Most recent estimates of by-catch in global fisheries show that 7.3 million tonnes of by-catch are produced annually, most of which result from trawl fisheries; only 5% of the total are from tuna fisheries. However, the issue of by-catch and discards in tuna fisheries has raised public concern particularly in the EU as some NGOs campaigned and put pressure on markets to source tuna products from pole-and-line and fish aggregating devices (FAD)-free sources alone. In that context, a study, undertaken by the EU supported programme Smart Fish, reviews the by-catch and discards issues in the Indian Ocean in pole-and-line, purse seine and longline tuna fisheries. Although these fisheries represent less than half the region’s tuna landings, they are the only sectors having sufficient statistical data to permit analysis and the application of mitigation measures.

The Indian Ocean free-school purse seine fishery (by French purse seiners) has by far the lowest by-catch (1.7%), while in the purse seine fishery fishing with FADs (by Spanish purse seiners) the by-catch reaches 5.3%. The study indicates that ‘none of their by-catch species are threatened, and the tonnage of each is too small to impact stocks’. In the pole-and-line fishery, most of the by-catch (8.3%) is canned for local consumption or consumed fresh. By-catch and discards from longline fisheries (including Spanish and Portuguese longliners) are higher, particularly when considering the bait used as ‘discard’, because bait catch amounts to half the total. Their by-catch comprises 87 species, including sharks, seabirds and turtles, many of which are regarded as endangered. Although not considered in this study because of the lack of data, the authors highlight that: ‘Northern Indian Ocean drift gillnet fleets appear to have by-catch of ecologically sensitive species in orders of magnitude higher than that of the other gears, to such an extent that the by-catch from pole-and-line, purse seine and even longline is probably inconsequential.’

The potential to replace FAD-associated purse seine fishing by pole-and-line or FAD-free production is also discussed. A total ban on FAD fishing might result in the purse seine fleet leaving the Indian Ocean, ‘with disastrous consequences to the economies of coastal countries providing services to the industry and processing fish, as well as massive loss of jobs’. The authors insist that substituting pole-and-line production for purse seine would actually result in a sixfold increase in the catch of non-target species and double the fuel used in the fishery, because fuel consumption per tonne of tuna caught is twice as high in pole-and-line fishery compared to purse seiners. Finally, lack of baitfish stocks and human resources experienced with the pole-and-line method are major barriers to the expansion of this type of fishery. Realistically, landings by pole-and-line will never be able to supply the volume of raw material that purse seine produces for the canning industry. The study concludes: ‘there is little chance that pole-and-line fishing can develop in the western Indian Ocean given limited baitfish resources unless a huge differential in landed price for pole-and-line caught tuna develops which is unlikely.’