A University of Otago researcher has pulled small fish from hundreds of metres down in Lake Manapōuri and Lake Te Anau, far deeper than fish life had ever been recorded in a New Zealand lake. The bait was Marmite.
Dr Roe Stuart, a Future Leader Fellow in the university’s Department of Zoology, spoke to RNZ’s Checkpoint on Friday about the find, which may turn out to be a fish new to science. RNZ reported that the fish, which looks a little like whitebait, is being DNA tested.
“Prior to my work, the deepest we’d ever found fish in New Zealand lakes was 90 metres, so finding them at 460m was quite remarkable,” Dr Stuart told Checkpoint.
The university first described the work in a newsroom story published on 1 September. It said the idea came to Dr Stuart during postdoctoral work at Lake Champlain in the United States, when they realised nobody knew what lived at the bottom of New Zealand’s big lakes. The team lowered traps on 2 kilometres of rope, set at different depths and baited with the famous yeast spread. When they came back the next day and hauled the traps up, there were fish in all of them. RNZ reported the traps went down last month.
“When I designed this project, everyone was quite sceptical that I’d actually find anything down there,” Dr Stuart told Checkpoint.
The Marmite was not a stunt. Dr Stuart told RNZ it is a common way to bait fish traps. “It’s got lots of salts and minerals and things in it, and it dissolves quite well into the water. So presumably it creates quite a plume that’s a very attractive scent to the fish to lure them into your traps.”
As for the obvious question, Dr Stuart said in the university’s story, “I’ve had quite a few people ask if vegemite also works, but why risk it?”
A depth sounder put Lake Manapōuri at 467 metres deep and Lake Te Anau at 430 metres, according to the university. On those readings, only Manapōuri goes deep enough for a catch at 460 metres. The Manapōuri reading is also deeper than the 444 metres that Te Ara, the online Encyclopedia of New Zealand, gives for the lake, and deeper than the 462 metres it gives for Lake Hauroko, which it names as the country’s deepest lake. That comparison is our own. The university has not claimed a new depth record, and one sounding is not a full survey of a lake bed.
The traps brought up native bullies and galaxiids, small, shimmering climbing fish about 12 centimetres long that are sometimes caught as whitebait. The team thinks the galaxiids are close relatives of the kōaro, a slender native fish whose young make up part of the whitebait catch, but they do not look quite right for it.
“We suspect the galaxiids are kōaro or kōaro-adjacent,” Dr Stuart said in the university’s story. “They’re very different from our standard assumption of what a kōaro is, so they’re either an adaptation or a new species.”
The differences are easy to see. “Each fish is slightly different, but all of them have really huge, quite bulbous-looking eyes, really large holes in their snout that we think are used for sensing things in the system,” Dr Stuart told Checkpoint. RNZ also quoted Dr Stuart as saying a fish found in Wānaka was so transparent that “you can actually see its brain through the top of its head.” The university’s story names only Manapōuri and Te Anau. Light levels that far down are so low that the fish’s skin does not need pigment, Dr Stuart told RNZ.
If DNA tests confirm a new species, Dr Stuart would like a say in the name. RNZ reported their suggestion as “Galaxis googly eye”.
Kōaro are not strangers to Fiordland’s lakes. The freshwater fish atlas kept by NIWA, now part of Earth Sciences New Zealand, lists Manapōuri among the lakes with landlocked kōaro populations. The atlas says lake populations “were decimated by predation from introduced trout” and are now much smaller than before European settlement, when they were a food fishery for Māori. Whether the deep-water fish are a separate species, or kōaro that have adapted to life in the dark, is the question the genetic work has to answer.
For Dr Stuart, the find says something about the lakes as well as the fish. “The fact the lakes have oxygen all the way down is informative in itself,” they said in the university’s story.
“It brings in questions about the human impacts on the surface. We don’t necessarily think about those really deep basins, so how our impacts transfer is something we should consider for future management of these iconic, deep-water lakes,” Dr Stuart said in the university’s story.
Te Ara describes Fiordland’s big lakes as freshwater fiords formed by glaciers, the same ice that shaped the country in our look at New Zealand during the last ice age. Lake Manapōuri in particular has been fought over before. Its water drives the Manapōuri hydroelectric power station, the country’s largest, and plans to raise the lake for more power led to nationwide protests from 1969 to 1972, Te Ara records. For all that attention above the waterline, nobody had looked properly at the bottom.
There is more work to do before a scientific paper. “It would be fun to be like the classic old science pioneer and write a paper like ‘we looked at the lake and there were fish!’ – but I need a bit more information,” Dr Stuart said in the university’s story.
The next step is to see the deep lake floor for the first time. “I’m really excited to get some cameras down there and see if I can see some bigger fish,” Dr Stuart told Checkpoint.
They also made the case for why any of this matters. “It’s hard to protect and care about something if you don’t know it exists,” Dr Stuart said in the university’s story.
Did you know fish could live that far down in our lakes? And would you back “Galaxis googly eye” as a name? Tell us what you think in the comments below.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job 🙂
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