[From the U.S. Government Printing Office, www.gpo.gov]



                                          FINAL REPORT
                                        New Grant Task #5
                                         NA89AA-H-CZ214





                                   Center for Environmental and Estuarine Studies



             AN ENVIRONMENTAL EVALUATION
                OF FINFISH NET-CAGE CULTURE
                           IN CHESAPEAKE BAY




                                            b y

                                     Donald  P. Weston
                      Center for Environmental and Estuarine Studies
                           Horn Point Environmental Laboratory


                                            



                                       



             Prepared   for:
                                                                      July 1991

             Maryland Department of Natural Resources
             Tidewater Administration
             





                                                        

                                              
           SH
           171
           W47
           1991
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                                  AN ENVIRONMENTAL EVALUATION OF
                                    FINFISH NET-CAGE CULTURE IN
                                           CHESAPEAKE BAY







                                                 by

                                          Donald P. Weston

                                       University of Maryland
                          Center for Environmental and Estuarine Studies
                                Horn Point Environmental Laboratory
                                            P.O. Box 775
                                     Cambridge, Maryland 21613






                                          Prepared for the

                              Maryland Department of Natural Resources
                                      Tidewater Administration







                                             July 1991

                    Funding for this report was provided in part by the Coastal
                    Resources Division, Tidewater Administration, Maryland
                    Department of Natural Resources through a grant from the
                    Office of Ocean and Coastal Resources Management, National
                    Oceanic and Atmospheric Administration.









                                              CONTENTS

              ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . .   i

              ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

              1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . .

              2.0 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . .    4

              3.0 CASE HISTORIES

                 3.1 Washington State   . . . . . . . . . . . . . . . . . . . . . .   8

                 3.2 Maine . . . . . . . . . . . . . . . . . . . . . . . . . . . .  10

              4.0 ENVIRONMENTAL ISSUES

                 4.1 Benthic effects  . . . . . . . . . . . . . . . . . . . . . . . 13

                 4.2  Water quality . . . . . . . . . . . . . . . . . . . . . . . . 25

                 4.3  Chemical usage  . . . . . . . . . . . . . . . . . . . . . . . 42

                 4.4  Genetic impacts . . . . . . . . . . . . . . . . . . . . . . . 53

                 4.5  Disease transmission  . . . . . . . . . . . . . . . . . . . . 59

              LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . . .  63










                                          ACKNOWLEDGMENTS


                    I am grateful to Reginal Harrell of the Horn Point Environmental
              Laboratory for discussions on striped bass culture and for supplying
               uch of the literature used in this report pertaining to culture
              techniques. Ben Florence of the Maryland Department of Natural
              m

              Resources and Brad Powers of the Department of Agriculture provided
              valuable insights on the Maryland aquaculture industry. I thank Deborah
              Penry for review of the draft manuscript.









                                             ABSTRACT


                   The declining harvest of striped bass in Chesapeake Bay and the
              success of finfish aquaculture elsewhere has renewed interest in the
              culture of striped bass or its hybrids in net-cages within Chesapeake
              Bay proper or its tributaries.   Culture may take the form of small
              operations of only a few net-cages producing 1 to 2 metric tons of fish
              for supplemental income. Larger commercial ventures will require 5 to
              20 net-cages and are likely to produce over 50 metric tons of fish per
              year. The histories of the salmonid net-cage culture industry in
              Washington State and Maine,are described, and these experiences suggest
              that growth of the industry in Maryland will require that potential
              environmental consequences of culture be addressed. This report
              summarizes data on the environmental effects of net-cage culture
              throughout the world, puts these data in the perspective of the
              Chesapeake Bay environment, and suggests means to minimize the impacts.
              Environmental effects within five principal areas are evaluated..


              Benthic effects - The deposition of fish fecal matter and waste feed on
              the seafloor results in physical, chemical and biological changes in the
              sediment typical of organic enrichment in general.   Based on past
              experience, net-cage culture in Chesapeake Bay is likely to result in
              dramatic changes in the composition of the benthic community, quite
              possibly to the point of creating areas devoid of animal life.    The
              areal extent of impact is, however, likely to be very restricted;
              generally under the farm and to a distance of 50 m or less.   Changes in
              the benthic community under the farm are likely to occur within a matter
              of a few months, while recovery will require several years after removal
              of the farm. Most areas of Chesapeake Bay are too shallow to provide
              the depth of water recommended for net-pen culture by environmental
              management agencies elsewhere. This limitation suggests benthic impacts
              are a virtual certainty, farmers may have to reduce stocking densities,
              and the cultured fish may be confronted with health problems caused by
              sulfide release from organically enrich ed sediments.









               Water quality - Finfish culture will decrease the dissolved oxygen
               content in surface waters by fish respiration and in bottom waters   by
               the biochemical oxygen demand (BOD) of organic-rich solid wastes.    These
               effects are likely to be localized and, in part, self-limiting through
               adverse impacts on the cultured fish themselves. Nitrogen, phosphorus
               and BOD loadi,ng from net-cage culture can be significant and comparable
               in,magnitude to treated sewage wastes from a small city or a large food
               processing facility. Elevated nutrient concentrations are often
               measured surrounding net-cage farms, but there is usually no measurable
               effect on phytoplankton biomass or productivity. Nutrients from fish
               culture are readily utilized by phytoplankton and will stimulate
               primary productivity if nutrients are limiting algal growth at the time.
               Rapid dilution of soluble wastes in most marine environments, however,
               would make this increased productivity unmeasurable by conventional
               environmental monitoring except in areas of very limited circulation.


               Chemical usage - Antifoulants are likely to be required for successful
               net-cage culture in Chesapeake Bay. Tributyltin, which has received
               much recent attention, would not be Used, and it is likely that the
               industry would rely on copper-based compounds similar to those widely
               used on boat hulls. Striped bass culturists are extremely limited in
               the choice of chemotherapeutants that could be legally used to combat
               disease in their fish. At present the use of all antibiotics would be
               precluded and even the regulatory status of chemicals generally
               recognized as safe (e.g. salt, sodium bicarbonate, acetic acid) is in
               question. It is presumed that the antibiotic oxytetracycline will
               ultimately be approved for use on striped bass. This compound persists
               in-marine sediments for months after treatment and stimulates antibiotic
               resistance in microorganisms, but the environmental or human health
               implications of these impacts are unclear.


               Genetic impacts - Interbreeding of escaped  cultured fish with wild
               populations raises concern about reduction  in genetic variability,
               reduction in population fitness, and wasted reproductive efforts by the
               wild fish. The culture of hybrid striped bass raises additional








              concerns since it seems reasonable to expect that hybrid fish are
              capable of backcrossing with wild striped bass within Chesapeake Bay.
              The genetic implications of this interbreeding will depend upon the size
              of the escaped population relative to the wild breeding population, and
              as yet unanswered questions on the existence of sub-populations of
              striped bass within Chesapeake Bay. These concerns can be alleviated by
              restricting culture to unhybridized striped bass, Chesapeake Bay stocks
              only, or triploid fish.


              Disease transmission - The transfer of fish or their reproductive
              products for aquaculture can result in the unintentional and undesirable
              importation of a pest or pathogen. As currently envisioned, however,
              culture of striped bass within Chesapeake Bay will not require the
              importation of fish from distant sources. There is no evidence to
              suggest that net-cages act as epicenters for disease that can spread to
              wild fish. Most diseases of concern to culturists are caused by
              facultative pathogens which exhibit no pathogenic effects unless the
              fish are stressed by poor water quality, malnutrition, over-crowding or
              other factors. Thus the cultured fish may be at risk, but wild fish are
              not placed at greater risk by virtue of their proximity to the culture
              site.










                               AN ENVIRONMENTAL EVALUATION OF FINFISH

                                 NET-CAGE CULTURE IN CHESAPEAKE BAY



                                         1.0 INTRODUCTION
                   The Chesapeake Bay and its tributaries have been a major source of
              seafood for many years, with harvest relying almost entirely upon wild
              stocks. Many of the fish and shellfish species upon which the seafood
              industry depends, however, have shown dramatic declines in abundance
              over the past twenty years including the striped bass, white perch and
              oyster. Bay-wide commercial striped bass harvests, for example, have
              decreased from a peak of 3200 metric tons (7 million lb) in 1973 to less
              than 450 tons (1 million lb) just prior to Maryland's imposition of a
              fishing moratorium in 1985. Over about the same period new techniques
              for finfish aquaculture have been developed and the finfish aquaculture
              industry has experienced phenomenal growth in Japan, Chile, New Zealand,
              and parts of North America and Europe. The decline in wild stocks
              within the Bay and the apparent viability of commercial aquaculture
              ventures elsewhere has created interest in the establishment of
              aquaculture facilities within Chesapeake Bay waters. The species most
              often cited as a potential candidate is the striped bass, Morone
              saxatalis, and its hybrids, although white perch Q1. americana) and
              yellow perch (Perca flavescens) have also been identified as having
              culture potential.
                   As a result of the rapid growth of finfish aquaculture in recent
              years, there has been a great deal of work on the effects of aquaculture
              on the surrounding environment, including the indigenous species. As
              noted in a recent report by the International Council for the
              Exploration of the Sea:
                   "Aquaculture effluents from conventional farming systems were,
                   in the past, considered to be 'clean' and 'natural' and the
                   possibility that aquaculture may affect the environment has
                   largely been overlooked. Like any other industry, aquaculture
                   has the potential to generate pollutants which are
                   continuously released into the natural environment.
                   Ecological concerns can no longer be ignored and have become a

                                                  I








                    risk factor for the industry itself." (Rosenthal et al.,
                    1988, p. 2)
                    The response of regulatory bodies in other states and countries to
               rapid industry growth indicates a need to examine potential
               environmental issues. In Norway there has been a great deal of concern
               about the potential effects of Atlantic salmon culture on the genetic
               integrity of the wild populations, and a salmon gene bank has been
               created. In Sweden there is concern that nutrient loading from
               aquaculture may accelerate eutrophication of the Baltic, although the
               most recent analysis suggests nutrient contributions from aquaculture
               are small in comparison to other sources (Ackefors and Enell 1990). The
               states of Maine and Washington have enacted, or are on the verge of
               enacting, strict siting guidelines to reduce benthic enrichment from
               culture and requiring National Pollutant Discharge Elimination System
               (NPDES) permits of net-cage culture facilities. The State of Alaska has
               entirely prohibited open water fish culture in response to pressure from
               the salmon fishing industry, citing the possible importation of exotic
               diseases.
                    Environmental issues are of particular concern with respect to open
               water net-cage aquaculture facilities. Unlike upland culture sites
               where settling basins or effluent filtration may be used, collection and
               treatment of solid wastes is greatly complicated at open water sites.
               At present there are no means available for the farmer to remove the
               biochemical oxygen demand (BOD), nitrogen or phosphorus from the waste
               stream other than by modification of fish diet and feeding strategy.
               Chemical treatment of culture water for therapeutic purposes or effluent
               disinfection is more difficult, and release of chemicals to open water
               is unavoidable. The opportunity for escape of the cultured fish due to
               physical damage to the culture structure is greatly increased, and thus
               the potential for displacement of or interbreeding with wild species is
               also greater.
                    This report examines the potential environmental impacts of finfish
               net-cage culture in open water within Chesapeake Bay and its
               tributaries. This study does not address culture in freshwater,
               including pond culture as presently practiced.   Section 2.0 discusses

                                                   2









              the current state of finfish aquaculture within Maryland, makes
              assumptions on future growth, and describes husbandry techniques insofar
              as they relate to potential environmental impacts. Section 3.0 provides
              case histories of net-cage culture within the states of Washington and
              Maine, the only other areas of the country with significant net-cage
              culture in marine waters. The history of the industry in these areas
              provides valuable insights into environmental concerns and the
              regulatory approaches available for their management. Section 4.0
              summarizes the environmental effects of net-cage aquaculture based upon
              research conducted at sites throughout the world. Much of this past
              work pertains to the culture of salmonids at higher latitudes, but when
              possible the data are put in the context of the environmental conditions
              found within the Chesapeake Bay. Most of the potential environmental
              impacts are independent of the fish species being cultured, but when
              necessary, differences are noted between salmonid culture, from which
              most of the data are derived, and striped bass culture, the primary
              focus of this report. Approaches for mitigation of potential
              environmental impacts are also identified.


























                                                 3










                                            2.0 BACKGROUND
                    The production of the Maryland finfish culture industry is   small in
               comparison to the production of many other states (e.g. catfish    culture
               in the southeast and salmonid culture in the northeast and northwest).
               Production has, however, rapidly increased over the past few years and
               further growth is anticipated (Table 1). Hybrid striped bass comprise
               the majority of Maryland finfish production, both in terms of biomass
               produced and harvest value. As a result of recent legislative action,
               the sale of striped bass and its hybrids from aquaculture facilities
               became legal as of January 1, 1990.   The first farm-raised hybrid
               striped bass from Maryland were marketed in August 1990. Total
               state-wide hybrid striped bass production for 1990 was estimated at 113
               metric tons (250,000 lb), based on questionnaires sent to culturists by
               the Department of Agriculture. This production could increase
               substantially over the next few years as several new facilities, now in
               the planning and construction phases, become operational.
                    The culture of hybrid striped bass to a  marketable size is
               currently practiced in many states including  Maryland, South Carolina,
               North Carolina, New York and California. In   some of these areas culture
               remains in the experimental or demonstration  stages, while in other
               areas full-scale commercial culture has been  on-going for several years.
               There are currently 85 to 90 farms for hybrid striped bass culture in
               Maryland (B. Powers, pers. comm.). Most of these are small operations,
               and the vast majority of fish are in the hands of four or five
               operators.  All Maryland finfish culture, including hybrid striped bass,
               is currently conducted in upland facilities; either raceways, tanks,
               ponds, or net-cages within ponds. Water supplies range from fresh to
               brackish water.
                    The emphasis of this report is on net-cage culture within open
               waters of Chesapeake Bay and its tributaries.   There has been very
               little prior finfish culture activity in open water within the Bay. The
               Department of Natural Resources (DNR) and the Cecil-Harford County
               Watermen's Association attempted net-cage culture in the Susquehanna
               River, but the attempt failed for a variety of operational reasons,
               unrelated to the feasibility of culture general.    Striped bass are

                                                    4










                                                       Tabl e 1
                            Maryland finfish culture production (in metric tons
                             with thousands of pounds in parentheses) as based
                             on a producer survey by the Maryland Department of
                                                Agriculture (MDA).


                      Sgecies                   1988          1989           1990          1991

                Hybrid striped                 (sale of cultured              113          136
                    bass                      bass not legalized)            (250)         (350)

                Catfish                           43             43            49          128
                                                (94)           (94)          (108)         (282)

                Trout                              3              5            22            27
                                                  (7)          (12)           (49)         (60)

                Tilapia                            5             10            10            35
                                                (12)           (22)           (22)         (78)

                Ornamental fish                    (data considered confidential by MDA)

                Yellow perch                       (data considered confidential by MDA)




























                                                          5









               occasionally held in net-cages at the DNR/National Marine Fisheries
               Service facility at Oxford for experimental purposes, but not for
               commercial culture. DNR has recently obtained approval for construction
               of a striped bass demonstration net-cage farm near the Bay Bridge, and
               stocking will commence in the spring of 1992.
                    In order to evaluate potential environmental effects of culture
               activities it is necessary to have some concept of construction and
               operational factors in finfish net-cage culture, but this effort is
               complicated by the absence of any existing farms in Chesapeake Bay.   It
               is, however, possible to speculate on how a "typical" farm may be
               constructed and operated based on experience in upland culture of
               striped bass and its hybrids and open water net-cage culture of other
               species, most notably salmonids.
                   A net-cage farm generally consists of a floating walkway, three to
               five feet in width, in a square configuration. The perimeter of the net
               is attached to the walkway, while the lower corners are weighted to keep
               the net from deforming due to water currents. A small cage may be only
               a few meters in each dimension, including depth. Commercial facilities
               would have to employ much larger nets, perhaps 6 x 12 m, 8 x 8 m, or 12
               x 12 m. These larger nets would extend 4 to 6 m below water level. Any
               number of net-cages could be grouped together depending on the intended
               production level. A facility providing fish only for supplemental
               income may require only a few small cages and produce I to 2 metric tons
               (2200-4400 lb) of fish annually. Large commercial ventures are likely
               to require 5 to 20 large cages and produce 50 to 150 tons (110,000 to
               330,000 lb) of fish annually. The largest salmonid net-cage farms in
               the United States are capable of producing over 450 tons (1,000,000 lb)
               of fish annually.
                   A few small net-cages may be located alongside an existing dock,
               but larger farms are likely to be anchored some distance from shore and
               serviced by small boats. There are generally few structures above the
               waterline other than the walkways, railings, and on the larger farms, a
               shed for storage of feed and shelter for workers. Predator nets are
               likely to be necessary over the tops of the net-cages to prevent loss of
               fish to herons and other piscivorous birds. Predator nets below the

                                                  6









              water line, as are used to prevent seal and sea lion predation on salmon
              farms in the northeastern and northwestern United States, would not be
              necessary in Chesapeake Bay and would only compound the fouling problems
              that the farmer is likely to face.
                   Based on the results of several experimental net-cage trials
              (Swingle 1971; Powell 1972; Valenti et al. 1976; Williams et al. 1981;
              Woods et al..1983) it is apparent that either juvenile (2 to 6 g) or
              advanced juvenile (about 40 g) striped bass or its hybrids can
              successfully be stocked in net-cages, although survival is greatest when
              using the larger fish. A period of 8 to 12 months, depending on water
              temperature and size at initial stocking, would be required to grow
              marketable fish within the size range of 300 to 500 g (0.7 to 1 lb).
              Throughout the culture period the fish would be fed a pelleted dry feed,
              dispensed either by hand or automatic feeder. The fish are generally
              provided feed at a rate of 2 to 3% of their body weight per day,
              although this rate can be substantially greater (5 to 10%) for juvenile
              fish. At present there are no foods formulated specifically to meet the
              nutritional requirements of striped bass. Upland growers now use a
              salmon or trout pelleted diet, and it is likely the same foods would be
              used in open water net-cage culture. Feed conversion efficiencies
              (ratio of the amount of food provided to the biomass of fish produced)
              are likely to be initially between 1.5 and 2, although with continued
              refinement of culture techniques and feed formulation conversion
              efficiencies may decrease to 1.3 to 1.5.
                   There are few data from which-to estimate optimal stocking
              densities. In experimental net-cage culture of striped bass and its
              hybrids densities as low as 16 kg m-3  and as great as 88 kg m'3 have been
              used without-apparent problems (Powell 72; Valenti et al 76). Salmonid
                                                        3
              farmers generally maintain about 12 kg m- , although  Norwegian growers
              have attained stocking densities as high as 40 kg m-.    The higher
              stocking densities are likely to exacerbate problems with water quality
              and fish diseases.







                                                   7










                                          3.0 CASE HISTORIES


                                         3.1 Washington State
                    The Washington net-cage industry is primarily dedicated to the
               culture of Atlantic salmon (Salmo salar) although an indigenous species,
               the coho salmon (Onchorhyncus kisutch), is also cultured at some farms.
               The chinook salmon (0. tshawytscha) and steelhead (Q. mykiss) have been
               cultured on an experimental basis. Commercial net-cage culture in
               Washington began in 1971 with the construction of a small farm operated
               jointly by the National Oceanic and Atmospheric Administration and
               private industry. By 1975 four farms were in operation. Currently
               there are 16 farms either in place or permitted, and an additional 9
               facilities used for delayed release (holding time in the cages of one to
               six months). Annual production has increased from 60 metric tons
               (1301000 lb) in the early 1970's to 4,400 tons (9.7 million lb) at
               present. A typical Washington farm covers two acres (at the water
               surface), is comprised of 30 to 50 cages, and produces 200 to 400 tons
               (440,000 to 880,000 lb) of fish annually..
                  . The state's first attempt to develop regulatory policies
               specifically for mitigating environmental effects of netncage   culture
               industry occurred in 1986 with the release of regulations known as "the
               Commissioner's order". The Commissioner of the Washington Department of
               Natural Resources announced that in order for a new farm to obtain a
               lease for subtidal lands from the state, the cage complex must be under
               two acres in size and be at least I mile from any existing farm.
                    Later in 1986 the Department of Ecology released the "Interim
               Guidelines" (SAIC 1986) which, in practice at least, have largely
               superseded the Commissioner's order. The Guidelines do not have any
               statutory basis, but were promulgated as guidance to the industry in
               selecting sites and to.state managers in reviewing applications. The
               guidelines include: 1) a minimum depth beneath the cages of 20 to 60
               feet (depending on currents and farm production) intended to maximize
               feed and feces dispersion and thus minimize benthic enrichment; 2)
               limits on production within specified embayments in order to avoid
               eutrophication; 3) a site characterization survey to assess

                                                   8









              site-specific hydrographic conditions and benthic community composition
              before cages are installed; and 4) annual monitoring of water quality,
              sediment chemistry and macrofaunal community structure to document any
              environmental changes. Items 3 and 4 have since been formalized as
              lease requirements by the Department of Natural Resources. Items 1 and
              2 remain only advisory, but have been the basis for most siting
              decisions over the past few years.
                   In 1989 the state initiated an industry-wide Programmatic
              Environmental Impact Statement (PEIS) in order to formalize the previous
              ad hoc management of the industry, and to serve as a basis for a future
              management plan. The PEIS addressed both impacts to the natural
              environment (e.g. benthic enrichment, eutrophication, introduction of
              exotic species) as well as impacts to the built environment (e.g. noise,
              odor, conflicts with commercial species, aesthetics). The document
              concluded that the environmental effects of salmonid net-cage culture
              were within acceptable levels if mitigated by minor modifications of
              existing regulations (Parametrix 1990a).
                  For the most part Environmental Impact Statements (EIS) have not
              been required of individual operators. They were required in only two
              instances. In the first case the applicant withdrew the permit request
              after soliciting bids for the EIS (cost estimated at $100,000). In the
              second case the EIS was completed, but after continued permitting delays
              and loss of financing the second applicant also withdrew.
                   In May 1989 the State of Washington determined that NPDES permits
              would be required of all net-cage farms in the state. The first farms
              to be permitted through this mechanism received their permits in April
              1990. These permits require: 1) water quality monitoring (dissolved
              oxygen, turbidity, inorganic nitrogen); 2) sediment trap collections
              (total solids and total volatile solids); 3) sediment chemistry
              monitoring (organic carbon, nitrogen, grain size); 4) macrofaunal
              community analysis; 5) underwater video survey by diver or remotely
              operated vehicle; and 6) under certain conditions the measurement of
              antibiotic resistance in the sediment microbial communities under the
              farm. Three farms have been issued NPDES permits.


                                                 9








                   The growth of the salmon net-cage culture industry in Washington
               has provoked extraordinary public controversy. Among the concerns
               raised are aesthetic impacts, potential devaluation of shoreline
               property values, economic and space conflicts with commercial fisheries,
               interference with water-based recreational activities, and environmental
               degradation. The primary stumbling blocks to permit approval have been
               at the county level. Most state agencies have been supportive of the
               industry, and the state has designated aquaculture as a "preferred use"
               in shoreline management. The federal government has not taken an active
               role. Established environmental groups (e.g. Greenpeace, Sierra Club,
               Audubon Society) have generally remained out of the debate or voiced
               only mild concern. The principal industry antagonists have been local
               citizen groups established in response to specific net-cage applications
               (e.g. Save our Shores, Griffin Bay Preservation Committee, Frenchman's
               Cove Defense Fund). As a result of pressure from local residents, and
               in contrast with policy at the state level, three Washington counties
               have enacted moratoria on new applications. In the remaining counties
               the applicant can expect protracted and divisive permitting battles with
               a significant chance of permit refusal. The 16 existing farms in
               Washington State provide a stark contrast to nearby British Columbia
               where the regulatory climate has been very receptive to the industry and
               about 200 farms are in operation.


                                              3.2 Maine
                   As elsewhere throughout the world, net-cage farming in the State of
               Maine is a recent phenomenon, with most of the industry growth occurring
               in the past 5 to 10 years. There are currently 41 sites leased for
               finfish culture, although only about half of-these have farms in place
               at present. It is estimated that 1990 production from these farms will
               be in the range of 1800 to 3400 metric tons (4 to 7.5 million lb) of
               Atlantic salmon. For comparative purposes, this production is about one
               half of that of Washington State and only about 2% of that of Norway,
               the world's largest salmon producer.
                   Maine net-cage facilities tend to be small in comparison to those
               of Washington, typically consisting of only 5 to 20 cages per farm.

                                                  10









              Water depths at the Maine sites tend to be much shallower (10-15 m vs
              >25 m), current speeds are greater, and many of the sites are located
              over hard bottoms.
                  Maine state agencies have been very supportive of the industry as a
              whole and smaller growers in particular.  The Maine Department of Marine
              Resources is respon-sible for issuing subtidal leases, which, although
              not required of a culturist, do afford some legal protection of the
              site. Lease regulations require a 2,000 ft. separation between farms
              unless reduced by mutual consent of the growers. Prior to considering a
              lease application the state will conduct a site review including a diver
              survey of marine resources at the site, collection of both phyto- and
              zooplankton samples, and hydrographic analyses using drogue tracking.
              After lease approval annual monitoring may be required including water
              quality monitoring and diver-collected samples for sediment chemistry
              analysis. It is noteworthy that the Maine Department of Marine
              Resources conducts and bears the cost of both the initial site survey
              and annual monitoring, whereas in Washington the farmer would generally
              be required to hire a consultant for these surveys.
                  The Maine Department of Environmental Protection (DEP) is a second
              state agency with a major role in net-cage aquaculture regulation
              through its issuance of a Water Quality Certificate. DEP requires that
              feed be provided in a pellet form, that dead fish and viscera are not
              disposed of in state waters and that only state-registered antifoulants
              be used (Parametrix 1990b). The Department also requires a minimum
              separation between the bottom of the cages and the seafloor of 10 ft.
              (3 m) and up to 60 ft (18.3 m) for larger farms in areas of slow
              currents. These requirements are based on Washington's Interim
              Guidelines, and are currently under evaluation for their applicability
              in Maine waters.
                  The federal government has taken a very active role in regulating
              net-cage culture in Maine through both Section 10 permits (Army Corps of
              Engineers) and the NPDES program (Environmental Protection Agency). The
              Corps regulations are currently in draft form, but many requirements are
              comparable to those of the state agencies. One notable addition is that
              the applicant must confirm that all fish or eggs will originate from

                                                 11









              east of the Continental Divide, and that only North American stocks will
              be used after 1995. The Environmental Protection Agency will be
              requiring NPDES permits from net-cage operations, but the operational
              and monitoring requirements will not be determined until after
              completion of an on-going Ocean Discharge Criteria Evaluation.
                   The growth of the net-cage culture industry in Maine has been as
              controversial as it has elsewhere, with the primary opponents  being
              local citizen groups, upland property owners and commercial fishing
              interests (principally lobstermen). These conflicts have intensified as
              the industry moves from the sparsely-populated northern coast to the
              more populous shorelines in the southern portion of the state. Faced
              with mounting criticism, regulatory agencies hastily adopted many of the
              siting and monitoring requirements of Washington State. With monitoring
              data from Maine sites now available, these requirements are now under
              review by both state and federal agencies. More permanent management
              approaches and greater stability in regulatory programs can be
              anticipated in the near future.



























                                                  12










                                     4.0 ENVIRONMENTAL ISSUES



                                        4.1 Benthic effects
              Solid waste production
                   Fecal material and waste feed are the primary solid wastes
              associated with finfish net-cage culture.  Fecal production of trout fed
              a diet of dry pellets is approxjmately 28% of ingested feed (dry weight
              basis, Butz and Vens-Capell 1982). Waste feed is the portion of the
              feed provided to the fish that passes through the cages without being
              ingested. In the worst case the quantity of waste feed can be as great
              as fecal production, but feed wastage is highly dependent upon the type
              of feed provided (dry, moist, wet), the method of feeding (hand, demand
              feeders, automatic feeders) and the frequency of feeding. Because of
              these variables, estimates of the amount of waste feed vary widely from
              only 1 to 5% of feed provided (VKI 1976) up to 40% (Thorpe et al. 1990).
                   Summing the contributions of feces and waste feed, it has been
              estimated that the production of 1 kg of salmon in a net-cage system
              will result in the production of 0.5-0.7 kg of solid waste (Weston 1986;
              Gowen and Bradbury 1987). The lower.limit approximates a best-case
              situation with little food wastage. No figures are available
              specifically for solid waste production in striped bass culture,
              although the magnitude of waste production is likely to be comparable.


              Sediment chemistry
                   At most net-cage sites, especially those where conditions are
              similar to those in Chesapeake Bay, much of the fecal matter and waste
              feed settles to the seafloor in the immediate vicinity of the farm. At
              some sites a visible accumulation of flocculent, organic-rich material
              overlies the natural sediment. This flocculent layer is often less than
              5 cm thick but can exceed 30 cm under worst-case conditions (Braaten et
              al. 1983; Ervik et al. 1985; Kaspar et al. 1988; H. Rosenthal, pers.
              comm.).
                   Fecal matter and waste feed represent a source of labile organic
              carbon, and the remineralization of this material*results in changes in
              sediment geochemistry that are typical of organic enrichment in general.

                                                 13








               Carbon cycling - Carbon fluxes in trout and salmon net-cage culture have
               been estimated by several investigators (Penczak, et al. 1982; Gowen and
               Bradury 1987; Hall et al. 1990). In general only about 20% of the
               carbon supplied to the farm in the form.of feed pellets is removed with
               the harvest. The remaining 80% is lost to the environment, either  as
               dissolved carbon (C02 produced by respiration and urea) or particulate
               carbon. The proportion of carbon reaching the sediments is seasonally
               variable and dependent upon the period of observation. Hall et al.
               (1990) estimated that on a seasonal basis 29 to 71% of the carbon
               provided to a farm was accumulated in the sediment. Over the long-term,
               and allowing for release from the sediment back to the water column
               (e.g. microbial remineralization to COV epibenthic grazing, methane
               ebullition), the sediment serves as a sink for 18% of the carbon input.
               It is therefore not surprising that sediment organic carbon
               concentrations have been used as one measure of the environmental effect
               of finfish net-cages (Hall and Holby 1986; Weston 1990).


               Sediment oxygen consumption - The remineralization of organic-rich
               sediments removes substantial amounts of oxygen from pore waters and/or
               the overlying bottom waters. The biochemical oxygen demand (BOD) of
               sediments beneath a finfish net-cage system in Washington State was
               approximately six times greater than the BOD of reference sediments
               (Pamatmat et al. 1973). Two-thirds of the total oxygen uptake was due
               to microbial respiration, while the remainder represented the chemical
               oxygen demand. Sediments beneath a farm in Sweden had a BOD 12 to 15
               times greater than normal (Hall et al. 1990). The depletion of pore
               water oxygen results in a shallowing of the aerobic portion of the
               sediment-column, measurable by both sediment color changes and more
               negative reduction-oxidation potentials in the sediment (Brown et al.
               1987; Weston and Gowen 1988). In some cases the dissolved oxygen
               concentrations in bottom water can be reduced as well (Brown et al.
               1987).


               Sulfur cycling - In the absence of oxygen, microbial degradation of
               organic matter is accompanied by the reduction of sulfate in seawater to

                                                  14









              hydrogen sulfide. Thus organically enriched sediments are characterized
              by low sulfate concentrations, high sulfide levels, and elevated sulfate
              reduction rates (Dahlbdck and Gunnarsson 1981). The microorganism
              Beggiatoa is found at oxic/anoxic boundaries and acquires energy by the
              conversion of sulfide back to sulfate. It is commonly observed as a
              white mat on the sediment surface under and in close proximity to
              net-cage farms (Brown et al. 1987; Kaspar et al. 1988; Weston 1990). In
              areas of extreme enrichment, gas bubbles containing hydrogen sulfide
              will be released from the sediment; a phenomenon of importance to the
              culturist since hydrogen sulfide is highly toxic to fish. Many farms
              have been forced to relocate as a result of sulfide release from

              enriched sediments.


              Nitrogen and phosphorus cyglin - Both nitrogen and phosphorus are
              introduced to the environment in the feed and approximately one-fourth
              of both elements are removed with the harvest. There are considerable
              differences between nitrogen and phosphorus in the environmental fate of
              the remaining three-fourths. Phosphorus is primarily associated with
              the particulate wastes, while nitrogen is primarily excreted as soluble
              metabolites (ammonium and urea'). Continued biodegradation of
              nitrogenous compounds will result in the diffusion of ammonium and
              dissolved organic nitrogen back into the water column, but nitrification
              (conversion of ammonium to nitrate) and denitrification rates
              (conversion of nitrate to nitrogen gas) are negligible due to the
              absence of oxygen in the enriched sediments commonly found under farms
              (Blackburn et al. 1988; Kaspar et al. 1988).


              Macrofaunal community structure
                   The deposition of organic-rich material from mariculture, and the
              consequent changes in the physical and chemical properties of the
              substratum, have profound influences on the structure and functioning of
              benthic communities. While structural changes in meiofaunal communities
              have been reported, such as high abundance of large nematodes near fish
              culture sites (Weston 1990; D. Duplisea, pers. comm.), most


                                                 15









               investigations have focused on the effects of organic enrichment on
               benthic macrofauna.
                    The depletion of dissolved oxygen and/or the high concentrations of
               dissolved sulfide in the pore waters of organically enriched sediments
               result in the mortality or emigration of most species characteristic of
               unperturbed soft-sediments. Since few species possess the behavioral,
               physiological or reproductive adaptations to exploit such environments,
               a reduction in macrofaunal species richness is a widely reported
               phenomenon in the vicinity of mariculture operations (Pease 1977; Brown
               et al. 1987; Ritz et al. 1989; Weston 1990). The effects are often
               dramatic such as a 90% reduction in species richness relative to
               undisturbed conditions (Figure 1) or, in the worst cases, a total
               absence of all macrofaunal species (Brown et al. 1987).
                    Often accompanying the reduction in the number of species is an
               increase in total macrofaunal abundance, largely reflecting the high
               densities of opportunistic polychaetes that are either absent or in low
               densities in surrounding, unimpacted sediments. The most widely
               reported of these enrichment opportunists are members of the Capitella
               capitata species complex. C. capitata appears to have a physiological
               requirement for organically enriched conditions (Tsutsumi et al. 1990),
               and is commonly associated with sewage outfalls, log rafting areas, pulp
               mill effluents and other sources of labile organic carbon. C. capitata
               has been reported in the sediments surrounding mariculture operations in
               Europe (Aure et al. 1988), North America (Pease 1977; Rosenthal and
               Rangeley 1989) and Asia (Tsutsumi and Kikuchi 1983). Densities of C.
               capitata in the vicinity of culture sites are commonly in the range of
                                             2
               1,000 to 10,000 individuals m- , although densities can fluctuate widely
               over time at a given site (Mattson and Linden 1983; Tsutsumi 1990).
                    In contrast to the increased abundance of certain polychaete
               species in enriched habitats, echinoderms, as a group, generally show
               the greatest decrease in abundance. They are the first species to
               disappear with increasing organic enrichment (Mattson and Linden 1983)
               and are often found only in unimpacted sediments far from culture areas
               (Tsutsumi and Kikuchi 1983; Kaspar et al. 1985).


                                                  16









                   0.2-




                        C*j
               50-       E3_
          N
            E      E
                         E

                         0


               25- E
                   0
                   CO
                                                                 43--
                                                      7A




                        i00-




                         E
              150-
          W
          E        E

                   AC   0
          Ci
              i00-
                          50-

                   E
                   0
          06       -
          CO       CO



              50-


                                      A.......



                              0               260               460         1400
                                           Distance from farm(m)

          Figure 1. Trends in areal species richness (S), biomass (B), and abundance
          (A) of macrofauna at two salmon net-cage sites. Data in upper figure from
          Scotland (Brown et al. 1987); data in lower figure from Washington State
          (Weston, 1990).

                                             17








                    Macrofaunal biomass shows no' consistent linear relationship with
               the degree of organic enrichment. While it will, of course, be reduced
               as azoic conditions are approached, lesser degrees of enrichment do not
               result in consistent responses in community biomass. Several authors
               have reported a decreased biomass (relative to controls) in the vicinity
               of fish and shellfish farms (Tenore et al. 1982; L6pez-Jamar 1985;
               Weston 1990), while others found little effect of culture on macrofaunal
               biomass (Kaspar et al. 1985). Brown et al. (1987) reported an increased
               biomass corresponding to peak densities of opportunists, and then an
               abrupt decrease with further increases in enrichment. It is not
               possible to predict either an increase or decrease in macrofaunal
               biomass as a result of enrichment since the parameter will be highly
               dependent upon the size and density of opportunistic species.
                    If the flux of organic material is not great enough to
               substantially alter sedimentary reduction-oxidation conditions, it is
               conceivable that low levels of organic enrichment from culture
               activities could provide an enhanced food supply to the benthos. This
               phenomenon, termed biostimulation (Pearson and Rosenberg 1978), is
               characterized by an increase in species richness and macrofaunal
               biomass. Two investigators have reported this effect near fish farms
               (Ervik et al. 1985; Brown et al. 1987), but in both cases the evidence
               presented was inadequate or open to alternative interpretations.
               Despite the lack of conclusive evidence specific to mariculture,
               biostimulation has been documented near sewage outfalls (Swartz et al.
               1985), and the appearance of a biostimulated zone at some distance from
               a net-cage facility appears plausible.


               Animal size and vertical distribution
                    It has been predicted that in areas subject to organic enrichment,
               the average macrobenthic individual has a smaller body size and that
               there is a shift inthe vertical distribution of infauna towards the
               sediment-water interface (Pearson and Rosenberg, 1978). One of the few
               tests of these predictions is that of Weston (1990) near a salmon
               mariculture facility. Two principal conclusions could be made with
               respect to the effects of enrichment on animal size.

                                                   18









                   Interspecific measures of animal size do, in fact, decrease with
              increasing enrichment. Organic enrichment selectively eliminates the
              largest species among the macrobenthos, resulting in a decrease in the
              mean individual size in the community (i.e. total sample biomass divided
              by total sample abundance). However, since these large species are
              relatively rare even in unenriched environments, measurement of
              enrichment effects based on mean size is prone to a high degree of
              interreplicate variability.
                   Intraspecific measures of animal size often increase with
              increasing enrichment. Among those species able to exploit enriched
              habitats, the organic input results in an increase in food quantity and
              quality, supporting growth to a larger body size. Individuals of
              Capitella capitata and other enrichment tolerant species may be 3 to 5
              times larger in the enriched area than individuals from populations at
              unenriched sites only a few hundred meters distant (Tsutsumi 1990;
              Weston 1990).
                   Organic enrichment also results in a shift in the vertical
              distribution of infauna within the sediment column, but this shift is
              best measured by the vertical distribution of biomass rather than
              abundance. The large species eliminated by organic enrichment are often
              deep burrowers. Consequently, their disappearance reduces the
              proportion of community biomass deep within the sediment column, and
              shifts the biomass profile towards the sediment-water interface. Since
              these species are relatively rare, their loss has little effect on the
              abundance profile. About 90% of macrofaunal individuals are found
              typically in the upper 5 cm of the sediment column regardless of the
              degree of enrichment (Weston, 1990).


              Spatial scales of disturbance
                   While the effects of mariculture on benthic communities may be
              dramatic, the areal extent of impact is generally very localized.
              Investigators studying net-cage farms of small to moderate size report
              dramatic community changes to distances of 15 to 50 m from the farm
              perimeter (Doyle et al. 1984; Brown et al. 1987; Aure et al. 1988;
              Weston and Gowen 1988; Lumb 1989). Even at a very large salmon net-cage

                                                 19









               facility (620 metric tons annual production) dramatic effects extended
               45 to 90 m from the farm, while more subtle macrofaunal changes were
               apparent at least 150 m distant (Weston 1990). While the effects of a
               single farm may be localized, it should be recognized that the benthic
               community of large areas can be altered by the cumulative effects of
               many closely-spaced farms (Arakawa et al. 1971; Tenore et al. 1982;
               o'Connor et al. 1989).


               Temporal scales of disturbance
                    The rate at which the benthic community is altered after
               installation and stocking of a mariculture facility, and the rate at
               which that community recovers after harvest or removal of the farm
               depends upon a wide variety of physical (e.g. currents, bathymetry) and
               biological variables (e.g. timing of recruitment cycles). As a general
               rule, however, alteration of the benthos occurs over the course of a few
               of months while recovery requires a period of years.
                    Mattson and Linden (1983) studied macrofaunal changes following
               installation of mussel longlines, and reported the appearance of dense
               populations of Capitella capitata and the disappearance of echinoderms
               three months after culture began. Other species present prior to
               culture gradually disappeared over about the first year. Similar
               results were reported in studies beneath a small salmon net-cage farm in
               Puget Sound (10-30 metric tons standing stock - Weston and Gowen 1988;
               Dickison, unpub. data). A baseline survey conducted one month before
               stocking of the cages, found no Capitella capitata and little difference
               in species richness among the sampling stations. Six months after
               initiation of culture C. capitata appeared near the farm perimeter
               (Figure 2), although species richness at all stations remained high.
               Eleven months after the start of culture, and in later samples, C.
               capitata attained densities of >1500 individuals M-2 and species
               richness within 6 m of the farm declined relative to control stations.
               Several other investigators of net-cage farms have reported evidence of
               benthic community changes after about one to three months (Gowen et al.
               1988; Lumb 1989; Ritz et al. 1989; Rosenthal and Rangeley 1989).


                                                  20



















                           2000-

                       CD
                    CO
                    CC% (D
                    := E
                    CL
                    Cz (D  1500

                    CZ
                                           8/88
                    CD (n

                                        2
                    CZ     1000
                       CL                   1/88



                                            8/87

                            5
                               0-1
                              0





                               0
                                0            20           40            60

                                          Distance from farm (m)














          Figure 2. Density of the polychaete Capitella cavitata with distance from a
          salmon net-cage farm. N o C. capitata were found at any stations in January
          1987. Fish were placed in the pens for the first time in February 1987
          (2/87). From Weston and Gowen (1988). 21









                   The rate and successional sequence of benthic recovery following
               harvest of a mariculture product or removal of the culture structures  is
               not well documented largely because the studies have been too short in
               duration. The macrofaunal community beneath a former mussel longline
               site remained very different from that of the surrounding areas one aT
               a half years after removal of the longlines (Mattson and Linden 1983),
               The benthic community beneath a former net-cage site showed virtually   o
               recovery 8 months after cessation of culture (Gowen et al. 1988). 7".                1
               only study to find a rapid response to the cessation of organic inp,-,
               was that of Ritz et al. (1987) who reported partial recovery
               of the benthos beneath a net-cage farm only ten weeks after feeding of
               the fish was stopped. Recovery of the benthos following closure of a
               pulp mill required 3-8 years (Rosenberg 1976), and it is likely that
               complete recovery of an area enriched by aquaculture would require a
               comparable period. The time required for recovery will depend upon the
               rate at which erosional/depositional processes and microbial activity
               reestablish the sedimentary reduction-oxidation profile to that typical
               of unenriched condition's, as well as the life history of the resident
               species and the timing of their reproductive cycles relative to
               availability of suitable habitat.


               Mitigation strategies
                    The simplest means of reducing the benthic impacts of net-cage
               mariculture is to minimize feed wastage. The magnitude of wastage can
               usually be assessed by diver inspection, and correction of the problem
               is both straightforward and of obvious economic benefit to the farmer.
               At one farm it was estimated that reduction in feed wastage from 30% to
               5% would reduce organic loading to the benthos from 5.5 g carbon   M-2 d-1
               to 3.5 g C M-2 d-1 (Gowen et al . 1988).
                    Rotation of cages among several culture sites is practiced in
               Norway. When sediments at a site become enriched to the point where the
               health of the cultured fish is threatened, the farmer may move to a
               second site and allow a year or more for recovery of the first site.
               While rotation of culture sites may be of some use in minimizing the
               adverse consequences of sediment enrichment on the cultured animal, it

                                                   22









              is of dubious value as a means to minimize environmental impact. Since,
              the response of benthic communities to organic enrichment is so rapid (a
              few months), and the rate of recovery so slow (a few years), it is
              unlikely that farm sites could be rotated rapidly enough to avoid
              disturbance or slowly enough to allow complete recovery. Similarly,
              other techniques which allow farmers to exploit marginal areas, such as
              periodic dredging of enriched sediments (Rosenthal and Rangley 1989),
              may provide some benefits to the culturist but offer little
              environmental protection.
                  Large funnel-like devices suspended beneath the cages have been
              used to capture solid wastes from freshwater net-cage culture. The use
              of these devices have been limited to experimental applications in
              Sweden (Enell et al. 1984), Finland (Leminen et al. 1986) and Poland
              (Tucholski and Wojno 1980). The Polish studies reported retention of
              45% of the solid wastes, and a 15'to 20% reduction in nitrogen and
              phosphorus loading. The Swedish investigators reported a 71% reduction
              in phosphorus input to the environment. These techniques have not
              progressed beyond the experimental stage, and significant engineering
              hurdles remain in application of the technology to marine sites where
              water currents are likely to be greater than at the lake sites where the
              devices have been tested.
                  The best mitigation approach generally used is the selection of
              sites where water currents will distribute wastes over a very broad area
              and accumulation beneath the farm is maintained to some acceptable
              level. In some areas of net-cage mariculture the objective has not been
              to protect the benthic environment, but only to protect the cultured
              fish from the toxic effects of hydrogen sulfide released from enriched
              sediments. In one study from New Zealand a 7.5 m separation under the
              cages was recommended to prevent problems with sulfide toxicity
              (Rutherford et al. 1988). British Columbia requires 10 m total water
              depth, and since the cages themselves typically occupy about 4 m, a
              distance of 6 m would be maintained beneath the bottom of the cages and
              the seafloor.
                   In other areas concern has extended beyond the protection of fish
              health and focused on protection of the benthic environment. The best

                                                 23









               example of this approach are the depth and current guidelines of
               Washington State (SAIC 1986 - Figure 3). The guidelines are based on
               the premise that the effect of net-cage culture on the benthic
               environment will be minimized if the wastes are dispersed over a very
               broad area. Solid waste loading per unit area of seabed is minimized by
               increasing the opportunity for horizontal transport of a settling
               particle (either by increasing current speed or water depth) or by
               reduction in farm size (i.e. fish production). The Washington
               guidelines require 20 to 60 ft (6 to 18 m) beneath the cages, and
               allowing for the cages themselves the total water depth would have to be
               about 10 to 22 m. It its not yet clear if the Washington guidelines
               totally eliminate benthic impacts, but substantial alteration of benthic
               biology and chemistry is expected at sites that fail to meet the siting
               guidelines.
                    Given the depth and current conditions of Chesapeake Bay and its
               tributaries, it is unlikely that many sites could be found with
               sufficient depth and currents to avoid the effects of organic enrichment
               of the benthos. If net-cage culture is to be permitted in the Bay
               alteration of the benthic community at least to the stage of dominance
               by opportunistic species, and possibly to the point of azoic conditions,
               must be expected. These effects, however, would be localized to the
               area under the farm and within about 50 m'from the farm perimeter.
               Net-cages should not be located over harvestable shellfish beds, near
               seagrass beds, or any other areas where substantial alteration of the
               benthos would be deemed unacceptable.
               Dissolved oxygen           4.2 Water quality
                    The culture of finfish can be expected to reduce the dissolved
               oxygen content of the surrounding water by two mechanisms: 1)
               respiration of the fish; and 2) the biochemical oxygen demand (BOD) of
               the feces, urine and unused food. The oxygen consumed by fish
               respiration will depend upon fish size, water temperature, swimming
               speed and many other factors so it is impossible to determine the oxygen
               needs of a net-cage operation with a high degree of precision. This

                                                  24








                                                   CLASS I I I = Over 100, 000 1 bs /y r
                80-                                CLASS I I  = 20,000 - 100,000 lbs/yr

                                                   CLASS I    = Up to 20,000 lbs/yr


                70-     1





                '0_


             _j                            1qS3
                50-



             C
             CL                                                             Minimum Class I I I
                '0_
                                                                                 Depth

             C

             a- 30                  C'4,q SS
             0

                                                                           Minimum Class  11
                                                                                Depth

             C  2u-                                                        Minimum Class  I
                      Ul
                      0                                                         Depth

                      >

                10-   4




                        1  0.2       0.4      0.6       0.8      1.0
                                             (knots)

                            10      20       30       40         50

                                            (cm sec)
                                      Mean Current Velocity


          Figure 3. Minimum depth for siting net-cages under the   Interim Guidelines of
          Washington State (SAIC 1986). For example, a culturist wishing to produce
          50,000 lbs per year (Class  II) in an area where average currents are 30 cm per
          second must locate the net-cages where the distance between the bottom of the
          cages and the seafloor is 35 feet or greater.

                                                  25









               assessment is made even more complicated by the fact that existing
               information on oxygen consumption by striped bass is largely for
               juvenile fish, and there are no data for fish >100 g in size.
               Nevertheless, if a water temperature of 16*C, a relatively slow swimming
               speed of 5 to 10 cm sec-1, and fish sizes of 20 to 100 g are assumed,
               then respiration rates are likely to be in the range of 180 to 260 mg 02
               kg fish-' hr-1 (Sherk et al. 1972; Kruger and Brocksen 1978).
                   The BOD of waste products can consume at least as much oxygen as
               respiration alone (Willoughby et al. 1972; Liao and Mayo 1974; Kalfus
               and Korzeniewski 1982; Institute of Aquaculture 1990). Most of this BOD
               is associated with particulate matter (i.e. feed and feces) and thus the
               oxygen would be provided by near-bottom waters, unlike respiration that
               would remove dissolved oxygen from surface waters.
                    Field investigations around net-cages have reported decreases in
               dissolved oxygen concentration of both surface and bottom waters. As    a
               worst case example, Kadowaki and Hirata (1984) reported a decrease of
               about 2 mg 1-1 in dissolved oxygen concentrations of surface waters
               among yellowtail and sea bream cages (Figure 4).   It should be
               recognized, however, that the farm under investigation contained 400
               tons of fish, a size several times greater than the largest likely to be
               located in Chesapeake Bay.
                    Depression of near bottom water dissolved oxygen due to the BOD of
               feces and waste feed has been observed at several farms.   A small salmon
               farm in Puget Sound usually had no measurable effect on dissolved oxygen
               levels, but on one occasion there was a 5 mg 1-1 decrease in bottom
               water dissolved oxygen while at the same time surface water dissolved
               oxygen concentrations were reduced 2 mg 1-1 (Pease 1977).  A decrease in
               dissolved oxygen of up to 2 mg 1-1 was reported in bottom waters beneath
               a salmon farm in Scotland containing only 35 tons of fish (Brown et al.
               1987). Oxygen concentrations of bottom water returned to normal levels
               at a distance of 15 m from the farm.
                    It would seem that the consumption of dissolved oxygen through fish
               respiration is, from an environmental perspective, likely to be a
               self-regulating impact.  Large active fish such,as striped bass are
               among the most sensitive animals to oxygen depletion, and would be

                                                  26


















                                                7.0


                                                                               100

                                  6.5%


                            6.00
                                    09 C',


                                                                                7.4
                                 6.5



                                       13



                                                                  0

                                                                      00


                                                                    7.0-











           Figure 4. Dissolved oxygen concentration of surface waters around a net-cage
           farm in southern Japan containing 400 tons of yellowtail and sea bream. From
           Kadowaki and Hirata (1984).
                                                27







               stressed if dissolved oxygen levels dropped below about 5 mg 1-1 for
               extended periods. Should fish respiration decrease dissolved oxygen
               concentrations to biologically limiting levels, the fish themselves
               would be the first to suffer the consequences and standing stock within
               the farm would decrease to sustainable levels.
                     Decreases in bott,om1water dissolved oxygen because of the BOD of
               solid wastes could affect benthic invertebrates and wild demersal fish
               without adverse consequences to the cultured fish themselves, although
               the work of Brown et al. (1987) suggests impacts would be limited to the
               seafloor in the immediate vicinity of the farm.


               Nitrogen and phosphorus
                     Ammonia, and to a lesser extent urea, are the principal nitrogenous
               wastes associated with fish culture. Both are produced as a result of
               the metabolism of proteins provided in the feed. Ammonia may be present
               either as the non-toxic ammonium ion (N.H4"'), or as the toxic un-ionized
               form (NH3). The relative proportions of the two forms is dependent upon
               both pH and temperature, with formation of the toxic NH3 favored by high
               temperature and high pH. Given the variability of pH and temperature
               within Chesapeake Bay it is difficult to determine the proportion of NH3
               without site-specific data. Generally speaking, however, at
               temperatures typi,cal of most of Chesapeake Bay (<300C) and pH values
               typical of marine waters (7-8) only about 0.2 to 5% of ammonia will be
               in the form of NH3 (Trussell 1972) and ammonia toxicity is not likely to
               be a significant problem. The greatest concern regarding ammonia input
               is more likely to be potential effects of the nutrient on phytoplankton
               communities.
                     Phosphorus, as phosphates, are also introduced with the feed and
               are released to the environment through urine and by leaching from the
               feces. Many feed manufacturers have substantially reduced the
               phosphorus content of the feed in recent years because of concern for
               nutrient loadings to the environment, particularly in the Scandinavian
               countries.
                     The environmental fate, and hence potential impacts, of nitrogen
               and phosphorus inputs from net-cage culture are very different

                                                    28









              (Figure 5).   Nitrogen is largely released in soluble forms, with only a
              small fraction in bottom deposits.    Conversely, phosphorus is largely
              associated with feces and waste feed, and the vast majority of
              phosphorus from net-cage culture is initially deposited in the
              sediments.   A large proportion of this phosphorus can later be released
              to the water column, particularly under anaerobic conditions (Enell and
              Lof 1983).
                   Field studies at marine net-cage sites have generally reported
              increased nutrient concentrations within the immediate vicinity of the
              cages. At a salmon farm in the northwestern United States there was a
              three-fold increase in ammonia concentrations within the cages and a
              two-fold incIrease 30 m downcurrent (Milner-Rensel Assoc. 1986).      At
              another small farm in the same area up to an eight-fold increase in
              ammonia concentrations was reported in the vicinity of the cages (Pease
              1977), and a farm in Finland was responsible for a two-fold increase in
              dissolved nitrogen. A small salmon farm (6 net-cages totalling 18 x
              30 m) in Scotland caused a four-fold increase in ammonium concentrations
              at the farm site but no measurable change at the next nearest stations
              1 km away (Gowen et al. 1988). Such increased nutrient concentrations
              are not universal, for example a Swedish trout and salmon net-cage farm
              with an annual production of 33 tons caused no measurable change in
              nitrate and phosphate (MUller-Haeckel 1986). Nevertheless localized
              increases in nutrient concentrations around marine net-cage sites appear
              quite common and would be anticipated in Chesapeake Bay waters. The
              spatial extent of measurable nutrient enrichment will depend upon
              hydrographic factors, but at all sites studied to date dilution of
              nutrients has been quite rapid and measurable increases have been
              limited to within ten's of meters of the farms.


              Quantification and comparison of waste loadings
                    In order to evaluate the potential environmental significance of
              nutrient input from finfish net-cage culture it is obviously necessary
              to have an estimate of the amount of nitrogen and phosphorus released
              from such facilities. Unfortunately, however, there is a complete
              absence of effluent monitoring data from upland striped bass culture

                                                   29





                                  Nitrogen

                           Feed ( 1 007o)
                                             )kFish production (21 -287o)






                                  ..........
                                 04.
                                                                    Soluble nitrogen
                                                                        (49-567o)





                             Particulate nitrogen
                                    (16-307o)


                                Phosphorus flow

                            Feed (I 007o)
                                                ish production     15-3070







                                                                    Soluble phosphorus
                                                                         (16-2670





                            Particulate phosphorus
                                     (54-597o)



           Figure 5. Nitrogen and phosphorus flow through salmonid net-cages, assuming
           100% of each nutrient is provided in the feed. Based on data in Ackefors and
           Enell (1990) and Phillips and Beveridge (1986).

                                               30









              sites and laboratory-derived data are limited to a single study on
              nitrogen excretion by juveniles Juncer 1988). It is therefore
              necessary to rely on data from salmonid culture as a rough approximation
              of potential waste loadings from striped bass. While it is recognized
              that there are likely to be significant differences in excretion and
              digestion between striped bass and salmonids, the data for salmonids are
              so variable and dependent upon numerous variables such as fish size,
              feed conversion efficiency and feed composition, that these data are
              probably acceptable alternatives for the degree of resolution necessary
              for this analysis.
                   Table 2 presents a summary of studies on nitrogen, phosphorus and
              BOD loading from salmonid culture. Most of these studies are based on
              data from rainbow trout cultured in freshwater. Most are also based
              upon effluent monitoring data, but two (Gowen and Bradbury 1987;
              Ackefors and Enell 1990) are based entirely on theoretical calculations
              and assumptions of feed wastage, feed conversion efficiency and the
              nitrogen and phosphorus contents of the feed. It is apparent that there
              is a high degree of variability among these studies, particularly among
              those studies in which waste concentrations in effluent were repeated
              measured. Such variability is not at all surprising given difference in
              operating practices compounded by differences in feed conversion
              efficiency and feed composition. The effect of these variables on
              nutrient loading is clearly evident in Figure 6. For example,
              decreasing the feed conversion efficiency from 1.3 to 2 (decreased
              efficiency = greater numerical value) results in a doubling of the
              nutrient load to the environment. The farmer has considerable control
              over nutrient loading by minimizing feed wastage and using feeds with
              the lowest nitrogen and phosphorus contents possible without comprising
              fish growth.
                   Figures 7-9 put estimated nutrient and BOD loadings from fish
              net-cage culture in perspective with loadings from other discharges to
              Chesapeake Bay. A variety of sewage treatment plant (STP) loadings are
              shown, from the small facilities which serve Queenstown and Prince
              Frederick to the large plant which treats sewage wastes from Annapolis.
              All loadings shown are based on effluent monitoring following treatment

                                                 31










                                                      Table 2
                                Loading of nutrients and BOD from fish culture



                 Reference                   Total nitrogen        Total phosphorus         BOD


                                                      Loading as q (kq    fish'-' d-'

                 Bergheim and                   0.3-0.8                  0.05            1.6-4.6a
                   Selmer-Olsen 1978

                 Bergheim et, al. 1982         0.13-3.8              0.005-0.43           1.6-2.7a

                 Korzeniewski et al               0.12                   0.10
                   1982


                 VKI 1976                         0.38                   0.1                1.8
                                               Loading as kq (ton fish produced)-' yr-1

                 Alabaster 1982                 37-728                22-110              510-990

                 Ackefors and Enell               78c                  9.5c
                   1990
                 Gowen and Bradbury               123'
                   1987

                 Ketola 1982                                         9.1-22.8

                 Penczak et al. 1982              100                    23

                 Solbe' 1982                        68                   16                  285 b

                 Warrer-Hansen 1982                 83                   11                  35 ob


                 a BOD7
                 b Unspecified whether value is BOD5 or BOD7
                 c Based on a feed conversion efficiency of 1.5
                 d Based on a feed conversion efficiency of 2





                                                          32










                        150-

                    0

                        125-

                    0
                    CL  100-


                        75-


                    0
                        50-


                    CD      50%
                    E   25- 45%
                    T-      40%

                         0
                          0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9'2.1 2.3 2.5
                                  Feed conversion efficiency



                        45-
                    0

                        40-

                    0
                    L-  35-
                    CL

                        30-

                    CO  25-

                    0
                        20-

                    CL
                    cn  15-
                    0

                        10- 2.0%
                    M       1.50%
                    E     5-
                    CU
                           .1.0%
                    0)
                         0 -
                          0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5
                                 Feed conversion efficiency



          Figure 6. Nitrogen and phosphorus loading to the environment from salmonid
          culture as a function of feed conversion efficiency. Loading is shown for
          feeds with 40 to 50% protein and phosphorus contents of 1.0 to 2.0%
          phosphorus. From Hakanson et al. (1988).

                                                33














              0-.
                 U:)


              Oj (D
              CL



              V@
                 C+                                                                                                            Total N Ob/day
              0-1





              (D
               50-                                                                                  0                     0                     0


                                                                                 Annapolis
              r) U:)
                                      r+
                                      -3                                                                       CD
                                      CD                                 Maryland City
              m  E3                                                                                            00
                                 r-+  3
              r+ CD              LO   (D CD                         Prince Frederick
              0 CI+                   D
              C--, A                  r-+
              =r W
                                                                             Queenstown


              (D P)
                                                                                      Perdue
              (D CA                      0
                                         =r         MD and VA Milk Producers
                                         CD


                                      (D
                                      3                 A. Powell fish hatchery
                                      U)
                                                                           250 tons/yr

                                      C: (D
                                         r+                                 100 tons/yr
                                      r+
                                      C
                                      3  C-D
                                      (D D
                                                                                2 tons/yr
                 0













           FO
         0
         C.+ -0                                                               Total P Obl

         CU

                                                                 0           0
                                                                 1          -1
                                                      Annapolis
         0
                            -3 Ln
                            C
                               CD
                              D                  Maryland City               1,D
         C+                 W  ::E-
         = --h              r-+W
         (D -'S             @3 CO
           0                                   Prince Frederick     CA
                            CD CD

                            r-+
           (D
           r+                                       Queenstown
     Qn  =r
         0)
           (D               CD-                          Perdue

                               0
         C+ ru              C) C-+*                                                     L4
         0 -S                        MD and VA Milk Producers
           =4                                                                           CO
         C-1) V)


                            (D
         vu                 -3          A. Powel I fish hatchery
         -0 . -,            U)

         7@                                        250 tons/ r

                            n  z3
                                                   100 tons/yr       ON
                            r-+


                               CD
                            CD                       2 tons/yr










                    500

                                                 453


                    400


                         328

                    300



                    200                            181
               

               

                    100      88



                                                    6     12 no 11    no           4
                                                           data     data



                             sewage           other               net-pen
                            treatment       discharges            culture
                             plants








Figure 9. BOD loading from net-cage farms of various sizes in comparison to
        loadings from other discharges to Chesapeake Bay.

                                    36
 







               (usually activated sludge and nutrient removal) and reflect actual
               discharges to the Bay.    Other discharges listed are Perdue Inc. (chicken
               processing), a milk processor, and a trout hatchery.       Estimated loadings
               from fish culture are based on the data of Ackefors and Enell (1990)
               (78 kg N and 9.5 kg P (ton fish produced)-' yr-1) and a BOD loading of
               300 kg (ton fish produced)-' yr-1.    These values are probably
               representative of actual farm loadings within a factor of two.         Loadings
               from three farms of varying sizes are shown. A production of 2 tons
               yr-1 would represent a small farm for supplemental income. A production
               of 100 tons yr-1 would be expected from a commercial venture of moderate
               size.  A production of 250 tons yr-1 is comparable to a typical salmon
               net-cage culture site in the northwestern United States, but may be
               larger than those farms likely to be located in Chesapeake Bay.        It
               should be noted that the wastes from net-cage culture are untreated,
               whereas the STPs and most or all of the other waste streams shown are
               treated prior to release.    The relatively high BOD of fish culture
               wastes probably reflects the efficiency of activated sludge treatment at
               the sewage treatment plants, and not an inherently greater BOD of fish
               wastes in comparison to human wastes.
                    It is apparent from these comparisons that nutrient and BOD
               loadings from all but perhaps the smallest net-cage farms are not
               trivial.  A commercial venture of moderate size (100 tons yr-1) will
               release about 7% of the nitrogen and phosphorus, and about half the BOD
               of the sewage treatment plant serving Annapolis. Loadings of nutrients
               from a farm of moderate size are comparable to loadings from a sewage
               treatment plant serving a small city or from a large food processing
               facility (e.g. Perdue, Maryland and Virginia Milk Producers). The BOD
               loading from such a farm is substantially greater than from these other
               sources.  The smallest farm shown (2 tons yr-1) has nutrient loadings
               comparable to those of an upland fish hatchery (e.g. Albert Powell
               rainbow trout hatchery) and unless released in an area of very
               restricted circulation, would be unlikely to have a measurable
               environmental effect.
                    It should be noted that while nutrient and BOD loadings from
               net-cage culture are comparable to those of other industries or domestic

                                                     37









               sewage treatment plants, the concentrations of these wastes are
               generally far lower (Weston 1986). Because of the open nature of the
               culture structure, in most situations wastes would be rapidly diluted
               with large volumes of water. Thus nutrient enrichment from net-cages
               often more difficult to measure, and measurable nutrient increases are
               very localized.


               Effects on phytoplankton
                    The nitrogen and phosphorus released from finfish net-cage culture
               can be readily utilized by algae, and in fact ammonia, the principal
               nitrogenous metabolite of fish, is taken up by phytoplankton
               preferentially over nitrite and nitrate. Not surprisingly, laboratory
               studies have found that fish carcasses and fish feces enhanced growth
               rates in the dinoflagellate Gymnodinium sp. (Nishimura 1982). Fish farm
               wastes could also provide micronutrients (e.g. vitamins) required by
               algae (Rosenthal et al. 1988). Phytoplankton growth may be limited by a
               number of factors (e.g. light availability, water column stability), but
               if limited by the availability of nitrogen and/or phosphorus it seems
               certain that net-cage culture can provide the limiting nutrients and
               stimulate algal growth.
                    Demonstrating an effect of marine net-cage culture on phytoplankton
               biomass or productivity has proven difficult. Three studies have found
               no measurable effect on phytoplankton including no change in chlorophyll
               a concentrations around farms in Washington State (Pease 1977) or
               Scotland (Gowen et al. 1988) and no change in algal cell density at a
               farm in Sweden (MUller-Haeckel 1986), although it should be noted that
               all these farms were relatively small with production of less than 40
               tons yr-1. The typical scenario is shown in Figure 10, in which a
               localized increase in ammonia is evident, but no effect on phytoplankton
               communities is reported. I am aware of only one report of enhanced
               primary productivity surrounding a marine fish farm (Halonen 1985), but
               the region studied was atypical in its lack of tidal currents.
                    The failure of past studies to demonstrate a change in primary
               productivity due to net-cage culture is probably attributable to both
               dilution of the nutrient-enriched water mass and the time lag before

                                                  38







                           FARM
                            SITE
                       v      v                              v
                                        .8
                                   0.4   0.6
             10-                          0.2

                                              0.4
             20-                               0.6

             30-                                         0.8

                      Ammonium                                             I km I
             40-      mg - at - M-5

                                                      0 7-

                                               2. 0
             10-
                                             1.0



             20-




             30-


                      Chlorophyll
             40.      Mg - M-3


           Figure 10. Cross-sectional profile of Loch Spelve, scotland illustrating the
           distribution of ammonium and chlorophyll in August 1985. Location of
                  I
















           profiling stations indicated on upper figure. From Gowen et al. (1988).

                                               39








                phytoplankton can convert the nutrients to algal biomass.        Phytopl ankton
                populations require a day or more to double in number and several days
                are necessary to increase to bloom proportions (Parsons et al. 1977).
                In most marine situations the nutrient enriched water would be broadly
                dispersed within that time and no localized effect on productivity or
                biomass would be anticipated. Localized effects would only be expected
                in areas of extremely limited circulations.
                     Phytoplankton blooms have been a major problem for marine net-cage
                culturists throughout the world. A bloom of the flagellate alga
                Chrysochromulina oolylepis in Norway in 1988 resulted in the loss of 500
                tons of net-cage cultured Atlantic salmon worth an estimated $5 million
                (Dundas et al. 1989). The flagellate Heterosigma akashiwo has been
                responsible for large losses in Japan, for mortalities in British
                Columbia in 1985 and 1986, and for a large kill of cultured salmon in
                Washington State in 1990. The diatom Chaetoceros spp. has been a major
                problem for culturists throughout the world, including Washington State
                where several farms experienced heavy losses in 1989 blooms. In none of
                these cases was it demonstrated that nutrients from the culture sites
                caused or contributed to the blooms, and given their spatial extent,
                regional hydrographic factors rather than culture activities were
   ---p-robably responsible.
                     In summary, nutrient inputs from finfish culture in Chesapeake Bay
                are likely to be utilized by phytoplankton in those areas and at those
                times when nutrients are limiting algal growth. In these instances
                culture will contribute to an increased phytoplankton biomass and/or
                productivity. In most cases, however, these increases have been
                dispersed over such a broad area as to be immeasurable, and the same is
                likely in most areas of Chesapeake Bay. More detailed assessment
                requires site-specific data on current regimes, farm production, and
                nutrient contributions from other sources in the area.


                Mitigation strategies
                     The open nature of the net-cage design prohibits most of the
                technological solutions to waste stream treatment that would be
                practiced in an upland culture site.      Nutrient or BOD removal would only

                                                       40








              be possible by suspending funnel-shaped collectors beneath the cages as
              discussed in Section 4.1. These devices are in the experimental stage
              of development and would probably remove very little of the nitrogenous
              wastes.
                  The only control measures feasible involve reduction of nutrient
              input to the culture operation rather than removal of nutrients from the
              effluent. The use of dry or semi-moist feed, now the norm in North
              American fish culture, results in a substantial improvement in water
              quality relative to wet feed (i.e. minced fish). Changes in feed
              formulation can also reduce nutrient loading without affecting fish
              growth. It has been estimated that even though finfish production in
              Finland has increased three-fold over the past decade, the loading of
              phosphorus to the environment has only slightly increased because of the
              reduction of phosphorus concentration in fish feed (ICES 1988).
                   Fish farmers in Chesapeake Bay will depend upon water currents to
              dilute and distribute the wastes, both to maintain environmental quality
              and protect the health of the cultured fish. In this regard the best
              sites are those with high current velocities and a high flushing rate.
              Enclosed, stagnant water bodies should be avoided. Areas considered
              highly sensitive to nutrient inputs would also be areas of concern for
              all but the smallest farms. Environmental managers may have to make use
              of water quality modelling techniques in evaluating permit applications.
              Swedish authorities require an applicant to construct a nutrient budget
              for the receiving waters which reflects how nutrient loading from the
              proposed facility compares with other sources in the area. Several
              farms in Washington State have been required to do computer simulations
              of net-cage inputs, illustrating the probable persistence and areal
              extent of nutrient enriched waters.


                                        4.3 Chemical usage
              Aquaculture chemicals
                   The maintenance of suitable culture conditions requires the use of
              a wide variety of toxic substances for purposes such as fouling control
              and treatment of disease. These substances are selected for their
              toxicity to the target organisms, but when environmental risks are not

                                                 41









               fully known or the chemicals are misused, they represent a potential
               threat to the cultured animal, wild fauna and the human consumer.
                   Aquaculture chemicals generally fall within three broad groups.
               First, a wide variety of potentially toxic substances may be introduced
               with the construction materials. For example, mortalities of fish in a
               private hatchery have been attributed to the release of toxic substances
               from the plastic lining of the pond (Zitko 1986). Antifoulants may have
               unwanted adverse effects on both non-target wild fauna and the cultured
               fish. The best example of these unwanted effects is the past use of
               'tributyltin (TBT) as a net-cage antifoulant. Treatment of net-cages
               with TBT has been linked to mortalities in the cultured fish (Short and
               Thrower 1987) and residues of the chemical have been found in cultured
               fish intended for human consumption (Short and Thrower 1986; Davies and
               McKie 1987). The chemical has been found in the sediments of harbors
               throughout the world, including Chesapeake Bay, because of its
               widespread use as a hull antifoulant (Cleary and Stebbing 1985; Grovhoug
               et al. 1986). Shell malformations in oysters has been attributed to the
               use of TBT as an antifoulant on boats moored in nearby areas (Alzieu et
               al. 1980), and the compound has proven to be toxic to many forms of
               marine life at concentrations in the parts per trillion range. As a
               result of the mounting evidence of adverse effects from TBT fish
               culturists in many areas voluntarily discontinued its use as a net-cage
               antifoulant, and many states and countries have since enacted
               legislation banning or severely restricting its use for most
               applications.
                    A second category of chemicals in aquaculture is hormones used for
               gender control (e.g. methyltestosterone) or inducement of ovulation
               (e.g. human chorionic gonadotropin). Little is known about potential
               environmental effects of these hormones, although since the quantities
               used are small major environmental impacts would not be anticipated.
               There are also unlikely to be any human health ramifications since the
               hormones are administered either in the juvenile stage years before
               human consumption or are given to broodstock that would not be marketed.
                    The third major class of aquaculture chemicals is those used to
               treat the fish or the culture environment for the purpose of disease

                                                  42









              therapy, pest removal, or stress reduction. A wide array of antibiotics
              are potentially effective against bacterial pathogens of cultured fish.
              Antibiotics of potential use in aquaculture include erythromycin,
              penicillin, doxycycline, chlortetracycline, streptomycin and
              chloramphenicol.   Erythromycin is used in Canada, England and Norway
              (ICES 1989).  Penicillin has received very limited use in salmonid
              culture in British Columbia (E. Black, pers. comm.), and doxycycline is
              used in Japanese yellowtail culture (Alderman 1988). Others, sUch.as
              chloramphenicol, are used in some countries but have been specifically
              banned by the U.S. Food and Drug Administration (FDA) for use in the
              United States. because of human health concerns.
                   Fish culturists in the United States in general, and striped bass
              culturists in particular, have extremely limited options for
              chemotherapy. This situation results from the rigorous registration
              requirements imposed by the FDA and the relatively minor market for
              aquaculture therapeutants in this country. For many drugs,
              manufacturers are reluctant to pursue registration and FDA approval
              because of concerns that a major proportion of marketshare would go to
              generic substitutes (Schnick 1987). The FDA and U.S. Department of
              Agriculture are currently attempting to speed the registration process
              for so-called "minor use" drugs, such as those that would be required by
              the finfish culture industry in Maryland. The chemicals currently
              approved by the FDA for use in food fish culture are listed in Table 3.
              This list includes chemicals likely to find applications in both fresh
              and saltwater.   The chemicals likely to be used in net-cage culture
              within marine and brackish water would comprise only a small sub-set of
              this list and would exclude virtually all of the water treatment and
              dyes, herbicides and algicides, and piscicides.
                   It should also be emphasized that while all chemicals listed in
              Table 3 are approved for culture of certain species of food fish or
              crustaceans, the FDA generally approves chemical usage on a
              species-by-species basis. A chemical approved for one type of fish
              (e.g. salmonids) can not legally be used to treat other fish for which
              the drug manufacturer has not explicitly sought and received approval.
              Since the striped bass culture industry is still in its infancy, the FDA

                                                  43










                                                  Tabl e 3
                Chemicals registered or approved by the U.S. Environmental Protection
                Agency and the U.S. Food and Drug Administration for use in food fish
                aquaculture. (Modified from Schnick 1988a).

                    Product                                   Use

                                                Therapeutants

                Copper, elemental               Antibacterial for shrimp
                Formalin                        Parasiticide
                Oxytetracycline                 Bactericide
                Sodium chloride                 Osmoregulatory enhancer and parasiticide
                Romet 30 (sulfadimethoxine      Antibacterial
                   and ormetoprim)
                Sulfamerazine                   Antibacterial
                Acetic acid                     Parasiticide

                                                Disinfectants

                Calcium hypochlorite            Disinfectant and algicide
                Didecyl dimethyl                Disinfectant
                   ammonium chloride
                Povidone iodine                 Egg disinfectant

                                         Water  treatment and dyes

                Fluorescein sodium              Dye
                Calcium hydroxide,  Ca oxide,   Pond sterilant
                   Ca carbonate
                Oxytetracycline                 Dye to mark fish
                Potassium permanganate          Oxidizer and experimentally
                                                  as parasiticide/fungicide
                Rhodamine B and,WT              Dye
                Tetracycline                    Dye to mark fish

                                                Anesthetics


                Carbonic acid                   Anesthetic
                Sodium bicarbonate              Anesthetic
                Tricaine (MS-222, Finquel)      Anesthetic

                                         Herbicides and algicides

                Acid blue and acid yellow       Herbicide and algicide
                Aluminum sulfate, calcium       Herbicide and algicide
                   sulfate, boric acid
                Copper, elemental               Algicide
                Copper sulfate                  Herbicide and algicide
                2,4-D                           Herbicide
                Diquat dibromide                Herbicide and algicide; experi-
                                                  mentally as antibacterial

                                                     44









              (Table 3 continued)

              Endothall                       Herbicide
              Fluridone                       Herbicide
              Glyphosphate (Rodeo)            Herbicide
              Potassium ricinoleate           Algicide
              Simazine                        Herbicide and algicide

                                               Piscicides

              Antimycin A                     Piscicide to remove scaled
                                                 fish from catfish ponds
              Rotenone                        Piscicide















































                                                   45









               .has not approved any therapeutants for use on striped bass. Formalin
               has been registered for use on largemouth bass but not striped bass
               (Federal Register 1986a). The antibiotic Romet 30 is approved for use
               on salmonids and catfish (Federal Register 1986b; Schnick 1988a), and
               the antibiotic sulfamerazine is registered only for use on salmonids
               (Federal Register 1986c). Oxytetracycline is currently registered only
               for salmonids, catfish and lobsters (Federal Register 1986d; Schnick
               1988a). There is even some question regarding chemicals classified by
               the FDA as "generally recognized as safe" (GRAS). These chemicals would
               include sodium chloride (salt), acetic acid, carbonic acid (carbon
               dioxide), sodium bicarbonate (baking soda), and lime (calcium hydroxide,
               oxide or carbonate). The FDA has not explicitly approved GRAS chemicals
               for use on striped bass and they have not yet taken a definitive
               position on whether their use would be allowed (R. Schnick, pers.
               COMM.).
                    The antibiotic oxytetracycline shows the greatest potential as a
               registered therapeutant for striped bass culture (Schnick 1988b). The
               manufacturer has prepared all necessary data to expand usage to striped
               bass, but has not yet submitted this information to FDA (Schnick, pers.
               comm.). Given the popularity of oxytetracycline in aquaculture within
               the United States it is likely to become the drug of choice for finfish
               culture in Maryland. The discussion below will emphasize
               oxytetracycline both because its high probability of eventual use in
               .Maryland and because research on the environmental effects of antibiotic
               usage, while minimal, have largely concentrated on this drug.


               Environmental considerations in antibiotic usage
                    Fish culturists typically administer antibiotics on a therapeutic
               rather than prophylactic basis; that is they are provided intermittently
               to combat disease instead of routinely for disease prevention. The r--ed
               for antibiotic therapy will depend upon water temperature and, to a very
               large degree, on husbandry practices. Salmon net-cage culturists in
               northwestern United States have generally found it necessary to treat
               the fish with antibiotics two or three times during the summer and fall
               months, and given the warmer temperatures of Chesapeake Bay treatment is

                                                  46









              likely to be necessary at least as frequently. Oxytetracycline is
              administered as a food additive at a rate of 2.5 to 3.75 g per 45 kg
              (100 lb) of fish per day over a 10-day treatment period (Federal
              Register 1986d). The FDA requires 21-day holding period before fish
              treated with oxytetracycline can be harvested for human consumption.
                  The quantity of antibiotics used in a large, well-established fish
              culture industry can be astounding. In 1989 the Norwegian salmon
              net-cage culture industry produced 115,000 metric tons of salmon. This
              production required the use of 19 metric tons of antibiotics including 5
              tons oxytetracycline, 12.6 tons oxolinic acid and 1.3 tons
              nitrofurazolidone (ICES 1990). Nearly 50 tons of antibiotics were used
              in Norway in 1987 due to a widespread outbreak of Hitra disease.
                  The heavy usage of antibiotics by the fish culture industry in some
              countries and the fact that much of the antibiotic is released to the
              marine environment has prompted much concern regarding potential
              environmental effects. Data useful in evaluating potential effects,
              however, are almost totally lacking. The scientific literature is
              replete with studies on the efficacy of a particular drug for treatment
              of a specific disease, but consideration of environmental effects is
              minimal or lacking. The FDA now requires that new drug applications
              include information on environmental persistence and degradation
              products, but data demands are minimal and comparable information on
              previously registered drugs is lacking entirely. The potential
              environmental concerns are given below, but all conclusions must be
              regarded as tentative given the paucity of information.


              Antibiotic accumulation in biota - A large proportion of antibiotic
              supplied to the fish in the form of medicated feed is not absorbed but
              is released directly to the environment. Waste feed will account for a
              loss to the environment of at least 5% of the antibiotic and potentially
              more. In addition the digestive absorption of ingested antibiotics
              varies greatly depending on the particular drug. For example, over 99%
              of ingested chloramphenicol is absorbed during gut passage, but the
              absorptive efficiency of oxytetracycline is only about 8% (Cravedi et
              al. 1987). Therefore over 90% of the oxytetracycline provided to the

                                                 47









               fish is released to the environment via the feces in a microbially-
               active form.
                    Concern has been expressed that fish farm antibiotics could
               accumulate in demersal fishes, crabs and molluscs living in the vicinity
               of cages, and that the harvest and human consumption of these organisms
               could result in dietary intake of antibiotics.   Harvest of the wild
               organisms would be unaffected by the 21-day post-treatment holding
               period for the cultured fish as required by the FDA since there is no
               way of knowing if or for how long wild organisms were exposed to
               antibiotics prior to capture. This concern is exacerbated by the fact
               that demersal fish and crabs are often found in higher densities around
               fish farms than in the surrounding environment (Weston 1991), and that,
               because of these densities, farm sites are often popular areas for
               recreational fishing.
                    There are reasons to expect that accumulation in wild organisms
               would not be a major problem.  Uptake is likely to be minimal given the
               low retention of ingested oxytetracycline and the fact that antibiotic-
               treated material is likely to comprise only a portion of the total diet
               of the wild organism. In addition, oxytetracycline's octanol-water
               partition coefficient, often used as a surrogate measure of
               bioaccumulation potential, is low suggesting little potential for
               bioaccumulation (Bureau of Veterinary Medicine 1983). Field research on
               accumulation of antibiotics in wild organisms is conflicting. In two
               unpublished studies of very limited scope, no antibiotics were found in
               oysters suspended in the water column near net-cage sites (E. Black,
               pers. comm.; J. Tibbs, pers. comm.).    Scandinavian investigators,
               however, have found oxytetracycline and oxolinic acid in wild fish
               and/or mussels (Moster 1986; Bjdrklund et al. 1990; Lunestad, in press).


               Environmental persistence of antibiotic residues in sediments - The
               available data suggest that oxytetracycline may persist in marine .
               sediments for a considerable length of time, particularly under the
               anoxic conditions that might be expected in fish farm sediments.
               Jacobsen and Berglind (1980) found oxytetracycline in marine sediment
               beneath a fish farm 12 weeks after cessation of antibiotic therapy, and

                                                   48









             laboratory studies indicated a half-life of 10 weeks. In other
             experiments (Samuelson et al. 1988) oxytetracycline concentration in
             organic-rich sediments decreased to 20% of initial concentration after a
             period of 200 days.


             Antibiotic resistance - The use of antibiotics promotes the development
             of bacterial strains resistant to the same or similar antibiotics,
             making further treatment less effective. 'Stimulation of resistance has
             been noted in the aquaculture industry as a result of antibiotic therapy
             using oxytetracycline. During treatment of a trout farm with
             oxytetracycline, 90% of the bacterial isolates from the effluent were
             resistant to the drug as compared to 0% in the influent (Austin 1985).
             Resistance to oxytetracycline is now common in the pathogen Aeromonas
             hydrophila found in catfish farms in the southern United States
             (MacMillan 1985; Motes 1987). Oxytetracycline resistance has been
             documented in Edwardsiella tarda, a pathogen of humans and other
             vertebrates including fish (Sinderman 1990), and resistance to
             tetracycline antibiotics has been found in the fish pathogen Yersinia
             rutkeri. (DeGrandis and Stevenson 1985). Several factors are probably
             responsible for the spread of oxytetracycline resistance among the
             microbial community. Among these are the low efficiency with which
             animals absorb it, its persistence in sediments, and the absence of
             other FDA-approved alternatives, forcing over-reliance upon
             oxytetracycline for most bacterial infections.
                  Antibiotic resistance is strongly selected during chemotherapy and
             during the period that antibiotic residues remain in the culture
             environment. In the absence of selective pressure for resistance (i.e.
             after completion of chemotherapy) the acquired resistance does not
             necessarily confer any advantage or disadvantage to the resistant
             strains. Resistance may therefore persist for long periods and is
             ultimately lost only by dilution with non-resistant strains (Brazil et
             al 1986; Levy 1986). There are few data on the temporal patterns of
             antibiotic resistance. Danish investigators have reported an increased
             resistance among Vibrio anguillarum-like organisms (VLO) following
             treatment of cultured trout with oxolinic acid. Two months after

                                                49









               treatment resistant VLO populations were found 50 m from the cultured
               site and 30% of the VLOs directly under the farm were resistant (ICES
               1990).
                   The stimulation of antibiotic resistance and the persistence of
               this resistance following cessation of antibiotic treatment are both of
               obvious concern to the culturist, but other potential consequences are
               unclear. The greatest problem would be encountered if the occurrence of
               antibiotic resistance in marine microbes decreased the efficacy of
               antibiotics used in human medicine. The fish pathogens of concern to
               the culturist are, with a few rare exceptions, unlikely to be human
               pathogens as well (Sinderman 1990). Antibiotic residues in the
               environment, however, can stimulate resistance in bacteria other than
               the target pathogen, and antibiotic resistance can be transferred among
               bacteria species by plasmid exchange. It is possible that antibiotic
               resistance resulting from finfish chemotherapy could be transferred to a
               bacteria of human health significance. Vibrio Parahemolyticus, for
               example, is a common marine microbe that can cause gastroenteritis in
               humans if ingested through uncooked or undercooked seafood. Any linkage
               between antibiotic therapy in fish culture and antibiotic resistance in
               human pathogens is entirely conjectural at this point since there is no
               documentation of any such association. Sewage effluents and runoff from
               livestock growing areas are undoubtedly far greater sources of
               antibiotics than the Maryland fish culture industry is likely to be in
               the near future. The subject, however, is worth further serious
               evaluation if the fish culture industry grows to a point where
               appreciable quantities of antibiotics are released to the environment.


               Impact of antibiotics on microbial community structure - The sediments
               near fish culture sites are extremely organic-rich because of feed and
               fecal matter accumulation. Degradation of this material is highly
               dependent upon microbial processes. The persistence of antibiotics in
               sediments could conceivably depress the rate and extent of this
               degradation. These effects would be manifested as changes in microbial
               biomass and rates of nutrient regeneration (e.g. sulfate reduction,
               nitrification and denitrification). There have been few studies of the

                                                  50









              effects of antibiotics on sediment microbial communities, but decreases
              in the density of bacteria following antibiotic treatment have been
              reported (Samuelson et al. 1988; ICES 1990).


              Mitigation strategies for antifoulants and antibiotics
                   The use of antifoulants is probably unavoidable in Chesapeake Bay
              net-cage culture. In other areas such as the northwestern United States
              farmers do not require the use of antifoulants. Nets are removed every
              few months, dried in the sun, and then resubmerged. German
              aquaculturists have developed spherical cages which are periodically
              rotated about the axis, located near the waterline. The fouled portion
              of the net is rotated into the upper position for air-drying while the
              clean portion is rotated to beneath the waterline.
                   The rate of fouling growth is very rapid in Chesapeake Bay, and the
              labor involved in changing or cleaning nets would be prohibitive without
              the use of antifoulants. Given the restrictions on the use of TBT and
              trends in the industry elsewhere, it is likely that a copper-based
              antifoulant would be used. These antifoulants have widespread
              applications in  the marine environment, and it is likely that net-cages
              would represent.a small source of copper to the environment compared to
              the quantity of  copper-based antifoulants used on boat hulls.
                   The use of  chemotherapeutants, and particularly antibiotics, is the
              other principal  issue pertaining to environmental effects of chemical
              usage by the aquaculture industry. The frequency of antibiotic therapy
              is, in large part, dictated by husbandry practices.   Many of the
              bacteria and viruses of concern to marine net-cage culturists are
              facultative pathogens; that is they manifest pathological effects only
              when the fish are stressed. Outside of the culture environment these
              diseases are often associated with polluted conditions. In marine
              net-cage culture they are often attributable to husbandry problems. The
              farmer can reduce the frequency*of infection, and therefore the need for
              antibiotics, by reducing stocking density, promptly removing dead fish,
              maintaining unfouled nets, and taking other measures to enhance water
              quality within the cages.



                                                  51









                   Another approach to mitigating the need for antibiotic therapy is
               vaccination. Initial efforts to combat vibriosis in salmonids, and to
               some extent current efforts as well, have relied upon antibiotic therapy
               using oxytetracycline, sulfamerazine, oxolinic acid and other drugs.
               Vaccination of juveniles, however, is becoming an increasingly popular
               alternative and is now used routinely for salmon culture in many
               regions. Vaccination of Atlantic salmon against vibriosis in Norwegian
               net-cage culture has substantially reduced the quantities of antibiotics
               used per unit of production. Vaccination is unlikely to totally replace
               antibiotic therapy since immunity does not last the life of the fish and
               disease resistance can be dramatically reduced by stress, but
               vaccination provides the means to substantially reduce the quantity of
               antibiotics released to the environment.


                                         4.4 Genetic impacts
               Potential consequences of interbreeding between cultured and wild fish
                    Occasional escape of cultured fish from net-cages in open waters is
               inevitable due to storm damage, ice damage, collision by boats, or poor
               farm maintenance. In the northwestern United States, for example,
               fishermen report the occasional capture of Atlantic salmon. Since   the
               species does not occur in the Pacific Ocean except in culture, these
               individuals clearly represent escapees or their progeny. Net-cage
               culturists in Chesapeake Bay must also expect escape of some fish and
               consider the genetic implications of interbreeding of cultured fish with
               the wild population. This discussion emphasizes the culture of striped
               bass, although similar considerations would apply to other species.
                    From a genetic perspective it would be preferable for a culturist
               to capture wild broodstock and rear the progeny in the waterbody (i.e.
               James River, Rappahannock River, etc.) from which the parents were
               taken. This scenario, however, will frequently not be possible. The
               availability of local juveniles may be limited, or the culturist may
               wish to raise fish with attributes (e.g. rapid growth rates) that are
               not characteristic of local stocks. If the cultured fish are obtained
               from hatcheries or from waterbodies different from that of the culture
               site, two concerns arise.

                                                  52









                  First, hatchery stocks often have reduced genetic variability
              relative to their wild counterparts; a phenomenon that has been
              repeatedly documented in hatchery trout and Atlantic salmon (Allendorf
              and Phelps, 1980; Ryman and Stahl 1980; Stahl 1983). Through the use of
              only a few individuals as broodstock, selective breeding, and a variety
              of other intentional and unintentional mechanisms hatchery practices
              often lead to a substantial loss of genetic variability (Meffe 1986).
              Interbreeding of hatchery-derived individuals with members of the wild
              population, if it occurred on a large scale, could reduce the fitness of
              the wild stocks by reducing the genetic plasticity that allows them to
              survive changing environmental conditions.
                  Secondly, it is presumed that wild fish have evolved genetic traits
              making them uniquely suited to the habitat in which they are found.
              Interbreeding of this native population with fish from other localities
              would, by definition, result in reproductive effort being wasted on the
              production of less fit progeny. The Chesapeake Bay stocks of striped
              bass for example, produce eggs containing an unusually large oil globule
              for flotation. If eggs produced in a cross between Chesapeake Bay
              striped bass and individuals from another estuary failed to contain this
              large oil globule, they might be unlikely to survive, and the
              reproductive efforts of both parents might be wasted (Kerby and Harrell
              1990). This potential reproductive waste is of particular concern for a
              stock such as that in the Chesapeake Bay that is already depleted.
                  The concept of stock identity is central to an assessment of the
              genetic consequences of interbreeding between cultured and wild fish and
              dictates the preferred sources of fish for culture in a given locality.
              It is generally accepted that striped bass along the Atlantic Coast can
              be segregated into four principal stocks: 1) Roanoke River; 2)
              Chesapeake Bay; 3) Delaware River; and 4) Hudson River (Rago and
              Richards 1986). It would be preferable to culture fish from the local
              stock. Any escaped fish would therefore be genetically similar to the
              wild population and interbreeding would not jeopardize the population
              fitness. It has not yet been clearly established whether Chesapeake Bay
              striped bass can be further segregated into identifiable sub-populations
              associated with specific river systems such as the James, Rappahannock-

                                                 53








               York, or Potomac-Patuxent. While some investigators have claimed that
               these populations can be discriminated by electrophoretic techniques
               (Morgan et al. 1973), and recent homing studies have demonstrated
               significant homing ability to a specific river system (Hocutt et al. in
               pres s), the data taken together provide inconclusive evidence of the
               existence of discrete sub-populations of striped bass within the Bay
               (Waldman et al. 1988).


               Striped bass hybrids
                    Assessment of the potential genetic consequences of net-cage
               culture is further complicated by the fact that a striped bass hybrid,
               rather than the striped bass itself, would probably be preferred by most
               culturists. There are four North American species within the genus
               Morone, and all are capable of producing fertile hybrids either in the
               wild or by artificial means (Table 4). Natural hybridizations between
               white bass and yellow bass (Fries and Harvey 1989), white bass and white
               perch (Todd 1986), and white bass and striped bass (Crawford et al.
               1984) have been documented or are strongly suspected to have occurred.
               Some crosses may occur only rarely or not at all in the wild but can be
               induced artificially. For example, female striped bass will not release
               their eggs in the presence of white bass, but the eggs can be manually
               stripped and artificially spawned to produce viable offspring (Bishop
               1975).
                    The hybrid cross between a striped bass (M. saxatalis) female and a
               white bass (t. chrysops) male has been the subject of most of the
               research. The hybrid exhibits a faster early growth rate, greater
               disease resistance, and generally greater hardiness than the striped
               bass parent. This hybrid is now in culture at a number of upland sites
               throughout Maryland and would likely be the preferred candidate for
               culture in open water net-cages as well.
                    Contrary to original expectations and experience with hybrids of
               many other animal species, all Morone hybrids are fertile and, at least
               in a hatchery environment, can be used to produce a variety of other
               crosses. F, (first generation) hybrids have been spawned with other F,
               individuals to produce F2 (second generation) fish, although the F2 fish

                                                    54










                                               Tabl e 4
                           Common names of striped bass hybrids recognized
                          by the Striped Bass Committee, Southern Division,
                     American Fisheries Society. From Kerby and Harrell (1990)



                   Female                    Male                   Common name

              Striped bass             White bass                  Palmetto bass
                 (M. saxatalis)           (M. chrysops)

              White bass               Striped bass                Sunshine bass
                 (M. chrysops)            (M. saxatalis)

              Striped bass             White perch                 Virginia bass
                 (M. saxatalis)           (M. americana)

              White perch              Striped bass                Maryland bass
                 (M. americana)           (M. saxatalis)

              Striped bass             Yellow bass                 Paradise bass
                 (M. saxatalis)               mississipiensis)




























                                                   55








               do not appear.to be as desirable for culture as the F1 is.  F1 fish have
               been "backcrossed" with one of the parental species, and have been
               "outcrossed" with a Morone species other than the parents.   F1 hybrids
               produced by crossing of two species (e.g. striped bass x white bass) can
               be spawned with F1 's from another cross (e.g. striped bass x white
               perch) to produce a "trihybrid". A summary of the various crosses that
               have been attempted and the potential for their use in aquaculture  can
               be found in Kerby and Harrell (1990).
                    Data are very limited on potential genetic interactions between
               escaped striped bass x white bass hybrids and wild striped bass within
               Chesapeake Bay, but experience from hybrid releases in several
               freshwater sites indicates that the hybrid is capable of backcrossing
               with at least the white bass parental species and/or naturally
               reproducing among themselves to produce F2 is.  Both white bass and white
               bass x striped bass hybrids were stocked in Lake Palestine, Texas.
               Later sampling revealed that 12 of 41 Morone individuals collected were
               the products of F1 individuals reproducing with white bass or other
               hybrids (Forshage et al. 1986). White bass x striped bass hybrids were
               stocked in the Savannah River drainage in which both white bass and
               striped bass wild stocks existed. In a later survey of 642 fish from
               the Savannah River system, six fish had genotypes not expected of either
               a first generation hybrid or a parental species, and one of these fish
               was clearly a product of hybrid reproduction (Avise and Van Den Avyle
               1984). Although the authors concluded that there was minimal hybrid
               reproduction in the Savannah River system, they presented data from
               other localities where hybrid reproduction appeared more common. Given
               experience with hybrids in these freshwater systems, and lacking
               evidence to the contrary, one would conservatively have to assume that
               hybrid striped bass escaping from net-cage facilities could backcross
               with wild striped bass populations within Chesapeake Bay. This
               interaction, if occurring with sufficient frequency, could compromise
               the gene pool of the wild striped bass population.





                                                   56









               Mitigation stratggies
                    A primary consideration in assessing potential genetic consequences
               of escapement from aquaculture is the size of the escaped population
               relative to the breeding population of the wild stocks. Genetic
               concerns become increasingly important as the number of fish in culture
               increases. Genetic concerns would also be greater if striped bass
               exhibited a strong homing ability (e.g. as do salmonids) and discrete
               sub-populations could be identified. In this case fish escaping from a
               culture facility may interbreed with only one specific sub-population
               and their potential genetic influence would be greater. There is now
               only limited evidence that these sub-populations exist.
                    The Maryland Aquaculture Taskforce has recommended that striped
               bass hybrids be grown only in upland sites where there is better
               protection against escape, and that net-cage culture be limited to
               unhybridized striped bass (MDA 1988). Furthermore, the Taskforce
               recommended that only Chesapeake Bay stocks be cultured in net-cages.
               Given the concerns and potential genetic interactions discussed above,
               these policies seem prudent and adequately protective. It should be
               noted, however, that such policies require the cooperation of all states
               surrounding Chesapeake Bay. Fishery management agencies in Pennsylvania
               are currently stocking hybrid striped bass in rivers and reservoirs
               having direct connection to the Susquehanna River, and hybrid striped
               bass already comprise 10-20% of the winter gill net catch in the upper
               Chesapeake Bay.
                    The induction of triploidy in hybrid striped bass provides one
               option for culturing the hybrid without concern for the potential
               genetic consequences of escapement. Triploid fish contain three sets of
               chromosomes rather than the normal two sets (diploidy), and can be
               produced by subjecting eggs to high hydrostatic pressure or thermal
               shock soon after fertilization. From a management point of view,
               triploid hybrid striped bass would be preferable for culture since they
               are sterile and should they escape, would present no risk to the gene
               pool of the wild striped bass. From the culturists perspective,
               triploid fish may be preferable since they sometimes exhibit faster
               growth and better survival rates than diploid fish. Past attempts to

                                                   57









               induce triploidy in striped bass have been very limited and have had
               only limited success (Kerby and Harrell 1990). Nevertheless the success
               of triploid induction in other fish such as grass carp and salmonids
               suggests that further efforts are warranted.


                                       4.5 Disease transmission
               Introduction of exotic pathogens
                    The transfer of fish from one region of the world to another is
               commonplace, and in fact much of the worldwide aquaculture industry is
               based upon the culture of exotic (non-indigenous) species. In the past
               these transfers have been done with little regulatory control. Without
               adequate safeguards, transfers can result in the unwanted introduction
               of a parasite or bacterial or viral pathogen into areas where it had not
               previously been found, and the infection of wild populations.
                    There are many examples of fish transfers, usually for purposes of
               fisheries enhancement, being responsible for the introduction of exotic
               parasites or pathogens. The protozoan Myxosoma cerebralis, the
               causative agent of whirling disease in salmonids, has been spread
               throughout the world because of fish transfers (Hoffman 1970). The
               infectious hematopoietic necrosis (IHN) virus is believed to have been
               introduced to Japan by eggs imported from the United States and has
               since spread throughout the country (Sano et al. 1977). Aeromonas
               salmonicida, the bacterium causing furunculosis, may have been
               introduced into Europe by the introduction of rainbow trout from North
               America (Rosenthal 1980). In the late 1970s the trematode parasite
               Gyrodactylus salaris began appearing in many Norwegian rivers. It has
               since spread to several dozen rivers, and has caused massive mortalities
               among wild salmon. In some cases authorities have treated the rivers
               with rotenone to remove the infected fish and thereby control the
               parasite. The parasite is believed to have been introduced by stocking
               of infected salmonids (Johnsen and Jensen 1988).
                    Fortunately, finfish net-cage culture in Maryland, as presently
               envisioned, will not require the importation of fish or their
               reproductive products from distant locales. At present the industry is
               dependent upon the capture of wild striped bass broodstock, and these

                                                  58






              fish are likely to come from the Chesapeake Bay'watershed.    Even if a
              striped bass x white bass hybrid is cultured, the white bass is likely
              to be obtained from freshwater bodies within the southea  stern states.
              As the industry matures, domesticated broodstock may be developed,
              reducing the dependence upon wild fish and further reducing the risk of
              accidental transfer of a parasite or pathogen.


              Transfer of disease to wild fish
                   Concern has been expressed that fish aquaculture facilities could
              function as reservoirs of disease, spreading infections to wild fish in
              the vicinity (Mills 1982; Sinderman 1990). In this scenario the
              pathogen may be naturally present in the environment (i.e. not exotic)
              but cause no clinical symptoms in the wild fish unless they are exposed
              to atypically high pathogen densities as might be encountered near a
              net-cage facility experiencing a disease outbreak.
                   Such a scenario has never been documented. There are numerous
              instances of wild fish transferring parasites and disease to caged fish
              (Munro and Waddell 1984; Harrell and Scott 1985), but no examples of
              transfer in the opposite direction -- a result that is probably at least
              in part due to the comparative difficulty of documenting disease in wild
              fish.
                   Forty-five parasitic organisms from viruses to Metazoa have been
              recognized in striped bass from Chesapeake Bay (Paperna and Zwerner
              1976). There are, however only four diseases anticipated to be
              significant problems in marine net-cage aquaculture of the species
              (Mitchell 1984; Hughes et al. 1990).


              Vibriosis - Vibriosis is a disease of striped bass and many other fish
              species caused by the bacteria Vibrio, most often Vibrio anquillarum.
              Vibrio species are ubiquitous in marine and brackish environments and
              many are facultative pathogens. Vibriosis has plagued salmon culture
              throughout the world, and Vibrio spp. have been isolated from moribund
              striped bass within Chesapeake Bay (Toranzo et al. 1983).




                                                   59






 MR









               Pasteurellosis - This disease, caused by the bacterium Pasteurella
               piscicida, has caused large losses among yellowtail (Seriola
               quinqueradiata) culturists in Japan. It has killed striped bass in
               culture (Hawke et al. 1987) and has been caused extensive mortalities in
               wild white perch (Morone americanus), and to a lesser degree striped
               bass, in Chesapeake Bay (Snieszko et al. 1964). The disease is most
               severe at high water temperatures (>230C) when water quality is poor
               (Fryer and Rohovec 1984).


               Aeromonas Pseuodomonas - Bacteria of these genera are capable of causing
               fin rot and motile aeromonad septicemia (MAS) in striped bass and other
               cultured fish. These bacteria are mostoften problems in freshwater
               culture, but can infect fish held in brackish and marine waters.
               Cultured striped bass became infected with Aeromonas hydrophila when
               held in warm (32*C) brackish water (Hawke 1976). It should be noted
               that A. salmonicida, the causative species for furunculosis and the
               cause of large losses for salmonid culturists is primarily a disease of
               salmonids and had not been reported to be a problem in striped bass
               culture.


               "Velvet disease" - This disease is caused by the protozoan parasite
               Amyloodinium ocellatum which attaches to the gills and skin of the host
               fish. It is a serious problem for striped bass in environments having a
               salinity over 3 ppt. A. ocellatum is generally controlled by placing
               the fish in a bath containing a copper solution.
                   Of the four diseases listed above, three are of bacterial etiology
               and are stress related. The bacterial species are ubiquitous
               inhabitants of brackish and marine environments but exhibit no
               pathogenic effects in marine fish unless the fish are stressed in some
               manner.  Cultured fish may be stressed as a result of handling,-
               over-crowding, malnutrition, poor water quality or other factors, and
               thus bacterial pathogens have become a significant problem for fish
               culturists. It is unlikely, however, that wild fish would be any more
               likely to contract such diseases simply by virtue of their proximity to


                                                  60








              the farm provided that the wild fish have not been made more susceptible
              to disease as a result of other environmental factors.



              Mitigation strategies
                   It has not been demonstrated that net-cage culture facilities
              function as epicenters of diseases that would spread beyond the farm
              into the wild fish populations.   The very limited data available suggest
              this is not likely to be a problem in striped bass culture in Maryland,
              but nevertheless it would seem prudent and of obvious advantage to the
              farmer to reduce the incidence of disease in the farm. This can be
              accomplished by reducing stocking density, minimizing handling, and
              taking other precautions to reduce stress on the fish.
                   It is clear that an exotic pathogen could be introduced to
              Chesapeake Bay as a result of fish transfers for aquaculture purposes,
              but as presently envisioned the Maryland striped bass culture industry
              is not likely to require transfers from beyond the southeastern United
              States. Should this situation change, the state would need to establish
              policies for importation of fish and their reproductive products.    For
              example, the salmon. net-cage culture industry in the northwestern United
              States is in part dependent upon eggs from European sources. Any
              importation must be accompanied by a disease-free certification, the
              eggs must be surface disinfected, and the fish are held in quarantine
              for 90 days after swim-up (i.e. depletion of the yolk sac and initiation
              of feeding).  Comparable programs may have to be initiated in Maryland
              depending upon the frequency of transfers, the location of the source,
              and disease history of the area.














                                                  61










                                           LITERATURE CITED


               Ackefors, H. and M. Enell. 1990. Discharge   of nutrients from Swedish
               fish farming to adjacent sea areas. Ambio 19(l):28-35.


               Alabaster, J.S. 1982. Survey of fish-farm effluents in some EIFAC,
               countries. In J.S. Alabaster (ed.), Report of the EIFAC Workshop on
               Fish-farm effluents. Silkeborg, Denmark, 26-28 May 1981. EIFAC Tech.
               Pap. 41.  pp. 5-20.


               Alderman, D.J. 1988. Fisheries chemotherapy: a review. In     J.F. Muir
               and R.J. Roberts (eds.), Recent Advances in Aquaculture, Vol.3, Timber
               Press, Portland, Oregon.


               Allendorf, F.W. and S.R. Phelps. 1980. Loss of genetic variation in a
               hatchery stock of cutthroat trout. Trans. Am. Fish. Soc. 109:537-543.


               Alzieu, C., Y. Thibaus, M. Heral, B. Boutier. 1980. Evaluation des
               resques dus a 1'emploi des peintures anti-salissures d.ans les zones
               conchylicoles. Rev. Trav. Inst. Peche Marit. 44(4):301-348.


               Arakawa, K.Y., Y. Kusuki and M. Kamigaki. 1971. Kaki yoshokujo ni
               okeru seibutsu gentaiseki gensho no kenkyu (I) yoshoku tekisei mitsudo
              .ni tsuite (Studies on biodeposition in oyster beds (I) economic density
               for oyster culture). Venus 30(3):113-128.


               Aure, J., A.S. Ervik, P.J. Johannessen and T. Ordemann. 1988.
               Resipientpavirkning fra fiskeoppdrett i saltvan (The environmental
               effects of sea water fish farms). Fisken Hav. 1988(l):1-94.


               Austin, B. 1985. Antibiotic pollution from fish farms: effects on
               aquatic microflora. Microbiol. Sci. 2(4):113-117.





                                                  62








             Avise, J.C. and M.J. Van Den Avyle. 1984. Genetic analysis of
             reproduction of hybrid white bass x striped bass in the Savannah River.
             Trans. Am. Fish. Soc. 113:563-570.


             Bergheim, A. and A.R. Selmer-Olsen. 1978. River pollution from a large
             trout farm in Norway. Aquaculture 14:267-270.


             Bergheim, A., A. Sivertsen and A.R. Selmer-Olsen. 1982. Estimated
             pollution loadings from Norwegian fish farms. I. Investigations
             1978-1979. Aquaculture 28:347-361.


             Bjdrklund, H., J. Bondestam and G. Bylund. 1990. Residues of
             oxytetracycline in wild fish and sediments from fish farms. Aquaculture
             86:359-367.


             Bishop, R.D. 1975. The use of circular tanks for spawning striped bass
             (Morone saxatalis). Proc. Ann. Conf. Southeast. Assoc. Game and Fish
             Comm. 21:35-44.


             Blackburn, T.H., B.Aa. Lund and M.D. Krom. 1988. C- and N-
             mineralization in the sediments of earthen marine fishponds. Mar. Ecol.
             Prog. Ser. 44:221-227.


             Brazil, G., D. Curley, F. Gannon and P. Smith. 1986. Persistence and
             acquisition of antibiotic resistance plasmids in Aeromanas salmonicida.
             In S.B. Levy and R.P. Novick (eds.), Banbury Report 24: Anfibi-ofic
             resistance genes: ecology, transfer and expression. Cold Spring Harbor
             Laboratory, New York, pp. 107-113.


             Braa ten, B., J. Aure, A. Ervik and E. Boge. 1983. Pollution problems
             in Norwegian fish farming. International Council for the Exploration of
             the Sea.C.M. 1983/F:26. 11 pp.





                                                63









               Brown, J.R., R.J. Gowen and D.S. McLusky.   1987.  The effect of salmon
               farming on the benthos of a Scottish sea loch.   J. Exp. Mar. Biol. Ecol.
               109:39-51.



               Bureau of Vet-erinary Medicine. 1983. Environmental assessment for
               National Academy of Sciences/National Research Council, Drug Efficacy
               Study Group, Finalization for oxytetracycline water soluble and premix
               formulations for food producing animals.


               Butz, I. and B. Vens-Cappell. 1982. Organic load from the metabolite
               products of rainbow trout fed with dry food.   In J.S. Alabaster (ed.),
               Report of the EIFAC Workshop on Fish-farm effluents.   Silkeborg,
               Denmark, 26-28 May 1981. EIFAC Tech. Pap. 41. pp. 73-82.


               Cleary, J.J. and A.R.D. Stebbing.   1985.  Organotin and total tin in
               coastal waters of southwest England.   Mar. Pollut. Bull. 16:350-355.


               Cravedi, J.-P., G. Choubert and G. Delous. 1987. Digestibility of
               chloramphenicol, oxolinic acid and oxytetracycline in rainbow trout   and
               influence of these antibiotics on lipid digestibility. Aquaculture
               60:133-141.


               Crawford, T., M. Freeze, R. Fourt, S. Henderson, G. O'Bryan, 0. Phillip.
               1984. Suspected natural hybridization of striped bass and white bass in
               two Arkansas Reservoirs. Proc. Ann. Conf. Southeast. Assoc. Fish and
               Wildl*. Agen. 38:455-469.


               Dahlbdck, B. and L.A.H. Gunnarson.   1981.  Sedimentation and sulfate
               reduction under a mussel culture. Mar. Biol. 63:269-275.


               Davies, I.M. and J.C. McKee. 1987. Accumulation of total tin and
               tributyltin in muscle tissue of farmed Atlantic salmon.   Mar. Pollut.
               Bull. 18:405-407.





                                                   64








              DeGrandis, S. and R. Stevenson. 1985. Antimicrobial susceptibility
              patterns and R plasmid-mediated resistance of the fish pathogen Yersinia
              ruckeri. Antimicrob. Agents Chemother. 27:938-945.


              Doyle, J., M. Parker, T. Dunne, D. Baird and J. McArdle. 1984. The
              impact of blooms on mariculture in Ireland. International Council for
              the Exploration of the Sea, Special Meeting on the Causes Dynamics and
              Effects of Exceptional Marine Blooms and Related Events, Copenhagen, 4-5
              October 1984.


              Dundas, I., O.M. Johannessen, G. Berge and B. Heimdal. 1989. Toxic
              algal bloom in Scandinavian waters, May-June 1988. Oceanography
              2(l):9-14.


              Enell, M., J. Lof and T.-L. Bj6rklund. 1984. Fiskkasseodling med
              Rening, Teknisk Beskrivning och Reningseffekt. Institute of Limnology,
              Lund.


              Ervik, A., P. Johannessen and J. Aure. 1985. Environmental effects of
              marine Norwegian fish farms. International Council for the Exploration
              of the Sea C.M. 1985/F:37. 13 pp.


              Federal Register. 1986a. Vol 51, No. 64, 21 CFR Part 529.1030 Certain
              other dosage form new animal drug's not subject to certification;
              formalin solution.


              Federal Register. 1986b. 21 CFR Part 558.575 Sulfadimethoxine,
              ormetoprim.


              Federal Register. 1986c. 21 CFR Part 558.582 Sulfamerazine.


              Federal Register. 1986d. 21 CFR Part 558.450 Oxytetracycline.





                                                65









               Forshage, A.A., W.D. Harvey, K.E. Kulzer and L.T. Fries. 1986. Natural
               reproduction of white bass x striped bass hybrids in a Texas reservoir.
               Proc. Ann. Conf. Southeast. Assoc. Fish and Wildl. Agen. 40:9-14.


               Fries, L.T. and W.D. Harvey. 1989. Natural hybridization of white bass
               with yellow bass in Texas. Trans. Am. Fish. Soc. 118:87-89.


               Fryer, J.L. and J.S. Rohovec. 1984. Principal bacterial diseases of
               cultured marine fish. Helgolander Meeresunters. 37:533-545.


               Gowen, R.J. and N.B. Bradbury. 1987. The ecological impact of salmon
               farming in coastal waters: a review. Oceanogr. Mar. Biol. Ann. Rev.
               25:563-575.


               Gowen, R.J., J.R. Brown, N.B. Bradbury and D.S. McLusky. 1988.
               Investigations into benthic enrichment, hypernutrification and
               eutrophication associated with mariculture in Scottish coastal waters
               (1984-1988). Department of Biological Sciences, University of Stirling,
               Stirling, Scotland. 289 pp.


               Grovhoug, J.G., P.F. Seligman, G. Vata and R. Fransham. 1986. Baseline
               measurements of butyltin in U.S. harbors and estuaries. In Oceans 86
               Conference Record, Washington D.C., pp. 1283-1288.


               Hall, P. and 0. Holby. 1986. Environmental impact of a marine fish
               cage culture. International Council for the Exploration of the Sea C.M.
               1986/F:46. 12 pp.


               Hall, P.O., L.G. Anderson, 0. Holby, S. Kollberg and M.A. Samuelsson.
               1990. Chemical fluxes and mass balance in a marine fish cage farm. I.
               Carbon. Mar. Ecol. Prog. Ser. 61:61-73.


               Halonen, L. 1985. Kalankasvatuksen vaikutukset rannikkovesissa,
               Vesihallituksen monistesrja nro 346.



                                                  6'6








              Harrell, L.W. and T.M. Scott. 1985. Kudoa thyrsitis (Gilchrist)
              (Myxosporea: Multivalvulida) in Atlantic salmon Salmo salar L. J. Fish.
              Dis. 8(3):329-332.


              Hawke, J.P. 1976. A survey of the diseases of striped bass, Morone
              saxatalis and pompano, Trachinotus carolinus cultured in earthen ponds.
              Proc. World Mariculture Soc. 7:495-509.


              Hawke, J.P., S.M. Plakas, R.V. Minton, R.M. McPhearson, T.G. Snider and
              A.M. Guarino. 1987. Fish pasteurellosis of cultured striped bass
              (Morone saxatalis) in coastal Alabama. Aquaculture 65: 193-204.


              Hocutt, C.H., S.E. Siebold, R.M. Harrell, R.V. Jesien and W.H. Bason.
              in press. Behavioral observations of striped bass (Morone saxatalis) on
              the spawning grounds of the Choptank and Nanticoke Rivers, Maryland,
              USA. Ichthyologie.


              Hoffman, G.L. 1970. Intercontinental and transcontinental
              dissemination and transfaunation of fish parasites with emphasis on
              whirling disease (Myxosoma cerabralis). Ln S.F. Snieszko (ed.), A
              symposium on diseases of fishes and shellfishes.    pp. 69-81.   American
              Fisheries Society, Spec. Publ. No. 5.


              Hughes, J.S., T.L. Wellborn and A.J. Mitchell. 1990. Parasites and
              diseases of striped bass and hybrids. In R.M. Harrell, J.H. Kerby and
              R.V. Minton (eds.), Culture and propagation of striped bass and its
              hybrids. American Fisheries Society, Bethesda, Maryland. pp. 217-238.


              ICES. 1988. Report of the Working Group on the environmental impacts
              of mariculture, Hamburg, Federal Republic of Germany, 19-21 April 1988.
              International Council for the Exploration of the Sea.


              ICES. 1989. Report of the Working Group on the environmental impacts
              of mariculture, Dunstaffnage Marine Laboratory, Oban, Scotland, 19-24



                                                  67









               April 1989. International Council for the Exploration of the Sea C.M.
               1989/F:11.


               ICES. 1990. Report of the Working Group on the environmental impacts
               of mariculture, Marine Laboratory, Department of Agriculture and
               Fisheries for Scotland, Aberdeen, Scotland, March 27 to 31, 1990.
               International Council for the Exploration of the Sea.


               Institute of Aquaculture. 1990. F.ish farming and the Scottish
               freshwater environment. Prepared for the@Nature Conservancy Council by
               the Institute of Aquaculture, University of Stirling, Stirling,
               Scotland.


               Johnson, B.O. and A.J. Jensen. 1988. Introduction and establishment of
               Gyrodactylus salaris Malmberg, 1957, on Atlantic salmon Salmo salar L.,
               fry and parr in the River Vefsna, northern Norway. J. Fish Diseases
               11:35-45.


               Kadowaki, S. and H. Hirata. 1984. Oxygen distribution in the coastal
               fish farm. 1. Effects of feeding on the distribution patterns. Suisan
               zoshoku 32(3):142-147.


               Kalfus, M. and K. Korzeniewski. 1982. A mathematical model for
               optimization of intensive trout culture in running waters. Polskie
               Arch. Hydrobiol. 29:693-702.


               Kaspar, H.F., P.A. Gillespie, I.C. Boyer and A.L. Mackenzie. 1985.
               Effects of mussel aquaculture on the nitrogen cycle and benthic
               communities in Kenepuru Sound, Marlborough Sounds, New Z6aland. Mar.
               Biol. 85:127-136.


               Kaspar, H.F., G.E. Hall and A.J. Holland. 1988. Effects of sea cage
               salmon farming on sediment nitrification and dissimilatory nitrate
               reductions. Aquaculture 70:333-334.



                                                 68









               Kerby, J.H. and R.M. Harrell.      1990.  Hybridization, genetic
               manipulation, and gene pool conservation of striped bass. In R.M.
               Harrell, J.H. Kerby and R.V. Minton (eds.), Culture and propagation of
               striped bass and its hybrids. American Fisheries Society, Bethesda,
               Maryland. pp. 159-190.


               Kerby, J.H., L.C. Woods III and M,T. Huish.       1983.   Culture of the
               striped bass and its hybrids: a review of methods, advances and
               problems.    In R.R.. Stickney and S.P. Meyers (eds.), Proc. Warmwater Fish
               Culture Workshop, Spec. Publ. No. 3, Louisiana State University, Baton
               Rouge.


               Ketola, H.G.     1982.  Effects of phosphorus in trout diets on water
               pollution. Salmonid, July-August 1982:12-15.


               Korzeniewski, K., Z. Banat and A. Moczulska.       1982.   Effect of intensive
               trout culture on contents of nutrients in water.        Pol. Arch. Hydrobiol.
               29(3-4):625-632.


               Kruger, R.L. and R.W.. Brocksen.     1978.   Respiratory metabolism of
               striped bass, Morone saxatalis (Walbaum), in relation to temperature.
               J. Exp. Mar. Biol. Ecol. 31:55-66.


               Leminen, E., T. Makinen and J. Junna.       1986.  Kalanviljelyn
               vesistokuormituksen vahentaminen varkkokassilaitoksella - kenttatutkimus
               meriolosuhteissa.    Vesihallituksen monistesarja nro 6., 1986.       32 pp.


               Levy, S.B. 1986. Ecology of antibiotic resistance determinants. In
               S.B. Levy and R.P.   Novick (eds.), Banbury Report 24: Antibiotic
               resistance genes:    ecology, transfer and expression. Cold Spring Harbor
               Laboratory, New York, pp. 17-29.


               Liao, P.B. and R.D. Mayo. 1972. Salmonid hatchery water resuse
               systems. Aquaculture 1:317-335.


                                                      69







               Lo'pez-Jamar, E. 1985.  Distribucion espacial del poliqueto
               Spiochaetopterus costarum en las Rias Bajas de Galacia y su posible
               utilizacion como indicador de contaminacion organica en el sedimento.
               Boletin del Inst. Espanol de Oceanografica 2(l):68-76.


               Lumb, C.M. 1989. Self poll  ution by Scottish salmon farms? Mar. Poll.
               Bull. 20:375-379.


               Lunestad, B.J. in press. Fate and effects of antibacterial agents in
               aquatic environments. In D.J. Alderman and C. Michel (eds.), Problems
               of chemotherapy in aquaculture: from theory to reality. Working
               Papers. Internati onal Office of Epizootics, Paris, France, March 12-15,
               1991. pp. 97-106.


               MDA. 1988. Action plan for aquaculture development in Maryland.
               Prepared by the Maryland Department of Agriculture, Maryland Department
               of Natural Resources, and the University of Maryland.


               MacMillan, J.R. 1985. Infectious diseases. In C.S. Tucker (ed.),
               Channel Catfish Culture, Elsevier, New York. 405 pp.


               Mattsson, J. and 0. Linden. 1983. Benthic macrofauna succession under
               mussels, Mytilus edulis L. (Bivalvia), cultured on hanging long lines.
               Sarsia 68:97-102.


               Meffe, G.K. 1986. Conservation genetics and the management of
               endangered fishes. Fisheries 11(l):14-23.


               Mills, S. 1982. Britain's native trout is floundering. New Scientist
               25:498-501.


               Milner-Rensel Assoc. 1986. Aquatic conditions at the Sea Farm
               Norway net-pen site in Port Angeles harbor in April, 1986. Prepared for
               Sea Farm of Norway, Port Angeles, Washington.


                                                  70








              Mitchell, A.J. 1984. Parasites and diseases of striped bass. In J.P.
              McCraren (ed.), The Aquaculture of striped bass: a proceedings.
              University of Maryland Sea Grant UM-SG-MAP-84-01, College Park,
              Maryland. pp. 177-204.


              Morgan, R.P., II, T.S.Y. Koo and G.E. Krantz. 1973. Electrophoretic
              determination of populations of the striped bass, -Morone saxatalis, in
              the upper Chesapeake Bay. Trans. Am. Fish Soc. 102(l):21-32.


              Moster, G. 1986. Bruk av   antibiotika i fiskeoppdrett. Sogn eg
              Fjordane Distriktshogskole, 5800 Sogndal, Norway. 58 pp.


              Motes, M.L., Jr. 1987. The incidence of antibiotic resistant bacteria
              in channel catfish culture with emphasis on Aeromonas hydrophila. M.S.
              Thesis, Auburn University, Auburn, Alabama.


              Mdller-Haeckel, A. 1986. Control of water   quality around a cage fish
              farm in the Norrby Archipelago (Northern Bothnian Sea). Vatten
              42:205-209.


              Munro, A.L.S. and I.F. Waddell. 1984. Furunculosis: experience of its
              control in the sea water cage culture of Atlantic salmon in Scotland.
              International Council for the Exploration of the Sea C.M. 1984/F:32.
              9 pp.


              Nishimura, A. 1982. Effects of organic matters prod   uced in fish farms
              on the growth of redtide algae Gymnodinium type-'65 and Chattonella
              antiqua. Bull. Plankton Soc. Japan 29(l):1-7.


              O'Connor, B.D.S., J. Costelle, B.F. Keegan and D.C. Rhoads. 1989. The
              use of REMOTS technology in monitoring coastal enrichment resulting from
              mariculture. Mar. Poll. Bull. 20(8):384-390.





                                                 71









               Pamatmat, M.M., R.S. Jones, H. Sanborn and A. Bhagwat. 1973. Oxidation
               of organic matter in sediments. EPA-660/3-73-005. U.S. Environmental
               Protection Agency, Washington, D.C.


               Parametrix, Inc. 1990a. Final programmatic environmental impact
               statement:   fish culture in floating net-pens.    Prepared for Washington
               State Department of Fisheries by Parmetrix, Inc., Bellevue, Washington.


               Parametrix, Inc. 1990b. State of Maine: aquaculture monitoring
               program. Prepared for the State of Maine Department of Marine Resources
               by Parametrix, Inc., Bellevue, Washington.


               Parsons, T.R., M. Takahasi and B. Hargrave.    1977.   Biological
               Oceanographic Processes. Second edition. Pergamon Press, New York.
               332 pp.


               Paperna, 1. and D.E. Zwerner. 1976. Parasites and disease of striped
               bass, Morone saxatalis (Walbaum), from the lower Chesapeake Bay. J.
               Fish Biol. 9:267-287.


               Pearson, T.H. and R. Rosenberg. 1978. Macrobenthic succession in
               relation to organic enrichment and pollution on the marine environment.
               Oceanogr. Mar. Biol. Ann. Rev. 16:229-311.


               Pease, B.C. 1977. The effect of organic enrichment from a salmon
               mariculture facility on the water quality and benthic community of
               Henderson Inlet, Washington. Ph.D. thesis, University of Washington,
               Seattle, Washington.


               Penczak, T., W. Galicka, M. Molinski, E. Kusto and M. Zalewski.      1982.
               The enrichment of a mesotrophic lake by carbon, phosphorus and nitrogen
               from the cage aquaculture of rainbow trout, Salmo gairdneri.     J. Appl.
               Ecol. 19:371-393.





                                                    72









             Phillips, M. and M. Beveridge. 1986. Cages and the effect on water
             condition. Fish Farmer, May/June 1986:17-19.


             Powell, M.R. 1972. Cage and raceway culture of striped bass in
             brackish water in Alabama. Proc. Ann. Conf. Southeast. Game and Fish

             Comm. 26:345-356.


             Rago, P.J. and R.A. Richards. 1986. Emergency striped bass research
             study, report for 1986. U.S. Fish Wildl. Serv., Natl. Mar. Fish. Serv.
             1989:55 pp.


             Ritz, D.A., M.E. Lewis and M. Shen. 1989. Response to organic
             enrichment of infaunal macrobenthic communities under salmon seacages.
             Mar. Biol. 103:211-214.


             Rosenberg, R. 1976. Benthic faunal dynamics during succession
             following pollution abatement in a Swedish estuary. Oikos 27:414-427.


             Rosenthal, H. 1980. Implications of transplantations to aquaculture
             and ecosystems. Mar. Fish. Rev. 42(5):1-14.


             Rosenthal, H. and R.W. Rangeley. 1989. The effect of salmon cage
             culture on the benthic community in a largely enclosed bay (Dark
             Harbour, Grand Manan Island, N.B., Canada). In K. Lillelund and H.
             Rosenthal (eds.), Fish Health Protections Strategies. Bundesministerium
             fur Forschung und Technologie, Hamburg/Bonn. pp. 207-223.


             Rosenthal, H., D. Weston, R. Gowen and E. Black. 1988. Report of the
             ad hoc study group on the environmental impact of mariculture.
             Cooperative Research Rep. 154, International Council for the Exploration
             of the Sea, Copenhagen, Denmark.


             Rutherford, J.C., R.D. Pridmore and D.S. Roper. 1988. Estimation of
             sustainable salmon production in Big Glory Bay, Stewart Island.


                                               73






 MOL









              Prepared for MAFFish by the Water Quality Centre, DSIR, Hamilton, New
              Zealand.


              Ryaman, N. and G. Stahl. 1980. Genetic changes in hatchery stocks of
              brown trout (Salmo trutta). Can. J. Fish. Aquat. Sci. 37:82-87.


              SAIC. 1986. Recommended interim guidelines for the management of
              salmon net-pen culture in Puget Sound. Prepared for the Washington
              State Department of Ecology by Science Applications International Corp.,
              Bellevue, Washington.


              Samuelson, 0., V. Torsvik, P.K. Hansen, K. Pittman and A. Ervik. 1988.
              Organic waste and antibiotics from aquaculture. International Council
              for the Exploration of the Sea, C.M. 1988/F:14.


              Sano, T., T. Nishimura, N. Okamoto, T. Yamazaki, H. Hanada and Y.
              Watanabe. 1977. Studies on viral diseases of Japanese fishes V1.
              Infectious hematopoietic necrosis (IHN) of salmonids in the mainland of
              Japan. J. Tokyo Univ. Fish. 63:81-86.


              Schnick, R.A. 1987. Aquaculture work group session report. Veter.
              Human Toxicol. 29(Suppl. 1):28-35.


              Schnick, R.A. 1988a. The impetus to register new therapeutants for
              aquaculture. Prog. Fish Culturist 50:190-196.


              Schnick, R.A. 1988b. Chemotherapeutants for marine aquaculture. In
              C.J. Sinderman and D.V. Lightner (eds.), Disease Diagnosis and Control
              in North American Marine Aquaculture, 2nd revised edition, Elsevier,
              Amsterdam. pp. 402-412.


              Sherk, J.A., J.M. O'Connor and D.A. Neumann. 1975. Effects of
              suspended and deposited sediments on estuarine environments. In L.E.
              Cronin,(ed.), Estuarine Research, Vol. II. Geology and engineering.
              Academic Press, New York. pp. 541-558.

                                                 74








              Short, J.W. and F.P. Thrower.  1986. Accumulation of butyltins in
              muscle tissue of chinook salmon reared in sea pens treated with
              tri-n-butyltin.  Mar. Pollut. Bull.  17:542-545.


              Short, J.W. and F.P. Thrower.  1987. Toxicity of tri-n-butyl-tin to
              chinook salmon, Oncorhyncus tshawytscha, adapted to seawater.
              Aquaculture 61:193-200.


              Sinderman, C.J. 1990. Principal Diseases of Marine Fish    and Shellfish,
              Vol. I, 2nd edition. Academic Press, San Diego, California. 521 pp.


              Snieszko, S.F., G.L. Bullock, C.E. Dunbar and L.L. Pettijohn.   1964.
              Pasteurella sp. from an epizootic. of white perch (Roccus americanus) in
              Chesapeake Bay tidewater areas. J. Bacteriol. 88:2809-2810.


              Solbe', J.F. de L.G. 1982. Fish-farm effluents; a United Kingdom
              survey. In J.S. Alabaster (ed.), Report of the EIFAC Workshop on
              Fish-farm effluents. Silkeborg, Denmark, 26-28 May 1981. EIFAC Tech.
              Pap. 41. pp. 29-55.


              Stahl, G. 1983. Differences in the amount and distribution of genetic
              variation between natural populations and hatchery stocks of Atlantic
              salmon. Aquaculture 33:23-32.


              Swartz, R.C., D.W. Schults, G.R. Ditsworth, W.A. Deben and F.A. Cole.
              1985. Sediment toxicity, contamination and macrobenthic communities
              near a large sewage outfall. In T.P. Boyle (ed.), Validation and
              predictability of laboratory methods for assessing the fate and effects
              of contaminants in aquatic ecosystems. ASTM STP 865. American Society
              for Testing and Materials, Philadelphia. pp. 152-175.


              Swingle, W.  1971.  A marine fish cage design.  Prog. Fish Cult.
              33(2):102.




                                                 75








              Tenore, K.R. (and 18 other authors). 1982. Coastal upwelling in the
              Rias Bajas, NW Spain: contrasting the benthic regimes of the Rias de
              Arosa and de Muros. J. Mar. Res. 43:701-772.


              Thorpe, J.E., C. Talbot, M.S. Miles, C. Rawlings, and D.S. Keay. 1990.
              Food consumption in 24 hours by Atlantic salmon (Salmo salar L.) in a
              sea cage. Aquaculture 90:41-47.


              Toranzo, A.E., J.L. Barja, R.R. Colwell, F.M. Hetrick and J.H. Crosa.
              1983. Characterization of plasmids in bacterial fish pathogens.
              Infect. Immun. 39:184-192.



              Trussel, R.P. 1972. The percent un  -ionized ammonia in aqueous ammonia
              solutions at different pH levels and temperatures. J. Fish. Res. Bd.
              Canada 29:1505-1507.


              Tsutsumi, H. 1990.    Population persistence of Capitella sp.
              (Polychaeta; Capitellidae) on a mud flat subject to environmental
              disturbanceby organic enrichment. Mar. Ecol. Prog. Ser. 63:147-156.


              Tsutsumi, H. and T. Kikuchi. 1983. Benthic ecology of a small cove
              with seasonal oxygen depletion caused by organic pollution. Publ.
              Amakusa Mar. Biol. Lab. 7(l):17-40.


              Tsutsumi, H., S. Fukunaga, N. Fujita and M. Sumida. 1990. Relationship
              between growth of Capitella sp. and organic enrichment of the sediment.
              Mar. Ecol. Prog. Ser. 63:157-162.


              Tucholski, S. and T. Wojno. 1980. Studies on the removal of wastes
              during cage rearing of rainbow trout (Salmo gairdneri Richardson) in
              lakes. 3. Budgets of mineral material and some nutrient elements.
              Rocz. Nau. Roln. 82:31-50.


              Tuncer, H. 1988. Growth, survival and energetics of larval and
              juvenile striped bass (Morone saxatalis) and its white bass hybrid (M.

                                                 76









             saxatalis, x M. chrysops).  M.S. thesis, University of Maryland, College
             Park. 137 pp.


             VKI.   1976.  Vandkvalitetsinst. & Jydsk Teknologisk Inst.:  Forskellige
             driftsparameters indflytelse pA forureningen fra dambrug.   Rapport til
             Teknologiradet. Horsolm, Denmark.


             Valenti, R.J., J. Aldred and J. Liebell.   1976.  Experimental marine
             cage culture of striped bass in northern waters.   Proc. World Maricul.
             Soc. 7:99-108.


             Waldman, J.R., J. Grossfield, 1. Wirgin.   1988.  Review of stock
             discrimination techniques for striped bass.   N. Am. J. Fish. Mgmt.
             8:410-425.


             Warrer-Hansen, 1.   1982.  Evaluation of matter discharged from trout
             farming in Denmark.   In J.S. Alabaster (ed.), Report of the EIFAC
             Workshop on Fish-farm effluents.   Silkeborg, Denmark, 26-28 May 1981.
             EIFAC Tech. Pap. 41. pp. 57-63.


             Weston, D.P.   1986.  The environmental effects of floating mariculture
             in Puget Sound. Prepared for the Washington Departments of Fisheries
             and Ecology.   School of Oceanography, University of Washington, Seattle,
             Washington.


             Weston, D.P. 1990. Quantitative reexamination of macrobenthic
             community changes along an organic enrichment gradient. Mar. Ecol .
             Prog. Ser. 61:233-244.


             Weston, D.P. and R.J. Gowen.   1988.  Assessment and prediction of the
             effects of salmon net-pen culture on the benthic environment. Technical
             Rep. 414, School of Oceanography, University of Washington, Seattle,
             Washington.




                                                 77









               Weston, D.P.  1991.  The effects of aquaculture on indigenous biota.   In
               D. Brune and J. Tomasso (eds.), Aquaculture and Water Quality. World
               Aquaculture Society, Baton Rouge, Louisiana.  pp. 534-567.


               Williams, J.E., P.A. Sandifer and J.M. Lindbergh. 1981. Net-pen
               culture of striped bass x white bass hybrids in estuarine waters of
               South Carolina: a pilot study. J. World Maricul. Soc. 12(2):98-110.


               Willoughby, H., H.N. Larsen and J.T. Bowen. 1972. The pollutional
               effects of fish hatcheries. Amer. Fish. U.S. Trout News 17(3):
               6-7,20-21.


               Woods, L.C., III, J.H. Kerby and M.T. Huish. 1983. Estuarine cage
               culture of hybrid striped bass. J. World Maricul. Soc. 14:595-612.


               Zitko, V., L.E. Burridge, M. Woodside and V. Jerome. 1985. Mortalities
               of juvenile Atlantic salmon caused by the fungicide OBPA.    Canadian
               Technical Report, Fisheries and Aquatic Sciences 1358. 29 pp.
























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