Capossela et at: Migratory and within-estuary behaviors of adult Paralichthys dentatus of the southern mid-Atlantic Bight 
195 
0 20 - 
0.15 - 
(/} 
o 
c 
.§ 0 10 - 
O 
CL 
O 
cl 
0.05 - 
0 00 
Jun Jul Aug Sep Oct Nov Dec Jan 
Month 
Figure 3 
The proportion of Summer Flounder ( Paralichthys dentatus ) in 
each month from June 2007 to January 2008 that dispersed 
or was censored. Censored fish were fish that did not disperse 
through Wachapreague Inlet but were no longer detected by 
our acoustic receivers and had unknown fates. Total monthly 
sample sizes were 45 (Jun), 31 (Jul), 30 (Aug), 25 (Sep), 23 
(Oct), 16 (Nov), 10 (Dec), and 2 (Jan). 
Dispersed 
Censored 
period and 29% (2 individuals) dispersed during the 
residency period. Consequently, the odds of returning 
to the lagoon system were 3.5 times greater 
for fish that departed during the emigration 
period than for fish that departed during the 
residency period (odds ratio=1.4/0.4). It is 
possible that other fish returned undetected 
to the Wachapreague system because of the 
limited number of receivers in the system 
between February and July 2008; however, 
returning fish likely re-entered the system 
through the inlet and were detected by our 
receivers. 
The emigration period was characterized 
by a larger seasonal variation in water tem- 
perature than that observed for the resi- 
dency period (coefficient of variation [CV] 
residency = 9-5%> C V e m 1 gratio n = 46%). Dispersal 
followed the steep decline in temperature 
more closely than it did the gradual shift 
in day length, which (in contrast to changes 
in water temperature) was smooth and al- 
most constant over time (CV res i c j ency =7.7%, 
CV ernigrat j on =5.8%; Figs. 4, 5). The multiple 
linear regression that included both tem- 
perature and photoperiod as predictors of 
dispersal was significant (P=20.3, P<0.05) 
and explained 89% of the variation in 
monthly dispersals. Temperature was a sig- 
nificant predictor of mean percent disper- 
sal (F=6.39, P= 0.05), but photoperiod was not 
(F=0.94, P=0.38). The length of time over which 
we observed returning fish (3 months) was in- 
adequate to statistically examine the effects of 
mean monthly temperature and photoperiod on 
the timing of return. 
The mean sizes at tagging for fish that dis- 
persed during the residency and emigration pe- 
riods were 437 ±21 mm TL and 367 ±13 mm TL, 
respectively. We found that the timing of dis- 
persal was inversely related to fish size at the 
time of tagging (% 2 =8.45, P<0.05). Larger fish 
were more likely to leave the system during the 
residency period (before October 11) than were 
smaller fish. Conversely, smaller fish were more 
likely to disperse during the emigration period. 
The goodness-of-fit of this model indicated that 
predicted and observed frequencies were not sig- 
nificantly different (% 2 =3.86, P- 0.80), indicating 
the adequacy of the logistic regression model as 
a descriptor of these data. 
Within-estuary behaviors 
Summer Flounder primarily used the upper 
channels during the residency period, although 
fish were detected in all habitats (Fig. 6, A and 
B). Fish occupied the upper and lower channels 
for 78% and 19%, respectively, of the total time 
that fish were detected (Table 1). With the exception of 
the single fish released in the tidal fiat, all fish were 
7 / 1/2007 
Figure 4 
The proportion of Summer Flounder (Paralichthys dentatus ) that 
dispersed from (^) and returned to (■) the Wachapreague lagoon 
system from 8 June 2007 to 7 April 2008 (when the last fish was 
detected returning), on the basis of the Kaplan-Meier estimator. 
Mean daily temperature (°C; gray line) is also plotted. Confidence 
intervals have been omitted for clarity. 
