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Traditionally, the age of sharks and rays is determined by counting the seasonally deposited growth layers in hard calcified structures such as fin spines. However, such techniques cannot be applied to the Greenland shark because it lacks such 'hard' structures.

 

To solve this mystery of the Greenland shark's life span, the research team analysed the eye lens nucleus of 28 female sharks sampled as accidental by-catch during the Greenland Institute of Natural Resources' annual fish and shrimp surveys. The centre of the shark's eye lens nucleus is composed of metabolically inactive tissue which does not change significantly from the time of their birth. Therefore, the paper explains, its chemical composition can be used to reveal the age of the shark. The researchers measured radiocarbon content of the lenses from which they could estimate age by matching and calibrating the data using chronologies and calibration curves representing temporal radiocarbon changes in the marine food web in the northern North Atlantic over the past 500 years.

 

The paper notes that another age indicator already reported is the slow growth of the Greenland shark that shows bodily incremental lengthening of no more than 1cm a year. The great size and expected slow growth of the Greenland shark supports the team’s dating evidence. The researchers find that the estimated life span of a fully grown Greenland shark female over five metres in length is at least 272 years. Moreover, they estimate that females are around 156 years old when they arrive at sexual maturity.