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Tuna - Oceanic species

Tuna are highly migratory and are distributed over large areas of the Pacific Ocean where they hunt smaller fish. There are four main commercial species of tuna. In Cook Islands waters these species are targeted by the longline fishery, purse seine fishery, and artisanal (small-scale) fishers. 

Pelagic fishes rely on speed to catch their prey and to avoid predators. And, as water is “thicker” than air (in fact, 800 times more dense than air), any part of the body which creates friction or turbulence causes a large amount of drag. Compared with travelling through the air, travelling through water is like moving through honey! In many fast fishes, the pectoral or side fins are used as brakes and rudders and fit into depressions in the body when the fish is swimming at speed. The caudal or tail fin, which provides the propulsion, may be shaped like a scythe, with both a long leading edge, and a small surface area (a high aspect ratio).

But the shape of the body is most important. The best shape is one of a spindle or tear-drop, called a fusiform shape, as this offers the least resistance or drag when moving through the water. Independently, this fusiform shape has evolved in aquatic mammals such as dolphins and whales. Not so independently perhaps, marine architects have used the shape in designing boats.

 

Life in the fast lane

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In addition to their shape, tuna have other adaptations that assist with its fast life. Unlike most other fish, tuna are warm-blooded and keep their bodies at higher temperatures than the surrounding water. A higher body temperature allows increases in muscle power and may account for a tuna's ability to swim at speeds of over 50 kilometres per hour to catch smaller fish.

 

 

Albacore Species:

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Photo Credit: SPC

 

 

Skip-Jack Species:

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Photo Credit: SPC

 

 

Yellow-Fin Species:

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Photo Credit: SPC

 

 

Big-Eye Species:

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Photo Credit: SPC

 

 

 

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