Large numbers of native eels are being killed while swimming through council-run pumping stations, according to several new reports.

The issue has been discovered in Waikato and likely extends throughout the country, where hundreds of pumps may be killing native fish. It is unknown how many are being killed, but the extent was likely "extreme", one report said.

The reports were commissioned after hundreds of dead eels, some of them dismembered, were found in Waikato's Motukarara River after heavy rain in 2015. The deaths were connected to a nearby pumping station.

SUPPLIED A bucket of dead and dismembered eels collected after tests at a Waikato pump station.

Waikato Regional Council commissioned the studies, with funding from other councils around the country. They were obtained and released by advocacy group Forest & Bird.

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In one study,eels were tagged upstream of a pump near Te Kauwhata in Waikato, which was due to be replaced. It was described as a "typical" pumping station.

SUPPLIED An eel with liquefied internal organs after passing through a pump.

After collecting the eels once they'd gone through the pumps, they found the mortality rate for adult females was nearly 100 per cent.

Those that survived were almost all smaller males; every eel longer than 600mm, roughly the size of a small female eel, was killed, meaning larger females migrating to breed were the most likely to die.

"The results of the current study, the first of its kind in New Zealand, have provided irrefutable proof of the impact of traditional flood pump stations on downstream migrant eels, especially large highly fecund females," it said.

SUPPLIED What a non-liquefied eel's internal organs look like.

A presentation to the Waikato Regional Council, dated July 2017, said there were likely no pumps in the country that would be deemed "fish friendly".

There are hundreds of such pumps nationwide, primarily in regions where wetlands were drained for agriculture. They are also used during extreme flood events.

The Waikato region alone has 124 pumps.

SUPPLIED X-ray images of eels. The top eel was an uninjured eel, the others had been through a pump.

A separate technical report by consultants Bloxam, Burnett & Oliver looked at the issue of pump kills broadly, and concluded fish deaths were likely widespread.

There was virtually no data to show how many fish were being killed by pumps, however, as it had not been seen as a problem before.

"There appears to have been limited efforts made by land drainage and flood scheme managers in New Zealand to address these adverse effects", it said.

"It is considered reasonable to assume that these adverse effects are relatively common and are resulting in both direct mortality and significant reductions in habitat utilisation by native fish."

New Zealand has two varieties of endemic eel – shortfins and longfins. Both live in freshwater, but migrate to the sea at the end of their lives to reproduce. Some longfin eels can be more than a metre long and up to 60 years old.

Shortfins are not at risk, but longfins are threatened with extinction. Eel populations globally are in decline due to habitat loss.

'ANNIHILATION'

In the Te Kauwhata study, deaths were not only frequent, but gruesome. Many of the eels were decapitated, or severed into pieces by impellers.

At least one tagged eel's internal organs were liquefied, while another had its skin and organs shredded from its body.

X-rays of dead, intact eels showed some had their heads crushed or spines twisted. Some were alive after passing through the pumps but were so disfigured they had to be euthanised.

Others had severe injuries from being spun while swimming through the pump.

Because the eels were so often dismembered into small pieces, which sunk to the bottom of the channel, it explained why mass eel kill incidents were not frequently reported, the study concluded.

The sound of an eel being churned through a pump was found to be distinct, which could be used to monitor how many eels are being killed.

Advocacy group Forest & Bird obtained the reports, some of which have not been publicly released. Its freshwater advocate, Annabeth Cohen, said the scale of native fish deaths was "horrifying".



"These reports show that regional councils all over the country are operating machinery that is deadly to our treasured eels, and yet there appears to be no urgency or coordinated management of the situation," she said.

"They must start replacing existing pumps with proven fish friendly versions, and returning ecologically significant areas to wetlands. This will mean a managed, long term project of returning waterways and wetlands to their natural state."

One report described the eels as being "annihilated", she said. "While some councils are taking steps towards ending this horrifying massacre, there is little sign of the urgency that the situation requires."

'A LEGACY ISSUE'

The need for safe fish passage is required in multiple pieces of legislation, as well as various regional policy statements.

The reports identified a handful of councils running schemes likely to be killing native fish, all of which had been involved in the research.

The Waikato Regional Council, which has the most pumps in the country, said its replacement "fish friendly" pump near Te Kauwhata was showing promise, and it was actively working on broadly improving the survival of fish.

"We are dealing with an inherited legacy issue that current and future generations now face and need to address and resolve," said council chairman Alan Livingston.

It had approved half of the funding for a $1.5m, three year trial, and was looking for other groups to contribute, he said.

The Hawkes Bay Regional Council, which has around 20 pump stations, said its pumps were unlikely to be killing fish en masse, but they may be preventing access to upstream habitats.

"There is a chance they are killing eels and we have not noticed – but there are unlikely to be huge numbers involved because otherwise we would probably have received more complaints and seen more birds cleaning up the diced fish," said water quality scientist Dr Andy Hicks.

The council would be watching the Waikato trial closely, and was exploring its own options, he said.

Wellington Regional Council operates several drainage schemes, including a large one near Lake Wairarapa. A spokesman said the council was aware of the findings and was awaiting recommendations from the work being done in Waikato.

Other councils with pumping stations include Whangarei District Council and Bay of Plenty Regional Council, and Horizons.

