Ontogenetic Spatial Distributions of Gag (Mycteroperca microlepis) and Red Grouper (Epinephelus morio) within the Northern Gulf of Mexico and Their Spatiotemporal Overlap with Red Tide Events

Mapping of fish populations is an integral component of an ecosystem approach to fisheries management, particularly for understanding the impacts of spatial processes such as harmful algal blooms. We develop age-specific spatial maps of gag (Mycteroperca microlepis) and red grouper populations (Epinephelus morio) in the northern Gulf of Mexico. We combined multiple fishery-dependent and -independent data sources to develop a logistic generalized linear model that predicted occurrence as a function of year, month, time of day, latitude, longitude, depth, sediment type, and the confounding factor of gear. Residuals were then kriged to map known areas of presence and the residual presence added to the model predictions. Resultant maps generally aligned with the current understanding of these species’ distributions in the region. Red grouper were estimated to have high probability of occurrence throughout the West Florida Shelf (depth <40 m). Both juvenile and adult gags were more likely to occur on the Florida Middle Grounds. The selected models predicted gag and red grouper abundances with an error rate ranging from 9.5-33%. Spatial analyses provided quantitative evidence of increased grouper exposure to red tide during severe years (e.g., 2005). These results support the continued consideration of red tide impacts on population dynamics.