Fishing nets are the most likely cause of death for common dolphins stranded on Cornwall's coast, research shows.
More than 860 short-beaked dolphins were stranded from 2018 to 2024 and the vast majority were dead, it found.
The Defra-funded study by the University of Exeter, Cornwall Wildlife Trust and Cornwall Marine Pathology Team examined 175 stranded dolphins and concluded 39% died after getting tangled in fishing gear.
A Defra spokesperson said: "We are taking action to help reduce the number of dolphins caught in fishing nets. Through our Clean Catch programme, we are trialling measures to warn dolphins away from nets in hotspot fishing areas like Cornwall."
The study suggests Cornwall is the hotspot for common dolphin bycatch, the accidental capture of unwanted marine life, possibly due to the large number of visiting animals, combined with the number of fishing vessels.
The study, carried out under the Defra-funded Cetacean Strandings Investigation Programme, found other principal causes of dolphin deaths were infectious disease (25%), live stranding of healthy animals (10%), non-bycatch trauma (8%) and starvation (7%).
James Barnett, co-author of the report, carried out most of the post-mortem examinations and found "smaller vessels fishing with gill or possibly drift nets" were the "likely cause of the marks we found on most of the dolphins that died due to bycatch".
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He added: "While diagnosed bycatch deaths have declined in the last 30 years, the bycatch cases in this study are still a significant concern in terms of potential conservation and welfare impacts."
Barnett said monitoring of fisheries needed to be improved to reduce bycatch through an "observer programme that encompassed the whole fishing fleet –
Fishing Nets Main Cause of Dolphin Deaths in Cornwall