According to scientists from the University of Exeter, an estimated 400,000 diving seabirds die annually by getting caught in gill nets intended to catch fish. A new study indicates that the majority of those deaths could be avoided, however, if the nets were to be equipped with inexpensive green LEDs.

Gill nets hang like vertical curtains in the water, with float lines at the top and anchors at the bottom. They're unseen by fish who swim into them and become entangled in the netting. Unfortunately, non-target species such as seabirds also don't see the nets, and likewise fall victim to them.

With that in mind, a U Exeter-led international research team experimented by deploying 114 pairs of ~600 meter-long (1,969-ft) gill nets in Peru's Sechura Bay. Each pair consisted of one regular net, along with another that had the LEDs distributed at 10-meter (33-ft) intervals along its float line. All of the nets were left in place from late afternoon until the following morning.

When the nets were pulled up, it was found that while the non-illuminated ones caught a total of 39 cormorants, the illuminated nets captured just six. In a previous study, the same technology apparently also worked to alert sea turtles to the presence of the nets – in that case, the regular nets captured 125 green turtles, while the LED-equipped ones caught 62.

In both studies, the capture rate of target fish was unaffected by the lights. The scientists are now looking at using additional colors of LEDs, to deter other types of non-target animals.

A paper on the research was recently published in the journal Open Science.

And for an example of technology designed to reduce seabird bycatch in longline fishing operations, check out the Hookpod.

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