Mercury in Seafood May Rise with Global Warming
April 25, 2012 -
Whole Foods, the Texas-based natural foods supermarket, no longer carries fish considered to be unsustainable. The Whole Foods ban includes fish that is either overfished or caught in a harmful way, according to their website. The popular Atlantic Halibut made the list, though the company will still sell Atlantic cod that is caught by hook and line or gillnets. "Stewardship of the ocean is so important to our customers and to us," David Pilat, the global seafood buyer for Whole Foods told the New York Times. "We're not necessarily here to tell fishermen how to fish, but on a species like Atlantic cod, we are out there actively saying, 'For Whole Foods Market to buy your cod, the rating has to be favorable.'" Here's a look at the list of fish that the superstore no longer sells and why.
Octopus Whole Foods uses ratings set by the Blue Ocean Institute, a conservation group, and the Monterey Bay Aquarium in California. The ratings are based on factors including how abundant a species is, how quickly it reproduces and whether the catch method damages its habitat.
Imported Wild Shrimp "At Whole Foods Market, we've been saying that our mission is to sell only wild-caught fish that has been responsibly caught. For a few years now, we've used color-coded sustainability ratings, from green (best choice) to red (avoid), to help you make an informed choice. Now we're putting our mackerel where our mouth is: To support greater abundance in our oceans, we're no longer carrying red-rated wild-caught seafood!" the company wrote on its blog.
Tuna (from specific areas and catch methods rated "red") On their website, Whole Foods says that they stopped selling "species that were extremely depleted in the oceans, such as orange roughy, shark and bluefin tuna" years ago. The company uses the sustainability ratings of the Marine Stewardship Council (MSC).
Rockfish According to the Monterey Bay Aquarium, "In recent years, reduced fishing has allowed many rockfish populations to recover from low levels. Gear concerns remain, however -- trawl-caught rockfish should still be avoided."
Swordfish Some of the gear used to fish swordfish "accidentally catches sea turtles, seabirds and sharks," according to the Monterey Bay Aquarium.
Skate Wing Skates are in the overfished category. Most are also caught with bottom trawls, which result in high levels of accidental catch.
Sturgeon According to Monterey Bay Aquarium, "Sturgeon farmed in the U.S. is a good alternative to most wild sturgeon, whose populations have seriously declined due to overfishing for sturgeon eggs (caviar)."
Tautog Also known as black fish, Tautog are considered a "vulnerable" species. They are found close to shore on hard-bottom habitats, occasionally entering brackish water.
Trawl-Caught Atlantic Cod Fishermen often catch cod with bottom trawl, large nets that skim across the seafloor. Trawling, according to the Monterey Bay Aquarium, "damages marine habitats and produces bycatch."
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Turbot A cousin of Pacific halibut, turbot are a right-eyed flatfish -- as they develop, their left eye migrates across the top of the skull toward the other eye on the right side. Turbot are yellowish or grayish-brown on top and paler on their underside.
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High levels of methylmercury are known to accumulate in the fatty tissues of large ocean-going fish such as tuna, swordfish and marlins. Though most people do not eat enough of these types of fish to result in mercury poisoning, pregnant women are advised to restrict their intake because of the risk to the fetus.
Now it looks like climate change may make the consumption risk even greater.
Biologists observed higher accumulation of methylmercury in killifish, a small fish, as temperatures increased both in the wilderness of Maine and in laboratories.
The contamination levels in the fish may increase with temperature because the metabolism of the tiny fish speeds up in warmer water, according to the recent research published in PLOS ONE. The cold-blooded fish eat more and thereby pick up more methylmercury from the environment.
Coal-burning power plants produce most of the mercury pollution in the atmosphere. When the mercury falls back to Earth’s surface it lands either in the ocean or on land where it can be washed into lakes, streams, and eventually the ocean. Certain bacteria transform the mercury into methylmercury, a more toxic form. After this bacterial conversion, the methylmercury enters the food chain, accumulating in fatty tissues. When people worry about mercury in their fish and other seafood, it is actually this bacterially-altered form of methylmercury.
In the lab, the biologists conducting the study replicated the increasing temperatures likely to occur as climate change continues. The highest levels of mercury contamination occurred in the fish in the warmest water (27 degrees Celsius or 80°F). They also fed the fish mercury-enriched food. “The fish in warmer waters ate more but grew less and had higher methylmercury levels in their tissues,” the authors reported in a press release.
In nature, killifish from different salt marsh pools on the coast near Wells, Maine, served to also replicate the effects of varying degrees of temperatures. The water in some pools reached higher temperatures than others, ranging from 18 to 22 degrees Celsius (65°F to 72°F). Once again, the warmer pools held fish with greater levels of mercury, even though they were only feeding on insects, worms and other natural food sources.
Many larger fish feed on the killifish, varieties of which live around the globe. Mercury in the smaller fish transfers to the larger fish. Mercury continues to build up in the food web, until it reaches the top predator on the planet, us.