On that way, a potential enabler of predictable resources could be fish farms. However, territoriality has been hypothesized in resident bottlenose dolphins from Scotland excluding visitors from productive deep waters during winter 26. In the open ocean, it is generally accepted that cetaceans rarely display territoriality due to the lack of spatially-defined environmental features that may promote individuals or groups to demarcate their territories and patrol or defend them 25, 26. In this regard, many cetacean species adjust their distributions patterns in response to variability in food availability 24. However, perhaps the most feasible explanation is that it may be influenced by competition for resources 23. One usually discarded hypothesis is that dolphins are attempting to predate on the smaller cetaceans, although in most cases there is no evidence of attempted feeding 23. Other options such as high testosterone levels or sexual frustration have been considered when assessing the possible reasons driving interspecific traumatic interactions 23. Alternatively, it has been suggested that these interactions may result from bottlenose dolphins practice-fighting with the small porpoises 23, or as a practice oriented to the acquisition of skills used in infanticidal attacks 13, 18, 23. Aberrant behavior has been proposed, referred as the pattern that is outside the usual behavior for the species. However, many hypotheses have been proposed to explain the causal factors behind the aggressive interactions between bottlenose dolphins and other cetacean species, which have been reviewed by several authors 13, 14, 18, 23. Intraspecific aggression is commonly observed in bottlenose dolphin behavior repertories in many different contexts such as male competition, dominance, or female access for copulation, supported by wide field data 19, 20, 21, 22. More recently, an interspecific kill of a common dolphin by bottlenose dolphins was filmed and analyzed in detail in Northwest Spain 18. 39 also reported that aggression from bottlenose dolphins might have led to the death of at least one Risso’s dolphin ( Grampus griseus), one long-finned pilot whale ( Globicephala melas), one striped dolphin ( Stenella coeruleoalba), and four short-beaked common dolphins ( Delphinus delphis) on the southwest coast of England. Such incidents of aggression are reported relatively frequently from UK and western USA waters and occasionally Northwest Spain, and may often lead to mortalities 11, 12, 13, 14, 15, 16, 17. An often-reported example of aggressive interactions between cetaceans are the attacks on harbour porpoises ( Phocoena phocoena) by bottlenose dolphins ( Tursiops truncatus). However, close encounters between species groups can also lead to aggressive interactions between individuals 5, 6, 7, 8, 9, 10. Many cetaceans form inter-species groups that could benefit in foraging strategies 1, though interspecific interaction in mixed groups could be complex to interpret 2, leading even to the birth of hybrids on rare occasions 3, 4. We discuss how habitat changes, dietary shifts, and/or human colonization of marine areas may be promoting these interactions. In all instances, these traumatic interactions were presumed to be the leading cause of the death. Indicatively, these lessons matched the inter-tooth distance and features of bottlenose dolphins. 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). 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). However, very few reports exist of aggressive interactions between bottlenose dolphins and other cetacean species. 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.
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