Diet and sexual maturity of yellowfin and skipjack tuna taken by hand lines from fish-aggregating 'payaw' off northwestern Luzon

Abstract

Skipjack tuna Katsuwonus pelamis and yellowfin or albacore tuna Thunnus albacares taken by hand lines from the 'payaw' off La Union and Ilocos Sur were sampled from April 1994 until August 1995. Skipjack ranged from 28 cm to 59 cm in fork length and from 0.35 to 4.2 kg in weight. Yellowfin ranged 24–67 cm and 0.25–6.4 kg. The common size landed was about 40 cm for both species. Size at first maturity of skipjack was about 41 cm in males and 42 cm in females. The yellowfin tuna taken by hand lines were almost all immature except two mature males about 60 cm long. About 18 prey species were identified in the stomachs of skipjack, and about 25 prey species in yellowfin. The preferred prey were mantis shrimps and squids. Small fishes and other invertebrates were also eaten. Mesopelagic lanternfish were eaten by yellowfin and epipelagic jellyfish were eaten by skipjack.