Source: Department of Conservation
Written by Sarah Wilcox.
The shock find came only days after the discovery of a cluster of shortjaw kōkopu eggs in the first ever documented ‘nest’ from Northland.
Freshwater ranger Fern Donovan found the eggs after hours of intensive searching along the banks of a tributary of the Waipoua River. She set up a trail cam on the nest site and checked it daily.
Left: Fern in her waders, with a waterfall the fish travel up to get to the spawning areas | Sarah Wilcox, DOC. Top right: Shortjaw kōkopu nest site | Fern Donovan, DOC. Bottom right: Translucent shortjaw kōkopu eggs on the leaves and rocks beside the stream | Fern Donovan, DOC.
“Each day there were less and less eggs – I assumed they were getting washed away by rain, but when I saw the video my heart sunk, I felt really, sad as I’d spent so much time studying the fish and got to really care about them.”
She describes the eggs as “protein pearls” that would be particularly attractive to the rodents in autumn, with high rat numbers and food supplies starting to dwindle with cooler temperatures.
The rat (or rats) was filmed returning multiple times over several nights to clean out the nest. Within 10 days the only eggs left were unviable or mouldy, and clearly no longer appetising.
A partnership with Te Iwi o Te Roroa
The rohe of Te Roroa is situated on the Kauri Coast and includes the Waipoua Forest, home of Tane Mahuta. Taoho Patuawa, science advisor for the iwi, has been closely involved with the shortjaw research project.
“With the discovery of the eggs has come the discovery of the problem. It’s a clear demonstration of the impact that pests are having on our taonga species. The work that’s been done to get to the discovery has been fantastic, but it highlights the real struggles facing the largely unheralded species.”
Taoho points out that even in a forest with good habitat, there are no guarantees of successful breeding.
“The species is clearly at-risk at this critical part of their lifecycle because of the ongoing pressures we have from pests.”
DOC and Te Roroa, along with other organisations, have been working together to restore the Waipoua River from mountains to sea for more than 5 years.
“We’re walking this journey together. There’s a lot to do, but it’s the good people who make the relationship successful. We’re working with nature for the betterment of our people and the landscapes we live and work in.”
Bait stations deployed for autumn 2024
Video footage of the rat predation provided evidence for Te Roroa and DOC to put intensive predator control in place ahead of this year’s spawning season.
“We were able to move swiftly to put in a line of bait stations 50 metres apart along the stream margins, as well as another line further back,” says Fern.
The bait stations are topped up regularly so they never run out.
“It’s a big forest so we’re assuming there will be constant re-invasion into the area. Especially at this time of year when rodent numbers are peaking.”
Tracking tunnels show that the strategy is working, with June 2024 results showing just 3% of the tunnels in the treatment area were visited by rats but 96% visited in the non-treatment area. At a control site (with no bait stations) in an adjacent area, shortjaw nests have been predated by rats.
2024 results looking promising
The 2024 breeding season at Fern’s study site got off to a great start.
“I’ve found three nests so far. The trail cam footage picked up rat predation at one nest but not all the eggs have been eaten – fingers crossed some of them make it. Hopefully they are finding the bait blocks more tasty!”
She is also pleased to report that some of the eggs developed tiny black eyes.
“I’ve never seen that before – last year the eggs were all eaten before that stage. I’ve also set up drift nets in the stream so I am hopeful that we might catch some larvae as they’re washed downstream on their way to the sea.”
Fern is waiting for the next big flood to wet the eggs and trigger hatching.
A story that remains incomplete
Taoho says the innovative and dedicated work at-place has led to some pretty immediate conservation strategies.
“What Fern’s found is a neat piece of the puzzle, but the story is incomplete. We don’t know yet what success looks like for this species or what numbers should be present in the catchment.”
“I’m looking forward to seeing what we achieve this year and beyond. It’s good to have such a concentrated effort in our forest. What we’re finding out here will be really valuable for protecting this taonga species both here and in other parts of Aotearoa, and ensuring it can thrive.”
Fern’s story
Fern grew up as a ‘bush baby’ in Hokianga and spent a summer during her undergrad study working for her family business, Donovan Ecological Management.
“We surveyed the reaches of the Waipoua River looking for different fish species as part of DOC’s restoration work. It was an incredible opportunity to visit some of the most beautiful and remote places in the catchment.”
“Shortjaw kōkopu were the fish we saw least frequently. I didn’t have to dig too deep to see there was a whole lot that’s not known about them. I spoke to the DOC scientists who helped me identify the most important knowledge gaps, and these formed the basis of my Master’s research project at Te Herenga Waka—Victoria University of Wellington.”
She intensively researched the population of shortjaw kōkopu in the Waipoua River and completed her thesis in early 2024. Fern was appointed to DOC as a freshwater ranger in September 2023.
The challenges of studying a rare, nocturnal fish
Shortjaw kōkopu are only found in Aotearoa New Zealand and are the rarest of six species of native fish caught as whitebait. Their conservation status is Threatened – Nationally Vulnerable. Until Fern’s discovery, spawning sites for this species had only ever been observed in Taranaki.
“The fish lay their eggs in moss or leaf litter just out of the water during a flood or high-water event. The eggs sit on the bank for at least 2–3 weeks to develop into larvae and are then carried downstream on the next big rain event. It’s the most bizarre life history with so much room for failure – the eggs could so easily dry out or be washed away before they’ve developed!”
Fern describes the searching as literally looking for a needle in a haystack.
“I go out when the water’s dropped and look above the waterline but below the wetted edge. I use a headtorch even in the daytime as the eggs are so tiny and hard to see – only 1-2 mm in diameter. To me they are like perfect pearls.”
Shortjaw kōkopu ‘nests’ are simply a collection of tiny translucent eggs | Fern Donovan, DOC.
“The searching is very intensive and quite soul-destroying. There are so many rocky crevices and patches of leaves to look at. You can only spend about 3–4 hours at a time doing it because it’s so intense. But when you do find the eggs, they’re really obvious – hundreds of eggs sitting there. It’s the most amazing feeling!”
Fern takes her cue to start looking for eggs by monitoring the adult fish in the stream. Because they’re nocturnal, the work starts 30 minutes after sunset and finish after midnight in the summer.
“We’ve been studying the fish here for a couple of years and we see the females getting heavier in autumn as their bellies become full of ripe eggs. If they suddenly lose weight and look skinny again, you know they’ve laid eggs, so that’s the time to go out looking.”
When nests are found, Fern takes 4–8 eggs from each site for DNA analysis to confirm their identity. She also records detailed information about the sites such as the location, slope, canopy cover and what material they were laid in.
“This is crucial information to inform our work to secure the species both in the Waipoua River and other catchments.”
More information:
This project is part of DOC’s Ngā Ika e Heke freshwater migratory fish workstream, securing populations of shortjaw kōkopu, īnanga, longfin eel/tuna and lamprey across Aotearoa New Zealand.
The Waipoua River is also in DOC’s Ngā Awa river restoration programme, which is working in partnership with others to restore the biodiversity of 14 rivers from mountains to sea.
