Low predator and conspecific density lead to larger juveniles

Abstract

Predation is a key size-selective mechanism structuring juvenile fish populations, given typically greater susceptibility of small juveniles in a population to predation compared to larger individuals. We tested the hypothesis that greater predator abundance selectively removes the smallest age 0 Atlantic cod (Gadus morhua) in nearshore habitat, truncating their size distribution in nursery habitats. We tested this hypothesis using fifteen years of historical data on nearshore fish abundance in Newman Sound, Newfoundland. Using skewness to estimate size-frequency distribution asymmetry, our analyses showed smaller age 0 cod were least prevalent under low predator and low conspecific densities. In contrast, high predator abundances corresponded to weak, size-selective removal of the smallest juveniles. Age 0 cod reached the largest sizes under lower predator and conspecific densities. Our analyses link size of individual juvenile fish in the wild with their survival, where predator abundance modulates the advantages gained by attaining larger size.