Climate change and migration of barramundi from North Queensland could be responsible for a population of barramundi living in the Brisbane River.
Secretary of Suntag Australia and Infofish Australia coordinator Bill Sawynok said fish tagging data showed 35 barramundi were tagged in the Brisbane River in 2021.
Mr Sawynok said, since 2013, just three had been caught in the city's major waterway.
He said the appearance of barramundi in the Brisbane River could be because of climate change, fish released during flooding from farm dams and private dams, and, in some rare cases, pet barramundi from fish tanks.
Climate change impacting barramundi
Associate professor from the University of Queensland's School of Biological Sciences Ian Tibbetts agreed that barramundi and other marine and land animals were migrating due to climate change.
"In other places in the world, they're also seeing other shifts in animals such as snails, clams, and fish moving towards the poles, which is called a poleward shift, and it's primarily because of increasing water temperatures," Dr Tibbetts said.
"These shifts towards the poles are worrying," he said.
Dr Tibbetts said the increasing populations of barramundi in South-East Queensland would not impact the populations further north.
"Some of the tropical species are moving into places they hadn't ever been before," he said.
"When a group of organisms or a species moves outside of what was regarded as its range, it's a signal and it's up to us to respond and maybe consider the effects of climate change more seriously."
Better temperatures down south
Animal ecologist Jasmin Annett said barramundi were stenothermal animals, which means they could only survive in areas within a narrow temperature range.
"The increase in ocean temperatures coupled with severe weather systems could potentially negatively affect the barramundi population in North Queensland," she said.
Despite this, Ms Annett said barramundi were quite adaptable.
She said barramundi were "catadromous euryhaline fish", meaning they could live in fresh, marine or brackish water, and that includes the Brisbane River.
"I have heard anglers talk about capturing barramundi in the Brisbane River that have North Queensland tags on them, which is very far to migrate from and isn't commonly seen," Ms Annett said.
"Alternatively, recreational fishing parks, although they do restrict interactions with their stock and local natural systems, aren't always perfect and can provide an avenue for fish to escape during floods, or even people stealing and releasing those fish for their own benefit."
Impact of temperature on breeding
Dr Tibbetts said male and some female barramundi migrated from freshwater to breed at the mouth of estuaries.
A spokesperson from Bli Bli Barra Fishing Park said the right water temperature was crucial for barramundi to breed.
"The barramundi at our park on the Sunshine Coast don't breed, and we put it down to the temperature of the water being too cool," they said.
"The lack of breeding success is not due to lack of effort as the fish can be seen to be attempting to breed when conditions are favourable."
