Skipjack Tuna

Synonym/common names:

Skipjack tuna, skipjack, arctic bonito, atlantic bonito, banjo, bonito, lesser tunny, mushmouth, ocean bonito, oceanic skipjack, skipper, skippy, stripe bellied bonito, striped bellied tunny, striped bonito, striped tunny, victor fish, watermelon, and white bonito.

Names in different languages:

Netherlands: Gestreept tonijn, Spain: Listado, Italy: Palometta, Denmark: Bugstribet bonit, Germany: Echter Bonito, Portugal: Palamida, France: Listao, Japan: Katsuo, Indonesia: Cakalang, Papua New Guinea: Tjakalang, China: Then chien, Philippines: Gulyasan.

Habitat:

The skipjack tuna is an epipelagic fish, occurs in seawaters ranging in temperature from 14.7 to 30°C. While skipjack tuna are known to remain at the surface during the day, and at night they may descend to depths up to 850 feet (260 m). Skipjacks have a tendency to school and exhibit many types of schooling behavior; they have been observed schooling with drifting objects, sharks, or whales. These schools may consist only of skipjack, or sometimes multiple tuna species are present, and they may swim slowly in circular paths or travel in a single direction. Skipjack are often divided into schools based upon their size. This may be due to the smaller fish being unable to maintain the same top speeds of larger fish, and smaller fish may feed in schools, whereas larger fish (20 cm or longer) tend to feed alone.

Distinctive Features:

The skipjack tuna have an elongate fusiform body, a typical tuna fish shape. They possess two dorsal fins, of which the first one consists of 14-16 spines. The second dorsal fin is directly behind the first one with a small space separating them, and is followed by 7 to 8 finlets. The pectoral fins are short compared to others and consist of 26 or 27 rays.
Skipjacks are practically scaleless tuna species, except along the lateral line and the corselet. Using their dark purplish-blue dorsal, Skipjack tuna camouflage themselves by maintaining a silvery hue both laterally and ventrally from predators below. There are also 4 to 6 dark bands running along the sides of the fish extending to the tail, which in live fish it may appear as a discontinuous line of dark blotches. Their teeth are small and conically shaped, and they are lacking a swim bladder.

Coloration:

The upper body is dark blue or purplish colored, while their belly and lower sides are silvery and they have 4 to 6 dark but broken lines running across the length of the body. These stripes running along the belly distinguish this tuna from other scrombridae species living in the same waters.

Size, Age, and Growth:

Like other of the tropical tuna species, skipjack grows fast, up to over 91 cm and 18 kgs within their first year. Skipjack tuna are opportunistic feeders, preying on a variety of fish, crustaceans, cephalopods, and mollusks. Cannibalism is also common. Large pelagic fishes such as billfish, sharks, and other large tunas prey on skipjack tuna.

Reproduction:

Skipjack tuna are oviparous, they spawn all year-round in the warm equatorial waters, while further away from the equator spawning season is limited to the warmer months.

Sexual maturity may occur at a length of about 45 cm and weight 2 kgs however most fish appear to mature at larger sizes. It has been known that larger females produce significantly more eggs than smaller females, with the average female adult producing 80,000 to 2 million eggs per year. The eggs are approximately 0.94 mm in diameter, with a clear shell. The larvae hatch at a size of 3.0 mm. They have large heads and jaws, and a lack of body pigmentation. By closely observing the larvae, they can be distinguished by their pigmented forebrains. Like most Thunnus species (with an exception of the Bluefin tuna) they also lack pigment in the caudal region.

Stock Status of Skipjack Tuna

Conservation:

The populations of skipjack tuna in all stocks has a healthy condition except in the Indian Ocean where it’s in an overfished state. The skipjack tuna is still not listed as threatened in the World Conservation Union (IUCN) “Redlist”, and is considered to be in no immediate threat.

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