Hypoxia and Gulf Menhaden in the Northern Gulf of Mexico: Interactions and Implications for Management

Extensive seasonal hypoxia (dissolved oxygen (DO) ≤ 2 mg/L) occurs in the northern Gulf of Mexico (GOM) and overlaps spatially and temporally with the Gulf Menhaden Brevoortia patronus (GM) commercial fishery. For pelagic species like GM, indirect effects of hypoxia on distribution and movement are more prevalent than direct effects of exposure to low DO. Changes in the spatial distribution of harvested species can lead to changes in catchability, which, if not properly accounted for in stock assessments, can lead to inaccurate determination of stock status indicators and non-conservative management advice. We analyzed detailed harvest records and fine-scale spatiotemporal predictions of bottom DO to evaluate hypoxia effects on the dynamics of the GM fishery. We found nearshore and westward shifts in the fishery as concentrations of DO declined. We then used simulations of the current GM stock assessment model to test whether these shifts had implications for the management of GM. We found that changes in catchability of GM had important effects on model-derived management quantities only under the most extreme assumptions about the relationship between hypoxia and catchability. Our work demonstrates the utility of using fine-scale datasets and simulations to explore the management implications of eutrophication on coastal fisheries.