The typical life expectancy of sharks has been greatly underestimated – white sharks, for example, can live not 50, but 70 years, the oceanologist writes in an article published in the journal Nature.
“Our current observations indicate that the age of all sharks is underestimated, not only those species that we studied or that our colleagues paid attention to. Now this problem can no longer be ignored, and we must actually re–measure the age of all cartilaginous fish” , – said Alistair Harry from James Cook University in Townsville, Australia.
Sharks are one of the longest-living fish and just vertebrates on Earth. For example, the Shrimp sharks Somniosus microcephalus live on average about two or three hundred years, and some individuals can live to the age of 500 years, which makes them the longest living creatures on the planet. Many other sharks, as scientists previously believed, can on average survive for about 20 or 40 years, depending on their size and metabolic rate.
How do scientists calculate the age of sharks and other marine fish, whose appearance does not change as their bodies age? For this, oceanographers catch fish and cut their vertebrae, counting the number of peculiar “annual” layers inside them. Similar measurements, as shown by observations of the growth of sharks in captivity, allow us to determine their age fairly accurately.
This idea, as Harry relates, has begun to cause doubts in recent years. For example, observations of ordinary sand sharks living in the wild, showed that their real age can be several tens of years higher than indicated by the number of “annual rings” in their bones.
Such publications forced Harry to analyze all the measurements of the age of sharks that were conducted in the last 50 years, and try to find errors in them and correct them. For this, the scientist calculated the typical growth rate of sharks, relying on the “traces” of nuclear tests in their bones and the special luminous marks that oceanologists introduced into the body and the bones of sharks before releasing them to freedom.
Comparing these data, the Australian researcher discovered that the age of all sharks was systematically underestimated, and that in reality it was 20-30 years longer than previously thought. For example, tiger sharks live not for 20 years, but for about 40 years, and herring sharks, the main source of the famous shark fins, live about 65 years, not 38 years.
This underestimation of the life expectancy of sharks, as Harry notes, may indicate that the populations of these fish in the Atlantic and the Pacific can be much more “elderly” than scientists currently believe, which can affect their ability to breed and adapt to new environmental conditions.
In addition, the long life of sharks can speak in favor of the fact that they grow slower than previously believed by scientists. This is extremely important for adjusting the catch quotas for sharks, based on the fact that these fish grow faster than they actually do.