Tuna-catching devices kill silky sharks

Devices used to catch tuna are killing hundreds of thousands of sharks per year in the Indian Ocean, researchers estimate.

Tuna tend to gather around objects floating in the sea. So over the last two decades, fisheries have attracted tuna by leaving masses of bamboo poles and netting, called fish aggregating devices (FADs), adrift in the ocean. Later, fishing boats return to catch the assembled fish.

To find out if sharks could become tangled in the nets, the study authors attached satellite tags to 29 silky sharks in the Mozambique Channel and near the Republic of Seychelles. The movements recorded by the tags suggested that four of those sharks became caught in the nets near the surface, the team reports in Frontiers in Ecology and the Environment. Divers also visited 51 FADs and found that 35 percent of them had ensnared one or more silky sharks.

Extrapolating from that data, the team estimates that FADs in the Indian Ocean kill about 480,000 to 960,000 silky sharks per year. Fisheries should replace the netting with biodegradable ropes, the authors say. Roberta Kwok | 4 July 2013

Source: Filmalter, J.D. et al. 2013. Looking behind the curtain: quantifying massive shark mortality in fish aggregating devices. Frontiers in Ecology and the Environment doi: 10.1890/130045.

Image © Sergey Dubrov | Shutterstock

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2 Comments

  • Karli Thomas July 7, 2013 at 10:00 pm

    These research results on silky shark impacts from Fish Aggregating Devices are shocking, and expose the true scale of this problem – much worse than I realised. However, the proposed solution of replacing the net design with biodegradable ropes only solves one part of the problem (entanglement in the FAD itself). The very nature – and intention – of FADs is to lure ocean life into their vicinity, for purse seiners to encircle and catch. The incidence of shark bycatch in purse seine sets made of FADs is much higher than sets on free-swimming schools of tuna. So far, there has been no credible solution to this impact of FAD fishing, and with tuna stocks also in decline (juvenile tuna of overfished species are also common FAD bycatch) the sensible solution would be to ban the use of FADs in purse seine fisheries altogether. Incidentally, while FADs are often touted as improving fuel efficiency (and do so, in more selective fisheries like pole and line) that claim has not proven true for purse seine fisheries. In fact, a study by the ISSF revealed that those vessels using more FADs also used more fuel. The authors noted: “Our results suggest that FAD use may not significantly improve FUI [fuel use efficiency] – indeed, it may have the opposite effect”. The growing list of tuna brands and retailers stopping their trade in FAD-caught tuna, including all the major brands in the UK, Australia and New Zealand, are on the right track. The fishing industry needs to get with the programme.

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  • Pedro Sousa de Jesus July 23, 2013 at 3:30 am

    Without a doubt FAD’s and other fishing gears when badely manage brings a very bad result to the enviroment.

    But worst than this FAD’s are the gillnets that are being used mostly in African and Asian countries supported by european fishing Co.

    Also I would like to see an article referring, explaining and calling to attention to the badly management done by US and Canadians fisheries in their waters and in the Pacific.

    I still remember the illegal fight done by US interests against tuna purse seiners to transfer live to cage in the mediterranean sea just because their tuna bussines wasn’t going well.

    I don’t mean that nothing needed to be done but I am tired of US hypocrisy in everything they are in…worst than overfishing in mediterranean was the BP accident right in Gulf of mexico where it is knowned to be one of the most important breeding places for tuna.

    What happen, what was the consequences for the tuna atlantic stock?

    What happen to the decreasing tuna stock in the Pacific?

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