Tuesday 25 October 2016

Huge mystery shark species 'is longest-living vertebrate'

Published 11/08/2016 | 20:41

A Greenland shark, which is the longest-living vertebrate in the world, scientists say (Science)
A Greenland shark, which is the longest-living vertebrate in the world, scientists say (Science)

An enormous but mysterious shark species which has been found in British waters is the longest-living vertebrate in the world, scientists say.

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Some Greenland sharks, which can reach more than five metres in length, can reach an age of around 400 years, according to the new research.

Writing in the journal Science they said the slow-moving giant had an average life expectancy of 272 years, surpassing other species known for long life, including turtles, tortoises and some whales.

Julius Nielsen, from the University of Copenhagen and Greenland Institute of Natural Resources, who led the research, said: "Greenland sharks are among the largest carnivorous sharks on the planet, and their role as an apex predator in the Arctic ecosystem is totally overlooked.

"By the thousands, they accidentally end up as by-catch across the North Atlantic, and I hope that our studies can help to bring a greater focus on the Greenland shark in the future."

According to the Shark Trust the Greenland shark is "a massive species with a heavy cylindrical body and short rounded snout" that can sometimes be found off Scotland, in the North Sea and part of the English Channel.

Its wider range, according to the Trust's website, is "the east Atlantic from the Seine River mouth, France, to Spitsbergen Island, Russia", and corresponding latitudes in the western Atlantic.

It can also be found at depths ranging from coastal shallows to more than 1,200 metres. Its diet consists of fish and crustaceans, plus mammals including seals.

The age of sharks can usually be measured by a method akin to using tree rings to age a tree, using the growth of hard cartilage. But Greenland sharks have very soft cartilage.

So the team, which included scientists from Oxford University, the University of Tromso in Norway and Aarhus University in the Netherlands looked at the eye lenses of 28 female sharks accidentally caught as "by-catch" by scientists analysing fish stocks off Greenland.

They used a radiocarbon dating method previously used to analyse the age of whales for the first time on a fish, studying sharks ranging in length from less than one metre to just over five metres.

They measured a life expectancy of almost three centuries, with one shark that was 5.02 metres long estimated to be 392 years old, with an error margin of 120 years, and a second that was 4.93 metres long 335 years old, with an error margin of 75 years.

They found that the sharks could live longer than the bowhead whale, which has been found to have a life expectancy of 211 years. Their paper says the only creature to live longer is the ocean quahog, a type of edible clam which has a life expectancy of 507 years.

The analysis supported previous research which suggested the species grows at a slow rate, of around 1cm per year.

Analysis of female sharks found that they also may not reach sexual maturity until they are around 156 years old, the team found.

Press Association

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