3 Jul 2014

Improving Inanga Breeding Habitat

From Our Changing World, 9:06 pm on 3 July 2014

‘People used to talk about catching cartloads of whitebait and using it as fertiliser on the farms. Now, if people get a 20-litre pail of whitebait over a season they think they’re doing pretty well.’

David Moss is a freshwater fish expert with the Department of Conservation, and he’s familiar with tales of how enormous catches of whitebait in the past have dwindled to very small catches today.

Les Mullen from Te Atiawa ki Whakarongotai has been whitebaiting for 40 years and he’s heard stories of the richness of whitebait in the Waikanae River in former years. ‘Over time there’s been good years and some real bad years’ he says. ‘The inanga is here but I’d still like to see more habitat.’

Habitat restoration was the focus of “The Great Inanga Exploration”, a free whitebait workshop hosted by the Department of Conservation on the banks of the Waikanae River in late March. Amelia Nurse attended the workshop, which explored the historical and cultural implications of inanga, methods for restoring whitebait spawning habitats, the whitebait life cycle, and tips for whitebaiting sustainably.

Whitebait are the juveniles of five native freshwater fish species. The five species belong to the fish family Galaxiidae, which was named after the Milky Way galaxy as the very first species described was sprinkled with dazzling spots.

Inanga is the most common kind of whitebait. David Moss says that inanga used to be known as cowfish, because they spawned in such numbers that the sperm and eggs at the side of the river turned the water a milky colour.

After spending the first phase of their life at sea, inanga spawn in the lower tidal reaches of streams and rivers. They follow the saltwater wedge upriver on a high spring tide, and deposit their eggs and sperm in amongst low vegetation on the river bank, preferring cool shady sites.

The inanga habitat restoration workshop showed people how to create instant shelter along river banks using bales of straw, but stressed that careful riparian planting was the best long-term way of providing suitable breeding habitat for inanga.

The other four species of fish that make up the whitebait catch are kōaro, banded kōkopu, giant kōkopu and shortjaw kōkopu. These four can spawn much further upstream says David Moss, ‘Right up in the headwaters.’ David says that some of the species that spawn further upstream can climb waterfalls. ‘Kōaro are beautifully adapted. They have ridges on their fins that they can use almost like rock climbing shoes.’ They’ve been recorded climbing more than five metres.

David Moss says it’s easy to tell the species of whitebait in your bucket apart ‘Looking into your whitebait bucket, the kōaro and banded kōkopu are the more vigorous catch, and they’ll be the ones climbing up the side of the bucket. The ones that sit in the bottom of the bucket and just don’t want to go anywhere are the inunga, who are a bit more chilled.’

This Our Changing World story features David Moss surveying streams at Zealandia Sanctuary in Wellington, searching for native fish after a trout eradication.