Contrasting Patterns of Maturity and Sex Transition in the Protogynous Hermaphrodites; Gag (Mycteroperca microlepis) and Red Grouper (Epinephelus morio)

Gag and Red Grouper in the Gulf of Mexico are heavily fished protogynous hermaphrodites. Increased fishing mortality on hermaphrodites can shift sex ratios and affect age and size at maturation. It appears that Red Grouper may compensate for both impacts by maturing and transitioning earlier, while Gag do not. In the 1960s Red Grouper matured between 5-6 years at >500 mm, with 50% male by age 16. Now Red Grouper mature at ~2.8 years and 292 mm, with 50% male by 11.2 years, and the population is ~28% male. For Gag however, males are substantially larger than females, transition begins ~age 5, and the population is currently 2-5% male, a significant drop from the 15-20% male observed in the 1970s. Differences in the mating system may explain the difference in ability to compensate. Red grouper have broadly distributed size-structured harems, which may socially mediate the process of sexual transition. Gag may compete to monopolize matings and remain at the best spawning sites (a lek) and thus may select for large male body size at the expense of resiliency. A significant increase in 11-ketotestosterone in Gag during summer months provides a physiological mechanism to suppress sexual transition in young Gag.