Fishing nets 'most common cause' of dolphin deaths
BBCFishing 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".
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 – from the smallest of fishing vessels to industrial-scale fisheries".
He said methods which reduced bycatch included modifying fishing gear and practices, using acoustic deterrents known as pingers, reducing the time nets were left in the water and closing fisheries in key places to protect dolphins.
Rebecca Allen, of Cornwall Wildlife Trust, which helps monitor strandings around the coast, said while many local fishermen were doing what they could, bycatch remained a significant issue in Cornwall and Devon.
"We need urgent, high-level action to achieve better management of the static net fishery and to support local fishers' access to appropriate bycatch mitigation technology," she said.
"Reducing bycatch is a win-win for both fishers and wildlife; reducing interactions with fishing gear both prevents unnecessary deaths of ocean wildlife and helps protects fishers' nets and catch."
Rob WellsDefra said its bycatch monitoring programme is testing a range of monitoring and mitigation approaches in known hotspot areas, including Cornwall.
It said acoustic deterrent devices could be an "effective way to alert and keep some species out of nets", however, they could also have "adverse environmental consequences".
The Marine Management Organisation, which regulates the fishing industry, said the devices, designed to disturb cetaceans to prevent them being caught, were required on fishing vessels more than 12m (39ft 4in) long using bottom set gill or entangling nets in areas where cetaceans are most common.
Vessels not required to use the devices must secure a marine wildlife licence to use them, as disturbance of cetaceans is otherwise against the law.
A spokesperson said: "We know fishermen never intentionally set out to catch or harm cetaceans. Their knowledge and experience working at sea is incredibly valuable, which is why we have a reporting mechanism in place."
Fishers in south-west England have campaigned for pingers to be available for all fishing vessels.
Why do dolphins die?
Other results from the dolphin stranding study include:
- Of the 43 cases in which infectious disease was the probable cause of death, 32 dolphins had been severely affected by parasites
- Starvation was mostly found in young animals, around the age of independence from their mothers – suggesting these creatures failed to make the transition to self-feeding or were prematurely separated from their mothers
- Of the 14 cases of non-bycatch related trauma, two animals had lesions consistent with attacks by bottlenose dolphins. One of these, an adult male weighing 107kg, is one of the largest animals known to have been killed by bottlenose dolphins in the UK
- Two dolphins had lesions consistent with ship strike, including one juvenile male with wounds consistent with propellor injuries
- Two animals choked to death on flatfish. The heads of the fish were lodged within the bony nasal passage of the dolphins
- The short-beaked common dolphin is the most frequently stranded cetacean species (whales, dolphins and porpoises) in Cornwall, with more than 100 strandings each year
