Whitebait species make a comeback at Tawharanui Open Sanctuary

Wednesday, 14 June 2017

Giant kokopu live to 30 years and are under threat as part of unregulated whitebait fishing.

It was all hands on deck as 10,000 rare whitebait were released into streams at Tawharanui Open Sanctuary in north Auckland last week.

Even inside the custom-built fish transport trailer and tank, the ride along windy Takatu Rd would have been pretty rough for the young giant kokopu.

Auckland Council senior ranger Matt Maitland overseas the fish transfer at Tawharanui by volunteers

Some tank water was replaced with stream water so the fish could acclimatise before Auckland Council rangers, TOSSI volunteers and others carted the six month old fingerlings to the streams by bucket, and gently releasing them.

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Large numbers of young Giant Kokopu were released at Tawharanui Open Sanctuary as many will be eaten.

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Aquaculture manager New Zealand Premium Whitebait Paul Decker and CEO Jeremy Gardiner catching the whitebait from one of the companies commercial culture tanks.

* Whitebait season disappoints so far**

The project was the brainchild of native fish specialist, conservationist and New Zealand Premium Whitebait (NZPW) manager Paul Decker. Restoring native fish in waterways has long been a goal for the self described 'fisho'.

With farmed white bait now available Paul Decker is among those calling for an end to commercial fishing from the wild.

Decker approached council to consider re-introducting of the fish to the area using young fish from their commercial operation.

Fish surveys by the council found giant kōkopu were no longer present in Tāwharanui Regional Park, or numerous other sites across the region, Auckland Council Senior Ranger Open Sanctuaries Matt Maitland said.

'There has been a significant decline in the numbers of giant kōkopu over the past two decades. Nationally, this is likely to have been a result of habitat loss, water quality decline and land-use changes,' he says.

Having disappeared from the streams in the Tawharanui catchment around 30 years ago, the sanctuary offers an ideal environment to study how the fish re-establish, for other restoration projects, Decker said.

Work on the streams and wetlands over the last couple of years by staff and TOSSI members, along with technical support and equipment from NIWA, has been under the watchful eye of Matthew Bloxham - the council's senior regional advisor for freshwater.

'This will be a test case for further Auckland releases and will tell us more about how previously modified freshwater environments can be restored for native fish species,' he said.

Increasing temperatures from climate change will also make fencing off waterways and planting for shade more important for whitebait, especially in the north.

Giant kokopu are at the limit of their range in the north and warmer water temperatures from deforestation allows more sunlight onto streams will be having an impact, Decker said.

They may not have time to adapt to fast-warming or high temperatures and could disappear from the region, he said.

The age of the Tawharanui fish means they will still be a meal to birds like kingfishers, herons and shags, along with eels. But, behind the 2.5 kilometre predator fence, the fish will be safe from rats.

Enough should survive that they will eventually breed, their offspring hatching along the streams and washing into coastal waters where they will feed and grow for around three months. Then its back up the rivers as the whitebait we know to live out the rest of their lives.

Young fish looking for a likely stream are attracted to the scent of adult fish already there. So, once adults disappear from waterways, it can take a long time for fish to re-establish naturally.

Having a marine reserve connected to some of the 588 hectare open sanctuary park will ensure at least some stream entrances remain safe for the fish from humans.

While birds like saddleback, bell bird and takahe have been successfully reintroduced to the park, along with gecko, this is the first freshwater fish.

Giant kokopu are one of the five species that make up whitebait and one of the rarest. All but one species are threatened.

The youngsters were bred and grown on for several months longer than usual at New Zealand Premium Whitebait (NZPW), New Zealand's only whitebait breeding facility at Warkworth.

Decker founded the Mahurangi Technical Institute at Warkworth and its native fish research department in part to fill a knowledge gap in fresh water fish conservation.

'DOC and others were getting involved with conservation of kiwi and other birds but no one was doing it with the fish.'

Decker and chief scientist Dr Tagried Kurwie were also behind the breeding and release of 10 adult giant kokopu in Nukumea stream, Orewa as part of mitigation for the northern gateway toll road in 2010.

Concerns have been raised for the fish after heavy silting in the stream caused by recent developments at West Hoe Heights.

But freshwater ecologist with Niwa, Dr Paul Franklin, who has been monitoring the fish annually since their release said, while none were found in March they had been healthy and growing and attracting young fish up the stream. Given the length of the stream, not finding the fish is not a surprise and it is too soon to speculate if silting has seen their demise, he said.

Now that large quantities of whitebait can be farmed in a closed loop, Decker is backing calls for more control of the whitebait fishery, including ending commercial fishing from the wild.