The State of Circumpolar Walrus Populations

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reproduction and survival rates, and length of the reproductive period (COSEWIC 2006). The
relative numbers of adult females of a given age are unknown, as is age at senescence. These gaps
increase the uncertainty in any estimates of sustainable yield for harvested populations and can
have a substantial influence on conservation and management. For example, modelling suggests
the Eastern Greenland (EG) population has recovered from its historical depletion, but the
trajectory of this recovery is uncertain due to lack of a population-specific growth rate estimate
(Witting and Born 2014). An understanding of whether or not populations have recovered is
critical to effective harvest management.
Climate change impacts/response
Many potential impacts from climate change are secondary, due to linkages with other stressors.
For example, the potential for population displacement by increasing Arctic shipping is unknown.
This could be of real concern for many walrus populations and merits proactive scientific study.
These studies will need to establish strong baselines against which changes can be measured,
followed by careful long term monitoring to establish trends, identify cause and effect, and inform
potential mitigation responses. The effects of climate change will need to be considered in all of
the various research needs identified above.
The mating system of Atlantic walruses in fast-ice (Sjare and Stirling 1996) differs from that of
Pacific walruses in pack ice (Fay et al. 1986). This suggests that sea ice stability may be an
important determinant of walrus breeding behaviour, and sea ice declines could therefore have
pronounced effect on reproduction and population. Research on walrus behaviour (and
movements and habitat use, see above) in pack ice environments is necessary. Reductions in sea
ice will increase walrus reliance on terrestrial haulout sites, and research on haulout occupancy
and dynamics will inform efforts to mitigate disturbance. Trail cameras could be used for
monitoring and to provide information on disturbance events.
Walruses are highly adapted for obtaining bivalves, but they also have the potential to switch to
other prey items if bivalves and other calcifying invertebrate populations decline (USFWS 2014).
Whether other prey items would meet their nutritional needs is not known (Sheffield and
Grebmeier 2009). There is also uncertainty about the extent to which other suitable non-bivalve
prey might be available, mainly due to uncertainty about the effects of ocean acidification
(USFWS 2014). Climate change impacts on walrus food sources are an important research avenue.
Research on diet requirements and flexibility in response to trophic shifts is needed, as is research
on energetic thresholds in Atlantic walrus (see Noren et al. 2012, 2014, 2015, 2016 for relevant
research on Pacific walrus).