131 walrus calves trampled to death in Alaska

Trampling by other walrus appears to be the cause of death for 131 young walrus found dead in Alaska. Photo USFWS

October 2009. Trampling by other walruses was the probable cause of death of 131 walruses carcasses found on the shore near Icy Cape in Alaska, according to an investigative team. The carcasses, the majority of which were young animals, were discovered along the beach above the high-tide line on 14th September by a U.S. Geological Survey (USGS) survey crew.

Investigation
In response to the discovery, the U.S. Fish and Wildlife Service put together a team comprised of representatives from USFWS, USGS, the Alaska SeaLife Center and the North Slope Borough to determine the extent and cause of the die-off. The National Marine Fisheries Service provided additional financial and technical support, with hunters from Barrow and Wainwright also assisting in the investigation.

An aerial survey of the Chukchi Sea coast conducted by USFWS and NSB confirmed the die-off was localized to the Icy Cape region.

To determine the cause of death, a smaller team examined as many carcasses as possible and conducted autopsies. Veterinarians and biologists from ASLC, USGS and NSB went to the area. The six-member team examined 71 carcasses and performed nine detailed necropsies. Because the necropsies showed extensive bruising and all of the carcasses were calves or yearlings, the investigative team concluded that the cause of death was consistent with trampling by other walruses.

Global warming to blame?
Trampling-related injuries and mortalities are not uncommon at coastal walrus haulouts. The potential for injuries and mortalities appears greatest in large herds of animals with a mix of walruses of different age and sex. Young animals appear to be more susceptible to trampling than older animals. However it is possible that, due to the lack of sea-ice, the walrus haulout was overcrowded, resulting in many deaths.

The cause of the disturbance or disturbances leading to the trampling deaths is unknown. Investigators found no evidence of hunting or other recent human activities near the carcasses.