Many shark species are in decline due to overfishing. Conservation can be difficult because sharks do not grow or mature very quickly so rebuilding population numbers takes decades. New research has shown that sharks grow even slower and can live significantly longer than what was previously believed - making rebuilding declining populations all the harder. This research was led by Li Ling Hamady from the Woods Hole Oceanographic Institution (WHOI) and was published in PLOS ONE.
Typically, it has been believed that great white sharks can live about twenty years in the wild. This was based off bands of alternating light and dark tissue that accumulate on the shark’s vertebrae over the course of their lifetime, not completely unlike counting rings to date a tree. This method was based on the assumption that the bands signify one year of growth. Unfortunately, it appears that that while annual growth can be observed in other fish, the technique does not really work for sharks.
The WHOI team was able to perform the first successful radiocarbon dating on sharks, made possible due to the thermonuclear testing that took place 60 years ago. Radiocarbons permeated the marine life and became fixed in their tissue. This spike of ∆14C in the vertebral layers was something the team could use as a fixed time reference and analyze the isotopes through mass spectrometry to estimate age with much greater accuracy than ever before.
Samples of vertebrae that were collected from eight white sharks between 1967 and 2010 by the NOAA’s Northeast Fisheries Science Center were all tested using this technique. Before doing the radiocarbon dating, the tissue bands were analyzed in the traditional manner to set a point of comparison. By using radiocarbon dating, the largest shark was estimated to have lived 73 years. The longest-lived female was 40. These results dramatically change the expected lifespan of great white sharks. The team concluded that there might be sexual dimorphism involved with maturation rates and the aging process.
It is critically important to understand the lifespan of sharks in order to better facilitate their conservation. If females are living twice as long as we thought they did, it means that it takes even longer for them to mature and begin to reproduce than we thought. This needs to be accounted for as conservation officials develop plans to recover the species. Great white sharks are listed as vulnerable by the IUCN's Red List, yet are still targeted by poachers for their teeth, jaws, and fins. Some falsely believe shark fins have special healing properties, while others merely fish the sharks for sport.
