Illumination of nets reduced by-catch and death of marine animals

(ORDO NEWS) — Green lights attached to fishing nets reduce the number of accidental deaths of turtles, sharks, squid and other animals, but do not affect the catch of major game fish.

Gill nets and other means of industrial fishing do not distinguish valuable commercial species from accidental prey. An octopus, turtle or stingray tangled in nets can be a big hindrance for fishermen.

In this case, the animals themselves often die, and if we are talking about a rare and protected species, then the difficulties often turn into a legal plane. By-catch is an important factor leading to a decrease in the number of many species, and remains one of the most urgent problems for the fishing industry.

A few years ago, conservationists at the US National Oceanic and Atmospheric Administration (NOAA) decided to use colored lights to alert ocean dwellers to the approach of a net. Turtles are particularly sensitive to green, and these are the kind of lights that have been installed on the net.

They did indeed reduce the accidental catch of turtles by 64 percent, and after this success, the scientists decided to evaluate the effect of the lights on the catch of other species. The results of this work are presented in a new article published in the journal Current Biology .

Field experiments were conducted with fishermen working off the Pacific coast of Mexico. There is an industrial fishing for groupers and halibut, and because of the richness of the marine fauna, turtles and other random animals often become victims of it. Jesse Senko and his colleagues used 28 pairs of experimental networks: LEDs were placed on one of each pair with an interval of 10 m, the other remained, as usual, unlit.

As before, by-catch in illuminated nets was significantly lower, by 63 percent. In captivity, there were 51 percent fewer turtles and 81 percent fewer cephalopods than in the same networks without LEDs. Most notable was the decline in accidentally caught elasmobranchs—sharks and rays—falling as much as 95 percent.

At the same time, the fires did not have a great influence on the catch of commercial fish. What’s more, the researchers note that installing the lights at a cost of just $140 per net cut the time it took fishermen to free entangled animals by half.

Biologists are still at a loss to explain why some species of marine animals reacted more actively to light than others. Perhaps this is due to their relatively complex vision. This is typical for both sharks and cephalopods, while most fish do not have a developed visual apparatus.

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