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Overfishing sharks: what exactly is longlining?

We all know fishing pressure on sharks is enormous, and many shark populations are severely declining because of this. One the methods used for this is ‘longlining’. But what is this exactly?

Longline vessels in port

According to the Food and Agriculture Organization of the United Nations a drifting longline consists of a mainline kept near the surface or at a certain depth by means of regularly spaced floats and with relatively long snoods with baited hooks, evenly spaced on the mainline. Drifting longlines may be of considerable length.  Small fishing boats can set out long lines of around 50 metres, but commercial longliners can run over 2.500 hand-baited hooks on a single series of connected lines many miles in length.

As target shark species, the FAO mentions blue shark, mako, hammerhead, bigeye thresher sharks, silky sharks and oceanic whitetips, bignose shark, silvertip shark and porbeagle shark and even the giant manta, depending on regio and season. Blue sharks are often taken as bycatch in tuna and swordfish fisheries.

As the FAO correctly states: “In the majority of the countries dealing with shark fishing, no accurate statistics exist of shark catches from both the artisanal and industrial fisheries. It would be advisable to develop an accurate statistic system that include shark fishing.”

Longline fishing is controversial in some areas because of bycatch, fish caught while seeking another species or immature juveniles of the target species. This can cause many issues, such as the killing of many other marine animals while seeking certain commercial fish. Seabirds can be particularly vulnerable during the setting of the line, an estimated 100,000 albatross per year are killed in this way.
Methods to mitigate incidental mortality have succeeded in some fisheries. Mitigation techniques include the use of weights to ensure the lines sink quickly, the deployment of streamer lines to scare away birds, setting lines only at night in low light (to avoid attracting birds), limiting fishing seasons to the southern winter (when most seabirds are not feeding young), and not discharging offal while setting lines.

 

Shark on a longline, picture FLMNH

Longline fishers leave lines drifting in the ocean for hours, sometimes days, then come back to collect the catch and throw away the dead animals they can’t sell.

Isn’t it time to review global fishing methods and policies?

 

 

 

More info:
http://www.flmnh.ufl.edu/fish/education/sharks/sharkfishing.html
http://www.sharkwater.com/education.htm
http://www.fao.org/fishery/fishtech/1092/en
http://www.iucn.org/about/work/programmes/global_policy/news_events_gpu/news_gpu/?1220/Shark-Depredation-and-Unwanted-Bycatch-in-Pelagic-Longline-Fisheries (downloadable report)

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