Incidence of shark-inflicted bite injuries on Australian snubfin (Orcaella heinsohni) and Australian humpback (Sousa sahulensis) dolphins in coastal waters off east Queensland, Australia

Abstract

The ecology and evolution of prey populations are influenced by predation and predation risk. Our understanding of predator–prey relationships between sharks and dolphins is incomplete due to the difficulties in observing predatory events directly. Shark-inflicted wounds are often seen on dolphin bodies, which can provide an indirect measure of predation pressure. We used photographs of Australian humpback and snubfin dolphins from north, central, and south Queensland to assess the incidence of shark-inflicted bite injuries and to examine interspecific differences in bite injuries and their relationship with group sizes, habitat features, and geographical locations characteristic of where these individuals occurred. The incidence of shark-inflicted scarring did not differ between species (χ2 = 0.133, df = 1, p =.715), with 33.3% of snubfin and 24.1% of humpback dolphins showing evidence of shark bites when data were pooled across all three study sites. Generalized additive models indicated that dolphins closer to the coast, with greater photographic coverage, and in north Queensland were more likely to have a shark-inflicted bite injury. The similar incidence of shark-inflicted wounds found on snubfin and humpback dolphins suggests both are subject to comparable predation pressure from sharks in the study region. Results highlight the importance that habitat features such as distance to the coast and geographical location could have in predation risk of dolphins from sharks, as well as the importance of considering photographic coverage when assessing the incidence of shark-inflicted bites on dolphins or other marine animals. This study serves as a baseline for future studies on shark-dolphin interactions in Queensland and into how predation may influence dolphin habitat usage, group living, and behavior.