Everyone has seen tuna – in little cans at the supermarket. But these fish are often more than a metre long, and live in the open ocean with other big species such as marlin and swordfish.
Where do they live?
Oceanic fish are wanderers, often with no native country. Some, such as the colourful sunfish, are found all around the world. They live in open waters, rather than down near the sea floor like some fish.
In New Zealand, oceanic fish visit the warmer waters of the Bay of Plenty, and the Bay of Islands in the far north. Albacore tuna go as far south as Fiordland, in the South Island.
Why do they come to New Zealand?
They arrive for the summer (from about November) when the water is warmer, in search of food such as smaller fish and prawns. Some species swim in schools for protection.
Tuna are speedy and streamlined. They can reach 80 kilometres an hour, chasing mackerel, herring and squid. Albacore is the main New Zealand tuna species.
Marlin and swordfish
Belonging to the billfish family, these have a pointed spear or bill. They feed on fish and squid.
- Marlin can reach 3.5 metres in length. If caught, they may lash out with their bills. Striped marlin are common off Northland’s east coast.
- Swordfish are about 2–3 metres long. They use their long, flat bill to stun and slice their prey, but are not known to attack people.
- Sunfish are the world’s largest bony fish. Occasionally one washes up on the beach. A sunfish swimming with its fin above the surface can be mistaken for a shark.
- Tropical dolphinfish (mahi mahi) visit New Zealand in summer. They live near the ocean surface, feeding on large fish. Once they’re caught, their bright greens and blues soon fade.
- Blue warehou have a short, blunt head. They are common around Cook Strait, where they feed on jellyfish and plankton.