By Karthic SS for Our Changing World
Checking traps for the lowland longjaw galaxias. Photo: Karthic SS
Tiny, rare and under the radar.
Just a few streams in Twizel, in the upper Waitaki catchment, are home to one of New Zealand's rarest fish: the lowland longjaw galaxias.
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"If you look closely, you can see the lower jaw is longer than the upper jaw - sort of like a bulldog... We affectionately call them 'Jaws'," says Department of Conservation senior ranger for biodiversity Dean Nelson.
Unlike their namesake, these 'Jaws' are tiny, growing up to just eight centimetres. Dean has been working to protect these small, brown-speckled fish for more than two decades in Twizel.
"They get under your skin a bit, you really get wound up about them. They've become my big passion these days," he says.
Dean Nelson checking traps. Photo: Karthic SS
There are two genetically distinct lowland longjaw populations: one in the Upper Waitaki catchment and the other in the Kauru Kakanui river in Otago. "They are treated as different species, but both are called lowland longjaws," says Dean.
Longjaws vs whitebait
Lowland longjaws are related to whitebait. Both are part of a family called Galaxiidae. This family of fishes is named for the gold flecks on their backs that resemble a starry galaxy pattern.
But there's one big difference. The whitebait species are migratory: adults migrate to the coast to spawn, and their young swim back upstream, where they are caught as whitebait.
Lowland longjaw galaxias. Photo: Dean Nelson
In contrast, lowland longjaw galaxias are homebodies. They are non-migratory, spending all their lives in the same gravely stream they hatch in.
New Zealand is home to 12 species of non-migratory galaxiids, plus 13 groups that are yet to be formally described and confirmed as a species.
All of them have been classified to be 'at risk' or 'threatened', as most of the populations are fragmented and prone to local extinctions.
Lowland longjaw galaxias (the smaller fish, on the left). Photo: Karthic SS
The Waitaki lowland longjaws are 'nationally endangered', which means they are at risk of extinction in the short term. Just seven known populations remain.
They face various threats such as invasive plants, land use changes, and introduced trout.
Trout trouble
Brown and rainbow trout from the northern hemisphere were released into the rivers of Aotearoa in the mid-to-late 19th century for sports fishing. They are one of the main threats to the lowland longjaw galaxias.
A brown trout eating a bignose galaxias. Photo: Dean Nelson
Trout can move through river systems, and when they get into streams and tributaries, they feed on native fish like the longjaw and other non-migratory galaxiids, causing a dramatic decline in their numbers.
At a field site near Twizel, Dean has witnessed this decline himself.
"We knew trout were here in Fraser Stream and hadn't done anything about it, and in 2009 we suddenly found that we were only getting a handful of fish.
"I think we caught 12 lowland longjaw and 25 bignose galaxiids in the stream. And we went, 'Uh oh, that's no good!' So we put a barrier in. That was our first barrier, and we've since modified it and changed it."
Fraser Stream landscape barrier. Photo: Karthic SS
Keeping out the trout
Martha Jolly, a PhD Candidate at the University of Canterbury, is studying how these artificial barriers and other interventions can help turn things around for the lowland longjaw.
"It's quite similar to fenced reserves in terrestrial conservation, where you might put a fence around a precious species and do predator removal to protect that species."
The barriers are designed to keep trout out of the habitat by creating a drop they can't jump. There are now 12 built barriers in the upper Waitaki catchment.
The barrier at the Waterwheel Wetland. Photo: Martha Jolly
"Some of our galaxias species just really cannot co-occur with trout. They tend to get predated on, and end up going extinct pretty quickly.
"Nobody is saying that we want to get rid of trout from our waterways at all. And what we're finding with the non-migratory galaxiid habitat is that actually it's tiny fragments, which isn't ideal for trout fishery, anyway.
"There's plenty of room for everybody. There are just some habitats where these introduced sports fish are really not helpful, and have a negative impact on our native fish."
Flood over the trout barrier at Fraser Stream, August 2022. Photo: Dean Nelson
Frequent monitoring of streams is crucial. Extreme weather events can result in floods that flow over the top of barrier, meaning trout get back into longjaw habitat.
Both Martha and Dean believe that the barriers alone might not be enough, and in the future, they might have to consider other conservation efforts. In the meantime, Dean says, they are using environmental DNA to help them search for more tiny 'Jaws'.
"I still hold hope that one day we'll find another population that we didn't know about that's surviving somewhere."
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