Banded kokopu— an urban legend

Banded kokopu is one of five native fish whose young (juveniles) are part of the whitebait run, swimming upstream from the sea to live their adult lives in rivers. It grows to 25 centimetres long and is easily identified by the thin, pale, vertical bands along its sides and over its back.

Photo copyright Angus McIntosh, Natural Sciences Image Library

Where do banded kokopu live?

Banded kokopu are only found in New Zealand, where it likes small, clean streams and plenty of shade. It has been found in rural and urban streams throughout the region. In urban areas, banded kokopu can usually be found where the streams are clean and forested, but not in other places where streams are less clean and there is no surrounding vegetation.

Banded kokopu habitat in the region

For example, we’ve found them in bush-lined streams behind Naenae and Stokes Valley in the Hutt Valley. To get there, the juveniles have migrated up the Waiwhetu Stream, which is one of the most modified and polluted streams in the region.

Banded kokopu also live in the upper reaches of urban streams like the Owhiro Stream, the Kaiwharawhara Stream and in streams in the Belmont hills behind Porirua.

The banded kokopu life story

Banded kokopu have a similar life cycle to other whitebait species, see Can fish fly? in this series. It lays its eggs on the edge of its home stream, which then carries the hatched eggs (larvae) out to sea. The larvae are carried around the coast for several months before the juveniles return to freshwater as whitebait and begin their journey upstream to live their adult lives in rivers.

Laboratory trials by NIWA suggest that juvenile migrating banded kokopu are attracted to the smells of the adult fish – so those migrating from the sea to rivers can choose the streams they swim up. If this is the case, banded kokopu are more likely to fi nd their way up streams containing adults than up streams with no adults.

Other research by NIWA also tells us why we aren’t likely to find banded kokopu in dirty streams. It seems that the movement of juveniles when they migrate upstream from the sea is strongly infl uenced by how turbid the stream is. The juveniles will avoid streams that are dirty and select cleaner streams to swim up and live in as adults.

Kaiwharawhara stream

Banded kokopu were found at this site ( right ) in the Kaiwharawhara Stream in Wellington. We’ve found them in urban streams around Wellington, Porirua and the Hutt Valley – but only those streams with suitable habitat. The fish avoid parts of streams with a lot of sediment or other pollutants.