Clues in shark vertebrae reveal where they’ve been

Posted: 01/13/2012 in all marine news

Li Ling Hamady –

It’s 1963. The escalating arms race and the horrific power of nuclear bombs cause world leaders to sign the Limited Test Ban Treaty, prohibiting weapons testing in the atmosphere and in the ocean. Fast-forward 49 years.

Escalating fishing has gravely diminished the populations of some of the world’s largest fish, including basking sharks, and they are fast disappearing.

In a curious connection, the lingering remnants of a past nuclear age are helping me find ways to conserve remnant populations of basking sharks and other endangered marine species.

Highly valued for their fins and overfished, basking sharks are now included on the Convention on International Trade in Endangered Species and are considered “vulnerable to endangered” by the International Union for Conservation of Nature.

They’re slow growing, long lived, slow to mature, and have low fertility, making them vulnerable to continued fishing pressure, whether they are caught intentionally or accidentally.

Basking sharks are often spotted lolling lazily at the surface, mouths agape, filter-feeding on zooplankton—hence the name “basking” shark.

They feed over large areas on vast quantities of food (in an hour, they can filter enough water to fill an Olympic-size swimming pool!). Thus, they play an integral role in the marine ecosystem and are indicators of its health.

Though they are the world’s second largest fish behind whale sharks, basking sharks remain a closed book scientifically. For conservation strategies to be effective, you first need basic knowledge of where marine animals live, mate, and give birth.

But all of that remains largely unknown for basking sharks. Pregnant females and young juveniles have never been spotted.

As for where they go, conventional knowledge has pegged basking sharks as a relatively shallow, temperate-water species, with populations in each hemisphere, along the margins of each continent.

Yet they seem to disappear for half the year.

Where are they going ?

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