The predicted arrival of El Niño conditions will impact weather across Australia and is forecast to bring warming conditions and lower rainfall on land, but what can we expect in oceanic waters off Western Australia’s coast and for the fisheries they support.
Department of Primary Industries and Regional Development (DPIRD) senior research scientist Arani Chandrapavan told an international Climate Change Symposium in Norway this year, the west coast of Australia has experienced a roller coaster of sea surface temperature variability, driven by the cycles of ENSO (El Niño Southern Oscillation Index) generating extreme climatic events, over the past decade.
Under an El Niño climate, WA usually experiences average to cooler than average sea surface temperatures from the mid-west to south coast, while the north-west shelf region can experience warmer than average sea surface temperatures, as this region also responds to what’s called the Indian Ocean Dipole (IOD) climate driver.
Unlike the extreme marine heatwave event associated with the La Niña in 2010-11, the recent extended La Niña period has been milder with water temperatures only raised by an average of 0.5 - 1 degree Centigrade around WA.
Management of wild fisheries is, however, challenging when confronting either marine heatwaves or marine cold spells as species respond differently to these conditions.
DPIRD fisheries researchers have reported warming ocean trends of the past three years have favoured recruitment of the 80 Mile Beach pearl stocks. Whereas for Abrolhos Island scallops, there was no fishing in 2022 due to very low recruitment in 2021, but the fishery reopened this year with commercial fishers reporting catches of much larger sized scallops.
The three back-to-back La Niña’s generated a long-lasting, strong Leeuwin Current, which can influence larval dispersal and distribution of fish species further down the west coast and eastward along the south coast, including the distribution of Australian salmon and herring juveniles along the south coast.
Historically, western rock lobster recruitment has increased during stronger Leeuwin Current years, however, in the past three years it did not increase to the same extent as seen in previous La Niña events.
On WA’s south coast, the La Niña conditions had a positive influence on blue swimmer crab catches and productive scallop fishing resumed along the south coast in 2021 and 2022, after prior years of below-average stock levels. The 2023 season is looking promising and should also deliver good scallop landings.
Dr Chandrapavan said the predictions of a moderate to strong El Niño for the summer of 2023-24 would provide a shift from the warmer ocean conditions experienced by the mid-west, south-west, and south-coasts of WA.
“For the north coast, however, the forecast is more uncertain as it is also influenced by the behaviour of other climate drivers like the Indian Ocean Dipole and the Madden-Julian Oscillation,” Dr Chandrapavan said.
“During the 2015-16 El Niño, a significant marine heatwave event occurred across tropical Australia, which led to coral bleaching events along our northern coastline.
“National forecasters have predicted there’s a medium likelihood that marine heatwave conditions could arrive on the Pilbara and Kimberley coasts by spring, with the potential to expand and become warmer by summer.”