM

                                                                                                go LK
                                                                                                -a-
                                                                                                00 am
                                                                 ADO







                                                                   0
                                                                    22 37 52 67 12 W7 112 127 141 157
                                                                                     SIM GLW



                                                    Figure 26. Total numbers of live and box oysters collected from all
                                                    sites in Maryland Chesapeake Say, 1990 and 1991.
                                                                                                   LK

































                                                                                       33








                              Monitoring Maryland's Oysters



                                        so

                                                                                          Uw                                                                                                    bw


                                                                          N
                                        Go



                                        44                                                                                                    As






                                           22  11 . 51 82       71  52   12 102 111 112 132 142  152 ;a                                          22  32   42  ING U   71  52   It  102 111 112 132 142 M 152
                                                                      UM  CLAM                                                                                              NBC ISL*23


                              Figure 27a. Total number of survey oysters by component,                                              Figure 27b. Total number of survey oysters by component,
                              Northern Bay - Cheater River harvest region, 1990.                                                    Northern Bay - Chester River harvest region, 1991.





                                        in                                                                                                    140

                                        121)                                                                                                  22D
                                        NOD                                         M Kw                                                      lob
                                        IND                                         M UVE                                                     :Do                                               LK
                                        lob                                                                                                   go
                                        :to                                                                                                   140
                                        20                                                                                                    120
                                                                                                                                           1100                    -AA-

                                        GO

                                        48                                                                                                    40

                                        20                                                                                                    20
                                           12  J@ 192 U S2 72 112 02 102 111 122 132 142 132 112                                                 12  32  42 U     U n     52 112 102 111 Iff 132 142 132 192
                                                                      WE CLA98                                                                                               smaAm


                              Figure 28a. Total number of survey oysters by component,                                              Figure 28b. Total number of survey oysters by component
                              Choptank River              Little Choptank River harvest region,                                     Choptank River              Little Choptank River harvest region:
                              1990.                                                                                                 1991.






                                        IND                                                                                                   IND

                                        IND                                                                                                   IGO
                                        140                                        M KES                                                      140
                                                                                                                                                                         ,A
                                        Ito                                              LIVE                                                 Ito                                               UVE






                                        40                                                                                                    44

                                                                                                                                              20


                                           12 31 42 91     02 71 U 12 102 111 112 132 142 152 182                                                12 31   42 ING  92 71    B2 12 102    111 112 1 U 142 192 162
                                                                                                                                                                            SEE CLAIS
                              L                                                                                                     L                                      L
                              Figure 29a. Total number of survey oysters by component,                                              Figure 29b. Total number of survey oysters by component,
                              Western Shore - Mid Eastern Shore harvest region, 1990.                                               Western Shore - Mid Eastern Shore harvest region, 1991.


                                                                                                                       34








                          Monitoring Maryland's Oysters


                                        Ion                                                                                              ion

 long

                                        go                                                                                               SO

                                                                                     UVE                                                                                               LIVE
                                                                    "A

                                                                                                                                         AS
                                                                                                                                                         .1116


                                        to
                                                                                                                                         20



                                        0
                                        12 31                                                                                            9
                                                42  U   12 71   52 111 102 111 112 132 142 152 182                                        12 31   42 a at     71      1 lot Ift 112 111 142 152 lot
                                                                  WE CLAM                                                                                           .2.112

                                                                                                              1             L
                          Figure 30a, Total number of survey oysters by component,                                          Figure 30b. Total number of survey oysters by component,
                          Eastern Bay - Miles River harvest region, 1990.                                                   Eastern Bay - Miles River harvest region, 1991.





                                        is                                                                                               ISO
                                        24:                                                                                              240
                                        220                                                                                              220
                                        200                                                                                              log
                                        ISO                                          LIVE                                                Igo                                           LIVE
                                        Igo                                                                                              Ion
                                        140                                                                                              M
                                        120                                                                                              12D
                                        100





                                        24
                                        9 12 32 42 51 12 71 52 92 lot Ill 112 132 142 192 192                                            912 31   42 51   It 71   St 12 102 1 .11 112 112 142 152 112
                                                                  NZE CLAM                                                                                          NZE CLASS


                          Figure 31 a. Total number of survey oysters by component,                                         Figure 31b. Total number of survey oysters by component,
                          Tangier Sound harvest region, 1990.                                                               Tangier Sound harvest region, 1991.





                                        iaD                                                                                              Ion



                                        50                                           OWES                                                go
                                                                                     LIVE                                                                                        = LIVE



                                                                                                                                                                    A



                                        to                                                                                               20



                                                                                                                                                                             k,
                                        12 31   42  51  92 71 52 92     102 Ill 112 132 141 152 162                                      9 12 31  42 U    92  71   52 12 lot Ill 112 IM 142 152 162
                                                                  SM CLAM                                                                                           SIM aim


                          Figure 32a. Total number of survey oysters by component,                                          Figure 32b. Total number of survey oysters by component,
                          Fishing Bay - Honga River harvest region, 1990.                                                   Fishing Say - Honga River harvest region, 1991.
                                         J@


                                                                                                                    35








                        Monitoring Maryland-s Oysters


                                    ISO                                                                                   Igo


                                    140                                                                                   140

                                    120                                     LIVE                                                                                 UVE
                                    100




                                    SO                                                                                    SO


                                    40



                                           42  S1 U 71 92 92 ID2 111 112 132 141 IS2 162                                                         MM CIAM         321 2 152 112
                                    12 31                                                                                 9.2 31 42 31 B2 71 52 02 102   111 112 1   4
                                                           WE CLAM


                        Figure 33a. Total number of survey oysters by component,                              Figure 33b. Total number of survey oysters by component,
                        Wicomico River - Nanticoke River harvest region, 1990.                                Wicomico River - Nanticoke River harvest region, 1991.







                                    ISO                                                                                   ISO
                                    140                                     Rom                                           140
                                    Ito                                     LIVE                                          120                                    LIVE

                                    IaD

                                    SO
                                    so                                                                                    SO   JNL:

                                    40                                                                                    44

                                    20                                                                                    20


                                    .12 31 41
                                    9         M U 71 St 12 102 111 112 1 141 152 192                                      12 31 42 ft  U 71   92 02 102: I'll 112 132 142 152 182
                                                          SOM 0-4m                                1           1                                 SOM
                        Figure 34a. Total number of survey oysters by component,                              Figure 34b. Total number of survey oysters by component,
                        Potomac River harvest region, 1990.                                                   Potomac River harvest region, 1991.





                                    AO                                                                                    Aa




                                                                            LIVE                                                                                 UVE



                                    2.0








                                    21 31 Al Al 61 79 B2 92 102 112 112 132 IA2 162 162                                   21 32 41 Al &1 72   82 92  102 fit 112 132 142 152 192
                                                          SW CLAW                                                                               am CUM


                        Figure 35a. Total number of survey oysters by component,                              Figure 35b. Total number of survey oysters by component,
                        Patuxent River harvest region, 1990.                                                  Patuxent River harvest region, 1991.
                                                AL





                                                                                                    36








                   Monitoring Marylands Oysters


                                                                   40




                                                                                                        LM



                                                                   10








                                                                     72 32 42 52  82 7Z 92 42 10211212213Zl4ZI52112
                                                                                          am CLM


                                                            Figure 36. Choptank River - Tilghman Wharf (CRTW) oyster
                                                            bar, 1991.





                                                                   40




                                                                                                        LNE











                                                                     0
                                                                     ',I n 42 52. 52 'n 52 112 ift ill IU 132142 152 Ifit
                                                                                          so mom


                                                            Figure 37. Tangier Sound - Back Cove (TSBC) oyster bar,
                                                            1991.






                                                                   40



                                                                                                        Bons

                                                                                                        Uw











                                                                     0  A
                                                                     22 M a " 112 n 92 M2 Ill IM 142 lU 162
                                                                                          ME CLAN


                                                            Figure 38. Holland Straights - Holland Straights (HOHO)
                                                            oyster bar, 1991.

                                                                                        37








                Monitoring Maryland's Oysters

                component of this is older seed plant cannot         also visible. This new year class       was also
                be determined. An almost total absence of the        showing high mortality levels.
                1 + year class (1990 spat or seed) was appar-
                ent. In 199 1, the presumed I + year class was
                a significant addition to the population. Be-
                cause spatfall was negligible in this region in      In 1990, the 2 + year class (- 80mm) and 3 +
                1990, the large I + year class may have repre-       year class (- 100-105mm) were beginning to
                sented extensive seed plantings in the Chester       show high levels of mortality (Figure 30). In
                River. The 2 + size group of 1990 grew               1991 ' these two year classes had grown very
                slightly to form the 3 + year class centered at      little and had experienced > 50 % mortality.
                approximately 100mm. There was a slight              Incorporation of a modest 1 + year class and
                increase in mortality in this size class in 1991.    or seed plantings occurred in 199 1. Ffigh mor-
                It was tempting to interpret the several clear       talities were apparent in this young age group.
                peaks of the 1991 distribution as discrete age
                classes, but not clear how these groups could
                have derived from the   11990 distribution.          A possible intrepretation of Tangier Sound
                                                                     data in 1990 would be a small I+ year class
                                                                     with a mode at approximately 40mm, and a
                The 1990 presumed 2+ year class (75 mm)              larger 2+ year class with a mode at approx-
                and a possible 3 + year class (95 mm) showed         imately 60mm. Light to moderate mortality
                moderate mortality (Figure 28). In 1991, these       was present in these year classes (Figure 31).
                two groups had > 50 % mortality. The I +             In 1991, the fate of'these year classes was not
                year class in 1991 (1990 set) was large in           entirely clear. Spatfall in the Tangier Sound
                comparison to the population, but was show-          region in 1990 averaged 100 per bushel. This
                ing the beginnings of high mortality.                age group (1+) might have been centered at
                                                                     50mm in 1991. The peak at 75mm, then,
                W*                                                   might have been the 2+ year class, i.e., the
                                                                     I+ year class in 1990. In any case, it ap-
                                                                     peared that one year class, either the 2 + or
                The 1990 population showed what appeared to          3 +, disappeared as a discrete entity from the
                be largely one year class centered at 75mm           population. All size classes showed very high
                (Figure 29). Mortality was light to moderate         mortality, with the larger size group having
                and expressed itself largely in the 60-75 mm         > 50% mortality.
                range. If year classes other than the apparent
                2+ year class were present, they were incor-
                porated within the structure of this age group.
                                                                     A liberal interpretation of the 1990 distribu-
                In 1991 , mortality was high for this age group      tion indicated three or more year classes (Fig-
                (possibly >50%). Slight growth (- 10mm)              ure 32), however, some of the peaks probably
                was shown by the live component of this age          reflect only sampling variability due to low
                class. Presence of a s 'Mall 1 + year class was      oyster counts and regional variation. The I +


                                                                 38








               Monitoring Marylmd's Oysters

               year class may have been present at - 50mm             In 1991, an influx of 1990 spat into the 1 +
               and the 2 + year class at - 60-75 mm. Mortali-         year class was seen in the 30-60mm group.
               ty was at a low level and relatively uniform           What may have been the 1990 mode, in
               over most size classes. In 1991, year class            general, moved to larger size classes (75-
               distinction may be more apparent. The 2+               105mm). Extreme mortality occurred for all
               year class grew to a center of - 70mm, and             size classes >50mm.
               the new I + year class appeared at - 55mm.
               Both of these year classes were showing
               significant mortality in 1991, unlike the situa-
               tion in 1990.                                          In 1990, a small 1 + year class was centered
                                                                      at 50mm and showed minor mortality (Figure
                                                                      35). The 2+ year class was grouped around
                                                                      75mm with moderate to heavy mortality. In
               It is difficult to establish year classes for these    1991, both of these year classes had high
               regions in both 1990 and 199 1. Site and               mortality as well as imperceptibly slow
               regional variability appeared to mask such             growth rate. Little to no incorporation of 1990
               distinction. In 1990 the 2 + year class oysters        spat into the 1991 1 + year class was appar-
               may have had a mode centered at approxi-               ent.
               mately 75mm (Figure 33). Oyster abundance
               dropped sharply in larger size classes. Mortal-        IndiWdual Site Age Structure
             'ity was very low for all size classes. In 1991          Age class distinction on individual oyster bars
               a similar yet truncated population profile was         was much clearer than for regions. Variations
               present. While the bulk of the 1990 population         in spatfall and growth rates are presumably
               appeared to have shifted to the right due to           less within a single oyster bar than within
               growth, the high mode of 1990 was absent.              regional aggregates. Three sites-Choptank
               Increases in mortality appear to be responsible        River-Tilghman Wharf (CRTW), Tangier
               for this. For oysters -65mm and larger, the            Sound-Back Cove (TSBC), and Holland
               impact of mortality was much greater than in           Straits-Holland Straits (HOHO)-were chosen
               1990. No great inclusion of a 1 + year class           to evaluate whether five 0.2 bushel subsam-
               (due to 1990 spat) was visible in 1991.                ples were sufficient to describe population size
                                                                      and age structure at a single site. These were
                                                                      the same sites used for analysis of recruitment
                                                                      of spatfall into the population structure (Figure
               In 1990, we observed what appeared to be a             15). Although the three sites exceeded the
               dominant age group centered at 75mm (Figure            means (particularly in box counts) for MFS
               34). Mortality was moderate to high, particu-          sites, examination of data from other sites
               larly within the small to medium size classes.         suggested that this effect did not lead to atypi-
               Because Potomac River sites vary greatly in            cal results. At sites where oysters were scarc-
               salinity and most likely in oyster growth rates,       er, size groupings were still apparent although
               the size distribution probably represented a           less abundant.
               mixture of year classes.



                                                                  39








                 Monitoring Maryland's Oysters

                 Size class modes appeared to be distinguish-            close to 75% mortality. A somewhat lower
                 able at each of the sites (Figures 36, 37, 38).         mortality rate was shown by a possible 3+
                 Although individual oysters within a year class         year class.
                 may exhibit variable growth rate, these peaks
                 probably represent modal sizes of separate              The I+ year class at HOHO exhibited high
                 year classes. At each site, the large peak of           mortality at sizes above 45mm. It may be
                 oysters centered between 30 and 60mm should             questioned whether 1) the size of the oysters
                 be the 1990 set at approximately 1.2-1.5 years          was a factor in the higher mortality, or 2) the
                 old (summer 1990 to fall 1991, i.e., the 1+             higher mortality was of an older year class.
                 year class). The 2+ year class was apparent             That is, it might have been a result of mortali-
                 in the second peak at both TSBC and CRTW.               ty in the 2+ year class which died the previ-
                 Older oysters of indeterminate age groups also          ous year and still remained as boxes. The
                 appeared at these three sites, although age             surviving 2+ year class grew approximately
                 class distinction beyond the 2 + age group was          20mm, then exhibited very high (75%) mor-
                 difficult to establish. Although variable yearly        tality during the summer of 1991, which
                 growth rates were evident between sites, the            virtually eliminated live oysters of this year
                 rule of thumb for oyster growth in the Ches-            class.
                 apeake Bay region (three years to market size,
                 or very roughly 25mm per year) was generally            Disease
                 satisfied.                                              Range and Intensity of Perkinsus marinus
                                                                         Infection
                 Marked decreases in relative abundance from             Forty-two sites were sampled for disease in
                 one year class to the next older were obvious           1990. In 1991, 43 sites were sampled-Chop-
                 at all three sites. Size structure from all 64          tank River-Royston (CRRO) was omitted in
                 monitored oyster bars indicated that these year         1990. Per*insus distribution and degree of
                 class decreases were typical. Harvest was               infection were at unprecedented levels and
                 unlikely to be a factor in the reduction of year        present virtually Baywide in Maryland during
                 class abundance with age at these three sites.          both years. Maximum disease intensities for
                 Available information indicated that none of            both years generally were found within the
                 the above bars were commercially harvested              lower reaches of Bay tributaries, with some-
                 within the previous two to three years (R.              what lower intensities in the Bay mainstem.
                 Scott, MDNR, pers. comm.). For TSBC, a                  At the lower salinity ranges, the disease was
                 substantial mortality of the I + year class was         present during both years, but levels of infec-
                 apparent (about 33 %). Reduction in live                tion were much lower than in higher salinity
                 oyster counts in the 2 + year class from the            areas (Figures 39 and 40). Disease statistics
                 I+ year class can largely be attributed to              on a site by site basis are presented in Appen-
                 > 50 % mortality of the 2 + year class. Similar         dix C.
                 mortality rates were exhibited by the 3 + year
                 class.                                                  Although disease levels differed greatly be-
                                                                         tween sites within a given locale, regional
                 At CRTW, the I+ year class exhibited low                differences were apparent (Figures 41 and
                 mortality. The 2+ year class, however, had              42). The regions were identical to those used


                                                                     40






             Monitoring Maryland's Oysters










                                                                                  14+






                                                                            1@4     4j












                                                                           4-T



                                  RAW                                         +3A
                                                                                                             +Le.

                                                                                                                +k3


                                                                                  +4A
                                                                                  +3.4                         +Z7

                                                                                                                 +L1                    3.5


             F'Oure 39- PWWn#us PP&dnw IntOrwItY Index by afto, 1990 frectal thioglycollate diagnasial.                                          MEN


                                                                          41






               Monitoring Maryland's Oysters















                                                                                      43

                                                                            4-T    YA

                                                                         +2B



                                                                              +4.5
                                                                                                             +3.1,

                                                                                                              0+12


                                                                                   +4A
                                                                                  +2.3                         +42






              Figure 40. PwrUnsus madnw Intensity index by site, 1991 (rectal thioglycollate diagnosis).





                                                                           42







             Monitoring Maryland's Oysters


              M 4                to 6               (3)
                       3         to 3.9            (3)
                        i        to 2.9          HO)
              M 0A               to 0.9            (3)










































             Figure 41. PwA*Wus modma intensity Index averaged over geographic region*, 1990 (rectal thioglYcollate diagnosis). Numbers
             in parentheses we the number of regions within each range.





                                                                        43







               Monitoring Maryland's Oysters


                M 4               to 6            (2)
                0 3               t o 3.9 (9)
                01/',    1        to 2.9          (7)
                ,-X      0.1      to 0.9          (2)


























              Figure 42. PWWns&m M&Wnw int*nafty index averaged over geographic regions, 1991 frectal 0doglycollate diagnosis) =Nm
              in parentimses are ttm number of regions within each ran".









                   Monitoring Maryland's Oysters

                   to present spatfall and mortality results.                           77mm and 74mm for 1990 and 1991, respec-
                                                                                        tively. Therefore, P. marinus statistics gener-
                   Perkinus intensity indexes increased                       from       ally represented "market" oysters, whereas
                   1990 to 1991. The lower mainstem Bay and                             average survey oyster sizes were close to the
                   Little Choptank regions exhibited severity                           3 in. (76mm) division between smalls and
                   levels greater than 4.0 for both years. Inten-                       markets.
                   sity in the Honga River region appeared to
                   decrease in 1991; however, only one site                             Evidence for a reduction in P. marinus infec-
                   (HRNO) was diagnosed. Prevalence of 100%                             tion pressure within any Bay region from 1990
                   was observed in both years, but with a moder-                        to 1991 was not found. Only 14 sites had
                   ate decrease in severity index in the 1991                           lower P. marinus intensity index values in
                   sample.                                                              1991 (Table 7). Twelve of these fourteen sites
                                                                                        maintained P. maqrqinus prevalences > 90 % for
                   The Patuxent and Manokin River regions had                           both years. There was only one site (PRLC)
                   high and stable intensity levels during both                         with prevalence less than 90% for both years
                   years. Regions of noticeable P. marinus                              (40% in 1990, 10% in 1991).
                   increases were Tangier Sound, Choptank                               Table 6. Comparison of disease and codition indiose, all
                   River, Eastern Bay, and the lower Potomac                            altes, 1990-1991. Prevalance, severity, and intensity indlose
                                                                                        are for Perkinsus merinus. Only two sites were diagnosed by
                   River.                                                               hemolymph culture in 1991.

                                                                                                                 1990                 1991
                   Baywide Changes in Perkinsus marinus, 1990-                                          RECTAL THIOGLYCOLLATE CULTURE
                   1991                                                                 Prevalence (%)             68                   63
                   The mode of regional intensity increased from                        Severity                      2.8                3.4
                   < 3.0 in 1990 to 3.0-3.9 in 1991 (Figure 43).                        Intensity                     2.3                3.0
                   Likewise, a larger percentage of sites Baywide                                      BLOOD THIOGLYCOLLATE CULTURE
                                                                                        Prevalence (%)                65
                   had higher intensities of P. maqrqinus in 1991                	    Severity			   2.7
                   (Figure 44); the major difference between                       	    Intensity				2.1
                   196% and 1991 was the much smaller number                            Mean condition			4.4		4.7
                                                                                     	Maximum condition			6		6	
                   of sites with intensity between 0 and 1.0 in                		Minimum condition			3		2
                   1991. Intensites in the 5.0-6.0 range were                         Mean length (mm)			83		86
                                                                                     	Maximum length (mm)	 	108		113
                   present only in 1991. No sampling sites were                        Minimum length (mm)			62		63
                   free of P. marinm disease in 1991.                                 Mean length (mm)			77		74
                                                                                     Cllone					5		6	
                   The mean prevalence of P. marinus infections                    	   Polydare					35		55
                   for all sites rose from 68 % in 1990 to 83 % in                    
                   1991 (Table 6). The mean intensity index rose                      Shell length of oysters diagnosed for P. marinus
                   from 2.8 to 3.4. An overall change in oyster					Shell length of all survey oysters.
                   meat quality due to this increased infection                         Perkinsus intensity was compared across the
                   load was not apparent. Average oyster sizes                          nine fishery regions (Figure 45) and gave a
                   diagnosed for P. marinus analysis were 83mm                          somewhat different result than for the twenty-
                   in 1990 and 85mm in 1991. Oyster sizes                               one geographic regions. Disease level increas-
                   sampled Baywide for population statistics were                       es from 1990-1991 were observed in six of the

                                                                                   45








                Monitoring Marylmd's Oysters

                nine regions. Those exhibiting decreases were          the severity index correlated closely with the
                the Wicomico-Nanticoke, Potomac, and Patu-             intensity index-dictated by the fact that at
                xent regions. The Wicomico-Nanticoke region            100% prevalence, the intensity index and
                had data from only one site (NRWS). Potomac            severity index are identical (same n in de-
                data combined sites from the mid- and lower            nominator). There was fair association of the
                Potomac as well as the St. Mary's and Wico-            intensity index with the percent prevalence at
                mico Rivers. Decreases in P. marinus intensi-          intensities <2. At prevalences, below 50%
                ty were apparent at several of these sites             there was no correlation of intensity indexes
                (Table 7), but in the majority of cases preva-         with severity indexes. That is, at low prev-
                lence was consistently high. The Patuxent              alences, infected oysters could have variable
                River was represented by only one site                 levels of infection.
                (PXBI). At this site, although the intensity
                index decreased slightly, percent prevalence           Rectal thioglycollate diagnosis for P. marinus
                increased to 100%.                                     was done for all disease sampling sites for
                                                                       both years. In 1990, blood thioglycollate
                Table 7. Sh" exhibiting decreasing A nwk" intetwity    cultures were done for all but five disease
                Indle". 1990-1991. See Table I for description of aft cod". sampling sites. There was a strong correlation
                Sift 00"    a @  0  V       Fmcon                      of the results for these two methods (r=0.96;
                          11"o   11"ll     low  1991                   p:50.0001), but marked variation at specific
                LCRP       4.0   4.6       100  100
                HRNO       4.3   3.4       100  100                    individual sites (Figure 47).
                WHO        4.2   4.0       100  100
                MCC        4.2   3.1       100  97
                MRTU       3.8   3.3       100  100                    The correlation between P. marinus intensity
                MW         3.8   2.8        97  90                     and salinity in 1991 was weak (Figure 48),
                VVVVLA     3.6   2.8        97  97
                PSMA       3.5   3.3        97  93                     although traditionally, P. marimis has been
                PXW        3.4   2.8        97  100                    expected to be more virulent at higher salin-
                PRCH       3.4   2.3        97  83
                SMPA       3.3   2.3        93  97                     ities (Andrews 1988). No sampling sites had
                CRTW       3.2   3.0       100  97                     salinity less than 8 ppt, however. Addition-
                NRW8       2.9   2.8        93  100                    ally, salinity at time of the Fall Survey may
                MLC        0.7   0.3        40  10                     not have reflected summer-long conditions.

                Relationships Among Perkinsus marinus Indi-            Association of 1991 Spat Densities iWth Perk-
                cators                                                 insus marinus
                The P. marinus intensity index is used to              Regions of high 1991 spatfWl were also areas
                integrate two components of disease pressure           of very high P. marinus disease pressure
                on an oyster bar: 1) disease prevalence (the           (Figure 49). Of the 12 sites with > 300 spat
                precentage of oysters infected); and 2) the            per bushel, 10 had intensities >3.0. Percent
                level or stage of disease within infected oys-         prevalence at nine of these sites was 100%. At
                ters (severity index).                                 two others, prevalence was 97%. One site
                                                                       (MESR) had only 27% prevalence. This
                In 1991, intensity indexes >2.0 produced               particular site was located in the mainstem of
                percent prevalences of between 90% and                 the Bay, generally away from other oyster
                100% (Figure 46). At these intensity levels,           growing areas.

                                                                   46








                 Monitoring Marylmd's Oysters



                    12-1


                                                                                         1990
                    10-1                                                                 m
                                                                                         1991


                 z
                 0

                 w
                 cc
                 LL   6f
                 0
                 cc

                 co
                 :2   4
                 z


                      2-'




                      0
                                    0        0.1-0.9       1-2.9       3-3.9        4-6
                                               INTENSITY INDEX RANGES


                 Rom ", Comarlmon of ft,"ww mm"m intensity Index rang. by gooor"Mc reglons.

                   30-,



                                                                                        1990
                   25-

                                                                                        1991

               w   20-


               LL
               0

               z
               w

               cc
               W.  10-1


                    5-
                    0 A.      L
                                0     0-<l 1-<2 2-<3 3-<4 4-<5 5-<6
                                              INTENSITY INDEX RANGE


                 Figure 44. Comparison of Poddmus madmo Intensity index ranges by ekes.






                                                                        47








                    Monitoring Marylmd's Oysters



                      4.0--
                      3.5--                                                                           1990
                                                                                                      M
                    X                                                                                 1991
                    w 3.0-
                    a
                    z

                      2.5--
                    F5
                    z
                    W 2.0-.
                    z
                    w


                    cc

                      1.0-



                      0.5-


                      0.0          NB      CR WS EB TS FB WS PR                                 PX
                                                               REGION



                    Figure 45. Awkkwus wwksw Intensity Index averaged by harvest regions.

                         100-                                                                                     7
                                                    Me M M         M ON         M             M IN


                         go-                           ME    Me
                                                                                                               -6
                         80-                    Mee
                                                                                                                    0
                                                                                                                 5  Z
                         70-                                                                                        z
                                                                                                                    0
                                                                                             E0                     F=                                          I
                    w                                                                                          -4   ( )
                    (-)  60-                                                                                        w
                    z                                                                                               LL
                    w                 ED                                                                            z
                    -i
                    <    50-        M                  M     c=1
                    >                   ME                                                                     -3   Z
                    w          M  M               C=)   F.11@
                         40- m          M)       C:1-1@
                                                                                                                    U)
                                          ED -I- 4-@                                                           -2   z
                         30-                                                                 PREVALENCE             W
                                                                                              (M               -    z
                                                                                             SEVERITY
                         20-                                                                  -4-
                                                                                             INTENSITY

                         10    w . . . . . . .                                                 I.     I . I I 1 0
                                         SITES BY INCREASING INTENSITY INDEX
                    Figure 46. Comparison of PwMnvuv m*nWus indices from all ekes, 1990 and 1991.





                                                                                48








                Monitoring Maryland's Oysters




                   4.5-


                     4-


                   3.5-


                     3-
                z                                                              WIN       IN 0

                z  2.5-                                                 IN
                Cw)
                0    2-
                0                                                     IN
                j                                   0
                m                                        IN

                                                      IN



                   0.5-             IN IN

                     0..
                        0     0.5             1:5        2     2.5      3       3.5      4      4.5       i
                                                       RECTAL INTENSITY


                Figure 47. Comparkon of Pwhksm nwkKm rectal and hemo4mVh lblood) diagnostic nwdw& from shm wtwm both rmdm&
                "Wowme plied to Ow earne sample, 1990 and 1991.
                   6




                   5-



                                                            IN
                X  4-                                    IN           IN IN                      IN
                w
                z                                                                       IN
                   3-                                    10-    000
                        IN
                z
                w                                                     IN

                   2-                                         IN







                                    IN
                                             IN

                   0
                     8           10          12          14           16          18          20          22
                                                  SALINITY (PPT)
                Figure 48. Pwidnesm madbus InterWay as a function of salinity at the tinw of sampling, 1990 and 1991.






                                                                      49








               Monitoring Maryland's Oysters

                                                                   this disease in the lower Maryland Bay in
               Table 8. Modified Fall Survey oyster bare with presumed 1990. Although relatively few sites were
               harvest activity, 1990-1991. C. Judy, R. Scott, and 0. selected for this analysis, intensity indexes up
               Krantz, Maryland Department of Natural Resources, pers. to 0.4 were observed in the Tangier Sound
               COMM.                                               region (Figure 52). Maximum prevalence for
               ohm                      ornew bw                   this disease was 20%.
               aWP      a" Wwio North   mouffledn Polm
               am"                      9@ Pam
               C0101k   chestm 1VVW     Buoir Pack
               CHOF                     06d FkAd                   In 1991, the range and intensity of H. nelsoni
               Cho&     Chopowifit Mvw  oystar W" Point
               am       r   a"                 N-                  increased in the Tangier Sound region (Figure
               RM       Ralh am         aooft cro*                 53). The parasite also was found in the Little
               MM       iNd 9- - M shwe som PACk
               N"WE     Nantlooke Xwer  Wedpkp"                    Choptank and Choptank Rivers, and to a
               NWS                      W11110" show
               PPM      ft-, - PNIUW    Ceder PoW                  lesser extent in Eastern Bay. Maximum inten-
               PX"      ftamem Over     Moak of IsimW
               usm      UPPW a"         H '                        sities for H. nelsoni in 1991 were 0.5, associ-
               UsTs                     Thr" Sitram                ated with prevaIences of 20%.
               WffiW    Wkwur"o Nver    MIL verfum Wind
               Wsau     Weelem Sham     auder
               Ws"                      R" PovW
               we"      we"" shore      "00 kiww                   Two analysis techniques were used for the
               WSW                      H - PWM
               WWIA     W500"doo we"    LWWM                      determination of H. nelsoni disease level in
               WWUW                     KM VAIrt                   1990 and 1991: blood histocytology and
                                                                   histology of tissue sections. The results shown
                                                                   in Figures 52 and 53 are a mixture of the two
                                                                   methods. In cases where techniques were
                                                                   duplicated, the method that gave the higher
               Association of Perldnsus marinus Intensity          intensity index is represented.
               %4th Mortality
               There was a strong positive correlation (r2         Harvest
               0.75, p<0.0001) between 1991 oyster mor-            Harvested Oyster Bar Identification
               tality and P. marinus intensity (Figure 50). At     Of the 64 MFS oyster bars, 21 (33 %) were
               intensities below 1.0, mortality was consistent-    characterized as harvested or productive for
               ly below 10%. Greater variation was shown           the purposes of this report (Table 8). The list
               by oyster bars with an intensity index @-_4.0;      was compiled with the aid of Maryland De-
               on these bars, mortality ranged from 25-95          partment of Natural Resources personnel who
                                                                   identified MFS oyster bars that had had har-
               The relationship between P. marinus intensity       vest activity, based upon overflight or re-
               and mortality was similar for 1990 and 1991         search vessel observations. The two harvest
               (Figure 51). Mortality, intensity, and preva-       seasons, 1990-1991 and 1991-1992, were not
               lence all increased in rough proportion from        separated; all oyster bars on this list were
               1990 to 1991.                                       considered as "harvest bars" throughout the
                                                                   two seasons. For interpretive purposes, it
               Reappearance   of Haplosporidium nelsoni in         should be noted that many productive oyster
               Maryland                                            bars were not represented on this listing,
               Analysis at selected sites for the appearance of    because they were not included in the MFS.
               H. nelsoni disease indicated a resurgence of


                                                               50






             Monitoring Maryland's Oysters


              E 4.5 t o 6 (3)
              N 3 t o 4.4 (7)
              i@/' 1.5 io 2.9 (1)
                       0.1 io 1.4 (1)


























            Rgure 49. PwMns&m marinus intensity at sites with spat counts greater than 3W per bushel. 1991.                               MEN


                                                                      51








                 Monitoring Maryland's Oysters

                      0-


                     80-


                     70-


                     Go-

                 q:
                 0   50-
                                                                                                        m


                 cr- 40-
                 w


                 z   30-
                 0

                     20-


                     10-


                      0--
                        0
                                                          INTENSITY INDEX


                 Figure 50. Correlation at oV*tor numlaft with PwA*wuv nwWmw intensity, 1990 and 1991; r0.96; p < 0.0001.
                      3-1                                                         E23             90
                                                                                  INTENSITY
                                                                                  m             -80
                                                                                  PREVALENCE
                    2.5 -                                                         m                  -
                                                                                  MORTAL"       -70


                      2- 'oo                                                                      60
                w
                0                                                                                    cc
                z                                                                               -50  0

                     1.5-
                F5                                                                              -40  z
                z                                                                                    <
                w                                                                                    w
                z                                                                                 30 Z
                                                                                                     w

                                                                                                -20  W>
                                                                                                     cc
                     0.5-
                                                                                                -10

                      0                                                                         -0
                                          1990                         1991

                 Figure 51. Pleridmus madnue Intensity Index, provalanoo, and oVater mortaft averaged over al slue.





                                                                         52







             Monitoring Maryland's Oysters










                                                       Of a





                                                                                                 44









                                                                                                  *U







           Figure 52. hapAwpoflAmn nakani prevalence (bold Italic numerals) and interwity, 1990. Ali altos sampled we showwn.






                                                                       53






              Monitoring Maryland's Oysters












                                                        7.&      092













                                                                                  .7




                       OL&

                                           V


                                                                                    top,--


                                                                                                44






           Figure 53. HapAwpod4um nek" prevalence lbold italic numerals) and Intensity, 1991. AN sit" sampled we shovm.





                                                                    54


0






                  Monitoring Maryl6qmd's Oysters

                  Six of the 21 MFS bars designated as harvest                        seeding. 0qTqIqle effect of seed on population
                  bars were located in the northern portions of                       structure could not be determined for the
                  the Bay. Another four were along the mid-                           harvest bars as a group.
                  western shore of the Bay. Together these two
                  regions comprised roughly half (10) of the                          Differential effects of disease and mortality on
                  harvest bars sampled. Noticeably absent in the                      harvested and non-harvested bars were appar-
                  harvest bar listing were many sites in Tangier                      ent. Long-term total mortality for non-harvest-
                  Sound, the Choptank River, the Potomac                              ed bars was 22% in 1990 and 38% in 1991.
                  River, and Eastern Bay. Together these tradi-                       Harvested bar mortality was 8% in 1990 and
                  tional oyster production regions contribute                         18% in 1991 (2Mle 9). P6q&0qMnsus prevalence
                  only three sites to the list of harvest survey                      for non-harvested bars was 85% (1990) and
                  bars.                                                               94% (1991). For harvested bars, these values
                                                                                      were 41 % and 66%. Pqeqr2qkns2qus intensity index
                  Comparison of Harvested Oyster Bars to All                          values for non-harvested bars were 3.3 (1990)
                  MFS Bars                                                            and 3.7 (1991). Harvest bar intensities were
                  Although these oyster bars may not have fully                       1.9 (1990) and 3.0 (1991).
                  represented where harvest activity was cen-
                  tered during the 1989-1990 and 1990-1991
                  oyster seasons, comparison of the harvested                         Table 9. Comparison of harvested and non4tervested oyster
                  bars against non-harvested oyster bars for                          bare, 1990-1991. Values we avaraqged over 42 oyster bars
                  1990 and 1991 showed distinct differences                           qI'nonq4tervested') or 21 bar* 2qMarvested"q).
                  (4qMle 9). Oysters were more abundant per                                           11q11001-4q@Wq!                     I"
                  bushel of substrate on harvested oyster bars,                                       1990   q1q99q1        11q9q9q0    q1q9q9q1
                  with harvested bars having 2-3 times as many                        cowqw
                                                                                      4qUve              84      71          121      119
                  market oysters as non-harvestqed bars. Predom-                       Markets          32      23          q6q2       qGqI
                  inance of small (< 3 in.) oysters was not so                        qsn,.0qf0qt           52      47          q59       q69
                  mar8qied on harvested oyster bars. This distinc-                      qgrnallqmarkot    1.63   2.04        0.9q5      0.9q6
                  tion was strongly reflected in smaqlql:market                         0qNorta0qwy q(8qSq)
                  ratios. On harvested bars, ratios were near 1: 1                    Total            22      38            q8      is
                  for both years. On non-harvested bars, the                          Markets          2q6      48            q8      19
                  ratios were 1.6:1 (1990) and 2.0:1 (1991).                          gnm0qf0qt            20      29            9      Is
                  The relatively lower number of small oysters                        sins 4q"4q&qht q(qMqMq)
                                                                                      All              7q6      71          79       79
                  could have had a relationship to spatqfall. Non-                     Market.          0qW       87          so       91
                  harvested oyster bars showed a significantly                        arn0qwqis           q62      q54                   q59
                  higher level of spatqfall for both sampling                          qPqwqkqkqwqm MaIRqIMUS,
                  years. The preponderance of harvested bars in                       Prevalence 18q%)   q9q5      94          41       q66
                  traditionally low spat8qfall areas must, however,                     Severity index   3.3     3.7         1.9      3.0
                  be considered in this relationship.                                 qIntqerm20qf20qt index   3.0     3.q6         1.2      2.0
                                                                                      Spat per bqt2qnhqe0ql  0q62      27          47       93
                  Of the 04 MFS oyster bars, 15 were subjected                        Most condition'  4.2     4.3         4.7      4q6.3
                  to recent (within 3 years) seeding. Of the 21
                  harvest bars, 9 (43 %) were subjected to recent                     14 = qn2qwdium m0qinuqe; 8q6     rnqedqlurn pk6qn.


                                                                                 855
 







                Monitoring Maryland's Oysters

                In general, harvested bars exhibited      <30%      The population of oysters on harvested bars
                mortality and P. marinus intensity <3.0             was similar in size structure to the composite
                (Figure 54). T`wo harvest bars on the Western       of all MFS bars in 1990 (compare Figures 24
                Shore-Hog Island (WSHI) and Butlers                 and 56) In 1991, this structural similarity was
                (WSBU)-did, however, exhibit mortality              no longer apparent (Figures 25 and 57).
                >50% and intensity >4.0.                            Harvest bars, while showing increased mortal-
                                                                    ity throughout all size ranges, still exhibited a
                Two non-harvest bars had low mortality              normally distributed population size structure.
                ( < 15 %) and intensity ( < 1. 5). The lack of      Ile composite of MTS bars, both harvested
                harvest activity on these bars apparently was       and non-harvested, exhibited strong erosion of
                not related to disease and mortality. They          this structure due to mortality in the 50-80mm
                simply did not have enough market oysters per       range. Likewise, a much higher proportion of
                volume of substrate (<25 per bushel of sub-         larger size classes was dead on the MFS bars
                strate) for practical harvesting. The majority      in 199 1.
                of non-harvested bars had P. marinus intensity
                > 3. 0 and mortalities > 30 %.                      Although MFS harvest bars may not have
                                                                    been reflective of fishing effbrt (only the
                There was an apparent trend toward a lower          presence of harvest activity) in a regional
                density of market oysters with increasing P.        sense, aggregation into five generalized re-
                mafinus intensity (Figure 55). Non-harvested        gions provided some insight (Figures 58-62).
                bars all had < 65 market oysters per bushel of      In 1990 the Northern Bay and Chester River
                sample substrate. There was not strong corre-       regions had population profiles very similar to
                lation between number of market oysters and         that of all 1990 harvest sites (Figure 58). In
                A marinus intensity for either harvested (r==-      199 1, the population profile separated into two
                0.32; p=0.23) or non-harvested (r=-0.21;            major size class modes. The mode centered at
                p=0.28) oyster bars. Harvested bars, in             60mm was related, to a large extent, to intro-
                general, had > 40 market oysters per bushel.        duction and growth of transplanted seed oys-
                Oyster bars with P. mafinus intensity <2.0,         ters, as spatfall was low in northern regions in
                combined with a sufficient density of market        1990. The second mode, centered at 90mm,
                oysters, were certain to be harvested.              was most likely the yearly carryover of the
                                                                    1990 central mode. A slight decrease in oyster
                A view of population profiles for harvested         numbers was apparent, as well as the begin-
                oyster bars in 1990 and 1991 indicated some         ning of apparent mortalities. There was some
                                                                    overall growth of this grouping of oysters, as
                differences. In both years, peak size class         seen by a slight rightward shift of the peak to
                abundance was - 75-80mm (Figures 56 and             a larger size.
                57). Mortality, however, was greater on the
                harvested bars in 1991 than in 1990. The total      Harvested bars in 1990 in the mid-Eastem
                number of market oysters decreased slightly in      Shore region likewise showed the same nar-
                1991.                                               row, highly pronounced central mode of
                                                                    oyster size structure (Figure 59). Again, the
                                                                    peak was centered at 75mm (3.0 in.). In 1991,


                                                                56








              Monitoring Mary&nd's Oysters

              a very similar peak was present at the same         density of oysters per volume of substrate was
              location. Incorporation of last year's spat/seed    lower by nearly half in 1991.
              can be seen centered at 45mm. Of note on
              these harvested oyster bars is the almost total     Estimation of Harvest Mortality
              lack of mortality (as compared to the high          Our estimate of annual (1990-1991) harvest
              mortalities previously shown for all MFS bars       mortality on harvested oyster bars included
              in this general region).                            within the MFS was 53 %. This value was
                                                                  obtained by;
              Maryland Western Shore harvested oyster bars
              in 1990 again showed the characteristic profile     1) Numerically subjecting the 1990 live oyster
              for harvest bars (Figure 60). The large central        population on these oyster bars to average
              population mode was centered at 67mm.                  1991 harvest bar mortality (18 %). Compar-
              Mortality was high within this mode. In 1991,          ison of the projected natural mortality to
              the effects of mortality due to disease were           the 1991 actual mortality (box counts)
              dramatic. Although growth was exhibited, as            showed strong similarity in the size and
              shown by a general shift to the right by the           shape of both distributions (Figure 63).
              population, the principal mode of population           Variations between sampling years in live
              abundance of 1990 was removed due to mor-              oyster counts due to seeding were apparent
              tality and or harvest. The high mortality cen-         in the 37-67mm size classes.
              tered at 75mm may, in fact, have been early-
              dying remnants of the oysters which grew            2) After adjusting the 1990 live oyster popu-
              from a central peak of 75mm in 1990 to a               lation for natural (including disease) mor-
              central peak of 90mm in 1991.                          tality, live oyster counts for each 5mm size
                                                                     class were adjusted upward 20mm to reflect
              The lower Eastern Shore in 1990 exhibited a            growth between annual sampling periods.
              population mode at 70-75mm (Figure 61). The            T'he difference between 1991 actual live
              effect of mortality on these harvested bars was        counts of oysters over 85mm and live
              negligible. In 1991, the impact of mortality           counts predicted by the above calctilations
              was more pronounced on larger oysters. The             produced the estimated harvest mortality
              total number of oysters collected in the sample        (Figure 64).
              was lower, due to the mortality within the
              1990 mode of oyster abundance. Little appar-
              ent recruitment from the previous year's spat
              was apparent.

              Harvest bars within the Potomac and Patuxent
              systems exhibited a narrow population struc-
              ture in 1990 (Figure 62). The population
              mode was centered at 75mm. This size class
              showed apparent overall growth to a central
              Peak of 90mm in 1991, but also showed a
              great increase in mortality for 1991. The


                                                              57








                 Monitoring Maryland's 0@sters



                     100-

                      go-      AL
                               HARVESTED
                               -+-                                                      4-
                      so-      NOT HARVESTED
                 A
                      70-


                      60-
                 cc
                 0                                                  4-
                      50-

                 cc   40-
                 w
                 @7              HARVEST MEAN
                 z    30-

                      20-

                                       A,                                     NO HARVEST MEAN
                      10-           A,


                        0-
                         0            1
                                                       INTENSITY INDEX


                 Figure 64. Correlation at oyster mortality with Pwkkwsw nww*= intensity on harvested and unharvested oyster bars, 1991.

                            160-


                            140-                                                  HARVESTED
                         co
                         Cr
                         LU                                                       NOT HARVESTED
                            120-

                         0
                         1.- 100-
                         Ui
                         y                               I HARVEST - MEA
                         ir
                               80-          A
                         cc                                                NO HARVE7ST 7-M7EA7N]
                         w                            C3
                         co                           AL
                               60-                                           A
                         z              A
                               40-                                 +    +


                               20-                                             4  4-
                                                               44-   -1:+-

                               0-
                                 0                                           4                     6
                                                         INTENSITY INDEX
                 Figure 66. Comparison of market oyster density (counts per bushel of substrate) with P&*Wsuv msaWus intensity an harvested
                 and unharvested oyster bers. 1991.
                                                                            4



                                                                       @NO HARI

                                                                     58








                     Monitoring Maryland's Oysters




                                                                   450

                                                                   4m
                                                                   no                  i              M BDXB
                                                                   Sao                    4                LIVE
                                                                 1
                                                                   50
                                                                   1100
                                                                   ISD






                                                                      11 32 It fig It 72  So It 101 112 122 131 142 lot lot
                                                                                           SM CUM


                                                           Figure 56. Harvested oyster bare population structure,
                                                           baywide, 1990.





                                                                   Am

                                                                   4m
                                                                   Uo                                      BDXES
                                                                                                           UWE
                                                                   130                    :A.

                                                                   IDD

                                                                   ISO

                                                                   100




                                                                      12 32 41  BU2 81 72    It 101 112 122 131 142 lot 152



                                                           Figure 57. Harvested oyster bar population structure.
                                                           baywide, 1991.























                                                                                               59








                             Monitoring Maryland's Oysters


                                      100                                                                                            Ian


                                                                                                                                                     J                             =T-R
                                                                                     un                                                                                            Uw

                                                                 .410,






                                                                                                                                     20


                                                     @A'
                                         12 31 42 51 92 71       B2  02  102 111 112 132 142 IU 181                                     22 31      at  U       792 12 lot 111 112 132 141 152 It
                                                                  SM CLASS


                             Figure 58a. Harvested oyster bar population structure by                                      Figure 58b. Harvested, oyster bar population structure by
                             component; Northern Bay, Chester River regions, 1990.                                         component; Northern Bay, Chester River regions, 1991.





                                      120                                                                                            120


                                      IOD                                                                                            100
                                                                                     am                                                                                            Koo

                                                                                     UVE                                                                                           LIVE



                                      an                                                                                             Be


                                      so                                                                                             44


                                      20                                                                                             20



                                         22 32 42 52 U 71 52 02 102 111 112 132 142         152112                                      12 31  42 U U      71  52 U I D2 111 192 132 142 192 162
                                                                  MR CL*2&                                                                                      312t aim


                             Figure 59a. Harvested oyster bar population                    structure by                   Figure 59b. Harvested           oyster bar population structure by
                             component; Mid Eastern Shore, Choptank River regions,                                         component; Mid Eastern Shore, Choptank River regions,
                             1990.                                                                                         1991.






                                      IIII)                                                                                          Ian


                                      160                                                                                            1"


                                      120                                                                                            Ito
                                                                                     Lrn                                                                                           LK
                                      log                                                                                            log
                                      an                                                                                                                       A

                                      Do


                                                                                                                                     40


                                         12 31 42 91    U 71    52 92 M     111 11;732'142 132 Iff                                      12 'n 42   U   U 71    B2 92  lot 111 112 132 142 152 189
                                                                  SIX CILM


                             Figure 60a. Harvested oyster bar               population structure by                        Figure 60b. Harvested oystre bar population structure by
                             component: Western Shore region, 1990.                                                        component; Western Shore region, 1991.

                                                                                                                 60








                   Monitoying Maryland's Oysters


                           160                                                                          ISO

                           ISO                                                                          1140
                           120                                                                                                        MBOM
                           IOD                                  LIVE                                    120                                LIVE
                                                                                                        '00


                                                                                                        00


                           so                                                                           so

                           48                                                                           44


                           20                                                                           20

                             11 31 42 51 62 71 92 12 112111112'11214110112                              0
                                                                                                        12 32 42 U 62 71 62 IpI 101 111 112 132 142 152 102
                                                                                                                            Sm CIAIS

                   Figure 61 a. Harvested oyster bar population structure by                                                                     --
                                                                                              Figure 61b. Harvested oyster bar population structure by
                    omponent; Lower Eastern Shore region, 1990.                               component; Lower Eastern Shore region, 1991.





                           log                                                                          100



                                                                                                                                           BoKTK

                                                                                                                                          UVE





                           40




                             12 31 42 81 62 71 92 01 101 111 122 132 1142 IS2 162                       12 32 42 111 62 71 62 *91 101 111 Z1,31142 IN 162
                                                                                                                            SIX


                   Figure 62a. Harvested oyster bar population structure by                   Figure 62b. Ham sted oyster bar population structure by
                   component; Potomac River, Patuxent River regions, 1990.                    component; Potomac River, Patuxent River regions, 1991.

























                                                                                        61








                   Monitofing Maryland's O@sters



                                                      30D

                                                                                          1991 LIVE OYSTERS

                                                      230



                                                  0200
                                                                                           1990 LIVE OYSTERS
                                                  V)
                                                  0   150
                                                  X

                                                                                                    ACTUAL MORTALITY




                                                      so
                                                                                                  PREDICTED
                                                                                                  1991 MORTALITY



                                                        22 32 42 52 $2 72 82 92 102 112 122 132 142 132 162 172 192
                                                                                 SIZE CLASS (MM)



                                           Figure 63. Comparison of 1990 harvested bare live oyster population structure subjected
                                           to a simulated 18% mortality to actual harvested bare 1991 live oyster counts.







                                                      300



                                                      250




                                                      200
                                                                           ?        0
                                                   0

                                                                               0.
                                                   W  150                      00   0
                                                                        io
                                                   1--                  0      00   0
                                                   (n                   0.     00   0
                                                   >-                   000    00   0
                                                   0                           00
                                                                        00     00
                                                   Ld 100               %0     000"o
                                                                      0   0    0000
                                                      J               0   0    0000
                                                                      0   0    0 0? 0
                                                                      0   0    000.0
                                                                      0   0    0000
                                                        50           of 0 0    0 ?0
                                                                      00  0    00?.
                                                                      00  0    000.0
                                                                    V00   0    0000
                                                        0          @, %.  %    $00M.P.         1.1111 . - .     -
                                                              22 32 42 52 52   72 02 92 102112 IZ2 132142152162172152
                                                                               . SIZE CLASS (MM)


                                           L
                                           Figure 64. Simulated harvest mortality on harvested oyster bare (53) based on a 20 mm.
                                           grow out of the 1990 live oyster population (Figure 61).
                                                                          0
                                                                          0
                                                                          0
                                                                          0
                                                                          0
                                                                          0
                                                                          0
                                                                          0
                                                                          00
                                                                                    00
                                                                           0          '0
                                                                           0           0
                                                                           0
                                                                                      :0.
                                                                           0
                                                                           0.
                                                                           0.
                                                                           01          $1. $1. $00. %.0.



                                                                                 62








              Monitoring Maryland-s Oysters

                                                      IV. DISCUSSION
              *
                    opsis of Oyster Population Results            Per*insus has historically been characterized
                   n                                              as a progressive, slowly killing disease. It
              Inspact of Disease                                  may take up to three years after initial infec-
              The MFS results suggest that parasitic infec-       tion to cause death in an oyster, although
              tions had the most important impacts on oyster      death in the second summer is typical (And-
              populations between 1990 and 1" 1. Although         rews 1988). High mortalities were exhibited
              both P. marinus and H. nelsoni have been            by 1 + and 2 + year claws in the 1990 and
              responsible for oyster mortalities in Chesa-        1991 MFS. High mortalities in the I+ year
              peake Bay since at least the 1950's (Kennedy        class at some sampling sites may have been
              and Breisch 1981; Andrews 1988), the current        caused by H. nelsoni or H. nelsoni in combi-
              level of P. marinus disease in Maryland             nation with P. mapinus (many sites were not
              waters is unprecedented. Pey*insus and H.           analyzed for H. nelsom).
              nelsoni are both microscopic protozoan para-
              sites with multiple life stages. Pei*insus is       An adage of some significance to the current
              strongly influenced by temperature, exhibiting      harvest situation is that an oyster takes three
              near dormancy in winter (Andrews 1988). The         years to grow to a marketable size (76mm or
              prevalence and virulence of H. nelsoni are          3 in.). Results from selected sampling sites
              largely related to salinity. High salinity can      and regional aggregations of sites support this
              increase the virulence and spread of the dis-       assumption. Despite small differences in
              ease whereas lower salinities can eradicate it      growth rate, the putative 2 + year class gener-
              (Haskin and Andrews 1988).                          ally was centered near 76mm. These oysters
                                                                  would have settled in the summers of 1988
              Pey*insus and H. nelsoni historically have had      (1990 survey) and 1989 (1991 survey), giving
              different patterns of mortality in oysters.         them roughly 2 'A growing seasons to approach
              When epizootic, H. nelsoni can kill oysters         market size. Some of these oysters would have
              throughout the summer after initial spring          entered the fishery during the W and winter
              infections. Springtime mortalities due to H.        of the survey, whereas others presumably
              nelsoni also may be caused by overwintering         would not have reached legal size until the
              dormant infections. There appear to be inter-       following harvest season.
              actions among temperature, salinity, and
              possibly other controlling factors that affect      The highest mortality of oysters was occurring
              the dynamics of H. nelsoni infection and            in the size class that was just entering the
              lethality (Haskin and Andrews 1988). The            fishery. Thus, just as oysters were approach-
              methods for numerical sta&g of H. nelsoni           ing a marketable size, they were dying at their
              and A marinus are simidar, but laboratory           fastest rate. Most of these mortalities were
              observations suggest that H. - nelsoni can cause    attributable to P. marinus. Also, heavily
              higher oyster mortalities at lower diagnostic       infected populations virtually ceased to grow.
              intensities.                                        This effect has been documented in experi-
                                                                  mental work (Paynter and Mallonee 1990),
                                                                  and the MFS results clearly showed the effect

                                                               63








               Monitoring Maryland's Oysters

               of this growth impairment on natural popula-         or increasing the prevalence of parasites in
               tions. Perhaps the clearest example of this was      areas where they are not abundant (Andrews
               at Patuxent River sites between 1990 and 1991        1988).
               (see Figure 35). The 2+ year class of 1990,
               which was showing the beginnings of high             Mortality as estimated by box counts does not
               mortality, grew an average of only about             show its full impact (due to disease or other
               10mm to the 3+ year class in 1991.                   causes) on an age class. An underlying as-
                                                                    sumption of these estimates is that boxes do
               Parasite-induced mortalities and         reduced     not remain articulated for more than one year.
               growth have important implications for harvest       Box counts largely reflect an annual, or more
               production. At the same time oysters are             specifically summer-long mortality, so they do
               approaching market size, they experience their       not indicate mortality of the age group in
               highest mortalities; and because their growth        previous years. Although age groups vary
               is stalled, mi effect they are subjected to          from year to year in abundance as they enter
               increased risk of mortality before they are          the I + year class, obvious declines in size of
               large enough to be harvested. A small increase       older age groups is a reflection of cumulative,
               in the time oysters remain disease-free in the       multi-year mortality for the age group.
               early life stages would greatly increase their
               chance of survival to market size. The combi-        RecrWtment and Broodstock
               nation of massive mortality in the 2 + year          There was a lack of readily definable year
               class and growth inhibition caused by A              classes over 3 + for most sites. Oysters over
               marinus indicates that if oysters were given a       150mm (6 in.) were virtually absent at all
               six month head start free from Peibnsus dis-         sampling sites. Oysters over I 10mm (4.3 in.)
               ease, they could survive to a marketable size.       were rare. Age estimates from length frequen-
               Rearing oysters in a disease-free aquaculture        cies are less reliable for older oysters. We
               environment for 6-12 months, followed by             have not attempted to identify age classes
               placement on natural oyster bars, is a potential     beyond 3+ or occasionally 4+.
               stock enhancement method. An alternative
               method would be immediate movement of                Despite variation between sites, individual site
               seed to low salinity areas prior to initial          population size structures identify the 2+ year
               infections during the summer disease season.         class as falling in general between 70-95mm.
               Whatever oyster movement scenarios were              'Me 3 + year class was identified as lying
               employed, the objective in managing around           between 80-115mm. On a Baywide basis, the
               P. marinus is to remove spat early from              I + year class was not obvious in 1990, pre-
               disease-prone areas. There are two reasons,          dictably so given the poor 1989 spat set
               however, why these schemes might not con-            (Krantz 1990). In 1991, the I + group was
               tribute to a significant increase in adult stocks    apparent in the 30-60mm range, with a peak
               or harvests. First, both hatchery rearing and        at 45mm. Spat set was substantial, although
               seed movement are expensive, and subject to          below average, in 1990 (Krantz 199 1). We
               failure for various reasons unrelated to dis-        expect that the 1992 survey will show a large
               ease. Second, movement of seed from areas            peak in the 1 + category because of the large
               with severe disease problems risks introducing       1991 spatfall (Krantz 1992), unless these


                                                                64








               Monitoring Maryland's Oysters

               oysters are killed by disease in the summer of        affected the reproductive potential of the
               1992. Lack of oysters older than 2-3 years            oyster resource. Full understanding of stock-
               within the surveyed population implies that           recruitment relationships in Maryland's oyster
               two consecutive years of poor spatfall could          populations will require additional research
               substantially reduce Maryland's already de-           directed toward these questions (Rothschild et
               pleted oyster populations.                            al. 1989).

               When considering the importance of spatfall           On a Baywide basis, spatfall at the level
               and recruitment into the fishery, observations        observed in 1991 should be able to sustain or
               help place the data in perspective. First, it         enlarge the Baywide oyster population and
               must be understood that spat counts represent         fishery (given their survival to harvestable
               counts per volume of substrate dredged, not           size). Spat counts, however, do not neces-
               Bay bottom volumetric or density per unit             sarily reflect fecundity of the breeding popula-
               area determinations. Thus, they may not               tion. Oyster larvae which survive to settle as
               accurately reflect how dense spatfall is on the       spat probably reflect only a very small propor-
               bottom itself. Second, spat survival can vary         tion of the free-swimming larvae which are
               greatly from year to year because of numerous         produced each year (Kennedy and Breisch
               potential sources of mortality. In general            1981). Thus, settlement densities may not be
               however, spat counts on individual oyster bars        reflective of reproductive activity. Also, after
               of :!@ 20 per bushel contribute little toward the     larval settlement, survival rates are highly
               fishery in future years; a spatfall of @-_ 300 per    variable on a yearly basis. Mortality of very
               bushel is considered a harvestable "set" (a           small spat can be extremely high (i.e. during
               density of 350-450 spat per bushel is consid-         the period between settlement and the time
               ered economical for seed replanting purposes;         when fill sampling occurs; Newell and Kenne-
               Krantz 1990). Barring high mortalities, a set         dy 199 1). Therefore, it is possible that the
               of > 300 per bushel will support a productive         approximately five-lbld greater spat counts in
               fishery 2-3 years later.                              1991 could in fact have been produced by a
                                                                     lesser amount of larval production in 1991
               Spat densities in 1990 were average to poor           than in 1990. Very favorable environmental
               compared to the historical record, whereas the        conditions for spat survival could also have
               1991 set was excellent and extremely high for         produced these results.
               recent history (Krantz 1991; 1992). Although
               historical trends in spatfall have been general-      A further uncertainty in evaluating the impli-
               ly downward, high variability between years           cations of the 1991 set for broodstock poten-
               is typical and is a natural response to environ-      tial arises from the sampling methodology:
               mental conditions in addition to broodstock           only spat densities are measured, not spat
               potential. The high 1991 spatfall may have            abundance. In a condition of limited suitable
               alleviated some concern that Maryland's               habitat, larvae will in effect be forced to
               oyster broodstock had Men below a level               congregate on what is available rather than
               capable of maintaining the resource. Results          disperse in a wider fashion. This available
               from the MFS can shed little light on the             substrate is then accumulated and condensed
               question of whether broodstock depletion has          from wide areas of the bottom by the dredge


                                                                 65








                Monitoring Maryland's Oysters

                for the sample. Thus, in the hypothetical                exactly where marketable size oysters oc-
                situation where available substrate decreases            cuffed on the horizontal axis (Figure 59).
                from year to year, the sampling method could             Except for some larger size classes in residual
                inflate spat counts. This is not to say that the         numbers, the slope is smooth, indicative of a
                apparent high spat-set in 1991 was simply an             well-defined 2+ year class.
                artifact of sampling methodology, but rather
                that the results are not useful for estimating           Similarity of these slopes      may be a direct
                the condition of broodstock. It is possible that         effect of harvest. For both     years, it must be
                the dredge samples could be calibrated with              recognized that the MFS was taken after a
                the aid of concurrent patent tong samples (for           summer of oyster growth.       Thus, peak abun-
                which the area of substrate sampled is known)            dance of the 2+ year class would have been
                to provide more useful estimates of spat                 even further to the right immediately after the
                abundance.                                               fall-winter-early spring harvest season. Be-
                                                                         cause disease, as represented by the bulk of
                Impact and Implications of Harvest                       observed mortality, was virtually absent, and
                Although disease has been identified as a                growth rate in the mid-Eastern Shore region
                major cause of the reduced numbers of mar-               traditionally been considered good, the popu-
                ketable oysters, the effects of harvest may also         lation appears to be almost totally cropped
                be identified. Figure 26 shows a remarkable              past harvest size.
                similarity in the right hand slope of live oyster
                size frequency between 80-150mm for 1990                 In 199 1, a I + year class in low abundance
                and 1991, despite great differences in the               apparently was entering the population from
                slopes for similar size classes of boxes. In             1990 spat. Lack of apparent shift to the right
                essence, oysters were "disappearing" at almost           of the 2 + year class was not due to inhibition
                identical rates with increasing size in both             of growth due to disease. Rather, it appears
                years despite great differences in disease               that the effect of harvest cropped the larger
                levels. This suggests some additional factor is          individuals in the 2+ year class, which in
                at play. Figures 56 and 57 show the typical              effect did not allow the age group to appear to
                high-peaked composite population structure of            increase in size. Presence of a narrower curve
                harvested oyster bars. Since site variation may          in 1991 was due to the increase in size of
                obscure year -classes, population structure on           smaller 1990 oysters found in the size range
                harvested oyster bars in the Mid-Eastern                 -60-65mm in 1990.
                Shore region will be used as an example of
                what effect harvest may have on this slope               The harvest model mortality estimates pre-
                profile.                                                 sented in the results require several assump-
                                                                         tions about natural mortality, growth, and
                Harvest bars in this region, and survey-wide,            recruitment. The assumption of 20mm growth
                are virtually dependent on the 2 + year class            throughout the population for all size classes
                and possibly to some extent the 3 + year class           is arbitrary, yet possibly conservative for the
                for harvestable oysters. The population pro-             large mode of 1990 oysters centered between
                files for this region in 1990 and 1991 had the           60-100mm. As this size range of oysters
                near vertical decline of the population slope            comprised the large majority of the model's


                                                                    66








              Monitoring Marylmd's Oysters

              predicted harvest, and were not of large (i.e.       oysters which entered the 1990 population
              slow-growing) size, the assumed growth rate          structure in the 57 and 62mm size classes
                ay not be overestimated. Clearly, better           would have grown out in the model to the 77
              information on growth rates would be helpful         and 82mm size classes.
              m

              in calibrating this or other harvest models.
                                                                   Estimation of 18 % as the true annual mortality
              Selection of the 85mm and larger size classes        was based on 1991 average mortality for all
              (as opposed to 76mm or 3 in. harvest size) for       size classes between 37 and 122mm. Larger
              calculation of harvest mortality was based on        and smaller size classes were excluded due to
              the following criteria. The two size classes         low counts of live oysters and boxes, resulting
              eliminated from the analysis (75-79mm and            in large apparent mortality fluctuations. Al-
              80-84mm) showed higher actual live oyster            though mortality within the selected size
              counts than predicted oyster counts. With            ranges varied between 27 % and I I %, no
              these two data points included in analysis,          pattern based on size class was noted. The low
              harvest mortality would be reduced to 31 %.          estimate of predicted natural mortality com-
              Elimination of these data points was done due        pared to observed mortality (Figure 63) was
              to the indeterminate effects of seeding in           not problematic because actual mortality of the
              spring-summer 1991 on the left side of the           1991 population was used in the model. Size
              predictive curve. As the population curve of         classes where observed mortality was higher
              the 1990 live oysters was adjusted to the right      than predicted (67-87mm) were size classes
              to reflect growth, no incorporation of small         where 1991 mortality was higher than the
              seed oysters could be made.                          average.

              Our quantitative knowledge of seed impacts on        Although Maryland oyster populations may
              thew oyster bars is poor. However, if the            appear to be at near remnant levels, the oyster
               negative harvest mortality' observed was            in Maryland should in no way be considered
              more than a sampling artiflact, the effects of       endangered. The crisis is one of the oyster
              this "artificial" source of recruitment were         industry and to some extent a way of life.
              significant. Because it was unlikely that the        Oysters are present in large numbers in Ches-
              seed oysters ever would have recruited to the        apeake Bay. Their density on oyster bars has
              fishery in their native habitats, due to slow        however been reduced to a level where har-
              growth and disease pressure, the seed program        vest is not economically feasible on the major-
              should be viewed as a source of "real" re-           ity of the Bay's oyster bottom. A small num-
              cruitment. This is an important subject for          ber of oyster bars largely within the Upper
              further analysis.                                    Bay and Chester River, which disease has not
                                                                   heavily impacted, and which to a large extent
              Comparison of the 1990 and 1991 live oyster          are supplemented by seed planting, currently
              population structure in this model prior to          support the entire Maryland fishery.
              "growing" the 1990 population shows the
              large number of small oysters in the 1991            Potentialfor Management
              population which were not present in the 1990        The current scenario has been caused by a
              population structure (Figure 63). These seed         combination of three factors: disease, habitat


                                                               67








               Monitoring Maryland's Oysters

               loss, and harvest. Although the individual           long term, removal of oysters (i.e. shell) from
               contribution of each of these three factors          oyster bars and physical disturbance associated
               cannot be determined quantitatively by the           with harvests may have contributed to habitat
               MFS at present, together they have created the       loss (USEPA 1983). The role of harvest on
               current situation (Newell and Barber 1991).          the condition of oyster habitat is difficult to
                                                                    determine, although detrimental effects on
               In the case of disease, little can be done in the    oyster populations and habitat were reported
               short term to mitigate the situation. Proper         as long as 100 years ago (Stevenson 1894).
               transplantation of seed can lessen to some           Replenishment of oyster bottom by the place-
               extent the overall impact of P. marinus dis-         ment of dredged fossil shell has been success-
               ease. No "cures" are available, or foreseen, to      ful in rejuvenating, some areas of the Bay
               lessen the effects of disease. Development of        bottom (Abbe 1988).
               natural or genetically selected resistance in
               oysters to these diseases continues to be inves-     A curious note concerning habitat condition is
               tigated, but again holds no short-term prom-         the effect of disease-induced mortality on
               ise.                                                 oyster bars. Oysters dying of disease are not
                                                                    going to be removed from the bottom by
               No one can predict how the diseases P. mar-          harvest. IMus, in a sense, they are a natural
               inus and H. nelsoni will behave in the future.       replenishment to oyster bars. This contribution
               Examination of historical Maryland data              should not be ignored in terms of its overall
               shows that both diseases have fluctuated in          contribution to habitat enhancement. Our
               their range and intensity in Maryland's Chesa-       results clearly show the large percentage of
               peake Bay from the 1950's onward. The                boxes being added to the substrate. In some
               recent series of warm winters and dry sum-           regions of the Bay where mortality is highest
               mers has contributed to the historically high        and adult oysters not abundant enough for
               level of P. marinus disease. Certainly if con-       harvest, dredge samples come aboard filled
               ditions become unfavorable for parasite sur-         with freshly dead shell. This fresh cultch is
               vival again, their impact will lessen. In the        available for spat settlement.
               short term, P. marinus disease will likely
               remain at high and lethai levels within the          IMe Modified Fail Oyster Survey-Design
               oyster population. In addition, H. nelsoni           Considerations and Evaluation
               appears resurgent in Chesapeake oyster popu-         Survey Design Criteria
               lations. Largely undetected in Maryland's Bay        SITE SELECTION
               in recent years (Cooperative Oxford Laborato-        Although the number of sites selected for the
               ry records), H. nelsoni is returning apparently      MFS was to a large extent dictated by logis-
               because of high salinities favorable for its         tics, the results presented in this report indi-
               increase and spread.                                 cate that 64 sites is an adequate number to
                                                                    characterize the condition of Maryland oyster
               Habitat loss is a chronic rather than a short-       populations (there are over 1000 recognized
               term phenomenon, largely attributed to sedi-         "oyster bars" in Maryland, however, many of
               mentation and burial of shell which spat             these currently exist in name only). Variations
               require for setting (USEPA 1983). Over the           in oyster mortality, spatfall, and size frequen-


                                                                68








              Monitoring Maryland's Oysters

              cy between 1990 and 1991 appeared to be              produce significant harvests or amounts of
              attributable to changes within the populations       seed oysters.
              and not sampling variability.                        SAwLiNG RwndE
              Site selection was not optimal with respect to       The fall (October-November) time frame for
              the regional aggregations presently employed         the annual survey was dictated by two factors:
              to represent geographic and fishery zones. The       1) spat which set in summer reach a size at
              zones contained different numbers of sites,          which they can be identified by the unaided
              complicating quantitative regional compari-          eye and are past the early period of extremely
              sons. The mapped zones used for this work            high mortality; and 2) most of the adult mor-
              were generic regions created prior to site           tality associated with H. nelsoni and P. mar-
              standardization in the MFS. We are exploring         inus occurs during the summer. One drawback
              alternative. schemes for regional aggregation of     of this sampling period is that the oyster
              the data.                                            fishery season begins in October. Thus, on
                                                                   some oyster bars, an unknown portion of the
              Subsetting the survey sites for disease diag-        adult population will be removed just before
              nosis (43 of 64 sites or 69 %) caused some           and during the MIFS. If an objective of the
              difficulty in comparative analysis with the          survey were to assess the effects of harvest,
              overall MFS bars. The number of disease sites        an earlier survey would be better, however, a
              chosen was based primarily on laboratory             September survey would cause problems with
              processing constraints. Laboratory diagnosis         mortality and spatfall estimates.
              of all MFS sites would be helpful in the future
              if staff and budgets would permit it.                Incorporation of a spring sampling period in
                                                                   addition to the fkU period has been recom-
              The validity of consistently sampling the same       mended (Newell and Barber 1991), primarily
              oyster bars every year can be questioned in          for the purposes of estimating spat survival
              light of the fluidity of oyster survival on          prior to the second year of growth and winter
              individual bars. For several of the sampling         mortality. A late spring or early summer
              sites, the number of live animals was less than      survey could also provide estimates of disease
              is generally considered characteristic of viable     mortality before the start of the harvest sea-
              oyster bars. Natural dynamics, in addition to        son. Initiation of additional surveys has been
              disease and harvest, are likely to result in         precluded by a lack of resources to gather and
              long-term changes in the locations of produc-        process samples.
              tive bars. However, historical consistency,
              and long-term trend information are important        GEAR CONSIDERATIONS
              objectives of the MFS, and sites should not be       A bottom dredge is used for oyster bar sam-
              replaced simply because they are relatively          pling in the MFS. Recent oyster stock assess-
              unproductive. A valid reason for deleting a          ment work has employed patent tongs as the
              survey site would be the virtual absence of          primary gear. Each gear type has merits and
              shell, indicating that it is no longer oyster        disadvantages which depend upon the objec-
              habitat. A valid reason for adding sites would       tives of the sampling program.
              be if new, unsampled, areas of bottom were to


                                                               69








              Monitoring Maryknd's Oysters

              Patent tongs remove a relatively constant           indicated that size class structure on oyster
              volume of the bottom, thus allowing for             bars having low to moderate oyster densities
              sample size quantification. The bottom dredge       was not readily apparent from a 0.5 bushel
              removes upper surface substrate over an             sample. Because prior Fall Survey data was
              unquantifiable swath of the bottom. Patent          multiplied by 2 prior to entry on field data
              tongs undoubtedly are superior to dredges for       sheets to represent 1.0 bushel of material, the
              statistical quantification of results when data     1.0 bushel total sample in the MFS is consis-
              are required for a discrete, homogeneous area       tent with historical data.
              of oyster bottom (Rothschild et al. 1989).
              Material in the tongs can provide absolute          Replicate sampling was initiated for two major
              abundance estimates for a given area or vol-        purposes: 1) to provide for more diversified
              ume of the bottom. Therefore, tong sampling         sample area coverage than a single trawl; and
              can provide population estimates with confi-        2) to allow statistical inferences to be made on
              dence intervals (e.g., total number of oysters      the portion of the oyster bar population where
              on a given oyster bar, or average number of         the sample was obtained. Results from one
              oysters km' in a given river system).               sample can provide only information about the
                                                                  sample itself; replicate sampling allows infer-
              Because the dredge integrates a relatively          ences to be made about the population on the
              large area of bottom, it provides repeatable        oyster bar.
              estimates of various population characteristics
              with minimum effort. Adaquate coverage of           The overall sample size and the number of
              64 oyster bars by patent tongs would require        replicates comprising the sample were a com-
              great increases in labor and logistics over         promise between statistical confidence and
              what is currently employed. The inability to        practicality. Also, unlike studies where sam-
              estimate absolute oyster abundance with             pling is conducted for a single variable and
              dredge results is a serious drawback for mak-       sample number can be optimized for a speci-
              ing reliable estimates on individual oyster         fied confidence limit, many variables are sam-
              bars, but is a less serious problem and a           pled in this survey. On an individual site basis
              necessary trade-off when evaluating the re-         sample size and replicate number were chosen
              gional condition of the stocks and long-term        to adequately represent, in order of impor-
              trends. Inclusion of a patent tong analysis in      tance, the following population parameters:
              conjunction with the MFS would be advanta-
              geous. Dredge data could then be calibrated to      0  Age structure and relative population size
              units per am.                                       0  Mortality by size class
                                                                  0  Disease pressure
              SAMPLE SIZE                                         0  Relative spatfan (spat density)
              The original   decision to take five dredge         0  Recruitment of spat into the population and
              replicates of 0.2 bushels each (1.0 bushel total       fishery
              at each site) was based on the following
              considerations. Cursory examination of histor-      The results for three sampling sites indicate
              ical Fall Survey data (0.5 bushels of shell         that interpretation of age class and population
              analyzed from a single trawl at each site)          size is adequately served by the existing


                                                               70








               Monitoring Matyland's Oysters

               sample size (see Figures 36, 37, and 38).            replicates. This was because the removal of
               Mortality as a component of age group also           replicates at random by chance removed the
               appears to be well-defined by the existing           higher spat counts. The remaining samples,
               sample size. A weekly survey conducted on            therefore, had a lower range and mean than
               the Choptank River in the summers of 1986-           the fun sample. Confidence limits on very low
               1988 indicated that trawl samples gave highly        mean spat counts are of little concern, because
               reproducible estimates of mortality when             they predict virtually zero potential recruit-
               repeated over relatively short time intervals        ment.
               (Christmas and Jordan 1991).                         Translation of yearly spat counts into future
               The sample size for disease analysis (a single       harvest potential is a basis for any predictive
               sample of 30 oysters from each site) was             model. As with most marine invertebrates, the
               based on an existing Cooperative Oxford              number of surviving young compared to
               Laboratory protocol. According to binomial           number of larvae produced is incredibly small
               probabilities, if no disease is observed in a 30     (Galtsoff 1964). However important this factor
               oyster sample, the upper 95 % confidence limit       is to ultimate oyster fishery recruitment, its
               on the prevalence of disease in the sampled          magnitude is unmeasurable; and no manage-
               population is 11.6% (Sokal and Rohlf 1973).          ment action can mitigate its effect. However,
                                                                    once a spat has obtained a reasonable size (i.e.
               Ile value of replicate sampling for spat             at the time of the Fall Survey), the chance of
               counts was demonstrated for three randomly           survival throughout the first year should be
               selected sites (see Figure 14). Results clearly      reasonably high, given the absence of adverse
               showed the value of increasing the number of         environmental factors such as disease. A
               0.2 bushel samples. The 95% confidence               determination of expected spat survival into
               limits evaluated are overly stringent for spat       the I+ year class (i.e. from one Fall Survey
               counts (e.g., 90% would be more reasonable);         to the next) would provide background into
               however, the pattern of increased resolution         potential recruitment and also might support        I
               would be similar for lower confidence levels.        an analysis of how environmental conditions
               With less than 4-5 replicates, confidence limits     affect recruitment.
               for spat counts were unacceptably broad.
                                                                    Our results (Table 4; Figure 15) suggest that
               A statistical assumption of some significance        sample size or method of analysis is not
               to the accuracy of these results is that spatf-all   adequate to determine incorporation of spat
               must be randomly distributed on substrate for        into the I + year class with any level of confi-
               the confidence limits to be valid. Because we        dence. Additional analysis and survey modifi-
               have not yet tested this assumption, the confi-      cations (e.g., spat measurements) may shed
               dence limits should be viewed more as general        more light on this question.
               indicators of possible sample error than as
               exact estimators.                                    Improvements to Sampling Methodology
                                                                    FIFECTS OF REPLETION (SEED AND SHELL)
               One site (MRAS) showed a narrower confi-             Seeding and shelling of survey oyster bars
               dence interval with decreasing numbers of            complicates interpretation of MFS results.


                                                                 71








               Monitoring Maryland-Is Oysters

               Because placement of these materials is not       bution to the 1+ year class the following
               uniform over the bottom, judgement based on       year. Inclusion of spat measurements would
               visual examination of each sample is necessary    be advantageous to the MFS. As spat counts
               to assess whether such material is present.       can be very large at some locations and times,
               The dates, locations, and areas within oyster     a measurement of perhaps the first 50 spat
               bars of seed and shell placement need to be       encountered might suffice to generate a rea-
               included in the MTS database.                     sonable size frequency curve. Note that be-
                                                                 cauise of the lack of spat measurements and
               Oyster bars within Maryland's Chesapeake          the somewhat arbitrary nature of the distinc-
               Bay may generally be considered as two types      tion between "spat" and "smalls", the area of
               from a management perspective: those which        the size frequency diagrams (e.g., Figure 36)
               are replenished with seed or shell, and those     below about 40mm is essenWilly meaningless.
               which are not. To the extent that the purpose
               of the survey is to assess natural populations    In the historical Fall Survey, spat box counts
               of oysters, it would be beneficial if the MFS     were made as an estimation of spat mortality.
               portion of oyster bars sampled were not sub-      This was not included in the current MFS.
               jected to seeding or shelling as a matter of      Disintegration of spat boxes is so rapid that
               policy. Although similar sampling methods         accurate estimates of mortality cannot be
               could be applied to modified oyster bars for      obtained from an annual survey.
               the purposes of assessing success of plantings,
               MFS bars could be reserved for assessing the      PHYSicAL DATA
               natural background conditions of the popula-      Currently surface salinity, temperature, and
               tions. From another perspective, however,         depth are the only physical or water quality
               seed and shell transplants are "real world"       data collected by the WS. Although salinity
               components of oyster stocks. They may com-        is correlated with the spread and extent of
               promise estimates of "natural" mortality and      both P. mafinus and H. nelsoni (Andrews
               recruitment, but we are left with a semantic      1988), salinity at the time of sampling has
               question of what is natural.                      little correlation with A marinus disease
                                                                 levels (see Figure 48). Although the overall
               SPAT MEASUREMENT                                  salinity regime during the previous summer
               Currently, spat are not sized due to time con-    surely would show stronger correlation, these
               straints. As oyster spawning may occur thr-       data are not available on a site-specific basis.
               oughout the spring and summer, great differ-      Baywide spatial interpolations of salinity and
               ences in spat size are observable during the      temperature data on a seasonally averaged
               MFS. Variations in growth rates and the           basis from the Chesapeake Bay Monitoring
               timing of spatfall may be great on all scales     Program could generate more useful estimates
               from Baywide to individual animals on a           of these variables for the MFS sites.
               single oyster bar.
                                                                 DISEASE SUBSAMPLE
               Variable size of spat at the end of their first   Currently the disease sample is selected from
               summer after settlement may be responsible in     the pool of oysters accumulated from the five
               part for the difficulty in identifying the contri- dredge tows. It has been suggested that dis-


                                                              72








               Monitoring Maryland's Oysters

               ease samples be selected from replicate trawls.        MANAGEMENT AND ANALYSIS OF SURVEY
               That is, six oysters could be chosen at random         DATA
               from each of the trawls to produce the sample          Extensive monitoring programs produce large
               of 30. This procedure would allow for better           amounts of data and can generate large
               estimates of variation and confidence for              amounts of information, some useful, some
               disease variables, however, the logistic bur-          not. Although many graphics and tables are
               den, especially for the laboratory, would be           contained in this report, they represent only a
               significant.                                           small portion of the data and statistics generat-
                                                                      ed by the MFS. One purpose of this report is
               Oysters collected for pathology were of larger         to solicit suggestions as to what data and
               mean size than the populations from which              analysis scientists and management personnel
               they were obtained in both 1990 and 1991.              would like to see presented and summarized
               Disease sample oysters were, on the average,           on an annual basis.
               market size; while survey oysters as a whole
               averaged at about the break point between              A successful oyster monitoring program
               smalls and markets. If the disease subsample           should be able to provide information on three
               is to be representative of the population as a         aspects of management:
               whole, selection should be random. In gener-
               al, the effect of selecting larger oysters for         0  Biological and ecological conditions and
               disease analysis should be to bias the results            trends of the resource;
               toward higher disease prevalence and intensi-          0  Determine where regional oyster enhance-
               ty. For the 1992 MFS, oysters will be selected            ment strategies should be undertaken and
               at random from the pool of dredged oysters.               monitor their progress;
                                                                      0  Assess the relative impact of harvest on the
               Box CumwicAmN                                             resource.
               Dead oysters are classified in the MFS as
               gaper, class 1, class 2, and class 3 in order of       Infbrmation provided in this report addresses
               increasing apparent time since death. This             only the the first of these issues. Incorporation
               classification is consistent with historical           of refinements discussed below should im-
               survey data. As the large majority of box              prove the program's ability to address the last
               classifications are class 3, short-term mortality      two issues.
               is generally a small portion of overall mortali-
               ty. In areas with high disease mortality rates,        DATA DEVELOPMENT AND PRESENTATION
               samples taken during the summer months                 FORMAT
               often show higher rates of recent mortality            Primary statistics currently generated (Ap-
               than Fall Survey samples (SJJ; personal obser-         pendix A) fall into nine general categories of
               vation). Indication of high recent mortality is        information types.'On a bar by bar basis these
               of interest on an individual oyster bar basis          are:
               but not of high overall importance in terms of
               yearly monitoring. Since box classification            0 Numbers of live oysters and boxes express-
               entails little extra effort, it is recommended            ed as "smalls" or "markets"
               that the procedure be retained in the MFS.


                                                                  73









                Monitoring Maryland's Oysters

                ï¿½  Mortality categorized as to recent or long           only when the infection is systemic, whereas
                   term for "small" and "market" size groups            the rectal method detects disease agents in the
                ï¿½  Size information for small and market oys-           digestive tract. Although the rectal technique
                   ters                                                 may be more sensitive to parasite detection,
                ï¿½  Spat densities                                       staging may not be representative of true
                ï¿½  Type and amount of fouling organisms                 infection as opposed to ingestion of infectious
                ï¿½  Impacts due to seeding and shelling                  agents.
                ï¿½  Disease indices for A ntafinus and H. nel-
                   soni                                                 Although the results of the two techniques for
                ï¿½  Oyster condition and other parasites                 the MFS were similar, this may not be the
                ï¿½  Population profiles comprising oyster size           case during other seasons. In spring when new
                   and comparative abundance information                infections occur, the rectal technique may
                                                                        detect initial infections prior to their entering
                Except for the last category, all components of         the blood. This effect is reduced during the
                the MFS data are traditional statistics which           MEFS when summer-long infections have had
                express the condition of Maryland's oyster              a chance to enter the blood.
                populations. " categories of information
                except fouling and seeding and shelling infor-          Analysis for H. nelsoni similarly has multiple
                mation have been synthesized to produce                 techniques. Results presented for 1990 and
                results for this report. Incorporation of disease       1991 used mixed techniques. As with P.
                data directly into survey computer files is a           marinus, a standardized analysis (blood histo-
                new component of the monitoring system.                 cytology) will replace tissue exan-dnation for
                This modification has indicated the need for            the presence of this disease in future surveys.
                consistency in laboratory analysis methods.
                Currently multiple techniques may be used for           SIZE-FREQUENCY ANALYSIS
                the analysis of P. marinus and H. nelsoni.              The incorporation of individual oyster mea-
                Standardization is important for long-term              surements in the MFS showed the distinct
                monitoring. In the case of P. marinus disease,          population age structures unique to individual
                results presented for both years were gener-            oyster bars. In effect, age classes on individu-
                ated by rectal thioglycollate culture technique.        al bars respond in different ways, and trans-
                Although this has been the historical analysis          late the impacts of factors of previous years to
                method, its use has been partially replaced by          year class size, growth, disease, and mortali-
                a blood thioglycollate procedure.                       ty. Representing data as an average for all
                                                                        year classes within a site or region produces a
                Although similarity of the diagnostics has been         useful composite average but does not effec-
                shown in the results, it is recommended that            tively describe the natural situation.
                blood analysis should be the standard tech-
                nique for the MFS. The technique is quantita-           Although there were clear modal size groups
                five in terms of clinical staging and most              at many sites, interpretation of the modes as
                likely to be more representative of disease             specific age classes was not straightforward or
                within an individual oyster than the rectal             certain. it is possible that when spat measure-
                assay. Positive identification of disease occurs        ments are added to the MFS, we will be able


                                                                    74








              Monitoring Marylmd's Oysters

              to track age classes from year to year on a        calibrate mortality estimates and to test the
              given bar, because it will be certain that the     validity of the annual mortality assumption.
              first mode will be age 0 +, except in the
              absence of spatfall.                               At some sites fouling may be extremely heavy
                                                                 during a given year. Although the sampling
              SURVEY CALEBRATION NEEDS                           protocol includes removal of fouling organ-
              Lack of area or volumetric quantification of       isms prior to selecting subsamples, in many
              the dredge samples, possible biases in mor-        cases this cannot be done completely. The
              tality estimates, and the volume of fouling        percentage of fouling in a sample could be
              organisms (especially tunicates, MoIgula           used to adjust substrate volumes so that all
              manhattensis) introduce potentially important      samples would be based upon equivalent
              sources of error into MFS results.                 volumes.

              No absolute density or abundance infbrmation       Recommendations for Future Improvements to
              can be derived from the current survey. Patent     the Survey andfor Uses of Data
              tongs could be used to develop calibration         INTERACTIVE STATISTICS
              coefficients for the dredge samples by estimat-    Oyster population variables have been pre-
              ing the amount of substrate (shell) per unit       sented in univariate mode fbr the purposes of
              area of oyster bar. By knowing bushels of          this characterization report. For example,
              shell ml (patent tongs), numbers of oysters        mortality is presented in one figure and dis-
              (spat, markets, etc.) per bushel (dredge sam-      ease levels in another. The following compo-
              ples), and the area of the bar (maps, patent       nents of oyster populations are linked in many
              tong surveys), absolute abundance estimates        ways: spatfall, recruitment to adult popula-
              could be made from the dredge survey.              tions, size and growth of year classes, disease,
              Whether these estimates could be generated         mortality, and harvest. Site or regional classi-
              with a reasonable amount of effort or would        fications that take all or some of these impor-
              have enough precision to be useful cannot be       tant variables into account could be very
              determined until the method is tried.              useful to management. Multivariate classifica-
                                                                 tion techniques (e.g., discriminant analysis)
              The traditional assumption is that the time        can be employed for this purpose. The classi-
              frame of mortality estimates is one year. That     fications would be objective, yet could be
              is, all of the boxes (dead oysters with the        tuned to reflect management interests as well
              valves still attached) counted during the MFS      as biological characteristics.
              are assumed to have died within the year since
              the previous survey. Spatial and temporal          For example, a region which was unsuitable
              factors such as salinity and temperature could     for the transplantation of seed might exhibit
              affect the hinge disintegration process and        moderate to high spatfWl, two well-defined
              cause variability in disarticulation time. Stud-   year class groups, near 50% mortality in the
              ies are currently underway to assess variation     2+ age group, beginnings of mortality in the
              in disarticulation based on oyster size and        I+ year class, and high disease indices. A
              location. This infbrmation will be used to         contrasting classification might be bars that



                                                              75








               Monito.ring Maryland's Oysters

               have low spatfall, low disease indices, and a       have great effects on population comparisons,
               substantial population of older year classes.       seed and shell variables must be included in
                                                                   the data. One method for using this informa-
               POTENTIAL FOR POPULATION MODELJNG                   tion is to assign a vector for each oyster bar,
               Additional types of data need to be incorpo-        with the X and Y coordinates representing the
               rated before the NFS data can be used for           cumulative weights of recent (5 year) seeding
               population modeling: harvest information,           and shelling activity. Given accurate data, this
               physical data, and historical data.                 system could be used to evaluate the effective-
                                                                   ness of repletion as well as its effects on
               Harvest data are not available on a bar by bar      population structure.
               basis. Regional records of landings are main-
               tained, but these largely reflect the point of      HIsToRicAL POPULATION Am DLSWE DATA
               landing and not necessarily the region of           Historical Fall Survey data can be verified
               harvest. Although oyster bars on which har-         back to approximately 1980 and are available
               vest activity was observed were segregated for      for inclusion within the NFS data base. Oys-
               purposes of analysis, the effect of harvest on      ter disease data are present from 1963 onward
               population structure cannot be properly quanti-     and currently available on disk. The major
               fied. Short of monitoring harvest on MFS            difficulty in incorporating these data sets with
               bars, there is no adequate way to determine         MFS data is the lack of site consistency.
               the impact of harvest on MFS bars. A second         Sampling sites were highly variable in number
               sampling of harvested oyster bars after the         and location from year to year. Interpolation
               harvest season (spring) might provide some          techniques where data for unsampled areas can
               intbrination on what was removed after fW1          be generated from areas which were sampled
               sampling. This activity would require consid-       may hold some promise for improving this
               erably less effort than the Fall Survey, be-        situation.
               cause only a fraction of NWS bars are harvest-
               ed each season.


               Without intbrination to determine what com-
               ponent of the population has been removed by
               harvest, an integral and necessary component
               of any model would be lacking. At a mini-
               mum, we should have reliable infbrmation on
               which of the sampled bars has been harvested
               each year.

               Repletion data were included in the data base
               in order to examine the effects of seed and
               shell on the oyster population. However,
               because the data were found to be inconsistent
               and in need of verification, they were not
               analyzed for this report. Because repletion can


                                                               76








              Monitoring Maryland's Oysters

                                                   V. LITERATURE CITED
                  @be , G.R. 1988. Population structm of the       Krantz, G.E. 1991. Maryland oyster popu-
                                                                   lation status report: 1990 Fall Survey. Mary-
              American oyster Crassostrea Wrginica, on an          land Dept. of Natural Resources CBRM-OX-
              oyster bar in cenh-al Chesapeake Bay: Chang-         91-1. Annapolis, Maryland.
              es associated with shell planting and increased
              recruitment. J. Shellfish Res. 7:33-40.              Krantz, G.E. 1992. Maryland oyster popu-
              Andrews, J.D. 1988. Epizootology of the              lation status report: 1991 Fall Survey. Mary-
              disease caused by the oyster pathogen Perk-          land Dept. of Natural Resources CBRM-OX-
              insus marinus and its effects on the oyster          92-1. Annapolis, Maryland.
              industry. In: W.S. Fisher (ed.), Disease             Newell, R.I.E. and B.I. Barber. 1991. Sum-
              Processes in Marine Bivalve Molluscs. Amer.          mary and recommendations of the oyster
              Fish. Soc. Spec. Publ. 18:47-63.                     recruitment and standing stock monitoring
              Christmas, J.F. and S.J. Jordan. 1991. Chop-         workshop held at Horn Point Environmental
              tank River Oyster Mortality Study: final             Laboratories November 6 and 71, 1990. Mary-
              report. Maryland Department of Natural               land Department of Natural Resources, An-
              Resources CBRM-HI-91-1. Annapolis, Mary-             napolis, Maryland.
              land.
                                                                   Newell, R.I.E. and V.S. Kennedy. 1991.
              Galtsoff, P.S. 1964. The American oyster             Spatfall monitoring and partitioning the sourc-
              Crassostrea Wrginica Gmelin. Fish. Bull. 64,         es of oyster spat mortality. Final report to the
              480p.                                                Maryland Dept. of Natural Resources. Annap-
                                                                   olis, Maryland.
              Haskin, H.H. and J.D. Andrews. 1988. Un-             Paynter, K.T. and M.E. Mallonee. 1990. Site
              certainties and speculations about the life Cycle    specific growth rates of oysters in Chesapeake
              of the eastern oyster pathogen Haplosporidium        Bay and impact of disease. In: New perspec-
              nelsoni (MSX). In: W.S. Fisher (ed.), Disease        tives in the Chesapeake system: A research
              Processes in Marine Bivalve Molluscs. Amer.          and management partnership. Proceedings of
              Fish. Soc. Spec. Publ. 18:5-22.                      a Conference, 4-6 December 1990, Baltimore.
              Kennedy, V.S. and L.L. Breisch. 1981.                Chesapeake Research Consortium Publication
              Maryland's oysters: research and manage-             No. 137. Solomons, Maryland.
              ment. Maryland Sea Grant Publ. No. UM-SG-            Ray, S.M. 1952. A culture technique for the
              TS-81-04. College Park, Maryland.                    diagnosis of infections with Dermocystidium
              Krantz, G.E. 1990. Maryland oyster popu-             marinum, Mackin, Owen and Collier, in
              lation status report: 1989 Fall Survey. Mary-        oysters. Science 166:360-361.
              land Deptartment of Natural Resources                Rothschild, B.J., C.F. Chai, B. Golden, P.
              CBRM-OX-90-1. Annapolis, Maryland.                   Goulletquer, M. Homer, A.L. Chai, and B.

                                                                77








              Monitoring Maryland's Oysters

              Haskell. 1989. A field study of the population
              dynamics of the American oyster Crassostrea
              Wrginica in the Chesapeake Bay. Final report,
              1989. Chesapeake Biological Laboratory,
              University of Maryland. Solomons, Maryland.

              Sokal, R.R. and F.J. Rohlf. 1973. Introduc-
              tion to Biostatistics. W.H. Freeman and Co.
              San Francisco. 368p.

              Stevenson, C.H. 1894. The oyster industry in
              Maryland. U.S. Fish Comm. Bull. 12:203-
              298.


              USEPA (U.S. Environmental Protection
              Agency). 1983. Chesapeake Bay: a profile of
              environmental change. USEPA, Region 3,
              Philadelphia. 200p.



























                                                            78








               Monitoring Maryland-s Oysters

                                                        V11. APPENDICES

                     W`p      dix A. Modified Fail Survey Data Storage Flies and Fleld DescrilitiOnS

               Disease and population data from the Modi-           Field Descriptions-ARRAYA.DBF
               fied Fall Survey are entered into dBase U1+          SITE: as in ARRAY.DBF
               files at the Cooperative Oxford Laboratory.
               Summary documentation for the data manage-           DATE: as in ARRAY.DBF
               ment system is presented below. Data are
               stored in three main files:                          sAL: salinity (ppt), water surface.

               ï¿½  ARmy.DBF-individual oyster records of             TBe: temperature (*C), water surflice.
                  mortality and shell length based on 0.2
                  bushel subsamples                                 DEPTH: as recorded on fathometer (feet).

               ï¿½  ARMYA.DBF-Spat counts by subsample,               SuRTYPE: survey type, currently Fall Survey
                  salinity and temperature for each sample,         (F) or Other Survey (0).
                  fouling data, and bar repletion history;          BARTYPE: currently Natural (N), Seed (S),
                  ARRAYB.DBF-disease and detailed popu-             Other (0).
                  lation data for each sample.                      sPATI: spat count subsample # 1.
               Fleld descriptions-ARRAY.DBF
               srrE: four letter oyster bar identifier. First two   sPAT2: spat count subsample # 2.
               letters represent Bay region, last two letters
               oyster bar name (see Table 1).                       sPAT3: spat count subsample # 3.

               DATE: date of field sampling, dBase American         sPAT4: spat count subsample # 4.
               date format (mm/dd/yy).
                                                                    spAT5: spat count subsample # 5.
               SMPNUM: subsample number I to 5.
                                                                    mus: mussel (generally Brachidontes
               CLAM: size frequency class by 5mm groups.            recurvum) fouling of sample (%), designated
               Represented in file by midpoint value of class       live or dead, currently percent of trawl sample
               (45-49mm listed as 47).                              volume due to fouling (prior to removal of
                                                                    subsamples). Fouling is removed from sub-
               BOXTYP: dead oysters G =gaper, I= class 1,           sample material prior to volumetric determina-
               2 =class 2, 3 =class 3. Field left blank for live    tion.
               oysters.
                                                                    moG: tunicate (MbIguld manhauensis) fouling
                                                                          determined as above.



                                                                 79








                Monitoring Marylmd's Oysters

                OTH: % other fouling (type noted - typically         ToTLiv: total number of live oysters from five
                barnacles), determined as above.                     subsamples (1.0 bu.).

                TOTPER: total percent fouling of trawl sample        ToTBox: total boxes (dead oysters), all stages,
                (sum of mus, moo, and oTH).                          combined for five subsamples (1.0 bu.).

                SEED: seeding impact to sampled portion of           ToTmRK: total number of "market" oysters
                oyster bar; field length six characters; leftmost    @t3 in. (75mm) in total combined samples.
                character is seeding conducted in present year;
                each character to right indicates seeding one        ToTsML: total number of "small * oysters ( < 3
                year prior to current year (i.e. character space     in.), excluding spat, measured if greater than
                5 is seeding four years previous). Character         15mm.
                space 6 is seeding any time prior to 4 years
                previous. Presence of *X" in space(s) denotes        SMLMRKRAT: small to market ratio.
                seeding; "Y" in space(s) denotes visual confir-      (TOTSMUTOTMRX).
                mation of seed in dredge sample; example-
                "Y XX " (1991 sampling)=1991 seed ob-                mRKBox: market box count, total number of
                served in sample, bar seeded 1988, not visual-       market boxes, all stages.
                ly noted, bar seeded 1987, not visually noted.       smLBox: small box count, total number of
                SmuL: shelling impact to sampled portion of          small boxes, all stages.
                oyster bar, both fresh and fossil shell; data
                representation as with "SEED".                       sTmRxBox: short-term market box count, box
                                                                     stages "gaper", "stage 1", "stage 20, included.
                Field Descripflons-ARRAYBMBF
                srrE: as in ARRAY.DBF                                sismLBox: short-term small box count, as
                                                                     with short-term market box count.
                DATE: as in ARRAY.DBF
                                                                     LTroTmRT: long-term total mortality, mortal-
                YEAR: two number character designator for            ity of combined small and market oysters, all
                year (i.e. "91").                                    stages (TOTBOX / (TOTIIV + TOTBOX)) * 100.

                SAL: as in ARRAYA.DBF                                LTmRKmRT: long-term market mortality, as
                                                                     with long-term total mortality, but market
                TEMP: as in ARRAYA.DBF                               oysters only.

                DEPTH: as in ARRAYA.DBF                              LismLmRT: long-term small mortality, as with
                                                                     long-term total mortality but small oysters
                SURTYPE: as in ARRAYA.DBF                            only.

                BARTYPE: as in ARRAYA.DBF




                                                                 80








               Monitoring Maryland's Oysters

               sTToTmRT: short-term total mortality, as with         seeding in current year = 16, one year prev-
               long-term total mortality but gaper, stage 1,         ious = 8, two years previous = 4, three years
               and stage 2 boxes only.                               previous - 2, four years previous = 1, prior
                                                                     to four years = 0.5); magnitude of impact is
               STMRKMT: short-term       market mortality, as        sum of values in which seeding occurred;
               with long-term market      mortality but gaper,       values assigned from character placements in
               stage 1, and stage 2 boxes only.                      file ARRAYA.DBF, field sEED; e.g., "X X X"
                                                                     (1991 sampling), 1991 seed = 16, 1988 seed
               mmij@m: short-term small mortality, as with           = 2, historical seeding = 0.5, total seed
               long-term small mortality but gaper, stage 1,         magnitude = 18.5.
               and stage 2 boxes only.
                                                                     YsHEu: impact of shelling described as dis-
               AVGToTsiz: average total size, average size           tance on Y-axis coordinate, determination as
               (mm) of market and small oysters combined.            with XSEED above.

               AVGMRKSI:Z: average market size, average size         impmAG: seed and shell combined impact;
               (mm) market oysters only.                             vector of X-Y coordinates reflecting combined
                                                                     impact of seeding and shelling [(XSEE& +
                                                                              -21
               AvGsmLsiz: average small      size, average SiZe      YSHELL)
               (mm) small oysters only.
                                                                     swsiz: disease sample size, typically 30
               Avomox: average short-term (gaper, stage              oysters.
               1, stage 2) box size (mm), markets and smalls
               combined.                                             Avow: average oyster size in disease sample

               AVGLTBox: average long-term (all stages) box
               size (mm), markets and smalls combined.               MAniz: maximum oyster size in disease
                                                                     sample.
               smus: spat per bushel, combined total of 5
               0.2 bu. subsamples.                                   MINSIZ: minimum oyster size in disease sam-
                                                                     ple.
               MUS: as in ARRAYA.DBF
                                                                     AVOCOND: average oyster meat condition,
               MOG: as in ARRAYA.DBF                                 total disease sample; individual oysters scaled
                                                                     1-9 (watery-, watery, watery+, medium-,
               oTH: as in ARRAYA.DBF                                 medium, medium+, fat-, fat, fat+).

               TOTPER: as in ARMYA.DBF                               mAxcoND: highest oyster meat condition in
                                                                     sample.
               XSEED: impact of seeding      described as dis-
               tance on X-axis coordinate, magnitude based           MINCOND: lowest oyster meat condition in
               on decreasing impact from current year. (i.e.         sample.


                                                                 81








                Monitoring Maryland's Oysters

                DBLDPREV: P. marinus blood prevalence (%);                   MTISSIZ: H. nelsoni tissue severity index (see
                percent of oysters in sample having detectable               text).
                P. marinus by blood analysis (hemolymph
                cultured in thioglycollate medium).                          CLIO: Cliona sp.: boring sponge which can
                                                                             weaken oyster shell and allow secondary
                DTALPREV: P. marinus rectal prevalence (%)                   invaders into the oyster (%) of sample infect-
                percent of oysters in sample having detectable               ed).
                P. marinus by rectal culture in thioglycollate
                medium.                                                      POLY: Polydora websteri-a tube-dwelling
                                                                             worm found inside of the shell of oysters;
                DBLDINT: P. marinus blood intensity index;                   with severe infestation it may stress oysters
                staging of parasitic infection in individual                 (% of sample infected).
                oysters, scored on a scale of 0 (not detectable)
                to 7 (highest stage); the index is defined in the       PROKA: prokaryotes, commonly Rickettsia and
                text of this report.                                    Chlamydia, associated with cell destruction in      
                                                                        shellfish species (% of sample infected).
                DTALINT: P. marinus rectal intensity index;
                staging and index as with DBLDINT.                      PAPA: Papova virus-located in and causes
                                                                        destruction of oyster gametes (% of sample
                DBLDSIZ: P. marinus blood severity index (see           infected).
                text).                                                  ANCIS: Ancistrocoma pelseneeri, ciliated
                DTALSIZ: P. marinus rectal severity index.              thigmotrichs found in the digestive sys-
                                                                        tem-indicators of stress (% of sample infect-
                MBLDPREV: H. nelsoni blood prevalence (%);                  ed).
                percent of oysters in sample having detectable
                H. nelsoni by blood analysis (histocytology             THIG: ciliated thigmotrichs found attached to
                rapid diagnosis).                                       oyster gills; in large numbers they may inter-
                                                                        fere with respiration and or cause mechanical
                MTISPREV: H. nelsoni tissue prevalence (%)                 damage or stress (% of sample infected).
                percent of oysters in sample having detectable
                H. nelsoni by microscopic tissue examination            BUC: Bucephalus cuculus, a digenetic trem-
                (histopathology).                                       atode which infects and destroys oyster gonad
                                                                        tissue, causing sterility (% of sample infect-
                MBLDINT: H. nelsoni blood intensity index                ed).
                (see text).                                             xcooRD: sampling site latitude on the oyster
                MTISINT: H. nelsoni tissue intensity index (see          bar expressed in decimal degrees, used for
                text).                                                  geocoding of data for graphic representation
                                                                        and analysis.
                MBLDSIZ: H. nelsoni blood severity index (see
                text).


                                                                    82








             Monitoring Maryland's Oysters

             YcooRD: sample site longitude in decimal
             degrees.

             Data Field Conventions
             -9 represents a missing numeric field.

             -8 represents data not available at present,
             typic"y used for disease data not yet pro-
             cessed.















































                                                         83








                 Monitoying Maryland's O@sters


                               pendix B. Spat Counts by Subsample (0.2 bushel of dredged material)
                                                     and Total per Site (1.0 bushel)

                    SITE          DATE               1       2        3       4        5       TOTAL


                    BCDN       10118/90              15      10       9       9        6       48
                    BCDN       10122191              96      102    129       68       73      468


                    BNMP       10128/90              0       0        0       0        0         0
                    BNMP       10/  28/91            0       0        0       0        0         0


                    Wdw        10/23190              0       0        0       0        0         0
                    BN&P       10127/91              0       0        0       0        1         1


                    CHOR       10/22/90              0       0        0       1        0         1
                    CHaR       10/26/91              0       0        0       0        0         0


                    CHOF       10/22/90              0       0        0       0        0         0
                    CHOF       10126/91              0       0        0       0        1         1


                    CRCP       10116190              6       2        1       6        2       17
                    CRCP       10121191              43      24     30        31       39      167


                    CRU        10/17/W               5       4      10        6        3       27
                    CRU        10121/91              77      103    96      100        as      460


                    CROS       10117190              2       1        0       0        1         4
                    CROB       10118191              22      a        6       19       12      67


                    CRRO       10118190              9       10     13        14       11      57
                    CRRO       10122/91           146        110    112     110    lie         696


                    CRSH       10/17/90              a       4        9       7        10      38
                    CRSH       10118191              37      26     38        43       36      179


                    CRTW       10116/90              11      28     27        is       20      101
                    CRTW       10/21/91           138        173    89      152    167         719


                    MU         10/22190              6       4        0       0        1       11
                    MU         10124/91              24      17     21        12       4       78
























                                                                      84








                Monitoring Marylmd's Oysters


                   UTE             DATE             1        2         3       4       6      TOTAL


                   EBM         10/24190             0        1         1       0       0          2
                   EBM         10/23191             1        3         3       2       2         11


                   ESPI        10119/90             2        2         1       0       2          7
                   EBM         10/24/91             6       30       26       30                127


                   awa         10/19/90             2        2         4       4       6         is
                   wwo         10/23/91            65       38       35       37      40        205


                   FBO         11105/90             3        4         6       3       4         19
                   FBCI        11112/91            51       55       38       64      67        266


                   FBW         10/06M               2        1         1       0       1          6
                   FOW         11112191            24       31       43       26                iS3


                   HCEP        10/18/90             0        6         2       5       6         19
                   HCEP        10122191            70      102       70       79      Ge        387


                   HOHO        10/06/90            19       28       36       51      35        lee
                   HONO        11/13/91            99       61       38       43      38        269


                   HRNO        10106/90             7        9       is        4      10         46
                   HMO         1111"1             211      240      233      219    256         IIS9


                   HRWI        11109190            38       23       20       36      36        152
                   HR"         11113/111          1"       176      1 "      132    1111        740


                   LCCA        10/16190            33       22       26               31        143
                   LCCA        10116191           623      182      382      506    247        1839


                   LCRP        lollem               6.      13       19       13      14         65
                   LCRP        10115191           232      192      176      229    207        1036



                   MADP        11114/91            27       36       26       26      24        140


                   MAGE        10109/90            11        0         1       1       1         14
                   MAGE        11114/91             7       13       10       12      10         52


                   MEBR        10/16/90             4        7         8       4      14         37
                   MEN         10121191            68       70       70       al      76        366


                   MRAS        10/18/90             0        0         1       0       1          2
                   MRAS        1044191              4        1         7       0       0         12


                   mm          10/22/90             0        1         0       1       0          2
                   mm          10/24191             2        4         4       1       1         12


                   MRLP        10/18190             0        0         0       0       0          0
                   URLP        10/24/91             1        0         2       1       0          4


                   MRTU        10122/90             1        4         1       5       0         11
                   MRTU        10124191            32       44       30       33      29        lee


                   NRMQ        10/08/90             9        7         a       6      10         40





                                                                        85










                                                                               98




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                     Monitofing Maryland's Oysters
                                                                        Appendix C. Mortality Data

                                                        LIVE            BOX MARKET       SMALL      SMALL/MARK. TOTAL          RECENT        MEAN          MEAN
                     SITE          DATE              COUNT        COUNT COUNT,           COUNT,           RATIO  MORT.1%) MORT.196) 04ZE Inun)' SIZE (nm4'
                     BCDN          10118/90             23              43        6            Is         3.6           66           26                      70
                     BCDN          10/22191             74              as        3            71         23.7                       6                       w

                     BMW           10128M               64              1         so           4          0.1           2            0            0          107
                     SNMP          10128191             43              2         43           0          0.0           4            0            0          94

                     ww            IQf2319O             64              2                      6          0.1           4            2            72         62
                     wap           10127/91             64              2                      5          0.1           4            2            82         100

                     CHOR          10122190             106             6         97           8          0. 1          4            2            74         84
                     CHBA          10/26/91             180             26        113          76         0.7           12           2            82         103

                     CHOF          10*2/90              113             9         79           34         0.4           7            2            74         81
                     CHOF          10125/91             167             6         as           119        1.8           3            0            97         M

                     CRCP          101IW90              17              2         8            9          1.1           10           0            0          127
                     CRcP          10121191             42              1         22           20         0.9           2            0            0          62

                     CRLI          10117190             w               6         40           9          0.2           8            6            79         77
                     CRLI          10121191             62              so        23           39         1.7           46           13           75         SO

                     CROS          10/17190             216             6                      122        1.3           2            0            77         99
                     CROS          10118191             317             a         119          198        1.7           2            1

                     CRRO          101119190            90              13        64           26         0.6           14           7            90         82
                     cow           10122/91             129             63        37           91         2.6           33           6            so         73

                     CRSH          10117/110            116             14        73           42         0.6           11           6            07         87
                     CPSH          10118191             36              100"      19           17         0.9           76           Is           78         86

                     CRTW          10114m               122             66        00           42         0. 5          31           Is           70         79
                     CRTW          10*1191              In              101       62           126        2.0           36           0            67         73

                     EBBU          10/22190             35              22        27           a          0.3           39           12           82         87
                     EMU           1=4191               Is              20        6            12         2.0           63           6            67         84

                     EBFIN         10/24190             92              1         79           14         0.2           1            0            0          92
                     EBM           1012"1               70              6         48           22         0.6           7            4        109            104

                     EBPI          10119m               77              6         64           13         0.2           7            0            0          90
                     ESPI          1Or2W91              61                        42           19         0.6           43           5            62         as

                     WING          10119M               61              9         39           22         0.6           13           0            0          82
                     ENWO          10123191             123             3         62           61         1.0           2            1            92         94

                     FBCI          11106190             37              3         10           27         2.7           9            3        102            89
                     FBC1          11111112MI           SO              14        34           36         1.0           17           4            94         77

                     FBGC          1010B/90             70              6         24           46         1.9           7            0            0          93
                     FBQc          11112191             101             31        53                      0:9           24           10           77         so

                     HCEP          1011111190           34              22        29           6          0.2           39           9        100            97
                     HCEP          lormill                              28        10           38         3.9           37           6            66         77

                     HOHO          10108190             of              22        7            79         11.3          20           4            73         71
                     HOHO          11/13f9i             127             70        20           107        6.3           36           7

                     HRNO          10/08190             77              26        8            69         8.6           26           12           67         66
                     HRNO          11/13191             63              49        10           43         4.3                        13           62         71












                                                                                         88











                                                                                  68










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                Monitoring Maryland's Oysters

                                           jj:0pendix D. Disem and Condition Data by Site
                                                                                             WX_BL00D3
                                 AKAN           N     DERMO-RECTAL'            DERNIO-BLOODR
                SITE    DATE    SIZE(@) CONDrMN       %      INT.   SEV.       %    Nff.   SEV.        WT.   &W.  CWNA' POLY.'
                BCDNI 10/18/90     82        4.1      100    4.9     4.9       100  4.1      4.1                     47      43
                BCDN 10122191      72        5.3      100    5.6     6.6                                             20      73

                ONSP 10/23190      96        4.9      7      0.1     1.0       7    0.1      1.0                     3       10
                BNSP 10127/91      90        6.1      27     0.7     2.6                                             0       33

                CHBR 10122M        92        5.0      23     0.5     2.0       20   0.4      2.0                     0       30
                CHBR 10125/91      90        5.9      90     2.6     3.1       -    -        -                       0       30


                CHOF 10/22/90      92        6.4      17     0.2     1.0       -    -                                0       63
                CHOF 10/25/91      as        6.4      20     0.5     2.3       -                                     0       so

                CRCP 10116190      81        6.2      17     0.2     1.0                                             0       33
                CRCP 10121191      92        5.2      23     0.3     1.1       20   0.4      1.0   3     0.1    4.0  0       93


                CRU 10/17190       87        6.3      90     2.3     2.6                                             0       23
                CRU 10/21/91       99        4.9      100    4.0     4.0       -                                     0       73


                CROG 10/17190      79        5.5      3      0.1     1.0       -                                     0       40
                CROG 10/18191      87        6.9      so     1.7     2.9       -                                     0       90
                CRRO 10122/91      so        4.4      100    4.6     4.6                                             13      @0

                CRSH 10/17/90      as        4.7      100    6.0     6.0       100  4.0      4.0                     0       67
                CROH 10118MI       96        4.4      100    5.7     5.7                     -     -                 0       so

                CKM 10116190       79        4.3      100    3.2     3.2       100  3.4      3.4   -                 13      67
                CRTW 10121/91      89        4.8      97     3.0     3.1       93   3.0      3.3   0     0.0    0.0  13      so

                EMU   10/22/90     92        4.4      100    3.4     3.4       100  3.9      3.9   -            -    7       10
                EMU   10124191     96        6.4      100    4.0     4.0       -    -                           -    3       73

                EBM   10/24/90     92        4.9      30     0.3     1.1       0    0.0      0.0                -    0       33
                EBHN  1012"1       89        6.5      73     2.0     2.7       -    -        -                       0       90

                EBR   10119/90     Go        5.0      20     0.5     2.3                                        -    0       13
                      10/24191     90        5.5      97     3.6     3.9                     -                  -    0       70

                FBQC 10108/90      76        3.8      so     1.8     3.0       70   1.0      2.6   0     0.0    0.0  0       20
                F0= 11112191       78        3.7      100    3.1     3.1                           7     0.3    4.0  0       7

                WHO 10108/90       76        4.0      100    .4.2    4.2       100  3.4      3.4   0     0.0    0.0  3       27
                HOH011113/91       76        3.8      100    4.0     4.0       -    -              17    0.6    2.8  3       70

                HRNO 10108/90      71        3.9      100    4.3     4.3       93   2.9      3.1   0     0.0    0.0  0       30
                HRNO 11113/91      78        3.5      100    3.4     3.4            -        -     0     0.0    0.0  3       23

                LCCA 10/15/90      97        3.3      100    3.4     3.4       97   3.2      3.3   0     0.0    0.0  37      63
                LCCA 10116/91      77        3.6      100    4.4     4.4                           -     -           17      37

                LCRP 10/18/90      78        4.3      100    4.8     4.8       100  4.3      4.3   0     0.0    0.0  7       63
                LCRP 10/16/91      74        3.6      100    4.6     4.6       -             -     17    0.3    2.0  0       60

                MAGE 10109/90      78        3.0      83     1.9     2.3       57   1.4      2.5   0     0.0    0.0  11      23
                MACE 11/14191      72        4.1      93     2.9     3.2       -    -              7     0.2    3.6  7       43









                                                                      91








                 Monitoring Marylmd's Oysters

                                    MEAN      MEAN     DERNIO-RECTAL'         DERMO-BLOOD' M8X-K00D      3
                 Srm        DATE  SIZEInun) COMMON     %     WT.     SEV.     %      WT.    SEV.         WT. SEV.GWNA' POLY'
                 MESR 10/16/90      79        3.5      47    0.5     1.1      3      0.1    1.0          9.0        0       53
                 MESR 10/21191      so        3.7      27    0.9     3.4                                 -          7       53


                 MRW 10122/90       92        4.4      83    2.8     3A       77     1.9    2.5                     0       23
                 MRM 10/24191       112       4.1      100   3.3     3.3      -      -                              0       so

                 MRLP 10/18/90      105       4.8      73    2.0     2.8      67     1.7    2.6                     0       53
                 MRLP 10/24/91      104       5.5      97    4.3     4.4                    -                       0       90

                 MRTU 10/22/90      as        3.7      100   3.8     3.8      97     3.1    3.2     0    0.0   0.0  23      40
                 MffrU 10/24/91     90        5.0      100   3.3     3.3      -      -                         -    3       53
                 NRWS 10108/90      so        4.0      93    2.9     il       47     1.2    2.5                     0       23
                 NRWS 11/12/91      87        4.6      100   2.8     2.8      -      -                              0       10

                 PRCH 11/01/90      70        4.2      97    3.4     3.6      90     3.1    3.4                -    17      40
                 PRCH 11104/91      76        3.7      83    2.3     2.8                            0    0.0   0.0  23      so

                 PRLC   10/30/90    89        4.7      40    0.7     1.7      0      0.0    0.0     -    -          0       13
                 PRLC 11/05/91      94        5.9      10    0.3     2.7                                       -    0       97

                 PRRP   10/30/90    90        4.0      97    3.8     4.0      87     3.1    3.6          -     -    0       20
                 PRRP   11/06/91    91        4.2      90    2.6     3.1      -                     0    0.0   0.0  0       100

                 PSMA 10109/90      76        4.2      97    3.5     3.6      97     2.9    3.0     0    0.0   0.0  0       17
                 PSMA 11118/91      74        3.8      93    3.3     3.6                            13   0.4   2.8  0       63

                 PXM 11/02/90       as        5.2      97    3.4     3.5      93     2.9    3.1          -     -    0       63
                 P)CM I I /oW91     93        4.7      100   2.8     2.8      -             -       -    -     -    0       27


                 MCC 10/29190       84        3.5      100   4.2     4.2      97     3.6    3.7     -          -    20      43
                 SUCC 11104/91      83        3.9      97    3.1     3.2                            0    0.0   0.0  23      so

                 amp^ 10129190      74        3.3      93    3.3     3.5      93     3.2    3.4                     0       40
                 SMPA 11/04191      70        3.4      97    2.3     2.4      -      -      -       -               7       17

                 TADM 10/17/90      99        4.6      97    3.6     3.7      97     3.2    3.3     0    0.0   0.0  0       37
                 TADM 10/22/91      96        5.5      100   4.9     4.9      -      -      -                  -    0       83
                 TSW 10108/90       71        3.7      100   2.7     2.7      100    2.8    2.8     0    0.0   0.0  0       20!
                 TSBC 11114/91      76        3.5      100   4.2     4.2             -      -       10   0.2   2.0  27      73

                 TBOW10109190       73        4.2      67    1.1     2.0      23     0.6    2.6     0    0.0   0.0  3       43
                 TSOWI1118/91       76        3.3      100   4.5     4.5      -                     13   0.4   3.3  37      13

                 TSPI 10109/90      72        3.8      94    2.7     2.9      93     3.2    3.4     3    0.1   1.0  3       3
                 TSM 11/14/91       72        3.6      100   3.9     3.9             -      -       17   0.5   3.0  27      10

                 Ts" 10108190       72        3.6      23    0.3     1.4      3      0.1    1.0     10   0.3   3.0  7       7
                 Tau 11/12/91       77        3.7      60    1.2     2.0                    -       20   0.5   2.5  0       7

                 UBHA 10/24190      as        4.8      so    0.0     0.0      3      0.1    1.0          -     -    0       13
                 UBHA 10/27191      103       5.8      27    0.8     3.1                    -       -          -    0       53

                 WSBUII/01/90       76        3.9      100   4.0     4.0      93     2.9    3.1     -          -    7       37
                 WSBU 11/07/91      79        4.3      100   4.0     4.0                    -       0    0.0   0.0  7











                                                                      92








                     Monitoring Maryland's Oysters


                                            MEAN          MEAN        DERIAO-RECTAL'                DERMO-SLOOD2       MSX_BLGOD3
                     SITE         DATE    SIZEfmm) CONDMON            %       INT.     SEV.         %      INT.      SEV.    %       INT.    SEV.CMNA' POLY.'
                     WSFP 11/01/90           so           5.1         30      0.8       2.6         27      0.6       2.4                      -     0         70
                     WSM 10/30,91            80           6.4         97      2,6       2*7         -                 -                        -     0         57

                     WSl* 11/01/90           76           4.9         90      3.0       3.6         so      2.4       3.0                      -     7         30
                     WSIV 11107/91           so           3.6         97      4.5       4.6         -       -         -       0      0.0       0.0   23        87

                     MHP 10/24190            916          4,9         20      0*5       2*3         7       0*2       3*5                            0         23
                     WSHP 10130191           97           6.4         47      1.1       2.3         -                                                0         53

                     VVWLA10131/90           89           4.8         97      3.6       3.7         97      3.2       3.4                            0         43
                     VVWLA1 1106/91          92           6.6         97      2.8       2.9                                                          3         13

                     WWMVND/31/90            82           5.5         0       0.0       O.D         0       0.0       0.0                            0         so
                     WWMWI/05191             87           5.6         so      2.0       2.5                                                          0         33

                     lpo@ mw*ww diagnosed by motel thlog@ate                              %    prevalence 11 ol oyaters Infoctedl, int,        intensity Index (see
                     text): sev. - Severity index lese text).
                     2P. mwkmw diagnosed by hemolynWh thloglycollate cultme; indices as above.
                     WaplampanUkan on(sw diagnosed by rapid hemolymph method; Indices as above.
                     'CAane op. (boring spongel; % of oveters infected.
                     'Pulydwe webaterf (boring polycheatel; % of oysters irrFected.







































                                                                                          93
























                THE FACILITIES AND SERVICES OF THE DEPARTMENT OF NATURAL RESOURCES
                  ARE AVAILABLE TO ALL WITHOUT REGARD TO RACE, COLOR, RELIGION, SEX,
                          AGE, NATIONAL ORIGIN, PHYSICAL OR MENTAL DISABILITY.




























               FOR FURTHER INFORMATION REGARDING THIS REPORT, PLEASE CALL 410-9744782.










                                                                                                                                 NOAA COASTAL SERVICES CTR LIBRARY



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