Decoupling the Effects of Year Class Strength on Density Dependent Growth

Per capita productivity changes in fish populations resulting from competition for limited resources is likely expressed along a spectrum of density dependent mortality to density dependent growth. Simulations and pond/tank-based experiments have shown both increased mortality and decreased growth at high densities. Identifying and quantifying tradeoffs between population numbers and per capita productivity changes in populations with high recruitment variation has largely been ignored. We sought to determine if variations in density and year class strength resulted in density dependent growth of a seasonally exploited fishery. Using linear regression, yearly estimates of L_∞ were compared to relative density. Estimates were negatively correlated with density, however this relationship was not as strong as expected. Because of high variability in numbers at age, L_∞ estimated for each year class was also compared with year class strength. Again, the relationship between age-class specific L_∞ and year class strength was not as strong as expected. These results suggest that changes in mortality or prey density were also occurring during the same time period that mitigated changes in growth. Decoupling density dependence effects caused by recruitment variation can lead to a better understanding of plasticity in naturally fluctuating populations and better management of exploited stocks.