Mycteroperca microlepis

Gag grouper

IUCN Red List Assessment VULNERABLE (2018)

Female (upper) and male (lower) gag grouper. Credit: Chris Koenig

Range Description: This species has a disjunct distribution in the western Atlantic from North Carolina south along the U.S., Bermuda, throughout the Gulf of Mexico except Cuba, and in southern Brazil from the State of Rio de Janeiro to Santa Catarina. It is rare in Bermuda and otherwise is not known from the Caribbean or northeastern Brazil. Juveniles have been recorded as far north as Massachusetts in the U.S. and one record from Cuba is likely a waif. Its depth range is 0-167 metres.

Species Summary: The gag grouper is reef-associated species usually found offshore on rocky bottoms and occasionally inshore on rocky or grassy bottoms. Overall, the species prefers habitats characterized by maximum structural complexity. Adults are either solitary or in groups of 5 to 50 individuals. Juveniles primarily inhabit seagrass beds but also oyster reefs and shallow estuarine structures. The species primarily consumes fish, some crabs, shrimps and cephalopods. Live footage underwater: https://www.youtube.com/watch?v=PYRT8vKDLVs

Juvenile gag grouper about 14 cm long. Credit: Don DeMaria​

This species is a protogynous hermaphrodite . Females reach maturity between 3-6 years of age around fork lengths of 71 cm and sex change occurs between 75-111 cm TL and about 8 years. Maximum ages reported in different locations range from 17 to 31 years and maximum total length is 145 cm. The gag spawns in aggregations and can migrate, according to tagging studies, up to hundreds of kilometres to reach spawning sites which are located on shelf-edge reefs and rocky ridges next to drop-offs. Fish are known to aggregate in their hundreds. Males remain near spawning sites in deep water year-round and in December and January females form pre-spawning aggregations in shallower areas prior to migrating to the spawning aggregation sites. Aggregations form in February through mid-April in the southeastern U.S. and from January to March on the Campeche Bank off Mexico.

Adult gag on spawning aggregation site. It has been recently tagged. Madison Swanson ground, USA-80 m. Credit: NOAA/Chris Koenig

Fisheries: The species is heavily exploited by recreational and commercial fisheries throughout its range, including direct targeting of spawning aggregations. It is the second most common grouper species in commercial catches of the United States (exceeded by red grouper, Epinephelus morio) and the most important grouper in recreational catches.This species is taken by handline, bottom longline and speargun. Spawning aggregations are targeted by fishers. Juveniles are often taken as bycatch in the bait-shrimp fishery that operates in seagrass beds.

Management/Conservation: As a result of overfishing, spawning aggregations have been greatly reduced or no longer form in some areas, and adult sex ratios have become highly female-biased in most areas. In Mexico a seasonal closure of the grouper fishery (main focus is E. morio) from February 15 to March 15 has been in place since 2003 off Yucatan, Campeche and Quintana Roo: in 2017, this was extended from February 1 to March 31 (SAGARPA 2016). Gag grouper regulations for the U. S. are provided and involve spatial (from marine protected areas), seasonal (Jan1 -April 30), trip limit and minimum size measures https://safmc.net/regulations/regulations-by-species/gag-grouper/. The effectiveness of protective measure is uncertain.

Key Recent Publications on biology, trade, fisheries and management: or earlier publications, please refer to IUCN Red List Assessment and book on spawning aggregations. Also: https://www.springer.com/gp/book/9789400719798; ‘Groupers of the World’: https://www.nisc.co.za/products/32/books/groupers-of-the-world-a-field-and-market-guide

Biesinger, Z., Bolker, B.M., Marcinek, D. and Lindberg, W.J. 2013. Gag (Mycteroperca microlepis) space use correlations with landscape structure and environmental conditions. Journal of Experimental Marine Biology and Ecology 443: 1-11.

Jue, N., Coleman, F., Koenig, C. 2014. Wide-spread genetic variability and the paradox of effective population size in the Gag, Mycteroperca microlepis, along the West Florida Shelf. Marine Biology 161: 1905–1918.

Jue N.K., Brulé, T., Coleman, F.C. and Koenig, C.C. 2015. From shelf to shelf: assessing historical and contemporary genetic differentiation and connectivity across the Gulf of Mexico in Gag, Mycteroperca microlepis. PLoS ONE 10(4): e0120676.

Koenig, C.C. and Coleman, F.C. 2013. Protection of grouper and red snapper spawning aggregations in shelf-edge marine reserves of the northeastern Gulf of Mexico: Demographics, movements, survival, and spillover effects. SEDAR33-DW02. SEDAR, North Charleston, NC.

Koenig, C., Bertoncini, A.A. & Ferreira, B. 2018. Mycteroperca microlepis. The IUCN Red List of Threatened Species 2018: e.T14050A46910927. https://dx.doi.org/10.2305/IUCN.UK.2018-2.RLTS.T14050A46910927.en

Lombardi, L.A., Fitzhugh, G.R., and Barnett, B. 2013. Age, length and growth of Gag (Mycteroperca microlepis) from the northeastern Gulf of Mexico: 1978-2012. Panama City Laboratory Contribution 13- 01 SEDAR33-DW22.

Renán, X., Montero-Muñoz, J, Garza-Pérez, J.R.and Brulé, T. 2016. Age and stock analysis using otolith shape in Gags from the southern Gulf of Mexico. Transactions of the American Fisheries Society 145: 1252-1265.

SAGARPA. 2016. Agreement for modification of the ordinance about the seasonal closure of the capture of all grouper species in Mexican federal waters from Gulf of Mexico and Caribbean Sea, including the littoral of Campeche, Yucatán and Quintana Roo. In: López-González, A. (ed.), Diario Oficial de la Federación, Tomo DCCL, No. 9, Primera Sección. Secretaría de Agricultura, Ganadería, Desarrollo Rural, Pesca y Alimentación Secretaría de Gobernación, México D. F

Sauls, B. 2014. Relative survival of gags Mycteroperca microlepis released within a recreational hookand-line fishery: Application of the Cox Regression Model to control for heterogeneity in a large-scale mark-recapture study. Fisheries Research 150: 18-27

SEDAR. 2016. SEDAR 33 Update Report Gulf of Mexico Gag Grouper. Southeast Fisheries Science Center