PREDATION BY JUVENILE PISCIVOROUS BLUEFISH (POMATOMUS SALTATRIX) - THE INFLUENCE OF PREY TO PREDATOR SIZE RATIO AND PREY TYPE ON PREDATOR CAPTURE SUCCESS AND PREY PROFITABILITY

Capture success, handling time, prey vulnerability, and prey profitabi lity were examined as a function of prey length/predator length ratio for age-0 juvenile bluefish (Pomatomus saltatrix) feeding on juvenile striped bass (Morone saxatilis) and Atlantic silverside (Menidia menid ia). For each prey species, bluefish capture success declined linearly and handling time increased exponentially with increasing length rati os between 0.20 and 0.65. However, bluefish capture success was lower and handling times increased at a faster rate when feeding on juvenile striped bass compared with Atlantic silverside. Prey vulnerability, m easured as bluefish predation rate, declined exponentially with increa sing length ratios for each prey species. Profitability curves were do me shaped for each prey species; however, profitability values and the location of dome peaks differed between prey species. Capture success functions were combined with field length distributions to generate e xpected frequency distributions of length ratios included in bluefish diets. Comparisons resulted in good agreement between expected and obs erved sizes in bluefish diets, illustrating the importance of capture success in determining piscivore diets. Our results indicate that, for juvenile fishes, prey-specific morphological and behavioral differenc es can have significant effects on the outcome of predator-prey intera ctions and that size-based predation components are best represented a s continuous functions of relative fish size.