Louisiana Estuarine and Coastal Fisheries and Habitats: Perspectives from a Fish's Eye View

Abstract

Stimulated by nutrients from the Mississippi River, the vast coastal wetlands of the river's past and present deltas interface with the Gulf of Mexico to form a complex and prolific marine ecosystem. This highly productive system has yielded annual fishery landings of Ͼ453.6 ϫ 10 6 kg (1 billion pounds) since 1969. The Louisiana ecosystem has been heavily exploited and significantly altered over the years to meet the demands for coastal development, seafood production, navigation, oil exploration, flood control, and other social, economic, and industrial activities. While not all impacts can be viewed as detrimental to fisheries or their habitat, some of these habitat impacts have contributed to significant ecological problems such as saltwater intrusion, loss of coastal wetlands, and development of vast areas of hypoxia along the coast. Management strategies to deal with some of these problems propose directed manipulations of the coastal environments to stop or reduce rates of degradation. Over the past 46 years, fisheries yields from Louisiana waters have remained strong. Although quantitative data are lacking to examine more than a few decades of environmental changes, an analysis of fishery-independent trends for selected inshore species of nekton over a recent 21-yr period suggests that many species have been remarkably resilient to significant changes in their habitats and pressures from exploitation. Over a longer period (60 yr), more significant changes to inshore demersal trawl assemblages are apparent, but data are lacking to conclusively identify their causes or quantitatively document the magnitude of change. We review some of the major changes that have occurred in habitat believed to be essential to fishes and review other factors likely to be significant in structuring fish populations. Given the significant number of environmental impacts affecting the system, we also discuss potential reasons why more dramatic changes in nearshore and estuarine fish populations of coastal Louisiana are not apparent.

Demersal fish and invertebrate biomass in relation to an offshore hypoxic zone along the US West Coast

“…Prior studies suggested that as adult fish in open systems can migrate away from areas affected by hypoxia (Craig et al, 2001) impacts will most likely be confined to health effects, behavioral alterations and changes in habitat selection (Chesney and Baltz, 2001). Additionally, efforts to link changes in fish production to hypoxia are often obscured by fishing effects (Chesney et al, 2000). Nonetheless, even in open systems, serious, long-term impacts such as altered distribution, changes in trophic interactions and mortality of early life-history stages are predicted (Breitburg et al, 2001).…”

Population genetic structure across dissolved oxygen regimes in an African cichlid fish

“…Although hypoxia occurs naturally in systems characterized by low light and low mixing (e.g. heavily vegetated wetlands), the frequency of hypoxia is increasing globally through the influx of municipal waste and fertilizers that accelerate eutrophication (Chesney et al 2000;Pollock et al 2007). It has thus become increasingly important to understand the consequences of low-oxygen stress on fish populations.…”

“…3), little or no overlap occurs between 'normoxic' and 'hypoxic' sites within region (Figs 2 and 3). Moreover, waters with dissolved oxygen that drops below 2.8 mg/L (Diaz & Rosenberg 1995;Wu 2002) or 2.0 mg/L (Chesney et al 2000) have been considered hypoxic in previous studies. While the oxygen at the Manywa, Juma, and Dead Duck Bay sites often rose above these values (Fig.…”

Processing watershed‐derived nitrogen in a well‐flushed New England estuary

“…The inputs of anthropogenically derived nitrogen (N) to the oceans may now exceed inputs from natural sources (Howarth et al 1996;Vitousek et al 1997), and much of these loads pass through estuaries. Estuaries mediate the N flux between nitrogen-rich watersheds and nitrogen-limited coastal oceans and have been suggested as important sites for nutrient attenuation, cycling, and support of secondary production (Nixon et al 1996;Chesney et al 2000;Eyre 2000). Despite the importance of this link between fluvial and marine environments, there is currently an incomplete understanding of the mechanisms of N transformations, storage, and export within estuaries.…”