Abstract

Blackfin tuna (Thunnus atlanticus) is a small epipelagic, oceanic species of tuna. It is only found in the western Atlantic from off Martha’s Vineyard, Massachusetts, and Cape Hatteras throughout FAO Area 31, south to Trinidad Island off the coast of Brazil and off Rio Janeiro. Blackfin tuna is an important species to the artisanal fisheries of the Lesser Antilles, yet very little is known about their biology, and they remain unmanaged in the Caribbean. In this study, the diet; sex ratio and size structure of the catch; length-weight and length-length relationships for males and females; gonadosomatic indices and state of maturity of males and females; and size at maturity were investigated during the period July to September, 2004 for blackfin tuna landed at the Charlotteville fish market, Tobago in the eastern Caribbean. The diet (assessed by numerical abundance of prey items) comprised mainly fishes (48%), crustaceans (46%) and cephalopods (6%). Prey fishes included small pelagics e.g. anchovies; juveniles of larger pelagics e.g. jacks; juveniles of fish found in coral reef communities as adults e.g. squirrelfishes; and some mesopelagic fishes. The Engraulidae family ranked as the most important prey overall. Diet differed significantly between the sexes with males consuming more fish and females more crustaceans. The blackfin tuna ranged in size from 32 - 91 cm FL (mean size: 71 cm FL) and in weight from 0.7 - 13.1 kg (mean weight: 7.36 kg). Sex ratio of males to females was 2.03:1. Length at first maturity was 53 cm FL for both males and females. Most sampled females (85.6%) were either maturing or mature and most males (90.7%) were mature. The length-weight relationships for females and males were W= 0.00007 L2.6988 and W = 0.00006 L2.7088 respectively. This study has contributed significantly to the knowledge on the diet of blackfin tuna in the Lesser Antilles and has provided useful biological information, with application to stock identification and fisheries management.

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