The growth rate of somniosus microcephalus in the northern Arctic Ocean is very slow, even less than 1cm a year, and their adult body length is very large, so its life span has become a very attractive topic. Researchers found that somniosus microcephalus have almost no tissue that can be used to determine their age like bony fish, but others use their eyes when studying the age of whales, 
By studying the lens nucleus, someone measured the actual age of whales.
 the researchers believe that the age of somniosus microcephalus can be measured by their eyes.