"Ramon Bonfil, of the Wildlife Conservation Society in New York, said that
for 61 per cent of the journey, the shark swam within 16ft of the surface,
indicating that it may have used visual cues to navigate. "I'm very
excited about the possibility that she was using celestial cues such as
the sun or the moon,' he said. "She travelled along a very straight track;
she knew where she was going. It just blew my mind. Why else would a shark
go to the surface in the middle of the ocean where there are no seals,
penguins or other food? There is no reason unless she was trying to look
at something."

"The real shark tale: Nicole makes record return trip from South Africa to
Australia":

http://news.independent.co.uk/world/environment/article317798.ece