Shark bite injuries on three inshore dolphin species in tropical northwestern Australia

Predation risk has a profound influence on the behavior of marine mammals, affecting grouping patterns and habitat use. Dolphins frequently bear evidence of shark bites, which can provide an indirect measure of predation pressure. Using photo-identification data, we investigated the prevalence of shark bites on three sympatric species of inshore dolphin, the Australian snubfin (Orcaella heinsohni), Australian humpback (Sousa sahulensis), and Indo-Pacific bottlenose dolphin (Tursiops aduncus), among four study sites in northwestern Australia. Bite prevalence varied markedly between species, with 72% of snubfin, 46% of humpback, and 18% of bottlenose dolphins exhibiting evidence of shark bites. Binomial logistic regression confirmed a high likelihood of bite presence on snubfin dolphins, and at one particular site for snubfin and bottlenose dolphins. The prevalence of tiger shark (Galeocerdo cuvier) bites on snubfin dolphins was high, and bites attributed to other carcharhinid sharks were observed on all species. While acknowledging methodological differences with other studies, the prevalence of shark bites on snubfin dolphins is among the highest reported for any dolphins, suggesting predation risk represents an important but varying influence thereon. This study provides a baseline for future investigations into the affect of predation risk on the behavioral ecology of these sympatric species.