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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