Effects of large-scale hypoxia on the distribution of brown shrimp (Farfantepenaeus aztecus) and Atlantic croaker (Micropogonias undulatus) in the northwestern Gulf of Mexico

The distribution of abundance in space reflects the relationship of a species to its environment. The distribution of aquatic organisms is influenced by multiple biotic and abiotic factors, as well as their interactions. Shifts in distribution when environmental conditions change may have consequences for processes that impact fitness. Using long-term, fishery-independent trawl surveys, I examined factors influencing the distribution of brown shrimp ( Farfantepenaeus aztecus) and Atlantic croaker (Micropogonias undulatus) on the northwestern Gulf of Mexico continental shelf.; The distribution of croaker was positively density-dependent, expanding in years of high abundance, while that of brown shrimp was negatively density-dependent, contracting in years of high abundance. These effects, however, were relatively weak and varied with size, sex, and the amount of habitat loss due to hypoxia. The lack of strong density-dependence in the distribution of these species raises questions regarding the generality of density-dependent geographic distributions that are commonly reported for other species and ecosystems.; The distribution of croaker and brown shrimp shifted both inshore and offshore during years of extensive hypoxia. Shrimp and croaker aggregated along the offshore edge of the hypoxic region, with catch rates declining exponentially with increasing distance from the edge. These shifts in distribution altered the temperatures that croaker and shrimp occupied, with croaker occupying cooler temperatures and shrimp warmer temperatures during years of extensive hypoxia. Shifts in temperature distribution associated with displacement inshore and offshore of the hypoxic region ranged from 2–6°C for both species. These results suggest hypoxia may alter growth rates of croaker and shrimp simply as a result changes in the temperatures occupied.; Brown shrimp are the target of an intense commercial fishery and croaker comprise a large component of the bycatch of this fishery. The degree of association between shrimp and croaker increased during years of extensive hypoxia. The distribution of shrimping effort also shifted offshore during years when hypoxia was extensive and distributed relatively close to shore. These results suggest the potential for bycatch interactions are intensified during years of extensive hypoxia, particularly in the vicinity of the inshore and offshore edges of the hypoxic region.