Nature can be brutal. Anyone who has cowered behind a cushion watching nature documentaries knows that. We like the idea that animals are cute and nice, so finding out that they are apparently more prone to, say, cannibalism than we had thought is a little shocking.
Researchers studying gray seals in the North Sea have discovered just that after witnessing and recording in detail an adult male catching, killing, and “feeding extensively” on a member of its own species.
It’s not the first time cannibalism has been observed in gray seals. In fact, it’s the third published paper on it. However, this is the first time scientists got to witness the whole thing up close and even perform a necropsy afterward on the unfortunate victim. Their findings are published in the Journal of Sea Research.
Being able to study the body afterward meant the researchers could look for patterns of bite marks that may be characteristic of cannibalism. Lead researcher, Abbo van Neer, thinks that if we go back through records of other seal attacks, we may find similar patterns that had previously been attributed to other causes of death, revealing that same-species nomming is more common than we had realized in gray seals.
This event occurred back in March 2018 on the island of Helgoland, part of a German archipelago in the North Sea between the UK and mainland Europe. Van Neer and colleagues witnessed an adult gray seal bull grab a juvenile male and hold it underwater while repeatedly biting at its throat. Rather dramatically, the researchers describe in their paper that the surrounding water turned red as the seal died.
Once dead, the bull completely changed its behavior and started feeding. Again, in great detail, the authors describe how the skin of the seal was almost fully detached and turned inside out, with the bull feeding on the rich blubber, swallowing chunks whole, for a full 90 minutes.
When it was finished, van Neer quickly grabbed the carcass before any scavengers could get to it and confuse the markings. This meant they could study the distinctive bites, tears, and damage to try and identify specific indicators that signify seal-on-seal predation.
Previous recorded instances of seal cannibalism include the rather grim 2016 study – and video, if you have the stomach – of a “rogue” bull killing and eating six pups in a week. Van Neer himself authored another paper in 2015 on gray seals observed killing and eating harbor seals in two separate instances, as well as discovering several carcasses bearing similar lesions to the cannibalized remains.
Another study from 2016 revealed that the mysterious "corkscrew" markings found in dead seals in Scotland, which had previously been attributed to boat propellers and/or sharks due to their spiral lacerations, were caused by seals. Photos of those wounds and the wounds of this seal do indeed show similarities. In fact, van Neer looked at a database of seal deaths going back to the 1990s and concluded that several deaths were more likely due to cannibalism – not that van Neer is suggesting it is a common lifestyle choice for seals.
“We hypothesize it’s probably a few specialized individuals," he told National Geographic. “It’s not going to be the majority of the gray seal population.”
So, why are they turning to the seal equivalent of dog-eat-dog? Experts cannot agree whether it's energy-saving for fasting males waiting to mate to grab the nearest nutrient-rich food, or just opportunistic or particularly violent individuals. But with mounting evidence and specific indicators that seal predation has occurred, it will be a lot easier to unravel this riddle in the future.
[H/T: National Geographic]