Sunday, February 13, 2011

India's Whale Sharks: a migrating population may be unique to India

For many years, marine scientists have studied the migration patterns of marine animals, trying to better understand the animal's behavior by unlocking the secrets as to why these long-range movement patterns exist. Spawning grounds, food opportunities, seasonal temperature changes - all have entered into the mix, depending on the species or the location.

In the South Pacific and Indian Ocean Ocean, there was a long held belief that a population of whale sharks migrated from Australia to waters off India's Gujarat coast. In the winter months, whale sharks would disappear from Australian waters and reappear in Gujarat, about 300 to 500 strong. The theory was that the sharks were migrating to warmer waters.

But a new study by Wildlife Trust of India (WTI), wherein genetic samples from Australian and Indian whale sharks, along with identifying photographs, were taken and compared, it appears that the two regions may, in fact harbor two distinct populations. According to Arun Kaul, WTI senior director, there were no corresponding DNA indicators between any of the samples taken.

“The samples collected so far have not found a match anywhere in the world, which means they are unique,” Kaul said.

Whale sharks, like many other sharks, can also be photographically identified because their white-spotted markings - along with any other distinctive scars or deformities - act like a fingerprint. The WTI study did not find photographs that showed a whale shark in both Australian and Indian locales.

WTI pointed out that this was a preliminary study and that more work needed to be done to further identify migration routes for these sharks (after all, the Australian whale sharks were going somewhere during the winter months; just, apparently not to India) and to determine whether any cross-breeding is taking place.

I recall when I first became interested in the white sharks at Isla Guadalupe and learned of the "White Shark Cafe" where it appeared that both sharks populations from Isla Guadalupe and the Farallon Islands were both migrating to. It was a tantalizing thought that these two distinct populations were meeting in the mid-Pacific to cross-breed and maintain a healthy gene pool. However, to date, all DNA samples taken have not yet shown any connection between the two groups. It's also not completely clear as to whether all of the sharks migrate or whether there are some who, for whatever reason, stay back. Some divers, who dive Guadalupe in the summer months before the usual return fall migration of the white sharks, have reported seeing a shark or two at the edge of visibility, hanging out in deep water.

Could this be happening in Gujarat? The seabeds in Gujarat are rich in plankton - a primary whale shark food source - and sea grass which feeds many small fish that end up as whale shark prey. But the whale sharks don't stay all year round, so if not Australia, then where are they going?

A coalition of research groups including WTI, Wildlife Institute of India, Space Applications Centre, National Institute of Oceanography, Australian Institute of Marine Science, University of Illinois and others is being formed to carry on a more intensive study. The prospect of a unique population of whale sharks at Gujaret is not only of scientific interest, it is also a source of national pride. In 2000, as many as 500 whale sharks were landed off Gujaret, but in 2001 whale shark hunting was banned and hunters became protectors, viewing the whale sharks as a valuable natural resource. Fishermen free whale sharks caught in their nets and discussion are underway regarding the economics of ecotourism, as several agencies step up an awareness campaign.

“Perhaps we have discovered a population that could be endemic to Indian territorial waters,” said Satish Trivedi, senior official, community development, Tata Chemicals, Ltd (who funds a "Save the Whale Shark" campaign in India), commenting that such a discovery is significant for India.

Read about Gujarat whale sharks in

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