More than 1,000 harbour porpoises are dying in UK waters each year having been caught in fishing nets, according to conservationists.
The shy and elusive cetaceans are accidentally trapped in gillnets – nets that are set at the surface or on the seabed – causing them to suffocate and die.
A report by WWF and Sky Ocean Rescue estimated that between 587 and 2,615 porpoises were killed in 2017.
The estimate is based on numbers recorded by observers onboard larger vessels using gillnets.
The conservationists said the scale of the problem could be far greater as smaller boats – under 10 metres in length – make up the majority of the gillnet fleet.
The report found that the South East and South West of England, as well as waters west of Shetland, saw a large number of fatalities.
These areas are rich in marine life, which in turn attracts both high numbers of porpoises and gillnet fisheries.
They said that the full extent of bycatch – wildlife, such as seabirds and turtles, accidentally captured in the nets – was unknown due to lack of monitoring.
Helen McLachlan, WWF fisheries programme manager, said: “The tragic deaths of harbour porpoises are a national scandal that can no longer be ignored.
“Many Brits will be horrified to learn of the scale of the issue and shocked that these beautiful mammals could be dying in the very nets used to catch the fish on their dinner plates.
“Yet UK governments have so far failed to combat this important threat to marine wildlife, despite aspiring for the UK to be a world leader in environmentally responsible fisheries.
“We need to see governments step up and work with the fishing industry to introduce effective mitigation or new capture methods that don’t harm porpoises or other marine wildlife.
“They also need to open up the secretive world of our fisheries by putting in place effective monitoring so that bycatch deaths no longer go unreported.”
In 2015 it was estimated the UK was home to around 177,000 harbour porpoises and two years ago six dedicated special areas of conservation were identified to protect the species across the UK.
The new report recommends that alternative gear should be reviewed for potential use in all UK gillnet fisheries, rather than trying to limit the damage that the gillnets themselves cause.
Ms McLachlan added: “What’s happening in UK seas echoes what’s happening on land: the governments are simply not doing enough to protect wildlife.
“We desperately need to take action now to protect and restore nature.”
A spokesman for the Department for Environment, Food and Rural Affairs (Defra) said: “It is vital we manage our seas in a more sustainable way for future generations, which is why we’re committed to protecting cetaceans from bycatch in our waters and beyond.
“We are working closely with stakeholders, including the UK fishing industry, to find ways of tackling this problem together.
“Only last month, we held a UK bycatch workshop to look at ways to effectively mitigate this problem and over the coming months will be working hard to develop and trial practical solutions to this critical issue.”