Grey seals do not only bite porpoises: new research shows first evidence of damage to dolphins
Researchers from Utrecht University and partners in the United Kingdom have found the first evidence that grey seals can also injure dolphin species. Until now, such interactions were known to occur almost exclusively with porpoises. The study, which was published today in the scientific journal Diseases of Aquatic Organisms, shows that grey seals may have a broader impact on small cetaceans in the North Sea than previously thought.
The research is based on post-mortem examinations of four stranded dolphins: a bottlenose dolphin, a common dolphin and two white-beaked dolphins. All animals had injuries consistent with grey seal bites, confirmed by pathological and microbiological examination.
Although none of the dolphins died immediately from an attack, the wounds and bacteria found indicate that grey seals also interact with cetaceans other than porpoises. This suggests that seals, as top predators, play a larger and more diverse role in the North Sea ecosystem.
The injuries were often several days to weeks old, indicating that the animals survived the encounter but later died from severe bacterial infections, including bacterial species specific to seals. This makes the cases particularly relevant for understanding disease spread among marine mammals.
Grey seal populations have grown significantly along European coasts in recent decades. With more animals, the chance of interactions with other marine mammals increases. Understanding how these species influence each other is essential for monitoring changes in the marine food web, better protecting the health of vulnerable species, and recognising potential zoonotic risks (transmissible bacteria).
According to the researchers, future dolphin necropsies should look more closely at possible interactions with grey seals. Lead researcher Lonneke IJsseldijk, Utrecht University: ‘Our findings show how valuable well-coordinated stranding research is. By combining information from different countries, we get a clearer picture of what is happening in the North Sea.’
This research was made possible thanks to close collaboration between various stranding networks:
- the Dutch Stranding Research Programme (Utrecht University),
- the the ZSL-led UK Cetacean Strandings Investigation Programme (CSIP), and
- additional contacts with Belgian, German and Scottish networks.
This collaboration makes it possible to detect changes in the behaviour of marine predators on a regional scale and to recognise patterns that would go unnoticed within a single country.
Dutch Strandingresearch is funded by the Ministry of LVVN. For more information, visit the Stranding Research website or follow our researchers on Instagram.