A simple technique to “illuminate the exits” in trawl fishing nets can almost halve the numbers of unwanted catch, new research has found, potentially protecting both the environment and fishermen’s livelihoods.
Attaching LED lights to larger holes in nets, intended to allow non-target species to escape, dramatically reduced the numbers killed unnecessarily, a team from Bangor University found.
The research, published in Journal of the Marine Biological Association of the United Kingdom, inverts an old fishing technique of shining a light on water to attract fish into a net.
The study, conducted between June and August 2017, tested the effect of lights in reducing the number of haddock and flatfish caught in a queen scallop fishery off the Isle of Man.
It found that while existing devices to reduce bycatch (species caught unintentionally) were effective at shallower depths of 29-40 metres, they had no effect in deeper, darker waters of 45-95 metres. But once LEDs were added to these “exits” in deep water, haddock bycatch was reduced by 47% and flatfish by 25%.
Bycatch is a problem in fisheries worldwide because it inflicts further damage on often depleted non-target species, and kills mammals and seabirds that become entangled in nets.
It can also be a huge cost to fishermen – under EU law, fishermen are required to bring ashore almost everything they catch, including fish that are not part of their quota.
If they end up catching too much of their non-target species, their fishery can be “choked” – closed for months – to allow vulnerable stocks to recover.
Lucy Southworth, lead author of the study, said: “Traditionally, and this goes back decades and maybe even centuries, fishers used lights to attract fish.
“We are turning that on its head to try and manipulate the behavioural responses in fish and other animals, to either repel them away from gear, or to manipulate their behaviour so they can escape from the net.”
She added: “We decided to attach the lights to the escape exit to try and guide fish towards it so they would escape more so than if the lights weren’t there.”
Southworth said the discovery that existing bycatch reduction devices without LEDs stop working at greater depths, and at night, was “very worrying”.
It meant fishermen trying to comply with the rules still risked their fisheries being closed early, and also causing unintended environmental damage.
The research team believes the LED solution could prove popular because the lights are relatively cheap, and easily applied to existing nets and reconfigured for different environments.
Separate research, conducted in Peru, has shown LED lights can reduce the numbers of seabirds entangled in gill nets, and is trying to establish if they can help protect turtles.
Anecdotally, the team on the Isle of Man found evidence of sharks escaping nets, and thought it could be an area for further research.
The LED solution could potentially reduce the numbers of dolphins, whales and porpoises unintentionally killed, with the lights alerting the mammals to the presence of nets – particularly gill netting, which forms a wall across the seabed – helping them to avoid danger.