Effects of alternative prey on cannibalism in age-1 bluefish

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 sugg esting strong selection for silversides. There was no evidence of prey-m it ching. The behavioral processes leading to age-1 bluefish selection of Atla ntic silversides was investigated. The proportion of attacks on each prey s pecies was distributed randomly, or slightly higher on age-0 bluefish; howe ver, 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 finding s suggest that prey snitching between age-0 bluefish and an alternative pre y probably does not act as a stabilizing mechanism in the bluefish populati on and confirm the importance of capture success in determining piscivore s electivity patterns. (C) 1999 The Fisherics Society of the British Isles.