Sharks' Swimming Patterns Affected By Moon Cycles, Water Temperature

Water temperature and the moon cycle have an effect on the diving behavior of sharks, according to a new study.

Research has shown that sharks tend to stay submerged in deep water during a full moon but surface to the shallows with the new moon.

The findings come from a team at the University of Western Australia's Ocean's Institute and the government-run Australian Institute of Marine Science.

Researchers tagged 39 grey reef sharks off the coast of Palau, east of the Philippines, and used acoustic telemetry to track their movements for three years.

The sharks' lunar-linked movements are not unique: the movements have also been observed in yellowfin and big eye tuna, which reportedly suggests the behavior was linked to feeding.

The temperature of the water also had a role in when sharks dove. 

"We also found that the diving behaviour of grey reef sharks was related to water temperature," said lead researcher Gabriel Vianna, according to an AFP report.

The sharks were recorded diving an average of 35 meters (114 feet) in winter when deeper water was colder and as deep more than twice as deep when the water was warmer.

The movements may also be an anti-predatory, as increased light near the surface may aid the hunting abilities of larger fish.Time of day also affected the sharks' behavior.

"We were surprised to see sharks going progressively deeper during the morning and the exact inverse pattern in the afternoon, gradually rising towards the surface," researcher Gabriel Vianna said.

"This matches how light changes on the reef during the day. To our knowledge, this is the first time such patterns have been observed in detail for reef sharks."

The research was published in the science journal PLOS ONE.