Every year, at least 7.3 million tons of marine life end up as bycatch. Sharks, turtles, whales, dolphins and seabirds are unintentionally caught in fishing nets, and then usually discarded, dead or dying, back into the water.
It’s a staggering waste of life that damages the marine ecosystem and the livelihoods of fishermen.
But new research may offer a lifeline. Scientists attached lights to fishermen’s nets and found that this significantly reduced turtle and seabird bycatch.
Ever wondered why canned tuna is labelled “dolphin friendly” or “dolphin safe”? It’s because during the 1960s, there was an outcry over the vast numbers of dolphins killed unintentionally by the tuna fishing industry – an estimated 6 million. As a result, fishing methods changed and dolphin bycatch reduced by 99%.
But sadly, one species of dolphin found only in China’s rivers is now believed to be extinct largely because of local fishing methods.
Seabirds, such as albatross and cormorants, that dive down into water to catch fish are also at risk of being caught in nets. Every year, around 400,000 seabirds become entangled in gillnets set up to catch fish such as salmon, cod and haddock. The problem is that birds and marine animals can’t see the nets.
It was the plight of these seabirds that motivated a group of scientists to look for a solution by using lights attached to gillnets.
Using lights to reduce bycatch
Previous research shows that putting LED lights on nets can reduce turtle bycatch by 64%. The lights act as a visual warning for the animals, but don’t affect the amount of fish caught in the nets.
A team of international researchers, led by Dr. Jeffrey Mangel from the University of Exeter, reasoned that such a visual cue may also be useful in reducing seabird bycatch, in particular, that of guanay cormorants.
Their experiment took place in the demersal (on or near the bottom of the sea) gillnet fishery of Constante, Peru.
Peru’s gillnet fisheries make up the largest part of the nation’s small-scale fleet. They set 100,000 km of net every year in which thousands of turtles and seabirds die as bycatch.
For the study, the researchers compared 114 pairs of gillnets, anchored in fixed positions at sea.
The nets were 500 metres in length. In each pair, one was illuminated every 10 metres along the gillnet floatline, and the other wasn’t.
They discovered that the nets fitted with the LEDs caught 85% fewer guanay cormorants compared to those without lights. The control nets caught 39 cormorants, while the illuminated nets caught just six.
The scientists surmised that lighting up the nets made them visible to the birds, allowing them to avoid becoming entangled.
Although it was a small-scale study, the results could have major implications.
The fact that the method worked well on two different species – turtles as well as seabirds – means that the adoption of the LED nets could be streamlined and the costs of implementing their use reduced.
Because there are so many coastal fisheries using similar nets, the potential for conservation is huge.
“It shows us that we may be able to find cost-effective ways to reduce bycatch of multiple taxa of protected species, and do so while still making it possible for fishers to earn a livelihood.”
The team is now working with larger fisheries in Peru and with different coloured lights to see if the results can be repeated and applied with more critically endangered species.