Nicola Davis - 400-year-old Greenland shark is the oldest vertebrate animal
She was born during the reign of James I,
was a youngster when René Descartes set out his rules of thought and the great
fire of London raged, saw out her adolescent years as George II ascended the
throne, reached adulthood around the time that the American revolution kicked
off, and lived through two world wars. Living to an estimated age of nearly 400
years, a female Greenland shark has set a new record for longevity, scientists
have revealed.
The discovery places
the lifespan of the Greenland shark far ahead of even the oldest elephant in
captivity, Lin Wang, who died aged 86. It is also far longer than the official
record for humans, held by 122-year-old Frenchwoman Jeanne
Louise Calment. “It kicks off the
bowhead whale as the oldest vertebrate animal,” said Julius Nielsen, lead
author of the research from the University of Copenhagen, pointing out that
bowhead whales have been known to live for 211 years.
But the Greenland
shark doesn’t scoop all the gongs – the title of the world’s longest-lived
animal is held by Ming, an Icelandic clam known as an ocean quahog, that made
it to 507
years before scientists bumped it off. Grey, plump and
growing to lengths of around five metres, the Greenland shark is one of the
world’s largest carnivores. With a reported growth rate of less than one
centimetre a year, they were already thought to be long-lived creatures, but
just how long they lived for was something of a mystery.
“Fish biologists have
tried to determine the age and longevity of Greenland sharks for decades, but
without success.” said Steven Campana, a shark expert from the University of
Iceland. “Given that this shark is the apex predator (king of the food chain)
in Arctic waters, it is almost unbelievable that we didn’t know whether the
shark lives for 20 years, or for 1000 years.”
The new research, he
says, is the first hard evidence of just how long these creatures can live. “It definitely tells
us that this creature is extraordinary and it should be considered among the
absolute oldest animals in the world,” said Nielsen. Writing in the journal Science, Nielsen and an international
team of researchers describe how they set about determining the age of 28
female Greenland sharks, collected as by-catch during scientific surveys
between 2010 and 2013.
While the ages of many
fish can be determined by counting the growth layers of calcium carbonate
“stones” found in their ears – in a manner somewhat similar to counting tree
rings – sharks do not have such earstones. What’s more, the Greenland shark
lacks other calcium-rich tissues suitable for this type of analysis.
Instead the team had
to rely on a different approach: scrutiny of the lenses in their eyes. The lens of the eye is
made of proteins that build up over time, with the proteins at the very centre
of the lens laid down while the shark is developing in its mother’s womb. Work
out the date of these proteins, the scientists say, and it is possible to
achieve an estimate of the shark’s age. In order to determine
when the proteins were laid down, the scientists turned to radiocarbon dating -
a method that relies on determining within a material the levels of a type of
carbon, known as carbon-14, that undergoes radioactive decay over time.
By applying this
technique to the proteins at the centre of each lens, the scientists deduced a
broad range of ages for each shark. The scientists then
made use of a side-effect of atomic bomb tests which took place in the 1950s:
when the bombs were detonated, they increased the levels of carbon-14 in the
atmosphere. The spike, or pulse, in carbon-14 entered the marine food web
across the North Atlantic no later than the early 1960s.
That provides a useful
time-stamp, says Nielsen. “I want to know when I see the bomb-pulse in my
sharks, what time does that mean,” he said. “Does it mean they are 50 years
old, or 10 years old?”
Nielsen and the team
found that the eye lens proteins of the two smallest of their 28 Greenland
sharks had the highest levels of carbon-14, suggesting that they were born
after the early 1960s. The third smallest shark, however, had carbon-14 levels
only slightly above those of the 25 larger sharks, hinting that it was actually
born in the early 1960s, just as bomb-related carbon-14 began to be
incorporated in marine food webs… read more:
