This native fish may soon be extinct, scientists warn

Wednesday, 8 August 2018

DOC senior ranger Anita Spencer holds a Canterbury Mudfish in her hand.

This mudfish is small, but staunch: It favours slow-moving, swampy creeks and can live outside of water for months on end, entering a kind of semi-hibernation beneath damp logs or burrowed in the dirt.

But scientists say the Canterbury mudfish is at risk of becoming the second native fish known to have become extinct in New Zealand.

A review of the conservation status of freshwater fish, released on Thursday by the Department of Conservation (DOC), concluded three-quarters of New Zealand's 51 known native fish species were threatened.

It was largely unchanged from the last report, in 2014.

* Native fish are being 'annihilated' by council-run pumps

* Efforts to save Canterbury mudfish include using 'electric fish-fence'

* Trout barriers in South Canterbury streams to save critically endangered native fish**

But the panel of scientists who authored the report made special mention of the Canterbury mudfish, which is on life support as a species.

'Little has changed to benefit the Canterbury mudfish since it was first classified as nationally critical [in 2009] and its persistence is now tenuous,' the report said.

'Urgent action to protect Canterbury mudfish habitat is needed to avert its extinction.'

The species, which is a taonga to Ngāi Tahu, is nationally critical with the qualifier 'conservation dependent', meaning it would likely move up a threat ranking if current management stopped.

The next threat ranking is extinct.

Only one fish species is known to have become extinct in New Zealand - the Grayling, which was last seen in 1923. The grayling, ironically, is our only freshwater fish specifically protected by law, a status it received several decades after its extinction.

Protecting the Canterbury mudfish has been a losing battle for authorities, in part because much of the species' habitat is on private land. Around 5 per cent of its known habitat is in DOC reserves.

Its total habitat has been estimated at 24ha, in small fragments spread across the entire Canterbury region. The species likely prospered before human settlement, when large parts of the plains were covered in wetlands. Around 90 per cent of those wetlands were drained, primarily for farming.

The scientists said drought conditions were also a threat to the species, exacerbated by water abstraction for irrigation.

The report's corresponding author, DOC freshwater science advisor Dr Nicholas Dunn, said that when the Canterbury mudfish was first listed as nationally critical, its population had been expected to fall by 70 percent within a decade.

'From the information we have, we're fairly confident it is above that 70 per cent decline rate,' he said.

'The habitats it occurs in are very small, on average a third of a hectare and often in ephemeral wetlands, which themselves are an endangered ecosystem type.'

Unlike migratory species, such as whitebait, if a population goes locally extinct it is unlikely to return naturally. Dunn said the greatest threat to the mudfish was the removal of habitat, which largely happened through agricultural development.

'These habitats have very little protection under either the district plans or the regional plans, and because they're ephemeral they can dry in prolonged droughts,' he said.

'With very little restrictions on activities, predominantly agricultural activities, they're quite prone to development.'

There were few changes to the conservation status of other species. The five whitebait species remained threatened, as did the longfin eel.

The panel noted that longfin eel populations appeared to be stable or increasing in commercial fisheries, which was promising. It remained concerned, however, about ongoing degradation of the eels' habitat in lowland areas, particularly declining water quality and issues with fish passages.

It was revealed earlier this year that longfin eels are likely being routinely maimed and killed by pump systems that are supposed to allow safe fish passage.

Conservation Minister Eugenie Sage said the plight of the Canterbury mudfish was a sad consequence of changes made to the landscape.

“Much of the Canterbury mudfish habitat is on private land and is severely impacted by agriculture,' she said.

'[I]t’s sad but not surprising that the loss of aquatic and other wetland habitat has had a major impact on Canterbury mudfish and other wetland-dependent indigenous freshwater fish.”

She said although the longfin eel's status was unchanged, it should not be an excuse for complacency, as commercial fisheries were only a small part of its habitat.

'The degradation and loss of longfin eel habitat outside these fishing sites is concerning, especially in lowland areas, and the obstruction of fish passage continues to be a problem.'

Five species had their conservation status changed. The lowland longjaw galaxias (Waitaki River) moved down a threat ranking due to conservation management, and two other species - Pomahaka galaxias and redfin bully - moved down due to better knowledge of their habitat.

Two species, the giant bully and southern flathead galaxias, moved up a threat status due to better knowledge of their habitat.