In 2015 the average life expectancy of human beings was 71.4 years. This seems like quite a good stint in comparison to some of our ancestors, but it is paltry when compared to the new world record holder for the oldest vertebrate: The Greenland shark (Somniosus microcephalus). The Greenland shark resides in the Arctic waters surrounding Greenland and can grow to lengths of over 5 metres. Despite its size though, growth is definitely not rapid in this species. The cool arctic waters mean that its metabolic rate is very slow, and as a result the reported growth rate of these giants is thought to be less than 1cm per year! This slow growth rate, coupled with its large potential length, has left scientists speculating on what age this species may be able to reach. Now, a team of scientist headed by Dr Julius Neilsen at the University of Copenhagen think they have found the answer (1).
Assessing the age of some species is not always a straightforward task. Normally, age is assessed using calcified tissues such as bones, but as this species does not have any bones (they are cartilaginous fish), the team had to think of a different method, so they turned to radiocarbon dating. The problem with using radiocarbon dating for animals is that most of their tissues are constantly being turned over in a process of metabolic breakdown. Ingeniously, the team realised that they could get around this problem by using the lens of the eye, as this is not subject to the same turnover. The nucleus of the eye lens is made up of metabolically inert proteins, so they essentially do not change from birth to death, and therefore are perfect for radiocarbon dating.
The team had to be careful when using this technique however, as carbon levels in tissue can be affected by external events. For this study, nuclear bomb tests which took place in the 1960s meant that assessing the age of any sharks which were 220 cm or smaller could prove difficult. Fortunately, only one of the specimens for this study was found to be below this threshold. All the others were found to be unaffected by the nuclear bomb events.
The team found that Greenland sharks have a lifespan of at least 272 years, beating the previous record of 211 years held by the bowhead whale (2). They found the oldest individual to be around 400 years old! To put that into perspective, she:
- Was born during the reign of James I.
- Survived the terms of 17 different British monarchs and 43 Presidents of the USA.
- Was alive when Captain Cook discovered Australia.
- Lived through the French Revolution.
- Was alive for the American War of Independence.
- Outlived great people such as Beethoven, Mozart, Picasso, Van Gogh, Einstein and Nelson Mandela.
- Saw Darwin’s Beagle voyage and the development of his theory of Natural Selection.
- Was cruising the oceans when the Titanic sank.
- Survived two World Wars, nuclear tests in its habitat and the Cold War.
- Bore witness to a man on the moon.
It was born during the reign of James I, survived the terms of 17 different British monarchs and 43 presidents of the United states, lived through the formation of the USA, the genius of Beethoven, Mozart, Van Gogh and Picasso, two World Wars, the whole of the Cold War and the birth and death of Nelson Mandela. Captain Cook discovered Australia, the first man was put in space and on the moon, Einstein developed his theories of special and general relativity, Darwin visited the Galapagos and developed his theory of Natural Selection, the French revolution, the sinking of the Titanic, the great fire of London and the plague.) They also found that individuals reach sexual maturity at the age of roughly 150 years old, meaning their rate of reproduction is likely to be quite low. As a result, the team are using their findings to push for conservation measures for this species, worried that population may suffer if they are put under pressure.
The shark cannot hold claim to the title of the world’s oldest known organism however. That goes to the ocean quahog (Arctica islandica) at a whopping 507 years old (3)! Best prepare yourselves for another extensive list…
- J. Nielsen et al., Eye lens radiocarbon reveals centuries of longevity in the Greenland shark Somniosus microcephalus. Science. 353, 702–704 (2016).
- J. C. George et al., Age and growth estimates of bowhead whales (Balaena mysticetus) via aspartic acid racemization. Can. J. Zool. 77, 571–580 (1998).
- P. G. Butler, A. D. Wanamaker, J. D. Scourse, C. A. Richardson, D. J. Reynolds, Variability of marine climate on the North Icelandic Shelf in a 1357-year proxy archive based on growth increments in the bivalve Arctica islandica. Palaeogeogr. Palaeoclimatol. Palaeoecol. 373, 141–151 (2013).
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