Effects of hypoxia on the shrimp fishery of Louisiana and Texas

Large-scale hypoxia, recently approaching 20,000 km(2), overlaps with habitat and fishing grounds of commercial shrimp species in Louisiana and Texas shelf waters. It is expected that an environmental impact of this magnitude would have an effect on the shrimp population that is reflected in catch statistics. In this paper, we examine the geographic distribution and amount of shrimp catch in relation to location and size of the hypoxic zone. The results are interpreted in context with what is known about the life cycles and habits of the two shrimp species involved and the behavior of shrimp fisheries. A significant negative relationship was evident between catch of brown shrimp from Texas and Louisiana waters versus the relative size of the mid-summer hypoxic zone. In addition, Texas catch was significantly dependent upon Louisiana catch, a relationship that has become stronger since 1980. Catch per unit effort of brown shrimp also has declined significantly during a recent interval in which hypoxia was known to expand. Importantly, the same relationships were not significant between hypoxia and catches of white shrimp. As hypothesized, owing to their more offshore habitat requirements, brown shrimp were impacted to a greater degree than white shrimp. The annual success of shrimp fisheries, like most commercial fisheries, is highly related to environmental factors. The combined evidence indicates that hypoxia in Louisiana, due to its large area of coverage, has increased as an environmental factor for shrimp in recent decades.