Habitat loss a threat to freshwater fish - study

More freshwater fish species are under threat than before as increasing development and demand for water push them towards extinction.

The first comprehensive threat ranking study of indigenous and introduced fish in four years will be published today in the New Zealand Journal of Marine and Freshwater Research.

The 2009 study paints an alarming picture of decline, depending on the species – as habitat is lost to development like dairy farming, and fish populations decline.

Most of the threatened species are in Canterbury and Otago – the ancient cradle of many of the country's native fish. However, species once protected by their remote or high-altitude locations are starting to suffer as human development encroaches.

Apart from traditional predators, such as trout, the country's native fish are battling a suite of human-induced problems, such as pollution from agricultural runoff, sediment muddying traditionally stony riverbeds and low flows from water abstraction.

Scientists say without formal protection for their habitat, such as conservation or reserve status, some species will become increasingly threatened and possibly extinct.

"I don't think in the next five to 10 years time frame we'll see extinction but we will see them retreat to far fewer places," said the paper's lead author, Richard Allibone, a freshwater ecologist for Dunedin-based Golder Associates.

In 1992, when the first threat ranking was done, only 10 species were classified as threatened or having conservation priority.

Now, 34 of 51 species, or 68 per cent, are listed as threatened or at risk.

The paper said demand for water was increasing pressure on previously unmodified catchments.

Dairy conversions were singled out as "leading to increased water demand, increasing habitat modification and potential declines in water quality. Land development and out-of-stream water use have impacts – and even with some of our most common fish it's starting to show up."

Many people will never see many of the threatened native fish, Allibone admitted, but he argued they were still worthy of protection.

The paper concludes: "It is apparent that more serious effort is now required to reverse the decline in native freshwater fishes and to manage the instrumental causes of their decline that are ongoing, and in some cases increasing, if the extinction of further freshwater fish is to be prevented."

A native fish hatchery and a holding facility, in case of drought, would help manage native fish populations, Allibone said.

Canterbury mudfish expert Dr Leanne O'Brien said the species was in a "dire" position because of the removal of wetlands.

The Press