Green LED lamps attached every ten meters to a junk network-obviously nothing more is needed to significantly reduce the by-catch. The light holds sharks, rays, but also calms and sea turtles from getting tangled on the net. At the same time, the fishing quantity of the desired food fish remains constant.
This is the result of a study for which a research group led by Jesse F. Senko from the University of Arizona laid out a total of 28 pairs of nets off the coast of California. One of them was equipped with the lamps, the other was not. She has now published the evaluation of her catch results in the journal »Current Biology«.
According to this, the amount of bycass fell by 63 percent, that of the sea turtles by 51 percent, that of the large Humboldt calm by 81 percent and those of sharks and rays by 95 percent. This also significantly decreased the time that the fishermen needed to catch up with their networks and for the sometimes dangerous sorting out of the by -catch. The boats were able to return about an hour earlier.
Gillnets are cheap and widespread, especially among small fishing companies, writes the team. The nets are fastened to the desired depth with the help of floats and then left to their own devices for a while. In addition to the desired fish, many other marine creatures also get tangled up in it. Turtles or marine mammals usually drown as a result, for sharks and rays it often means death as well. Why a green light prevents them – but not the edible fish – from getting caught in the net, the group does not know exactly. Presumably, they recognize the lights better than other sea creatures, but that is not enough as an explanation.
Members of the team have already observed the effect of the green lamps in 2016 and have now examined in detail. Currently it costs about $ 140 (123 euros) to equip a network with the lights, Senko told the magazine "Science". That could still be too expensive for many small businesses. A further developed technology could possibly be installed directly from the factory in the networks and thereby make it a matter of course, says Senko.
