Species of tuna fish to be found in the world’s oceans

We provide here information about the various species of tuna fish to be found in the world’s oceans. This information gives an indication of their commercial importance and whether they are being fished sustainably. Principal information is sourced from Marinelife.about.com and Wikipedia.

Tunas are large, powerful fish that are distributed worldwide from tropical to temperate oceans. There are several species of fish known as tuna and they are members of the family Scombridae, which includes both tunas and mackerels.
Their circulatory and respiratory systems are unique among fish, enabling them to maintain a body temperature higher than the surrounding water. An active and agile predator, the tuna has a sleek, streamlined body, and is among the fastest-swimming pelagicpelagic The ecological area consisting of the open sea away from the coast and the ocean bottom. The pelagic zone contains organisms such as surface seaweeds, many species of fish and sharks and some mammals, such as whales and dolphins. Pelagic animals may remain solely in the pelagic zone or may move among zones. fish – the yellowfin tuna, for example, is capable of speeds of up to 75 km/h (47 mph). Found in warm seas, it is extensively fished commercially and is popular as a game fish. As a result of over-fishing stocks of some tuna species, such as the Southern bluefin tuna, have been reduced dangerously close to the point of extinction.

Tunas (from top): albacore, Atlantic bluefin, skipjack, yellowfin, bigeye
Atlantic Bluefin Tuna (Thunnus thynnus)
“Photo: “NOAA / www.photolib.noaa.gov

Atlantic Bluefin Tuna (Thunnus thynnus)

Atlantic bluefin tuna are large, streamlined fish that live in the pelagic zonepelagic The ecological area consisting of the open sea away from the coast and the ocean bottom. The pelagic zone contains organisms such as surface seaweeds, many species of fish and sharks and some mammals, such as whales and dolphins. Pelagic animals may remain solely in the pelagic zone or may move among zones.. Tuna are a popular sport-fish due to their popularity as a choice for sushi, sashimi and steaks. Consequently, they have been heavily overfished. Atlantic bluefin tuna were once relatively abundant in UK seas but are now commercially extinct, and the Mediterranean commercial population is now under severe pressure from over-fishing. Bluefin tuna are long-lived animals. It is estimated that they can live up to 20 years.

Bluefin tuna are bluish-black on their dorsal side with a silvery colouration on their ventral side. They are a large fish, growing to lengths of 9 feet and weights of 1,500 pounds.

The Southern bluefin tuna (Thunnus maccoyii), like the Atlantic bluefin tuna, is a fast, streamlined species. The Southern bluefin is found throughout the oceans in the Southern Hemisphere, in latitudes roughly from 30-50 degrees south. This fish can reach lengths up to 14 feet and weights up to 2,000 pounds. Like other bluefin, this species has been heavily overfished.

Albacore Tuna/Longfin Tuna (Thunnus alalunga)

Albacore are found throughout the Atlantic Ocean, Pacific Ocean and Mediterranean Sea. Their maximum size is about 4 feet and 88 pounds. Albacore have a dark blue upper side and silvery white underside. Their most distinctive characteristic is their extremely long pectoral fin.

Albacore tuna is sold commonly as canned tuna and may be called “white” tuna. There are health warnings about consuming too much tuna because of high mercury levels in the fish.

Albacore are sometimes caught by trollers, who tow a series of jigs, or lures, slowly behind a vessel. This type of fishing is distinct from trawling and is more eco-friendly than the other method of capture, longlines, which can have a significant amount of by-catch.

Yellowfin Tuna (Thunnus albacares)

The yellowfin tuna is a species you’ll find in canned tuna, and may be called Chunk Light tuna. These tuna are often caught in a purse seine net, which faced an outcry in the U.S. for its effects on dolphins, which are often associated with schools of tuna, and were therefore captured along with the tuna, causing the deaths of hundreds of thousands of dolphins each year. Recent improvements in the fishery have reduced the dolphin by-catch.

The yellowfin tuna often has a yellow stripe on its side, and its second dorsal fins and anal fins are long and yellow. Their maximum length is 7.8 feet and weight is 440 pounds. Yellowfin tuna prefer warmer, tropical to subtropical waters. This fish has a relatively short lifespan of 6-7 years.

Bigeye Tuna (Thunnus obesus)

The bigeye tuna looks similar to the yellowfin tuna, but has larger eyes, which is how it got its name. This tuna is usually found in warmer tropical and subtropical waters in the Atlantic, Pacific and Indian Oceans. Bigeye tuna can grow up to about 6 feet in length and weigh up to about 400 pounds. Like other tunas, the bigeye has been subject to overfishing.

Skipjack Tuna/Bonito(Katsuwonus pelamis)

Skipjacks are a smaller tuna that grow to about 3 feet and weigh up to about 41 pounds. They are a wide-ranging fish, living in tropical, subtropical and temperate oceans around the world. Skipjack tunas have a tendency to school under floating objects, such as debris in the water, marine mammals or other drifting objects. They are distinctive among tunas in having 4-6 stripes that run the length of their body from gills to tail.

Skipjack is the most fecund of the main commercial tunas, and its population is considered sustainable against its current consumption. Its fishing is still controversial due to the methodology; with rod and reel or fishery options being promoted as ecologically preferable.

Skipjack is considered to have “moderate” mercury contamination. As a result, pregnant women are advised against eating large quantities.

Little Tunny (Euthynnus alletteratus)

The little tunny is also known as the mackerel tuna, little tuna, bonito and false albacore. It is found worldwide in tropical to temperate waters. The little tunny has a large dorsal fin with high spines, and smaller second dorsal and anal fins. On its back, the little tunny has a steel blue colouration with dark wavy lines. It has a white belly. The little tunny grows to about 4 feet in length and weighs up to about 35 pounds. The little tunny is a popular game fish and is caught commercially in many locations, including the West Indies.

True tuna species

The ‘true’ tunas are those that belong to the genus Thunnus. Until recently, it was thought that there were seven Thunnus species, and that Atlantic bluefin tuna and Pacific bluefin tuna were subspecies of a single species. In 1999 Collette established that based on both molecular and morphological considerations, they are in fact distinct species.

The genus Thunnus is further classified into two subgenera: Thunnus (Thunnus) (the bluefin group), and Thunnus (Neothunnus) (the yellowfin group).

Other tuna species

The Thunnini tribe also includes seven additional species of tuna across four genera. They are:

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