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Despite often being considered top predators, small delphinids (2.5 m total length) in several marine ecosystems around the globe. Yet, estimating relative shark predation pressure and risk to cetacean species and populations, and how they might vary across ecological contexts, has been challenging. Evidence of unsuccessful predation, such as bite wounds, epidermal scarring, and related injuries, has been reported across multiple taxa and locations, providing broad insights into the extent of predation risk to odontocetes in several populations. Here, we synthesize 41 published studies that reported the prevalence of shark-inflicted injuries on 17 cetacean species across 62 locations globally to gain insights into the dynamics and drivers of shark predation on cetaceans. Using a subset of studies on small coastal delphinids, we further assess factors influencing variation in shark-inflicted injuries. Prevalence of injuries caused by sharks was significantly greater in populations from the southern hemisphere. Binomial logistic regression of proportions of individuals with shark-inflicted injuries across 3 coastal dolphin genera ( Tursiops , Orcaella , and Sousa ) suggests a lower prevalence in areas with high fishing pressure, large shark population declines, and other human impacts. Overall, our results suggest that throughout much of their ranges, coastal and estuarine delphinids currently experience lower than expected predation pressure, likely due to fishing pressure and the resulting declines of large sharks. However, conservation efforts focused on restoring shark populations may begin to reverse these trends in countries with strong fisheries management measures. Establishing and investigating baselines in predator-prey interactions among upper trophic level consumers can provide critical insights for understanding marine community dynamics and ecosystem-based management.
Moxley et al. (Wed,) studied this question.