Abstract
Aggressive encounters involving cetacean species are widely described in the literature. However, detailed pathological studies regarding lesions produced by these encounters are scarce. From January 2000 to December 2017, 540 cetaceans stranded and were necropsied in the Canary Islands, Spain. Of them, 24 cases of eight species presented social traumatic lesions produced by cetaceans of the same or different species. All the cases presented severe multifocal vascular changes, 50% (12/24) presented fractures affecting mainly the thoracic region, 41.7% (10/24) acute tooth-rake marks, 37.5% (9/24) undigested food in the stomach, 33.3% (8/24) tracheal edema, and 12.5% (3/24) pulmonary perforation. In 10 cases with tooth-rake marks, the distance between the teeth, allowed us to further identify the aggressor species: four cases were compatible with killer whales (Orcinus orca) affecting three species [pigmy sperm whale (Kogia breviceps), Cuvier's beaked whale (Ziphius cavirostris), and short-finned pilot whale (Globicephala macrorhynchus)] and four cases compatible with common bottlenose dolphins (Tursiops truncatus) affecting two species [short-beaked common dolphin (Delphinus delphis) and Atlantic spotted dolphin (Stenella frontalis)]. We also described two cases of intraspecific interaction in stripped dolphin (Stenella coeruleoalba). Microscopically, 70.8% (17/24) of the cases presented acute degenerative myonecrosis, 66.7% (14/21) presented vacuoles in the myocardiocytes, 36.8% (7/19) pigmentary tubulonephrosis, 31.6% (6/19) cytoplasmic eosinophilic globules within hepatocytes, 21.4% (3/14) hemorrhages in the adrenal gland, and 17.3% (4/23) bronchiolar sphincter contraction. The statistical analysis revealed that deep divers, in good body condition and nearby La Gomera and Tenerife were more prone to these fatal interactions. Additionally, in this period, three animals died due to an accident during predation: a false killer whale (Pseudorca crassidens) died because of a fatal attempt of predation on a stingray, and two Risso's dolphins (Grampus griseus) died as a consequence of struggling while predating on large squids.
Highlights
The term “intra-interspecific interactions” refers to interaction with individuals of the same species or with other species
This study aims to investigate the prevalence and the pathologic findings associated with social traumatic interactions between cetacean species and foraging fatalities in the Canary Islands, based on postmortem examinations
In 88.9% (24/27) of the cases, social traumatic interactions between cetaceans of the same or different species produced blunt-force traumas that led to death
Summary
The term “intra-interspecific interactions” refers to interaction with individuals of the same species (intraspecific) or with other species (interspecific). When the interactions become aggressive it may lead to serious injuries and/or death of the animal [1,2,3,4]. Social intra-interspecific interactions can produce mild multifocal lesions over the skin known as “tooth-rake marks” (external linear and parallel erosions on the skin inflicted by teeth), frequently observed healed in stranded animals. When interactions became aggressive, tooth-rake marks could be severe and ulcerate the skin affecting the subcutaneous and muscle tissue. Other lesions that had been reported in fatal encounters include: blunt traumas with subcutaneous focal or multifocal extensive hemorrhages, hematomas, tearing of the blubber, vertebral and/or ribs fractures, myonecrosis, tearing of the parietal pleura with associated-pulmonary hemorrhages, hemothorax, retroperitoneal hemorrhages, perforation of the abdominal wall, and liver rupture [3,4,5,6]. Pulmonary fat emboli [8] and myo-/hemoglobinuric nephrosis [4] can be observed by specific staining
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