Frequency of Strong Year Classes: Implications for Three Life-History Strategies of Fishes

We examined how the frequency of strong year classes affects fish harvest and size structure for three fish species with varying life histories.  Random and systematic occurrence of strong year-classes were modeled for white bass Morone chrysops (short lived), largemouth bass Micropterus salmoides (intermediate longevity), and blue catfish Ictalurus furcatus (long lived).  For white bass and largemouth bass, intermediate strong year-class frequencies incrementally reduced harvest but improved population size structure under current fishing regulations.  Greatest improvements in size structure, with minimized harvest reductions, occurred with strong year classes every three years for white bass and five years for largemouth bass.  In contrast, strong year classes of blue catfish every six years maximized harvest and resulted in a fivefold increase in PSD, compared to strong year classes every one or two years.  Annual variability in harvest and size structure was reduced for intermediate- and long-lived fishes in systematic relative to random models; variability was not reduced by systematic strong year-classes for short-lived fishes.  Our results suggest that intermediate frequencies of strong year-class production, relative to species life history, serve to balance harvest and size structure characteristics.