Murdoch University scientists say climate change could result in recreational fishers being able to catch tropical marine species in South-West Australian estuaries, but at a price.

In a paper for the journal Regional Environmental Change, lead author Dr Christopher Hallett said tropical crab species including mud and coral crabs had already been documented in the temperate Swan-Canning Estuary.

“Warming marine waters will enable some species to move more easily between estuaries and thrive,” said Dr Hallett.

“Elevated water temperatures will also extend the growing periods of popular fishing species like the Western School Prawn and the Blue Swimmer Crab.”

However climate change could also bring less welcome changes to our popular estuaries, including the Peel-Harvey, the Swan-Canning and the Leschenault.

“Our estuaries are particularly vulnerable to long term warming and drying trends because they tend to be shallow, have weak tidal influence and variable seasonal river flows, and, in many cases, are periodically closed by sand bars,” said Dr Hallett.

“Shallow waters tend to be warmer, and these heated estuarine waters will impact species which cannot tolerate high temperatures.

“In the Swan-Canning Estuary for example, seagrass mortalities have been reported due to warmer temperatures.

“Warmer waters also mean higher salinities, less oxygen and potentially dangerous algal blooms.

“Most freshwater fish species are unable to tolerate rising salinities and mass mortalities may result if salinities become extreme. In 2001, hypersaline conditions (saltier than seawater) caused the death of an estimated 1.3 million Black Bream in the Culham Inlet near Hopetoun.”

Dr Hallett said estuaries that become closed from the ocean by sand bars at their mouths will more frequently develop high salinities and water temperatures. They may also accumulate more nutrients and silt due to climate change, which is bad news for the species they support.

“These estuaries will remain closed for longer periods, stopping marine species from entering, and reducing species diversity,” he said.

However, Dr Hallett also said that estuarine species in the South-West of Western Australia had already adapted to cope with variable conditions and so may be hardy enough to survive significant changes to their environment.

“Our understanding of the biology of many estuarine species, including their environmental tolerances, is relatively poor, particularly those species that are not important commercially,” he said.

“We have to hope that they can adapt quickly enough to the impacts of climate change.”

Dr Hallett said there is much that can be done by humans to nurse estuaries through the changes they are experiencing, including reducing our domestic water use and the use of fertilisers.

Artificially increasing water flows into estuaries, oxygenating vulnerable areas and covering parts prone to evaporation are other options that could be explored, he said.

Dr Hallett’s research paper can be read here.