Fisheries Induced Evolution in Sportfish Populations? a Comparison of Metabolic Rates in Replicate Exploited and Unexploited Populations of Largemouth Bass

Commercial harvest in the marine environment can cause evolutionary responses in target populations, but separating genetic from environmental effects on phenotypes is difficult.  Freshwater environments offer advantages for studies of fisheries induced evolution (FIE) due to the presence of replicate study systems.  Selective breeding with Largemouth Bass (Micropterus salmoides) has shown that angling vulnerability is heritable and correlates with elevated resting metabolic rates (RMR) and higher fitness.  However, whether or not such differences are present in wild populations, or simply a result of strong experimental selection regimes, remains unknown.  The present study sought to quantify differences in metabolic rates between replicate exploited and unexploited populations of largemouth bass.  We collected age-0 Largemouth Bass from two Connecticut drinking water reservoirs unexploited by anglers for almost a century, and two exploited reservoirs.  Field RMR for one individual from each population per day was quantified using intermittent-flow respirometry.  Individuals from unexploited reservoirs had mean RMR values 6% higher than individuals from exploited populations, and there were no further differences among the populations.  These findings are consistent with expectations of FIE on exploited populations, which suggest that recreational angling can act as an evolutionary force influencing the metabolic rates of fishes in the wild.