Two studies tested the theory that attaching glass or plastic bottles to gillnets could prevent dolphins from getting caught\u00a0<\/p>\n
The harm plastic pollution does to ocean animals is no secret but what if plastic could be used to save lives instead? Some scientists think it can.<\/p>\n
Two new studies have explored the possibility of using plastic bottles to prevent dolphins getting caught in fishing nets and found that it can work.\u00a0\u00a0<\/p>\n
Gillnets are a type of fishing net that hang vertically in the water to trap fish but they often unintentionally catch other marine life, including dolphins.\u00a0<\/p>\n
\u201cIn the UK, static gillnets are responsible for more deaths than any other gear type,\u201d writes\u00a0Whale and Dolphin Conservation<\/a>\u00a0(WDC) on its website. \u201cWe know that around 1,000\u00a0porpoises<\/a>\u00a0and hundreds of dolphins, including 250\u00a0common dolphins<\/a>, die in gill nets in UK seas every year.\u201d<\/p>\n The nylon filaments that make up the net are almost invisible to dolphins, which often struggle to detect the nets using\u00a0echolocation<\/a>\u00a0\u2013 the process of bouncing sound waves off nearby items to build a picture of what\u2019s around them.\u00a0<\/p>\n \u201cSome fisheries use nets with very thin mesh which may be difficult for a dolphin to detect,\u201d writes WDC. \u201cPerhaps such materials don\u2019t produce an echo and so it could be that dolphins and porpoises swim \u2018blindly\u2019 into them, simply not detecting that they are there. Or perhaps they can detect the nets but do not\u00a0 perceive the danger.\u201d<\/p>\n Per Berggren<\/a>, a professor at Newcastle University wondered whether adding plastic and glass bottles to gillnets could help the dolphins locate the nets and avoid getting entangled.\u00a0<\/p>\n The idea is that the air inside the empty plastic bottles help to reflect the sound from the dolphins\u2019 echolocation clicks while metal bolts were put inside the glass bottles to create a clinking sound as they moved in the water.\u00a0<\/p>\n Two studies \u2013 now published in\u00a0Fisheries Research<\/a>\u00a0and\u00a0Marine Mammal Science<\/a>\u00a0\u2013 set about to test the theory.\u00a0<\/p>\n The first study attached glass and plastic bottles to more than 1,600 fishing nets in Zanzibar, Peru and Brazil and compared the results with nets that didn\u2019t have bottles.\u00a0<\/p>\n The results were mixed. In Peru, where nets are hung near the surface of the water, the bottles didn\u2019t make a difference to the number of dolphins, porpoises or turtles caught in the nets but did increase how many of their target fish they caught. The use of plastic bottles also increased the number of sharks caught.\u00a0<\/p>\n Similarly, in Zanzibar, the addition of bottles to nets on the surface resulted in them catching more tuna but they didn\u2019t catch any dolphins (including in the control nets, which didn\u2019t have bottles) so they couldn\u2019t come to a conclusion about how effective this was.\u00a0<\/p>\n They had more luck in Brazil, where nets are anchored to the seafloor. \u201cPlastic bottles showed promise in Brazil, potentially reducing dolphin bycatch while increasing fish catch, though further trials are needed to confirm this,\u201d the authors write in the paper.\u00a0<\/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 explains Berggren.<\/p>\n Following on from this work, the researchers tried again on bottom-set nets and found that the bottle reflectors reduced dolphin bycatch by 88%. The amount of target fish caught was not affected.\u00a0<\/p>\n