Fisheries-Induced Evolution in Largemouth Bass: Linking Vulnerability to Angling, Parental Care, and Fitness

Long-term studies in Ontario, Canada on Largemouth Bass Micropterus salmoides and Smallmouth Bass M. dolomieu have demonstrated that angling nesting males (both catch and harvest and catch and release) can have negative impacts on the reproductive success for the captured individual. They have also demonstrated that within a population, the male bass that provide the best and longest parental care for their offspring are the most capable of having the greatest relative contribution to the year-class. Furthermore, those males are also the most aggressive toward potential brood predators and, hence, the most vulnerable to angling. Based on those relationships, we postulated that angling in general, and especially angling for nesting bass, results in selection against aggressive individuals in a population, and as a result, the angled population evolves to become less aggressive, containing males with diminished parental care attributes, an example of fisheries-induced evolution (FIE). We recognize, however, that some change towards less aggressive behaviors may also result from learning and phenotypic plasticity. Controlled, long-term selective breeding experiments over 30+ years have, however, documented the heritability of vulnerability of bass to angling and, hence, the potential for selection to act on that trait. Reproductive competition experiments further demonstrated that the highly vulnerable strain of bass produced in those selective breeding experiments indeed had greater reproductive success than the less vulnerable strain. Because angling for Largemouth Bass has been occurring for decades, we also postulated that there should be some evidence in the wild of this FIE. In fact, we did find that the level of vulnerability to angling of nesting male Largemouth Bass in lakes that have had little to no exploitation was significantly greater than that observed for nesting males in moderately and heavily angled populations.