Effects of alternative prey on cannibalism in age-1 bluefish

Abstract

Age-1 bluefish Pomatomus saltatrix were offered both age-0 bluefish and age-1 Atlantic silversides Menidia menidia in the following proportions: 0:1·0, 0·25:0·75, 0·5:0·5, 0·75:0·25, 1·0:0. Atlantic silversides were consumed in greater proportion than offered throughout all treatments suggesting strong selection for silversides. There was no evidence of prey-switching. The behavioural processes leading to age-1 bluefish selection of Atlantic silversides was investigated. The proportion of attacks on each prey species was distributed randomly, or slightly higher on age-0 bluefish; however, capture success was greater on silversides than on age-0 bluefish prey. Therefore, age-1 bluefish did not actively select for silversides and the observed selection pattern is a result of passive processes. These findings suggest that prey switching between age-0 bluefish and an alternative prey probably does not act as a stabilizing mechanism in the bluefish population and confirm the importance of capture success in determining piscivore selectivity patterns.