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Fish Dive Deep to Beat the Heat

Fish could beat rising ocean temperatures by retreating to deeper waters, according to a study of redthroat emperor fish at Heron Island. James Cook University scientists tracked the fish with transmitters that identified them individually and signalled their depth to an array of receivers around the island.

The experiment, published in Coral Reefs, monitored fish for up to a year and found that the fish were less likely to be found on the reef slope on warmer days.

The research team considered temperature, air pressure, rainfall, wind and moon phases as reasons for this shift, but the only significant correlation was with temperature.

Lead researcher Dr Leanne Currey said that most studies looked at how ocean warming would affect fish biology and not on how they would behave to overcome higher temperatures. “This is a commercially important fish and we are looking at a significant depth shift,” she said.

Redthroat emperors are caught by commercial and recreational anglers near coral reefs, and are the second most favoured fish for the reef line fishery behind coral trout.

“If it’s not around in the shallows in the future then fishers will have to redirect their efforts, and it may be significantly harder to catch them,” she said. The fish has been known to tolerate depths of up to 160 metres.

Currey said that instead of diving deeper, the species may instead shift south in search of cooler water at the same depth. Already some redthroat emperor have been caught off Perth, far from their normal habitat further up the Western Australian coast.

Currey said the next phase of the research is to investigate whether the fish could adapt physiologically to warmer sea temperatures, as it appeared other species could.