How to Help: Safe, Sustainable Seafood

While there are a few species to avoid, such as tilefish, shark, king mackerel, swordfish, and contaminated sport fish, eating seafood is generally good for you. Mercury poisoning, however, can be deadly, and mercury contamination can lead to a host of neurological problems.

A fish's mercury level depends on a number of factors, including where the fish lives, how old it is, how big it is, and what it eats. Mercury travels up the food chain, so fish that eat other fish are more likely to be contaminated. Mercury levels accumulate over time, so older fish are more likely to have larger concentrations of mercury than younger members of the same species. That means smaller aquatic species (shrimp, scallops, tilapia) are safer bets to guard against contamination. Anchovies and sardines, being small and short-lived, also have low mercury levels. Large, predatory fish (large tuna, sharks, swordfish) contain higher levels of mercury. In fact, fish at the top of the food chain can contain mercury levels that are 10,000 to 100,000 times higher than those of their environments. This helps explain why sharks are on the list of high-mercury foods and wild salmon are not.

While the Harvard study stressed that the benefits of eating fish outweigh the risks, note that—in addition to pregnant and nursing women—small children and women of childbearing age should also be careful to avoid contaminated fish.

Shopping for Seafood: What to Ask and Why
When shopping for seafood, be prepared to ask questions and look for information to help you figure out the best fish to buy. There are many factors to consider, and these questions will give you a place to start.

Where did the fish come from?
Knowing where in the world your fish came from will give you an idea of the strength of the regulations—if they exist at all—aimed to protect the consumer. You'll also be able to gauge whether sustainable fishing methods were likely to have been used and if the species is being overfished. Different fishing methods affect the marine environment and its marine animals differently. For instance, California's Monterey Bay Aquarium recommends avoiding farmed tilapia from Taiwan and China because of poor oversight and pollution concerns but recommends farmed tilapia from the United States.

Was the seafood raised on an aquatic farm or caught in the wild?
This question brings up a host of issues, including sustainable fishing and contamination. Farmed salmon, for instance, may have higher levels of dioxin and PCBs than its wild cousin. Studies have shown that farmed salmon can have some of the highest levels of PCBs of any fish in the world. Fats and oils in fishmeal consumed by farmed salmon are the problem; toxic PCBs concentrate in these substances.

What method was used to catch the fish?
If you can find out the answer, you'll gain an idea of the environmental effects of your choice. A Dungeness crab caught in a trap means there is little chance that other marine animals are caught and then discarded as bycatch. Atlantic haddock caught by trawling can destroy habitat and lead to other fish being discarded as bycatch. Haddock caught using hook-and-line methods is a better alternative.

Tuna: Know Your ABCs
Tuna has gotten a lot of press lately—both good and bad. Tuna is a good source of omega-3s, which are great for healthy cell membranes, but there are issues of moderate mercury contamination and sustainability of certain populations.

Ahi and albacore
Ahi is the Hawaiian word for tuna and can refer to yellowfin or bigeye tuna—both higher in mercury than canned, light tuna. Being called ahi doesn't necessarily tell you what tuna you are about to eat.

The Environmental Protection Agency (EPA) estimates that albacore, or solid white tuna, has three times the mercury on average of canned, light tuna.

Bigeye and bluefin
Both bigeye and bluefin tuna suffer from overfishing and low numbers, not to mention being higher in mercury than other kinds of tuna. Bigeye has the highest mercury level of all tuna listed on the EPA's website. Bluefin is not listed. Overall, it's best to avoid both.

Chunk light and chunk white
Read the can when you buy tuna: chunk white is not the same as chunk light. Chunk white comes from albacore tuna, which is on average higher in mercury than chunk light. Chunk light usually consists of skipjack. Since skipjack are smaller than other tuna and mature quickly, they have less body mass to accumulate mercury. However, a 2005 Chicago Tribune investigation found that some cans labeled "chunk light" also contained yellowfin tuna, which the EPA estimates averages one and a half times the amount of mercury as that of skipjack. Canned albacore tuna averages three times the amount of mercury as that found in other canned tuna, according to the EPA.

Seafood Seal of Approval
If you don't have room in your pocket for a seafood guide but still want to buy fish responsibly, look for the blue logo of the Marine Stewardship Council (MSC). This nonprofit based in the United Kingdom has developed a standard for sustainable fishing using principles put forth by the Food and Agriculture Organization of the United Nations. In order to receive permission to use the logo, a fishery must have sufficient numbers of fish and use methods that do not harm the surrounding marine environment.

Today, hundreds of seafood products from some 20 certified fisheries display the council's blue oval. Products with the logo are sold in supermarkets in 27 countries worldwide. In 2006 Wal-Mart, the world's number-one retailer, pledged that within three to five years it would buy all of its fresh and frozen seafood from MSC-approved fisheries. If you still can't find certified fish in your local market, the council urges you to pass along their contact information where you buy fish to spread the word about sustainable fisheries management.