Many Sharks Live A Century—Longer Than Thought

2017-11-15T15:01:55+00:00 November 15, 2017|
New study shows that Marine Protected areas are successful in protecting grey reef sharks. (Credit Yzx / Wikimedia Commons)

(Click to Enlarge) (Credit Yzx / Wikimedia Commons)

We humans go to great lengths to appear younger than we are. Sharks, it seems, do it naturally.

(From National Geographic / by Elizabeth Armstrong Moore) — About a decade ago, studies began to hint that many sharks have longer lifespans than previously suspected. Now, a new analysis that pulled together data from more than 50 studies suggests a “widespread” underestimation of lifespans among many sharks, rays, and cartilaginous fish. (Explore the interactive: “Sizing Up Sharks, the Lords of the Sea.”)

That’s because newer methods of aging sharks—such as bomb carbon dating—are proving more accurate than the traditional method of counting the growth bands on vertebrae, says study author Alastair Harry, a fisheries scientist at Australia’s James Cook University.

“Scientists were definitely already aware of [age underestimation], but perhaps did not quite realize the magnitude and prevalence of it,” Harry says.

 The results, published recently in the journal Fish and Fisheries, suggest that many sharks—from great whites to sand tigers to dusty sharks—may roam the oceans for decades longer than believed.

And just last year, scientists found that Greenland sharks, native to cold Arctic waters, might live for centuries. (See “272-Year-Old Shark Is Longest-Lived Vertebrate on Earth.”)

The problem, researchers contend, is that aging sharks incorrectly can spell trouble for conservation.

By reviewing 53 previously studied populations of sharks, Harry revealed that the ages of 30 percent of those populations are underestimated.

Estimating a shark’s age is tricky. They lack otoliths, lumps of calcium carbonate in the inner ear that build layers at a regular rate throughout a bony fish’s life. It’s much like counting tree rings, and it works. (Read about the animal that lives for 11,000 years.)

So for decades, shark scientists have used the next best thing: calcified growth bands that form on a shark’s cartilaginous vertebrae.

Counting these bands is an art as much as a science, as scientists can see different numbers of bands on a given shark, and those bands are sometimes averaged, says George Burgess, former director of the Florida Museum of Natural History’s Program for Shark Research, who wasn’t involved in the new study. (Watch our favorite collection of shark videos.)

The new findings show that the older a shark is, the less its growth bands correspond to its age—meaning the bands are not always reliable indicators, according to Harry.

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