The seafood we eat has an enormous impact on our health today and the health of our oceans tomorrow.

The seafood we eat has an enormous impact on our health today and the health of our oceans tomorrow.

The weekend after Thanksgiving, I steer my boat, First Light, out of the harbor knowing this will be my last fishing trip of the year. It's become a tradition. What my partner, Patricia, and I seek will provide reason enough to give abundant thanks.

Off the very tip of Long Island, migrating ducks and loons enliven the sea's wintery surface. Already a few seals from the north are appearing. Gannets on long wings have come from coastal Canada following the same prey that we are after today, and we watch the birds carefully. When I see them raining into the sea like white missiles, I turn the wheel toward them.

They're all here for the same reason I am: the strong currents keep this place awash in plankton, enriching the whole food chain, concentrating wildlife of all kinds.

As soon as I drop a line, I will become part of this complex web of interdependence-that's what I most love about being here.

Today, though, the fish we pursue are different from what you might expect or what I would have sought several years ago. (Click here to find 6 super green fish to serve.) I've fished these waters since I was a teenager in the 1970s, and I've seen the ocean change. The big offshore fish-the swordfish and sharks I once thrilled to see, catch and eat-are now so scarce I just don't feel good about hooking them anymore. (Click here to find 6 fish to avoid.) U.S. fishermen now often catch less than 20 percent of the bluefin tuna they're allowed because they can't find enough to fill their quotas. Hammerhead sharks-common when I started fishing offshore in the 1980s-are down about 90 percent and other shark populations are severely depleted too.

The dominoes often fall in unpredictable ways, upsetting the natural balance. As sharks off the East Coast have been fished down to low levels, the stingrays they used to eat have proliferated. So much so that the rays now demolish shellfish beds, putting some clammers out of business.

In the North Atlantic, commercially important fish like cod and halibut declined by two-thirds between 1950 and 2000. Atlantic cod had been a source of riches for 500 years, but in the early 1990s Canada's cod fishery "collapsed" (declined more than 90 percent) due to overfishing, bringing long-term devastation to communities up and down the seaboard.

In 2006, an international team of scientists analyzing global fisheries data wrote in Science magazine, "Accelerating loss of populations and species... is increasingly impairing the ocean's capacity to provide food, maintain water quality, and recover." They found that since 1950 about a third of all fished species worldwide have collapsed. They also noted that, at current rates, the rest would collapse by 2050.

Of all the things that are changing the ocean-including pollution, climate change and coastal development-fishing has brought the most profound change so far.

I've often said fishing is the last buffalo hunt-the last wild food we hunt and consume en masse. And it's worth recalling the cautionary tale of North America's most abundant bird, the passenger pigeon. In 1810, the pioneering ornithologist Alexander Wilson estimated one "almost inconceivable multitude" of pigeons as being roughly 240 miles long, containing 2.2 billion birds. After a century of being hunted for food, the last passenger pigeon on Earth died in the Cincinnati Zoo in 1914.

Though "there are plenty of fish in the sea"-or were-abundance doesn't make them immune from overexploitation. But the same researchers who warned of a total fisheries collapse before 2050 added that "at this point, these trends are still reversible," if we improve management and declare ample no-fishing zones where fish can reproduce. (Click here to find 6 fish to serve.) The buffalo herds are gone and the passenger pigeon has passed-but there remains hope for the ocean.

Pledging to Eat Right

This may take a sea change in how we eat. Last fall, more than two dozen top chefs, including Alton Brown, Rick Bayless, John Ash and Barton Seaver, pledged not to serve any fish on Seafood Watch's red "avoid" list. That means no more farmed salmon. Goodbye to Chilean sea bass and red snapper. Orange roughy and monkfish are also off their menus. Walmart, which currently spends $259 billion on sustainably sourced seafood, has pledged that it will purchase all wild-caught fish for the U.S. market from Marine Stewardship Council (MSC)-certified fisheries by 2011. It will also work with Global Aquaculture Alliance and Aquaculture Certification Council, Inc. to certify that all foreign shrimp suppliers adhere to Best Aquaculture Practices standards in the U.S. Gradually, food-service giants, such as Sysco, Compass Group and Aramark, are making the shift too.

Will It Work?

It has before. In the late 1990s, when Atlantic swordfish reached an all-time low, environmental groups and high-profile chefs began working together to promote a ban on eating swordfish. They reduced demand enough to soften the price and bring commercial fishing groups to the bargaining table. Environmental groups also won a lawsuit to close fishing areas where juvenile swordfish congregate. Consequently, swordfish numbers are about 150 percent of what they were in the mid-1990s. The population is rebounding and may soon be sustainable again.

Around that same time, a conservation magazine asked me to create a list that evaluated popular seafood from most sustainable to least. Before that, a piece of fish was simply a piece of fish. You didn't think about it, you just ate it, like a piece of bread. Today that database has grown and spawned various regional sub-lists, making it easier for consumers to make the right choices.

And America's fisheries have gotten better, realizing that their own future livelihood is at stake. Though they still have problems, they also have some of the better management rules in the world. U.S. fisheries must now be evaluated biannually, and since 2006 federal fishery managers have been required to establish annual catch limits that allow depleted populations to begin rebuilding. Better yet, they're required to end all overfishing in U.S. waters this year. Alaska, the state with the highest seafood landings, has perhaps the best-managed fisheries in the world, with tight quotas, strict environmental regulations and close monitoring so that fisheries are closed before they exceed critical limits.

The Simplest, Healthiest Solution

When people ask me now what fish to eat, I pause. The answers can seem confusing: Atlantic cod is not sustainable but Pacific is. Alaskan salmon is fine. Most farmed salmon-even organic-is not, as many salmon farms are infecting and threatening the wild species. Most domestic shrimp is farmed sustainably or caught in ways that limit by-catch of fish and sea turtles. Much of the shrimp from overseas is not.

So my new rule of thumb is very, very simple: if a whole fish is small enough to fit on your dinner plate, it's probably a good choice for both the environment and your own health.

Here's why: smaller fish that are lower on the food chain tend to be abundant, fast-reproducing and more resilient to fishing pressure. Bigger fish usually live longer, taking years to mature and begin breeding. Because they're near the apex of the food pyramid, there are fewer of them to begin with. So they're much more vulnerable to overfishing and easily depleted. And slow-growing, long-lived, late-maturing fish like sharks and big tunas can't just bounce back. Rebuilding will take time. And so far, we're not giving them much of a chance.

Consequently, though I used to love grilled mako steaks, I won't kill sharks anymore; it's not good for them, and just as important, eating them is not good for me. Simply put, big, older fish accumulate more mercury than small and younger ones.

Most of the mercury people acquire gets into the environment from burning coal, but we usually get it into our bodies through eating seafood. Most animals we eat are killed when they are young (six weeks for a chicken) and have not accumulated that much mercury. By contrast, the large bluefin tuna we catch are 10 years old. Contaminants like mercury, pesticides, PCBs and other metals and toxic chemicals aren't just passed along in the food chain; they accumulate and concentrate toward the top. Think of the ocean food chain as a simple pyramid, with, say, a shark at the top, a large number of herring in the middle and a vast horde of planktonic plants and animals at the base. (In real life, it's more complicated, of course, with more steps.) The plant plankton absorb minute quantities of contaminants as they turn nonliving components of seawater into living cells. Think of the total of all the contaminants in all the plankton along the pyramid's base, and imagine it all concentrating into fewer herring and ultimately in the one big old shark. Basically, that's what happens.

The higher on the pyramid you eat, the more likely you'll be getting a larger portion of concentrated contaminants. Dining on plankton-eating herring is better than eating the shark that ate all those herring. Herring, anchovies, Atlantic mackerel, clams and oysters (small plankton-eaters) have among the lowest mercury concentrations; sharks and tunas (big fish-eaters) have among the highest. And even with farmed fish, smaller is better. Big, carnivorous fish must be fed smaller fish that have been caught in the ocean. Many of those nutrient-rich smaller fish that are turned into fishmeal-like herring and sardines-are healthy for people and would be better used as human food.

But what if everyone ate herring and sardines; wouldn't that further skew the foodweb? You'd think so, but not if we were to eat these nutrient-rich fish in place of some of the meats we currently consume. Consider this: right now, about a third of the world catch of those fish is fed to farmed fish, pigs and chickens. This is a great waste of potential human food, because up to five pounds of fish-edible, nutritious, delicious wild fish-must be fed to the farmed livestock in order to produce one pound of meat.

So, farmed freshwater fish that can be fed a vegetable-based diet, like tilapia or catfish, are better choices than large carnivorous fish. Better yet are farmed clams, oysters and mussels, which require no feeding and actually filter the waters around them (that's how they eat), helping improve water quality and helping prevent plankton from overproducing and then crashing, which can devastate oxygen availability and kill many other creatures.

Catch of the Day

By the time I reach the diving birds, the sonar shows dots representing schools of fish near the bottom in 50 feet of water. Patricia and I have two fishing rods, each rigged with a row of six tiny lures the length of my thumbnail. Here in the same ocean where I've decked big tuna and battled bruising sharks and fought 40-pound striped bass, this is decidedly-and deliciously-small game fishing.

Our sinkers mail the rigs to the bottom. I feel a bump and my rod tip dips, dips more, then more. Pat's already reeling up. And we've struck silver, all right. Into view come the wiggling, shimmering shapes we're looking for. I lift six herring, each about 10 inches long, over the side and into the cooler. Patricia has four herring and two mackerel about the same size. At this rate, it doesn't take long to get about five dozen before we hang up our rigs and head for the dock.

We'll smoke some of these, cook some up fresh, and fillet and pickle most of them. They'll show up on our dinner table and as snacks and in gift jars. For weeks they'll give us good food and a good story.

Marine biologist Carl Safina is the founder of the Blue Ocean Institute, author of Song for the Blue Ocean, and winner of the Pew Fellowship in Marine Conservation Award, the MacArthur Fellowship and the Lannan Literary Award. He won a 2011 James Beard Award for this story published in EatingWell Magazine.

March/April 2010