Tasmanian fisheries hotting up, study confirms

A severe marine heat wave off Tasmania’s east coast lasted 251 days in 2015/16, impacting on area seven times the size of the island, a new study shows.

The study published in Nature Communications states that "human-induced climate change was almost certainly responsible for the marine heatwave off Tasmania’s east coast.

The area off the east coast of Tasmania is already known as a global warming hotspot, with temperatures in the region warming at nearly four times the global average rate.

In 2015 and 2016, around one-quarter of the ocean surface area experienced a marine heatwave that was either the longest or most intense recorded since global satellite-records began in 1982.

IMPACTS ON FISHERIES
On the downside, the marine heat wave reduced the productivity of Tasmanian salmon fisheries, led to a rise in Blacklip abalone mortality, and sparked an outbreak of Pacific Oyster Mortality Syndrome.

But it also saw new fish species move into Tasmanian waters, as anglers often reported to data gathering sources like Redmap.

The warm temperatures were also associated with out-of-range observations of several fish species, including yellowtail kingfish, snapper, dusky morwong, mahi mahi, blue moki and moonlighter fish, which may have been carried southward by the anomalously strong East Australian Current Extension.

Although these species have been occasionally found in Tasmanian waters, the number of species and sightings were higher than in recent years.

Recreational fishers were particularly excited by the presence of kingfish and mahi mahi, indicating that some impacts are viewed as positive outcomes, the study said

IN HOT WATER
At its peak intensity, waters off Tasmania were 2.9°C above expected summertime temperatures.

Lead author from the ARC Centre of Excellence for Climate System Science (ARCCSS), Dr Eric Oliver, said marine heat wave events of this kind were likely to increase in the future because of climate change.

"We can say with 99 per cent confidence that anthropogenic climate change made this marine heat wave several times more likely, and there’s an increasing probability of such extreme events in the future," Dr Oliver said.

"This 2015/16 event was the longest and most intense marine heatwave on record off Tasmania."

GLOBAL TRENDS
The research team led by scientists from ARCCSS and the Institute for Marine and Antarctic Studies (IMAS) at the University of Tasmania, in collaboration with the CSIRO and the Australian Institute of Marine Science, found the heatwave was driven by a surge of warm water in the East Australian Current, which has been growing stronger and reaching further south in recent decades.

Co-author Associate Professor Neil Holbrook from IMAS said it was vital to monitor and research these marine heat waves because if identified early it would allow fisheries and aquaculture industries to adapt and manage their resources.

"The evidence shows that the frequency of extreme warming events in the ocean is increasing globally," Associate Professor Holbrook said.

Associate Professor Holbrook said Studying these events plays an important role in helping industries, governments and communities to plan for and adapt to the changes and their growing impacts on our environment and ecosystems.

The ARC Centre of Excellence for Climate System Science is based at UNSW. Dr Sarah Perkins Kirkpatrick, from UNSW's Climate Change Research Centre, was also an author on the paper.

More on the open access study and paper at The unprecedented 2015/16 Tasman Sea marine heatwave.