The effects of anthropogenic sound on behaviour and physiology in female Port Jackson sharks Heterodontus portusjacksoni (Elasmobranchii)

Elasmobranchs play a key role in marine ecosystems that continue to face many threats from human activities. Anthropogenic sound is now recognised as a global pollutant, but the effects on sharks are poorly understood. Using a behavioural playback laboratory experiment, we exposed adult female Port Jackson sharks (Heterodontus portusjacksoni) to biological and anthropogenic sounds. We focused on females due to their distinct seasonal behavioural patterns. Sharks were exposed to two acoustic conditions containing ambient or anthropogenic sounds in a 'before - during - after' exposure experiment. Recorded behaviours included activity levels, vertical swimming behaviours, tracking distance from the sound-source, use of a shelter structure, and gill movement counts as a proxy for respiration rate to predict physiological changes. While no significant differences were observed across their activities during treatment phases of playback, Port Jackson sharks increased use of the shelter during anthropogenic playback versus ambient sound conditions, and an increase in respiratory rate in the 'during' phase of anthropogenic playback that was not observed in ambient sound trials. In the 'after' phase of exposure to anthropogenic sounds, an increase in inactivity was observed, coupled with a decrease in respiratory rate. These findings suggest that there is a complex relationship between physiological and behavioural impacts to sound that requires further research. We demonstrate that anthropogenic sound affects H. portusjacksoni, but these effects may not be solely determined by measuring behaviour alone. Future research should include direct physiological measures to assess the overall impact of anthropogenic sounds on elasmobranchs.