Bluefin Trevally

The bluefin trevally is a large fish, growing to a maximum known length of 117 cm and a weight of 43.5 kg, however it is rare at lengths greater than 80 cm. It is similar in shape to a number of other large jacks and trevallies, having an oblong, compressed body with the dorsal profile slightly more convex than the ventral profile, particularly anteriorly. This slight convexity leads to the species having a much more pointed snout than most other members of Caranx. The dorsal fin is in two parts, the first consisting of 8 spines and the second of 1 spine followed by 21 to 24 soft rays. The anal fin consists of 2 anteriorly detached spines followed by 1 spine and 17 to 20 soft rays. The pelvic fins contain 1 spine and 20 soft rays. The caudal fin is strongly forked, and the pectoral fins are falcate, being longer than the length of the head.

The bluefin trevally is widely distributed, occupying the tropical and subtropical waters of the Indian and Pacific Oceans, ranging along the coasts of four continents and hundreds of smaller islands and archipelagos. In the Indian Ocean, the species easternmost range is the coast of continental Africa, being distributed from the southern tip of South Africa north along the east African coastline to the Red Sea and Persian Gulf. The species' range extends eastwards along the Asian coastline including Pakistan, India and into South East Asia, the Indonesian Archipelago and northern Australia. The southernmost record from the west coast of Australia comes from Exmouth Gulf. Elsewhere in the Indian Ocean, the species has been recorded from hundreds of small island groups including the Maldives, Seychelles, Madagascar and the Cocos (Keeling) Islands.

The bluefin trevally is a fast swimming, mainly piscivorous predator which shows a wide range in hunting techniques. Two studies of adult fish in Hawaii found fish to be the dominant food type in the species, making up over 95% volume of the stomach contents by weight. Here the main fish selected were small reef dwellers, with fish from the families Labridae, Mullidae, Scaridae and Priacanthidae being the most common. Despite the preference of several families, bluefin trevally do take a very wide variety of fish in small amounts, including various species of eel. The species appears to have a preference for fish of a specific size, which depends on its own length and age.

The bluefin trevally is a schooling species as a juvenile, transitioning to a more solitary fish with well defined home ranges as an adult. Adults do school to form spawning aggregations or temporarily while hunting, with evidence from laboratory studies indicates bluefin trevally are able to coordinate these aggregations over coral reefs based on the release of dimethylsulfoniopropionate (DMSP) from the reef. DMSP is a naturally occurring chemical produced by marine algae and to a lesser extent corals and their symbiotic zooxanthellae. The number of fish present in an area is also influenced by tidal factors and possibly the abundance of prey and other environmental factors.

The bluefin trevally is an important species to both commercial fisheries and anglers, with the popularity of the fish leading to extensive aquaculture trials. The catch statistics for the bluefin trevally are poorly reported in most of its range, with only parts of the western Indian Ocean supplying information to the FAO. In this region, catch levels have fluctuated between 2 and 50 tonnes in the past decade. Hawaii also keeps catch records, with these showing the species is taken in far less numbers than the giant trevally, with only 704 pounds taken compared to 10 149 lbs of giant trevally in 1998. In Hawaii, the nearshore stocks of the species have been in decline since the early 1900s, with commercial landings dropping over 300% from 1990 to 1991, and have not recovered. Most bluefin trevally sold in Hawaii are now imported from other Indo-Pacific nations.