Effects of Variable Mortality and Recruitment on Performance of Catch-Curve Residuals as Indicators of Fish Year-Class Strength

Abstract

We built a simulation model to assess the performance of catch-curve residuals as an index of year-class strength for a short-lived and a long-lived fish life history type across a range of assumed values for the variation in recruitment (CV _R ) and fishing mortality (CV _F ). The magnitude of CV _R strongly influenced the utility of catch-curve residuals in assessing year-class strength. The probability of finding a significant correlation between catch-curve residuals and true recruitment values exceeded 0.9 when CV _R was greater than 0.5 for the long-lived and greater than 1.0 for the short-lived life history types. This suggests that larger recruitment values have a greater probability of being successfully “tracked” through the age structure. Conversely, the magnitude of interannual variation in fishing mortality weakly influenced the performance of catch-curve residuals. The inspection of individual catch-curve residuals relative to the known recruitment values that produced them showed considerable scatter, indicating that the utility of this metric in assessing individual year-class strength is small. Sensitivity analyses showed that the performance of catch-curve residuals improved modestly with equal sampling vulnerability across ages and decreased slightly with increased fishing mortality. Our results suggest that catch-curve residuals can serve as a rudimentary measure of recruitment under ranges of recruitment and mortality variation similar to those frequently observed in field studies.