Barataria Basin salinity changes and oyster distribution

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BARATARIA BASIN:
SALINITY CHANGES AND
OYSTER DISTRIBUTION

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BARATARIA BASIN: SALINITY CHANGES

AND OYSTER DISTRIBUTION

V. R. Van Sickle
B. B. Barrett
T. B. Ford
L. J. Gulick

CENTER FOR WETLAND RESOURCES
LOUISIANA STATE UNIVERSITY
BATON ROUGE, LOUISIANA 70803

Sea Grant Publication No.
LSU-T-76-002

This work is a result of research
sponsored by the National Oceanic
and Atmospheric Administration,
US Dep. Commerce, through the Of-
fice of Coastal Zone Management
and the Office of Sea Grant.

SPRING 1976

CONTENTS Page

ACKNOWLEDGMENTS . .. . . . . . . . . . . . . . v
ABSTRACT . . . . . . . . . . . . . . . . . . 1
INTRODUCTION . . . . . . . . . . . . . . . . I
ENVIRONMENTAL FACTORS AFFECTING
OYSTER POPULATIONS . . . . . . . . . . . . . 3
Temperature . . . . . . . . . . . . . . . 3
Food . . . . . . . . . . . . . . . . . . . 5
Water Circulation . . . . . . . . . . . . 6
Bottom Character . . . . . . . . . . . . . 7
Salinity . . . . . . . . . . . . . . . . . 9
Predation . . . . . . . . . . . . . . . . 11
Competition and Commensalism . . . . . . . 13
Turbidity and Sedimentation . . . . . . . 14
Pollution . . . . . . . . . . . . . . . . 16
-Disease . . . . . . . . . . . . . . . . . 18
OYSTER PRODUCTION CURRENT
AND HISTORICAL . . . . . . . . . . . . . . . 21
EFFECTS ON OYSTERS OF ENVIRONMENTAL
CHANGES OCCURRING IN BARATARIA BAY 24
Land Loss 26
CHANGES IN MISSISSIPPI RIVER FLOW . . . . . . 29
CHANGES IN OYSTER PRODUCTION AREAS
IN BARATARIA BASIN IN PAST YEARS . . . . . . 30
APPENDIX 35
LITERATURE CITED . . . . . . . . . . . . . . . 41
FIGURES (after page 44)

VS Department of Commerce
FOAA Coastal Servicea center Library
2234 South Hobson Av,@nue
Charleston, sc 29405-2413

LIST OF FIGURES

1 Louisiana Oyster Landings.(Reported)
1880-1974 46
2 Southern, Gulfward Portion of Barataria
Basin 47
3 Area Leased for Oyster Culture in
Barataria Basin in 1947 48
4 Area Leased for Oyster Culture in
Barataria Basin in 1959 49
5 Area Leased for Oyster Culture in 50
Barataria Basin in 1975
6 Linear Salinity Trends 1961-1974 @1
7 Histogram of Normalized Data 52
8 Salinity vs. Salinity Ratio Comparison 53

LIST OF TABLES

1 Acreage of Oyster Leases in Barataria
Bay (By Parish). 45
2 Changes in Width of Major Passes in
Barataria Bay Area 45
3 Acreage of_Oyster Leases in Little
Lake (By Parish) 45

ACKNOWLEDGMENT�
This work is a result of research sponsored
by the National Oceanic and Atmospheric Adminis-
tration,@U.S. Department of Commerce, through the
Office of Coastal Zone Management and the Office
of Sea Grant. The activity is coordinated through
the Louisiana State Planning Office.
The nature of this study required assistance
and information from a relatively large number of
individuals and agencies. Work primarily involved
collection, analysis, and interpretation of
existing data located at a number of sources.
The authors are particularly indebted to the
individuals, departments, and agencies listed
below:

The Study Management Team of the Louisiana Coastal
Zone Management Program: Patrick Ryan, Director,
State Planning Office; Lyle. St. Amant, Assis-
tant Director, Louisiana Wildlife and Fisher-
ies Commission; Vernon Behrhorst, Director,
Louisiana Coastal Commission; and Jack R.
Van Lopik, Director, Louisiana Sea Grant
Program.
Louisiana State Planning Office, Coastal Resources
Program: Patrick W. Ryan, Director, Paul R.
Mayer, Jr., Assistant Director, Coastal
Resources Program; Paul H. Templet, Program
Coordinator; Lynne Hair, Assistant'Program
Coordinator; John M. Bordelon, Chief Planner;
and Jim Renner, Economic Planner.
Louisiana Wildlife and Fisheries Commission,
Oysters, Water Bottoms and Seafoods Division:
Harry E. Schafer, Chief; Max W. Summers,
Assistant Chief; Miller Fairman and Ernest
Dugas, Oyster Leasing and Survey Section;
Ronald J. Dugas and -Ralph Latapie, biologists.
Louisiana State Department of Health: Charles
Bishop, Chief, Section of Categorical Programs;
George Robichaux, Engineer, Permits and
Monitoring; Richard Cousins, Public Relations
Coordinator; Gerald A. Mathes, Sanitarian.
U.S. Department of Commerce; National Marine
Fisheries Service, Statistics and Market News
Service Office, New Orleans: Ovide Plaisance,
Fishery Reporting Specialist.
Dr. Harry J. Bennett, Department of Zoology,
Louisiana State University, Baton Rouge.

Special thanks are due the following members of
the Louisiana oyster industry, who were most
helpful in establishing historical oyster
distribution and production: Heyman Pitre,
Buddy Zibilich, Peter Vujnovich, Baldo V.
Pausina, Zelko Franks, Joseph M. Jurisich, A.
J. Buquet, Willie Guidry, and Louis Eymard.

ABSTRACT
The biology, production, and distribution of
the American oyster in the Barataria basin have
been correlated with environmental factors that,
determine spatfall, growth, reproduction, and
mortality. Mortalities resulting from predation
and disease are often associated with increased
levels of salinity and temperature. Oysters
thrive in the mixture of fresh and salt waters
found in many of our estuaries; their distri-
bution is found to be directly related to salin-
ity. This paper explains the interrelationships
that exist between salinity and other environ-
mental parameters affecting oyster populations.
Salinity data accumulated over a twenty-year
period has.afforded the documentation of salinity
changes in the lower Barataria basin. The trend
is towards increased levels of salinity in the
Barataria estuary. During the past 30 years
natural oyster spatfall has been observed further
and further inland, in areas that had previously
been too fresh to support oyster growth. If
oyster growth is displaced further northward at
the present rate, the.Barataria oyster fishery
may suffer, as encroaching levels of pollution
intrude southward into areas of current and
futu re oyster production.

INTRODUCTION
During the past 30 years there has been an
increasing concern for the protection of the
various species that inhabit Louisianals richly
endowed coastal zone. This interest has prompted
an investigation into the abundance and distri-
bution of commercial and noncommercial species
that exist in estuarine communities. Presently,
the Coastal Zone Management team of the Center
for Wetland Resources (Louisiana State Univer-
sity) is attempting to evaluate the interrelation-
ships that exist between marshland inhabitants
and their biophysical habitats. The Division of
Oysters, Water Bottoms, and Seafoods of the
Louisiana Wildlife and Fisheries Commission
(LWFC) is responsible for much of the research
activity and the collecting and achieving of
environmental data describing these aspects of
the coastal zone.
Historically, our most valuable commercial
fisheries have been shrimp, menhaden., and oysters
(in that order). Each of these organisms depends
heavily on estuarine environmental systems such

as those found in Louisiana. The productivity of
such systems is predetermined by the balance of
several factors that comprise the delicate estuar-
ine framework. Recently the U.S. Environmental
Protection Agency stated that "it is currently
assumed that none of the major commercial species
.would continue to exist in commercial quantities
if estuaries were not available for development"
(U.S. EPA 1971). This is particularly true for Or
the American oyster (Crassostrea virginica
Gmelin), which inhabits estuarine waters during
its entire life cycle. The dependence of this
organism on the mixture of fresh and saline
waters--coupled with its benthic development and
feeding behavior--@-account for its extreme sensi-
tivity to sporadic environmental fluctuations
that can result in increased mortalities.
Louisiana has been subject to fluctuations in
production since the beginnings of the oyster
industry in the latter half of the nineteenth
century. Several oyster.surveys conducted around
the turn of the century have facilitated this
investigation.
Currently the most widely used means for the
quantitative assessment of commercial species is
the use of catch data. However, the lack of
consistent and realiAble reporting of oyster
landings has restricted the use of conventional
methods for the inventory and analysis of the
Louisiana oyster resource. Accordingly, sources
other than catch data had to be utilized to
construct a program that would reveal current and
historical aspects of oyster production, distri-
bution, and relationship with a dynamic and
changing environment.
The approach for accumulating data was broken
down into five basic tasks:

1) Survey of previous efforts to locate and
quantify Louisiana oyster populations.
2) Personal interviews with qualified members of
the oyster fishery to establish production
estimates from private leases.
3) Consultation@with LWFC (Division of Oysters,
Water Bottoms, and Seafoods) to obtain lease
charts and records.
4) Analysis of water quality in areas of oyster
production as,recorded by the Louisiana State
Department of Health.
5) Evaluation of the interrelationships between
oyster production and environmental factors.

The Barataria Basin was selected as a pilot
study area because of the quantity and quality of
available environmental data. It is a semiclosed
basin that receives its freshwater input mainly
from rainfall and agricultural runoff. The
northern head of the basin is dominated by fresh
to brackish waters while salt water environments
dominate the southern seaward end. This basin is
one of the major oyster producing areas in the
state.
This report first discusses environmental
factors affecting oyster population and the
history of oyster production in the Barataria
Basin. Then, in the context of information
presented in these two sections, the effects on
oysters of environmental changes in the Barataria
Basin are presented. The reader is urged to give
full attention to this final section, which
documents clearly forthe first time the steady
northward movement of oyster producing areas in
the basin due to salinity encroachment (and the
accompanying problems of predation and disease
from marine organisms). As oyster producing
areas move northward, further problems arise@from
encroaching pollution levels from the north.
These problems pose a real threat to oyster
production in the Barataria Basin, and the intro-
ductory information on the biological require-
ments of oysters should be read with them in
mind.

ENVIRONMENTAL FACTORS AFFECTING OYSTER
POPULATIONS
Any investigation into the causes of mortal-
ity, decline in production, or changes in distri-
bution of oysters should take.into consideration
many possibilities. Principal factors that
produce favorable growth rates, propagation, and
general welfare in an oyster community are optimal
temperature, food supplies, water circulation,
bottom character, and salinities. A second set
of factors, which may adversely affect oyster
populations, includes disease, competition,
predation, turbidity and sedimentation, and
pollution. The interactions of the positive and
negative factors of the environment act simul-
taneously on an oyster community to determine its
productivity (Galtsoff. 1964).

Temperature
A great difference in climatic conditions

exists within the geographical range of the
American oyster. Temperature is one of the
principal variants in benthic communities of this
type. The oyster is a poikilothermic organism
that has been observed in waters with temperatures
ranging 34-97*F (Galtsoff 1964). The external
temperature directly affects the life of the
oyster by controlling gonad formation, spawning,
respiration, feeding, and water transport.
Ciliary motion of the gills, which is res-
ponsible for the transport of water, is maximum
at a temperature of about 77-79'F. The ciliary
activity declines rapidly below 70*F and ceases
completely at 41-45'F. Growth of oysters main-
tained at temperatures below 46*F is often
referred to as hibernation (Galtsoff 1964). At
temperatures above 90*F there is also a decline W
in ciliary movement. The effect of ciliary
activity is very important to the physiology of
the oyster because of the direct relation of
water transport to other vital processes. In
addition to respiration, the celia of bivalve
gills play an important role in feeding. As the
tiny, whip-like celia beat to transport water
over the gill filaments, dissolved organic
substances and microscopic life are trapped on
the surface of the gills. These particles are
transported to the mouth by continuous ciliary
motion associated with water transport. Galtsoff
(1964) observed that feeding does not occur below
temperatures of 43-44*F.
The second set of functions that are directly
related to environmental factors, primarily
temperature, are gonad formation and spawning.
As the temperature of the water begins to rise in
late winter and spring, the sperm and egg cells
developP thickening the gonadal.epithelium
(Hopkins et al. 1953). Spawning of ripe gonads
is triggered by a rapid rise in temperature but
is not determined by a specific critical tempera-.
ture, as others had originally suggested (Nelson
1931).
The number of sex cells produced during a
single season varies, depending upon environ-
mental conditions. Greater gonadal development
is more likely to be found in oysters from lati-
tudes north of the Chesapeake Bay rather than in
.the south Atlantic and Gulf of Mexico waters.
However, in these northern populations the repro-
ductive season is of short duration, lasting only
4 to 6 weeks. In our warmer southern waters,
gonadal formation and spawning continue for
several months. The peak of the spawning season

for Barataria Bay oysters occurs early in May
(Mackin and Wray 1950). Mackin and Wray (1949)
state that oysters in the lower region of Bara-
taria Bay are kept at near gonadal exhaustion for
6 to 8 months of the year, due to prolonged high
temperature stimulation. Postreproductive degener-
ation of tissue and glycogen loss in these oysters
is partly responsible for the shortened life span
of oysters found in our southern habitat.
Indirectly, temperature is a controlling
factor in that it, along with salinity, determines
solubility of oxygen in water and affects the
matabolism, reproduction, and behavior of associa-
ted organisms. Metabolic rates of predators,
parasites, and competitors are accelerated in
spring and summer months at precisely the time
when oysters are most vulnerable to damage due to
spawning and glycogen losses.
Mackin and Hopkins (1961) noted that seasonal
mortalities of oysters were obviously correlated
with temperature. However, Mackin and Wray
(1950) stated that the effect of temperature is
secondary as high temperature alone has little or
no effect, but high temperature combined with
some factor associated with high salinity, such
as predation, is effective in producing lethal
results.

Food
Observations of various investigators indicate
that diatoms, dinoflagellates, and other groups
of phytoplankton and zooplankton plus bacteria
and organic detritus comprise the diet of the
oyster. Selection is made primarily on the size
and shape of the food particles. Jorgenson and
Goldberg (1953) observed that the American oyster
filters about 10 to 20 liters (2.6-5.2 gallons)
of water for each milliliter of oxygen consumed.
At this rate, under normal conditions at 75-77*F,
an oyster may filter 1,500 liters (396 gallons)
of water daily. Actual food requirements of
oysters do not exceed 0.15 mg of utilizable
organic matter per liter of water used (Jorgenson
1952). The organic matter of the phyt6plankton
found in American coastal waters has been shown
to range from 0.17 to 2.8 mg per liter (Riley
1941; Riley and Gorgy 1948). Research along the
coast of Louisiana conducted by M. H. Owen (1955)
for LWFC indicates that "at all times and at all
stations sampled there were sufficient numbers
and kinds of microorganisms present in the water
to support existing populations of oysters."

The abundance of plankton is critical only
during the period when the oyster is actively
feeding and accumulating glycogen. Conditions
are ideal for the feeding of oysters when non-
polluted water containing a low concentration of
small diatoms and dinoflagellates runs over a
bottom in nonturbulent flow (Galtsoff 1964).
High concentrations of phytoplankton, such as
those seen during algal blooms, are not desirable
and can be harmful. Sudden development of red
tide dinoflagellates, Gymnodinium breve, may
cause extensive mortalities of oysters growing in
water along the shores of affected areas. Con-
sumption of the poisoned shellfish may produce
lethal results in the consuming organisms. Toxic
algal blooms are not common in Louisiana waters;
no reports of the poisoning of shellfish exist in
the recent literature.

Water Circulation
"Free exchange of water is essential for the
growth, fattening and reproduction of oysters"
(Galtsoff 1964). Ideally, an oyster bed is
supplied with a steady, nonturbulent flow of
water. The current need only be strong enough to
carry away liquid and gaseous metabolic wastes
and feces and to provide oxygen and food. The
distribution of planktonic populations, eggs
spawned within the estuary, pollutants, and any
other material dissolved or suspended in water is
determined by the circulation of fresh and salt
water in the estuary. These waters are mixed and
distributed constantly within the estuary as a
result of daily winds and tidal oscillations.
River flow and rainfall also effect water circu-
lation but on a more seasonal basis (Ketchum
1951).
Tidal currents and other water movements in
the northern Gulf area have been described by
Marmer (1947, 1948, 1954). Tides of the Bara-
taria Bay area are diurnal (one high and one low
per day). Mean tidal levels fluctuate in a
regular rhythm throughout the year; the lowest
mean levels are in January and the highest in
September (Marmer 1954). There is an increase in
mean tidal level from August to September. This
is of greatest significance in its effect on
salinity levels in bays.and marshes. During this
same period, with low rainfall in the marsh
drainage area, high evaporation rates due to
summer temperatures coupled with high transpir-
ation rates of lush summer vegetation cause a net
flow of water from the Gulf into Louisiana bays

and marshes. As would be expected, this has a
pronounced effect on the salinity of the estuaries
(Mackin and Hopkins 1961).
The velocity of currents over an oyster bed
will determine the amount of sediment deposition.
Natural oyster reefs are commonly located in
areas free from sediment deposition or siltation.
Oyster spat require hard clean surfaces for
attachment. Planted shell or cultch placed in
areas of relatively high current velocity tend to
collect more spat than those placed in low velo-
city areas (Keck et al. 1973). In addition to
being relatively free from the problem of sil-
tation, these high current areas are exposed to a
greater volume of water and hence a higher number
of larvae will come in contact with the shell.
Perkins (1952) showed that oyster larvae concen-
trations are high where current is fairly strong
and salinity shows no stratification.
Oyster communities are most vulnerable to
occasional turbulent currents of high velocities,
such as those associated with hurricanes. These
movements may dislodge and carry away young and
adult oysters not attached firmly to some bottom
feature. Oysters.that are attached to the bottom
,are also harmed by such currents. Valve injury
is incurred if sand is present to act as an
abrasive material.

Bottom Character
One of the physical factors of great impor-
tance to the oyster grower is the character of
the bottom. Oysters grow best on bottoms that
are hardened with firm mud, rock, or shell.
Oysters do not grow well on sandy or soft mud
bottoms. The abrasive action of shifting sand
will cause valve injury; shifting mud may cause
death by suffocation-.
Barrett (1971) mapped sediment type distri-
bution in Barataria Bay and vicinity. He des-
cribes the sediment type in this area as being
predominantly clayey silt. The Gulf side of the
bay has a higher sand content than that of the
north and central regions, which have a siltier
character. Clay content in the bottoms of Bara-
taria Bay is low.
A soft muddy bottom may be improved by -
planting cultch to form an artificial reef. The
most common cultch materials are oyster and clam
shell. These materials give the bottom an arti-
ficial but functional firmness desired for oyster
culture. Louisiana oystermen prefer clam shell
as a cultch material because it produces more

single, rounded oysters that are desirable in the
counter trade. Pollard (1973) found that "no
cultch material candidate could approach clam
shell for suitability as cultch, because of its
abundance, low cost, and ready availability with
a minimum of transportation difficulties." The
limitations of the practice of planting cultch
are primarily those of time and money. The
current price of clam shell and oyster shell is
$5.00/yd3. Louisiana oyster fishermen may plant
cultch at densities as high as 500 yd3/acre on
relatively small plots, while the LWFC plants
cultch at rates of 30-50 yd3/acre on the seed
oyster grounds or reservations. The fishermen
apply cultch at higher rates because they are
generally trying to build a hard reef-like bottom
that will endure dredging operations from year to
year.
The bays of southern Louisiana are typically
hard bottomed around the periphery with the
bottom increasing in softness toward the center
(M4ckin and Hopkins 1961). Galtsoff (1964)
states that the most valuable type of bottom for
oyster culture is firm and stable, composed of
rocks and hard or sticky mud. Louisiana oyster-
men prefer a bottom type that is a mixture of
coarse particles of hard mud and clay, which
easily supports the weight of cultch or natural
oyster growth; rocky bottoms are rare in coastal
Louisiana. The reinforcement of oyster bottoms
by shell is the principal practical method used
on a large scale for the improvement of oyster
bottoms or the establishment of new ones.
New oyster reefs may also be established
naturally. This is partly due to the innate
ability of oyster larvae to choose a substratum
upon which to settle. As a result of this ability,
soft muddy bottoms may be gradually converted by
the oysters themselves into oyster reefs in a
process that may require several years. The
process begins with the attachment of larvae to a
single shell or other hard object lying on the
surface of the bottom. Other larvae attach to
those that have already settled. Soon a cluster
of oysters is formed. As the oysters grow,
natural and artificial processes will determine
mortality. Dead oyster shells drop from the
cluster and provide additional surfaces for
larvae attachment. The cycle begins again and
the reef grows horizontally and vertically
(Galtsoff 1964).

Salinity
Perhaps the single most important environ-
mental factor affecting oyster populations is
salinity (Butler 1949). The direct relation of
rainfall to salinity makes surplus precipitation
another important parameter to consider. Coastal
Louisiana is an area of high annual rainfall,
averaging 59 in/yr. In Barataria Bay, high
rainfall serves to decrease salinity whereas
tides drive Gulf water into the bay through the
passes, increasing salinity. Thus, during periods
of high rainfall there is usually a significant
decrease in salinity. During periods of drought
and high temperature, salinity may be expected to
rise.
Oysters are euryhaline organisms, able to
live in waters of a very wide range in salinity.
Chanley (1957) reported that optimum salinity for
growth and development of C. virginica falls
between 15 and 22.5 ppt. Galtsoff (1964) found
oysters inhabiting waters with a range of salin-
ity from 5 to 40 ppt. The optimum salinity for
oyster populations in the Chesapeake Bay area is
from 10 to 28 ppt. The optimum salinity for
natural oyster growth and survival in Louisiana
is much lower, 5 to 15 ppt (Galtsoff 1964; St.
Amant 1964). Oysters inhabiting waters of more
northern latitudes seem to be more adapted to
higher salinity levels. Lindall et al. (1972)
explain these differences as being preferences
exhibited by distinct ecotypes, possibly even
subspecies.
Oysters are somewhat adapted to diurnal,
seasonal, and.annual fluctuations of salinity.
The mean values of these salinities are of little
significance because ofthe oysters' ability to
isolate itself from the environment by tightly
closing its valves. In this way it may survive
adverse conditions, provided they do not last
indefinitely (Galtsoff 1964). Direct effects of
change in salinity on C. virginica are determined
by two factors: the range of the fluctuations
and the suddenness of changes Barataria Bay is
periodically subjected to dra;tic changes in
salinity. During Hurricane Carmen, which passed
near the Barataria coastline on September 7,
1974, the salinity at St. Mary's Point (see Fig.
1) was increased from 7 to 30 ppt within 3 hours
(Maurice Lasserre, personal communication, LWFC,
Baton Rouge, La.).
Several studies have attempted to relate
oyster mortalities to salinity. Lowered salin-
ities have been directly correlated with increased

mortalities (Butler 1949). Marine bivalves have
little power of osmo-regulation when placed in
dilute seawater; they can prevent loss of salts
only by closing their valves. The first physical
reaction of oysters to lowered salinity is the
slowing or cessation of water current through the
gills. This is accompanied by partial or complete
contraction of the adductor muscle. This behavior
may last for several hours with no permanent
injury to the oyster (Galtsoff 1964). of course,
if the exposure is prolonged, the oyster will
become weakened or permanently injured and may
die.
The reproductive capability of oysters is
reduced by low salinity. Butler (1949) showed
that gametogenesis is inhibited in oysters main-
tained in salinities less than 6 ppt. He attri-
butes this failure of gonad development to vari-
ations in food availability and feeding rather
than direct inhibition of sexual activity.
Loosanoff (1952) found that normal gonadal
development may proceed in salinities near 7.5
ppt, but oysters with ripe gonads subjected to
lower salinities spawn at 5 ppt. He also noticed
abnormal feeding behavior and little growth at
salinities of 5 ppt or less. Davis and Calabrese
(1964) related rate of growth to type of food
organisms available. The type and abundance of
food organisms is determined by environmental
factors.such as salinity.
Barataria Bay oyster fishermen usually
transplant young oysters from water of low
salinity into water nearer the Gulf. The in-
crease in salinity results in an increase in the
rate of growth and fattening of the oysters. In
addition, the taste.of the oyster is improved as
the salt content is increased.
Galtsoff (1964) reported a gradual increase
in ash (mineral matter) and salt content of
oysters from May to September. Variations in the
chemical composition of'oys,ters follow distinct
patterns related.to the environment and season of
the year. "The major environmental factor affect-
ing the chemical composition is the salinity of
the water" (Galtsoff 1964). Lynch and Wood
(1966) showed that amino acid content of oyster
adductor muscle increases proportionally with
increased salinity. The increase in solids and
corresponding decrease in water content is
associated with an increase in glycogen content
(Galtsoff 1964). These factors directly affect
the commercial quality of oysters.

Continued exposure to salinities above the
optimum range has an unfavorable effect on oyster
populations. However, most investigators feel
that the combined effects of high salinity and
high temperature are much greater than the effect
of either, variable when taken singularly. The
synergistic effects of high temperature and high
salinity have been the topic of much research
interest. Mackin and Wray (1950) and Owen (1955)
found that excessive mortalities in the Barataria
Bay region occur when there is a combination of
high temperature and high salinity. These mor-
talities are the primary reason for low production
in certain years (Owen 1955).
.The influx of fresh water into ah estuary is
often quite beneficial. Decreased salinities
have lethal effects on carnivorous gastropods'.
flatworms, and fungi that are highly destructive
or debil'itating to oysters. Brackish water
constitutes a barrier through which these pre-
dators and parasites cannot penetrate and survive
for extended periods. Periodic flushing restores
the productivity of oyster beds by reducing these
harmful organisms and introducing nutrients.

Predation
Predation is one of the more obvious environ-
mental factors associated directly with oyster
mortality. Representative flatworms, molluscs,
echinoderms, crustaceans, fishes, birds, and
mammals prey on oysters. Not all of these
enemies are equally destructive to oyster popu-
lations; the.:most dangerous are those that prefer
oyster meat to other types of food (Galtsoff
1964).
Every oyster fisherman questioned agreed
that the most serious predators found in Louis-
i.ana waters,(excluding man) are the Louisiana
Conch or,oyster drill (Thais haemostoma) and the
black drum (Pogonias cromis). The stone crab
(Menippe mercenaria) was mentioned as having been
a serious pest during the 1930s and 1940s. The
starfish, Asterias forbesi, a highly destructive
predatorin Atlantic coast oyster grounds, is
usually not found in Louisiana estuaries, pro-
bably because of its low tolerance to reduced
salinities such as those found in Barataria Bay.
The deadliest enemy of Louisiana oysters is
the conch, a carnivorous gastropod common to
waters of the south.Atlantic and Gulf of Mexico.
The organism feeds chiefly on oysters and other
molluscs by drilling a neat round hole, approxi-
mately 0.004 inches (1 mm) in diameter, through

the shell. The oyster flesh is removed by means
of an extensible proboscis. The conch seems to
prefer small oysters to large ones. Selective
destruction of young oysters may result in
extinction of natural reefs (Burkenroad 1931).
The conch poses a threat to the Barataria Bay
oyster fishery, with normal attacks occasionally
resulting in near total depletion of oysters
grown in the lower bay region.
Several studies have been conducted to
elucidate the biology of the Louisiana conch and
its relation to the American oyster. St. Amant
(1938) presents a detailed, informative disser-
tation concerning Thais and its effect on oyster
populations. Burkenroad (1931) and Galtsoff
(1964) have published brief accounts of the
predacious nature of this organism.
Many years ago, before the oyster fishery
became so extensive, the oystermen would set
traps for the conch. These were wire baskets
that were baited with clam or oyster meats.
Another method for control of this predator
was the use of palmetto fronds. During breeding
season, the conchs develop a tendency to climb as
high as possible (below low tide mark) on struc-
tures elevated above the surrounding bottom. The
eggs are fastened to these elevated objects.
Because of this habit, the animals and their eggs
can be trapped during the breeding period. At
one time, Louisiana oyster fishermen used stakes
withlbunches of palmetto fronds wired to them
throughout an infested area. The animals climbing
up accumulated on The palmetto fronds as they
deposited their eggs. The oyster.fishermen
pulled up,the stakes periodically and shook the
palmetto fronds over the bottom of their boat,
removing predator and potential offspring (Gates
1910). One oyster fisherman stated that in one
year he harvested as many conchs from his leases
in lower Barataria Bay as he had oysters.
One of the most beneficial effects of
freshets (sudden influxes of fresh water) that
occur in the Louisiana estuaries is the effect
they have on the conchs. The limiting factor in
the distribution of the conch is considered to be
salinity. The organism cannot survive prolonged
exposure to salinities less than 10 Opt (Galtsoff
1964).
Schools of black drum often invade the
northern waters of th e Gulf of Mexico where they
feed on molluscs such as the oyster. These fish
possess powerful jaws and pharyngeal teeth that
can crush oyster shell. Piles of crushed oyster

shells are the only remains of productive oyster
reefs that-have been attacked by the voracious
black drum.
These fish seem to be especially partial to-
ward oysters that have been freshly transplanted
or bedded. The damage to natural reefs is slight,
but in areas where oysters are transplanted to
saltier waters, the ravages of the drum are more
frequent (Gates 1910). If a bed is accidentally
disturbed by a tugboat, crewboat, or other object
scraping over a reef, the drum are more likely to
attack that particular bed. For this reason,
once harvesting operations are begun, Louisiana
oyster fishermen often continue dredging an indi-
vidual lease until all the oysters are removed.
During the early years of the fishery,
oysterfishermen fenced their oyster beds with
galvanized wire to prevent attacks by the black
drum. The use of this technique has disappeared
because the fence interfered with navigation in
the coastal zone. Since the days of fencing,
oyster fishermen have no means for controlling
thi's predator.

Competition and Commensalism
Oyster competitors are those organisms that
live in close proximity to oysters and struggle
with them for available food and space. Commen-
sal organisms live in a related capacity to
oyster populations, sharing the food gathered by
their oyster host. Some commensals may become
parasites or cause injury to the oysters as a
result of their habits or fecundity.
The oyster is subject to several commensal
and competitive relationships as the shell and
body of the oyster are the natural abodes for
many plants and animals that attach themselves to
the shell surface or bore through it to make for
themselves a well protected.residence (Galtsoff
1964). The list of such species and their be-
havior is well documented and described by
Gaitsoff (1964).
The major species of this group common to
Barataria. Bay waters are Polydora, Cliona, and
Diplothyra. Mackin and Wray (1949) refer to
these three as lithe shellpest triumvirate."
Polydora is a genus of mudworm, found in the
intertida'1 zone of Atlantic, Pacific, and Gulf
waters of the United States. P. websteri is
found in Louisiana oyster shells and on the
lateral inner surfaces of the valves. The worm
builds a U-shaped tube in the shell that is
covered by shell material (conchiolin) secreted
by the oyster; the formation on the inner shell
surface is usually called a blister. Hopkins

surface is usually called a blister. Hopkins
(1958) presents a report describing the behavior
of the organism and its occurrence throughout
Louisiana. Mackin and Wray (1949) feel that
abnormally high populations of these worms are
probably due to high organic detritus content of
the waters.
Two species of boring sponge, Cliona celata
and Cliona truitti, have been observed in Bara-
taria Bay. The major difference between the two
species is their distribution, which is based on
different tolerances to low salinities. C.
truitti is more tolerant of low salinities and is
found in upper bay areas (Mackin and Wray 1949).
The presence of the boring sponge is revealed
by small round holes on the surface of oyster
shells. Heavy infestations may result in brittle
valves that break under slight pressure. If the
oyster has been subjected to adverse conditions,
delayed deposition of conchiolin may result. In
this case the sponge makes direct contact with
the oyster flesh. This results in dark pustules
forming directly opposite the holes in the shell
(Galtsoff 1964).
Oyster shells in Louisiana are often infested
with the boring clam, Diplothyra smithii. This
species reaches about 0.5 inches in length and is
found inside oyster shell material in a cavity
that increases in size as the clam grows. The
clam is rarely found to directly contact the
oyster flesh, again because the oyster secretes
conchiolin ov&r nearly perforated areas. The
presence of the boring clam is indicated by small
holes in the outer surface of the valves. Infes-
tations of boring clams are harmful to oysters
because they weaken shell structure (Galtsoff
1964).

Turbidity and Sedimentation
Several factors contribute to turbidities
found in bays and bayous of the Mississippi River
delta depressions. Much of the autochthonous
turbidity is because of materials introduced into
Gulf waters by the Mississippi River. As river
waters reach the Gulf, decreased velocities and
flocculation precipitate most of the silt load;
the remainder enters the tidal zone. A portion
of these highly turbid waters ultimately reach
the estuaries. Other important causes of turbid-
ities in the estuaries are high surplus precipi-
tation and runoff, wind agitation of inorganic
debris on the water bottom, and human activity
such as boat traffic and dredging. Both natural

and man-induced production of turbidities is
present in Barataria Bay, which always seems to
have high turbidity.
The effects of turbidity on shellfish are
quite complex, with.beneficial and harmful aspects.
Several investigators agree that low levels of
turbidity do not harm either adult oysters or
oyster larvae (Ingle 1952; Mackin and Hopkins
1961; Loosanoff and Davis 1963). Loosanoff and
Davis (1963) suggest that suspended silts and
clays may even absorb toxic pollutants and thereby
allow oysters and other filter feeders to survive.
Abnormally high levels of turbidity are
dangerous to estuarine communities. Prolonged
excess turbidities can be detrimental to primary
producers, which determine the productivity of
estuarine environments. Planktonic plants are
dependent upon sunlight as the energy source for
photosynthesis. As the suspended solids content
of the water increases, the depth of light pene-
tration decreases. Therefore, the compensation
depth (level at which rate of photosynthesis
equals the rate of respiration) decreases or
approaches the surface. If light penetration
does not reach compensation depth, respiration
may exceed productivity4 In this case, the
:system loses energy and the biological community
undergoes degradation (Brehmer 1965).
Estuarine communities are adapted to cope
with turbid-environments- but man-made levels of
turbidity often exceed t@e tolerance level of
such systems. Shellfish are especially vulner-
able to damage by inorganic suspended solids.
These filter feeding organisms remove suspended
solids from the environment as water is trans-
ported across the gills. Feeding activity is
inhibited by high suspended solid levels (Galt-
soff 1964).
As the velocity of water containing sus-
pended materials is decreased, the amount of
deposition of the suspended matter is increased.
The role of siltation in the destruction of
aquatic habitats is well documented. Siltation
can smother benthic forms of life. Louisiana
fishermen say that oysters are suffocated by 1 to
3 inches of silt, depending upon the size of the
oysters. Investigators of siltation damages to
oyster leases by LWFC biologists strongly suggest
that oysters may be able to cope with a slow,
gradual siltation by maintaining a clear area for
water intake. However, rapid siltation of several
inches usually results in high mortalities.

increased dredging activities have presented
serious problems to oyster fishermen working in
areas of active oil and sulfur operations. About
50 percent of oyster damage complaints registered
with the LWFC involve dredging and siltation
(Lindall et al. 1972). Brehmer (1965) states
that "turbidity and subsequent siltation reduce
the quality of estuarine waters for intended uses
and degrade the system as a biological habitat."
He describes turbidity and siltation as forms of
pollution which have been greatly increased by
manis activities.

Pollution
Brehmer (1965) defines water pollution as
"the introduction into the water of any material
that reduces the value or utility of the water
for any intended use." The generality of such
statements has made for complex social, economic,
and biological points of view on the subject of
pollution'. The term means different things to
different people, depending upon their particular
interest. Public health officials are primarily
concerned with the health hazards associated with
pollution. The ecologist relates pollution to
changes in the environments. To.the oyster
grower, pollutants are any materials that decrease
the availability of oysters.
Detailed descriptions of all types of pollu-
tion that may affect oyster populations are
beyond the scope of this paper. Basically, there
are two groups of pollutants commonly found in
oyster growing areas: domestic sewage and indus-
trial or trade wastes.
The discharge of domestic sewage is one of
the most ancient forms of pollution, common to
all geographic areas inhabited by man. Increased
population has necessitated the use of sewage
treatment and organized disposal. The introduc-
tion.of domestic sewage sludge directly into
oyster growing waters may immediately produce
lethal effects as oyster beds are smothered with
the material. This type of pollution also increases
the BOD (biological oxygen demand) of affected
waters, reducing the amount of dissolved oxygen
available to the shellfish.
The most significant problems associated
with domestic sewage pollution and oyster consump-
tion are due to the oysters' feeding behavior.
These filter feeding molluscs retain and accumulate
bacteria found in their aquatic environment.
This characteristic makes the oyster a potential
source for a concentrated number of pathogens

associated with.domestic waste, such as the
microorganisms causing typhoid fever and hepa-
titis. The U.S. Department of Health, Education,
and Welfare (HEW) determines the degree of con-
tamination of oyster growing waters by the
abundance of Escherichia coli, a nonpathogenic
coliform bacterium found in mammalian fecal
waste.
The Louisiana State Department of Health
(LSDH) monitors coliform, levels of all oyster
growing waters along the coast. If the MPN (most
probable number) of E. coli exceeds the permis-
sible maximum of 70 per 100 ml and more than 10
percent of the samples exceed an MPN of 2 30 per
100 ml, the area is restricted and cannot be used
for harvesting (HEW 1965). However, under certain
specified conditions, the oysters in these areas
may be transplanted to unpolluted areas where
they are allowed to depurate for a period of
several weeks.
The Louisiana State Health Department records
temperatures PH, turbidity, salinity, total
coliforms, and fecal coliforms (E. coli) at
stations located in each oyster growing area of
the state. This data is compiled and published
in Louisiana Oyster Water Surveys, which are
available.through the Engineering Division of
LSDH. Barataria Bay lies in sample areas desig-
nated III-A and III-B. These areas receive some
sewage contamination from Mississippi River
discharge that drifts northwestward and enters
the bay through various passes and inlets. Other
sources for contamination are settlements and
camps found in Barataria Bay and along adjacent
bayous and marshes.
No industrial wastes are known to be dis-
charged directly into Louisiana oyster growing
waters (LSDH 1972). However, several types of
industrial pollutants enter oyster producing
areas via Mississippi River discharge and various
drainage systems in the basin. Common industrial
pollutants flushed into growing areas include
those from oil, sulfur, paper, chemical, plastics,
and food industries that characterize the south
Louisiana region. The type of pollutant varies
with the product.
State and federal laws forbid the discharge
of oil into coastal waters. Yet many of our bays
and marshes are heavily polluted by oil (Galtsoff
1964). The parishes of the Barataria Basin
produce almost one-half of Louisiana's oil and
natural gas. Petroleum exploration and extraction
activities have been among the more evident

sources of industrial pollution in this area.
When oil is spilled onto the surface of water, it
spreads rapidly to form a thin film. In highly
turbid waters such as those found in Barataria
Bay, suspended particles of clay, silt, and
organic detritus absorb oil, coalesce, and gradually
sink to the bottom (Owen 1955). The crude oil
may remain in the sediments for several weeks,
retaining toxicants that impart "oily" tastes to
the oysters of the affected bottom (Blumer et al.
1970).
Runoff from agricultural areas presents
multiple pollution problems in oyster growing
areas. In 1967, the Public Health Service of HEW
published a study of pesticides in shellfish and
estuarine areas of the Lower Mississippi River
region and southern Barataria Bay. Oyster meats
and water samples were collected during three
separate time periods'between January 1964 and
June 1966. All of the oyster meats sampled were
found to contain one or more chlorinated pesti-
cides. The amounts of pesticide residues occur-
ring in the oyster samples were not significant
as health hazards (HEW 1967).
The Louisiana State Department of Health
monitors agricultural pesticides and heavy metals
in oysters and performs radiation analyses of
oyster meats. The available data indicate no
contamination of growing waters by radioactive
materials, heavy metals, agricultural pesticides
or other objectional materials (LSDH 1972).

Disease
OyIsters, like most other living creatures,
are subject to both noncontagious and infectious
diseases. The oyster's resistance to disease is
a reflection of environmental conditions that can
weaken or strengthen the organism. Symptoms of
disease in oysters are usually nonspecific. The
more common symptoms are slow growth, failure to
fatten, inhibition of gonadal development, or
abnormal spawning activity. If the oyster is
severely diseased the adductor muscle is weakened
so that the valVeB do not close tightly. In the
literature these oysters have been called gapers.
Abnormal deposition of shell in diseased oysters
is a chronic condition resulting in the formation
of short and thick shells. The body of a sick
oyster is often discolored (dirty green or brown),
watery, and bloody with blood cells accumulating
on the body surface and gills (Galtsoff 1964).
This condition is not to be confused with that of
a firm-bodied, healthy oyster highly pigmented in

red or brown as a result of the food it has
consumed. These oysters are considered top
quality in the counter trade.
A number of pathogenic and nonpathogenic
organisms have been associated with periodic
mortalities of oysters in waters of the United
States. However, widespread oyster mortalities
can rarely be attributed to a single factor such
as disease. In most cases, a combination of
several adverse conditions, including infection,
are responsible for these occurrences.
The most dangerous parasite associated with
infectious oyster disease in Louisiana is a
fungus called Dermocystidum marinum for many
years (Mackin et al. 1950). Recent taxinomical
advances have resulted in a reclassification of
the organism as Labyrinthomyxa marina. During
1947 and 1948, Mackin and Wray (1949) observed
that almost 100 percent of oysters in Louisiana
waters, including Barataria Bay, were infected by
this fungus.
The many phases of the life history of
Labyrinthomyxa and various degrees of infection,
coupled with environmental factors that affect
the resistance of the oyster to disease, result
in a complex collection of symptoms, including
some of those previously mentioned. For the
purpose of this study, it will be sufficient to
mention the following information concerning the
fungus and its relation to the oyster (from Owen
1955).

1) Labyrinthomyxa marina is a causative agent of
oyster disease, which is histolytic in nature.
2) The disease is lethal to oysters under con-
ditions of high temperature.
3) High temperature and high salinity produce
optimum conditions for the spread of the
organism.
4) Oyster production in Louisiana is seriously
affected by the disease.
5) Infected oysters in an optimum environment
usually recover from the infection, based on
degree of the infection.
6) This fungus is probably the major cause of
unusual, widespread mortalities of Louisiana
oysters.
7) The consumption of infected oysters by humans
does not, under any circumstances, produce or
have any detrimental effect.

No other pathogenic organism seems to be as
persistent in Louisiana waters as Labyrinthomyxa.

However, other pathogenic organisms do exist and
have been correlated with oyster disease in
coastal Louisiana. Hexamita sp. is one such
organism (Mackin et al. 1952). Heavy infestation
of this flagellated protozoa@n causes breakdown of
connective tissue cells, general inflammation,
and necrosis of tissues containing the dormant
cyst stage of the parasite (Galtsoff 1964).
Reports of the presence of Hexamita in Louisiana
waters are rare, as are reports of another para-
site, the oyster leech, Stylochus sp. (Owen
1955). Young oysters seem to be easily attacked
by this flatworm, which has no difficulty enter-
ing the slightly opened valves of diseased oyster
and spat. Stylochus is often found in Florida
waters where it frequently inflicts serious
damage to oyster communities, but the signifi-
cance of the parasite in Louisiana is "minutely
minor" (Owen 1955). Some authors feel that
Stylochus is probably best classified as a pre-
dator (Caltsoff 1964), not a parasite that may
cause disease (Owen 1955). The exact difference
between these types of relationships is most
difficult to discern.
The trematode, Bucephalus gracilescens, is
an intestinal parasite of certain marine fishes.
The oyster is the intermediate host of this
trematode or fluke. The eggs of Bucephalus
which are liberated from the intestine of infec-
ted fishes', are ingested by the oyster as it
feeds. A ciliated larvae or mi.racidium develops
within the egg, emerges, then migrates to the
gonadal tissue of the oyster where it goes through
several stages of its life cycle. The growth of
the organism in the oyster may become so extensive
as to practically replace most of the reproductive
tissue. Eventually the free living larval forms
of Bucephalus.develop and enter the water where
they may infect the definitive host. Bucephalus
does kill oysters and has been found in Louisiana
waters, including lower Barataria Bay. Frequency
with which Bucephalus occurs in Louisiana is very
low, probably owing to its rather complicated
life cycle (Owen 1955).
Owen (1955) found that practically all
oysters from the major producing areas of Louis-
iana are infected with the wormlike sporozoans
Nematopsis ostrearum. The spores and cysts of
this nonpathogenic gregarine are found in the
body tissues of infected oysters. Owen (1955)
gives a full description of his observations of
this organism in Louisiana waters during the late
1940s. He found that infected oysters were

usually not harmed by most infestations of
Nematopsis but suggested that heavy concentra-
tions of the organism could be debilitating to
their oyster host. Landau and Galtsoff (1951)
indicate no correlation between oyster mortality
and Nematopsis.

OYSTER PRODUCTION CURRENT AND
HISTORICAL
Since 1880, attempts to record commercial
oyster landings have been made by various state
and federal agencies. The National Marine Fisher-
ies Service of the U.S. Department of Commerce
has recorded Louisiana oyster harvests on a
monthly and annual basis since 1945 (Figure 1).
The lowest catch was recorded in 1880 with a
total of 1,189,000 pounds of meat. This figure
is not surprising as the demand for oysters did
not stabilize until the mid-1930s. The highest
annual production was recorded in 1939 at
13,586,000 pounds. Some state fisheries manage-
ment personnel believe that a greater amount of
oysters were marketed in recent years than indi-
cated by these statistics because of changed
landing practices. However, they do believe that
the statistics reflect accurately year to year
trends.
The recorded catch or harvest of oysters
cultured and taken from Louisiana waters includes
only those used in canning operations. Oysters
harvested for sack or counter trade, which may
comprise a very large portion of total landings,
are generally unreported (Lindall et al. 1972).
Oysters suitable for counter stock are of uniform
rounded shape and are high in salt and solid
content (fattened). These oysters are cultivated
most carefully and are usually served raw on the
half-shell at oyster counters in restuarants.
Oysters used in steam canning and packing may
vary from I to 3 inches in size and may not have
the taste or nutritional value of oysters served
in the counter trade. These oysters are usually
not cultured in highly saline waters that produce
the quality preferred in raw, counter stock.
Thus, fluctuations in sack or counter grade
oyster production may never be realized, as this
portion of the landings is seldom reported.
Oyster production is not recorded by specific
area. Reliable production estimates are not
available for Barataria Bay.

During the past 30 years, total reported
oyster production has fluctuated around 9 million
pounds annually. Several investigators have
attempted to relate Louisiana oyster production
to singular parameters such as rainfall and
temperature (Owen 1955), season (Hopkins et al.
1953), salinity (Gunter 1955), and proximity to
oil operations (Mackin and Hopkins 1961). For
details of these studies, one should consult the
individual publications.
Meaningful interpretation of catch data must
consider fishing effort since fishing pressure
and market demand often determine production. In
1913, there were 1,762 oyster fishermen working
state and private reefs along our coast (Hart
1913). Today, oyster fishermen in Louisiana
number 1,062 (Dugas' 1975). These men lease
oyster growing areas from LWFC annually at a
price of one dollar per acre. Leases are surveyed
by LWFC and marked with stakes by the oyster
fishermen indicating private oyster beds.
The state manages several Areas where spat-
fall (settlement of oyster larvae) is induced by
salinities lower than those required for maximum
growth, development, and reproduction in adult
oysters. The more productive of these areas are
located east of the Mississippi River in Plaque-
mines and St. Bernard parishes. These nursery
grounds are opened to the public except during
summer (April or May to September) when seed
oysters are taken. The young oysters are trans-
planted to private leases, usually in areas of
higher salinity. Some oyster fishermen maintain
private leases in upper bay areas as an addition-
al source of seed.
.During the early days of the Louisiana
oyster industry, around the time of the Civil
War, seed oysters were gathered, transplanted,
and harvested by the bare hands of fishermen
wading in waist-deep water. During the late
1800s tongs appeared as the first tools used in
oyster culture. oyster tongs were constructed by
blacksmiths and professional tong makers by
hinging two rake"like tools with curved teeth
that formed a basket. This enabled the fishermen
to remove oysters from deeper waters. They were
no longer limited to the shallows or restrained
by intolerable temperatures (Vujnovich 1974).
Oyster to'ngs are still used today but to a much
less extent.
In 1905 the first pair of oyster dredges was
installed on an oyster boat by Leopold Tali-
ancich, a Yugoslavian immigrant. This method of
fishing oysters is still being used today with a

few modifications. Oyster dredges consist of V-
shaped iron frames with ring-mesh sac-like en-
closures, usually about 3 to 4 feet in length.
The dredge is connected to the oyster boat or
lugger by chains attached at the head of the
frame. The apparatus is then dragged slowly over
the oyster reef by a boat that circles at a
moderate speed. The cumbersome dredges were
hoisted aboard by manual winches until 1913 when
two fishermen, John and Anthony Zegura, installed
the first power-operated dredges. During that
same decade, the oyster industry experienced a
vessel transition. Sailing luggers were grad-
ually replaced by or converted into motorized
boats. By 1920, the entire sailing fleet had
disappeared (Vuj.novich 1974).
Since those early years (1920s) there have
been few notable changes in methods or techniques
for oystet culture. However, improvements in
dredges and refrigeration and faster, larger
boats have allowed the oyster fisherm..,n to expand
his efforts with his efficiency. Today, fisher-
men may travel 200 miles to bed their oysters on
prime reefs.
Recently, some oyster fishermen have report-
ed a marked decrease in yield per.acre. There
has actually been no significant decline or
increase in cannery production. However, the
amount of acreage leased for oyster growing
purposes has increased almost tenfold since 1913.
During that year Hart (1913) reported 17,073
acres leased.to Louisiana oyster fishermen.
Today, more than 140,000 acres are privately
leased (Dugas 1975). Likewise, acreage leased
for oyster culture in Barataria Bay has greatly
increased over the past 35 years. The average
size of.a lease in that area has doubled since
1940 (Table 1).
It has been estimated that less than 30
percent of the acreage leased to oyster fishermen
is actually used each year. This is partly
explained by the fact that many oyster fishermen
use productive leases every other year. They
feel that this allows a planted lease to recover
naturally from dredging operations. In addition,
the fishermen agree that this practice helps
reduce predators, especially the conch. In areas
of lower salinity, where the conch is not a
problem, leases may be used every year.

EFFECTS ON OYSTERS OF ENVIRONMENTAL CHANGES
OCCURRING IN BARATARIA BAY
Environmental processes operating in Bara-
taria Bay are altered continuously as a result of
seasonal trends in factors such as temperaturep
rainfall, and salinity. These primary factors
have pronounced effects upon a variety of bio-
logical processes that correspondingly fluctuate
on a seasonal basis. High temperatures play an
important role in seasonal oyster mortalities.
However, the pattern of temperature change varies
little from year to year. Rainfall, although
somewhat cyclic in nature, does not seem to be
significantly decreasing or increasing in south-
ern Louisiana. The demise of oyster populations
as a result of the diluting action of surplus
precipitations has been observed in several upper
bay areas. Yet, during the year following such
high rainfall, a new growth of oysters may settle
and thrive in the very same areas. Similarly,
predation, competition, disease, and many other
secondary factors also show seasonal trends and
effects but usually show no pattern of change
from one decade to the next.
Salinity is probably the most variable
component of estuarine environments as it is
determined by a combination of factors, primarily
wind, rainfall, and river discharge. Salinity
regimes in Louisiana bays and marshes are partic-
ularly interesting in that they not only seem to
change seasonally but may show trends on a long
term basis as well. Trends appear to be towards
increased levels of salinity in most of Louisiana's
coastal zone (Mackin and Hopkins 1961; Lindall et
al. 1972; Pollard 1973). Symptomatic of the
transition to higher salinities are a loss of
seed oysters to predation associated with high
salinity and an opening up of more inland areas
to*oystering (Lindall et al. 1972). During the
past 75 years, areas formerly considered too
fresh for oyster culture have become some of the
prime oyster growing areas in the state. Low
salinity, which had previously been associated
with a great portion of oyster mortalities in the
early 1900s, ceased to be mentioned and the
association of mortalities with encroachment of
highly saline water became more and more frequent.
Saltwater intrusion seemed a feasible explanation
for these phenomena, yet increasing salinity had
never been demonstrated by the presence of actual
salinity data supporting the thesis (Mackin and
Hopkins 1961).
Barataria Bay, whichis considered a typical
Louisiana bay or marsh in most respects, has been

the subject of much -research activity during the
past 30 years. Physical factors such as tides,
winds, temperature, turbidity, erosion, sedimen-
tation, and salinity have been observed during
the course of several research projects conducted
in this area. Concomitant with these investi-
gations have been various biological studies of
marshland or estuarine ecology. Many of these
studies have been specifically concerned with
oysters, shrimp, crabs, and the various species
of the sport fishery. .
The advantage of these interests was real-
ized by LWFC, prompting the establishment of
sampling schedules for parameters such as temp-
erature, tide, rainfall, and salinity not only in
Barataria Bay, but across the Louisiana coast.
The value of this data has been realized during
the last ten years as various agencies have
attempted to monitor changes occurring in the
endangered Louisiana marshlands. Our interest in
salinity as it relates to the oyster resource has
revealed several interesting possibilities.
The available salinity, Mississippi River
discharge, and rainfall data have afforded us the
opportunity to investigate trends in salinity
regimes of Barataria Bay. A number of sampling
stations are located in the Barataria Bay area,
but the amount and consistency of salinity data
are best at two sites: St. Mary's Point and
Grande Terre (refer to Fig. 2 for locations
discussed in this section). The latter is one of
the barrier islands fringing Barataria Bay.
Salinity at Grande Terre usually lies within the
polyhaline range, 18 to 30 ppt. St. Mary's Point
is one of the innermost sampling stations across
the bay'from Grand Terre. This station is char-
acterized by average salinities which are found
in the lower portion of the mesohaline range, 5
to 18 ppt. Salinity was sampled regularly at St.
Mary's Point during the years 1945-49 and 1956 to
present. Grand Terre salinity has been monitored
continuously on recorders since 1961. Salinity
changes at Grand Terre are highly influenced by
the diluting action of Mississippi River dis-
charge, which seasonally drifts northwestward
into Barataria Bay.
River discharge, rainfall, and salinity data
were subjected to intense mathematical-statis-
tical analysis. A brief summary of the details
of the analysis is given as an appendix at the
end of this report. At this point it will be
sufficient to present the findings of the anal-
ysis as they relate to this study:

1) Preliminary studies indicate that salinity at St
Mary's Point has increased since 1961 at a rate of
0.009 ppt per month, with little correspondence to
river discharge.
2) Salinity at Grand Terre did not uniformly increase or
decrease over the period 1961 to 1974. A recent drop
of 0.007 ppt per month was noted to correspond with
an abnormal period of rising Mississippi River dis-
charge during the past few years. Before this
period, the river showed a slight falling rate of
discharge.
3) The data indicate that mean salinity at St.
Mary's Point was probably about 6 ppt at the
turn of the century.
4) If changes continue at the present rate,'
salinity at St. Mary's Point will be approxi-
mately the same as that at Grand Terre in 100
years.

The measurement of salt water intrusion gives
some quantitative evidence of the rapid deterior-
ation of our estuaries. To more fully understand
the increasing salinities and rate of change we
must relate the encroachment of salt water and
direct physical loss of wetland habitat in coastal
Louisiana to specific natural and artificial
processes. The rate and quality of change may
vary significantly from one part of the coastal
zone to another. Changes in salinity regime of
Barataria Bay are largely the result of two basic
factors: land loss and changes in the flow of
the Mississippi River.

Land Loss
Coastal Louisiana is rapidly losing' land area
to the sea. Between 1932 and 1969 the average
rate of coastal erosion within the Barataria
basin was 119 acres per year (B. W. Gane, personal
communication, Center for Wetland Resources,
Louisiana State University, Baton Rouge). During
the last 600 years, the erosional forces of the
sea were, to some extent, counteracted by natural
land 'building processes in this area--specifi-
cally Mississippi River delta formation. The
land building processes have been greatly reduced
while the erosion rate continues and has probably
accelerated in recent times due to the activities
of man.
In.1971 the barrier islands Grand Terre and
Grand Isle were categorized as areas of "critical
erosion" by the U.S. Army Corps of Engineers,
National Shoreline Study. Between 1960 and 1972,
18 percent (172 acres) of the principle Grand
Terre island was lost to the sea. From 1893 to

1960, Barataria Pass, the inlet separating Grand
Terre and Grand Isle, doubled in width from 1,600
to 3,500 ft. Since 1960, this pass has not
changed appreciably, primarily because of the
stabilizing effects of Fort Livingston, located
on the western end of Grand Terre, and a stone
jetty that is maintained at the eastern tip of
Grand Isle.
Major erosion has occurred in Pass Abel,
which was 1,200 ft in width in 1960 and 3,417 ft
in 1972. Most of the erosion of this pass has
occurred on its eastern side. Of the increase in
width of Pass Abel of 2,217 ft between 1960 and
1972, only 758 ft were eroded from the eastern
end of Grand Terre. In 1960, the eastern Grand
Terre island was continuous from Pass Abel to Bay
Dispute. By October of 1969, this island had
been severely eroded and was reduced to only 51.7
acres; by 1972, only 30.1 acres remained. The
accelerated eros16n rate of this island east of
Pass Abel was principally because of pipeline
canals that were dredged parallel to the beach
near the high tide level. The banks of these
canals were rapidly eroded by waves and currents.
Quatre Bayou Pass increased from a width of
3,000 ft in 1960 to 3,542 ft in 1972. Additional
measurements for the major passes connecting the
Barataria Bay area with the Gulf of Mexico are
shown in Table 2.
Inland land loss has also occurred at a high
rate. In 1965, Hurricane Betsy, which came
inland in the Barataria Bay area, totally des-
troyed the emerged portion of Independence Island
and reduced Saturday Island to less than one 1
acre.
Land loss in the Barataria Bay area has been
attributed to the following factors:
Hurricanes--Since 1831, some 23 hurricanes
have struck the Barataria Bay area (U.S. Army
Corps of Engineers 1972). Severe storms such as
hurricanes can have immediate and drastic effects
on coastal land area. Wave action and winds
along with the storm surge of a hurricane erode
within a few hours what may have taken hundreds
of years to build up. Entire islands and sand
beaches are occasionally washed away by these
storms; large expanses of marsh vegetation may be
uprooted and deposited on the water bottom.
Hurricanes sometimes create new passes and there-
fore alter the hydrology of an area.
Waves--Hurricanes and lesser winds generate
wave action, the most,constant erosional agent in
the coastal zone. In addition to beach erosion,

small coastal lakes are enlarged by waves; the
larger the lake becomes, the more effect waves
have on its shoreline. Intense wave action tends
to create circular lakes commonly found in coastal
Louisiana. In the shallow Barataria Bay area,
with depths averaging less than 5 ft, wave forces
affect the bottom, redistributing sediments and
other bottom materials.
Longshore currents--These currents are gener-
ally cyclic, building beaches during one season
and eroding during another. The shoreline
retreat along the Barataria coastline is approxi-
mately 16 ft/yr (Morgan and Larimore 1957). Part
of the shoreline retreat can be attributed to the
dislodging of beach material and transporting it
away from the area by longshore currents.
Sea level rise and subsidence--The gradual
rise in mean sea level during the present century
(Marmer 1954), coupled with normal deltaic subsi-
dence, has accelerated rates of marshland deter-
ioration and bay enlargement.
Subsidence, the gradual lowering of the land
with respect to sea level, is a dominant and
highly significant coastal priocess. The rate of
subsidence is determined by several interrelated
processes: regional geosynclinal downwarping of
the coastal zone, compaction of unconsolidated
sediment, and variations (mainly rise) in sea
level. Although geosynclinal downwarping is an
important process when considered in terms of
geological time, it is too gradual a process to
be considered significant in terms of historical
time spans. Sediment compaction, however, occurs
contemporaneously with deposition. Therefore,
the effects of subsidence due to compaction are
much more apparent in the modern delta (Morgan
1972).
Loss of mangroves--One of the principal
vegetation types in the Barataria area prior to
1962 was the black mangrove, Avincennia nitida.
This tropical and subtropical species functions
as a landbuilder and impedes erosion (Odum 1971).
Mangroves are among the few emergent plants that
can tolerate salinities of the open sea. They
are, however, easily damaged by low temperatures.
Freezing temperatures during the winters of the
early 1960s killed these plants. Latest reports
indicate that young mangroves are once again
appearing in the Barataria Bay area.
Dredging--Before 1930 there were only a few
large canals in Barataria Bay, most constructed
by trappers and loggers limited to small areas.
Since the 1930s the demands of the oil industry

changed the system as larger channels were re-
quired to reach well sites and to transport oil
and gas out of the area (Davis 1973). Today
there are over 9,000 acres of marshland that have
been dredged in the Barataria basin (Barrett
1970).
Channels are constructed for many purposes
other than those relating to the petroleum in-
dustry. Frequently channels are created inci-
dentally to obtain fill material to form new land
in a bay or to raise the level of adjacent marshes.
Channels are also dredged to drain wetlands,
provide for waste disposal, transport water,
obtain minerals or buried shell, and for many
other reasons (Chapman 1968).
The effects of channel construction and
deposition of spoil have been directly correlated
with saltwater intrusion and subsequent physical
loss of habitat. Chapman (1968) noted that "deep
channels permit high-salinity waters from the sea
to penetrate the upper reaches of an estuary and
disperse throughout its area." Effects of chan-
nelization were discussed in the LWFC Biennial
Report 1956-1957 as follows: "In recent times an
increasing number of canals and deep water
channels with their spoil levees have been cut
across the marsh both laterally and vertically.
This has resulted in changed direction of water
flow, [and) the damming of flow by levees, and
has greatly increased the velocity of salt water
flow into the marsh and fresh water flow through
the marshes to the sea. The net result has been
drastic increases in salinity in some areas and
a rapid deterioration of productive marsh and bay
conditions" (St. Amant et al. 1958).

CHANGES IN MISSISSIPPI RIVER FLOW
At one time the Mississippi River occupied a
course down what is now Bayou Lafourche, which
borders the Barataria basin on the west. Approxi-
mately 600 years ago, the river abandoned the
Lafourche course in favor of its present route to
the Gulf of Mexico (U.S. Army Corps of Engineers
1971). Presently, Bayou Lafourche discharge has
little or no effect upon Barataria Bay salinity.
Upon reaching the Gulf, the fresh water and
sediments transported in this bayou are most
often carried westward by littoral currents, away
from the mouth of the Barataria Basin.
Historically, the erosional forces of the sea
have been checked by the land building processes--

particularly Mississippi River delta formation.
Land is formed from river transported sediments
that precipitate as the velocity of the river
decreases upon nearing the Gulf of Mexico. A
portion of the sediments are carried northwest-
ward by offshore currents and deposited in areas
such as Barataria Bay.
The river appears to be shifting its course
to the Gulf once more. Within the last 50 years,
the Atchafalaya,River, main distributary of the
Mississippi River, has increased in size, and the
portion of Mississippi River discharge carried by
it has increased from 10 percent to 30 percent
(U.S. Army Corps of Engineers 1971). Atchafalaya
Bay is the only place along the coast where major
land building is taking place today. It is
expected that a major delta will be formed in
this area by the year 2000. Land has already
appeared above the water surface in Atchafalaya
Bay (Day 1975).
Changes other than natural are occurring
along the Mississippi. The river has been leveed
by state, federal, and private concerns down the
west bank from the Arkansas River to Venice, La.,
about 50 miles below New Orleans. Continuous
levees have been constructed on the east bank
from Baton Rouge to below Pointe a la Hache,
which lies about 30 miles below New Orleans.
Extensive leveeing of the river hAs.prevented
natural overbank flooding, a major source of
sediment input in the coastal zone.
"The construction of the Mississippi levees
below New Orleans has reduced the amount of fresh
water entering Breton Sound and Barataria Bay
areas".(U.S. Army Corps of Engineers 1971).
Leveeing not only eliminates the introduction of
fresh water but also restricts subsequent nut-
rient and organic matter deposition.
Land loss and changes in natural river flow
are directly related to the destruction of our
existing wetland habitats. These are the causes
of significant environmental changes occurring in
Barataria Basin--specifically changes in salinity.

CHANGES IN OYSTER PRODUCTION AREAS
IN BARATARIA BASIN IN PAST YEARS
The effects onoysters of increases in
salinity over short-term periods have been dis-
cussed in the first portion of this paper.. Gill
-ciliary activity, spawning, growth, and fattening
..of oysters are directly and immediately affected

by salinity. Seasonal changes in salinity
indirectly affect-oyster populations by con-
trolling predation, disease, and food supply.
Saltwater intrusion does not constitute the
magnitude of change in salinity required to
affect seasonal factors. At the computed rate of
change, salinity.in north Barataria Bay is only
increasing at a rate of 0.009 ppt per month.
These changes are too subtle to affect oyster
populations found in this area during any given
year.
Twenty years or more of gradual increase in
salinity is expected to have major effects on
marshland inhabitants. Vegetation types have
been observed to change; that is, plants less
tolerant to highly saline water are redistributed
to areas of lower salinity, altering processes of
natural succession. The distributions of other
forms of estuarine life are changed gradually as
these organisms seek waters with optimum mixtures
of fresh and saline components. For example, a
creature that cannot survive salinities below 10
to 15 ppt is able to-move into bays, marshes, and
lakes that previously had salinities less than 10
ppt. Such is the case with the conch, Thais, in
Barataria Bay. At one time conchs were only a
problem to fishermen who transplanted oysters
into the southernmost portion, of the bay. In
recent years of low rainfall, the effects of this
predator are seen more and more frequently in
middle or upper bay areas.
In attempts to.trace historical oyster popu-
lations in Barataria Bay professional oyster
fishermen and LWFC personnel were consulted.
Historical publications concerning Louisiana
oysters were also utilized, when available.
Current lease charts and records were obtained
from LWFC, Division of Oysters, Water Bottoms,
and Seafoods. The Division does not keep lease
charts on an annual basis; as individual leases
are surveyed, they are plotted on a base map that
is used from year to year. One old map wa's found
showing leases of Barataria Bay in 1959. This
map was compiled by the Division during the
planning of the Barataria Waterway that was
completed in 1963. This map is Ikept at the
Oyster Leasing and Survey Section of the LWFC
district office in New Orleans. Another lease
chart was obtained from Dr. Harry Bennett (De-
partment of Z6ology, Louisiana State University,
Baton Rouge), who directed a study on oyster
mortalities in Barataria Bay in the mid-1940s.
Dr. Bennett visited the New Orleans office of the

LWFC and obtained an oyster lease chart of the
Barataria Bay area during the summer of 1947.
Copies of this map are on file at the Center for
Wetland Resources, Louisiana State University,
Baton Rouge.
The lease information obtained for 1947,
1959, and 1975 is given in Figs. 3, 4, and 5.
Ten oyster fishermen who held extensive leases in
Barataria Bay during the last 30 years were
questioned to determine which leases on the old
charts were used for seed or transplanting.
Oysters have been cultured in Barataria Bay
for more than a century. During the late 1800s,
the Barataria Bay oyster fishery suffered tre-
mendously from what appeared to be a combination
of factors. Moore and Pope (1910) reported that
Barataria Bay oyster beds had been "exterminated
by overfishing coupled with natural causes." By
1910 the fishery had recovered somewhat with
oyster reefs locatedlin the southern half of the
bay, the northern half having never produced
oysters within the recollection of the inhabi-
tants, probably owing to its low salinity" (Moore
and Pope 1910). Barataria Bay is connected to
Little Lake (Fig. 2) by Bayou St. Denis and Grand
Bayou. In 1898 these bayous were reported as
being almost constantly fresh. At that time,
Little Lake was fresh enough to harbor a continu-
ous population of largemouth bass (Moore and Pope
1910).
The lower half of Barataria Bay remained the
primary region of oyster culture in Lafourche and
Jefferson parishes through the 1930s and early
1940s. By 1947, the northern half of the bay had
become a reliable area for natural spatfall. The
holders of the leases around St. Mary's Point
(Fig. 3) stated that upper bay leases had become
their most valuable private source of seed by the
1950s.
In 1959, numerous leases were charted in both
upper and lower bay areas, with the most extensive
oyster.culture practiced around the periphery of
the bay, where the bottom is firm enough to
support the weight of dense oyster growth. Water
bottoms were also leased in Grand Bayou and Bayou
St. Denis. Lower Little Lake had begun to pro-
duce some seed oysters during years of low rain-
fall. A history of acreage leased for oyster
culture in Little Lake is given in Table 3. This
table should be used with Fig. 4 for an adequate
representation of changes in oyster culture in
the Little Lake-Barataria Bay complex during the
1950s and 1960s. Members of the Barataria oyster

industry attribute a portion of increased leasing
activity in upper bay areas to the expanding
nature of the fishery, as well as changes in
salinity.
During the relatively low rainfall years of
the late 1960 s, natural oyster growth was ob-
served in upper Little Lake. By 1975.(Table 3),
almost 4,000 acres ofwater bottoms had been
leased in Little Lake. During years of heavy
rainfall, oysters grown in Little Lake may be
killed by prolonged exposure to low salinity.
Such was the case in 1973 and 1975, years of
unusually heavy spring rains.
Northern Barataria Bay, Grand Bayou, Bayou
St. Denis, and Little Lake have become increasing-
ly dependable areas of natural spatfall during
the past 30 years. This is probably directly
related to the encroachment of saline waters into
the upper end of the Barataria Basin. In this
respect, saltwater intrusion has been beneficial
to the Barataria Bay oyster fishery, affording
the fishermen much needed sources of seed.
However, most effects of the gradual but steady
increase in salinity are not quite so advantageous.
Increased predation and disease accompany the
intruding Gulf waters into prime areas of oyster
culture, where reefs have been laboriously estab-
lished through several years of planting seed
oysters and.cultch.
Furthermore, as oysters are redistributed to
more inland waters, they may be found more and
more frequently in areas presently polluted by
domestic and industrial wastes. This problem is
amplified by increased population and industrial-
ization in the coastal zone, which serve to
continually extend the zone of pollution Gulfward
into the estuaries.
In essence, the oyster industry in Barataria
Basin is steadily being squeezed between encroach-
ing salinity (and the accompanying predation and
disease problems) from the south and encroaching
pollution from the north. Oyster production
areas are being forced further inland where
existence of high coliform (domestic sewage)
levels may force closure of oyster harvesting.
As these two forces continue, availability of
areas suitable for oyster production will de-
cline. These problems and management altern"
atives to help alleviate them will be discussed
in a subsequent report in this series.

APPENDIX
Preliminary studies indicate that salinity at
St. Mary's Point is increasing. We must put many
qualifications on these findings, but the bulk of.
our reservations concern the extent of such a
rise rather than its existence. In the following
paragraphs we present some specific analyses
showing this trend as well as other points of
possible interest. All of the data used was
supplied by LWFC.
For the purposes of our initial study we used
only salinity data at St. Mary's Point and Grand
Terre. The earliest available data are at St.
Mary's Point and cover the years 1945-1949, with
some gaps. These data were contributed to LWFC
by Dr. Willis G. Hewatt. A second set of data at
St. Mary's Point covers the years 1956 to the
present. In both the above sets the data consist
of regular sampling, with samples taken in most
cases once each week. The data at Grand Terre
extend from 1961 to the present and were gathered
on continuous recorders. We cannot, of course,
reconcile this difference in the methods of data
gathering at the two sites, and the sporadic
nature of the data at St. Mary's Point must place
some reservations on our findings. We can,
however, make two notes in this regard. First,
as we will cover specifically in following
paragraphs, some measure of internal consistency
was apparent in the St. Mary's Point data,
especially regarding long-term trends. Second,
during the current year LWFC began to record
salinity at both St. Mary's Point and Grand Terre
with punched tape recorders taking readings every
hour. Therefore, our findings here will be
subject to welcomed testing and updating. We are
continuing in-depth study of salinity data, and
increasingly it becomes clear that these two
locations offer a valuable contrast in such a
study.
For the purposes of investigating the long-
term trends, monthly averages were used. This
was necessary for the St. Mary's Point data to
have some measure of coherency. Even at this
level some points are averages of only two or
three samples. Furthermore, it appears that
monthly means may be desirable in any case to
gain comparability between different years. The
processes affecting salinity are to a large
extent seasonal and to a reasonable extent
monthly. For instance, we can certainly say with
a high degree of accuracy that we expect, in any
year, to obtain significantly different readings

in May and October with the extreme likelihood
that the October readings will be higher. Suffic-
ient comparability of a given month from year to
year allows us to normalize the data so that all
readings are comparable. We have not had time or
data to vigorously demonstrate such sufficiency
in this case, although we used such a normal-
ization, and therefore attempted, whenever possible,
to also apply our analysis to a "control" set of
data for comparison.
The most direct method of investigating long-
term trends is to simply fit a straight line
varying over time to the salinity data. This
technique is quite valid for the purpose of
detecting either a rise or fall under certain
conditions. We must first have enough data so
that our line conforms to the long-term variances.
We do not have these conditions in this case; we
would, perhaps, if our St. Mary's Point data were
complete from 1945-1974. However, the fit to the
available data set is significantly influenced by
the inclusion or exclusion of certain portions.
Therefore, we have chosen to look at the period
1961-1974 so that similar analysis can be per-
formed on the Grand Terre salinity data as a
control. Figure 6 shows the result of such
Analysis. The St. Mary's Point data shows a rise
of 0.009 ppt per month whereas Grand Terre exhibits
a falling of 0.007 ppt per month over the same
period. Due to other analysis, we do not propose
that Grand Terre salinity is appreciably falling,
but the above fact is at least some indication
that we have not simply chosen a time period of
general rise in salinity. The line depicted in
Figure 5 is actually only a mean or average over
time and is quite appropriate for this analysis
since it can only represent a simple directed
trend. We can note, as a point of interest only,
that if this trend could be accepted as accurately
describing the trend over a longer period, it
would indicate that mean salinity at St. Mary's
Point stood at approximately 6 ppt at the turn of
the century.
In seeking to substantiate the existence of
such trends we examined various possibilities.
In either case a year or two of salinities that
deviate significantly from the norm would account
for these results by chance, assuming such devia-
tion was in the right direction and in the
proper half of our data set. Furthermore, the
processes that affect the two locations are to
some extent dissimilar, and it is possible that
one of these accounts for our result. Finally,

there is the possibility that the results are so
small as to occur by chance in any case, or as a
normal long period fluctuation.
In order to examine the possibility of unusual
occurrences in the data, we computed, for each
month, a mean and standard deviation over the
period of years studied. We then expre6sed each
salinity reading as a function of its deviation
from the mean. This procedure reduced our data
to a uniform, comparable set and singled out any
unusual readings. For each month we then had a
data set with a mean of zero and a standard
deviation of one, and similar statements will be
true for the entire set. An interesting result
was thus obtained. At St. Mary's Point the
largest negative fluctuation (relatively low
reading) occurred in the eleventh month of the
tenth year (1970) and the largest positive fluct-
uation (relatively high reading) occurred in the
third month of the third year (1963). These
values are -2.414 and 1.941, respectively, and it
can be seen that not only are these values (and
thus the entire range) reasonable, but the lower
extreme is actually significantly greater than
the upper. In fact, we may go further and examine
a histogram of the values as opposed to a normal
curve. In this case (Fig.,7) the largest number
of readings occur in the range 0 to +0.2 with 22
readings. The next largest interval is -0.2 to
-0.4 with 14 readings, followed by the interval
0.2 to 0.4 with 13 readings. These figures give
considerable support to the validity of the
apparent rise in salinity over the period.
The largest deviations at Grand Terre are
.-2.415 in the eleventh year and +2.091 in the
third year. The histogram reveals a more spread
pattern having 16 values in both the ranges -0.2
to *0.4-and 0.4 to 0.6 with 15 values in the
range 0 to -0.2. Again, in this case, the
apparent fall is not caused by the extremes but
rather by the bulk of data occurring at values
only slightly different from the means. In both
cases, the lack of conformity to the "bell curve"
illustrates, our deficiency of data.
We also performed@a linear fit to this ad-
justed data with expected results. The St.
Mary's Point data showed a rise of 0.0014 units
per month, while Grand Terre showed a fall of
0.0025 units per month. The units. here are in
terms of standard deviation of the month in which
the data falls. The agreement between those and
earlier figures is significant, because it is
independent of the actual level of salinity.

Using the actual salinity data, the fit (or mean)
can be weighed in favor of differences in the
higher salinities. Therefore, we stress that the
agreement rather than certain values are of
importance here.
To further test the meaning of these results,
we also analyzed rainfall and river discharge for
the same period. Rainfall showed a rise of
0.0002 units per month, only 10 percent of the
magnitude of either of the above salinity changes
and illustrative of the small size of our data
set, as most readings were below average while
one was +3.15. This data conforms least to the
bell shape as illustrated in Figure 7. River
discharge showed a rise of 0.007 units per month,
the largest figure of all, and somewhat skewed
from the bell curve. It is quite conceivable
that either the increasing river discharge or its
causative forces are responsible for the fall in
salinity at Grand Terre. Further efforts are
being made to study the possible relationship in
some detail.
Finally, when the entire set of St. Mary's
Point salinity data was processed in this manner,
the result was a rise rate of 0.003 units per
month (a higher rate than the reduced set) with
normal hi stogram values. The river from 1945
through 1974 showed a fall rate of 0.0005 units
per month; the discrepancy between this and the
earlier figures again illustrates the deficiency
of data.
We wish to address a final point indicated by
the above and possibly more revealing in a quanti-
tative manner. We cannot, at this time identify
and remove all of..the processes other tLn intru-
sion affecting salinity at St. Mary's Point and
Grand Terre and cannot, therefore, directly
measure the intrusion. However, whatever these
processes are, and whatever the actual effect of
intrusion, we can note that Grand Terre is
essentially a coastal point whereas St. Mary's
Point is across a bay from Grand Terre. We can
then ask to what extent St. Mary's Point salinity
is similar to that at the coastal point and what
trends, if any, exist. By asking to what extent
they are subject to identical influences, we can
then disregard, to a certain extent, the exact
nature of these influences.
To this end we formed a data set whose ele-
ments were the ratio of St. Mary's Point salinity
to Grand Terre salinity. Since our earlier
discerned trends were falling salinity at Grand
Terre and rising salinity at St. Mary's Point, we

could certainly expect the ratio to rise over the
time period, as it does (0.036 percent per month).
However, in automatically compiling plots of our
various parameters under study we were struck by
a comparison of the ratio vs. St. Mary's Point
salinity and the ratio vs. Grand Terre salinity.
These plots are shown in Figure 8. A distinct
pattern exists,in the former plot, showing that
the ratio is relatively high only when salinity
at St. Mary's Point is also relatively high and
correspondingly low only when St. Mary's Point
salinity is also low. There are no significant
deviations to this relationship. However, a
glance at Figure 8 reveals that low salinity at
Grand Terre is not a contributor to a high ratio.
The comparison is striking, as is the former
figure itself. In fact, we also found a linear
fit of the ratio to a combination of time and St.
Mary's Point salinity. Such a doubling of
independent variables would normally produce a
significantly better fit in any case since it can
only improve, the fitting mechanism having the
ability to simply reject the new.variable. The
results were interesting in every respect. We
found a ratio of change due to time alone of
0.049 percent per month, and to salinity alone of
0.337 percent per month, but with the dependency
on salinity level decreasing by 0.0002 percent
per month. The latter is a significant figure
since it indicates a lessening dependency.as St.
Mary's Point salinity approaches that of Grand
Terre. Originally the linear fit of time to
ratio values had produced a starting mean of 62.1
percent and, as noted, a rate of change of 0.036
percent per month. Fitting time to ratio values
computed using the above model, the comparable
values were a starting mean of 62.6 percent and
an identical rate of change of 0.036 percent per
month. The closeness of these figures was not
expected. In either case they suggest that
salinity at St. Mary's Point will be approxi-
mately the same as that at Grand Terre in 100
years if the trend given by the data continues.
The above trends indicate that the rise in
salinity at St. Mary's Point and the rise in the
ratio of St. Mary's Point salinity to Grand Terre
salinity are uniform over the period whereas the
fall of salinity at Grand Terre is not. The fall
in Grand Terre salinity also corresponds to a'
rising period of river discharge while no such
correspondence was found at St. Mary's Point.
Furthermore,.it should be remembered that the
rise at St. Maryls Point consisted largely, if

not entirely, of a large number of points slightly
exceeding the mean, rather than a few points
glaringly exceeding mean values for the period.
Returning to Figure 6, the accumulation of
results of our analyses rather than any one set
of figures causes us to suggest that, while the
apparent drop of salinity at Grand Terre is
probably due to normal fluctuations, the upward
slope of the line depicting the mean over time of
St. Mary's Point salinity is very likely due to a
small but persistent rise in salinity at the
station. The actual amount of the rise is probably
not sufficiently accurately determined by such a
relatively small data set, but the data are
surprisingly consistent in this one respect.

LITERATURE CITED

Barrett, B. B. 1970. Water measurements
of coastal Louisiana. Louisiana Wildlife and
Fisheries Commission (LWFC), New Orleans.
1971. Cooperative Gulf of Mexico
estuarine inventory and study, Louisiana.
Phase II, Hydrology; Phase III, Sedimentology.
LWFC, New Orleans. 191 pp.
Blumer, M., G. Souza, and J. Sass. 1970. Hydro-
carbon pollution of edible shell-fish by an
.oil spill. Mar. Biol. 5(8):195-202.
Brehmer, M. L. 1965. Turbidity and siltation as
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Burkenroad, M. D. 1931. Notes on the Louisiana
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to the-oyster Ostrea virginica. Ecol. 12(4):
656-664.'
Butler, P. A. 1949. Gametogenesis in the
oyster under' conditions of depressed salinity.
Biol. Bull. 96(3):263-269.
Chanley, P. E. 1957. Survival of some juvenile
bivalves in water of low salinity. Proc.
Nat'l. Shellfish Assoc. 48:52-65.
Chapman, C. 1968. Channelization and spoiling
in Gulf coast and south Atlantic estuaries,.
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the Marsh and Estuary Mgt. Symp., 1968. T.
J. Moran's Sons, Inc., Baton Rouge, La.
Davis, H. C. and A. Calabrese. 1964. Combined
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Davis, W. D. 1973. Louisiana canals and their
influence on wetland development. Ph.D.
diss., Louisiana State University, Baton
Rouge, La.
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at Amer. Inst. of Biol. Sci., Corvalis, Ore.
Dugas, R. 1975. Operation: Oyster! La. Conser-
vationist 27:18-31.
Etzold, D. J. 1974. Data relative to the intro-
duction of supplemental fresh water under
periodic controlled condition for the purpose
of enhancing seafood productivity in Missis-
sippi and Louisiana. Univ. S. Miss., Hatties-
burg.

4.I

Galtsoff, P. S. 1964. The American oyster,
Crassostrea virginica (Gmelin). U.S. Dep. of
the Interior, Fish and Wildl. Serv., Fish.
Bull. Vol. 64.
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Gulf Biol. Sta., Cameron, La., Bull. No. 15.
Gunter, G. 1955. Mortality of oysters and abundance
of certain associates as related to salinity.
Ecol. 36(4):601-619.
Hart, W. 0. 1913. The oyster and fish industry
of Louisiana. Trans. Amer. Fish. Soc. 42:151-156.
Hopkins, S. H. 1958. The planktonic larvae of
Polydora websteri Hartman (Annelida, Polychaeta@
and their settling on oysters. Bull. Mar.
Sci. Gulf Carib. 8(3):268-277.
J. G. Mackin, and R. W. Menzel. 1953.
The annual cycle of reproduction, growth, and
fattening in Louisiana oysters. Paper read
at Nat'l. Shellfisheries Assoc. Conv. 1953.
Ingle, R. M. 1952. Studies on the effects of
dredging operations upon fish and shellfish.
Florida State Board of Conservation, Tech.
Ser, No. 5, Tallahassee, Fla.
J@rgensen, C. B. 1952. On the relation between
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and E. D. Goldberg. 1953. Particle
filtration in some ascidians and lamellibranchs.
Biol. Bull. 105(3):477-489.
Keck, R., D.,Maurer, and L. Watling. 1973. Tidal
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distribution of the American oyster. Hydro-
biologia distribution of the American oyster.
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Ketchum, B. H. 1951. The exchanges of fresh and
salt waters in tidal estuaries. J. of Mar.
Res. 10(l):18-38.
Landau, H. and P. S. Galtsoff. 1951. Distribution
of Nemetopsis infection in the oyster grounds
of the Chesapeake Bay and in other waters of
the Atlantic and Gulf states. Tex. J. of
Sci. 3(l):115-130.
Lindall, W. N.11 J. R. Hall, J. E. Sykes, and E.
L. Arnold, Jr. 1972. Louisiana coastal
zone: Analysis of resources and resource
development needs in connection with estuarine
ecology. Sections 10 and 13, fishery resources
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water of low salinities. Nat'l. Shellfisheries
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Loosanoff, V. L. and H. C. Davis.' 1963. Rearing
of bivalve molluscs. Pages 1-136 in Advances
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Table 1. Acreage of Oyster Leases in Barataria Bay (by
parish)

Average no.
Year Parish Acres ocresIleose

1975 Plaquernines 3607
Jefferson 4616
8223 Total 33.56

1968-70 Ploquemines 4839
Jefferson 4677
9516 Total 33.39

1959-60 Ploquernines 2456
Jefferson 3883
6339 Total 25.56

1948-51 Ploquemines 99
Jeff erson 2651
2750 Total 21.83,

1940-41 Ploquemines 011.
Jefferson 929
929 Total 15.48

*Probably classified under"Jefferson Parish

Table 2. Changes in width of major posses in the
Barataria Bay area (in ft)

Pass 1932 1954 1969

Barataria 2,149 2,373 3,500
Abel 212 499 1,233
Quatre Bayou 2,181 2,921 3,700

Table 3. Acreage of Oyster Leases in
.-.-Little Lake (by @ parish)

Jefferson Lafourche
Year Parish Parish Total
1975 1,445 23437 3,882
1968-70 902 942 1,844
1963 143 428 571
1961-63 301 238 539
1959-60 449 379 828
1958 378 217 595
1957 173 204 377
1955 43 0 43
1953-54 22 0 22
1951-53 2 0 2
1950 0 0 0

14-

10-

C: A,
co 6-
-j
101
4-

0
.1880 90 1900 10 20 30 40 50 60 70 80

Fig. 1. Louisiana Oyster Landings (Reported), 1880-1974. 46

-P

Area Mapp.@
Little\Lake

Denis

12)
IN Ts' mitry's Pt.
0" &Saturday
1z 4:@Fpl Island
x Barataria Bay c@- -
-N-

0*0@

Independent-
'Island
-P
........ Boundary in Dispute "'rc

0 1 2 3 4 5 6 7 a M'.
0@
0 5 10 15 1 20 25 30 K..

Fig. 2. Southern, gulfward portion of the Barataria Basin. 47

f
f

1 2 3 4 5 6 7 8 Mi.

0 1 2 3 4 5 6 7 8 9 10 11 12 Km.
AT;

Fig. 3. Area leased for oyster culture in the Barataria Bay area in 1947. 48
(Oyster leases shown in black.)

-N-

0 1 2 3 4 5 6 7 8 mi.

0 2 3 4 6 6 7 8 9 10- 1-1 12 Km.

Fig. 4. Area leased for oyster i--ulture in the Barataria Bay area irt 1959. 49

VIQA
'Sol-

dp,
Iv

04
4,

Ap
YT@ A,
-N-

t@@ 6 #1 1 V

t-x@ 4. VI
Oiii@ J@

0 1 2 3 4 5 6 7 a mi.

0 j 2 3 4 5 C, 7 8 9 10 11 12 Km

Fig. 5. Area leased for oyster culture in the Barataria Bay area in 1975.

SALINITY (PPTj 25-

20- River

15-

10-

:j:j:j:j:
.............. ......
. . .........
5-
. .......

.... ......
.................... ........
...............
X...............
. ... ..... ........ ......
.......... .
X. ..........
..X.X
0

0
Rainfall
0. '20 -
io

141
15

Fig. 6. Linear salinity trends 1961-1974.
10-

. ...........

. ........
5 - .... ..........
............. ........ 7-

20- Grand Terre

15- .... ..

10 -
.... .... ...

5
.....................

...........
...................... . . .......
0 . ... .. .... .... .........

20- St. Mary's

15 -

10-

5t- .......

0 . . .....
-2 -1 0 1 2 3

Fig. 7. Histograms of normalized data.

lid
ST. MARY'S PT. S 1-41TY/GRAND TERRE SALINITY
0.0 03 0.6 0.9 1.2 1,5

3:
>
rt

Ef)

L&
0

ST, MARY'S PT. SALINITY/GRAND TERRE SALINITY

0.0 0.3 06 ..09 12 15

-CD

>
z

%-n

I
1 3 6668-14103 2245 - I
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