Over three to four years, 16 sites across the Whanganui catchment were surveyed to address gaps in knowledge of fish distribution. Photo / Department of Conservation
Native migratory fish have been detected nearly 300km up the Whanganui River during river restoration research.
The panoko, or torrentfish, an endemic freshwater species most closely related to cod and tuna (eels), were found at Waimiha in the Ōngarue River, 297km from the river mouth.
Department of Conservation (DoC) programme lead Jane Taylor said it was a good sign for the awa to see the migratory fish so far inland.
“There’s a lot against these fish. The tiny juveniles that migrate upstream are swimming against the flow, steep climbs, waterfalls, pollution, floods and predation, not to mention human-made barriers.
“The fact that any of them make it is astounding.
“It means there are no barriers for them to get there at the moment. But there are a lot of other places in the catchment where they can’t.”
Taylor said natural waterfalls, man-made dams, fords and culverts could block their passage.
“If a fish isn’t able to complete both the freshwater and saltwater parts of its life-cycle, you can imagine which way the population will go,” she said.
Various methods had been used to ease migration, such as introducing ramps and ladders, she said.
The research involved surveying 16 sites across the catchment using methods such as environmental DNA analysis (eDNA).
Information was collected over three to four years to address gaps in knowledge of fish distribution in the Whanganui catchment.
Surveys were typically done with spotlights, nets and electric fishing methods but eDNA offered a slightly costlier but easier method, Taylor said.
It provided a snapshot of fish biodiversity in specific locations, aiding decisions on which habitats should be protected and where to prioritise water quality improvements, she said.
DoC conducted the research in partnership with Ngāti Hāua Iwi Trust.
World Fish Migration Day is on May 23 to raise awareness of the importance of free-flowing rivers. This year’s theme is “we are river people”.
Kuru Ketu, Pou Taiao of Te Whiringa Kākaho, said Whanganui iwi, as river people, had an inalienable interconnection with Te Awa Tupua, the Whanganui River, and its health and wellbeing.
“Through this joint effort, we take another step towards fulfilling our shared responsibilities as tāngata tiaki,” Ketu said.
“Enhancing both the wellbeing of Te Awa Tupua and the relationships that connect people to it.”
The study reinforced the Manganui-o-te-Ao River and its tributaries as a biodiversity hotspot.
Seven threatened and at-risk species were found in the Ōngarue sub-catchment, including piharau (lamprey), panoko, īnanga, whio and two mayfly species.
Taylor said the information would help build a better picture of biodiversity in the catchment and influence future restoration efforts.
Noam Mānuka Lazarus (Ngāti Whātua o Kaipara) is a multimedia journalist at the Whanganui Chronicle.