The West Australian 25 May 09;
Ningaloo Reef may be a nursery for whale sharks, say scientists who are still striving to work out the full life cycle of the oceans’ biggest fish.
About 80 per cent of sharks that visit Ningaloo are juvenile males, suggesting that the area may be a “school playground” visited by the elusive giants before they head out to roam the Asian seas.
The male skew of the population means that scientists still know little about the lifestyle of female whale sharks, according to Mark Meekan, of the Australian Institute of Marine Science.
The researchers have just finished attaching high-tech tracking tags to 15 sharks at the reef to monitor their travels over the next few months.
Since 2005, Dr Meekan and his team have tagged 55 whale sharks at Ningaloo, although results had been mixed because several of the tags were bitten off by predatory toothy sharks.
The tagging work has already shown that Ningaloo’s whale sharks range as far as East Timor, Christmas Island and Java, but that they rarely make the trip right across the Indian Ocean.
“We know that many of the animals show site fidelity, returning to Ningaloo over a period of decades,” Dr Meekan said.
“Their migratory patterns show that after leaving Ningaloo they head north to Java, Timor and Sumatra, and possibly even further afield, before returning.”
The research has been hindered by the untimely demise of some of the sharks. Dr Meekan said one shark tagged during the 2007 season headed straight to Moa Island, north-east of Timor, and made a beeline for a fishing village visible on satellite images of the region.
It then mysteriously disappeared — whether it ended up as several families’ dinner was open to conjecture, he said.
The new tags used this season were more ingenious than previous models, Dr Meekan said.
Older versions required the shark to breach the water’s surface so they could send a signal to a waiting satellite.
The newer versions produce a more complete archive of the shark’s travel, using sensitive light meters to record depth, as well as latitude and longitude data. The team has also been able to include genetic and photographic records of the sharks to compare populations, because each has its own markings.
That has shown that there is no mixing between Ningaloo’s whale sharks and those found at the Seychelles, Madagascar and the Maldives. “They don’t go right across the Indian Ocean, as you might have thought,” Dr Meekan said.
MICHAEL HOPKIN
