Spotted sawtail (Prionurus maculatus) profile

The spotted sawtail is a subtropical species found throughout the Southwest Pacific from the Great Barrier Reef to New South Wales and Lord Howe Island (20-24 degrees C water temperature).

This species has also been recorded at Norfolk Island and the Kermadecs. In New Zealand mainland waters, the spotted sawtail is the most commonly encountered surgeonfish and is found on the east and west coasts from the Marlborough Sounds north. Although it is the most common surgeonfish in New Zealand, it is still considered rare and is generally encountered sporadically and individually.

Within their native range, spotted sawtails are usually encountered in small schools in sheltered bays and rocky estuaries at depths of 2m down to 30m. These schools are often seen feeding on their favourite food, benthic and drifting algae. In New Zealand, most mature spotted sawtails have been encountered on rocky reefs, but all the juveniles have been found in sheltered estuaries and bays.

The mature spotted sawtail is a very distinctive fish, and there are really no common New Zealand species that it could be confused with. They are blue-grey and have bright yellow dots and dashes all over their body. There is also a series of faint orange vertical bands that run along the sides of their body.

A mature spotted sawtail showing the distinctive blue and yellow colouration, vertical bands and 'blade-like' spines it is named after.

Additionally, all species in the family Acanthuridae have sharp ‘blade-like’ spines on their caudal peduncle (the narrow part between the fishes’ body and the tail fin), and this species is no exception, hence the painful sounding name “sawtail”. Juveniles of the species tend to lack the distinctive colouration and can be more difficult to identify. They are generally deeper bodied and silvery in colour, but they do still have the vertical yellow stripes and tiny little ‘blade-like’ spines.

A juvenile spotted sawtail from Parengarenga Harbour in the Far North. As you can see, it is a lot more cryptic than the mature fish but the vertical yellow bands are just visible.

A variety of life-stages of the spotted sawtail have been recorded from mainland New Zealand. A number of large mature fish have been encountered by divers and spearfishers in the Bay of Plenty and Taranaki, and the largest specimen in museum collections from mainland New Zealand is 45cm long. These fish have long lives, with individuals of 45cm being up to 70 years old. The maximum size recorded globally is 55cm, making the spotted sawtail one of the largest surgeonfish species.

Although large spotted sawtails are encountered in New Zealand, it is unlikely they are reaching sexual maturity due to our relatively cool water temperatures. Spotted sawtails probably arrive in mainland New Zealand waters as larvae during warm summers.

So where are the New Zealand spotted sawtail larvae coming from? The most likely source populations for larvae and juveniles include Lord Howe Island, Norfolk Island and southern parts of eastern Australia.

Surgeonfish larvae can drift on ocean currents for up to 85 days, long enough for them to cross large areas of open ocean to New Zealand. It is likely that we will continue to see pulses of juvenile spotted sawtails arriving in New Zealand waters, facilitated by prevailing ocean currents and storm events. If ocean temperatures increase, we may also see these fishes starting to reach sexual maturity and potentially establish breeding populations here in mainland New Zealand.

If spotted sawtails extend their range south to mainland New Zealand, we may see them compete with native herbivorous fishes like parore and moki for food – so, it’s important for us to keep an eye out for this species. If you think you have seen a spotted sawtail or any other surgeonfish in New Zealand waters, send a photograph to WhatsThatFishNZ on Facebook, or a fish taxonomist to confirm the identity. We are particularly interested in photos of juveniles to understand where they may be coming from!