Saturday, November 14, 2009

Dead Zones, Conservation and Commercial Fishing

I’ve just read in the local news that Kevin Craig from the Florida State University’s Coastal and Marine Laboratory will be heading-up a collaborative four-year project funded by NOAA's Northern Gulf of Mexico Ecosystem and Hypoxia Assessment Program. The project’s goal is to assess the impact of the Gulf of Mexico’s ‘dead zone’ on marine ecosystems with a particular focus on shrimp and the shrimping industry.

It has long been known that agricultural run-off carrying excesses of fertilizer from the ‘bread basket’ of the United States are finding their way into the tributaries of the Mississippi River, and in turn, into the Gulf of Mexico. Once in the Gulf they consequently spawn explosions of algae growth resulting in hypoxic conditions and the conception of massive Dead Zones. Surges in the growth of algae and other noxious plants as a product of fertilizer facilitated Nitrogen and Phosphorous loading is called eutrophication. Eutrophication leads to de-oxygenated environments, and the resultant death of those organisms that require oxygen - of which there are many. The loss of oxygen-dependent organisms leaves vacant important positions in long established food-webs, potentially leading to the total breakdown of ecosystem function. To make matters worse, far from being stationary the dead zones move or “creep” from their epicenters corrupting ecosystems both far and wide. For Florida, the Gulf of Mexico Dead Zone may contribute to “Red Tide” and the death of everything from phytoplankton to manatees in the State’s coastal waters.

Kevin Craig is certainly the person for the job; back in 2005 he wrapped-up a research project that examined the effects of hypoxia on the abundance and distribution of Farfantepenaeus aztecus - the Gulf of Mexico’s ‘brown shrimp’. In that study, Craig, Larry Crowder, and Tyrrell Henwood used shrimp trawl surveys to compare the distributions of shrimp between hypoxic and non-hypoxic areas. What the team found was that the spatial distribution of shrimp in hypoxic regions was substantially different that those associated with non-hypoxic areas. The researchers also concluded that the effects of hypoxia contributed to as much as a 25% loss in F. aztecus’s available habitat.

The new NOAA funded project will undoubtedly have implications for both the science of ecology and in that of conservation. Shrimping is a major industry in the United States, and as such the participating fishermen and other commercial industries hold considerable economic and political clout. I'm eerily reminded of the warnings from biologists that were left unheeded and initially overthrown by rule-makers during the collapse of the Northern Cod Fishery…

Craig, J., Crowder, L., & Henwood, T. (2005). Spatial distribution of brown shrimp (Farfantepenaeus aztecus) on the northwestern Gulf of Mexico shelf: effects of abundance and hypoxia Canadian Journal of Fisheries and Aquatic Sciences, 62 (6), 1295-1308 DOI: 10.1139/f05-036

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