Hypoxia in the Neuse River Estuary: Responses of Blue Crabs and Crabbers

The fishery for blue crab Callinectes sapidus is the most valuable commercial fishery in North Carolina. In 1998, hard blue crab landings totaled more than 27 metric tons and were worth US$40.5 million. This fishery depends on a healthy estuarine habitat for crab growth and survival. In addition, nearly all the landings are taken in shallow estuaries and sounds. Like estuaries all over the United States, the Neuse River estuary, North Carolina, receives substantial nutrient loading. A shallow, wind-driven system, it experiences only intermittent density stratification and subsequent hypoxia. Blue crabs respond to this spatially and temporally dynamic hypoxia by moving to the oxygenated shallow edges of the river. When the system is well oxygenated, blue crabs also can occupy the deeper habitats in the river. Categorical and regression tree analyses show crabs occupied habitat with oxygen concentrations above 2.4 mg/L. We estimated average temporary habitat loss attributable to low oxygen in our study area as 27% in 1997 and only 7% in 1998. We also surveyed Neuse River crabbers to determine how they respond to environmental variation in oxygen and subsequent crab movements. Crabbers recognize water with low oxygen content as “dead water” and consider poor water quality a threat to their fishery. Nearly all the crabbers we interviewed respond to intermittent hypoxia in the estuary by moving their pots and so are able to fish adaptively in response to this environmental variation. However, if these zones with low dissolved oxygen concentrations grow larger or persist longer, crowding of crab pots could lead to more intense interactions among crabbers and potentially impact the sustainability of the resource.