Predator size - prey size relationships of marine fish predators: interspecific variation and effects of ontogeny and body size on trophic-niche breadth

We utilized a long-term data base collected over a broad geographic range t o examine predator size-prey size relationships for 18 species of marine fi sh predators from continental shelf waters off the northeast US coast. Regr ession analysis was used to illustrate interspecific variation in ontogenet ic patterns of prey size use, gape allometries, and ratio-based trophic nic he breadths. Size-based feeding strategies were assessed through comparison of frequency distributions of relative prey sizes eaten and were related t o general predator feeding tactics and gape morphology. The results demonst rated that the range of prey sizes eaten expanded with increasing predator body size for each of the marine predators examined, leading to asymmetric predator size-prey size distributions. Absolute maximum prey size and slope s of maximum prey size versus predator size varied widely among predator ta xa. Distinct size-based feeding strategies were evident, as diets of some p redators were dominated by prey that were 10 to 20% of predator size, where as other predators frequently consumed prey >50 % of predator size. Gape si zes and allometric relationships with body size were also diverse among pre dators and often were closely associated with maximum prey sizes. Ratio-bas ed trophic-niche breadths generally did not expand with predator ontogeny a nd tended to narrow for the largest predators, which may be common for anim al taxa.