Evolutionary and demographic impacts of sex change rules and size-selective exploitation on sequential hermaphrodites

Abstract Relatively few studies have addressed fishery-induced-evolution of sequential hermaphrodites although declines in the mean size-at-maturation and/or sex change have been documented for several species. We sought to explore the evolutionary impacts of size-selective exploitation on maturation and sex change of a protogynous hermaphrodite using an individual-based model accounting for growth, survival, maturation, sex change, and reproduction. Because sex change rules are unknown for many exploited species, critical size-at-sex change (static and genetic control) and social control of sex change were evaluated to determine how life-history-traits (maturation, sex change) and population reference points change due in part to evolution. When simulating critical size-at-sex change, mean length-at-maturation increased, contrary to typical predictions for dioecious species, and mean length-at-sex change decreased (when under genetic control) from exploitation. These changes occurred slowly and resulted in lower male: female sex ratios, sperm limitation, and extirpation at high exploitation rates. Under social control of sex change, both the mean lengths-at-maturation and sex change decreased relatively rapidly from exploitation. These populations maintained high male: female sex ratios, avoided sperm limitation, and withstood higher exploitation rates than critical size-at-sex change populations. Results from these models highlight the need for a better understanding of sex change rules for exploited hermaphrodites.