NORFOLK, Va. (AP) – The second death of a pregnant right whale this year after it was struck by a ship is prompting calls by biologists to change sea lanes and set speed limits in the mid-Atlantic to protect the critically endangered species.

Northern right whales were overhunted in the 19th and 20th centuries. Only about 300 are thought to exist.

“At the rate we’re killing them off, we’re really looking down the curve at extinction,” said Scott Kraus, vice president for research at the New England Aquarium in Boston. “The slowing of ships would immediately reduce this risk.”

Right whales travel through the Gulf of Maine each year as they migrate between their winter grounds off the southeastern United States and their summer feeding grounds in the Bay of Fundy.

The National Marine Fisheries Service is weighing new rules, such as speed limits, for ships entering and leaving East Coast ports to reduce collisions with whales.

Researchers are encouraging the federal government, commercial shipping lines and the Navy to talk about what could be done immediately.

A recreational boater reported seeing an injured whale in the mouth of the Chesapeake Bay the week before Thanksgiving. He called the stranding team at the Virginia Aquarium & Marine Science Center in Virginia Beach, saying that the tail was almost sliced off and the animal was bleeding profusely. The carcass washed ashore in Ocean Sands, N.C.

Susan Barco, stranding program coordinator, examined the carcass with other scientists, and conducted a necropsy. “It was a typical necropsy until we found the fetus,” Barco told The Virginian-Pilot. “Then this pall just went over everybody.”

The same team had necropsied a pregnant right whale in February near Oregon Inlet, N.C., also killed by a ship.

The mid-Atlantic does not have protection measures similar to those in the South and Northeast. Marine biologists say they are needed, though.

“You’ve got thousands of transits of ships and military vessels and barges and tankers going in and out of the Chesapeake Bay every year,” he said. “It’s basically just squirrels trying to cross the road. The whales are going to get hit.”