Mass Stranding Offers Rare Insight into Lives of Pilot Whales
Scientists report they have uncovered rare insights into the feeding habits of long-finned pilot whales following a mass stranding event in the Western Isles.
The pod, consisting of 55 whales, perished after encountering difficulties in Tolsta Bay, Lewis, in July 2023.
Research published last month suggested the stranding was initiated by a female whale experiencing a challenging birth.
The new study reveals evidence about the whales' seasonal feeding grounds and how these locations may contribute to the risk of stranding for these elusive animals.
Led by the Scottish Marine Animal Stranding Scheme (SMASS) at the University of Glasgow, the study was published in the scientific journal PLOS One.
By analyzing skin tissue samples, scientists identified "chemical signatures" indicating that the whales were healthy and had likely been hunting fish and squid near the deep waters of the continental shelf surrounding the UK.
The researchers noted that long-finned pilot whales are a deep-water species and are "notoriously difficult" to study in their natural environment.
Because it is possible to collect tissue samples from stranded animals, stable isotope analysis was employed to reconstruct their feeding history.
The data suggested that the pod had primarily been feeding along the edge of the continental shelf and the slope descending into deeper offshore waters.
This area is believed to support substantial populations of fish and squid during spring and early summer.
Scientists observed that the whales were in good nutritional condition at the time of death; however, their stomachs were found to be empty.
This finding raised questions regarding their foraging activity immediately prior to the stranding, the research team stated.
They added that the study represents the first direct evidence that long-finned pilot whales utilize shelf-slope habitats as significant seasonal feeding grounds, which in turn places them at risk of stranding in shallower waters.
The continental slope is a geological feature where the seabed descends from shallower coastal seas to the deep ocean.
In some regions, the slope is a long, gentle gradient, while in others it is steep.
Various water currents mix in this zone, and the nutrients they stir up create a habitat that attracts plankton, fish, and larger animals such as whales.
Researcher Comments and Conservation Implications
Anna Kebke, a PhD researcher at the University of Glasgow and lead author of the study, stated:
"Understanding the feeding habits of large marine predators such as long-finned pilot whales is critical for the development of conservation strategies. However, dietary data are often lacking."
"Our findings demonstrate the importance of deep water food sources to long-finned pilot whales, providing valuable insights into their early spring-summer feeding habits."
SMASS director Dr Andrew Brownlow commented that the analysis adds to information already obtained from post-mortem examinations of the whales.
"Together, they allow us to move from asking what happened at the moment of stranding to asking what set these animals on a course towards it."
The research team noted that two additional mass strandings involving long-finned pilot whales occurred in Scotland in 2024 and 2025, underscoring the urgency for further study.
'Distressed Individual'
During the 2023 incident, members of British Divers Marine Life Rescue and other volunteers attempted to save some of the pilot whales.
In its report released last month, SMASS found that a mature female had experienced a difficult birth.
The scientists suggested this event may have served as a "possible social trigger for the stranding."
"Strong social cohesion may have then led the entire group to follow the distressed individual into shallow waters. Once stranded, the animals were unable to refloat themselves due to a combination of surf generated by onshore winds and the soft sand substrate on the beach."
Long-finned pilot whales are large dolphins and are described by Whale and Dolphin Conservation as having "incredibly strong bonds."
