TROPICAL fish are venturing as far south as Tasmania in response to ocean warming.
Recent tropical sightings include turtles, a yellow-bellied sea snake, a green moray eel, tiger shark and a mahi-mahi dolphinfish.
The unusual sightings have been documented on the website Redmap, based on reports from divers, anglers and scientists.
Warmer waters are also attracting increasing numbers of big gamefish, such as marlin and yellowtail kingfish, which anglers say is a boon for the sport in Tasmania.
The "out-of-range" fish are being documented by Redmap so scientists can use sightings by recreational anglers and divers to help research into marine species' changing geographical range.
Redmap, the Range Extension Database and Mapping project, will extend from its current state focus when it goes national this week.
Redmap principal investigator Dr Gretta Pecl, from the Institute for Marine and Antarctic Studies, said all Australians would be able to report their unusual findings to Redmap after the national launch on Thursday.
Dr Pecl said the migrating tropical fish had been detected in increasing numbers over the past few years, and other popular fishing species from NSW and Victoria were becoming frequent visitors too.
"Some species that only appeared on the mainland, or only appeared in the north of Tasmania, are venturing further south," she said.
She said there were also growing numbers of eastern rock lobsters, including a population of about 35 living off the East Coast.
And snapper, not often sighted in the South until recently, is now so common it has a bag limit.
Dr Pecl said the migration of northern marine species could be for a range of reasons. While climate change was a major driver, other potential causes included changes in ocean currents, habitat availability, pollution and changes in mainland fishing activity.
The migration of new species has been welcomed by recreational anglers, who say the new species have created a boom.
Tasmanian Association for Recreational Fishing (TARFish) chief executive Mark Nikolai said anglers had noticed a rise in the number of popular sportsfish, including yellowtail kingfish, King George whiting, marlin and snapper.
He said these four species were extremely popular and would potentially increase fishing tourism to the state.
"It's all good news for Tasmania, as they expect more of these species to call Tasmania home," Mr Nikolai said.
He said the migrating sportsfish species were of little threat to local marine life, because the baitfish they ate moved down with them.
But Dr Pecl warned the warming oceans did attract some damaging species, such as long-spined sea urchins which were destroying habitats essential for rock lobsters and abalone.
Mr Nikolai said warmer waters had been detected by the CSIRO this year, as a result of the extension of the East Australian Current.
Data shows sea temperatures off the East Coast are warming at three times global average.
Redmap invites people to take photos of uncommon marine species and post them on www.redmap.org.au
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