Deep Sea Mercury Mystery Solved
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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Predatory fish that feed deeper in the Pacific Ocean, including swordfish, accumulate higher levels of dangerous mercury than piscine predators at the surface, such as yellowfin tuna, but biologists weren’t sure why. Environmental scientists recently uncovered the cause and warned that the threat may increase in the future.
Oceanic bacteria transform the element mercury into toxic methylmercury. At the surface, sunlight destroys up to 80 percent of the methylmercury produced by these bacteria, according to a recent study published in Nature Geoscience. However, in murky waters between 165 to 2,000 feet (50-610 meters) below the ocean’s surface, methylmercury remains in the food web as bacteria devour mercury-contaminated detritus sinking from the surface.
Those bacteria become food for other creatures and mercury thereby spreads through the Pacific’s food web. Methylmercury accumulates higher in the food web because prey pass on mercury contamination to predators, which lack a biological means to dump the poison.
Humans sit at the top of the oceans’ food web and accumulate methylmercury after making lunch of oceanic predators, such as mahi-mahi fish. Mercury itself harms humans, but people face the greatest threat from methylmercury consumption because our bodies lack sufficient defenses against the toxin, according to a U.S. Geological Survey fact sheet. Severe exposure can kill a person, while lower-level doses cause neurological problems, including reduction in motor skills and sensation.
People likely produce the mercury that eventually contaminates seafood.
The mercury entering the Pacific ecosystem bore the chemical signature of pollution from coal plants and other human-related sources. This suggests the mercury menace may increase in the future. Pollution in the winds blowing from Asia onto the Pacific will continue to carry ever-increasing amounts of mercury as the regions’ industrial production and demand for energy increases.
“The implications are that if we’re going to effectively reduce the mercury concentrations in open-ocean fish, we’re going to have to reduce global emissions of mercury, including emissions from places like China and India,” lead author Joel Blum of the University of Michigan said in a press release. “Cleaning up our own shorelines is not going to be enough. This is a global atmospheric problem.”
The rising mercury in thermometers may cause a rise in mercury levels in seafood. Marine biologists have observed an expansion of oxygen-deprived waters below 1,300 feet. Mercury munching bacteria thrive in these oxygen-poor regions. Climate change may be accelerating the expansion of these regions.
“In the next few decades there will be changes in mercury concentrations in the Pacific Ocean, and those changes are likely to be different for surface waters than for deep waters,” co-author Brian Popp of the University of Hawaii said in a press release. “Understanding the competing processes that produce and destroy monomethlylmercury at different depths in the ocean is critical to tracing its bioaccumulation in fishes and the potential consequences for human food supply.”
IMAGE: A swordfish skeleton appears on display at the National Museum of Natural History in Washington. (Postdlf from w, Wikimedia Commons)