Whitebait stocks get boost

 

Kokopu in net ready for release.

Media Release: July 13, 2018

New Zealand’s largest and rarest whitebait species is getting a helping hand to re-establish in the wild this weekend (July 14) with 140 adult fish being released into a stream in the Tāwharanui Regional Park, near Auckland.

Manāki fish breeder Paul Decker says what the average consumer of a whitebait fritter doesn’t know is that whitebait can grow up to 2.5kg as adult fish and live for 30 years.

“While the fertilised eggs can only develop in fresh water, once hatched the fry of these five native fish species immediately get swept out to sea, grow into whitebait and return to spawn up rivers and streams,” Decker says. “But if the juveniles can’t sense the pheromones of their own species they will not go up them. This is one of the reasons whitebait catches have been declining in the wild. As adult populations are decimated inland more fresh water courses are not seeing the whitebait runs they once had.”

The joint project between Manāki and its new owners Tahu-Whoa Group Holdings, Ngati Manuhiri (Tāwharanui is in its rohe), Auckland Council and NIWA follows the release last year of 10,000 juvenile, giant kōkopu (Galaxias argenteus) in two of the park’s main waterways – the largest reintroduction of whitebait in New Zealand.

Giant kōkopu disappeared from Tāwharanui around 30 years ago following the construction of a dam to create a pond in the lower reaches of Waikokowhai Stream. But restoration efforts since have seen it returned to an environment that scientists believe can now provide the habitat giant kōkopu need. Fish that have grown on after last year’s release have been found at Tāwharanui.

The aim is to establish self-sustaining populations of the native fish throughout New Zealand and to support its conservation.

Tahu-Whaoa became involved because its runanga trust is among iwi managing the restoration and conservation of the Waikato River. Evelyn Forrest, the trust’s environmental spokesperson, says the Tāwharanui release is part of a pilot project that will ultimately see tens of thousands of these native fish released into the Waikato.

Efforts by the council to unearth giant kokopu populations has reinforced just how rare the species has become in Auckland. A handful of “new” populations have recently been uncovered by members of the public, but giant kōkopu have all but disappeared from their former habitat.

Auckland Council senior ranger Matt Maitland says much needs to be done to create a future for the species in the region.

“The reintroduction of giant kōkopu to the Waikokohai and Mangatawhiri streams is of significant conservation value to the region,” he says. “The integration of farming and public recreation within the pest free Tāwharanui Open Sanctuary provides opportunities to restore the whole ecosystem, allowing us to return this rare and threatened species alongside takahē, kiwi and saddlebacks.”

Manāki, a commercial breeder of whitebait for sale and export, has supplied the fish for this project and implanted tags for ongoing monitoring by NIWA.

NIWA principal scientist Dr Cindy Baker and staff have installed antennae at the dam exit, in the dam itself and in the stream that feeds into the dam, that will pick up the movements of the giant kōkopu.“We want to understand how fish use the environment – how much time they’re spending in the dam, compared to in the stream, whether they’re adapting to this habitat or whether they leave the system,” Dr Baker said.

At night and in summer the water is particularly anoxic – or depleted of dissolved oxygen – which does not provide ideal water quality for freshwater fish.

“However, there are already similar species such as eels and banded kōkopu, living happily in the water, which suggested to us that perhaps the giants, which also breathe through their skin, could survive as well,” Dr Baker said.

Release details:

When: Saturday July 14, 1pm – 3pm

Where: Waikokowai (Ecology) stream dam, Tāwharanui Regional Park. Signposted from Anchor Bay car park. Come prepared for the weather and a short walk.

Tahu-Whaoa Group Holdings is a Trio client.