DeCelles and Cadrin: Movement patterns of Pseudopleuronectes americanus in the southern Gulf of Maine 
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Figure 3 
Temporal patterns of winter flounder (Pseudopleuronectes americanus) 
detections obtained by using passive acoustic telemetry in the Plymouth 
Estuary, MA, between January 2008 and October 2008. (A) The total 
number of detections each day. (B) The number of tagged winter flounder 
that were detected each day. (C) The percentage of acoustic receivers that 
detected a tagged winter flounder during each day of the study. 
the 25 winter flounder (28%) released 
in Plymouth Bay during 2008 and 2009 
were observed to be estuarine spawn- 
ers. A G-test for independence revealed 
no significant interannual variability 
(P=0.56) in the ratio of coastal and 
estuarine spawners between the two 
years. In total, only 12 of the 49 (25%) 
tagged winter flounder were noted to 
be estuarine spawners. The 95% upper 
confidence limit for this proportion was 
calculated to be 0.70. If spawning was 
restricted to estuaries, the proportion of 
winter flounder classified as estuarine 
spawners would be one (100%). There- 
fore, our results demonstrate that in 
the Plymouth Bay region of the Gulf of 
Maine, winter flounder spawning is not 
restricted to estuaries. 
Eleven winter flounder were observed 
to be gravid females at the time of 
release. Only one of the three gravid 
females tagged in Plymouth Bay in 
November 2007 was later detected in 
the estuary, but not until May of the 
following year. Eight gravid females 
were tagged in Plymouth Bay on 8 
May 2009. Two of these individuals 
migrated rapidly to the mouth of the 
estuary. These females were detected 
at the mouth of the estuary six and 
ten days after release, respectively. 
Whether these individuals spawned in 
the estuary, or migrated to the estuary 
after spawning in coastal waters is un- 
known. It was apparent that the six of 
eight gravid winter flounder remained 
in Plymouth Bay after being tagged. 
Seasonal distribution 
The seasonal distribution of tagged 
winter flounder in the Plymouth Bay 
region became apparent after two years 
of passive telemetry. Adult winter flounder were largely 
absent from the Plymouth estuary during the winter 
months in both years. Only four of the 38 tagged winter 
flounder at large during the winter of 2008 and 2009 
were detected in the Plymouth estuary (Figs. 3 and 4). In 
the winter of 2008, temperatures were warmer and more 
stable in Plymouth Bay (range = 1.2-5.0°C) than in the 
Plymouth estuary (range = -1.24-5.2°C) (Fig. 5). In the 
winter of 2009, the observed temperature ranges were 
similar in Plymouth Bay (— 0.6-5. 0°C) and the Plymouth 
estuary (-0.9-5.9°C). 
The movement of winter flounder into the Plymouth 
estuary began during the spring and was coincident 
with an increase in water temperature. Some tagged 
winter flounder began to migrate into the estuary in 
mid-April, when estuarine temperatures ranged from 
9° to 12°C. In 2008, the mean temperature observed 
when winter flounder migrated from Plymouth Bay in 
to the Plymouth Estuary was 10.9°C. Tagged floun- 
der were most abundant within the estuary between 
May and early June (Figs. 3 and 4) when temperatures 
ranged from 9° to 16°C, and this was also the only 
period when we were able to capture adult flounder in 
the estuary. The majority of winter flounder tagged in 
2009 remained in the coastal waters of Plymouth Bay 
in late spring, where water temperatures ranged from 
9° to 13°C. 
We observed an emigration of tagged winter flounder 
from the Plymouth estuary during the onset of summer, 
as water temperatures increased. The mean observed 
temperature when tagged winter flounder emigrated 
from the estuary was 13.9°C, and 89% of all recorded 
