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Inanga monitoring is underway for autumn, with a great start to the season

Thursday  6 April, 2023

Autumn is the season teams go out looking for inanga eggs. Inanga is a native fish that’s one of five whitebait species in Aotearoa New Zealand.

Between March and June, Te Ngahuru Tikoitikoiere team from Rongowhakaata Iwi Trust will monitor three significant sites for signs of any spawning.

After the spring high tides in March, Te Ngahuru Tikotikoiere team found an abundance of eggs at one of the significant sites they monitor, showing much more success than last year’s breeding season.

“This is great news, especially after the cyclones this summer,” says Council environmental scientist and inanga habitat restoration project manager Isabella Clere.

“Inanga, and their spawning success rate, play an incredibly important role in our ecosystem.

“Looking for inanga eggs is done on spring tides after the full moon. Adults usually spawn in late summer or autumn, and eggs are generally found in areas of long grass along the stream banks where the saltwater meets the freshwater, this area is known as the ‘saltwater wedge’.”

Artificial habitats are used on stream banks that do not have suitable habitats for spawning to check if inanga are spawning in that area. Artificial habitats are created using coconut matting, meadow hay/straw and flax to make a long roll that gets staked to the side of the stream. The artificial habitat is partially submerged in a spring high tide and inanga are able to swim within the habitat and lay their eggs.

The mats are checked after the spring high tides to see if any eggs are present and counted if they are present. The eggs remain above the water level until the next spring tide when they become submerged and hatch and are then taken out to sea.

The mats are re-visited a couple of weeks later to check on eggs in case of predation by rats, or other threats such as floods or sediment loading which affects the habitat. Predator traps have been installed at the monitoring and restoration sites to reduce the likelihood of predation on the inanga eggs.

Inanga use the same spawning sites in rivers and streams each year, so by identifying and protecting these places, we can increase the number of eggs, juveniles and eventually adult fish.

Of the five native fish species that make up whitebait, inanga, giant kokopu, kōaro and the shortjaw kokopu are either in decline or threatened.

Council is in partnership with Rongowhakaata Iwi Trust to monitor the success rates of spawning and improve the habitat of spawning sites.

Ms Clere says fencing off waterways, allowing grass to grow long and dense, is the first step to improving spawning success. Planting native sedges and small grasses can help to improve the spawning success by re-introducing the native habitat back to the spawning sites.

If you would like any further information on spawning locations around Tairāwhiti or would like to get involved in inanga spawning habitat restoration, please get in contact with Council project coordinator Isabella Clere

To find out more about this work see Council’s website and visit the Inanga spawning programme page.

Photo captions:

  1. Trapping is reducing pest numbers during spawning to stop them from eating the inanga eggs.
  2. Inanga eggs found after the spring high tides in March. Eggs are small and opaque and look very similar to slug eggs.
  3. This is what artificial habitats beside streams look like, they could have eggs inside so be careful and give them space if you see them.
  4. Plantings survived Cyclone Hale and Cyclone Gabrielle at one of the monitoring sites.
  5. New signs have been installed at monitoring sites Rongowhakaata Iwi Trust are restoring.
  6. Shaavone Brown from Te Ngahuru Tikotikoiere team of Rongowhakaata Iwi Trust installs artificial habitat at one of their monitoring sites.

Predator control

Inanga eggs

Artificial habitat on side of stream

Plantings survived cyclones 2023

Inanga signs

RIT Shaavone Brown Inanga eggs