Building up whitebait stocks

Whitebait. Photo / Paul Taylor.

Whitebait numbers have been dropping but water quality and other measures are helping.

To New Zealanders īnanga (whitebait) – those teeny slivers of silver we look forward to every spring – are a national treasure.

For most people "treasure" means the joy of fritters but to Auckland Council's senior fresh water ecologist Matt Bloxham, these fish are an even more important treasure – a bellwether of the health of our freshwater streams and waterways.

With the help of the Whitebait Connection (part of the Mountains to Sea Conservation trust), local boards and volunteers, he is trying to reverse a decline in the population of these native species.

"Only one of the five native īnanga species - banded kōkopu - is non-threatened or not in decline on the mainland or Waiheke. Inanga, kōaro, giant kōkopu and shortjaw kōkopu are in decline," he says. "We don't monitor every one of our streams (we estimate there are some 10,000 streams and rivers between Pukekohe and Warkworth) but have representative sites for invertebrates.

"Now, after seven years of fish monitoring, [we find] they're having a hard time."

But help is on the way. Programmes are being put in place to eradicate predators, control erosion or sediment and manage habitats nowadays often exposed to high intensity rains.

One of those projects is run by Matt Maitland, whose job as senior ranger includes restoring the wild life at Tāwharanui and Shakespear regional parks.

At Tāwharanui, clean-up work paved the way for the release of 8000 fingerlings in 2017. They were farmed at Manāki Premium New Zealand Whitebait, New Zealand's only sustainable whitebait farm, and this winter another batch of adults (2-5 years) were released to see how best to re-build declining populations.

Maitland says: "Obviously, it is easier to make fingerlings in the factory, rather than taking up to five years to farm older fish. We put electronic tags into the fish and have antenna in the sanctuary to understand the movement of the fish. We'll put all the bits together and follow the 12-month natural cycle of the waterway to see what happens over the summertime."

Local communities are also playing a role. The Henderson-Massey Local Board, Community Waitakere and the Whitebait Connection are assessing sites for potential inanga spawning and installing artificial spawning habitats at four sites in their area.

They've now got the community on 'Īnanga Lookout' and are planning to restore five more spawning sites, remove weirs and protect egg sites from pests. Meanwhile, Hibiscus and Bays Local Board has started surveying streams for potential spawning sites with the Whitebait Connection and local community members are also helping as are Ōrewa North Primary and Ōrewa Primary schools.
The need is pressing. Bloxham says: "In 2014 we returned to 25 sites where historically there had been populations to find there were none in any of those sites. Since then we've gone back to look at other parts of the same streams and found other populations. But it's slightly unnerving that these are dominated by older fish, not many young ones, and that makes them really vulnerable."

Inanga lay their eggs on land, so for the first 1-2 months are vulnerable to dessication, sunburn, or, if the stream is on a farm, trampling by livestock (though New Zealand dairy farmers have fenced 97 per cent of waterways to prevent cows accessing waterways). They are also eaten by predators like rats. Hatched larvae then have to make it to sea and, Bloxham says, only one to two per cent will make the return to their adult habitat as whitebait.

Whitebait Connection's Auckland manager Sophie Tweedle says that the fish needs are simple - "clean, clear, cool" water - but getting that is hard. The water needs to be free of sediment (which runs off urban spaces and steeper farm land stripped of trees and vegetation), it needs to be cool (again, vegetation does that) and free of things that obstruct the movement of fish through their life cycle (such as culverts, barriers and weirs that trap fish away from their breeding habitats or injure them as they try to get up).

Bloxham says Auckland streams are vulnerable in two ways. They are soft bottomed, meaning habitats are limited (the fish like cover such as logs, rocks or undercut stream banks), and run-off keeps juvenile fish away (they don't like brown or cloudy water, as they are visual feeders, and are sensitive to changes in oxygen levels).

"We are trying to identify and isolate the stressors," he says. "Improving the water quality by planting and controlling predators that eat the eggs or adults will create a future."

While Maitland's monitoring is at the sophisticated end of the spectrum, Tweedle and Bloxham are turning to local communities to monitor their patches. Bloxham has been excited by local success stories where members of the public have stumbled across new giant kōkopu nests, helped find spawning zones and are systematically mapping and protecting the fish habitat.

"They've picked it up with great verve, it's very exciting," he says.

Tweedle says: "I've got plans, my personal goal is that it would be awesome if every river and stream in Auckland was mapped," she says.

"We get the community to do this, and they'll make it theirs, they'll have ownership. In just three years we've had great traction in Auckland, and now it's a huge project with Auckland Council."