14 December 2016

Whale shark genetics revealed by water samples


How many whale sharks can fit into a liter of water? From just a few water samples collected off the coast of Qatar, scientists at the University of Copenhagen in collaboration with the Qatar Ministry of Environment and Maersk Oil Research and Technology Centre have obtained detailed genetic information about the whale shark population.

The new environmental DNA method is a breakthrough in the study of marine animals and it does not require an encounter with and direct sampling of the animal itself.

Genetic variation in the DNA fragments isolated from water samples can be used to estimate population sizes, as well as investigating relatedness between different populations of the same species. The new results are published in the international journal Nature Ecology & Evolution.  

Every year from May to September off the coast of Qatar, one of nature’s most impressive phenomena plays out. Hundreds of whale sharks come together to feed on eggs from the tuna fish that spawn in the area.

The whale shark is the world’s largest fish. It can grow to a size of 15 meters and weigh over 30 tons. Nonetheless, the shark is harmless, as it is adapted to a diet of microscopic animals, or zooplankton. The whale shark is endangered globally, and scientists all over the world are following the state of the populations. The species is particularly threatened by overfishing. To make things worse, efficient monitoring methods for large oceanic species are lacking.

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