DeCelles and Cadrin: Movement patterns of Pseudopleuronectes americanus in the southern Gulf of Maine 
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Winter flounder tagged between November 2007 and 
June 2008 (n = 47) were tracked within the Plymouth 
estuary by using a moored array of 15 wireless receiv- 
ers (model VR2 and VR2W, Vemco Ltd.; Fig. 1). Six of 
these receivers (I, J, K, M, N, and O; referred to as the 
“inner gate”) were configured as a parallel curtain that 
spanned the mouth of the Plymouth estuary, allowing 
the movements of fish traveling between Plymouth Bay 
and Plymouth estuary to be recorded precisely. Parallel 
curtain arrays are advantageous because they allow the 
direction of movement for each fish to be obtained ( Heu- 
pel et al., 2006). Range testing was performed at the 
mouth of the estuary by placing transmitters on the bot- 
tom in different locations for ten-minute intervals. After 
range testing, receivers within the parallel curtain 
were positioned to ensure that overlap existed between 
the detection radii of adjacent receivers. Tagged winter 
flounder were monitored within the upper reaches of 
the Plymouth estuary by using nine receivers positioned 
in a nonoverlapping grid array. These receivers were 
placed within the deeper channels of the Plymouth 
estuary to maximize their detection radii. 
During the second year of the study, the receiver 
array was expanded from 15 to 30 wireless receivers 
(Fig. 1). Ten receivers (P-Y; referred to as the “outer 
gate”) were deployed across the mouth of Plymouth 
Bay, from Gurnet Point in Duxbury southward to 
Rocky Point in Plymouth. This arrangement allowed 
us to track the movement of tagged winter flounder 
between Cape Cod Bay and Plymouth Bay. An ad- 
ditional five receivers (Z-DD) were placed within the 
upper reaches of the Plymouth estuary. Expanding the 
receiver array allowed us to test more directly our hy- 
potheses about the spawning behavior of the 25 winter 
flounder that were tagged between 10 December 2008 
and 8 May 2009. 
Before their retrieval in 2009, six of the 30 acoustic 
receivers were lost, likely because of boat traffic, in- 
teractions with commercial fishing gear, or because of 
winter storms. Receivers P and Y were lost from the 
outer gate between Cape Cod Bay and Plymouth Bay. 
Receivers I, M, and O were lost from the parallel cur- 
tain between Plymouth Bay and the Plymouth estuary. 
Subsequently, receiver G was moved from the “Cowy- 
ard” and placed adjacent to the position of receiver M 
to improve the coverage in this area. Receiver H in 
Plymouth Harbor was also lost, likely because a high 
volume of boat traffic in the area. 
Data analysis 
The movement track of each tagged fish was visualized 
by using GIS software (ArcMap vers. 9.3, ESRI, Red- 
lands, CA). Estuarine residence time was calculated as 
the time elapsed between the first and last detection 
for each individual within the Plymouth estuary. If a 
tagged winter flounder was recorded within the estuary 
on more than one occasion, the total days spent within 
the estuary during each visit were combined to calculate 
residence time for that individual. 
Winter flounder were classified as either estuarine 
or coastal spawners on the basis of their observed lo- 
cations during the peak spawning months of March 
through May. Fish that were detected within the Plym- 
outh estuary at any time over this three month span 
were classified as estuarine spawners, whereas winter 
flounder that remained in coastal waters were classified 
as coastal spawners. A G-test for independence (Sokal 
and Rohlf, 2001) was performed to examine whether 
significant interannual variability was present in the 
proportion of tagged winter flounder that were classi- 
fied as estuarine spawners in 2008 and 2009. The ratio 
(with 95% confidence intervals) of estuarine to coastal 
spawners observed over the two-year period was calcu- 
lated (Sokal and Rohlf, 2001). 
Abiotic monitoring 
During the study, bottom water temperature was moni- 
tored at four locations within the study site. Three 
temperature loggers (Vemco Ltd.; 8-bit minilog TR) 
were attached to the moorings of receivers A, E, and 
K within the Plymouth Estuary. These temperature 
loggers were placed 0.5 meters above the bottom and 
were programmed to record bottom water temperature 
every 30 minutes. A temperature logger placed in the 
southeastern portion of Plymouth Bay recorded bottom 
water temperature once every two hours in 2007 and 
2008. In September 2008, another temperature logger 
was placed on the mooring of receiver T to record bottom 
temperature in Plymouth Bay. In 2009 some of the tem- 
perature loggers failed. When available, bottom water 
temperature data were averaged weekly at each site. 
Results 
With passive acoustic telemetry, we successfully gath- 
ered high-resolution data on the migration, spawn- 
ing behavior, and seasonal distribution of adult winter 
flounder in the southern Gulf of Maine. Twenty eight of 
the 47 winter flounder tagged during the first year of 
the study were later detected within the Plymouth estu- 
ary, yielding a total of 16,956 detections in our array 
of acoustic receivers. Twenty two of the 25 fish tagged 
during the second year of the study were later detected 
in the receiver array, resulting in 97,394 unique detec- 
tions. A summary of data for each tagged winter flounder 
that was later detected is given in Table 1. 
Spawning behavior 
Based on the observed movements of tagged winter 
flounder during the spawning season, the presence of 
two contingent spawning groups of flounder was evident 
in the region: coastal spawners and estuarine spawners. 
In both years of the study, the majority of tagged winter 
flounder exhibited coastal spawning behavior. Only five 
of the 24 winter flounder (21%) tagged in Plymouth Bay 
in 2007 were classified as estuarine spawners. Seven of 
