The impact of obstacles preventing native fish species and trout movement in Taranaki waterways was highlighted during a recent electric fishing research programme carried out by Fish & Game.
The national study also revealed kōaro and eel populations in Nelson/Marlborough are recovering after being decimated by Cyclone Gita in 2018.
Fish & Game teams in regions including Otago, Central South Island, West Coast, North Canterbury, Nelson Marlborough, Wellington and Taranaki have been sweeping rivers and streams with a pole that emits a low-voltage, high-current charge.
Fish are temporarily stunned and scooped up in a net. They are identified, weighed and measured before being returned to the water.
The electric fishing programme helps Fish & Game monitor populations of trout and salmon, but also record native freshwater fish such as various species of galaxiids, kōaro, kokopu, bullies, eels, torrent fish and lamprey. Staff also note waterway condition, macroinvertebrates, and barriers to fish movement.
“Electric fishing is helping to protect New Zealand’s freshwater fish and rivers,” said Fish & Game chief executive Corina Jordan.
“It may sound unusual but it’s an effective way to keep watch on the state of our fish species, including indigenous populations, and the places they live. These surveys support other research that show native fish populations, as with juvenile trout, are at risk from the increased frequency and size of flooding.”
“Monitoring identifies waterways with declining water and habitat quality, and the effects of barriers to fish passage.”
Data is entered into NIWA’s New Zealand Freshwater Fish Database for use by other freshwater scientists and to inform both regional and national policy.
In Taranaki, electric fishing surveys are monitoring the effects of barriers to fish passage for native species and trout. It has highlighted a decline in water and habitat quality that occurs down the length of ringplain catchments.
Fish & Game staff in Nelson and Marlborough, with assistance from the Department of Conservation (DOC), are tracking a recovering kōaro and eel population after native fisheries were annihilated by Cyclone Gita in 2018.
Staff in the region have also found increased climate-change-generated floods pose just as much, if not more, risk to native fish populations as they do to trout.
In Hawke’s Bay, Fish & Game staff plan to partner with other local agencies and iwi to resume electric fishing in small streams before Cyclone Gabrielle brought the monitoring programme to a halt.
Fish & Game mostly uses electric fishing to confirm the presence of juvenile trout, a marker of successful spawning.
“Because juvenile trout stay within the stream their parents spawned in, any observation proves that trout spawning occurred somewhere within the reach or further upriver,” Jordan says.
“The presence of trout means Fish & Game can advocate for that habitat, which benefits all aquatic life ─ native and valued introduced species.”
Electric fishing is also used to educate school and catchment groups about stream habitat and health.
Fish & Game also shares data with agencies such as the DOC for resource consents and partners with universities on electric fishing monitoring projects.