An image of an octopus appearing to grip the fin of a Risso’s dolphin in the UK’s southwest waters showcases how warming seas are reshaping marine food webs in South West England, researchers have said.

The images, captured by volunteer Bill Coulson off Berry Head as part of the Risso’s Dolphin Project South West,

Risso’s dolphins are usually associated with deeper, offshore waters – preferring depths between 400 and 1,000 metres – their diet is thought to be dominated by squid and other cephalopods.

The sighting comes as researchers investigate an unprecedented surge in common octopus numbers along the South West coastline, described as the largest such bloom in at least 75 years. 

Marine Biological Association (MBA) researchers, who surveyed fishermen, divers and snorkellers, believe the population may have originated from breeding grounds near the Channel Islands and northern France, with warming waters and shifting currents carrying juvenile octopuses into UK seas.

Josh Symes, an MSc researcher at the University of Exeter studying Risso’s dolphins through photo identification, said the images captured more than an unusual encounter. 

“These photographs offer a fascinating glimpse into the feeding ecology of Risso’s dolphins,” he said, adding that the sighting helps researchers understand how the animals are “responding to changing prey availability.”

Dr Bryce Stewart, senior research fellow at the MBA, said the encounter illustrated the wider ripple effects of the octopus bloom across the region’s marine ecosystem. He said the sightings were: “a powerful reminder of how interconnected our marine environment is.”

The findings echo the State of South-West Seas in 2025 report, which describes the octopus “outburst” as exceptional and links it to a wider pattern of marine heatwaves and shifting species distributions along the South West coast. 

Researchers also said the images underline the value of citizen science in monitoring the UK’s marine wildlife, and have urged members of the public to report octopus and dolphin sightings via the Risso’s Dolphin Project South West Facebook page or the iNaturalist app, to support ongoing monitoring efforts.

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