Shrimp trawling may boost mercury in red snapper, stud...( Fishery experts have known for years...)

Fishery experts have known for years that shrimp trawling operations in the Gulf of Mexico are contributing to sharp declines in the ranks of Red Snapper, one of the most delicious and popular marine fish on the seafood menu.

While it's clear that thousands of young snapper are killed and wasted after being inadvertently "by-caught" in shrimp nets, new research from Texas Christian and Louisiana State universities finds shrimp trawling also may be raising the level of toxic mercury in juvenile snapper.

"Our study demonstrates that mercury concentrations are elevated in juvenile red snapper in coastal areas where commercial shrimp trawling occurs," says Matthew Chumchal, Ph.D., an assistant professor of biology at Texas Christian University in Fort Worth.

Titled the "Effect of Trawling and Habitat on Mercury Concentration in Juvenile Red Snapper from the Northern Gulf of Mexico," the paper is in the November 2008 issue of the journal Transactions of the American Fisheries Society, vol. 137, number six.

Co-authors include R. J. David Wells and James H. Cowan Jr., both of the Department of Oceanography and Coastal Sciences, Louisiana State University (LSU), Baton Rouge.

Chumchal, an aquatic ecologist who specializes in mercury contamination of fish and other aquatic organisms, notes that Red Snapper typically have lower mercury levels than many other marine fish on the menu, such as larger tuna and swordfish. He also emphasizes that nothing in his study suggests that trawling in itself raises mercury to levels that pose a public health concern.

The key point, he suggests, is that this study establishes a clear relationship between mercury levels in fish and the disturbances caused by dragging a huge net through delicate coastal marine environments, a process that stirs up sedimentary deposits of mercury and may alter the composition of the predatory food chain.

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