Status and Trends of Marbled Grouper in the North-Central Gulf of Mexico

Marbled Grouper Dermatolepis inermis were categorized as near threatened by the International Union for Conservation of Nature in 1996, and the status of the species was set for review in 2018. Analysis used to support its global threatened status included basic parameters, such as numbers seen in a year and spatial maps of positive observations, but included no statistical approaches to interpret abundance trends. In an effort to improve the understanding of Marbled Grouper status and trends, we used the Southeast Area Monitoring and Assessment Program reef fish video survey time series in the northern Gulf of Mexico, USA, to estimate relative abundance, proportion of positive stations, and the impact of habitat variables on fish abundance. Marbled Grouper were consistently observed in low numbers on the Louisiana shelf-edge banks throughout the survey. Generalized linear mixed models using a negative binomial data distribution showed significant effects for the presence of reef and depth, while the percent coverage of rock was marginally significant. These results indicate that detection and abundance of Marbled Grouper are strongly associated with high rugosity and deep (60-100 m) reef tracts. Interpretation of annual trends was difficult due to high interannual variability, but the data appear to show no detectable trends. Given that the previous classification of near threatened was based primarily on the consistent but rare observation of the species in its preferred habitat on a global basis, and given that the annual indices produced for the northern Gulf of Mexico region were highly variable, we recommend that the current International Union for Conservation of Nature regional status be maintained. This study highlights the utility of optical surveys for collecting data on species that are rare or that are not observed using traditional fisheries sampling gears and also indicates the importance of synchronous collection of habitat information.