Effects of predation risk on foraging behavior: mechanisms altering patch choice

Abstract

Responses of foraging young-of-year black surfperch Embiotoca jacksoni Agassiz to benthic predators, kelp bass Paralabrax clathratus (Girard) and grass rockfish Sebastes rastrelliger (Jordan and Gilbert), were investigated in laboratory and field experiments. Young-of-year black surfperch fed on crustacean prey from a variety of benthic algal substrata. In laboratory experiments using uniform patches of a favored alga, black surfperch avoided kelp bass or grass rockfish by reducing time spent feeding in a patch containing a predator, although no effect on the feeding rate of the surfperch was observed. Surfperch showed no difference in their response to kelp bass or grass rockfish. Field experiments indicated that, under conditions of safety, the low-growing alga Zonaria farlowii Setchell and Gardner was the most highly favored substratum. As risk of predation increased, preference for Zonaria declined sharply and the tall, bushy alga Sargassum palmeri Grun became the most highly favored feeding substratum. The mechanisms producing the shift in preference involved an increased number of visits to Sargassum and a longer duration foraging bout per visit. The responses of young-of-year black surfperch to piscivorous fishes appear to enable the surfperch to reduce mortality risk while still continuing to feed actively.