Stuart Grant ABC News 13 Aug 10;
Scientists say fish on Australia's east coast are moving further south in line with an increase in ocean water temperatures.
A report in Global Ecology and Biogeographyby researchers from the CSIRO claims south eastern Australia has become a climate change hotspot with well documented changes in the physical marine environment.
The report found 45 fish species representing 30% of inshore fish families in the region, exhibited major distribution shifts thought to be climate related.
"The work is based on fish distribution changes published in scientific accounts, surveys, spear fishing and angling competitions, commercial catches and underwater photographic records from the late 1800's to the present," says CSIRO research scientist Alistair Hobday who helped compile the study.
Dramatic increase
Hobday says the waters off the coast of south-eastern Australia have experienced a change in temperature.
"40 years of sea temperature observations along the east coast has shown a dramatic increase, four times the global average of about 0.6°C per hundred years," he says.
"The current along the east coast generally flows north to south, so warm water is flowing south anyway, and when you add warming on top of that, it's a kind of double effect.
Hobday says this has resulted in a number of fish species moving south.
"It means fish formally confined to Queensland are moving into New South Wales, New South Wales species are migrating to Victoria, and Victorian fish are heading into Tasmanian waters," he says.
While seasonal water temperature fluctuations along the east coast can range from 12°C to 22°C, Hobday says it's the breeding temperature that is having the biggest impact.
Causes
A report in 2006 found fish species were moving south, but it did not examine the cause.
This latest study points the finger at higher water temperatures and pollution.
"40 years of ocean readings have shown a consistent temperature increase, and growing CO2 levels in the atmosphere has increased the amount of CO2 being dissolved in the oceans lowering the pH level," says Hobday.
Pollution runoff into the coastal waters of Queensland and New South Wales are also playing a part, but according to Hobday, it's not an issue further south.
He says changes caused by new species moving in will need to be examined.
"For example, sea urchins crossing Bass Strait into Tasmanian waters have decimated some kelp beds which is bad news for some species, but have provided new habitat opportunities for others."
"New South Wales fish moving into Tasmanian waters will be seen as good news for anglers," says Hobday.
"The bad news is coastal fish currently confined to Tasmania have no where further south to go, so we are going to see a loss of some of those species."
