Latour et al.: The trophic dynamics of Paralichthys dentatus in Chesapeake Bay 
51 
n c = 688 
n,= 1780 
Figure 4 
Percent weight of prey types present in the diet of summer flounder 
( Paralichthys dentatus) collected from the mainstem of Chesapeake 
Bay from 2002 through 2006. The total number of clusters collected is 
given by n c , and n t represents the total number of specimens included 
in this study. Standard error estimates, represented by error bars, 
were calculated from cluster sampling variance estimates and all 
were less than 0.03%. 
of sand shrimp to the diet of these fish was 
approximately the same as in the small- 
est size-category, whereas that of mantis 
shrimp increased. Fishes were again of sec- 
ondary importance and were represented 
mainly by bay anchovy, weakfish, and At- 
lantic croaker. Weakfish was the primary 
prey of the large-medium summer flounder 
and, although the contribution of bay an- 
chovy declined, anchovy still represented 
15.4% of the diet. The contribution of spot 
to the diet of summer flounder increased 
from less than 1% in the small-medium fish 
to 13% in the 375-574 mm TL size-group. 
Mantis shrimp was the most important in- 
vertebrate prey of the large-medium fish. 
Sciaenids (i.e., spot, weakfish, and Atlan- 
tic croaker) were the main prey of of the 
largest summer flounder and accounted for 
67.3% of the diet. Our representation of 
the diet composition of these fish should be 
viewed as preliminary because of the small 
cluster sample size (n c = 23). 
Seasonal changes in summer flounder 
diet likely mirrored the temporal variabil- 
ity of prey assemblages in Chesapeake Bay. 
The contribution of sand shrimp and spot- 
ted hake peaked in the spring and early 
summer (Fig. 6B). Atlantic brief squid (Lol- 
liguncula brevis), Atlantic croaker, mantis 
shrimp, silver perch ( Bairdiella chrysoura), 
spot, and weakfish accounted for a greater 
portion of the diet throughout the sum- 
mer and autumn. Bay anchovy and mysid 
shrimp were always two of the top three main prey 
types in the diet of summer flounder from May to No- 
vember. 
The diet of summer flounder was dominated by mantis 
shrimp and bay anchovy in 2002, whereas mysid shrimp 
was the main prey from 2003 through 2006 (Fig. 60. 
Atlantic brief squid, crab, mantis shrimp, and spotted 
hake generally decreased in importance over this time 
period, whereas the contribution of mysid shrimp and 
spot generally increased. 
Predator-prey size relationships 
The available data on sizes of whole prey consumed by 
summer flounder (the primary prey types excluding 
mysid shrimp) were examined with respect to summer 
flounder size. For all prey types, the size of the prey con- 
sumed increased significantly with increasing summer 
flounder size (P<0.05, Fig. 7). With respect to Atlantic 
croaker and spot, the majority of the individuals con- 
sumed were likely young-of-the-year (YOY), and a few 
of the larger individuals were age-1. However, summer 
flounder appear to have preyed exclusively on YOY weak- 
fish. At a given size of summer flounder, the sizes of bay 
anchovy, mantis, and sand shrimp consumed were more 
variable than the sizes of the sciaenid prey, and this 
finding may indicate less probability of a size-modulated 
predator-prey relationship. 
Discussion 
Summer flounder feed on a diverse array of prey in 
Chesapeake Bay, as evidenced by over 120 prey types 
encountered in the diet. However, despite this diversity, 
approximately half of the diet comprised only two prey 
types, mysid shrimp and bay anchovy. The other half 
of the diet consisted of a few fishes (sciaenids-weakfish, 
spot, and Atlantic croaker) and invertebrates (mantis 
and sand shrimps). Similar results have been reported 
for other upper trophic level predators in Chesapeake 
Bay (i.e., striped bass [Morone saxatilis] bluefish [Poma- 
tomus saltatrix ] and weakfish) — results that further 
support the notion that although the Chesapeake Bay 
food web is complex, the number of prey species sup- 
porting these predators is relatively few ( Hartman and 
Brandt, 1995). 
Mysid shrimp dominate the diets of summer flounder 
in other estuarine and coastal habitats (Smith and 
Daiber, 1977; Link et al., 2002). Our study shows that 
mysid shrimp also play an important role in the tro- 
phic dynamics of summer flounder in Chesapeake Bay. 
