The lifespan of a shark depends on the species (over 500). While most sharks live between 20 and 30 years, there are exceptions, notably the blue shark with an average lifespan of fifteen years and the Greenland shark, which may be the longest-lived vertebrate in the world.
Greenland Sharks Have the Longest Lifespans
The Greenland shark (Somniosus microcephalus) has the longest lifespan of the shark species and in fact may be the longest-lived vertebrate in the world.
While scientists realized that Greenland sharks had long lifespans, they didn’t know how long. In 2016, a report in Science shed light on the subject.
John Steffensen, a marine biologist at the University of Copenhagen, set out to determine the longevity of the Greenland shark by taking some vertebrae from a shark to count the growth rings – only to find it didn’t have any. On the recommendation of a colleague, Steffensen and his graduate student Julius Nielsen checked the specimens’ eyes for accumulations of carbon-14, an isotope produced by the atom bomb tests of the late 1950s.
Two test sharks, both smaller than 2.2 meters long, were determined to have been born after 1960, the date that carbon-14 has been determined to have infiltrated the ocean. Armed with the knowledge that Greenland sharks grow about one centimeter per year, the team was able to create a growth curve to estimate the ages of additional sharks based on their sizes.
The biggest and oldest shark sampled turned out to be 390 years old plus or minus 120 years.
The Short-lived Blue Shark
At the other end of the spectrum is the blue shark (Prionace glauca). In the wild, blue sharks live for 15 years on average, but some individuals have survived for as long 20 years. Adults are usually around 11 feet (3.4 meters) long, but some can be over 13 feet (4 meters) long. Females tend to be larger than the males. Blue sharks have one of the largest ranges of any shark species; they have been found in all of the oceans except the Arctic.
Challenges of Determining Longevity
Determining how long sharks live is difficult, for they are active swimmers and many species are migratory. Unlike many animals, sharks do so poorly in captivity that captive sharks have shorter life expectancies than their free brethren. Whale sharks (Rhincodon typus) are believed to live at least a century in the wild, but they survive only eight years at most in captivity. It is thus pointless to use captive sharks in longevity studies.
ResourcesBoucree, Alexandra Axtell and Joseph. “Prionace glauca (Blue Shark).” Animal Diversity Web. N.p., n.d. Web. 13 Mar. 2017.Elizabeth PennisiAug. 11, 2016 , 2:00 PM. “Greenland shark may live 400 years, smashing longevity record.” Science | AAAS. N.p., 11 Aug. 2016. Web. 13 Mar. 2017.“How Long Do Sharks Live?” Shark Facts and Information. N.p., n.d. Web. 13 Mar. 2017.