Trampling likely killed 131 mostly young walruses on the northwest shore of Alaska, according to an examination by an investigative team that included federal scientists.
Young animals can be crushed in stampedes when a herd is startled by a polar bear, human hunters or even a low-flying airplane.
With no human witnesses, a preliminary report stopped short of saying the animals died in a stampede. The report referred only to possible "disturbances" that led to a trampling — presumably less serious than a stampede.
"A stampede event was never observed," said U.S. Geological Survey walrus researcher Chad Jay.
The dead animals were spotted from the air by U.S. Geological Survey researchers on their way to walrus satellite radio tagging projects. They were hoping to study movement and foraging habits of walruses forced to shore by sea ice that again melted far beyond the relatively shallow outer continental shelf.
Walruses cannot swim indefinitely. Many walruses, especially females with young, use sea ice as a platform most of the summer to dive for clams and other sea bottom creatures.
An estimated 3,500 walruses had been reported Sept. 12 at Icy Cape, about 140 miles southwest of Barrow. However, as the USGS researchers passed overhead two days later, they saw a large number of walrus carcasses along the beach and smaller number of carcasses to the north and south.
The U.S. Fish and Wildlife Service, which manages walruses and polar bears, organized an investigation.
Signs of bruising
Most of the dead animals were found at Icy Cape, though a few also were found near the village of Wainwright to the north and locations up to 26 miles to the south. All appeared to be calves or yearlings.
Veterinarians and biologists from the Fish and Wildlife Service, USGS, the Alaska SeaLife Center and the North Slope Borough examined 71 carcasses and performed nine detailed necropsies.
Of the 71 carcasses examined, three were female yearlings, 25 were female calves and 43 were male calves, according to their preliminary report.
"All of the necropsied animals showed similar abnormalities, primarily extensive bruising in muscles in the neck and chest," the report said. "One animal had a fractured skull, and one animal had separation of some ribs from the backbone. Most of the animals had blood coming from the nostrils. The blood coming from the nostrils indicated damage to the neck, head, nose, or internal organs."
The extensive bruising and the age of the animals indicated cause of death likely was trampling.
Investigators found no evidence of hunting or other recent human activities near the carcasses.
Several carcasses had been scavenged by polar or grizzly bears but investigators could not say whether bears were responsible for frightening the walruses and creating "disturbances."
"Exhaustion and separation from mothers may have also contributed to the death of some animals."
After the carcasses were spotted, the Fish and Wildlife Service and the North Slope Borough surveyed the entire Chukchi Sea coast from Barrow to Cape Sabine. About 1,000 walruses was spotted on a barrier island northwest of Point Lay but no other dead animals were seen.