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Deep, spiral-shaped lesions found in grey seal pups on Sable Island have puzzled scientists for decades, but new field observations linked the attacks to adult males of their own species and changed old suspicions about sharks and boat propellers
A mystery observed for decades in grey seal pups gained a more precise explanation after new scientific observations on Sable Island, Canada. The lesions, marked by a spiral pattern, start in the mouth area and extend to the animals’ chests, reaching the bone in some cases.
According to a study published in the journal Marine Mammal Science, the attacks were caused by adult males of their own species. The discovery changed old hypotheses raised by researchers, who previously considered shark attacks or accidents with boat propellers.
Field observations changed the investigation
The conclusion gained strength during fieldwork conducted in 2024, when researchers recorded an adult male directly attacking a grey seal pup. Sable Island is considered one of the main breeding areas for the species in the world, which made the record decisive for the investigation.
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According to Science magazine, the pattern of injuries was repeated in several analyzed pups. The marks started near the mouth and continued towards the chest, forming a deep, spiral-shaped trail.
Hundreds of pups showed the same pattern
During the 2024 breeding season, the team identified 765 pups with similar injuries. In 2025, researchers even recorded 359 carcasses in a single day, a volume that reinforced the severity of the phenomenon observed in the region.
Bite and scratch marks found on the bodies strengthened the hypothesis of attacks by adult males. The analysis also indicated that the injuries did not match mechanical accidents or attacks by external predators.
Researchers are still investigating the reason for the attacks
Despite identifying the probable perpetrators, scientists are still investigating why the attacks occur. One hypothesis raised in the study involves the search for energy reserves during the breeding season, a phase that requires great physical effort from adult males.
Marine biologist Claudia Hernández-Camacho, from the Interdisciplinary Center for Marine Sciences at the National Polytechnic Institute of Mexico, did not participate in the study. Still, she stated that witnessing such widespread and violent mortality is deeply disturbing.
Scientific mystery gains new explanation
The discovery shows how direct field observations can change scientific interpretations held for decades. For years, spiral injuries were associated with external causes, such as sharks and boats.
Now, the study points to an explanation linked to the species’ own behavior during the breeding season. On Sable Island, scientists continue to analyze records to better understand this pattern.
So, what leads adult male grey seals to attack pups of their own species during the breeding season?
