2010 NORTHEASTERN NATURALIST 17(3):373–386
Aspects of the Wintering Biology of Striped Bass at a
Power Plant Discharge
Kimberly Williams1,2 and John Waldman3,*
Abstract - The warm water outflow at a power station in Northport, NY aggregates
Morone saxatilis (Striped Bass) in winter, which creates unnatural angling
opportunities. Substantially more Striped Bass were available to anglers in the
winter of 1995–1996 than in the winter of 1996–1997. Although Striped Bass
were observed within and around the heated effluent of the plume, tracking using
ultrasonic transmitters indicated they were not “trapped” in the area by the colder
water surrounding the discharge. However, there also was little evidence of a
natural forage base. Tag returns from marked Striped Bass over subsequent years
suggest that they displayed similar movement patterns to Striped Bass found in
Long Island waters during other seasons. Differences in availability of Striped
Bass among years may reflect seasonal changes in temperature, cohort abundance,
and other factors.
Introduction
More than 20 electric generating stations in New England rely upon intake
from nearby coastal waters to reduce heat formed as a byproduct of their
operations. However, there has long been concern about the effects of power
stations on the environment. Issues regarding aquatic life in the vicinity of
power stations include direct physical harm to fishes and other organisms
from entrainment and impingement (Boreman et al. 1981, Kerr 1953, Marcy
1973), alterations to near-field water quality (Kerr 1953), and thermal pollution
from heated discharges (Kerr 1953, Setzler et al. 1980).
During autumn in North Temperate regions, elevated temperatures of
power plant effluents appear to attract some organisms that would normally
migrate south as waters cool. As waters surrounding a power plant plume
continue to cool with the coming of winter, fish and other animals appear to
become “trapped” within the thermal influence of the plume. Organisms that
remain at these sites become subject to starvation or stress during the coldest
months if they deplete their forage base or if water quality deteriorates (Pawson
and Eaton 1999, Wagenheim 1974). Another hazard is the potential for
rapid temperature changes due to plant shutdowns. Disruptions of thermal
discharge have been observed to cause excessive mortality to fish and other
organisms (Englert et al. 1988, Silverman 1971).
1Marine Sciences Research Center, SUNY Stony Brook, Stony Brook, NY 11794.
2Smithtown High School Science Department, 100 Central Road Smithtown, NY
11787. 3Biology Department, Queens College, 65-30 Kissena Boulevard, Flushing,
NY 11367. *Corresponding author - john.waldman@qc.cuny.edu.
374 Northeastern Naturalist Vol. 17, No. 3
In New England and some Mid-Atlantic states, the fish that aggregate
in heated effluents from power plants represent an important winter recreational
angling opportunity (Marcy and Galvin 1973, Moore and Frisbie
1972). Even as far south as Maryland, anglers fish for Striped Bass in
heated effluent (Hart 1997). Moore and Frisbie (1972) found that substantially
more fish were captured in heated power plant waters than were
captured when these waters were not heated. However, most of the recent
information available regarding the attraction of fish to power plants in
New England is anecdotal, existing primarily in the sportfishing media
(e.g., Sampson 1996).
The anadromous Morone saxatilis (Walbaum) (Striped Bass) is one of the
most popular sport fish and economically important commercial fish along
the mid-Atlantic and New England coasts of the US (Richards and Rago
1999). The prey items of these carnivores include a variety of invertebrates
and fishes, depending on age, season, and availability of prey (Dunning et
al. 1997, Manooch 1973).
Major migratory populations of Striped Bass occur in Chesapeake Bay
and the Delaware and Hudson Rivers (Waldman and Fabrizio 1994). Subadult
and adult Striped Bass from these populations occur routinely in Long
Island Sound during spring, summer, and autumn (Hickey 1981, Schaefer
1968). Some enter the Long Island Sound via the East and Harlem Rivers
(Waldman et al. 1990); others enter through the “Race” between Long Island
and Connecticut (Austin and Custer 1977). Most Striped Bass are believed
to exit the Sound by late autumn, to overwinter in their natal estuaries or in
coastal waters between the New York Bight and Cape Hatteras (Waldman et
al. 1990).
Due to their ecological and economic importance, movements of
Striped Bass have been well studied. Tagging studies indicate that many
Striped Bass undergo coastal migrations which are generally northward
in the spring and summer, and southward in the autumn and winter (Merriman
1941, Waldman et al. 1990). Not all, however, undertake “typical”
migration patterns; some have been reported to overwinter in embayments
along the coast rather than following their migrating conspecifics. Striped
Bass have been documented overwintering in northern Atlantic coastal
sites including bays of the Long Island Sound (Neville 1940, Raney 1952),
the Thames River, CT (Sampson 1996), and the upper Bay of Fundy, Canada
(Rulifson and Dadswell 1995).
For almost a half century, the sportfishing media have focused attention
on the fishery associated with a power plant located on the north shore of
Long Island in Northport, NY. The heated effluent from the Long Island
Power Authority (LIPA; formerly known as LILCO) station in Northport
supports the only major recreational Striped Bass fishery of its kind on Long
Island (Fig. 1). However, little research has been performed on the nature of
this fishery or of the biology of the Striped Bass that support it.
2010 K. Williams and J. Waldman 375
In one of the first studies of the Northport power plant fishery, Austin
et al. (1973) described the presence in winter 1971–1972 of Pseudopleuronectes
americanus (Walbaum) (Winter Flounder), Menidia menidia (L.)
(Atlantic Silversides), Morone americana (Gmelin) (White Perch) and two
hakes, Urophycis chuss (Walbaum) (Red Hake) and Merluccius bilinearis
(Mitchill) (Silver Hake). That winter, the recreational fishery was characterized
as small. A creel study conducted at the site showed most anglers
capturing no fish of any species during February, with only one Striped
Bass landed. In another study of the Northport power station, Young (1979)
described the winter fishery as being substantial enough to support both
sport and commercial fisheries, with commercial rod and reel landings of
950 pounds that January. It was unknown how many pounds were taken by
sport anglers.
During winters when Striped Bass are abundant at the Northport plant,
recreational angling is popular. In 1984, harvest of Striped Bass in winter
was prohibited, so the winter Striped Bass fishery at Northport became
strictly catch and release.
This study characterizes the winter Striped Bass fishery associated with
the heated effluent around the power station in Northport. Biological data
regarding length, weight, age, and condition of Striped Bass are presented
and compared with similar data for specimens captured during winter across
Long Island Sound off the coast of Connecticut. Additional information
on the sex, diet, local and long-distance movements, and stock origins of
Striped Bass captured in the study area also is provided.
Figure 1. Map of power plant region and location in Long Island Sound.
376 Northeastern Naturalist Vol. 17, No. 3
Methods
Field-site and sampling season description
Our primary site was the outflow of the power station on the north shore
of Long Island at Northport, NY (Fig. 1, site A). Water from Long Island
Sound is drawn into the station through pumps fed from an intake lagoon.
After being used, the water is released into a cooling lagoon before spilling
as a thermal plume into Long Island Sound at Crab Meadow Beach.
Fish collection was conducted from 14 January 1996 through 6 April
1996 (Field Season I), and from 22 December 1996 through 18 February
1997 (Field Season II). Unless otherwise noted, for the purpose of this study,
“winter” will refer to the months of December through April.
Results from trawl sampling in open waters across Long Island Sound
were also used in the study as a result of notification from the Connecticut
Department of Environmental Protection that Striped Bass were bycaught
in both mobile and fixed fishing gear at substantially higher rates than usual
during the winter of 1995–1996.
Data collection
All fish sampling was conducted during daylight hours. During each sampling
day, salinity, air temperature, and water temperature at 30 cm of depth
were measured at the heated effluent waterfall (Fig. 1, site A) and at the shoreline
approximately 100 m east of the outfall (Fig. 1, site B).
With the assistance of volunteers, Striped Bass were captured at site A
across both field seasons using a variety of gears. During Field Season I, 776
specimens were caught via angling. During Field Season II, all 42 Striped
Bass caught were captured via angling. Fishing was conducted at all tidal
stages. However, most tagging occurred during the first two hours of the
outgoing tide, when captures appeared to be highest.
In Field Season I, three gill nets also were used to capture specimens
from the thermal plume. Each net measured 46 x 3 m, with mesh sizes of
either 10 cm, 18 cm, or a combination of 8 cm and 13 cm. These nets were set
by boat within 15 m of shore in depths from 1 to 9 m and retrieved by hand.
Set times of the gill nets ranged from 15 min to 1 hr. One-hundred-fifty-one
Striped Bass were captured in the 10-cm net, 5 were captured in the 18-cm
net, and 153 were captured in the 8-cm and 13-cm net.
Additionally, 149 Striped Bass were captured with a bottom trawl operated
by the US National Marine Fisheries Service (USNMFS) near Milford,
CT, over several dates during Field Season I. The 27-m mouth-size otter
trawl had 1-m x 1-m doors and was towed at about 3 knots for 30 min at
depths ranging from 9 to 15 m. Data also were obtained from nine Striped
Bass that had been victims of a fish kill and had been found in the impingement
grating of the power plant on 16 January 1996.
Biological data were recorded from 1281 Striped Bass. Total length was
measured to the nearest mm, and weight was measured with a spring scale
2010 K. Williams and J. Waldman 377
to the nearest 45 g. Specimens were examined for external signs of illnesses
such as lymphocystis, with its white to gray tumor-like patches on the body
and fins, and for gross injuries and abnormalities.
All specimens were scanned with a Northwest Technologies handheld
coded-wire-tag detector. The machine detects the presence of a wire
(1.5 mm long x 0.25 mm in diameter) implanted in the cheek prior to their
release from hatcheries. The wire tags are scored with a code for each
specimen and include state, hatchery, and ancillary information. Most
specimens with coded wire tags were sacrificed for later tag recovery. Once
recovered, tags were sent to the United States Fish and Wildlife Service
(USFWS) for code interpretation.
Ten to fifteen scales were removed from below the dorsal fins on the left
side of each individual. Acetate impressions of scales were made to facilitate
reading of the annuli in estimating the age of individuals.
Striped bass diets were characterized by examining stomachs from 80
sacrificed specimens: 32 from the coast of Connecticut and 48 from the
power station. Additionally, 33 live individuals were examined for diet
by the use of gastric lavage (Light et al. 1983): 2 from Connecticut and 31
from the power station. Gonads from 79 Striped Bass were examined for
sex determination.
Prior to releasing them in their area of capture, 1177 Striped Bass were
tagged with externally visible tags. This effort was coordinated with an ongoing
mark-recapture study of Striped Bass along the east coast of the US.
Using a scalpel, a 4-mm long subcutaneous incision was made in an area
posterior and ventral to the pectoral fin on the fish’s left side, into which a
Floy FM-84 tag was inserted. Instructions for anglers who caught tagged
Striped Bass were posted at the sampling site as well as in local tackle shops.
Similar postings appear in tackle shops and fishing media along the Atlantic
coastal range of the Striped Bass.
During Field Season II, Striped Bass distribution and movements around
the thermal plume were studied by tracking the positions of seven specimens
tagged with Sonotronics Sonic Temperature Sensing Tags (Model CTT-83-
2-E), Manual Tracking Receiver (Model USR-5W), and Hydrophone (Model
DH-2) with headphones. Tags were 62 mm by 16 mm, weighed 8 g in water,
and had an expected 14-month battery life. Sonic tags were distinguished
from one another by a unique sequence of “pings” that emitted from each tag
and were audible through the hydrophone.
The seven specimens tagged with temperature tags (9–18 February
1997) ranged in total length from 441 mm to 635 mm. A hollow needle was
used to create two holes in the dorsal musculature of the fish through which
a stainless steel wire was fed to attach the tag. The site was visited 12 times
during different tidal stages between 9 February and 4 April 1997, using the
hydrophone to determine the presence of tagged fish.
378 Northeastern Naturalist Vol. 17, No. 3
Results
Angler use
Observations and questioning of anglers using the site revealed that
the most popular angling times were afternoons, weekends, and holidays.
Although a few anglers indicated that they fished at night, no surveying
was performed from dusk to dawn. Anglers fishing in and around the heated
effluent in boats were less common than anglers fishing from shore. Even
though the average air temperature was colder during the first sampling season,
anglers did not have difficulty capturing Striped Bass, many of which
were made available for use in this study. Angler use of the sampling site was
greatly reduced during Field Season II when anglers reported having to invest
more effort to capture few, if any, Striped Bass. The sampling crew and
the recreational anglers frequently described the fish they captured during
Field Season I as having a relatively “healthy” appearance. This was noted
in sharp contrast to the “sick” or “ragged” appearance of the specimens that
were landed during Field Season II.
Environmental conditions
During Field Season I, salinity at the site ranged from 25 to 32 ppt. Water
temperatures measured ranged from 6 °C to 13 °C inside the plume (Fig. 1,
site A) and -3 °C to 9 °C outside the plume (Fig. 1, site B). During Field Season
II, temperatures ranged from 9 °C to 13 °C inside the plume and 2 °C to
4 °C outside the plume. To gauge differences in regional seasonal temperatures,
monthly mean air temperatures during the two autumns preceding the
field seasons were obtained from the National Climatic Data Center for their
Setauket Station, approximately 16 km east of Northport. Autumn 1995 was
cooler. For the months of September through December of 1995, monthly deviations
from long-term means were -0.9, +0.8, -2.9, and -3.0 °C; whereas for
the same months in 1996 the deviations were +0.7, -0.2, -1.5, and +3.0 °C.
Length, age, and sex of specimens
Striped Bass captured in this study ranged in total length and weight
from 167 mm to 995 mm, and 0.2 kg to 10.4 kg, respectively; the mean
size of Striped Bass examined was 450 mm and 1 kg. Total lengths differed
significantly among the gear types used (ANOVA: P < 0.001), and each gear
differed significantly from all other gears (post-hoc test of all combinations:
P < 0.007). Captures made by hook and line produced the broadest range
in lengths, from 275 mm to 770 mm. Among the gill nets, the 10-cm net
captured a smaller range of lengths than the 8-cm and 13-cm net. Striped
Bass caught in the power plant impingement were the largest of all examined
(799 mm ± 118 std). The shortest specimens (383 mm ± 54 std) were
those captured by trawl in Long Island Sound off Connecticut. Ages at time
of tagging of Striped Bass that had been tagged at the study site and later
recaptured ranged from 2 to 9 years.
2010 K. Williams and J. Waldman 379
Most of the Striped Bass sacrificed and examined were female (ratio =
68:12). Ratios of females to males were highest among fish caught in the
Connecticut trawl survey in February (23:4) and were lowest among hookand-
line catches at the power plant in March (1:1). Striped Bass that were
caught in the impingement grating at the power plant were the only collection
in which the sex ratio favored males (5:4).
Incidence of lymphocystis and other abnormalities
During Field Season I, physical abnormalities were recorded in 76 (7%)
of 1094 Striped Bass examined. Some abnormalities involved non-fatal
wounds that had been incurred recently or in the past; others involved illness
or deformity. The most common non-fatal wound—observed in 56 (5%) individuals—
was missing part or all of a caudal fin or caudal peduncle. Other
abnormalities included physical deformities, such as lordosis (curvature of
the spine) and abnormally shaped opercula. Wounds such as gashes or cuts
were most often documented in the body, head, or fins. Illnesses included the
presence of parasitic copepods and lymphocystis.
During Field Season I, lymphocystis was present in 3% (34 of 1094)
of Striped Bass examined at the Northport sampling location and in 2%
(3 of 149) of specimens captured by trawl and examined at the other
(Long Island Sound) sampling location. These fractions were not significantly
different (2 x 2 test of independence: P < 0.480). Forty-six percent
of Striped Bass captured that had lymphocystis lesions during Field Season
I had them on 25% or less of their body. Lymphocystis was found
in 29% (12 of 42) of Striped Bass examined and was significantly more
prevalent during Field Season II (2 x 2 test of independence: P < 0.001).
During Field Season II, the majority (83%) of Striped Bass with lymphocystis
lesions were afflicted on 75% or greater of their body surfaces.
Hatchery origin
In total, nine Striped Bass tested positive for coded wire tags (0.7% of
specimens examined). All were captured during Field Season I and all were
from the 1992 year class. Seven of these were sacrificed. All were female
and were determined to have been reared in hatcheries around the Chesapeake
Bay in 1992. Three of these were reared by the State of Maryland in
the Pepco hatchery and were released into the Patuxent River in Maryland
in 1992. These three individuals were captured together in the same gill net
set at the Northport study four years later, in March 1996.
Diet
Of Striped Bass examined for stomach contents, 77% of specimens
sacrificed for the study had empty stomachs. Even though 70% of the individuals
upon which gastric lavage had been performed had some food in
their stomachs, the fullest stomach examined contained only six Gammarus
spp. (amphipods). Amphipods were the most common food item present.
380 Northeastern Naturalist Vol. 17, No. 3
Other food items observed included polychaetes, crabs, mantis shrimp, and
Menidia sp. (Atlantic silverside).
Large-scale movements
As of 2006, about 21% of Striped Bass tagged in the Northport study had
been recaptured and reported to USFWS, 228 from Field Season I and 8 from
Field Season II (Table 1). Four individuals, all of which were tagged and
released in 1996, were reported with insufficient recapture data to be used
in recapture assessments. Tagged individuals were recaptured from North
Carolina to Maine, with most recaptures reported from New York (32%),
Massachusetts (22%), and Rhode Island (14%).
The majority of recaptures were made during the spring and summer immediately
after tagging, with many of these occurring in Long Island Sound,
Rhode Island, and Massachusetts. During the tagging process, cooperating
anglers reported recapturing at the power station 26 individuals that had
been marked for this study. In winters subsequent to tagging, none of the
Striped Bass marked for the study were recaptured at the Northport site.
Local movements
During the time that the seven Striped Bass with sonic tags were monitored,
ambient Long Island Sound water temperatures outside the effluent
varied between 2 °C and 4 °C. However, Striped Bass marked with sonic
tags occupied temperatures between 2 °C and 14 °C. The tag signal pattern
indicated that some individuals repeatedly occupied the heated water of
the effluent, in water temperatures at least 1 °C above ambient Long Island
Sound temperature, while others were observed both in and out of the plume.
Six of the seven Striped Bass fitted with sonic tags were heard again after
Table 1. Recaptures by year from 1146 Striped Bass tagged and released in winter 1995–1996
and 31 tagged and released in winter 1996–1997 that were recaptured from 1996 to 2006. Recaptures
from winter 1996–1997 releases appear in parentheses. Ns = no state reported
Total
Year recaptured per
State 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 State
ME 2 3 - - - - - - - - - 5
NH 1 - 1 1 - - - - - - - 3
MA 27 12(1) 7 3 1 1 - - - - - 52
RI 25 2 2 2 - 1 1 - - - - 33
CT 15 4 3 1 - 1 - - - - - 24
NY 53 6(5) 2(1) 4(1) 2 1 - - - - - 75
NJ 1 8 3 4 1 1 - - 1 - - 19
DE 1 2 - 1 - - - - - - - 4
MD 1 4 1 1 1 - - 2 - 1 - 11
VA 1 2 1 - - - - - - 1 - 5
NC - - - - - - 1 - - - - 1
Ns - 2 1 - 1 - - - - - - 4
Total 127 45(6) 21(1) 17(1) 6 5 2 2 1 2 - 236
2010 K. Williams and J. Waldman 381
their initial capture; however, as time progressed, sonically tagged fish were
located less often. The longest time between tagging and observation of an
individual in the plant vicinity was 33 days. This individual had been initially
fitted with a sonic tag on 16 February 1997, and was last detected on
21 March 1997. By the end of Field Season II on 4 April 1997, none of the
individuals fitted with sonic tags were detectable.
Discussion
Thermal discharges of electric-generating stations can aggregate Striped
Bass in temperate waters and, consequently, provide winter angling opportunities
that might otherwise not exist. The station at Northport, NY is well
known for this phenomenon and it sometimes supports substantial catchand-
release Striped Bass fishing. The popularity of this site is indicated by
the fact that shore-based anglers must hike 1 km of sand beach, often in
frigid conditions, and that it draws anglers from across Long Island and even
New Jersey. However, our two-year study revealed surprisingly high interannual
differences in the availability of Striped Bass. Levels of angling activity
appeared correlated with these differences, probably through direct feedback
from individual angler success and from word of mouth and printed and internet
reports of catch levels.
We don’t know if the winter abundance of Striped Bass in western Long
Island Sound during either of the two field seasons was anomalous compared
with long-term averages; however, catch data from Field Season I are far
more robust and may allow a more meaningful examination of the characteristics
of the Striped Bass that seasonally occur there. The length and age
range of Striped Bass captured from all sources in Field Season I indicate
they were composed of both immature and mature individuals (Hoff et al.
1988). The significantly different lengths of specimens captured by the different
sampling gears used at the Northport site may reflect gear biases, with
hook and line being the least selective. The trawl-caught individuals showed
the shortest average lengths. However, it is unclear if the trawl was selecting
for smaller fish or just encountered an aggregation of smaller fish at the time
of sampling.
The overall female-to-male sex ratio of 5.7:1 during Field Season I may
reflect stock origins. Striped Bass of Hudson River origin are believed to
migrate seaward at approximately 1:1 sex ratios (McLaren et al. 1981).
However, Striped Bass from Chesapeake Bay have shown pronounced female
biases, perhaps as much as 10:1 (Merriman 1941, Schaefer 1968). The
observed sex ratio is between the values estimated for the two primary stocks
and is suggestive of a mixed stock, as would be expected in northeastern
coastal waters (Waldman and Fabrizio 1994).
Long-term recaptures of Striped Bass tagged in this study at the power
station also show a wide geographic range for these fish that is suggestive of
382 Northeastern Naturalist Vol. 17, No. 3
Chesapeake, Hudson, and possibly Delaware River origins. This is not true,
however, for recaptures of tagged hatchery-released Striped Bass. Individuals
of hatchery origin composed 0.7% of all specimens examined. Despite the
proximity of the Northport site to the Hudson River and the large releases that
had occurred from the hatchery on the Hudson River, all seven specimens sacrificed for retrieval of their coded wire tags were of Chesapeake Bay origin.
This corresponds with results from the ocean side of Long Island’s south fork
where the ratio of hatchery-origin Chesapeake to Hudson River fish was 62:1
in autumn 1991 and 37:2 in autumn 1992, despite approximately only twice
as many individuals being stocked in the Chesapeake vs. the Hudson between
1983 and 1989 (Waldman and Vecchio 1996). Waldman and Vecchio believed
this imbalance between the ratio of releases in each system and subsequent
recaptures was due to differences in survival that may have stemmed from a
larger average size at release of Chesapeake Bay stockings, in addition to differences
in condition. The recapture together, in one gill net set at the power
station in March 1996, of three Striped Bass released together in 1992 from the
Pepco Hatchery on the Patuxent River suggests that some long-term schooling
occurs in this species.
Although food consumption rates for Striped Bass typically decline
sharply in winter (Dunning et al. 1997, Hurst and Conover 2001), the individuals
in the thermal plume were actively feeding, as indicated by their
willingness to strike artificial lures and by the presence of food in some
stomachs. However, food items in Striped Bass stomachs were not numerous
and were mainly crustaceans, with piscine prey limited to Menidia.
Evidence of Striped Bass feeding was not limited to the thermal plume.
Striped Bass captured in trawls in open Long Island Sound waters also contained
prey items.
Capture rates at the site were substantially higher in Field Season I than
in Field Season II, probably reflecting a larger number of Striped Bass in the
region that winter. This difference was true not only for the Northport study,
but also was reported by USNMFS scientists performing a trawl survey for
winter flounder in Long Island Sound (R. Alix, USNMFS, Milford, CT, pers.
comm.). This trawl survey, initiated during winter 1980–1981, captured few
Striped Bass until 1995–1996, when voluminous catches of Striped Bass of
approximately 400–450 mm in length were made. The first large catch occurred
on 25 January with more than 600 in one tow, followed by a tow 6
days later that included an estimated 2000–3000 Striped Bass, with smaller
but substantial catches also made in early February. However, large Striped
Bass catches were not repeated the following winter.
There was a pronounced difference in the incidence of lymphocystis between
Field Seasons I and II, but in an unexpected direction. Lymphocystis
virus replicates in the cytoplasm of hypertrophic connective tissue cells
that form the external lesions (Lorenzen et al. 1991). The waterborne virus
then enters the new host via its epithelium, most often on its gill surfaces.
2010 K. Williams and J. Waldman 383
This transmission mode favors crowded conditions, like those that may
occur in thermal plumes (Krantz 1970). However, we saw a manifold
greater incidence and a higher degree of external coverage of individuals
in Field Season II, when there appeared to be far fewer Striped Bass present
at the Northport site. Indeed, the incidence at the Northport site in Field
Season I was not significantly different from that seen in aggregations of
Striped Bass trawled in unheated waters in Long Island Sound, suggesting
that their higher densities in the thermal plume did not favor transmission
of lymphocystis. Weather associated with Field Season I was colder than
in Field Season II. However, it was during Field Season I that Striped Bass
showed fewer physical abnormalities and lymphocystis. This is counterintuitive
to the idea that a harsher winter should be more stressful to fish.
It would seem that a winter in which the temperature is closer to that preferred
by the fish should create an environment where fish are less stressed
and thus, appear to be in better physical condition. One possible explanation
for this finding is that during Field Season II, when the weather was
milder, healthier individuals did not need to use the site for refuge. Perhaps
healthier individuals were able to continue on a southern migration pattern
that is typical of Striped Bass in winter. In this case, perhaps the fish that
used the heated effluent of the power plant plume for refuge were those in
poorer condition.
Although our study provided insights into the biology of Striped Bass
wintering at power plants and the Northport station in particular, many
unknowns remain. A fundamental question is what controls the numbers
of Striped Bass that utilize the site in a given year? We revealed a large
difference in the apparent availability of Striped Bass between the two
years of our study. One common theory mentioned by anglers is that the
schools become attracted to and then “trapped” in the warm water as ambient
temperatures of Long Island Sound decline. A corollary is that more
individuals become trapped when temperatures decline unusually rapidly
towards the end of the stock’s southerly migration than if temperatures
remain higher longer, allowing a greater percentage of the stock to pass to
the south. However, in Field Season II, we demonstrated movement of individuals
in and out of the thermal plume. Moreover, in Field Season I, trawl
surveys in the open waters of Long Island Sound, ≈35 km from Northport
and far from the influence of power station discharges, held large numbers
of Striped Bass. Thus, we reject the notion that Striped Bass are thermally
trapped at this location.
An alternative hypothesis is that the numbers of Striped Bass wintering
at the latitude of Long Island Sound varies interannually and that the availability
of individuals at the Northport site is correlated with the number
of individuals wintering in open waters. We see several possible and not
mutually exclusive explanations for this variability. One is that the autumn
migration southward is influenced by the rate of declining water temperatures
384 Northeastern Naturalist Vol. 17, No. 3
and that a temperature threshold at which migration ceases may be crossed
in different years with varying percentages of the migratory stock having
moved past Long Island. There was some support for this on a gross level
from the autumn temperature data available across the two field seasons.
Another possible influence is the proportion of southerly migrating individuals
that pass through Long Island Sound vs. the alternative of traveling
along the south shore of Long Island; Merriman (1941) believed that storms
influenced Striped Bass to move farther towards the Sound before crossing
to Long Island. Austin and Custer (1977) also discerned intra-Sound autumn
movement patterns in which Striped Bass from both sides of the Connecticut
shore moved towards its center before crossing the Sound to Long Island and
then exiting in both directions.
Finally, there may be density-dependent factors in the size of the wintering
range of Striped Bass. The range of marine fishes often is positively
correlated with population size (MacCall 1990). Large abundances of Striped
Bass may have more northerly migrating individuals (Merriman 1941) and
thus, more northerly wintering individuals than lesser abundances. The 1993
Maryland Striped Bass juvenile index, at nearly 40, was (at that time) the
highest recorded since the inception of the index in 1957, was far higher than
the 1992 (9.0) and 1994 (16.1) values, and would be expected to generate
large numbers of first-time migrants from the bay as two-year olds in 1995.
Acknowledgments
For many kinds of assistance, we thank Robert Alix, Mark Bain, Jeff Buckel,
Tony Calabrese, Pam Carlsen, Roy Cash, Nancy Craig, Felix Edwards, Guy Hilbert,
Tom Hurst, Bill Kobel, Terry Marburger, Andy Matthews, Conky Nostrand, Kim
Roberts, Teresa Rotunno, Art Schweitheim, Nancy Steinberg, Byron Young, and,
especially, Carl Lobue. We also thank for financial support the Long Island Beach
Buggy Association and the Sounds Conservancy Grants Program.
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