A new report on the conservation status of New Zealand's freshwater fish is the most comprehensive yet, sharpening focus on the most crucial aspect of fish survival - spawning habitat.
An independent panel of experts, led by Department of Conservation Senior Science Advisor Dr Nicholas Dunn, assessed 78 freshwater fish species using New Zealand Threat Classification System criteria.
The report shows New Zealand's freshwater fish are in trouble with 28% of freshwater fish species classified as threatened with extinction and 32% at risk of becoming threatened. Only 8% are identified as not threatened.
"Eggs are the most vulnerable stage for freshwater fish, so assessments were focussed on the area of spawning habitat where they are laid," Dr Dunn says.
"Spawning habitat is critical for the fish life cycle. They need the right conditions for egg fertilisation, development and hatching. Nearby rearing areas are also key for the survival of young fish."
Since the previous report in 2017, 11 species have worsened in status and 12 have improved, largely due to better data rather than reduced threats.
Dr Dunn says inanga – one of the six species fished as whitebait – has experienced a notable change in conservation status, moving from 'At Risk – Declining' to 'Threatened – Nationally Vulnerable'.
"The worsened status reflects the vulnerability of inanga spawning habitat, which is estimated as less than 100 ha nationally and is under increasing pressure."
Despite the small size of these areas, inanga still produce lots of eggs and young fish. Protecting inanga habitats is an important part of DOC's efforts to manage the whitebait fishery.
Dr Dunn says Stokell's smelt, found predominately in Canterbury, has experienced the most dramatic status decline since the 2017 assessment, moving from 'At Risk – Declining' to 'Threatened – Nationally Critical' – the final step before extinction.
"Severe population declines since the 1980s of Stokell's smelt, which inhabit hāpua (river mouth lagoons), are linked to sedimentation, predation by birds and fishes, and marine heatwaves affecting young fish."
Greater knowledge of habitat area, has seen other freshwater fish species assessed with an improved status such as Eldon's galaxias and dusky galaxias. Both have moved from 'Threatened – Nationally Endangered' to 'Threatened – Nationally Vulnerable'.
Dr Dunn says that with much of threatened freshwater fish habitat lying outside public conservation land and water, collaborative efforts are needed to look after and protect these species.
DOC works to protect and restore freshwater fish populations by reducing the threat of invasive species, improving the ability for fish to move freely through freshwater systems, and restoring habitats including spawning areas in partnership with iwi, landowners, regional councils, and other agencies.
People wanting to help native fish on their properties and in their communities, can do their bit through naturing activities like joining a local stream care group, fencing streams from stock, reporting barriers to fish movement and planting native plants along stream edges.
Report: Conservation status of New Zealand freshwater fishes, 2023
You can help New Zealand freshwater fish
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