'Disappearing' Fish Dive Deep to Escape Climate Change

It's no secret that fishing industries across the globe have been having a hard time. As demand for fish continues to spike, many nets are coming up empty. Now new research has shown that fish populations might not be declining, but simply moving to deeper depths.

That's at least according to a study recently published in the journal Coral Reefs, which details how researchers went about tracking the movement of 60 redthroat emperor fish (Lethrinus miniatus) at Heron Island in the southern Great Barrier Reef.

After being tagged with transmitters that signaled each individual's depth on any given day, the fish were monitored for up to 12 months, revealing swimming habits that did not coincide with contemporary fishing knowledge.

Traditionally, fishing boats lay out nets where their quarry is known to frequent - a consistent depth that generations of redthroat emperor fish have been captured at. In this way, commercial fishing has become a practice of careful timing and routine - relying on a deep understanding of the local fish habits to fill bellies and wallets. (Scroll to read on...)

Unfortunately, according to lead researcher Leanne Currey of James Cook University, that time-tested understanding may be rendered useless by climate change.

An analyses of the tagging results revealed that, contrary to local fishing knowledge, the Great Barrier's redthroat emperor fish were frequenting deeper depths than ever seen. After considering air pressure rainfall, wind, and even moon phases as reasons for the shift, Currey and her colleagues have concluded that water temperature shifts - a consequence of climate change - is the only reasonable explanation. The fish appeared to avoid depths any warmer than 24 degrees Celsius (75°F).

"This is a commercially important fish and we are looking at a significant depth shift," Currey warned, adding that it could lead to many empty nets. "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."

Still, diving deeper isn't the only option these redthroats have. To avoid warming water, the species could also shift south in search of cooler water at their traditional depth. This would allow fishermen to more easily track them, even it still means that the industry must adapt.

There is also the chance the fish may simply adapt physiologically to the warm waters on-hand, as past studies have shown that many fish species are genetically prepared to adapt to warming seas.

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