Senior freshwater ecologist Alicia Williams checks nets for eels to be tagged for release ahead of the monitoring programme. Photo / Waikato Regional Council
Senior freshwater ecologist Alicia Williams checks nets for eels to be tagged for release ahead of the monitoring programme. Photo / Waikato Regional Council
The “fish-friendliness” of a new flood water pump in northern Waikato was put to the test during the summer migration of native tuna (eels) and scored 100 per cent.
All 206 eels to pass through the enclosed Archimedes screw pump did so safely, marking another step in the Waikato RegionalCouncil’s mission to provide native fish with safe passage to the sea for spawning.
The pump was designed and built by the Netherlands company FishFlow Innovations and is the first of its kind in New Zealand. It is installed at the Mangawhero pump station in Aka Aka on the eastern side of the Waikato River about 7km from Waiuku.
The new screw pump is part of Pathways to the Sea, a research and strategy development programme by the regional council to help manage flood pump impediments to fish passage and which will lead to the development of a regional fish passage strategy.
A sock net installed at the outlet of the screw pump captured tuna that passed through the pump. Photo / Waikato Regional Council
Pathways to the Sea project manager Michelle White says the safe passage of all 206 tuna was an extremely pleasing result. The objectives of the monitoring programme, which was developed in collaboration with Ngāti Te Ata, are:
assess if tuna can pass through the pump safely, without injury
determine if large tuna (over 1 metre) can safely pass through the pump
assess if tuna avoid entering the pump.
In January, 162 shortfin and three longfin tuna were sourced from nearby catchments and the Te Kauwhata eel factory, tagged with passive integrated transponders (PIT tags), measured and weighed, and released upstream of the pump station ahead of the migration season.
A large sock net was installed at the outlet of the screw pump to capture any tuna that would pass through the pump, which started operating on January 27 following heavy rainfall from Cyclone Hale.
A total of 206 tuna were captured in the net and assessed for injury, measured, weighed and scanned for PIT tags. They included 66 of the tagged shortfin tuna and all three tagged longfin tuna.
How the Mangawhero pump station at Aka Aka works. Photo / Waikato Regional Council
Senior freshwater ecologist Alicia Williams says the tuna, which ranged in length from 328 millimetres to 956mm, were given an injury score from 0 to 4: 0 signifies no injury or minor abrasions up to 4 meaning death or fatal wounds.
Nearly all (99.2 per cent) of the tuna scored 0, signifying no injury or minor abrasion, and two tuna scored 1 (0.8 per cent), exhibiting moderate bruising, potentially caused by passing through the pump.
“At the end of the day, 100 per cent of the tuna survived and 99 per cent of them had no or minor injuries,” says Williams, who hopes to source and tag tuna longer than 1 metre to include in a repeat of the monitoring programme next year.
“The pump performed really well, safely passing eels over 600 millimetres in length. No eels of this size or greater tend to survive through the traditional pumps that make up much of New Zealand’s flood protection schemes.
“It’s extremely important that the large eels get through, as they tend to be the breeding females. Safeguarding these species is critical given the longfin eel is currently at risk and declining’ in New Zealand.”
Niwa freshwater fish technician Emily White tagging eels. Photo / Waikato Regional Council
Waikato Regional Council received $4.48 million from Kanoa - Regional Economic Development & Investment Unit, administered by the Ministry of Business, Innovation and Employment, towards upgrading five pumps in Waikato catchments to enable safe downstream passage of native fish.
The PIT data will be analysed by Niwa later this year to assess whether any of the tagged tuna that didn’t go through the pump avoided doing so.
The Archimedes screw pump is 10 metres long and 1.6 metres in diameter. It was installed and commissioned in March 2022.
In the Netherlands, trials reported very little impact on fish that pass through the pump, but New Zealand eel species tend to be larger than European eels.
The regional council has about 125 pump stations in the Waikato which help protect communities’ lives and livelihoods.
As part of its Pathways to the Sea programme, it is developing a regional infrastructure fish passage strategy that will identify and prioritise pumped catchments for fish passage and the appropriate measures to do so, such as fish-friendly pumps.
The council is also working with MacEwans Pumping Systems and Callaghan Innovation to develop a fish-friendly pump to replace existing MacEwans PPF axial pumps – found widely in New Zealand – without the need to make any civil structure modifications to pump stations.
Monitoring to assess the fish friendliness of this new pump will take place in the next tuna migration season, in the autumn of next year.
Pathways to the Sea is a research and development project, funded by Waikato Regional Council, other councils, iwi and industry, to improve downstream fish passage at the council’s pump stations. The regional council works closely with iwi, stakeholders and industry on all aspects of the project.
