Mortality risk and social network position in southern resident killer whales (Orcinus orca): sex differences and the importance of salmon abundance

• Main Authors: Ellis, Sam, Franks, Daniel, Nattrass, Stuart, Cant, Michael, Weiss, Michael, Giles, Deborah, Balcomb, Kenneth C., Croft, Darren
• Format: Text
• Language: English
• Published: Western CEDAR 2018
• Subjects: Killer whale; Social behavior; Fresh Water Studies; Life Sciences; Marine Biology; Natural Resources and Conservation; Terrestrial and Aquatic Ecology; Killer Whale; Orca; Orcinus orca
• Online Access: https://cedar.wwu.edu/ssec/2018ssec/allsessions/43; https://cedar.wwu.edu/cgi/viewcontent.cgi?article=2478&context=ssec

An individual's ecological environment affects its mortality risk, which in turn has fundamental consequences for life-history evolution and population viability. In many species, social relationships are likely to be an important component of an individual's environment, and therefore mortality risk. Here, we examine the relationship between social position and mortality risk in Southern resident killer whales (Orcinus orca) using over three decades of social and demographic data. We find that the social position of male, but not female, killer whales in their social unit predicts their mortality risk. More socially integrated males have a significantly lower risk of mortality than socially peripheral males, particularly in years of low salmon abundance, suggesting that social position mediates access to resources. Male killer whales are larger and require more resources than females, increasing their vulnerability to starvation in years of low salmon abundance. More socially integrated males are likely to have better access to social information and food-sharing opportunities which may enhance their survival in years of low prey abundance. Our results show that observable variation in the social environment is linked to variation in mortality risk. Furthermore, our results highlight the importance of considering sex differences in social effects on survival when developing conservation strategies for long-lived social mammals.