The State of Circumpolar Walrus Populations

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of the population (Born et al. 1995). Contamination due to increased shipping traffic and oil and
gas development is likely to increase as a stressor of walruses in the Chukchi Sea (Jay et al. 2011),
and elsewhere, as ice reductions make areas occupied by walruses more accessible to human
activities.
Species introductions
As circumpolar shipping increases, the risk of introducing non-indigenous species into walrus
habitats on fouled ships hulls or in discharged ballast water also increases. Little is known about
what non-indigenous species might be introduced, their ability to establish, or potential impacts
to indigenous species such as the Atlantic walrus (Stewart and Howland 2009; Chan et al. 2012;
Stewart et al. 2015). It is important that there be a better understanding of this pathway, given
that shipping is likely to increase substantially over the next decade and vessels involved in
resource extraction from mines and wells in the circumpolar Arctic will arrive empty and in
ballast. Vulnerability of walruses to changes in the species composition, abundance, and growth of
benthic invertebrates is unknown but potentially serious. Walruses eat a wide variety of
organisms (e.g., Fay et al. 1986; Fisher and Stewart 1997; Seymour et al. 2014a, 2014b) and may
be able to shift their foraging patterns to compensate for changes, but they also eat a lot and thus
would be vulnerable to declines in the abundance and/or size of key prey species. The
introduction of a non-indigenous disease that causes shellfish die-off could therefore be serious.
Little is known about diseases of walruses or the potential for harm from parasites or diseases
that might be introduced via biota carried in ballast water or on ships hulls.
Climate change
Major changes in sea ice conditions are occurring throughout the circumpolar region, including
the eastern Canadian Arctic (Parkinson and Cavalieri 2008; Sahanatien and Derocher 2012;
Parkinson 2014). The effects of a decrease in the extent and duration of Arctic sea ice in response
to warming will depend upon the geographical location. Quality of the ice cover, water depth,
bottom substrate, and availability of suitable terrestrial haulouts will be particularly important.
Loss of ice cover in areas with terrestrial haulouts may increase food availability for walruses by
improving access to feeding areas in shallow inshore waters that are currently covered in winter
by landfast ice (Born et al. 2003; Born and Wiig 2005; Laidre et al. 2008). This effect will be
greatest in areas with extensive landfast ice and offshore waters deeper than ca. 100 m. On the
other hand, loss of ice cover in shallow feeding areas that are situated offshore, far from suitable
terrestrial haulouts, may greatly reduce the seasonal feeding distribution, leading to crowding at
haulouts and reduced abundance (Kovacs et al. 2011; Taylor and Udevitz 2015).