Effects of Fishery-Induced Sex Bias on Selection in a Wild Alaskan Sockeye Salmon Population

Concerns about fisheries induced evolution have primarily focused on changes in maturation and growth. Even though many fisheries are sex selective, less emphasis has been placed on changes in sex ratios, which may disrupt the dynamics of natural and sexual selection in wild populations. Here, we present data on reproductive success in a wild Alaskan sockeye salmon population, which shows highly female-biased sex ratios, likely because of male-selective fisheries on returning adults. The population is also under heavy bear predation in their spawning creek, which likely selects heavily against larger and deeper-bodied fish. In 2004, four distinct waves of spawning adults were observed, with proportion of males ranging between 18 and 45%. Preliminary analyses suggest that small males were more successful than larger males at low relative male abundance, while no differences were found at more even sex ratios. Strikingly, sex ratios also affected the reproductive success of females – large females were more successful when sex ratios were even, while there was no selection when males were rare. The interaction between bear predation, selective fisheries and sexual selection produced complex patterns of reproductive success. Sex selective fisheries may cause considerable modifications in patterns of sexual and natural selection in wild populations that may impact individual reproductive success and local adaptation.