Could a shark be the longest-lived vertebrate?

Until recently scientists thought that the longest-living vertebrate (a creature with a spine) was a bowhead whale, which was known to have lived to 211 years. But this week a team led by Julius Nielsen of the University of Copenhagen announced that they had successfully determined the age of a Greenland shark as being (wait for it) almost 400 years.

How did they do this? They used an adapted form of radiocarbon dating, a technique commonly used in archaeology. It measures the different types of carbon in an organic material, and uses information about how quickly these chemicals decay to estimate the material’s age. In order to obtain suitable specimens the team spent several  years collecting Greenland sharks that had been accidentally caught and killed by trawling nets. They used radiocarbon dating to measure the age of the proteins which are laid down in the shark’s eye lens while in its mother’s womb. The introduction of carbon-14 to the north Atlantic marine food web as a result of nuclear testing in the 1950s also provided a useful timestamp; any sharks whose proteins contained this type of carbon had to have been born in or after the early 1960s.

A diagram of a Greenland shark from 1947. (Image: EOL Learning and Education Group).
A diagram of a Greenland shark from 1947. (Image: EOL Learning and Education Group).

The scientists knew that a newborn Greenland shark is just 42 centimetres long but that a adult can grow to more than 6 metres, and so were able to create a model estimating its rate of growth. This, combined with the radiocarbon dating, gave the team rough estimates of the sharks’ ages. The largest of the creatures is estimated to have been between 272 and 512 years; this kind of range is common with this dating technique and the midpoint is generally taken to be the most likely. That makes the age in this case 392 plus or minus 120 years, and you may see this written as 392 ± 120.

This particular shark was therefore probably born around the year 1624. To put that in perspective, the English and Scottish thrones were occupied by James I (of England; he was James VI of Scotland). Louis XIII was king of France and overseeing the construction of the palace of Versailles. The Safavid empire recaptured Baghdad from the Ottomans while the Shogun expelled the Spanish from Japan. The shark would have been around 40 years when the Great Fire of London occurred; roughly 150 years when the American Declaration of Independence was adopted and approaching 300 when World War One began.

Some scientists are sceptical that a vertebrate could live to such a great age, but further research should clarify the matter.

Featured image: A Greenland shark photographed in 2013. (Image: NOAA Photo Library)

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