Contrasting patterns of resource utilization between juvenile estuarine predators: the influence of relative prey size and foraging ability on the ontogeny of piscivory

Abstract

In aquatic systems, ontogenetic patterns of resource utilization strongly influence growth and survival, particularly during early life stages. We compared prey resource use and evaluated potential factors affecting the timing of the shift to piscivorous feeding in two juvenile estuarine fish predators: striped bass ( Morone saxatilis ) and bluefish ( Pomatomus saltatrix ). In New York Bight estuaries, bluefish shift to piscivory earlier in ontogeny and consume larger relative prey fish sizes compared with striped bass. Predator gape allometries are similar and did not determine maximum prey sizes eaten. Experimental results revealed marked differences in foraging abilities between predators, with bluefish realizing much greater foraging efficiency compared with striped bass feeding on identical fish prey. Both predators demonstrated lower feeding efficiency and grew relatively poorly when feeding on invertebrates compared with fish prey. When held together under limited prey conditions, bluefish exploited a greater proportion of available prey at the expense of striped bass. Our findings highlight the importance of the availability of appropriately sized forage fishes to the ontogeny of piscivory and provide evidence that predator–prey size relationships and disparate foraging abilities can generate inter- and intra-specific variation in patterns of resource utilization and predator growth.