The State of Circumpolar Walrus Populations

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Bering Sea (Garlich-Miller et al. 2011). Haulouts in the Bering Strait Region (Big Diomede, King
Island, and the Punuk Islands) are also occasionally used by large numbers of walruses in late fall
and early winter, prior to the onset of ice formation (Fay and Kelly 1980). Male walruses that have
summered in the Bering Sea begin to move northward towards winter breeding areas in
November (Jay and Hills 2005).
Status of Population
The Pacific Walrus population was historically depleted by commercial over-harvesting. Fay
(1982) speculated that the pre-exploitation population was at least 200,000 animals given the
large harvests that were sustained throughout the 18th and 19th centuries. Population size is
believed to have fluctuated markedly in response to varying levels of human exploitation since
that time (Fay et al. 1989). Extensive commercial harvests reduced numbers to an estimated
50,000-100,000 animals in the mid-1950s (Fay et al. 1997), and the population then increased
rapidly in size during the 1960s and 1970s in response to reductions in hunting pressure (Fay et al.
1989).
From 1975 to 1990, visual aerial surveys were carried out by the United States and Russia at 5-
year intervals (USFWS 2014; Allen and Angliss 2015). Population estimates ranged from ca.
201,000 to 246,020 animals with 95% confidence intervals that include zero. All estimates have
low precision and large associated variances, which adds uncertainty for detecting trends in
population size (Gilbert et al. 1992; Hills and Gilbert 1994; Fay et al. 1997; Gilbert 1999). The
estimates generated from these surveys are considered minimum values. They are negatively
biased because they were not adjusted for walruses in the water and because the walruses tended
to aggregate in large closely packed groups when hauled out that made it difficult to obtain
accurate counts of animals observed (USFWS 2014; Allen and Angliss 2015).
Efforts to survey the population were suspended after 1990 due to these methodological issues
(Gilbert et al. 1992; Gilbert 1999). A 2000 workshop concluded that it would not be possible to
obtain a population estimate with adequate precision using the existing visual methodology and
any reasonable amount of survey effort (Garlich-Miller and Jay 2000). Remote sensing systems
were viewed as having potential to address the problem of accurately counting walruses in large
groups (Udevitz et al. 2001) in addition to being able to sample larger areas per unit of time and
reduce observer error (Burn et al. 2006). To account for walruses in the water that were not
available to be counted, satellite transmitters that recorded haul-out status (in water or out) were
used to estimate the proportion of animals in the water and correct walrus counts (Udevitz et al.
2009). American and Russian scientists developed a survey method that uses thermal imaging
systems to reliably detect groups of walruses hauled out on sea ice (Burn et al. 2006; Udevitz et al.
2008).