Management of protogynous hermaphrodites: Using gag grouper as a case study

Groupers are demersal reef-associated fishes that can be found across tropical and subtropical latitudes, where many support important recreational and commercial fisheries. In the GOM, these include red grouper Epinephelus morio, gag Mycteroperca microlepis, black grouper M. bonaci, scamp M. phenax (pictured), yellowedge grouper Hyporthodus flavolimbatus, warsaw grouper H. nigritus, and snowy grouper H. niveatus.

Many groupers are sequential protogynous hermaphrodites, being born females and transitioning to males. Management of protogynous hermaphrodites may be tricky, as traditional stock assessments focus on female spawning stock biomass. While managing protogynous hermaphrodite stocks, managers must also be aware of potential sperm limitation within the populations. This is currently an issue of concern while trying to manage gag in the GOM, where recent studies estimate the gag male sex ratio to be under 10% (Lowerre-Barbieri et al. 2020).

To further complicate their management, gag demonstrate complex spatial dynamics. in the GOM, spawning peaks around springtime and occurs near the shelf edge (> 50m). Males reside in the deep spawning grounds year-round, while females and transitionals (females in the process of transitioning to males) migrate to the spawning grounds from shallower waters. Larval pelagic development is believed to last 30-60 days before settling in estuaries where juveniles spend months growing in seagrass meadows. Around age 2, the juveniles start moving out to nearshore/coastal waters where they recruit to the fisheries.

As a slow-maturing species, it takes around 2-4 years for gag to reach sexual maturity and over 10 years to transition to males (Lowerre-Barbieri et al. 2021). Consequently, most of the landings are female fish. While male gag may have some natural protection from fishing mortality by being furthest offshore, it is believed that the harvest of transitionals in the female groups migrating to deeper waters during spawning season may be contributing to a bottleneck effect in male recruitment (Lowerre-Barbieri et al. 2021). Ongoing research by Dr. Susan Lowerre-Barbieri (Florida Fish and Wildlife Conservation Commission and the University of Florida) is trying to address these concerns.

References

Lowerre-Barbieri, S., H. Menendez, J. Bickford, T. S. Switzer, L. Barbieri, and C. Koenig. 2020. Testing assumptions about sex change and spatial management in the protogynous gag grouper, Mycteroperca microlepis. Marine Ecology Progress Series 639:199-214.

Lowerre-Barbieri, S., H. Menendez, and C. Friess. 2021. Gag grouper reproduction in the Gulf of Mexico. SEDAR72-DW-08. SEDAR, North Charleston, SC. 26 pp.