Use of Techniques from Foraging Theory to Quantify the Cost of Predation for Benthic Fishes

Abstract

Field assays of survival and foraging behavior were used to estimate the energetic cost of predation risk in terms of reduced prey consumption for two freshwater benthic cottid fishes that (1) opportunistically exploit high resource availability, particularly during their early life history, and (2) compete for resources at the patch scale in estuaries. Both species' spatial occurrence tended to reflect avoidance of a larger marine predatory cottid, the Pacific staghorn sculpin Leptocottus armatus, but the predator overlapped more with prickly sculpin Cottus asper than with coastrange sculpin C. aleuticus. Survival of coastrange sculpin was reduced more than threefold in experimental assays that exposed juveniles to predation risk, which was statistically consistent with the principle of mortality-to-growth ratio (μ/g) minimization. A subsequent experiment measured foraging on depletable food patches during exposure to the threat of predation risk (from an enclosed predator that was prevented from causing lethal effects); juvenile and adult coastrange sculpin reduced their foraging effort 20-30% relative to a predator-free situation. Examining the foraging cost of predation for both coastrange sculpin and prickly sculpin yielded ambiguous results regarding the partitioning of resources and predator avoidance. Adults of each species differed in their responses to predation risk, but the juvenile comparison was complicated by variable resource densities (marine invertebrates) for each species.