Bottlenose dolphins (Tursiops truncatus) aggressive behavior towards other cetacean species in the western Mediterranean

Abstract

Aggressive behavior of bottlenose dolphins (Tursiops truncatus) towards conspecifics is widely described, but they have also often been reported attacking and killing harbour porpoises (Phocoena phocoena) around the world. However, very few reports exist of aggressive interactions between bottlenose dolphins and other cetacean species. Here, we provide the first evidence that bottlenose dolphins in the western Mediterranean exhibit aggressive behavior towards both striped dolphins (Stenella coeruleoalba) and Risso’s dolphins (Grampus griseus). Necropsies and visual examination of stranded striped (14) and Risso’s (2) dolphins showed numerous lesions (external rake marks and different bone fractures or internal organ damage by blunt trauma). Indicatively, these lessons matched the inter-tooth distance and features of bottlenose dolphins. In all instances, these traumatic interactions were presumed to be the leading cause of the death. We discuss how habitat changes, dietary shifts, and/or human colonization of marine areas may be promoting these interactions.

Post-mortem examination on a striped dolphin (Stenella coeruleoalba) reveals a potential fatal interaction with bottlenose dolphins (Tursiops truncatus) in Italian waters

“…Both in Spain (Crespo-Picazo et al, 2021) and France (Dhermain, 2020;Gannier, 2021), it has been noted that strandings of striped dolphins with injuries referable to bottlenose dolphins' aggressions were mostly located in areas with a very narrow continental platform, similar to the area of this case study, rather than in areas with a larger continental platform, presenting scarcer possibilities of encounter between the two species. The partial overlap in habitats could, in fact, result in territory defence behaviours by bottlenose dolphins and/or the competition for available resources between sympatric species as reported in other cases worldwide (Cotter et al, 2012;Methion and Díaz López, 2021).…”

Long‐term associations of common bottlenose dolphins with a fish farm in Hawaiʻi and impacts on other protected species

“…As noted, aggression by bottlenose dolphins towards other cetaceans has been increasingly documented off Hawaiʻi Island in recent years. Interspecific aggression in itself is not surprising—bottlenose dolphins have a reputation for such behavior, and are known to regularly associate with other species in contexts ranging from cooperative foraging to frequently documented aggressive socio‐sexual behaviors and infanticide (Cotter et al, 2012; Crespo‐Picazo et al, 2021; Dunn et al, 2002; May‐Collado, 2010; Methion & Díaz López, 2021; Patterson et al, 1998; Syme et al, 2021; Wedekin et al, 2004; Zaeschmar et al, 2013). However, the repeated documentation of aggressive encounters directed towards spinner dolphins off Hawaiʻi Island, many near the Makako Bay farm and involving farm associated dolphins, is particularly striking.…”

“…Similar situations have resulted at locations where wildlife are regularly provisioned as part of tourism activities; for example, provisioning of stingrays and primates has led to aggregations of individuals, many of whom displayed increased aggression towards conspecifics (Newsome et al, 2004; Wrangham, 1974). While not proven, the aggregation of multiple predator species has also been suggested as a potential explanation for interspecific aggression in bottlenose dolphins in waters near aquaculture facilities in the western Mediterranean (Crespo‐Picazo et al, 2021).…”

Social and community structure of striped dolphins in a semienclosed Mediterranean embayment

“…No sharks were observed during the seven years of this study, totaling approximately 30,000 km of navigation throughout the Gulf (Bearzi et al, 2016; Dolphin Biology and Conservation, unpublished data). Bottlenose dolphins do not predate or feed on striped dolphins, but they are known to harass and occasionally kill smaller cetacean species, including striped dolphins in European and Mediterranean waters (Barnett et al, 2009; Crespo‐Picazo et al, 2021). In the Gulf of Corinth, risks may come from the small community of bottlenose dolphins that inhabits these waters.…”