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Fishery Bulletin 106(1) 
CCA axis 1 (variance 51.2%) 
Figure 5 
Canonical correspondence analysis (CCA) biplot for summer flounder 
(Paralichthys dentatus) diet in the mainstem of Chesapeake Bay from 2002 
through 2006. Arrows represent the significant explanatory factors and 
dots represent prey types. The canonical axes represent linear combina- 
tions of the three explanatory variables (fish size, month, and year). 
Moreover, mysid shrimp have dominated the diets of 
other teleost piscivores in the bay over the past sev- 
eral years, which indicates that this prey represents a 
crucial linkage between lower and upper trophic level 
production. Despite the importance of mysid shrimp 
in the diets of fishes, very little is known about the 
population dynamics and abundance of this species 
(when compared to other prey types, e.g., bay anchovy) 
in Chesapeake Bay. Data on mysid shrimp abundance 
would be instrumental to better understanding not only 
trophic interactions of summer flounder, but those of 
other top teleost predators in this estuary. 
Significant ontogenetic changes in the diet were docu- 
mented; small flounder mainly consumed small inver- 
tebrates and bay anchovy. The diversity of the diet in 
terms of numbers and sizes of prey types increased with 
increasing summer flounder size. Medium-size flounder 
continued to consume prey types found in the diet of 
small flounder, but the diet of medium-size flounder ap- 
peared to be an expansion of rather than a shift from 
the diet of small flounder. Fishes (primarily sciaenids) 
were found almost exclusively in the diet of the largest 
summer flounder, and because bay anchovy and the 
aforementioned invertebrate prey types were absent in 
the stomachs of these fish, there appeared to be a diet 
shift at approximately 575 mm TL. Although similar 
changes in the diet of summer flounder (>500 mm TL) 
have been documented in offshore waters (Link et ah, 
2002), cephalopods were the primary prey type as op- 
posed to fishes. This contrast in the diets of the larger 
summer flounder is likely due to the lack of an abun- 
dant and comparable large soft-bodied invertebrate prey 
in Chesapeake Bay. 
Seasonal trends in summer flounder diet composi- 
tion were not surprising given the well documented 
spatiotemporal patterns of summer flounder prey. Sand 
shrimp and spotted hake abundance generally peaks 
during late winter and early spring in the mainstem of 
the lower bay; hence, it follows that they composed ap- 
preciable fractions of the summer flounder diet during 
this season (Haefner, 1976; Murdy et ah, 1997). Faunal 
diversity in Chesapeake Bay reaches a maximum dur- 
ing late August and September and corresponds with 
a highest diversity of prey types in the diet of summer 
