tracking-a-whale


Recovered whale shark tag. Image: Conrad Speed.

Sometimes tracking marine creatures can take some unexpected twists and turns. AIMS scientist Dr Mark Meekan and PhD student Conrad Speed from Charles Darwin University tagged the world's largest fish, whale sharks, off Christmas Island in January 2008. The creatures were visiting the Indian Ocean island, as they do every year, to partake in the annual feast of red crab larvae. When the crab season was over, one of the tagged whale sharks travelled 4,000 kilometres over four months to Java, Scott Reef, the Kimberley Coast, Banda Sea and the top of Irian Jaya before heading back towards Australian waters. The animal made many deep dives to over 1,000 metres in the Banda Sea. Whale sharks are known to travel about 30km a day, so they can cover huge distances in four months.

Then the satellite tag from this whale shark made a sudden trek inland. Reconstructing what is likely to have happened, Dr Meekan speculates that the tag was probably ripped from the gentle whale shark by a big predator like a shark not far from the West Timor coast. The tag was found by a villager collecting turtle eggs on a beach and taken back to the village. Dr Meekan was tracking the whale shark using Google Earth and noticed that it seemed to be an awfully long way inland for a sea creature. Calling upon local contacts and Charles Darwin University colleagues, Dr Meekan was able to organise for Mr Speed to get to the village and negotiate for the return of the tag, which was duly handed over with some ceremony. The scientists were very happy to get the tag back as it contains a unique record of information on the movement and diving behaviour by the tagged animal. Data downloaded from it are being prepared for publication.

Whale sharks are mysterious animals and much more needs to be known about their lives. AIMS research on whale sharks is adding to knowledge about the movements of sharks in the Indian Ocean after they visit well-known aggregation sites in Australian waters like Ningaloo Reef and Christmas Island and defining their habitat in relation to physical and biological oceanography. AIMS work on tagging, photo-identification and genetics contributes to international efforts to learn more about these rare and endangered animals so that they can be better protected.