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Is Pole-and-Line fishing for tuna really still that sustainable?

Pole-and-line fishing is a simple approach to catching tuna with a hooked line attached to a pole (Majkowski 2003b). Vessels tend to be up to 40 metres in length, with between 10 and 20 fishers fishing simultaneously with a rigid pole and a strong short line, from which hangs a lure mounted on a barbless hook (Majkowski 2003b; FAO 2001). In the Maldives, there are at least 1,000 pole-and-line fishing vessels, that catch around 110,000 tonnes of tuna per year (Sources: (Miyake et al. 2010; Gillett 2011a; Oceanic Fisheries Programme 2010; ICCAT 2009), Miyake et al. (2010). In itself, pole-and-line fishing for tuna is much more sustainable than the devastating longlines, which catch not only tuna, but many sharks and other marine creatures, as well as sea birds.

But when I visited the Maldives for a conservation project, I noticed something weird. Many reefs had only one fish species left: blue triggerfish. A few days later I was enjoying the sight of a well populated reef, when a baitfishing boat arrived. Within minutes, a large round net was thrown into the water and lowered until just above the coral reef. It was then lifted again by snorkelers. All small blue triggerfish were thrown back – they are useless as baitfish. An hour later, all reef fish were gone…

Normally in the Maldives anchovies, prats, fusiliers and cardinals are used as bait. When the preferred bait species is not available, pole-and-line vessels, particularly those operating in island areas, will take any fish of the correct size that can be obtained in sufficient quantities (Hester 1974). Almost all small coral reef fish can be used as bait, including bycatch species (Baldwin 1977), and the species composition of the bait catch can fluctuate wildly over short periods of time (1-2 years in some cases) (Rawlinson et al. 1992). An important factor is the tuna–baitfish ratio: how much tuna is caught with a certain amount of bait. On average, 12 to 15 tonnes of bait is needed to catch 110,000 tonnes of tuna. Baitfish species are food for numerous other species of reef fish, so catching them on a large scale may detrimentally affect others in the food web, and further, capture of top predators by artisanal fishers might decrease the mortality on smaller-sized carnivores, increasing predation on bait fish species (Anderson 2009.

What is the influence of pole-and-line fishing in the Maldives on the coral reefs? These days, sustainable fish is in high demand. Many rave about the Maldives and a Dutch company and the Marine Stewardship Council even had a competition you can enter to win a trip to the Maldives to see the tuna fishermen at work. But will this demand in the end make these fisheries unsustainable??
I was shocked to see how ‘empty’ the Maldivian reefs are these days, compared to my previous visits, somle 20 years ago. And after reading the report by IPNLF (2012), Ensuring Sustainability of Livebait Fish, International Pole-and-line Foundation, London, 57 pages, it is clear that not all effects of extensive baitfish fisheries are know, and that more research is badly needed.

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