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Marine biologists might have discovered a surprisingly low-tech answer to bycatch

Early trials of a new type of fishing net have revealed that porpoises largely avoided getting entangled in them

Putting plastic in oceans is rarely good news for marine life, but this solution to the fishing industry’s bycatch problem could help to save thousands of porpoises, dolphins and whales from drowning.

Some 300,000 whale species die after getting tangled in fishing gear – including nets and lobster pot lines – each year. The creatures use echolocation to navigate obstacles, but as many nets are ‘invisible’ to their built-in sonar, they can easily become trapped.

Now marine biologists in Germany have hit on a way to make nets audible to cetaceans’ acoustic signals: by threading them with tiny beads made from acrylic glass.

The polymer bounces back biosonar signals as echoes, providing a warning to animals. Early trials of the low-tech solution in the Baltic Sea suggest porpoises largely avoided beaded nets.

Marine biologist Daniel Stepputtis, of the Thünen Institute of Baltic Sea Fisheries in Rostock, is pairing his creation with an acoustic device that sounds artificial porpoise warning signals, in the hope of addressing one possible shortfall: his research found that some animals were still becoming entangled despite the presence of beaded nets. He has theorized that they may have been asleep (though dormant porpoises continue swimming, they mute their echolocation).

Stepputtis plans to tune the beads to species’ specific frequencies and says that can be applied in other settings including freshwater rivers.

The acrylic glass beads bounce back biosonar signals to dolphins. Image: D stepputtis

Similarly low-tech initiatives have yielded encouraging results elsewhere. Research published earlier this year in Current Biology, a scientific journal, found that attaching green lights to fishing nets significantly reduces the amount of unintentional marine life that gets tangled up in them, without impacting fish catches.

The lit nets were trialled off the coast of Baja California in Mexico, where they were found to bring in 63 per cent less bycatch than unlit nets; including 51 per cent fewer turtles and 81 per cent fewer squid.

Meanwhile, a 2019 study by the University of Exeter found that lights on fishing gear reduced turtle bycatch by 70 per cent. A separate study noted an 85 per cent reduction in seabird bycatch when nets were lit.

Main image: NOAA

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