Officials at the Scottish Marine Animal Strandings Scheme (SMASS) are working to solve a bit of a mystery. What caused a female pilot whale to strand on a beach on the island of Skye recently?
While the necropsy (an autopsy performed on an animal) is still underway, initial reports suggest the young whale had a violent run-in with some unexpected adversaries: bottlenose dolphins.
According to SMASS, the whale appeared in good condition aside from having multiple, deep lacerations along her body. "These rake marks were spaced 10-12 millimetres apart, consistent with the spacing of dolphin teeth," the team explains.
It's still too early to tell what happened on Skye, but is it even possible for dolphins to kill a pilot whale? Interestingly, the short answer is yes.
The dolphins in Scottish waters are particularly large compared to their cousins elsewhere, and it's possible that a pod could have charged the whale, but as dolphin researcher Dr Justin Gregg explains, it's not a likely scenario. "I am not aware of reports of the death of a pilot whale being linked to bottlenose dolphin attacks," he says. "But bottlenose dolphins – especially the ones in the area where this stranding occurred – have been known to attack harbour porpoises and dolphin calves."
What makes this case a slightly befuddling is that unlike harbour porpoises, pilot whales are larger than bottlenose dolphins. "Most 'attacks' by bottlenose [dolphins] have focused on animals smaller than themselves," says Gregg, adding that it's possible the tooth rakes were caused during play, or only after the animal appeared injured to the dolphins. It could also be that the injuries were caused by fellow pilot whales, perhaps while trying to aid a struggling pod member. "It's too early to say how or why they occurred," he says.
The animal's stomach revealed a mass of squid beaks and chyme (the fluid that moves through the intestines during digestion), suggesting the dolphin was healthy enough to hunt at least somewhat recently.
"If the [full] necropsy reveals the kind of blunt force trauma and internal damage that are typical of bottlenose 'attacks' on other species, then that is more suggestive of the possibility that the bottlenose fatally injured the pilot whale," explains Gregg. "But even then it’s all quite speculative."
These kinds of encounters are still poorly understood, but scientists believe they're likely the result of tussles over territory, competition for food or mating behaviour.
The SMASS team will be running further tests, and quite literally digging deeper to get to the bottom of the mystery, looking for telltale signs like cracked ribs, muscle tearing, organ ruptures, deep tissue bruising and brain bleeds (yeah, dolphins are hardcore). We'll be updating you as news comes in, so watch this space.
You can see some cetacean-on-cetacean carnage in these images of a harbour porpoise necropsy performed by the SMASS team. Scroll at your own risk; some might find the photographs disturbing.
Top header image: Alexandre Roux, Flickr