Whale sharks have built in sperm bank

September 20, 2010

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Embryos found in the whaleshark

A new discovery has shown that female whale sharks may store sperm from one mating, fertilising eggs at different times and leading to hundreds of embryos being carried at various stages of development.

Murdoch University Adjunct Lecturer, Brad Norman, was one of the researchers who analysed 29 embryos found in a whale shark that was caught off the coast of Taiwan in 1995.

“The embryos that were available for study represented approximately 10 per cent of the original litter and ranged from individuals still in egg cases to hatched and free-swimming near-term animals,” Mr Norman said.

“The range of developmental stages in the litter suggested ongoing fertilization over an extended period of time.

“Testing of the available embryos confirmed that they were sired by the same male.”

Despite increasing targeted research on whale sharks, very little remains known about their breeding habits.

“No one has ever witnessed whale sharks mating, so this research represents an exciting discovery,” Mr Norman said.

“We are keen to learn where it is that this threatened species is breeding and pupping (birthing) and encourage increased international protection for these locations.

“One possible location is the western Pacific Ocean, between Japan and the Philippines.

“Two females carrying eggs have also been found off China – a location where the species is still legally hunted and where the fins are highly sought after.

“Our research and conservation work is ongoing in the region.”

Mr Norman said the varying development of embryos could be a way of protecting the species.

“Young whale sharks have been found in the stomachs of blue sharks and blue marlin – so a large delivery of whale shark pups all at one time could attract large numbers of predators to an area,” he said.

“By staggering the delivery of pups, the strategy serves to reduce the risk of losing an entire litter at any one location.”

Brad Norman was one of six authors of the research paper Paternity analysis in a litter of whale shark embryos published in Endangered Species Research.  The lead researcher was Jennifer Schmidt from the University of Illinois, Chicago.

Mr Norman is the leader of a whale shark citizen science project that encourages individuals to photograph whale sharks and upload them onto a catalogue.  The resulting library of photos allows researchers to analyse the encounter information and learn more about these creatures.

The citizen science project is a Finalist in the Banksia People’s Choice Award.  The Banksia Environmental Foundation awards are regarded as the most prestigious environmental awards in Australia.

Click here to vote.

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