Mass haulouts of female Pacific walrus as a sign of population health

Mass haulouts of female Pacific walrus and their calves in fall don’t happen all the time but they do occur. I recently pointed out (here and here) two instances of such incidents from the 1970s.

I said this provided evidence that the September 2014 incident reported in the media was not “a new phenomenon” for this region, as WWF spokepersons and Alaskan biologists have claimed (reiterated in this PBS interview).

Figure 1. Walrus females and calves hauled out on a beach in Svalbard, photo accompanying an October 6, 2014 news report in “Eye on the Arctic” of the rapidly increasing Atlantic walrus population there. (Photo: Thomas Nilsen/Barents Observer).

Figure 1. Walrus females and calves hauled out on a beach in Svalbard, photo accompanying an October 6, 2014 news report in “Eye on the Arctic” of the rapidly increasing Atlantic walrus population there. (Photo: Thomas Nilsen, Barents Observer).

One aspect of the recent occurrence of a large herd on an Alaskan beach that apparently needs reiterating is that the population of walruses declined rather markedly after a 1970s peak and has rebounded since. This suggests that huge herds of females and calves hauling out on beaches in the fall to feed might only be seen when the population is very large.

By late September, Chukchi Sea walrus females must contemplate their annual migration south, away from the pack ice.

What determines the actual start date of their migration (which entails swimming hundreds of kilometers south, well before the ice starts to expand) – is it changes in ice extent, food supply, air temperature, or daylight? The walruses know but we are still largely in the dark.

Walrus females could wait until the ice itself moves south, as it will next month, but they don’t. Even in 1978, they didn’t wait for the ice to move south (Fay and Kelly 1980). Even though the ice was well south of Point Lay in October 1978 (ice maps here), female walrus took their calves and swam ~300 km south to St. Lawrence Island, and the nearby Punuk Islands, to haul out in massive herds on the beaches there.

The reason the females head to St. Lawrence ahead of the ice every year is so that they can use the beaches there as a resting platform for foraging bouts in the shallow waters offshore. The notion that females and calves are never found hauled out anywhere except the sea ice in fall and never use beaches as foraging platforms in the fall is simply not true (Figure 1).

The recent haulout at Point Lay is probably the start of the annual migration of females and calves and they’ve simply stopped to rest and feed. And they are feeding – they are not “stranded” or starving.

Said US Geological Survey walrus biologist Chad Jay last week:

“…the tally of 35,000 walruses is a rough and preliminary estimate.

“Basically, they’re just kind of looking out the window as the plane goes by. It’s basically just a guesstimate,” he said. And the gathering onshore represents only some of the walruses in the area, he said.

There’s at any given time some number of animals that are off the haulout in the water, feeding,” he said.

Walruses usually spend about 80 percent of their time in the water, he said.” [my bold]

In my previous post, I was perhaps not clear enough that walrus numbers in the 1970s were high (~200,000 – 250,000) but then declined due a combination of natural “density dependent” starvation (not enough food for the huge population) and a fairly high take from hunters (Fay et al. 1989).

Follow-up studies agreed with this assessment (Garlich-Miller et al. 2011). The population appears to have rebounded again since then but by how much (exactly) is unclear.

The most recent estimate (from 2006), cited as 129,000, was ridiculously low – one of the lowest estimates since the 1950s – and came with an enormous error range (55,000-507,000, see Garlich-Miller et al. 2011:13):

“It should be noted that the most recent abundance estimate is believed to be negatively biased to an unknown degree because inclement weather conditions precluded full coverage of available habitats.” [my bold]

So, they know the estimate of 129,000 is way too low and not realistic at all. But when pushed, they use it anyway.

Officially,the current size and trend of the Pacific walrus population is unknown” (US Fish & Wildlife 2011 Factsheet).

In fact, the population may be as high as it was in the 1970s, when huge numbers of females and calves also massed together onto small stretches of beach.

In other words, huge numbers of females and calves massed together onto small stretches of beach may be an important indicator of large numbers of females and calves in the population, not an obvious sign that lack of sea ice is causing some kind of catastrophic trauma to the animals.

This means we have potentially high population numbers of walrus now and in the 1970s, with lower population numbers in between.

[Sidebar: Note that despite not having any kind of accurate estimate of the size of the walrus population or its trend, in February 2011 the US Fish and Wildlife Service (FWS) decided that the walrus warrants being listed as a threatened species because of future threats predicted by computer models. However, uplisting the walrus to “threatened” is not a high priority for the FWS – right now it is too busy with listing other species: “We will develop a proposed rule to list the Pacific walrus as our priorities allow.” (Federal Register 2011:7634)]

If females and calves hauling out on land in very large numbers in late summer/fall is a behaviour only seen when the walrus population is very high, you would expect to see this phenomenon in the 1970s and over the last few years, but not in between – which is exactly what has been reported.

The common factor associated with mass haul-outs of females and calves in September/October appears to be the large size of the walrus population, not a change in the position of late summer/fall sea ice in the Chukchi Sea. A more accurate population assessment might change that interpretation but for now, it is a reasonable one to make.

References
Department of the Interior 2011. 12-Month Finding on a petition to list the Pacific walrus as endangered or threatened. Federal Register 76 (28): 7634-7679. http://www.fws.gov/alaska/fisheries/mmm/walrus/esa.htm

Fay, F.H. and Kelly, B.P. 1980. Mass natural mortality of walruses (Odobenus rosmarus) at St. Lawrence Island, Bering Sea, autumn 1978. Arctic 33:226-245. http://www.aina.ucalgary.ca/scripts/minisa.dll/144/proe/proarc/se+arctic,+v.+33,+no.++2,+June+1980,*?COMMANDSEARCH [open access] and PDF

Fay, F.H., Kelly, B.P. and Sease, J.L. 1989. Managing the exploitation of Pacific walruses: a tradegy of delayed response and poor communication. Marine Mammal Science 5:1-16. PDF.

Garlich-Miller, J., MacCracken, J.G., Snyder, J., Meehan, R., Myers, M., Wilder, J.M., Lance, E. and Matz, A. 2011. Status review of the Pacific walrus (Odobenus rosmarus divergens). US Fish and Wildlife Service, Anchorage, Alaska. http://www.fws.gov/alaska/fisheries/mmm/walrus/esa.htm and PDF

U.S. Fish and Wildlife Service 2011. Walrus Factsheet. Anchorage, Alaska. http://www.fws.gov/alaska/fisheries/mmm/walrus/esa.htm

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