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Sharks and Climate Change: How Well Do We Know Sharks?

Aug 19, 2015 06:14 PM EDT
Tiger sharks like this one follow sea turtles, their favorite prey.
What's driving all the recent shark encounters on East Coast beaches, as well as the sightings of shark fins in waters near San Francisco? James Sullivan talks about some possible reasons.
(Photo : Wikimedia Commons)

If you've been following the news this summer, you'll know that East Coast shark attacks are an unavoidable topic. A total of 23 have occurred in the United States so far, three of which happened on the shores of North Carolina. In terms of happening all in one place, that's a scenario that hasn't been seen since five attacks took place on the Jersey Shore in 1916. While the odds of being struck by lightning is greater than the possibility of being attacked (only one of those 23 attacks was fatal), sharks play on our primal fears of the ocean as well as our fear of predators.

Sharks also have the sometimes-scary mystery of the unknown. After all, they have been on Earth for millions of years, and survived a number of its worst extinction events--but we are still learning about them. In recent research, it's becoming clear that many of the larger shark species are globe-trotters with fins. A study that tagged 24 tiger sharks revealed that the animals typically travel nearly 5,000 miles annually -- from the Caribbean to sometimes as far north as Connecticut, depending on the season.

As though the attacks weren't reminiscent enough of the movie Jaws, lines of great white sharks have been spotted in the waters around San Francisco. While no danger has yet cropped up regarding those Pacific Coast sharks, there is plenty of reason for concern. There's enthusiasm, too, from people who camp on the beaches and scan the horizon for shark fins. Nearly 15 sharks have been sighted. These juveniles up to 12 feet in length are seeking their favorite food: elephant seal pups. It turns out that sharks, even larger predators, are not at all opportunistic feeders that go after anything, as was previously thought. Tiger sharks tend to prefer sea turtles over nearly anything else, and tend to mimic the migratory patterns of their prey.

Sharks' sudden appearance along many Atlantic Coast beaches is unprecedented, as sharks have traditionally been thought to prefer warm water. Another 17 great white sharks gathered near the Monomoy National Wildlife Refuge in Chatham, Massachusetts -- twice the usual summer number, according to the Atlantic White Shark Conservancy's president Cynthia Wigren.

So what's driving these numbers? An ever-present concern is the rise in ocean acidification, which occurs as the oceans act as a carbon sink to break down CO2 in the atmosphere. As a result, mollusks have declined and many fish species now need search for food in new territories--and possibly sharks are following some of those patterns. At the same time, ocean currents are growing weaker, meaning that the transition of cold and warm waters may not be happening as efficiently as the Arctic ice continues to melt. Many coral reefs are already suffering bleaching as a result. Coral too is a living creature, and the centerpiece of this vast ecosystem, of which sharks are at the top of the chain.

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

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