Dogtooth tuna

Description

Gymnosarda unicolor can reach a length of 190–248 centimetres (75–98 in) in males. and a weight of 130 kg. The average size commonly observed is around 40 to 120 cm. They have 12-14 dorsal soft rays and 12-13 anal soft rays. The lateral line is strongly undulating. These large size tunas have a streamline shape and a distinctive body coloration: brilliant blue green on the back, silvery on the side and whitish on the belly, with two white tips on the two back fins close to its caudal peduncle. They are always swimming with open jaws. The upper jaw of the large mouth reaches the eye.

Distribution

The dogtooth tuna is widespread throughout the tropical waters of the Indo-Pacific area from the eastern coast of Africa, Red Sea included, to French Polynesia and oceanic islands of the Pacific Ocean (Hawaii excluded), north to Japan, south to Australia.

Ecology

These offshore fishes can be found mainly in reef environments with smaller fish being more commonly found near shallow reef areas and larger ones haunting deep reef drop off areas, seamounts and steep underwater walls. Usually they are solitary or occur in small schools, to a depth of 10–300 metres (33–984 ft).

The dogtooth tuna is one of the apex non-pelagic predators in its environment, sharing that position with giant trevally, Napoleon wrasse, and large groupers, as well as reef, bull and tiger sharks.

These aggressive opportunistic predators feed on small schooling fishes and squids, and are capable of taking a wide variety of prey items. In most areas, the mainstay of its diet probably consists of pelagic schooling fish found near reef habitat (mainly, Caesio, Cirrhilabrus, Pterocaesio, carangids such as rainbow runners and Decapterus, mackerel scad, and scombrids).

Fishing

These fishes are usually marketed canned and frozen. Adults may be ciguatoxic. The dogtooth tuna is appreciated in most of its range as a fine food fish and also as a game fish sought by both rod and reel anglers and spearfishermen. Dogtooth tuna used to be mostly taken as an incidental catch by anglers trolling for other gamefish - with natural baits for black marlin, for instance, or with lures for wahoo and Spanish (narrowbarred) mackerel. In the last 10 to 15 years there has been more dedicated effort directed at this species because of its rarity and sporting qualities. Dogtooth tuna are now a highly coveted prize by many European and Asian sports anglers. Large specimens are seldom found where there is significant fishing pressure and can be one of the most difficult gamefish to capture.

Their habit of making high-speed downward runs when hooked, even on heavy tackle, often sees the line being cut as it contacts deep bottom structure. Sharks frequently mutilate both hooked and speared fish during the later stages of the fight, adding to the difficulty in landing them. The majority of dogtooth tuna captures have tended to be made by trolling with dead and live baits or with lures, particularly deep-swimming plugs.

These techniques are still often used, with one niche specialty being the use of live bait such as rainbow runners to tease dogtooth tuna within range of light tackle and fly-casting anglers. High speed jigging with a variety of metal lures has increased tremendously in popularity in the last several years as advancements in tackle technology have resulted in lightweight rods and reels that are capable of handling heavy spectra-type braided lines. Some of the more popular destinations for anglers seeking this species include Okinawa and other islands of southern Japan, Rodrigues and other Indian Ocean islands such as the Maldives, Andaman & Nicobar Islands, Bali and elsewhere in Nusa Tenggara in Indonesia, the Great Barrier Reef and its outlying atolls, and many Western Pacific islands such as Vanuatu, Fiji, Tonga, Samoa and Palau.