First published 18 March 2020, for the autumn edition of Forest & Bird magazine.
Erin Maessen gets up close and personal with our largest freshwater residents and discovers some of the threats tuna face in the wild.
In oversized waders, I stumble down steps cut into the bank, using a length of rope to make my descent into the stream slightly more dignified. Sloshing towards the middle, I turn back to take a bucket and a long-handled metal spoon. Down at my feet are the huge velvety black bodies of longfin eels, come for their midday meal.
Pūkaha Mount Bruce, in the Wairarapa, has been a sanctuary for native wildlife since 2001. It is well known for Manukura, the pure white kiwi born there in 2011, and for the large flock of kākā that fly in for feeding every afternoon at the “kākā circus”.
Less well known is a group of equally precious creatures generally hidden away under the banks of this tiny stream. They emerge each day when a pair of excited visitors descend into the water to feed them from the end of a spoon.
Having recently been one of those lucky feeders, I can set to rights the idea that longfin eels are slimy to touch, like the rest of the fish species they are classed with. When I reached my hand down to run it along the back of one especially large individual, it was soft, silky, and generally more mammalian in feeling than any fish I’d encountered before.
There are about 40–50 eels living here. From their large size, some individuals are estimated to be 50 or 60 years old, but no one is entirely sure. The eels swim around my ankles. They rely on a combination of touch and smell to find food, as their eyesight isn’t as strong as their other senses. They bump into one another, into my boots, and into the end of the spoon holding the tasty treat.
Eels typically eat live food, like insect larvae, worms, and snails when they are young and fish, crayfish, and even small birds as they grow bigger. At Pūkaha Mt
Bruce, they get a minced mixture of liver, kidney, and vegetables left over from what the kiwi are fed the night before.
Eels are secretive in nature, generally preferring to remain hidden in the dark areas under rocks and logs or close to overhanging riverbanks. These ones, used to being handfed, were not shy at all, and as I lowered the spoon with a generous helping of the meat concoction towards the head of each one in turn, they rose out of the water to reach it.
I was not a stranger to the longfin eel before this day. But standing there in the water I was reminded of how unique and beautiful these creatures are.
A few individuals, identifiable by distinctive characteristics, such as a missing fin, have been known to disappear over time. Presumably they have headed off to make the long, dangerous journey to the deep ocean trenches of Tonga, and give rise to a new, much needed generation.
Given the potential for added stress that climate change poses by altering ocean temperatures and current patterns, I only hope they and their descendants survive the trip and make it back to cleaner, safer waterways here in Aotearoa.
HUMAN IMPACTS
The longfin eel, Anguilla dieffenbachii, is one of two native eel species present in New Zealand’s freshwaters. Unlike the far more common native shortfin eel, which is also present in Australia and parts of the Pacific, longfins are not found in rivers anywhere else in the world except here in Aotearoa.
But our longfin eels are vulnerable to human activities. According to the Department of Conservation’s latest threat classification list, they are classed as “at risk and declining”, with the qualifier that this status is “conservation dependent”. This means that, if current management were to cease, the species would be in a far worse situation.
In a story that should hardly be surprising by now, human actions have been the root cause of the longfin’s decline.
Threats to longfin eels are many and varied, as Forest & Bird freshwater advocate Annabeth Cohen explains: “Eel populations depend on a clean and safe path with connected rivers, lakes, wetlands, and streams. Despite being excellent climbers, our longfins are hitting sometimes dangerous blockades in rivers all over the country – from large hydro dams to overhanging pipes under roads to flood pumps draining land.”
Water-based pollutants also tend to accumulate along the course of a river, meaning downstream zones closer to the sea are more polluted and therefore a less suitable habitat for eels than the cleaner waters upstream.
While longfins are clearly in need of greater conservation assistance, New Zealand’s endemic freshwater fish in general haven’t traditionally received the same protection as our charismatic and endangered native birds.
However, recent amendments to the Conservation Act and the Freshwater Fisheries Regulations will soon provide more protection – it will be prohibited to kill a native freshwater fish except for human food consumption.
In addition, DOC’s freshwater fish management plans can take effect nationwide, which will be of particular benefit to eels because of their wide-ranging habitat. “The proposed freshwater regulation changes, due to take effect before the end of this year, would see water quality measures prioritised for fish health and the introduction of fish passage requirements at the regional level,” adds Annabeth.
“While we are backing all these changes as long overdue, they are only a start to what is required for native freshwater fish.”
COMMERCIAL HARVESTING
Overfishing without controls devastated eel numbers, said Don Jellyman, of NIWA, in his report to the Parliamentary Commissioner for the Environment in 2012.
Despite this and their “at risk” conservation status, longfin eels continue to be commercially harvested – with no distinction made between this species and the shortfin eel.
While North Island allowable catch limits were reduced in 2018, many believe it is still too high given the longfin eel’s conservation status.
Commercial fisheries in New Zealand have a requirement to release any eels that are less than 220g and more than 4kg, aiming to protect the younger eels and large migrating females.
However, because eels only breed once in their lifetime, when they are fully mature, any eel caught will be one that never gets to breed.
Restoring longfin populations will be a challenge within the current system and New Zealanders’ relationship with eel fishing. However, as Annabeth says, “We owe it to this taonga species to keep existing waterways healthy and free flowing while we restore what has been damaged and destroyed over the last century.”
FROM AOTEAROA TO TONGA AND BACK
Eels have a unique life cycle. They are catadromous, meaning they begin and end their lives in the ocean, despite spending most of their lifetime in freshwater. After reaching sexual maturity, which occurs between 15 to 45 years for males, or 30 to 100 years for females, adult longfin eels make their way out to sea and complete an epic migration to a currently unknown region – probably in deep sea trenches near Tonga.
There, far away from Aotearoa, they spawn and then die. The young eels hatch and swim back to New Zealand on the south Equatorial current, a journey of about 18 months. By the time they arrive, the young have developed into “glass eels”, a transparent and far smaller version of their adult selves.
These travel upriver, managing vertical climbs up waterfalls and even traveling over land at times, making their way much farther upstream than any other eel species. Eventually, they settle in suitable deep pools where they feed and grow for many years until they reach maturity.
Tuna are incredibly significant to Māori. Stories of longfin eel are interwoven into whakapapa (ancestry) and creation stories, and carvings alongside tūpuna (ancestors) are found in marae around the country, further denoting their deep-rooted significance.
Erin Maessen is a freelance science writer, based in New Plymouth, Taranaki. The former Kiwi Conservation Club member studied New Zealanders’ attitudes to eels for her Science in Society Masters at Victoria University.
Erin Marieke Maessen 
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