Fish ladders offer hope to native fish

25 Aug 2016

The idea of installing ladders for something without arms or legs may seem a little crazy; but for Whangarei's threatened native fish it might literally prove a life saver.

More than two-thirds of New Zealand's 35 native fish species are classed as 'threatened' or 'at risk' and many of these need to migrate hundreds of kilometres between rivers and streams and the sea to reach suitable habitat/spawning areas.

However, regional council Freshwater Ecologist Carol Nicholson says all too often migrating fish – including whitebait (the juvenile fish of five species of galaxiidae) – encounter obstacles in the form of culverts, weirs, tide gates, dams or other structures.

While some fish like banded kokopu are strong climbers able to negotiate natural barriers like waterfalls, for others obstacles, especially man-made ones, can stop them reaching critical habitats altogether.

Fish ladder under the Western Hills Drive bypass.Whangarei Harbour Catchment Group lead Darryl Jones checks out a new fish ladder under the Western Hills Drive bypass.

Ms Nicholson says legally both the Department of Conservation (DOC) and regional council have responsibilities to manage fish passage in waterways.

"Regional plans provide some protection and structures built since 1984 can't impede fish passage without a DOC permit, but there are still a number of mainly older structures in rivers and streams in and around Whangarei, many linked to historical flood protection work."

She says for native fish desperately attempting to reach (or return from) Whangarei Harbour, the region's biggest city sits tantalisingly close to their destination, yet still throws up some serious impediments to doing so.

To help overcome this, council staff – including its rivers and environmental monitoring teams – are working to remove barriers where possible, and where they can't, have been installing a variety of fish passes.

Falling into the latter category is a Kirikiri Stream culvert under Whangarei's Western Hills bypass, where a potentially life-saving steel 'fish ladder' has recently been installed.

The Kirikiri Stream culvert ladder was championed by the Whangarei Harbour Catchment Group, which successfully sought the roughly $3000 funding required from the Whangarei District Council.

Ms Nicholson says most people would probably not give the small and relatively simple stainless structure a second glance, but it – and others like it – can make a huge difference to the long-term survival of native fish species.

"Most of the structures currently posing obstacles to successful fish migration were installed years ago and before we knew as much about these fish and their life cycles as we do now. It's great to be able to take some quite simple steps today give them a much better chance in the future."