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Isotopes reveal that whale sharks stay close to home

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Whale sharks, the world’s largest fish, roam less than previously thought. Local and regional actions are vital for the conservation of this globally endangered species moving forward, according to a new study by researchers from the Marine Megafauna Foundation, University of Southampton, and Sharkwatch Arabia. Their findings are published in the journal Marine Ecology Progress Series.

Previously, genetic research indicated that whale sharks mixed within distinct populations in the Indo-Pacific and Atlantic Ocean, respectively. This new study used stable isotope analysis, a biochemical technique, to demonstrate that whale sharks feeding at three disparate sites in the Western Indian Ocean (Mozambique and Tanzania) and the Arabian Gulf (Qatar) rarely swim more than a few hundred kilometers north or south from these areas.

“Whale sharks are amazing swimmers, often moving over 10000 km each year, and they can dive to around 2000 meters in depth. Biochemical studies tell us more about where they go and what they do when they’re out of our sight”, said Dr Clare Prebble, who led the research as part of her PhD project at the University of Southampton.

The researchers used isotopes of nitrogen and carbon that have similar chemical properties, but vary in their atomic mass. Ratios between the heavier and lighter isotopes of these elements vary naturally across...

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