Earth's oceans are in peril. Over fishing, pollution, use of destructive fishing methods, coastal development, and commercial aquaculture have all contributed to dwindling numbers of fish in the sea. Long before the BP oil spill in the Gulf of Mexico, Bluefin tuna populations were already at 15 percent of their historical average. In fact, up to 76% of the world's fish stocks are presently being exploited by fisheries. Annually 900,000 metric tons of fish are wasted as a product of fishermen discarding undesirable species that turn up in their catch. Gulf Coast shrimpers alone discard 4 kilograms of 'bycatch' for every kilogram of shrimp they keep. Human waste has assuredly taken its toll on the planet's most diverse bionetwork, but by gaining an understanding of which fish and shellfish are well-managed and which are depleted the consumer can take conservation into their own hands.

A variety of organizations such as the Blue Ocean Institute, Fishwise, and the Environmental Defense Fund offer guides to sustainable seafood selection. Some even offer small cards that can slip into your wallet for on-the-go seafood decision making. However, with a little knowledge and common sense you can make smarter purchases even without a seafood guide.

A good rule of thumb for fish consumption is "the smaller the better." Typically, large slow-growing fish like Orange roughy, Chilean seabass, and Bluefin tuna are most susceptible to depletion by poorly managed fisheries. These species breed later in life and, if caught and consumed early in their life cycles, may never have the opportunity to reproduce. Anchovies, sardines and other fish at the bottom of the food chain don't play quite as crucial a role as they reproduce quickly, more plentifully and earlier in their lives. This makes them a far more sustainable choice. Also, because of their shorter lifespan and eating habits small fish typically take in less mercury than larger fish making them a healthier choice as well.

Avoiding carnivorous fish is another step consumers can take that has a two-fold benefit. Carnivorous fish such as tuna, swordfish, and mackerel have become hugely popular since fish became a "super-food" thanks to the omega 3s they produce. These large carnivorous fish, however, get there sustenance by feeding on small fish lower on the food chain. This means that they are ingesting more mercury and hence storing more mercury in their fat. By avoiding these carnivorous fish the savvy consumer can lower their mercury intake while aiding in making fish supplies more sustainable.

Substituting shellfish for fish fillets is one of the greenest seafood decisions the consumer can make. Most shellfish, such as oysters, clams and mussels, are raised on shellfish farms that have a very minimal environmental impact. Even with shellfish, though, some choices are better than others. Farmed crawfish, for example, is an excellent substitute for lobster. Although lobsters are plentiful in the ocean, they are often harvested at minimum size and have often not yet had a chance to reproduce before they are caught.

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