Their appearance in New England about 10 years ago alarmed both environmentalists and traditional fisherman, who are concerned that the trawlers’ efficiency is depleting herring stocks and depriving other fish, birds and sea mammals of a critical food source.

“They’re on the bottom of the food chain. Everything eats the herring — the whales, the mammals, the birds. If you don’t have a good stock of herring, nothing else is going to stick around,” said Mr. Robbins, who used to operate a trawler but does not anymore.

The new rules require midwater trawlers to have independent observers on every trip, and establish guidelines for weighing and sampling their haul. Such measures can help fishery managers get a better idea of whether the trawlers are depleting herring stocks and taking other species with them, as some fishermen and environmentalists insist. The new rules will also allow the council to cap the amount of river herring that trawlers looking for sea herring can scoop up by accident.

“While we’re trying to rebuild cod stocks and keep small boats alive, reintroducing industrial-scale fishing is a really bad idea, and doing it without any monitoring is real folly,” said Peter Baker, the director of Northeast Fisheries Program for the Pew Environment Group.