The Science Behind Ageing Sharks: Study Reveals Great Whites Can Live More Than 70 Years

 @KukilBora
on January 09 2014 4:59 AM
white-sharks
According to the researchers, the age of the oldest female white shark sampled was 40, and that of the oldest male was 73. Reuters

Adult white sharks, also known as great whites, can live up to 70 years or more, which is far longer than previously thought, according to a new study that used radiocarbon dating to determine age estimates for white sharks in the northwest Atlantic Ocean.

Scientists said that a shark's age is typically calculated by counting alternating opaque and translucent band pairs that are deposited in their spinal column. It's unclear though if these band pairs are deposited annually, which makes it difficult for scientists to accurately estimate the age or provide estimates for the longevity of many shark species. The new study, published on Wednesday in PLOS ONE, addresses this concern by determining the periodicity of band-pair deposits in white sharks from the northwest Atlantic using radiocarbon dating. The scientists believe that once validated, the band-pair counting method could be useful in determining minimum estimates of longevity in white shark populations.

“Ageing sharks has traditionally relied on counting growth band pairs, like tree rings, in vertebrae with the assumption that band pairs are deposited annually and are related to age,” Lisa Natanson, a fisheries biologist in the Apex Predators Program at the National Oceanic and Atmospheric Adminstration's Northeast Fisheries Science Center, said in a statement. “In many cases, this is true for part or all of a species' life, but at some point growth rates and age are not necessarily in sync.”

Natanson, who is a co-author of the study, said that deposit rates of band pairs in sharks’ vertebrae can change once the sharks reach sexual maturity, resulting in very thin band pairs that are unreadable. The new radiocarbon dating study analyzed vertebrae from four male and four female white sharks that were caught between 1967 and 2010 in the northwest Atlantic. Scientists believe that the method will help determine the absolute age of a fish and can also be used to confirm or refute annual age in a species.

As part of their research, the scientists used a technique called bomb radiocarbon dating, which uses a separate radiocarbon pulse in the environment caused by the explosion of nuclear bombs in the 1950s and 1960s as a “time stamp.” The researchers found that the estimated bomb radiocarbon dating age of the oldest female white shark sampled was 40, and that of the oldest male was 73.

Previous studies of white sharks from the Pacific and Indian Oceans had suggested that none of the examined specimens were older than 23 years.

Researchers believe that either white sharks are living significantly longer and growing slower in the northwest Atlantic than their counterparts in the Pacific and Indian Oceans or the longevity of the fish was underestimated in previous studies.

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