Behaviour 2019
The Effect of Sex, Age, and Calf Presence on Rate of Shark Injury in Bottlenose Dolphins (Tursiops aduncus)
Courtney Collins-Pisano1,2, Vivienne Foroughirad2, Ewa Krzyszczyk2, Caitlin Karniski2, Janet Mann2. 1Wesleyan University, Middletown, CT, United States; 2Georgetown University, Washington, DC, United States

Previous research has shown that Indo-Pacific bottlenose dolphins in Shark Bay, Western Australia have high rates of non-lethal shark encounters, but little is known about individual risk factors of shark attack. Female dolphins with dependent offspring are hypothesized to be more likely to sustain non-lethal shark wounds due to their interventions in attacks on their calves. Using 32 years of longitudinal data of 494 dolphins, we determined whether a dolphin was observed with a new shark wound in a given year. A generalized linear model revealed no significant effect of sex (p=0.229, N=1223), but sexual maturity increases the risk of shark injury by a factor of 1.35 (p=0.001). There is a significant cross-over interaction such that the effect of sexual maturity on increasing risk of shark injury is less strongly observed for male than female dolphins (p=0.005). A second generalized linear model showed that calf presence increases female dolphin’s risk of shark injury by a factor of 1.54 (p=0.011, N=669). Given other observations of mothers protecting calves from sharks, these results suggest that female dolphins’ risk of shark injury increases due to efforts to protect their calf.