WASHINGTON – Although only two nations still hunt whales, the giants of the oceans still face a threat from humans – being struck by ships.

Between 20 percent and 35 percent of whales found dead show signs of having been struck by ships, more in some species, recent studies found.

Right whales in the western North Atlantic appear to have been particularly affected. Their population is estimated at 300 to 325.

“Nearly half of the known mortality of the species is due to ship collisions or net entanglement. Ship collisions probably account for 40 percent,” said David W. Laist of the federal Marine Mammal Commission. “It’s a very significant share … it’s clearly preventing their recovery.”

Scott Kraus, director of research at the New England Aquarium, estimated that ship collisions are killing off one to two right whales a year, “and probably more that we don’t see the bodies of. In a population this small, that’s a significant percent.”

Prized for their oil, right whales were heavily hunted in the past. They were named because they were considered the right whale to hunt.

After most hunting ended, the majority of whale deaths and strandings were written off to disease, old age or similar reasons, said James G. Mead, a whale specialist at the Smithsonian Institution’s National Museum of Natural History.

As researchers began studying the animals, however, they discovered signs of bruising. “You can’t bruise a carcass; an animal has to be alive to bruise,” Mead said. The most likely cause of bruising, he said, was a collision with a ship.

Some whales also had rows of slash marks left by propellers, while others suffered massive internal injuries in collisions, researchers found.

“I would say [ship collisions] is at least comparable and probably exceeds hunting mortality,” Mead said.

A Japanese whaling fleet that returned home recently killed 440 Minke whales during a six-month hunt.

While the International Whaling Commission bans hunting whales, Japan and Norway still conduct hunts, ostensibly for research purposes.

Among recent cases of whale deaths:

. A baby right whale was found dead off Long Island, N.Y., in June 2001, the fourth calf of the endangered species to perish that year and the second believed killed in a collision with a ship; and

. The following month, a 45-foot humpback whale died of a crushed skull near Glacier Bay National Park in Alaska. Park officials said the whale had been struck by a cruise ship.

Janice M. Straley, who teaches marine biology at the University of Alaska Southeast in Sitka, said park officials are urging cruise ships to reduce their speed to less than 14 knots (16 mph) in Glacier Bay.

In 1999, the federal government launched a mandatory ship reporting system for vessels of more than 300 tons entering designated areas known to be right whale habitats off Cape Cod, Mass.; Florida and Georgia. The goal is to understand ship traffic patterns in the areas so efforts can be made to protect the whales.

In the first year of operation – the most current data available – there were 699 ship reports in the northern area and 279 in the southern district. Officials believe, however, that many vessels failed to report in and others filed inaccurate reports that had to be dropped from the analysis.