Development of a Molecular Approach to Age Pacific Walruses: A Novel Application of Epigenetic Aging for Close-kin Mark-recapture

The Pacific walrus is an ice-associated pinniped that ranges over continental shelf waters in the Bering and Chukchi Seas. Sea ice provides habitat for numerous Pacific walrus life history events and provides a platform for animals to rest between foraging bouts at productive, remote offshore areas. Estimating abundance and vital rates of the Pacific walrus population is, therefore, logistically and scientifically challenging. In 2013, the U.S. Fish and Wildlife Service initiated a five-year genetic mark-recapture project to test the efficacy of an alternative approach to estimating population abundance, survival, and reproduction. Age is an important piece of information in mark- recapture studies that can reduce uncertainty and increase precision of parameter estimates. Although a method to age walrus based on facial characteristics is available, preliminary results indicated a high level of observer error. An improved aging technique is needed to allow development of more complex traditional mark-recapture models and aid development of closekin mark-recapture models.

Goals

We are developing an approach to age walruses based on epigenetic signatures, which only requires DNA from sampled individuals. We have identified potential age-related epigenetic markers in walrus by whole methyl DNA sequencing samples derived from calves (0 year old) and adults (≥6 years old) with museum specimens of known age based on tooth cementum annuli analyses. We are partnering with coastal communities to obtain samples from hunter harvested walrus to quantify the accuracy and precision of age-related markers across age classes.