For decades, the main defense has been battery-powered alarms called pingers, which work in some places but cost far more than many small-scale fishers can afford.<\/p>\n That price tag is the real sticking point. In the coastal fisheries where most bycatch happens, a fisher weighing a season\u2019s income cannot spend a small fortune wiring up every net.<\/p>\n The problem with invisible nets<\/p>\n Gillnets hang in the sea like long curtains, some stretching nearly two miles. <\/p>\n A dolphin<\/a> scanning ahead with echolocation gets almost nothing back from that thin mesh.<\/p>\n The echo is too weak, and by the time the animal senses the net, it is often already tangled. So a group of researchers asked a different question: what if you could make the net easier to hear?<\/p>\n Turning trash into a warning<\/p>\n The idea came from Per Berggren, a professor of marine megafauna conservation at\u00a0Newcastle University<\/a>.<\/p>\n He noticed that empty glass and plastic drink bottles wash up along the very coastlines where these fisheries operate.<\/p>\n Rather than treat them as waste, he wanted to bolt them onto the nets and let them warn the dolphins away. <\/p>\n How the bottles speak<\/p>\n A plastic bottle holds a pocket of air, and air is one of the strongest sound reflectors in ocean water. <\/p>\n When a dolphin\u2019s click strikes it, a sharp echo bounces back and a net that used to disappear suddenly stands out.<\/p>\n The glass bottle works by making noise instead. Each one carries a metal bolt on a string inside, so every time a wave rocks the net the bolt swings and clinks, mimicking the steady tap of a commercial pinger.<\/p>\n Lab tests in a sound tank supported the idea. A single plastic bottle made a net somewhere between 100 and 1,000 times easier to detect \u2013 a giant leap for an animal<\/a> listening for faint returns.<\/p>\n Three fisheries, one question<\/p>\n The team took the bottles to three very different fishing grounds. <\/p>\n Off Zanzibar and Peru, fishers set driftnets that float near the surface, while off southern Brazil the nets rest on the seabed.<\/p>\n More than 1,600 net deployments were watched by onboard observers and matched against ordinary nets. <\/p>\n The comparison would show whether cheap bottles could really change the odds for a dolphin.<\/p>\n A promising result in Brazil<\/p>\n Brazil gave the clearest sign of hope. In the seabed nets fitted with plastic bottles, not a single dolphin was caught, while the plain control nets still killed them.<\/p>\n Even better for the fishers, the weight of fish they hauled in actually went up. <\/p>\n One of the dolphins at risk there, the franciscana, is listed as Vulnerable by the\u00a0International Union for Conservation of Nature\u00a0(IUCN<\/a>).<\/p>\n Where the bottles fell short<\/p>\n The surface fisheries were a letdown. Neither glass nor plastic bottles reduced the capture of dolphins<\/a>, porpoises, or turtles off Peru or Zanzibar.<\/p>\n There was a silver lining, though. In those same waters the plastic bottles lifted the catch of tuna and other target fish \u2013 easing a worry many fishers have about tampering with their gear.<\/p>\n The glass pingers brought a twist of their own. Off Peru they shifted the balance of sharks and rays that landed in the nets.<\/p>\n This shows that a device built to help dolphins can ripple through the rest of the catch.<\/p>\n Why depth may matter<\/p>\n The contrast between the seabed and the surface points to one likely culprit. <\/p>\n Deeper water is darker and calmer, so dolphins there lean harder on echolocation and pick up the bottle echoes cleanly.<\/p>\n \u201cThe difference we saw in the success of the bottom set nets compared to the nets near the surface, may be that the surface water is a noisier environment reducing the efficacy of the plastic bottle reflectors,\u201d Berggren said.<\/p>\n A simple solution for dolphins<\/p>\n The first Brazil trial was encouraging but not yet conclusive, so the team pressed on. They expanded the work and tracked 318 fishing trips, once again setting bottle-fitted nets against standard ones.<\/p>\n This time the result was striking. Nets carrying plastic bottles cut dolphin bycatch by 88%, and the catch of commercially valuable fish held steady.<\/p>\n \u201cThis is a good news story and something that we strive for \u2013 a simple solution which benefits both dolphins and the fishers who use the gear,\u201d Berggren said. <\/p>\n \u201cAttaching plastic bottles to fishing nets can reduce dolphin bycatch globally and is something that every fisher can afford.\u201d<\/p>\n \u201cIt\u2019s also rewarding to know that we are using some of the plastic waste that spoils our oceans.\u201d <\/p>\n Berggren noted that the bottles were securely attached to the nets and no plastic bottles were lost during the trials.<\/p>\n What comes next<\/p>\n The beauty of the method is that it barely costs anything. <\/p>\n An empty bottle is free, which puts it within reach of fishers who cannot buy an electronic pinger.<\/p>\n Trials are now under way in Cambodia and Congo to see how far the idea can travel.<\/p>\n \u201cWe are excited to share this method and spread the word and work with governments and agencies around the world to encourage the adoption of this low-cost mitigation method to reduce marine mammal mortalities in fisheries,\u201d Berggren said.<\/p>\n \u201cThis is genuinely recycling that rescues dolphins.\u201d<\/p>\n The study is published in the journal Fisheries Research<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"Every year, dolphins and porpoises swim into fishing nets they never sensed in time. The gear is thin…\n","protected":false},"author":2,"featured_media":778880,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[64,63,128],"class_list":["post-778879","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-au","tag-australia","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/778879","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/comments?post=778879"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/778879\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media\/778880"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media?parent=778879"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/categories?post=778879"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/tags?post=778879"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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