Immature and mature female Red Snapper habitat use in the north-central Gulf of Mexico

Abstract Red Snapper (Lutjanus campechanus) is a popular reef-associated fish species in the northern Gulf of Mexico (GOM) that supports both commercial and recreational fisheries. In this region, there is a large overlap in fork length (FL, 90%) and age (93%) range between mature and immature females. Therefore, here we investigate how age and FL of mature and immature female Red Snapper vary by artificial reef type and depth. Red Snapper (n = 695) were sampled using vertical long lines from March or April through November of 2016 – 2018 off the coast of Mississippi at different artificial structure types (platforms, artificial reefs, rigs-to-reefs) and depths (shallow, 20 m; mid, 20-49 m; deep, 50-100 m). To investigate habitat use of mature and immature fish respectively, we developed linear mixed-effects models. For both immature and mature fish, FL and age increased significantly with depth. Immature fish captured at artificial reefs were older than those captured at platforms, and mature fish were older and had longer FL at rigs-to-reefs than platforms and artificial reefs. The effect of depth on FL or age did not differ between mature and immature fish while the effect of structure types did. First, structure types were important to predict FL for mature fish, but not for immature fish. In addition, the differences in age between rigs-to-reefs and both platforms and artificial reefs were significantly larger in mature fish than in immature fish. Larger and older mature females are found at deeper depths where fishing pressure is lower, while smaller and younger, immature fish are most often found in shallower, reef-based areas where pressure is highest. These spatial differences in maturity can help inform management regulations for the species.