A study published in the journal Nature has reviewed data collected by previous research on major marine predators. In this, he concludes that many of the estimates made of the threat level of many species, and consequently decisions on sustainable levels of fishing, are based on incorrect data.
The traditional method of assessing the age of sharks is the observation of visible “rings” when the vertebrae of the animals are cut, similar to the method used to evaluate the age of the trees, through the visible rings in a cut of the trunk.
However, “sharks are not trees”, says Alastair Harry, a researcher at James Cook University in Australia, who points out a study in 2014 that had already revealed that bull sharks (Carcharias taurus) have a life time twice as long as the approximately 20 years previously estimated. In 2007, another study in New Zealand found that Sardinian sharks (Lamna nasus) live on average 20 years longer than previously estimated.
For the most popular shark species, the white shark (Carcharodon carcharias), the longevity of the shark may reach 70 years, against the estimated 50 years or so.
Reviewing existing data has shown that, in many cases, the vertebrae rings fail to grow when sharks reach adulthood and maximum size, which means that counting the number of rings on a mature shark can result in the impression of that the animal is younger than it actually is.
According to Alastair Harry, of the 53 populations of sharks and rays (close relatives of sharks) for which there are consistent data, about 30% have longevity underestimated.
Alastair Harry’s study reports on two methods of reviewing the age estimate of sharks: chemical markers and traces of radiation based on the Pacific nuclear tests conducted in the Pacific in the 1950s.
Of the approximately 400 known shark species, 64 are listed as endangered by the International Union for Conservation of Nature (IUCN). Environmental organizations estimate that 100 million sharks are killed each year by commercial and sport fishing.