brisbane, australia
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Along a 9-mile stretch of river between two waterfalls in the Australian rainforest is a tiny fish that has been around for millions of years, hiding among riverbank rocks during the day and emerging at night to feed.
This is the only place in the world where you can find the only tropical cod on the planet. This cod is a relic of the past, thought to have split from its nearest southern cod about 25 to 30 million years ago.
Meanwhile, the tiny cod swam undetected and unexplained by modern science until 1993, when two researchers, Mark Kennard and Brad Pusey, encountered the fish in the Bloomfield River along the northern edge of the Daintree Rainforest, recognized by UNESCO as the world’s oldest rainforest and full of rich and unique biodiversity.
“This is a beautiful little fish,” said Kennard, now deputy director of the Australian River Research Institute at Griffith University. More than 30 years later, he is still collaborating with Pusey, a senior research fellow at the university.
At the time, Kennard and Pusey named the fish the Bloomfield River Cod and gave it its scientific name, Guyu Ujaluujalensis, after the Aboriginal fish name and the traditional owners of the land, the Ujal-Ujal community. Also called tropical night fish.
But this ancient species, which grows to just 10 centimeters, is now under threat from exotic predators and severe storms caused by human-induced global warming.
Cyclone Jasper, one of Australia’s most destructive tropical cyclones, destroyed cod habitat between Broomfield’s two waterfalls two years ago, felling trees, flooding rivers and flushing more exotic predators into the reserve.
In October, Kennard and Pusey returned to the river to survey the damage and count the cod in the hopes of officially listing them as endangered under Australia’s Biodiversity Act and increasing their protection.
“If we lose this, we’re going to lose a representative of a really complex and long evolutionary period,” Pusey said. “It would be a tragedy… definitely a personal tragedy.”
Mark Kennard chasing Bloomfield River Cod
Mark Kennard chasing Bloomfield River Cod
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It takes at least four hours to reach the Bloomfield River from Cairns by inland road, and tourists visit the Great Barrier Reef by boat.
Longer, wilder and more scenic, this route winds along the coast on dirt roads through ‘croco country’, where Australia’s giant saltwater crocodiles dominate the salty waterways and smaller freshwater crocodiles occupy the rivers and streams.
At this time of year, the summer heat and humidity are even higher, sudden downpours cause steam to rise from the roads, and the air smells of sweat mixed with sunscreen and insect repellent.
Kennard and Pusey were on a research trip to the Wet Tropics of Queensland when they discovered the fish in the 1990s.
At first they had no idea what it was. But when they returned several years later, they found enough information to confirm that it was a new species.
“When we find new species here, they’re almost always very small differences, and most of the time they’re not discovered until people do the genetics and find out, ‘Oh, this is a new species.’ But this is obviously something new and it’s very exciting to find it,” Pusey said.
The area of the river that is home to the Bloomfield cod is inaccessible to most visitors, but it is not far enough to guarantee the cod’s safety.
Their biggest predation threat is the Tully Granter, a large endemic Australian fish up to 35 centimeters long, which scientists believe was introduced into the river by recreational fishermen looking for a decent catch.
These grunts are currently competing with Bloomfield cod for food and may eat their eggs and young.
“Cod populations have exploded over the past five to 10 years, and that’s why we’re so concerned. Cod is prevalent in most of the upper reaches where cod populations exist,” Kennard said.
In parts of the river where there were no tally granters, cod could be seen swimming fearlessly from the riverbank. But when researchers snorkeled in the grunt habitat, they found the cod hiding behind rocks.
In addition to the grunting animals, researchers also found eel-tailed catfish, which live in rivers further south, and guppies, which are native to Central America, suggesting that the pets were released and then began breeding.
But what they were most interested in assessing from their recent trip was the impact of Cyclone Jasper.
“You can still see the scars on the landscape,” Kennard said. “They say it’s one of the most violent weather events in Australia’s history.”
Cyclone Jasper had weakened by the time it made landfall in December 2023, stalling over the Cape York Peninsula for several days and dumping rain on already saturated land.
Approximately 975mm of rain fell in one day in some places, making it the highest reliably measured 24-hour rainfall total in Australia.
So much rain has fallen that the Bloomfield River has turned into a raging torrent.
“What typically happens in forested rivers like this is that trees fall into the river and provide habitat for fish and other animals that live in the river,” Kennard said.
“But a lot of it is being removed and washed downstream.”
Scientists feared that some small fish might also be swept downstream, into the path of other predatory fish such as barramundi and mangrove jacks, or into salty estuaries where they might not survive.
Much has changed in the 30 years since Kennard and Pusey first discovered this fish.
At the time, they were traveling in pairs and didn’t even have a cell phone to notify them of their whereabouts. “You might be lucky not to get lost, dead, or stuck in the mud,” Kennard said.
Drones now map rivers and vegetation from above, and environmental DNA samples indicate the presence of life in the water without having to capture it.
With funding from the National Environmental Science Programme, the team was joined by scientists from James Cook University and natural resource management organization Terrain NRM, who know this rugged terrain better than anyone.
Brad Pusey of Bloomfield River Tara
Brad Pusey of Bloomfield River Tara
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Most importantly, scientists are working closely with the Jabalbina Yalanji Indigenous rangers who manage the land to learn more about Tara.
Bobby Kulka, a traditional owner of eastern Kuku Yalanji, said there was no mention of the mysterious fish in the stories passed down by his ancestors.
“It’s good to know they’re here. I didn’t know they were here before. I’d never heard about them,” he said.
Local Aboriginal people are being trained to help monitor the fish so their research can help fill in the blanks about Bloomfield cod after the scientists leave.
Little is known about how this fish reproduces, and no one has successfully bred it in captivity.
One option to save the species may be to start a captive breeding program in case it becomes extinct in the wild.
Another possible solution is to try to establish other populations in nearby catchments where introduced species do not pose a threat.
However, given the dense forest surrounding the river and the prevalence of invasive species, finding protected watersheds can be difficult.
Introducing populations elsewhere also carries risks. Will the balance of nature be disrupted? Or will it have unintended consequences for other species that live there?
Kennard said clearing the river of invasive species is not an option.
“You might be able to eliminate isolated populations, but when you’re on a big river like this and everything is connected, that’s not possible,” Kennard said.
The Bloomfield cod was listed as “endangered” on the International Union for Conservation of Nature’s Red List of Threatened Species, but that was before Cyclone Jasper and before researchers discovered the invasive fish in the watershed.
The focus now is on gathering enough data to designate this fish for legal protection.
It would create a new opportunity to save one of Australia’s rarest fish, which Mr Kennard warned could become extinct within 10 to 20 years.
“I think it’s on the verge of extinction,” he says. “That doesn’t happen on my watch.”
