Whale sharks all closely related, says study

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A new study has discovered that whale sharks around the world are all related which puts them at risk from overfishing.

A new study has discovered that whale sharks around the world are all related which puts them at risk from overfishing.

Whale sharks Rhincodon typus are the largest fish in the world and live in tropical waters which form a band around the equator. Very little is known about their biology or ecology and they have only been studied in any depth in the last 10-15 years.

Unfortunately, the meat of whale sharks is considered to be a delicacy by many people in China, Taiwan, Singapore, Korea and Japan. Here, whale shark meat is one of the most expensive fish that can be bought with each shark being worth an estimated $20,000. These active fisheries mean that whale sharks are severely overexploited in this part of their range.

Until recently, it wasn t known if overfishing in some areas would affect overall whale shark populations as no one knew if the sharks were migratory or if they tended to stay in their own territories.

To assess this, a team led by scientists at the University of Illinois in Chicago took DNA samples from 68 whale sharks from the Indian and Pacific Ocean and the Caribbean Sea. DNA microsatellites were compared between the sharks and found to be remarkably similar throughout the whale sharks range.

This means that these sharks migrate between populations and interbreed, and that any fisheries focussed on these sharks can have a global impact.

Although this species is listed in Appendix II of CITES, and with strict quotas in place, the financial gains for anyone exceeding their quota far outweigh the potential fines and consequences.

Lead scientist Jennifer Schmidt said: Our data show that whale sharks found in different oceans are genetically quite similar, which means that animals move and interbreed between populations.

From a conservation standpoint, it means that whale sharks in protected waters cannot be assumed to stay in those waters, but may move into areas where they may be in danger."

"The only real threat to whale sharks is us. To design proper conservation plans, we need to understand the sharks' lifestyle. We can only protect their habitat if we know what habitat they use."

Schmidt hopes that more countries will close whale shark fisheries and place more effort into alternatives such as ecotourism programs.

She added: People in many countries have come to realize that whale sharks are more valuable alive than dead."