McDonald et at: Spatial and seasonal abundance of Cynoscion arenarius and C. nothus off the coast of Texas 
31 
o 
Figure 6 
Average seasonal abundance (individuals collected/hr, mean ±standard error), averaged over twenty years 
of trawl data (1987-2006), for sand seatrout (Cynoscion arenarius) (top) and silver seatrout ( C . nothus) 
(bottom) averaged by different water depths collected in sampling areas of the Gulf of Mexico (A-E). Depths 
are represented by shades. 
abundance tended to drop dramatically. This find- 
ing is similar to the results of DeVries and Chit- 
tenden (1982) who also described a reduction in 
silver seatrout abundance offshore in summer and 
may also be due to offshore migrations, die offs, 
or sampling errors. 
Low silver seatrout abundance during the sum- 
mer season may be due to their migrations farther 
offshore. Although summer migration outside of 
CF-TPWD sampling areas (>16.7 km from shore- 
line) has not been reported for silver seatrout, 
they do migrate during winter (DeVries and Chit- 
tenden, 1982) and summer migrations occur in 
similar species (Vetter, 1982). A spatial analysis 
of offshore sampling areas indicated that samples 
of both species were commonly collected in the 
outermost (most offshore) grids sampled (data not 
shown). Thus, it is possible that the true center of 
distribution of silver seatrout was not sampled in 
our study and that offshore migration during sum- 
mer months is reflective of seasonal movements 
into deeper water. 
Low silver seatrout abundance during the sum- 
mer season may also be due to adult die offs of a 
species with a short life span. DeVries and Chit- 
tenden (1982) estimated a maximum life span for 
silver seatrout of one to one-and-a-half years of 
age. Not only are they short-lived, but they are 
also summer spawners. Thus, the reduction in abun- 
dance in summer may reflect cyclic spawning, followed 
by the die-off of spawners. 
Finally, low silver seatrout abundance during the 
summer season may be due to sampling bias in that 
CO 
=3 
~o 
O 0 - 
y=- 2. 5845X+ 3.6943 
r 2 = 0.3762 
v 
A 
Gulf area A 
• 
Gulf area B 
O 
Gulf area C 
w 
Gulf area D 
A 
Gulf area E 
■ 
— 1 1 1 1 1 1 
0.8 0.9 1.0 1.1 1.2 1.3 1.4 
Logio water depth (m) 
Figure 7 
Least-square regression for annual mean water depth (m) and 
annual mean abundance (individuals collected/hr), averaged 
over twenty years of trawl data (1987-2006) for sand seatrout 
(Cynoscion arenarius) collected across sampling areas in the 
Gulf of Mexico. Each gulf area (A-E) is represented by a 
different symbol. 
the capture of the larger-size silver seatrout may have 
been limited. Sheridan et al. (1984) captured numer- 
ous silver seatrout >200 mm TL; our samples were 
rarely >200 mm TL. However, Sheridan et al. (1984) 
did not describe their trawl methods, specifically their 
