Sharks dive for cover from full moon

Last updated 10:25 17/04/2013

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While it might bring out the werewolves, it appears the full moon sends sharks diving for cover, according to a new study.

Researchers from the University of Western Australia tagged 39 grey reef sharks near the Philippines, and studied them for two years and nine months.

They examined how deep sharks would dive, where they went to breed and where they lived.

When it came to the creature's connection with lunar phases, diving depths would change by up to 20 metres.

"Depths of sharks at night increased from 40m during the new moon, to 60m on the full moon," the study said.

"We suggest that daily, lunar and seasonal cycles in vertical movement and residency, are strategies for optimising both energetic budgets and foraging behaviour."

Water temperature also changed how far they descended.

In winter, when the deeper waters were colder, the sharks stayed closer to the surface where the water was warmer.

In summer, when the water was warmer, they tended to swim deeper.

The study also showed that from year to year, especially during summer, most sharks headed back to the same spots.

"Seventeen of the 26 sharks (65 per cent) tagged in 2008 and 2009 displayed inter-annual residency," said the study.

"On average, individuals were detected for around 14 hours per day, suggesting that although individuals could have exited the array several times they remained in the vicinity of receivers for extended periods during the day."

The authors concluded the use of deeper waters during the full moon could be because their prey moved there.

Similar patterns were recorded in swordfish, yellowfin tuna, and big eye tuna.

The researchers said their observations needed to be integrated into the wider understanding of how reef sharks behaved.

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- © Fairfax NZ News

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