Sharks Are Getting Smaller and Weaker — Here’s Why

posted: 11/12/15
by: Danny Clemens
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Often considered a symbol of strength and power, the ocean's sharks are expected to grow progressively smaller and weaker throughout the next century as temperatures rise and oceans acidify.

In a laboratory setting, University of Adelaide scientists found that higher concentrations of carbon dioxide and rising temperatures make hunting more difficult for the ocean's apex predators. Specifically, sharks' olfaction is heavily impacted, making it more difficult to sniff out prey -- a life or death skill for bottom-feeders.

Rising water temperatures also negatively impacted sharks' metabolic efficiency; the sharks had to eat more in order to obtain fewer nutrients. As sharks in the lab hunted more poorly and obtained fewer nutrition from their meals, their average size dwindled "considerably," scientists say in a new study published in the journal Scientific Reports.

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Carl Roessler/Digital Vision

Reduced hunting activity by sharks would send shockwaves throughout already fragile oceanic ecosystems.

"With a reduced ability to hunt, sharks will no longer be able to exert the same top-down control over the marine food webs, which is essential for maintaining healthy ocean ecosystems," study leader and U-Adelaide Associate Professor Ivan Nagelkerken explains in a news release.

As sharks' ability to hunt decreases, the proliferation of the small, herbivorous animals on which they prey could also contribute to climate change, Griffith University researchers explained in an October study published in Nature Climate Change.

According to study co-author Rod Connolly, well-maintained coastal wetlands keep up to a quarter of a trillion kilograms of carbon out of the atmosphere annually. Much of that carbon-sequestering capacity is found in certain plants, like mangroves and seagrass, which are capable of storing carbon up to 40 times more efficiently than plants in terrestrial ecosystems.

With more herbivorous animals in the ocean, higher numbers of carbon-harboring marine plants are consumed, reducing the carbon-sequestering capacity of marine ecosystems.

"Predators play an important and potentially irreplaceable role in carbon cycling. The effect of the disproportionate loss of species high in the food chain cannot be underestimated," Connolly explains in a news release.

Click here for more ways that you can #StartWith1Thing and take a stand for sharks.

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On Wednesday, December 2nd, Discovery will present a global broadcast of Racing Extinction, a powerful eco-thriller that exposes issues of endangered species and mass extinction. Visit RacingExtinction.com for more information.


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