Home TUNA FISHERIES Tuna Species
Tuna Species caught in the WCPO
Monday, 19 July 2010 14:01

Tuna is not a single species of fish, but rather several species.  Scientists often use the term “tuna and tuna-like fish” which includes a total of 61 species, fourteen of which are considered “true tuna”. Four species are of major commercial importance in the Pacific Islands: skipjack, yellowfin, bigeye, and albacore.

These four species of tuna are quite distinct with respect to many properties such as how they are captured, the amount presently captured, the size of the populations, and the end use of the product.

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Skipjack
Wednesday, 24 November 2010 14:04
Skipjack are a surface–schooling tuna which are easily distinguished from other species of tuna due to their small size, small dark pectoral fins and three to six distinct dark longitudinal lines (stripes). It is found year-round concentrated in warmer tropical waters of the WCPO, with that distribution expanding seasonally into subtropical waters to the north and south. Skipjack are caught mainly on the surface by purse seine and pole-and-line gear and are used for producing canned tuna.

The typical capture size for skipjack is between 40 and 70cm, corresponding to fish between one and three years of age, with very few captured fish exceeding 80cm. However, rare records of skipjack over 100cm and weighing more than 30kg have been reported historically.

Skipjack tuna is a fast growing species (reaching 42-45cm within its first year), are relatively short-lived (few live longer than 3 - 4 years) and mature early (~ 1 years of age). These biological characteristics promote rapid turnover in skipjack populations.

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Yellowfin
Wednesday, 24 November 2010 14:05

Yellowfin tuna are a relatively large tuna, easily distinguished as adults by their large second dorsal and anal fins which, along with finlets, are typically bright yellow. However, they can be less easy to distinguish from other tuna (like bigeye) as juveniles (<70cm).

Yellowfin tuna are distributed throughout the tropical and sub-equatorial waters of the WCPO, and typically spend most of their time in the warmer mixed surface waters (above the thermocline). Small yellowfin are caught on the surface by a range of gears including handline, ringnet, purse seine and pole/line gear and are used mainly for canning, while the majority of larger/older fish are caught by both purse seine and longline fisheries, with the longline catch often shipped fresh to overseas markets.

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Bigeye
Wednesday, 24 November 2010 14:06

Bigeye tuna are among the largest of tuna species and are distinguished as adults by their body depth, colouring (iridescent blue longitudinal band)  and smaller anal and dorsal fins (relative to yellowfin). However, they are more difficult to distinguish from yellowfin tuna as juveniles (~50cm).

In the WCPO, bigeye tuna have a relatively broad distribution, both geographically between 40°N and 40°S,  and vertically between the surface and 500 m deep (occasionally to 1000 m) due to their tolerance of low oxygen levels and low temperatures. In the tropical and subtropical waters or the WCPO, adult bigeye migrate from cooler deeper waters (beneath the thermocline) where they live during the day to shallower warmer waters (above the thermocline) at night.  Juvenile bigeye tend to inhabit shallower waters and can form mixed schools with skipjack and yellowfin, which results in catches by the surface fishery, particularly in association with floating objects.

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Albacore
Wednesday, 24 November 2010 14:06

Although colour and shape can be similar to other species of tuna, adult albacore are distinguished by their very long pectoral fins. Albacore are segregated into two discrete stocks in the WCPO, with the equatorial area (where albacore are rare) separating the southern component from those of the north. Mature albacore (age at first maturity is about 4 to 5 years) spawn in tropical and sub-tropical waters between 10 to and 25 degrees from the equator, with individual fish becoming available to surface fishing about 40 degrees from the equator approximately one to two years later, at a size of 45-50 cm. From this area, albacore appear to gradually disperse towards lower latitudes, but may make seasonal migrations between tropical and sub-tropical waters.

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