Dozens of headless walrus carcasses have washed up on Alaska beaches this summer, prompting an investigation by the U.S. Fish and Wildlife Service.

While rotting, headless carcasses are not uncommon along beaches, the number of them this summer has been a cause of alarm.

In late June and early July, 79 walrus carcasses were counted along one 40-mile (64.3-kilometer) stretch of beach — about twice as many as in any year in the past decade, said Steve Oberholtzer, a special agent in Anchorage.

"Every one of them had the head removed," he said. The ones that investigators got a close look at had been shot.

Federal authorities do not know if a crime has occurred, Oberholtzer said. But he said investigators are looking into two possibilities: either someone who is not an Alaska Native is poaching walruses, or Alaska Natives are not salvaging enough of the animals.

Only Alaska Natives are allowed to subsistent hunt for walrus. The tusks are often carved or used in Native arts and crafts. Non-Natives can harvest walrus tusks if they find a carcass, but they cannot sell or profit from them.

A non-Native illegally killing a walrus is unusual, Oberholtzer said Wednesday.

Pacific walruses are not considered threatened or endangered. The population was estimated at more than 200,000 in 1990, the most recent count.

In 2005, Alaska Native subsistence hunters harvested 1,590 walrus. Another 1,470 were killed by Russian subsistence hunters.

Local residents said the whole walrus head usually is harvested to get the ivory. The heads are either cooked to loosen the tusks or buried in a hole where maggots eventually eat the flesh and loosen the tusks.