Relative Abundance and Size Composition of Tuna Caught by Major Fishing Gears Landed in the General Santos Fish Port Complex, Philippines

Abstract

Tunas (family Scombridae) are the most abundant fish species caught by purse seine, ring net, and handline landed in the fish port markets of General Santos City. In this study, an assessment of tuna fisheries was conducted from January 2013 to December 2017. A total of six fish classifications, seven families, four genera, and seven species were observed from Market 1, Market 2, and Market 3 landing sites in the General Santos Fish Port Complex. On average, tuna catches contributed about 89% of the annual catch production and showed an increasing trend throughout the five years. The four genera of tunas were Katsuwonus (53.7%), Thunnus (25.9%), Auxis (8.4%), and Euthynnus (0.5%). The composition of tuna species comprised of oceanic tunas (Katsuwonus pelamis, Thunnus albacares, Thunnus obesus) and neritic tunas (Auxis rochei, Auxis thazard, Euthynnus affinis). Katsuwonus pelamis was the most dominant among the scombrid species with 53.66% relative abundance, followed by Thunnus albacares with 24.03%. Mainly, mature tuna sizes were observed using handline, which caught oceanic tunas ranging from 105 cm to 170 cm. Other gears, purse seine and ring net, caught immature sizes of most neritic tunas. Thus, tunas were caught throughout the year, and two peak seasons were observed from May to June and October to December during the five-year study period. The study's results on relative abundance, size composition, seasonality, and length-frequency distribution provide analysis and information that help implement fisheries management of tuna stocks in Region 12 and high seas pocket. Thus, this paper needs further investigations on catch per unit effort (CPUE), reproductive biology, and the value chain of the landed tuna catches to determine their significance to the economy of General Santos City.