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Blue devil fish discovery in deep waters raises questions around climate change

ABC News logo ABC News 4 days ago Nick McLaren
The rare and protected eastern blue devil fish is prompting many questions from researchers. © Provided by ABC News The rare and protected eastern blue devil fish is prompting many questions from researchers.

The discovery of a rare, protected fish in deep water off the New South Wales south coast is raising questions about what it is doing there and whether it has been pushed to greater depths by climate change.

Marine biologists came across the eastern blue devil fish in October 2013 between Jervis Bay and Bawley Point.

The vast area is the known habitat for the small, brightly-coloured fish, but in waters less than 30 metres deep.

The researchers, from various local organisations, were surveying what was meant to be a fairly benign section of sandy sea floor at a depth of 51m.

Their findings have just been published in the European Journal of Ecology and point to the need for more studies to determine how the fish came to be there and why.

Seeking refuge in the deep

University of Wollongong PhD candidate and a co-author of the report, Lachlan Fetterplace, said surprisingly the team was able to capture the fish on film, well outside its expected range of depth.

"We went through the entire hour-long video sample and there it was — the unmistakable electric blue colouring, white stripes, and shy emergence of an eastern blue devil fish from a crevice to investigate a baited camera," he said.

Mr Fetterplace said the discovery could be a sign that the fish is seeking refuge in the deeper, cooler waters as a consequence of climate change, but further evidence of the fish swimming in deeper depths still needs to be found.

"If the range of the eastern blue devil can be further corroborated down to at least 50m and potentially well beyond, this would significantly expand the known habitat of a rare and protected fish.

"Could deep reef habitats act as cooler water refugia, increasing the resilience of a rare and protected temperate reef species against climate change?"

Probing impact of climate change

One theory is that certain fish may be shifting both their swimming range and latitude to deeper water as sea waters increase in temperature.

The joint study also found samples of several other fish species, including the immaculate damsel, red morwong, mado, white-ear, silver sweep, and crimson-banded wrasse, in large numbers well outside their published depth ranges.

"The knowledge can help give conservation measures for these species the greatest chance of success, while also benefitting the management of offshore reefs," Mr Fetterplace said.

Scientists behind the study said without further sampling of deeper reefs on the continental shelf, the extent and range of the deeper populations of eastern blue devil fish will not be known, nor how they and other reef fisheries are being affected by climatic changes.

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