Estimating cetacean bycatch from tuna gillnet fishereies
The Indian Ocean is the second-largest tuna production area in the world and provides important economic benefits to global fishery markets. However, bycatch is a major issue for tuna fisheries in this area, particularly for interactions between drift gillnets and several species of cetaceans. The issue is particularly acute in the Arabian Sea (northwestern Indian Ocean), where drift gillnets are the primary fishing method used by most countries. However, development of effective bycatch reduction strategies is hampered by a lack of data about fishing effort and bycatch in this region. The present study employed a systematic literature review to develop a coarse estimate of cetacean bycatch, using data collected during port surveys and from observer programs for the three largest tuna drift gillnet countries: Sri Lanka, India and Pakistan, during the period from 1984 to 2019. Cumulative estimates of bycatch increased over this period, driven by increasing tuna captures over time. The study provides only a coarse estimate of bycatch, with many uncertainties associated with the extrapolations, but the magnitude of bycatch is large enough to warrant immediate management action. Current information needs in the Arabian Sea include better information on fishing effort, such as from the use of electronic monitoring systems on fishing vessels, and tests of bycatch mitigation technology, such as net illumination. However, funding for such ventures is inadequate and the scientific capacity of countries around Arabian Sea is limited. This study provides three recommendations to address this situation: 1) identify priority bycatch areas in each country, and conduct a rapid bycatch assessment in those areas; 2) strengthen cooperation between national governments and international organizations, such as the IOTC and IWC, to address bycatch in the region; and 3) focus research on bycatch mitigation strategies.