Variability in survival of larval fish: Disentangling components with a generalized individual-based model

Many factors, including intrinsic characteristics of the fish themselves and extrinsic factors of the biological environment, have the potential to regulate mortality rates during the early life of fishes. We used a detailed simulation model to rank the effects of variability in these factors on larval and early juvenile survival. Our major finding was that proportional changes in the intrinsic and extrinsic factors in the model had equal effects on cohort survival. Of the intrinsic factors, growth capacity (metabolism and assimilation efficiency), not foraging ability or starvation resistance, explained the most variance in survival. Of the extrinsic factors, predator size explained 83% of the variability in survival but proportional changes prey availability had only a minor effect. Variability in prey density required a 3-fold increase to equal the effects of predator size on survival. Despite the important effects of predation pressure on survival, it had only a minor impact on how fish died. Whether fish died from predation or starvation depended much more on the intrinsic variables related to metabolism and starvation resistance and on the density of the smallest prey type.