Disentangling the effects of size-dependent encounter and susceptibility to predation with an individual-based model for fish larvae

Abstract

We investigated the effects of size-dependent encounter and susceptibility, the role of variation in the size distribution of predators, and the timing of prey-predator interaction during the larval phase in shaping the length frequency distribution of surviving fish larvae. These analyses based on general empirical size-dependent relationships may have broad implications in understanding larval fish cohort dynamics. We demonstrated that the formulations of encounter and susceptibility to predation counteract each other, an increased range of predator sizes reduces only slightly the evidence for size-selective mortality, and synchronous spawning and hatching events have the potential to yield strong size-selective mortality of a cohort of fish larvae. The important factors in generating size-selective mortality are either the timing of encounters between fish larvae and their predators or high mortality rates. We demonstrated a direct relationship between the potential of size-selective mortality and the overall mortality rate of the cohort. We suggest that it may be difficult to detect the effect of size-dependent processes in the field. A better understanding of the factors influencing encounter represents a critical element in extrapolating laboratory studies of predation to the field.