Walruses as polar bear prey and sea ice were on my mind last night and I remembered that we DO have detailed sea ice information for 1978 and 1972 – from the sea ice atlas put together by University of Alaska Fairbanks (UAF), which has ice concentration maps for Alaska going back to 1850 — and for every year up to 2013 (reported previously here).
I’ve copied some of the ice maps below.
It is clear that ice was available close to Wrangel Island in 1972 when walruses chose to haul out on the island in huge numbers. And in 1978, there was ice present to the north of the walrus herd, but they had moved away from the ice to get to St. Lawrence Island, where they hauled out in large numbers.
This means it is more likely that food resources were the issue, not sea ice.
UPDATE OCTOBER 3 2014:
See another interesting follow-up elsewhere: Walrus inconsistencies
Recall from yesterday’s post that this year’s gathering was at Point Lay and that the incidents I mentioned occurred during November of 1978 on and around St. Lawrence Island in the northern Bering Sea and in September of 1972 on Wrangel Island (Fay and Kelly 1980), see map below.
This means ice conditions relevant to these incidents are October and November of 1978, and August and September of 1972.
Regarding incidents on and around St. Lawrence Island
Ice maps from UAF Atlas: below, October 1978
Below, November 1978
From Fay and Kelly (1980:227), regarding the St. Lawrence Island (and Punuk Islands) incident in 1978:
“Eyewitness accounts at some of the haulouts indicated that many animals were dying, apparently of natural causes, and that many fetuses had been aborted prematurely. Numerous other carcasses of animals that died at sea were washing ashore in many areas. The animals coming ashore were said to be mostly very lean, whereas walruses in autumn have tended to be very fat in previous years.
At the time when these events occurred, the weather was very stormy, with high winds and heavy seas from the south. The walruses, mainly adult females and young, were arriving from the northwest, presumably having swum from the edge of the pack ice which was then just north of Bering Strait, some 300 km away. The Eskimos remarked that the animals coming ashore appeared to be weak and physically exhausted, sleeping so soundly that it was possible to walk up and touch them without waking them.” [my bold]
Regarding incidents at Cape Blossom, Wrangel Island August 1972
Below, August 1972
Below, September 1972
Fay, F.H. and B.P. Kelly. 1980. Mass natural mortality of walruses (Odobenus rosmarus) at St. Lawrence Island, Bering Sea, autumn 1978. Arctic 33:226-245.
ABSTRACT: In October-November 1978, several thousand living walruses came ashore in at least four localities on St. Lawrence Island where they had not been present before in this century. They hauled out also at two other sites which they have occupied annually but in much smaller numbers. At least 537 animals died on the haulout areas at that time, and approximately 400 other carcasses washed ashore from various sources. This was by far the greatest mortality of walruses ever recorded in an event of this kind. At least 15% of the carcasses on the haulouts were aborted fetuses, 24% were 5-6-month-old calves; the others were older animals ranging in age from 1 to 37 years old. About three-fourths of the latter on the haulouts were females; in the non-haulouts areas the sex ratio was about 1:1. Forty of the best preserved carcasses were examined by necropsy. The principal cause of death was identified as extreme torsion of the cervical spine, with resultant cerebrospinal hemorrhage, apparently due to traumatization by other walruses. Nearly all of the dead were extremely lean, having less than half as much subcutaneous fat as healthy animals examined in previous years.
http://www.aina.ucalgary.ca/scripts/minisa.dll/144/proe/proarc/se+arctic,+v.+33,+no.++2,+June+1980,*?COMMANDSEARCH [open access]