Fish and seafood can be a more environmentally friendly protein choice than other animal foods like beef, pork, and chicken. But you need to choose carefully.
Not all fish are sustainable. And it’s more complicated than opting for certain species over others, because the sustainability and nutritional value of fish is affected by a host of factors.
So, we asked the experts to school us in seafood. Here’s what they had to say.
Think small
From both a health point of view and an environmental perspective, “the smaller, the better,” said Sebastian Heilpern, a sustainability scientist at Cornell University.
Small fish tend to be an especially good source of omega-3 fatty acid (there are plant-based sources, too, like nuts) and essential nutrients like iron and zinc. When you eat small fish, you’re usually eating bits of skeleton, too, which increases your calcium uptake. And, smaller fish reproduce quickly, so they are generally more abundant and less vulnerable to environmental changes.
Larger fish, on the other hand, generally accumulate more contaminants like mercury and lead. That’s because they’re usually predators. They eat a lot of smaller fish. So, moderate amounts of contaminants in those small fish can accumulate to harmful levels in the larger fish.
So, go for sardines and anchovies. “They are really, really nutritious sources of food,” Dr. Heilpern said, “and they tend to be pretty productive and able to withstand all of that exploitation that humans put on them.”
An exception to the “small” rule is farmed shrimp, according to Kathryn Fiorella, an environmental scientist and epidemiologist at Cornell.
Shrimp span the gamut of sustainability much more broadly than other smaller fish and seafood. Some varieties — like whiteleg farmed in certain types of ponds in the United States, Ecuador, Honduras and Thailand — meet good environmental standards. But others — raised in different types of ponds in places like China, India, and Mexico — do not.
The problem is, detailed information isn’t usually available to consumers. So, “I try really not to eat shrimp,” Dr. Fiorella said.
Mollusks are good, too
Bivalves like oysters, scallops, and clams are highly nutritious and abundant in omega-3, B-12 and iron.
And, when they’re farmed, “consuming mollusks likely has a benefit to the ecosystem,” Dr. Fiorella said. They don’t have to be fed by farmers, she noted, and they remove pollutants like nitrogen and phosphorus from water and convert them into substances that aren’t harmful. They also consume phytoplankton, which can help to limit harmful algal blooms. And they grow in reefs, providing structures that help a rage of species to thrive.
Rankings from 2021 confirmed that farmed bivalves are among the most environmentally sustainable foods overall.
Wild-caught bivalves, though, aren’t nearly as good for the environment, because the methods used to harvest them are often destructive. So, read the label.
Farmed fish? It’s complicated.
Today, more than half of the fish consumed worldwide is farmed. This type of production tends to cause fewer emissions of planet-warming carbon than fishing in the wild. But, it’s sometimes done in dense conditions where disease can spread easily and contaminants and antibiotics can escape into rivers and oceans.
Plus, unlike mollusks, farmers often need to feed their fish with more fish.
“Quite a lot of the time, if you’re eating one kilogram of salmon, just over one kilogram of wild fish is needed to produce it,” said Alice Moore, who manages the Good Fish Guide at the Marine Conservation Society, a British nonprofit organization. Feed made of grains and vegetables generally doesn’t give fish enough of the nutrients they need.
Catching fish in the wild avoids these problems, but fishing vessels can emit a lot of carbon and can damage ecosystems. For instance, bottom trawling can devastate the seafloor and increase a vessel’s fuel consumption.
Water-column fishing, below the surface and above the bottom, avoids that. But it often sweeps up the wrong species, reproducing females and fish that are too small.
Crabs and lobsters are caught in traps, so there is more precision, no bycatch and no dragging. But some kinds of gear can entangle endangered whales, with deadly consequences.
“It’s a minefield,” Moore said about sorting out the pros and cons of farmed and wild-caught fish.
Her team’s guide can be used to look up the sustainability of fish at the supermarket, as can the Monterey Bay Aquarium’s Seafood Watch Guide.
Aim for variety
Simply eating a wider range of seafood can go a long way. In the United States, just 10 species make up almost 80 percent of the seafood consumed, with shrimp, salmon, canned tuna, tilapia and Alaskan pollock topping the charts. That puts a lot of pressure on just a few species, and that can make them less resilient, more vulnerable to diseases and pests, and more likely to be destabilized by climate and environmental changes.
And, not every species has it all from a nutrition standpoint. So, variety ensures a larger gamut of nutrients.
“If you had salmon last week, grab that tin of sardines,” Dr. Heilpern said. “Mix it up.”
