Abstract
Tropical tuna fisheries are among the largest worldwide, with some having significant bycatch issues. However, pole-and-line tuna fisheries are widely believed to have low bycatch rates, although these have rarely been quantified. The Maldives has an important pole-and-line fishery, targeting skipjack tuna (Katsuwonus pelamis). In the Maldives, 106 pole-and-line tuna fishing days were observed between August 2014 and November 2015. During 161 fishing events, tuna catches amounted to 147 t: 72% by weight was skipjack, 25% yellowfin tuna (Thunnus albacares) and 3% other tunas. Bycatch (all non-tuna species caught plus all tuna discards) amounted to 951 kg (0.65% of total tuna catch). Most of the bycatch (95%) was utilized, and some bycatch was released alive, so dead discards were particularly low (0.02% of total tuna catch, or 22 kg per 100 t). Rainbow runner (Elagatis bipinnulata) and dolphinfish (Coryphaena hippurus) together constituted 93% of the bycatch. Live releases included small numbers of silky sharks (Carcharhinus falciformis) and seabirds (noddies, Anous tenuirostris and A. stolidus). Pole-and-line tuna fishing was conducted on free schools and schools associated with various objects (Maldivian anchored fish aggregating devices [aFADs], drifting FADs from western Indian Ocean purse seine fisheries, other drifting objects and seamounts). Free school catches typically included a high proportion of large skipjack and significantly less bycatch. Associated schools produced more variable tuna catches and higher bycatch rates. Fishing trips in the south had significantly lower bycatch rates than those in the north. This study is the first to quantify bycatch rates in the Maldives pole-and-line tuna fishery and the influence of school association on catch composition. Ratio estimator methods suggest roughly 552.6 t of bycatch and 27.9 t of discards are caught annually in the fishery (based on 2015 national catch), much less than other Indian Ocean tuna fisheries, e.g. gillnet, purse-seine, and longline.
Highlights
Bycatch in fisheries is a major environmental and resource management problem
The main tuna species taken were skipjack (72.3% of the tuna catch by weight) and yellowfin (25.0%), with bigeye, kawakawa, and frigate tuna together making up the balance (2.7%) (Table 2)
Even small ones, were retained for sale or home consumption, and the only tunas that were discarded were one skipjack and one yellowfin which had been depredated by sharks (Table 3 and S3 Table). 15,749 tunas were measured
Summary
Permission to conduct this research within the Maldives was granted by the Marine Research Centre, Republic of Maldives; no specific permits were required. The Republic of Maldives is an archipelagic atoll chain straddling the equator in the central Indian Ocean, running northsouth along 73 ̊E from about 7 ̊N to 1 ̊S (Fig 1). There are some 1,200 islands, grouped across 26 natural atolls. Some 185 of these islands are inhabited. Pole-and-line fishing is carried out using traditional fishing boats known as mas dhonis. There are currently about 1,000 such vessels, which are typically about 18–30 m long. While the fishery remains fundamentally the same as it has been for centuries, mechanization and technological improvements and mechanization have dramatically increased efficiency in recent decades
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
