Dolphin deaths due to trauma in the waters of the Canary islands: interaction as a cause?

Abstract

The University Institute of Animal Health (IUSA) has been routinely conducting post-mortem examinations of cetaceans found stranded in the Canary Islands in order to diagnose the cause of death. In the last three years, thirteen cetaceans were found stranded with traumatic lesions consistent with violent interactions, of which three animals were calves and one was a juvenile: two common dolphins (Delphinus delphis) and two striped dolphins (Stenella coeruleoalba). These dolphins exhibited injuries characterized by extensive bruising and hemorrhage in the subcutis and underlying musculature, particularly over the dorsum and flank. The four animals showed several ribs fracture, three of which presented massive hemorrhage on pleura and lungs associated with broken ribs. Both common dolphin calves and striped dolphins presented deep parallel linear skin abrasions similar to interespecific tooth-rakes seen in cetaceans. Interactions between bottlenose dolphin (Tursiops truncatus) and delphinid calves had been seen occasionally in the waters of the Canary Islands. These results are highly consistent with inter or intraespecific interactions causing death of young dolphins as it has been described in other areas of the world. These are the first cases reported in Canary Islands and more attention to this cause of death should be taken into account when young dolphins are found stranded.