Retrospective Study of Traumatic Intra-Interspecific Interactions in Stranded Cetaceans, Canary Islands

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.

Contribution to Herpesvirus Surveillance in Beaked Whales Stranded in the Canary Islands

“…Most of the distribution information of BWs is based on stranding records. They face threats from entanglement in fishing gear, ingestion of marine debris, and ship collision, among others [2][3][4]. They are also of particular interest because of a notable relationship between military operations employing mid-frequency sonar and the mass stranding of BWs in different geographic areas, including the Canary Islands [5][6][7][8].…”

Retrospective Study of Fishery Interactions in Stranded Cetaceans, Canary Islands

“…In bycaught dolphins, the adrenocortical response and hyperthermia (45) induce injury to the skeletal muscle, similar to that described in live stranded cetaceans (26,27,31). Acute degenerative changes have also been observed in severely polytraumatized free-ranging stranded cetaceans, such as in cases of ship strikes (23,28) and fatal social traumatic intra-interspecific interactions (23,32). Previous studies have reported cardiac changes (29,46,47), as well as intracytoplasmic hepatocellular hyaline globules (13,27,48) in agonal situations.…”

“…A conservative approach was adopted to determine fishery interactions, based on previous studies (5-7, 12, 13, 21-24). All stranding cases were reviewed retrospectively, as we looked for individuals with findings that were consistent with fishery interactions, and excluded cases in which other possible traumatic etiologies, such as ship collision, intra-interspecific interactions, or live stranding, could not have been ruled out (25)(26)(27)(28)(29)(30)(31)(32). Different types of fishery interactions were determined based on gross findings.…”

“…The body condition index is a good indirect indicator of the nutritional status of cetaceans (17). Previous studies have described bycaught dolphins in good body condition (4), but this is common in cetacean deaths due to the fatal trauma of ship strikes (5,7,12,13), and social traumatic intra-interspecific interactions (32).…”

Distribution of Cetaceans in the Canary Islands (Northeast Atlantic Ocean): Implications for the Natura 2000 Network and Future Conservation Measures

“…Although the waters of the Canary Islands are considered a hotspot for marine biodiversity, for cetaceans in particular, this does not exempt marine mammals from being subjected to pressure and threats. Some of these threats are due to natural causes, such as predation, but, for the most part, they are consequences of direct or indirect anthropogenic activities (Parsons, 2012), including by-catch, competition with fisheries, habitat degradation (Ruíz de la Rosa et al, 2015), marine pollution (Baulch and Perry, 2014;García-Álvarez et al, 2014García-Álvarez et al, , 2015Puig-Lozano et al, 2018), acoustic/ noise disturbance (Aguilar de Soto, 2006;OSPAR, 2009), stranding (Tejedor and Carrillo, 2018;Puig-Lozano et al, 2020), and maritime traffic, including high-speed ferries-nearly 60% of sperm whale deaths are due to ship collisions in the Canaries (Arregui et al, 2019). These marine mammals are a highly mobile species; their distribution areas cover extensive oceanic areas, which pose a major challenge for their conservation.…”