butterfly tuna, warm northern visitor

Size
Length: 50–80 cm, Weight: 5–15 kg
Lifespan
8–12 years
Diet
Carnivorous – feeds on small fish, squid and crustaceans. Uses its enormous pelvic fins to stabilise during high-speed chases. Hunts in open water with rapid acceleration and sustained swimming.
Habitat
Open ocean waters from the surface down to 300 metres depth. Prefers cold, temperate seas between 5°C and 15°C. Often found near current boundaries and upwelling zones.
Range
Found in southern waters around New Zealand from Cook Strait to the subantarctic islands. Most common off the Chatham Rise and Campbell Plateau. Also found in southern Australia and the Southern Ocean.
Endemism
Native
Main Threats
Bycatch in commercial tuna longline fisheries is the primary threat. Also threatened by climate change affecting prey distribution in southern oceans, and ocean warming which may shift its range further south. No targeted fishery in New Zealand waters.
Population
Population trends are poorly understood due to the species' offshore habitat and low commercial value. It is caught occasionally as bycatch in the southern tuna fishery. No stock assessments have been conducted. Better data collection is required to determine population status.
Conservation Status
Not Threatened
Only tuna species with scales. It is a tuna that has wings. The enormous pelvic fins are bright black. They extend like wings behind its body. This rare and unusual fish lives in the cold southern waters of the Chatham Rise. It is sometimes called the scaled tuna. Its body is covered in large, armour-like scales. These are unlike any other member of its family. A tuna that is different. The body is streamlined and muscular. It is built for speed. The head is pointed, with a terminal mouth. The colour is a dark blue on the back. This fades to silver on the belly. The pelvic fins are enormous. They extend far behind the body. This gives the fish its name. The scales are large and rough. They form a protective armour. The enormous pelvic fins act as stabilisers. They help the fish maintain its balance during high-speed chases. They are also used for steering. This allows the fish to make sharp turns while pursuing prey. It is a fast-swimming predator. It feeds on small fish, squid, and crustaceans. It hunts in open water. It uses its speed and agility to chase down prey. It is not a schooling fish. It is usually found alone or in small groups. It is a rare visitor to New Zealand waters. It is most common off the Chatham Rise and Campbell Plateau. The cold, nutrient-rich water there supports large populations of prey. Not targeted by commercial fisheries, it is occasionally caught as bycatch in tuna longline fisheries. The cold southern sea is dark. The butterfly tuna swims alone. Black fins look like wings. Armoured scales gleam. The longline sets. The tuna is caught. It is returned to the water, if it is lucky. It does not know it is rare. It does not know it has wings. It just wants to eat a squid. A fish that seems to have been designed by someone who started with a tuna and then added wings. The butterfly tuna is proof.