Space technology to identify whale sharks off Gujarat
Indian scientists will try to distinguish individual whale sharks off the Gujarat coast, using a technique employed by NASA to identify galaxies.
Just as each tiger is distinguished by its stripes, whale sharks too can be identified through a unique pattern of spots that form points of numerous triangles on their bodies, say experts.
As the whale shark grows, the distance between these spots increases, but angles of these triangles remain the same, thus identifying the whale shark.
The method is also used by NASA to identify galaxies.
This initiative is part of a study to understand the migratory pattern, breeding and habitat of whale sharks for future conservation measures, says Dhiresh Joshi of the NGO Wildlife Trust of India (WTI) that is working on the project in partnership with the Gujarat forest department.
It involves taking underwater pictures of whale sharks and storing them in a global database managed by the NGO Ecocean.
If whale sharks spotted here are also sighted elsewhere in the world, it will help reveal their migratory path to the Arabian Sea through the oceans.
Initially, the forest department and WTI will be the main collaborators of the project. Later, fishermen will be roped in too, for sighting and the photo identification programme, says Joshi.
The project started last November, when Brad Norman, director of Ecocean Australia, trained forest staff on uploading photos on the online database and techniques of underwater photography.
Experts say horizontal shots of the spots around the fifth gill and pectoral fin on the left side of the fish are taken at an angle perpendicular to the fish. However, with the improvement on the software slightly angular pictures could also be corrected for identification.
The frame should show a bit of the water above and below the outline of the fish so as to get the orientation right.
Besides spot patterns captured in photographs of the fish, scarring and other markers were used in the past for identifications. Now by adapting a computer algorithm, an automated process has been developed originally used in astronomy for comparing star patterns in images of the night sky.
Each time a whale shark is photographed, details of the location, water conditions and other factors are recorded. The photographs help identify individual whale sharks, facilitate population estimation by the ‘mark recapture’ method and migratory pattern, he added.
Mr. Joshi says past record shows whale sharks aggregate in larger numbers off Gujarat than off any other state in India.
A survey by the NGO Traffic India recorded over 500 whale shark sightings between 1999 and 2000.
“The whale shark aggregation is less understood but from the satellite images it is clear there are large plankton blooms off the coast of Gujarat compared to any other maritime state and this could be the reason for such frequent sightings,” Mr. Joshi said.
“To date, Ecocean has identified 2,109 whale sharks worldwide, from 9,800 whale sharks sighted in 43 countries. Many identified sharks have been re—sighted on several occasions,” Mr. Norman said.
Ecocean has received support from the UN Environment Programme to promote the global whale shark library.
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