Tunas are large, oceanic fish and are highly migratory pelagic species inhabiting tropical and subtropical waters of the world oceans. Tunas in general are considered to be opportunistic feeders, with teleost fish, crabs, squids and shrimps as their major food items. Tuna and tuna like species are the primary sources for a number of distant water fishing countries in both the high seas and Exclusive Economic Zones (EEZs) of coastal states. Main fishing gears used are pole and line, long-line, troll line, purse seine and drift gillnet. Tunas are the second largest product in the international seafood trade, with a value of total tuna export trade at $7,500 million in 2008 ($1,900 million in 1987). Because of the high demand for tuna and the significant overcapacity of tuna fishing fleets most of the stocks of principal tuna species are either optimally or even overexploited (Pillai, 2010; IOTC, 2011). Leading tuna catching nations in the Indian Ocean are Japan, Taiwan, Indonesia, South Korea, Spain and France.

In Indian Ocean, tuna catches increased rapidly from about 237,986 tones (T) in 1980 to 654,754 t in 1995. They have continued to increase up to 2005; the catch was 1,318,648 t forming about 26% of the world catch. However, since 2006 onwards there was a decline in tuna catch and in 2010 the catch was only 1,257,908 t (Figure 1). The principal species caught in the Indian Ocean is skipjack and yellowfin. The catch of bigeye has also increased to around 150,000 t, due to increased targeting of tunas by longliners for Sashimi market and the use of FADs in the surface fishery. Although the catch of yellowfin tuna increased gradually in the past five decades, its relative importance decreased rapidly. Skipjack constituted about 38% of the total catch, yellowfin 26%, kawakawa 10%, bigeye 9%, albacore 3% and blue fin 1%. Purse seiners account for about 36% of the total tuna catch followed by gillnetters 31%, long liners 15%, bait boat 10%, pole and line 7% and the remaining by other gears (1%) as shown in Figure 2. In 2008 Indian Ocean tuna production declined to 1,148,911 t with estimated landed value of US$ 2.5 billion. Present decline in production of the Indian Ocean tuna fisheries may have serious ecological and socioeconomic consequences in the region. Analysis of landing data clearly indicated that overexploitation of targeted species threatens the sustainability of tuna populations. Though there had been substantial increase in the production of tunas in the Indian Ocean, the fast pace of development has ignored several patterns which are vital to sustain the tuna production in the capture fisheries. Information on a few of these vital parameters is either not available, and for a few other parameters, the available information has not been properly utilized. The IOTC has implemented certain measures to improve compliance of conservation and management measures. However, many of the member countries do not provide the required information needed to monitor the compliance of fishery management regulation.

Figure 1 Trends in tuna catch in Indian Ocean from 1950-2010

Figure 2 Gear-wise contribution of tuna in Indian Ocean from 1950-2010

3.2 Stock status

Stock should be closely monitored. Evidence from retrospective records strongly suggests that major structural and functional changes due to overfishing of tunas occurred in Indian Ocean in recent years. Severe overfishing derives species ecological extinction because overfished populations no longer interact significantly with other species in the community (Jackson et al., 2001). Periodic reassessment of the tuna potential is also required with adequate inputs from exploratory surveys as well as commercial landings and this may prevent any unsustainable trends in the development of the tuna fishing industry in the Indian Ocean.

3.3 Tuna production of EEZ of India

Annual marine fish production in India during 2010 was 3.07 (mt) against a catchable potential of 3.93 (mt) (CMFRI, 2011). The Indian tuna fishery comprises two distinct segments, the coastal fishery and oceanic fishery. The oceanic fishery uses exclusively longlines, targeting large deep-swimming yellowfin and bigeye tunas. Tuna constitutes one of the important marine fisheries resources of India having an estimated annual catchable potential of about 2.78 lakh t in the EEZ.Coastal resources almost fully exploited and current focus is on oceanic/deep sea resources. India is yet to find a place in the tuna map of the Indian Ocean. The fishery resource of estimated potential tuna and tuna like species is 250,000 t; however, current production is around 65,863 t, most of which constituted by coastal tuna species. Figure 3 illustrates all Indian tuna production which has continued to increase with fluctuations from 63,633 t during 2001-2005, 78,400 t during 2006-2010, and 65,863 t in 2010. However, during the last couple of year’s landings in drift gillnet, hook and line and troll lines operated by small and medium sized mechanized vessels are reported to have increased marginally (IOTC, 2011). Of the total tuna landings oceanic species formed 47% and neritic species 53%. Among the oceanic species skipjack constituted 21% followed by yellowfin 12%, bigeye 7%, and albacore 3% (Figure 4). Among the neritic tunas, kawakawa (Euthynnus affinis) was dominant (30%) followed by frigate tuna (14%), longtail tuna (7%) among others. In the tuna landings from the Indian coast, gillnets accounted for about 35% of the catch, pole and line 29%, long line 14 %, purse seine 14%, and the remaining by a variety of other gears 8% (Figure 5). The present annual export of tuna and tuna products amounts to 35,000 t valued at $53.22 million dollar, the major importing countries were Southeast Asia, Japan, UK and Middle East. Tuna capture from Indian seas has fallen by more than 25% in the last one year pushing down most tuna long-liners into great loss (Pillai, 2010).

Figure 3 Trends in tuna catch in Indian EEZ from 1950-2010

Figure 4 Species-wise contribution of tuna catch in Indian EEZ from 2006-2010

Figure 5 Gear-wise contribution of tuna in Indian EEZ from 2006-2010

Worm B., Sandow M., Oschlies A., Lotze H.K., and Myers R.A., 2005, Global patterns of predator diversity in the open oceans,Science, 309: 1365-1369
http://dx.doi.org/10.1126/science.1113399