Life history correlates of density-dependent recruitment in marine fishes

Abstract

Understanding the relationships among life history traits, density dependence, and population dynamics is a central goal in ecology. It is also vital if we are to predict how populations respond to and recover from exploitation. We used data for 54 stocks of commercially exploited fish species to examine relationships between maximum annual recruitment at low stock size and the density dependence of recruitment at high stock size. We then related these recruitment measures to life history. At low stock sizes, stocks with high maximum recruitment (maximum spawners per spawner) showed the weakest density dependence of recruitment at high stock sizes. Spawning biomass per recruit in the absence of fishing (SPRF=0) showed a strong positive correlation with both maximum spawners per spawner and the strength of density dependence. Stocks with high SPRF=0 were typically large-bodied, slow-growing, late-maturing, and highly fecund with long generation times. These stocks produced low numbers of recruits each year, but survived to breed repeatedly and had strong density dependence of recruitment. In contrast, small-bodied, early-maturing fish had high annual recruitment and weak density dependence. These results place species on a continuum from "highly reproductive" to "survivors". But we also demonstrate that density dependence is an important feature of the population biology of survivors.