Abstract

The northern Gulf of Mexico supports substantial commercial and recreational fisheries. While landings have remained strong throughout recent years, the seasonal formation of hypoxic bottom waters is a threat to longterm sustainability of regional fisheries production. Because nekton are mobile, the greatest threat to fisheries resources is likely to be the effects of reduced oxygen on habitat quality, potentially forcing movement of individuals away from favorable habitat as well as altering migration pathways. As a basis for understanding potential effects of hypoxia on nekton in the northern Gulf of Mexico, we explored temporal and spatial patterns of community structure in coastal Louisiana and Mississippi. We defined community structure in terms of relative densities of sixty-six species that were either abundant, of commercial and/or recreational importance, or thought to be especially susceptible to hypoxia. Several fisheries-independent data sources were summarized to generate yearly density summaries by season (summer and fall), bathymetry (inshore, nearshore and offshore), and alongshore zones (central Louisiana and eastern Louisiana/Mississippi). Differences in community structure were most pronounced bathymetrically; densities of most species varied significantly among depths. Alongshore differences were less prominent, and were primarily driven by higher densities of bay anchovy in the eastern zone as well as higher densities of Atlantic croaker and commercially important macroinvertebrates in the central zone within inshore waters. Seasonal differences in community structure were most evident in nearshore zones as well as inshore in central Louisiana, areas historically prone to the formation of hypoxic waters. Although no substantial long-term changes in community structure were detected, temporal coverage of these data sets (1982 - 2000) may be inadequate to identify temporal alterations due to a shifted baseline. Future efforts that expand the spatial and temporal coverage of these analyses, incorporate environmental variability, and focus on areas especially susceptible to hypoxia are recommended.

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