The Scottish Government has launched an investigation after “mountains” of dead shellfish and fish were found “dumped” near Gigha.
Footage of thousands of dead prawns covering the sea floor near the Isle of Gigha’s pier has provoked outrage.
Also among the shellfish were five different species of shark, fish and the critically endangered flapper skate.
It is believed the haul was caught by a prawn trawler, which then dumped them overboard.
While campaigners say this discarding of bycatch fish is a hidden problem, catching it on camera is “very rare”.
The Scottish Government said they are now investigating the incident.
‘I’ve never seen anything like it’
The film of the haul was captured by local marine ecologist Peter Hume of Sea Kintyre.
When carrying out a seagrass mapping project on Gigha on June 9, he noticed a lot of dead langoustines.
A few days later, following a tip from Shark and Skate Scotland, he returned to find thousands more in the “crystal clear west coast water” by Gigha’s pier as well as hundreds of dead skate, dogfish and squid.
“I’ve never seen anything like it,” he said. “It’s absolutely shocking that this can happen and also that whoever did it, did so in shallow water.
“It’s completely visible. The fact that they’d dump it there is a real slap in the face to everyone who lives there. Gigha is a very environmentally-minded island.
“This is pretty much happening with every catch. In some ways, it’s good they did because we now have evidence that it’s happening.”
It is common for trawl boats to discard prawn heads at sea, as it is permitted on the West Coast.
But discarding most bycatch fish is illegal under the 2019 Landing Obligation.
Although accidental bycatch is not a crime, the law requires all skates and rays to be “released immediately” to try and ensure their survival.
However, campaigners said this was not the case with this incident.
Flapper skates ‘thoughtlessly dumped’
There were several critically endangered mature flapper skates – relatives of sharks – among the fish found dead.
The species are slow growing and late to mature, making them highly susceptible to overfishing.
Lauren Smith is one of the co-founder’s of the Shark and Skate Scotland group which gathers data on the species.
After seeing Mr Hume’s footage, the Newburgh resident said: “It’s just so disappointing.
“They’re supposed to release them as soon as they realise they have flapper skate etc within the net. The fact they were basically with all the prawn heads and stuff – that’s a later discard.
“That’s not instantly happened. That’s been brought in and they’d been thoughtlessly dumped over the side after.
“It’s kind of why we wanted to get the video out there to show that this is what happens, this is the cost of trawling for scampi. And we need to be able to ask ourselves, does this make sense?”
Charity said video shows sad reality of scampi
Large volumes of fish and other marine life are regularly caught in the bottom-trawl nets used to sweep the seabed.
Scottish marine sustainability charity, Open Seas, said unintended bycatch by bottom-trawl nets is a bigger problem in the prawn trawl fishery due to the small mesh size of the nets used.
While they say it has led to the declining health of many fish populations, it is a difficult issue to monitor.
The charity is calling for better mandatory vessels tracking for bottom trawlers to stop this from happening.
Nick Underdown, head of campaigns at Open Seas, said: “The environmental impact of bottom-trawling is usually hidden from public view, but this footage shows the sad reality of trawling for prawns.
“Most people have no idea that their scampi and chips are caught using this fishing method which routinely involves catching and discarding other fish.
“This film shows clearly why the Scottish Government must progress measures to restrict bottom-trawling in our sensitive coastal waters and help the trawl fleet transition to a more sustainable management regime.”
Peter Hume reported the incident in his video to Marine Scotland and Police Scotland.
A Scottish Government spokesman said: “The Scottish Government is aware of the alleged incident.
“An active investigation is underway. It would be inappropriate to comment further.”
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