swims in the cold southern ocean waters

Size
Length: 50–80 cm, Weight: 5–15 kg
Lifespan
8–12 years
Diet
Carnivorous feeding on small fish squid and crustaceans. Uses enormous pelvic fins to stabilise during high-speed chases while hunting in open water.
Habitat
Open ocean waters from 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 subantarctic islands. Most common off Chatham Rise and Campbell Plateau. Also found in southern Australia and Southern Ocean.
Endemism
Native
Main Threats
Bycatch in commercial tuna longline fisheries is primary threat. Also threatened by climate change affecting prey distribution in southern oceans and ocean warming which may shift range further south.
Population
Population trends poorly understood due to species' offshore habitat and low commercial value. Caught occasionally as bycatch in southern tuna fishery. No stock assessments conducted. Better data collection required.
Conservation Status
Not Threatened
Human Risk
harmless
Handling Note
migratory tuna, harmless to humans unless harvested
Conservation Note
Native marine fish; not assessed by NZTCS as marine fish are outside the scope of current threat classifications.
Te Ao Māori
The butterfly tuna has no traditional Māori name or significance. It lives in deep cold southern waters far beyond the reach of traditional fishing. Its unusual appearance was unknown to Māori. It is the only tuna with scales. In modern times it is known only to deep-sea researchers and the crews of tuna longliners. It is a reminder that even the open ocean still holds surprises. Mana whenua observe these distant ecosystems with interest.
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.