Shark bycatch in the experimental tuna longline fishery in Lakshadweep Sea, India By K. V. Aneesh Kumar 1 *, P. Pravin 1 , B. Meenakumari 2 , P. S. Khanolkar 1 and M. V. Baiju 1 1 Central Institute of Fisheries Technology, P.O. Matsyapuri, Cochin, India; 2 Indian Council of Agricultural Research, New Delhi, India Summary Bycatch from the experimental longline operations in the Lakshadweep Sea were studied. The experiments were con- ducted on converted Pablo boats, originally used for pole and line fishing operations, to capture skipjack tuna in the Lakshadweep Islands. The overall bycatch rate was very high, with a mean hooking rate of 8.05/1000 hooks com- pared to the targeted tuna catch (1.75/1000 hooks). Bycatch contributed 82.4% of the catch in comparison to the tuna (17.6%) Thunnus albacares, in the longline operations. Silky shark (Carcharhinus falciformes) with 89.9% was the domi- nant shark species followed by C. amblyrhynchos, Galeocerdo cuvier, Alopias pelagicus, Negapriion acutedens and Sphyrna lewinii with 4.7, 2.7, 1.4, 0.7 and 0.7%, respectively. Sharks contributed to 74.1% of the catch, followed by 15.7% sailf- ishes and 10.2% miscellaneous fishes. Higher bycatch rates were evident during evening hours compared to mornings, but the results were not significant statistically. Studies on the effects of depth on the overall fishing performance and species selectivity failed to establish any significant relation- ship at a depth range of 35–100 m. Soaking time had a significant effect on bycatch rates. The hooking rate of sharks declined with an increase in soaking time. Considering the high shark bycatch in the fishery, an accurate monitoring of the longline fish catches in the Lakshadweep waters is an important step towards ensuring the sustainability of other populations, especially sharks. Introduction High seas tuna fishery in the Indian Ocean is supported mainly by four species: yellowfin tuna (Thunnus albacares), bluefin tuna (T. thynnus), albacore tuna (T. alalunga) and bigeye tuna (T. obesus) (Joseph, 1972). India does not have an organized longline fishery for the capture of yellowfin tuna. Converted trawler longliners are operating in many coastal states in India for the catch of large pelagic fishes such as yellowfin tuna and sharks; however, the targeted and bycatch rates from these boats are the least-monitored and - reported. In 2010, total tuna landings in India were 60 512 tonnes (t) along the mainland and 7883 t in Lakshadweep waters. The resource potential of tunas in the Lakshadweep Sea has been estimated at 50 000 t, indicating further scope for development of the tuna fishery in the Lakshadweep Islands (Pillai et al., 2006). Among tunas, Katsuwonus pela- mis (80%) was the most important species landed in the Lak- shadweep waters (Anon, 2010). Pole and line is the principal fishing gear for the capture of skipjack tuna, with a contribu- tion of 94.8% followed by troll line, drift gillnet and hand- lines, contributing 3.3, 1.66 and 0.28%, respectively. Information on oceanic tunas in Indian EEZ indicate that tuna longlining can be carried out throughout the year, with better hooking rates during the pre-monsoon and monsoon seasons in the Arabian Sea and during the monsoon and post-monsoon season in Andaman and Nicobar waters (Somvanshi and Varghese, 2007). Small-scale longline fisheries are considered to be the least monitored and documented fisheries sector and the bycatch poorly understood. Thorough research is needed to quantify the bycatch from the small-scale fisheries sector, as it is sus- pected of producing large bycatch quantities (Peckham et al., 2007; Mangel et al., 2010). Considerable work has been carried out worldwide on by- catch issues regarding longline fishing operations (Alverson et al., 1994; Kelleher, 2005; Gillett, 2011). Previous studies have shown that the longline bycatch or discard rate ranges from 20 to 40% (Kelleher, 2005; Huang and Liu, 2010). Tuna longlines have been reported to catch many other non- targeted species such as seabirds, marine turtles, sharks and cetaceans, posing a threat to the global efforts for conserva- tion of marine biodiversity (Belda and Sanchez, 2001; Gil- man et al., 2006; Garrison, 2007; Donoso and Dutton, 2010; Varghese et al., 2010). The incidence of bycatch has been reduced effectively by certain adjustments and modifications in the fishing gear and fishing operations. Mitigation mea- sures include deep setting of the hooks, magnetic repellents, avoidance of peak areas and periods of bycatch abundance, in addition to other approaches (Francis et al., 2001; Lokke- borg, 2001; Kerstetter and Graves, 2006; Cocking et al., 2008; Gilman et al., 2008a,b; Beverly et al., 2009; Piovano et al., 2010). Sharks and cetaceans cause significant damage worldwide in pelagic longline fishery operations. Damages are in the form of bite-offs, loss of gear, catch displacement, reduced gear efficiency, and depredation of the catch (Yano and Dahlheim, 1994; Secchi and Vaske, 1998; Garrison, 2007). *Present address: Centre for Marine Living Resources and Ecology (CMLRE), 6th Floor, C-Block, Kendriya Bhavan, P.B. No. 5415, CSEZ P.O., Cochin 682037, India U.S. Copyright Clearance Centre Code Statement: 0175-8659/2015/3102–301$15.00/0 J. Appl. Ichthyol. 31 (2015), 301–307 © 2015 Blackwell Verlag GmbH ISSN 0175–8659 Received: February 24, 2014 Accepted: September 5, 2014 doi: 10.1111/jai.12682 Applied Ichthyology Journal of