Vulnerability of Atlantic herring larvae to predation by yearling herring

Abstract

This study quantifies age-related changes in the vulnerabhty of Atlantic herring Clupea harengus larvae to predation by larger herring through experimental investigations of capture probabil- ity in the laboratory and gross vulnerabhty in large enclosures (mesocosms) Seventy-six laboratory predation trials were staged involving larvae averaging 8.6 to 32.0 mm in length (4 to 118 d posthatch- ing). In all, 1067 attacks were observed. The proportion of larvae responding to an attack was constant (6.2 %) for lengths < 26 mm. Responsiveness of larger larvae increased rapidly with length. This was probably due to the functional development of auditory bullae. The proportion of responding larvae that successfully escaped an attack (response effectiveness) increased throughout the larval period, as did predator errors. Increases in responsiveness, response effectiveness, and predator error rate contributed to a decline in capture probability as larvae grew. Nevertheless, in mesocosrns the number of larvae consumed in 8 h by 1 predator increased with larva length, suggesting that encounter rate and possibly attack rate increased with larva length, probably due to increased conspicuousness of larvae.