Saturday, 20 April 2013

Sharks Dive Deep Under Full Moon

Megan Gannon, News Editor
Date: 15 April 2013 Time: 05:33 PM ET
A full moon and warm waters may send some sharks diving deep, according to a new study.
Over the course of nearly three years, researchers from Australia observed 39 mostly female grey reef sharks (Carcharhinus amblyrhynchos) living near coral reefs in Palau, Micronesia, east of the Philippines.
Gray reef sharks (Carcharhinus amlyrhynchos)
at Kure Atoll in the Papahanaumokuakea
 Marine National Monument, Hawaii. 
CREDIT: P. Ayotte 

In the winter, the sharks stayed closer to the surface, at an average depth of 115 feet (35 meters), where water was consistently warmer, the team found. Meanwhile, the sharks plunged deeper in when seasonal temperatures started rising in the spring, averaging depths of 200 feet (60 meters).

The sharks also changed their behavior in sync with the lunar cycle, diving deeper during the full moon but sticking to the shallows with the new moon. Previous tagging studies showed that other open-water predators — including swordfish, yellowfin and big eye tuna — also go to greater depths as the lunar cycle progresses. This suggests the moon's brightness might sway the movements of many big fish.

And the sun seemed to have an effect, too; the sharks hit their greatest depths at midday when the most sunlight broke through the water column and began floating back up to the surface in the afternoon. 

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