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An odd thing happens when a harbor porpoise swims into a net. It doesn't spin like a shark or fight like a tuna. It calmly and quietly gives up.

That's not what I expected from a marine mammal that, in the wild, seems as highly strung as an Irish setter. But the North Atlantic's smallest and least studied cetacean is full of surprises. Hard to spot with their hand-size black dorsal fins, harbor porpoises are also fearful of boats and divers, making research and photography difficult. No underwater images exist of harbor porpoises in their natural habitat, though pictures of dead ones abound. In the early 1990s up to 3,000 a year drowned in the Gulf of Maine region, mostly in gill nets. A hundred or so also died in herring seines. That prompted Duke University biologist Andy Read to work with herring fishermen on Grand Manan Island to rescue the animals—and learn something about them in the bargain.

"Where there are herring, you're gonna find those little porpoises," Grand Manan fisherman Herbert Lambert told me, dispensing a bit of local knowledge that has endured around the Bay of Fundy for centuries. Passamaquoddy and Micmac Indians caught herring in brush weirs and also ate harbor porpoises that preyed on the herring. Today's porpoises are merely bycatch, a nuisance in modern weirs and gill nets. Fence-like weirs can hold 20,000 dollars' worth of herring and often a dozen porpoises or more. As fishermen seine out the catch, herring and porpoises jam into a roiling ball. "It's a frightening environment for them," says Andy Read, who started the rescue program in 1991. "There's a lot of noise, and it's the first time in their lives they've been restrained." A decade ago most harbor porpoises trapped with the herring died. Now fishermen call Read's team when they spot a porpoise in their weirs and head out in their boats to help free it. Fishermen are paid for their time, scientists get valuable data, and the survival rate has hit 95 percent. Thanks to such conservation efforts—and to a steep decline in gillnetting—population estimates in the Gulf of Maine have doubled in the past decade to nearly 90,000.

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