Enhancing diet analyses of piscivorous fishes in the Northwest Atlantic through identification and reconstruction of original prey sizes from ingested remains

Biological interactions among species can play a dominant role in structuring marine fish communities. Specifically, predation may represent a significant source of mortality for larval and juvenile fishes. Analysis of predator diet requires accurate information on the identity as well as the sizes of prey consumed. In examinations of stomach contents of piscivorous fishes, the condition of recovered prey items varies substantially not only in the large range of digestive states encountered but also in the occurrence of partially consumed fishes. To estimate the original sizes of well-digested and partially consumed prey fishes we constructed a series of predictive equations relating total length, fork length, and weight of fish to seven morphometric measurements including dorsoventral body depth, eye diameter, caudal peduncle depth, pectoral-fin length, opercle length, cleithrum length, and dentary length for ten common prey fishes in the Northwest Atlantic. All relationships were highly significant, with coefficients of determination typically exceeding 0.90 and mean percent prediction errors less than 10%, indicating that reliable original size estimates are obtainable from incomplete fish remains. To aid in field-based identification of prey fishes, we extracted and examined opercles, cleithra, and dentaries from each fish. Careful examination of bones revealed prominent diagnostic characteristics with clear differences among family taxa, demonstrating their potential utility as identification tools. Used collectively, the predictive equations and the diagnostic features of the bones should allow for inclusion in diet analyses of prey items previously designated as unidentifiable or unmeasurable, and thus increase the amount of dietary information obtainable from stomach contents analyses of Northwest Atlantic piscivores