A review of bycatch and discard issues in Indian Ocean tuna fisheries

Citation
Ardill D, Itano D, Gillett R (2011) A review of bycatch and discard issues in Indian Ocean tuna fisheries. In: 7th Session of the Working Party on Environment and Bycatch. IOTC, Maldives, p 44
Abstract

Public awareness and concern over the environmental impact of food production and security is rising rapidly. Whether real or perceived, scientifically justified or completely false, these perceptions can shape fisheries by influencing marketing, demand and product flow. In the fisheries sector, impacts can include overexploitation of both target and non-target stocks, damage caused to the environment by lost or discarded fishing gear, “ghost fishing” and pollution caused by discards, as well as the “carbon footprint” of fishing and baiting operations. The most recent estimates of non-target, associated and dependent species (NTAD) taken by global fisheries is of 7.3 million tonnes annually, 63% of which results from trawl fisheries with only 5% of the total from all tuna fisheries combined. There is general agreement that this level of waste is unacceptable. Furthermore, although retained non-target catch may be recorded and reported to flag state authorities and Regional Fisheries Management Organizations (RFMOs), no track is usually kept of discards of dead organisms, whether or not of target-species, resulting in wastage and distortions of data sets used for stock-assessments. A clear distinction should therefore be made between bycatch and discards. This study, based on official statistics and published material, concentrated on pole-and-line, purse seine and longline tuna fisheries of the Indian Ocean, which, although representing less than half the region’s tuna landings, are the only sectors having sufficient statistical data and governance to permit analysis and the application of mitigation measures. It should be noted that, while often having significant non-target catch, artisanal fisheries rarely discard and fully utilize their retained catch. Various Non-governmental organizations (NGOs) have embarked on media campaigns and direct action, pressuring markets to source surface tuna fishery products from pole-and-line and FAD1-free sources alone. NTAD fishing mortality and discarding practices are reviewed here from pole-and-line, purse seine and longline fisheries in the Indian Ocean to establish the environmental impact of each fishery. Where possible, measures to mitigate unwanted NTAD mortalities are proposed. The target species of the surface fisheries are skipjack, yellowfin and bigeye tunas. In the longline fishery, the latter two species are joined by albacore, swordfish, and now by blue sharks for some fleets. Management of tuna fisheries is under the responsibility of the Indian Ocean Tuna Commission which has determined that none of the target species of the surface fishery are at present overfished, although the level of exploitation of albacore by the longline fishery is unsustainable. Skipjack is however the most robust stock, the other two tropical oceanic species being longer lived and slower maturing, thus more vulnerable to overexploitation, with possible interactions between surface and high value longline fisheries. The free-school purse seine fishery has by far the lowest bycatch (1.7%), but with only 20% skipjack, the most robust species and 80% yellowfin and bigeye tuna which are more sensitive to overfishing. Skipjack catches rise to 61% in the FO2 purse seine fishery, but with 5.3% bycatch. In the two fishing modes combined, the bycatch level is 3.55%, 54% of which were neritic tunas and albacore. No bycatch species are threatened, and the tonnage of each is too small to impact stocks. Piracy has changed fleet operating patterns towards FO directed effort. A number of mitigating measures are being studied in the context of the EU-MADE3 and ISSF4 projects. In the pole-and-line fishery, skipjack with some yellowfin and bigeye tunas make up 87% and bycatch 4.3% and bait 8.3% of landings. As in the purse seine fishery, most of the bycatch, largely neritic tunas, is canned for local consumption or consumed fresh. In addition, the fuel used by pole-and-line fleets is estimated to be twice that of purse seine fisheries per tonne of catch. By far the largest incidence of bycatch and of discards in the Indian Ocean tuna fisheries studied here comes from longline fisheries. Bait used in the fishery, which can be considered a “discard”, amounts to half the total catch. Bycatch consists of 87 species or species groups, including sharks, seabirds and turtles, many of which are listed by the International Union for the Conservation of Nature (IUCN) as being threatened or endangered. Mitigation measures appear to have reduced seabird mortality in temperate waters, but in those fleets not targeting sharks, the actual shark catch was probably up to three times that reported. The Portuguese fleet that utilizes wire leaders records high mortality levels of blue, mako, silky, whitetip and thresher sharks while 75% of blue sharks and most rays appears to survive. The France-Reunion fleet which uses monofilament nylon leaders registered 80% reduction in the number of sharks caught. Mitigation measures could thus include mandating the use of nylon leaders in those fleets not targeting sharks. Other mitigation measures suggested include full catch retention, which would improve food security and nutrition in coastal communities where bycatch is landed and mandatory monitoring of tuna vessels via observer programs or remote sensing devices. The potential to replace floating object-associated purse seine catches by pole-and-line or FAD-free production is also examined. A total ban on FO sets in the purse seine fishery is not seen as a viable option as it 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 employment. Substituting pole-and-line production for purse seine would actually result in a six fold increase in catch of non-target species and doubling the fuel used in the fishery. Finally, lack of baitfish stocks and human resources experienced with the pole- and- line method, as well as of investment capital are seen as major barriers to the expansion of the pole-and-line fishery. Realistically, landings by pole-and-line will never be able to supply the volume of raw materials that purse seine produces for the canning industry. This study concludes that the Indian Ocean tuna fisheries discussed in this paper have a very low level of bycatch, particularly in comparison with other gear types fisheries. The level of discarding also appears to be negligible, other than that of sharks in some longline fleets.