Freshwater crayfish live in streams and waterways throughout New Zealand. Photo: Stella McQueen

An insecticide spray meant to kill a beetle feasting on eucalyptus plantations is probably responsible for massacres of kōura. The chemical is due to be reassessed, but at the moment is available for a variety of crop pests. Its active ingredient is known to kill crayfish without leaving a trace.

Twice death rained down from above – possibly.

Twice – almost exactly a year apart – Putaruru’s Oraka stream was filled with bodies of kōura (fresh water crayfish).

In December 2016, local resident Erin Hampson-Tindale had taken his children for a swim in the stream. He said kōura were initially “thrashing around, leaping out of the water, really agitated”.

Shortly after they stopped moving. 

The lifeless bodies, some large, some babies, tumbled down the stream for over four hours.

Hampson-Tindale returned home to get a camera to video the kōura. When he returned they were still washing down the stream, although fewer in number.

“If I had been able to net from the start, I would easily have filled a small car trailer.”

Other locals were collecting the dead kōura to eat. Hampson-Tindale suggested that without knowing what killed them it probably wasn’t a good idea. He didn’t think there was anything natural about their deaths.

In December 2017 it happened again. This time 60 dead kōura were collected by the Waikato Regional Council, along with water and sediment samples.

A ‘possibility, albeit probable’

To be fair, no one is completely certain what killed the kōura came from above. The chemical suspected of causing their deaths can kill without leaving a trace. It’s possible it was a perfect, unintended, crime.

What is known is both years, hours before the wash of bodies was spotted, a helicopter sprayed the insecticide Alpha-Scud over a eucalyptus plantation in a bid to kill the eucalyptus tortoise beetle. The beetle is capable of defoliating trees to the point of death. The trees were no more than 60 metres away from the stream. Guidelines suggest 300 metres as a buffer zone, however, these guidelines aren’t regulations.

Alpha-Scud’s label has explicit warnings to keep the spray away from waterways and states it is “very toxic” to aquatic organisms.

The Waikato Regional Council (WRC) embarked on a mission to pinpoint the crayfish killer. After a year of “frustrated” work their January 2019 overview of the incident says:

“We have not been able to conclusively establish the cause of death therefore it only remains a possibility, albeit probable, that the aerial spray was responsible.”

“It’s a great sort of chemical warfare agent against crayfish. It kills in concentrations that are undetectable and that leaves no trace.”

No prosecution could be made without concrete evidence. Despite WRC’s extreme effort which included a staff member escorting frozen crayfish to an English laboratory – the only laboratory capable of testing for the chemical and willing to front in a court case – evidence stubbornly remained circumstantial.

“Though not to an evidential standard we believe that we identified the cause of the crayfish deaths, being the aerial spray operation and that, in all probability, Cypermethrin is the primary killer of these creatures.”

Chemical warfare which leaves no trace

University of Waikato’s associate professor Nicholas Ling completed a toxicological assessment of the dead kōura. In hindsight he said in some ways it was an exercise in futility. The flesh of the dead kōura had cypermethrin below detectable levels. No other toxin was found, including 1080 and glyphosate.

“This stuff [cypermethrin] is incredibly toxic to crayfish. They are so sensitive to it. It kills at concentrations that are virtually undetectable by most normal analytical chemical techniques and doesn’t leave residues in the tissue.”

The chemical is a nerve agent, killing almost immediately before residues are accumulated in tissue.

“It’s a great sort of chemical warfare agent against crayfish. It kills in concentrations that are undetectable and that leaves no trace.”

He told WRC he has seen literature showing instances where crayfish had been given 100 times more than a lethal dose, and yet on testing, no trace had been found in their flesh.

One concern he has is Alpha-Scud is not just used on eucalyptus. Its label lists it as effective controlling insects on brassicas, maize, sweetcorn, tomatoes, onions, stone fruit and shelterbelts.

It’s one of many chemicals he worries about.

“In most cases we haven’t done any significant testing of those chemicals on local species or habitats. For a lot of them there is fairly limited data available.”

He said some products like 1080 are tested extensively, but others have not been tested to the same degree.

In Europe, Alpha-Scud’s active ingredient is expressly used to kill pest exotic crayfish to help native species re-establish.

New Zealand’s kōura species are not pests. Native fish expert Stella McQueen said there were two identified species. The northern species is not classed as threatened, but the larger southern species is listed as declining in numbers. 

She said finding kōura even in the North Island where they aren’t classed as threatened is “patchy”. Some streams will have none, while others will have large populations.

“Humans find crayfish very tasty, so does everything else.”

Pregnant kōura are described as “in berry” as the fertilised eggs, which change colour from caramel to red like tiny berries are carried under the tail. Photo: Stella McQueen

Grounds for reassessment

Waikato Regional Council’s investigation manager Patrick Lynch said the council had been in touch with the hazardous substance team at the Environmental Protection Authority (EPA) and asked them to review the classifications given to Alpha-Scud.

The EPA is currently reviewing several approved chemicals. Alpha-cypermethrin is on the priority list of chemicals to be reassessed according to the EPA’s website:

“It is categorised in Priority Group A due to its very high scoring for both human health risk and environmental risk. Availability to home users was also a contributing factor to the score.”

The reassessment process could result in no changes being made, additional rules being placed on the chemical’s use, such as requiring notification be given to local councils prior to use, or the chemical being banned.

The application for reassessment is expected to be complete late 2019, with any proposal made by the EPA then open to public and industry comment. If the reassessment concludes changes are required these will likely come into effect in 2020.

There is a spray-free way to kill the tortoise beetle.

A predator of the beetle is a wasp named after a Game of Thrones character. Eadya daenerys was approved for release as a biological control in New Zealand in February by the EPA.

The success of the release may depend on Scion being able to breed enough wasps by summer. Over 22,000 hectares are planted with eucalyptus and thousands of wasps will be needed to halt the beetles’ “voracious feeding” on eucalyptus leaves. 

Scion’s Dr Toni Withers who is busy raising the E. daenerys wasp army in a high-security wasp nursery said her wasp rearing is not all plain sailing. E. daenerys is proving to be more difficult to breed than other wasps.

“The best outcome would be able to instantly move from insecticide spraying straight into biological control. There could be a way of phasing it in over a year or two, it’s just going to be a bit of a balancing act.”

What next?

WRC contacted both the land owner and manager of the block of forest sprayed with Alpha-Scud. The council’s report says:

“The land owner made it clear here that they did not want any operation conducted on their property which may result in the death of kōura. Therefore, the forestry company were left to come up with a solution or not conduct the operation.”

The report notes the company was looking at options other than spraying, but these were long-term:

“This is a large issue for them.”

WRC is awaiting the results of the EPA’s reassessment of the chemical. Until then there’s nothing stopping the spray being used again and enforcement can only be taken if breaches are able to be proved through water, sediment or tissue samples. The council’s report notes confirming spray is drifting into water is almost impossible:

“Using our current sampling regime is commensurate with an extreme version of ‘needle in a haystack’ for collecting meaningful water samples.”

The local resident Erin Hampson-Tindale, who raised the issue in 2016 after seeing dead kōura float down Oraka stream for hours, feels some vindication the spraying is thought to be the “probable” cause of the carnage. He wonders how many times it’s happened before. When he raised the issue on Facebook he said he received abusive messages from people saying it was a natural event.

“People told me I was talking crap, that they had seen this sort of thing happen before.”

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