DeCelles and Cadrin: Movement patterns of Pseudopleuronectes americanus in the southern Gulf of Maine 
417 
was also found in previous studies. Ichthyoplankton 
sampling has been conducted in this region for decades 
to assess the impacts of the Pilgrim Nuclear Power 
Station (PNPS), which is on the southeast shore of 
Plymouth Bay. Researchers at Marine Research, Inc. 5 
used a physical model to estimate the time it would 
take for eggs spawned in the Plymouth estuary to drift 
to Plymouth Bay near the power plant. They collected 
and aged eggs at PNPS and found that a proportion 
of the eggs had been spawned too recently to have 
originated from the estuary. They concluded that these 
eggs had been spawned in Plymouth Bay, rather than 
the estuary. 
Evidence for coastal spawning has also been not- 
ed in other regions of the Gulf of Maine. Howe and 
Coates (1975) suggested that coastal spawning groups 
may exist on the basis of their observations of tagged 
flounder captured in coastal and offshore waters dur- 
ing the spawning season. Data collected during the 
NOAA Northeast Fisheries Science Center annual 
spring trawl survey have shown that the mean depth 
occupied by winter flounder in the Gulf of Maine has 
increased significantly over the last 40 years (Nye et 
al., 2009). This increase in depth may reflect a broad 
shift from estuarine to coastal spawning in the Gulf 
of Maine stock. 
Winter flounder do not require estuaries as spawning 
habitat. This is evidenced by the large, self-sustaining 
stock of winter flounder that is present on Georges 
Bank (NMFS, 1999). Rather, estuarine spawning ap- 
pears to be a strategy to maintain localized population 
structure. Tagging studies have shown that winter 
flounder display homing to their spawning grounds 
(Perlmutter, 1947; Saila, 1961). Dispersal is limited or 
nonexistent during the egg stage. In addition, larval 
behavior and estuarine hydrographic features promote 
the retention of larvae within estuarine spawning areas 
(Pearcy, 1962; Crawford and Carey, 1985; Chant et al., 
2000). These characteristics, which promote local popu- 
lation structure, also make winter flounder vulnerable 
to human impacts. 
Anthropogenic impacts such as dredging, pollution, 
eutrophication, and elevated temperatures often occur 
in estuaries (Nelson et al., 1991), and these activities 
can reduce the survival of winter flounder eggs, larvae, 
and juveniles. Estuaries are relatively small in size and 
are more susceptible to changes in water temperature 
than are coastal waters (Abood and Metzger, 1996). 
Elevated temperatures have been shown to reduce the 
survival and fitness of winter flounder eggs (Keller and 
Klein-MacPhee, 2000) and winter flounder has been 
identified as a species that is particularly vulnerable 
to global warming (Rose, 2005). A closed population 
5 Marine Research, Inc. 1986. Winter flounder early life 
history studies related to the operation of Pilgrim Station — A 
review 1975-1984. Pilgrim Nuclear Power Station Envi- 
ronmental Monitoring Program - Report Series No. 2, 111 
p. Boston Edison Company, Boston, MA. 
of winter flounder that relies solely on an estuary as a 
spawning and nursery ground will likely exhibit poor 
recruitment, if that estuary has been degraded by hu- 
man activities. Homing to spawning grounds by adults 
may be unfavorable when conditions do not inhibit the 
act of spawning but do diminish the survival of eggs 
and larvae (Harden Jones, 1968). Harden Jones (1968) 
also concluded that strict natal homing was not a sus- 
tainable life history strategy and that diverse migration 
behaviors are needed for a population to persist in a 
changing environment. 
Divergent migrations impart resilience to populations 
against spatial variability in mortality (Secor, 1999). 
Passive telemetry revealed that winter flounder in the 
southern Gulf of Maine exhibit spatial heterogeneity in 
their use of spawning habitat and that coastal spawn- 
ing was prevalent. Compared to estuarine spawning, 
coastal spawning likely leads to a greater dispersal of 
larvae. Therefore, a single coastal spawning contingent 
may provide a larval source for one or more estuarine 
nursery grounds. Coastal spawning contingents may 
confer resilience in a regional population during periods 
when estuarine productivity is low. 
Our results indicate that coastal waters may provide 
essential spawning habitats for winter flounder in the 
Gulf of Maine. However, future research is needed to 
identify the prevalence of coastal spawning in other 
regions of the Gulf of Maine. Acoustic telemetry is a 
promising tool for conducting this research. For exam- 
ple, receiver gates could be placed across the mouths 
of estuaries along the coast, in a design similar to 
the one proposed by Grotheus and Able (2007). Ich- 
thyoplankton studies could also be used to compare 
the densities of winter flounder eggs in estuarine and 
coastal waters. High-resolution trawl surveys could 
be used to sample the reproductive condition of win- 
ter flounder throughout the Gulf of Maine. Finally, 
coupled biophysical models would allow an examina- 
tion of the dispersal of coastal spawned larvae in the 
Gulf of Maine. 
Seasonal distribution of winter flounder 
Bigelow and Schroeder (1953) and McCracken (1963) 
observed that flounder north of Cape Cod are more 
abundant in deeper, coastal waters during the winter 
months. Our observations in one region of the Gulf of 
Maine support this claim because only 10% of tagged 
of winter flounder at large during the winter months 
were detected within the shallow waters of the Plym- 
outh estuary. Contrary to our observations, Howe and 
Coates (1975) claimed that flounder in the Gulf of 
Maine moved farther inshore into estuaries during the 
winter months. However, their analysis may have been 
hampered by a lack of tag returns during the fall and 
winter months. 
Winter flounder in Newfoundland are thought to move 
to deeper coastal waters during the winter to avoid ice 
formation and extreme turbulence during storm events 
(Van Guelpen and Davis, 1979). Winter flounder may 
