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A key mystery has been solved for seal pups at Sable Island.(Image credit: sandra standbridge via Getty Images)
The new paper, published Feb. 4 in the journal Marine Mammal Science, reports these firsthand accounts of gray seal cannibalism on Sable Island. Reanalyzing drone footage from 2023 as well, the research team recorded instances of adult male gray seals feeding on gray seal pups from 2023 through 2025.
Overall, the researchers found 765 seal pups with corkscrew markings during the 2024 breeding season. On a single day in 2025, they found 359 pups that had died from these injuries. However, this may not necessarily indicate that there was a spike in attacks but rather that scientists improved their searches for these pups.
“We were certainly relieved to have an answer to the cause of these deaths,” Damian Lidgard, a biologist at Fisheries and Oceans Canada and co-author of the new study, told Live Science in an email. For years, the cause was assumed to be shark predation, Lidgard added, but without any observations of sharks causing these deaths at Sable Island. With instances of male gray seal cannibalism elsewhere, the researchers were not surprised to discover the cause, he said.
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(Image credit: Damian Lidgard)
(Image credit: Damian Lidgard)
A seal carcass shows the corkscrew pattern of attack from cannibalism.
The researchers don’t necessarily think the behavior is a cause for alarm. “The most recent estimate of grey seal pup production on Sable Island is about 75,000,” Lidgard said. “Given that the number of pup deaths from male grey seals is estimated at under 1,000, there is no significant impact of cannibalism on the seal population on Sable Island.”
However, understanding the cause of seal pup deaths is important for the management and conservation of the island.
Although cannibalistic behavior has only been recorded in male gray seals on Sable Island, Lidgard said, it is possible that male gray seals are also targeting harbor seal (Phoca vitulina) pups that live on Sable Island, since this has been observed in Europe.
“Grey seals not only practice cannibalism, but also kill other marine mammals such as harbour seals,” Siebert said, “[so] it can become a threat to those populations.”
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“Harbour seal pup production on Sable Island is very small,” with populations in decline in recent decades, Lidgard noted, so this is potentially concerning.
The researchers added that the cause behind the cannibalism remains unknown.
“We are not sure why this is occurring on Sable or in other locations,” Lidgard said. “This may be a natural behaviour of grey seal males (as observed in other species) that has only recently been observed and documented. It might be a learned behaviour from an individual but that is unlikely given that it occurs on Sable and in the UK which are genetically/behaviourally isolated. I could keep providing hypotheses but really we don’t understand the cause.”