The northern Gulf of Mexico has some of the most productive estuarine-based fisheries in the United States. Over the past two decades, though, the ecosystems in this region have experienced large-scale natural and anthropogenic disasters. To assess the status of the local aquatic organisms and habitats, we analyzed fishery-independent data from trawl and beach seine samples collected over three decades (1986-1995, 1996-2005, and 2006-2015) during spring (April-June) and fall (September-November) from southeastern Louisiana, Mississippi Sound, and coastal Alabama. Our first goal was to determine if these three areas differed in regard to aquatic community species composition and environmental conditions (including static habitat conditions). We defined the aquatic community as consisting of all finfish species combined with three ecologically and economically important crustacean species: Blue Crab (Callinectes sapidus), Brown Shrimp (Farfantepenaeus aztecus), and White Shrimp (Litopenaeus setiferus). Our second goal was to determine if individual species and environmental conditions changed from 1986-1995 to 1996-2005 to 2006-2015, with an emphasis on detecting which species experienced the most significant declines during this period.
Results/Conclusions
Species composition differed significantly among the three states in trawl collections for both spring (ANOSIM, R=0.543, p<0.001) and fall (ANOSIM, R=0.722, p<0.001) while beach seine collections were not significantly different across the states for either the spring (ANOSIM, R<-0.06, p=0.61) or fall (ANOSIM, R<0.167, p=0.14). The greatest habitat factor contributing to these differences was the presence of more shell substrate at the Louisiana sites (LINKTREE analysis, B%=86, p<0.05). While 31 species exhibited significant (INDVAL, p<0.05) declines in at least one state-season-gear scenario over the three decades, Blue Crab and Least Puffer (Sphoeroides parvus) experienced the most declines overall. Four species of flatfishes also experienced multiple declines over the same period. Louisiana trawl sites became significantly more saline in both seasons over time while Mississippi spring trawl sites and Alabama trawl sites for both seasons became significantly warmer (ANOVA, p<0.02 for all comparisons). The observed declines in relative catch and occurrence of important species in parallel with large-scale environmental changes emphasize the need for continued monitoring and expanded assessment of the cumulative effects of climatic variability and harvest impacts on the sustainability of estuarine-based fisheries and associated populations.