The deaths of nearly 200 eels in Bay of Plenty rivers have sparked an investigation into whether pump stations are “mincing up tuna”.
By Mathew Nash, Local Democracy Reporter
The Bay of Plenty Regional Council’s regional delivery and evaluation committee was told on Tuesday that a major research programme would seek to better understand how communal pump stations affect migrating shortfin tuna (eels) and whether mitigation measures are needed.
The report follows a mass mortality event in the east of the region, near the Old Rangitāiki Canal and Tarawera River.
Each year, some mature eels migrate downstream from lakes such as Tarawera and Rotomahana, travelling through the Tarawera River to the sea as part of their final migration to their Pacific spawning grounds.
In March, eels on this migration path met pumping infrastructure after adverse weather, with 190 shortfin tuna later found dead.
But staff told councillors the real toll could be much higher.
“That’s just the dead bodies that were found at the mouth of the Tarawera,” integrated catchments manager Chris Ingle said.
The incident sparked an emergency trap-and-transfer operation in early April.
About 500kg of eels were relocated downstream of pump stations before Cyclone Vaianu, in an effort to prevent a repeat mortality event.
The council’s investigation will seek to identify which pump stations posed the highest risk to migrating eels, what proportion were successfully diverted around pumping infrastructure, and how effectively trap-and-transfer operations reduced losses.
Staff said significant gaps remained in understanding how many eels were affected by pump stations and how many were successfully protected through existing mitigation efforts.
Councillors heard the next migration period was expected in February and March, with research and mitigation work planned before then.
Councillor Anna Grayling said any future discussion about fish-friendly infrastructure would also need to grapple with a contradiction between conservation efforts and commercial harvesting.
“We’re potentially rescuing, at great cost – thousands and thousands of dollars per eel – to still be potentially harvested from a legal fishery,” she said.
“It would be like picking up a snapper and saying, ‘we’ve rescued the snapper’, but it can still be caught.”
Councillor Ken Shirley said the March mortality event was concerning but expressed caution.
He noted it was shortfin tuna impacted, as opposed to the endangered longfin species, which is only found in New Zealand.
“I know all deaths are bad, but to that extent, we don’t want to blow the incident out of proportion.”
Committee chairwoman Kate Graeme said the work was part of a broader effort to understand the long-term sustainability of the region’s flood protection and drainage systems.
“It might seem like it’s a focus on tuna, but it’s about the sustainability of the whole [river] scheme.”
Councillor Kat MacMillan said the prospect of pump stations “mincing up tuna” highlighted the need to understand the full implications of future infrastructure decisions – especially as some was privately-owned.
“If we discover all this and there is an issue, and we need to change the infrastructure, how do we fund that?”
Ingle said it was too early to estimate future costs because the council was only beginning to determine the scale of the problem.
Any future funding discussions would be done as part of the council’s long-term plan process, he said.
Council staff said the investigation would draw on lessons from a Waikato Regional Council programme, and be supported by local iwi groups, including Ngāti Awa experts, alongside former commercial eel fishers and freshwater scientists.
The field programme was expected to begin with population surveys later this year, with intensive monitoring planned during the next downstream migration season in early 2027.
LDR is local body journalism co-funded by RNZ and NZ On Air
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