DNA sampling of the species at seven widespread locations revealed few genetic differences from the Pacific to the Indian Ocean, according to marine biologist Dr Bonnie Holmes.

“We analysed samples from the Indian Ocean off Western Australia, in multiple locations in the Western Pacific and as far away as Hawaii in the Central Pacific,” she says. The samples were obtained during tagging operations.

The Pacific and Indian oceans account for about half of all the water on the Earth’s surface, and the study contradicts previous claims that there is, for example, a distinct Hawaiian tiger-shark population.

However, genetic differentiation beyond the Indo-Pacific region was noted when the samples were compared to those from Brazil in the western Atlantic.

Dr Holmes said that the study highlighted the need for international co-operation to ensure that fishing of large migratory sharks was sustainable.

“In Australia these sharks have a higher level of protection than when they move into international waters, where they are often targeted for their large fins,” she said.

“There needs to be co-operation between international authorities to ensure that there are adequate no-take zones within our oceans.”

However, she added that the tiger shark’s long-haul migratory behaviour might be helpful in maintaining its genetic diversity.

“For instance, there is evidence of migrating sharks from both the east and west coasts of Australia moving into Northern Territorial waters,” said Dr Holmes.

Dr Holmes said that the Molecular Fisheries Laboratory at the university’s School of Biomedical Sciences would continue to investigate migratory sharks, using a new method to extract DNA from the jaws of tiger and white sharks held in museums and trophy collections, even those dating back to the 19th century. 

The study “Population Structure and Connectivity of Tiger Sharks (Galeocerdo cuvier) across the Indo-Pacific Ocean Basin” is published in The Royal Society journal "Open Science" here

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