Trends of Indonesia’s bigeye tuna longline fisheries in the Eastern Indian Ocean: Catch per unit effort and length distribution

Abstract

Bigeye tuna, Thunnus obesus (Lowe, 1839), is one of the primary target species for Indonesian tuna longliners operated in the eastern part of the Indian Ocean. However, the fishing trend and biological information are still scarce despite their importance in developing harvest strategy in the region. The study provides nominal catch per unit effort (CPUE) and length compositions of bigeye tuna caught by the Indonesian tuna longliners from the area. Data were obtained from records made by the onboard scientific observers assigned by the Research Institute for Tuna Fisheries (RITF) from 2006 to 2021. The data covers records from 3180 longline settings in 118 fishing trips in which more than 4 million hooks deployed. The fishing efforts were distributed between 0-35°S and 75-130°E, with 10 to 15 hooks between floats. The highest CPUE was 0.29±0.05 fish per 100 hooks in 2014, and the lowest was 0.09±0.05 fish per 100 hooks in 2021. From 8150 fish measurements in 2006 to 2021, the average size was 117.66±24.13 cm FL, and the dominant size class was 120–130 cmFL. While the average size of BET shows an increasing trend the CPUEs were declining.