Changes in the feeding grounds of pilot whales may increase the risk of mass strandings, a study has found. Researchers from the University of Glasgow examined the deaths of 55 long-finned pilot whales that stranded on the Isle of Lewis in 2023, one of the largest such events in Scottish history.
Study Details
The study, led by the Scottish Marine Animal Stranding Scheme (Smass) at the University of Glasgow and published in the journal PLOS One, used stable isotope analysis to reconstruct the whales' feeding patterns in the weeks before the stranding. This technique examines chemical signatures in skin tissue to reveal where the animals had been and what they ate.
Post-mortem examinations had already confirmed the whales were in good health. A separate report by the Scottish Government's Marine Directorate suggested a combination of biological, behavioural, and environmental factors caused the event, with the highly social whales likely following a female experiencing a difficult birth into shallow water.
Feeding Behaviour
The new study provides evidence on the period leading up to the stranding. The isotopic data indicated the pod had been feeding primarily along the continental shelf edge and slope, deep offshore waters that support fish and squid populations in spring and early summer. Although the animals were in good nutritional condition, their stomachs were empty, raising questions about foraging activity just before the stranding.
This is the first direct evidence that long-finned pilot whales use shelf-slope habitats as important seasonal feeding grounds. The proximity of these habitats to rapidly shallowing coastal zones may represent a risk factor, placing foraging animals closer to conditions where stranding is likely.
Expert Comments
Anna Kebke, PhD researcher at the University of Glasgow and lead author, said: “Understanding the feeding habits of large marine predators such as long-finned pilot whales is critical for conservation strategies. Our findings demonstrate the importance of deep-water food sources and highlight the value of stable isotope analysis in advancing cetacean trophic ecology.”
Dr Andrew Brownlow, director of Smass, added: “Post-mortem examination tells us about the animals’ condition at the moment of stranding; stable isotope analysis tells us where they had been and what they had been eating. Together, they allow us to move from asking what happened to asking what set these animals on a course towards it.”
The scientists say understanding where these animals feed and how patterns may shift due to environmental change is essential to assessing human impact and minimising future risks.
