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Phil Levin knows that for seafood lovers wishing to eat sustainably, there are plenty of meals to avoid: shark, imported swordfish, wild shrimp from Mexico, Chinese abalone.

He is, after all, a Seattle marine scientist, and familiar with the bible of ecologically friendly ocean foods — the Monterey Bay Aquarium Seafood Watch buyer’s guide.

But Levin also recognizes those creatures from another “do not serve” list: the menu of dietary restrictions stemming from kashrut, the body of Jewish law that dictates what is kosher.

So Levin, who works at the Northwest Fisheries Science Center, embarked on an unusual scientific inquiry. He sought to find out if there was a difference in how much kosher and nonkosher eating hurt wild seafood.

“It turns out there is, and it’s huge,” Levin said. “Eating kosher is way more sustainable.”

At least to a point.

Levin’s findings come with tons of caveats and appear largely to be a fortuitous coincidence. But the discovery highlights a phenomenon the conservation biologist finds important:

Cultural or religious mores, often without meaning to, can have a profound environmental impact — for good or ill.

“There’s nothing about keeping kosher that is intentionally about marine conservation or that would purposefully influence seafood sustainability,” Levin said. “But to me, that’s what makes it interesting.”

For sea creatures to be considered kosher they must at least have fins and scales, ruling out many popular items like oysters, lobster, eel and squid. Even so, many fish that do have scales still aren’t considered kosher, including sailfish and marlin, sculpins, sand lance and paddlefish.

So, in one of the only experiments of its kind, Levin, California State University biology professor Sean Anderson and a group of students examined the sustainability and carbon footprints of seafood found at nearly 200 markets and restaurants from Los Angeles to Santa Barbara. They sampled 4,500 wild marine items and interviewed fishmongers and chefs to track how each was caught and from where.

Levin analyzed the data and learned the distance traveled and carbon dioxide emissions associated with delivery of wild seafood that would be considered kosher was, on average, far less than marine food that was not. The same held true both in restaurants and stores.

At a Simi Valley sushi joint, a roll made from wild Alaskan salmon — a kosher fish — had one-third the carbon footprint of a nonkosher caterpillar roll made from Australian spiny lobster. The main ingredient of nonkosher “shark and chips” at one Santa Monica restaurant had traveled 300 times farther than the kosher sea bass at a nearby market. The all-you-can-eat kosher fish meal in Camarillo had traveled from Alaska. The nonkosher all-you-can-eat shrimp on the same menu had come from somewhere in Asia.

In fact, Levin found that the two most popular seafood items, both in restaurants and in markets, tended to dramatically skew the findings.

“It really comes down to salmon and shrimp,” Levin said. “Shrimp aren’t kosher, and most found on the West Coast are generally imported from Asia. Salmon, on the other hand, is kosher and it just doesn’t get any better than wild salmon.”

Levin’s study has been accepted for publication in the journal Ecology & Society.

“That’s so cool,” said Lise Stern, author of the 2004 cookbook “How to Keep Kosher.” “I think the whole exercise is fascinating.”

Experts in Jewish dietary law say the findings are surprising, given that there doesn’t appear to have been a major ecological element to the initial determination of what is kosher and what is not.

Levin concedes his discovery more closely resembles a correlation than a cause-and-effect relationship.

“I’m not even sure I would call it a correlation,” he said. “The whole thing is a complete accident as far as I can tell.”

And certainly there are many exceptions.

Plenty of nonkosher seafood is quite sustainable — from Dungeness crab and geoduck to most clams, oysters and U.S. octopus. But many others are not, including octopus from the Philippines that is fished with little oversight and Russian king crab, which is often stolen by the millions.

A surprising number of nonkosher finfish also happens to be fished unsustainably, such as imported spearfish, most of which are actually caught by accident so that no one knows the health of the population.

Meanwhile, most seafood with a low CO2 footprint that is served in the United States would probably have been fished in U.S. waters. And a great number of the fish considered unsustainable by Seafood Watch are brought in from overseas.

“The United States is leading the world in fisheries management systems,” said Ken Peterson, spokesman for the Monterey Bay Aquarium. “If you are eating U.S. wild-caught finfish, then you are getting a more sustainable choice. If more countries adopted U.S. management systems … they’d have a much more sustainable approach.”

But that doesn’t mean eating only kosher seafood is the answer to our ocean woes.

Scientists in recent years have documented declines in large ocean predators and suggest that commercial fishermen around the world increasingly are forced to fish lower and lower on the food chain.

Encouraging all consumers to keep kosher would do nothing to reverse that trend, Levin said.

And kosher eating is hardly the only religious custom with inadvertent, if coincidental, conservation implications.

Exotic fruit gardens on the island of Borneo also serve as sacred burial grounds. As a result, few people can visit, which has allowed hundreds of plant species to flourish and transformed the gardens into hot spots for ecological biodiversity.

On the flip side, the release of captive American bullfrogs in Buddhist ceremonies into ponds in China’s Yunnan province has spread a deadly fungus that is helping wipe out native amphibians.

“People go about their daily lives, and for reasons you might not suspect they have an impact on their environment,” Levin said. “I think that’s important. It gives us a whole new way of thinking about influences on human behavior and the environment.”

Craig Welch: 206-464-2093 or On Twitter @craigawelch