Environmental attributes of red snapper clusters in the Gulf of Mexico

Red snapper (RS) is one of the most important managed species in the northern Gulf of Mexico (nGOM) because of its high value to commercial and recreational fisheries. Stocks have been severely depleted and continue to be “overfished” despite management measures for their recovery. Understanding RS spatial distribution patterns and which factors are useful in predicting (un)favorable habitat may assist managers in devising more effective stock management strategies. We analyzed juvenile RS catch data collected by the NMFS fisheries-independent surveys over 21 years in the nGOM. To select and examine the environmental drivers of juvenile RS occurrence, we constructed a classification tree on presence/absence of RS using 30+ predictors, including bathymetric, biological, geographic and anthropogenic categories.

Our multivariate model retained 18 environmental predictors. The most influential were bathymetric followed by geographic and biological predictors; physical and anthropogenic categories ranked lowest. Notably, complexity in predictors was related to scale and location. For instance, the “Western Coastal” cluster required the most partitions and was the only cluster where both anthropogenic variables, oil/gas platform density and shrimping effort, were useful predictors. 21% of the observations, were classified by the first split as absence of RS attributed to habitat that was either too shallow (depth strata < 13m) or too deep (> 73m). The “Western Offshore” cluster had the highest probability of predicting presence of RS. In this group, a few shallower and deeper strata, corresponding to ranges of 15-18m and 27-55m, respectively, had very high probability of RS presence (0.86), accounting for about 1/3 of the presence cases. Our findings may provide useful insights to prioritize Essential Fish Habitat for red snapper in the nGOM.