London, June 19 : Researchers have discovered although whale sharks, which are the world's biggest fish, seem sluggish on the surface, deep down they are deceptively fast.
According to a report in Nature News, despite its status as the largest known fish, and despite being listed as vulnerable by the International Union for Conservation of Nature, very little is known about the whale shark's behaviour.
Now, a research team studying male whale sharks at Ningaloo Reef Marine Park, off the coast of Western Australia, noticed they used their weight and gravity to nose-dive to the ocean floor like airborne hawks hunting for mice.
The surprising dive patterns were recorded using a new tracking device that has enabled researchers to track the movements of eight immature whale sharks (Rhincodon typus ) in detail for the first time.
"We found they are basically not using any energy to move - they are diving down in a glide like an eagle or a falcon. Because they are using no tail beats they are literally sinking," said Brad Norman, one of the research team, from Murdoch University in Perth.
The actual speed at which they descend remains a mystery. Norman's team is still deciphering the thousands of data points collected during their latest trip.
But, the team believes the discovery reveals how these ocean giants manage to travel across the world and find enough food to fuel their large bodies, which can measure up to 12 metres in length.
According to Norman, besides diving to feed, the Ningaloo Reef whale sharks also seem to use their dives as part of a 'bounding' pattern - swimming up and down in this way might allow them to take advantage of gravity for propulsion.
Information about the whale shark's deep-water life was collected using an electronic tag attached to its fin by a clamp mechanism. The clamp is designed to corrode over time and then drop off, leaving the tag to float to the surface where it transmits a location signal to researchers.
Norman's team now has tagging data spanning some three months, detailing the orientation and environment of the whale sharks, including water temperature and depth. hey also plan to fit new tags to the sharks to collect yet more information.
"This is just the first little snippet to come out of learning about whale sharks. This will now be broadened to long-term deployment on the sharks, to work out what they are doing over long periods of time," said Norman.