Fishing and Eutrophication Effects on the Northern Gulf of Mexico Demersal Nekton Community

The northern Gulf of Mexico (nGOM) has historically been one of the most productive fishery ecosystems in the United States, but has been subject to increasing eutrophication and associated hypoxia (DO ≤ 2 mg l^-1) as well as an intense shrimp bottom trawl fishery.  We quantified spatial and temporal patterns in several ecosystem indicators over 25 years (1987-2011) of  trawl surveys in relation to annual variation in shrimping effort and hypoxia severity. Temporal trends in species biomass, diversity, and pelagic to demersal ratio were strongly related to recent (post 2000) declines in shrimping effort and only weakly related to annual measures of hypoxia severity. These patterns were strongest for targeted (penaeid shrimp) and bycatch (several demersal fishes) species of the shrimp fishery and were similar across regions (Louisiana vs. Texas) differing in hypoxia severity, further indicating they were associated with changes in the shrimp fishery. Our results indicate that recent striking declines in shrimping effort have identifiable effects on population, community and ecosystem indicators, and that efforts to quantify the population- and community-level effects of hypoxia in harvested ecosystems must account for fishery dynamics and associated effects on both target and bycatch species.