A North Atlantic right whale feeds on the surface of Cape Cod bay off the coast of Plymouth, Mass., March 28, 2018. Credit: Michael Dwyer / AP

Federal fishing regulators are asking boaters in southern Maine to slow down after scientists detected endangered right whales off Portland.

The National Oceanic and Atmospheric Administration sent a notice out Friday asking boaters to avoid an area about 68 nautical miles east of Portland or transit through it at 10 knots or less. The “slow zone” is voluntary and runs through Dec. 16. It was implemented because scientists say an underwater glider detected multiple loud right whale calls in the area on Dec. 1.

Right whales swim up and down the East Coast annually and are critically endangered. There are only about 340 whales left and their protection is at the heart of multiple lawsuits between federal regulators, environmentalists and Maine’s lobster industry.

NOAA says that fishing gear is one of the biggest threats to right whales, so-called because they were the “right” whale to hunt when whaling was legal. But Maine lobstermen vehemently deny they are the cause of the whale’s downturn and say they never see them swimming through the state’s lucrative fishing grounds.

The federal government has also proposed rules to cut down on ships striking whales.

A right whale was seen last fall off Portland Harbor. The new slow zone is one of several throughout the East Coast. Slow zones have also been implemented off Maryland, New Jersey, Massachusetts, New Hampshire and New York.