Meet the 'tremendous cannibals' who hit puberty on their 150th birthday
Greenland shark can live 400 years but is 'uniquely susceptible to extinction'
A new study that reveals Greenland sharks can live 400 years and don't even reach puberty until their 150th birthday makes them "uniquely susceptible to extinction," says a Halifax scientist.
The "tremendous cannibals" can swim at depths of 4,000 metres and grow up to five metres long, according to research published this week in the American Association for the Advancement of Science.
"These things are huge and they're only rivalled by the great white shark in terms of large predatory sharks," said Chris Harvey-Clark, a marine biologist at Halifax's Dalhousie University.
He has travelled to the north side of the St. Lawrence River each summer since the late 1990s, looking for — and sometimes coming "eyeball to eyeball" with — the sharks, which have a range in the North Atlantic that includes the Maritimes.
"[I've] probably spent more hours swimming with them than anybody else on the planet in order to study them, and you're always thinking in the back of your mind, how ancient is this giant animal? Is it 500 years old, is it 1,000 years old?"
'An ancient creature'
Traditional methods for figuring out a shark's age don't work for the slow-growing Greenland sharks, so scientists used radiocarbon dating on their eyes. The lens is formed before the shark is born and creates crystalline proteins that don't change throughout the shark's life. That gives biologists an accurate read on their age.
"But ultimately it does jive with other things we know about this animal. We know from [studies earlier in the 20th century] that they live a long time," Harvey-Clark told CBC's Mainstreet.
The method leaves a lot of "wiggle room," he says, as the oldest shark they looked at was 392 — plus or minus 120 years. "One thing's for sure: a five-metre shark is not a 20-year-old shark. It's an ancient creature. It is hundreds of years old."
That makes them the oldest vertebrates on Earth. They have some ancient company in the oceans:
- Bowhead whales live 200 years.
- Galapagos tortoises live 250 years.
- Some fish live 150 years.
Longevity 'fascinating thing to explore'
Humans, like Harvey-Clark, average about 82 years, according to the World Health Organization.
"We're not going to make it to 400. So the biological mechanisms behind how this creature can live, perhaps, twice as long as other long-lived vertebrates — it's got to be a fascinating thing to explore," said Harvey-Clark.
The shark population has suffered over the years as humans use the oil in their livers for fuel, lubricant and to light street lamps. It takes them 15 decades to hit puberty, and even longer to reproduce. That makes them "uniquely susceptible to extinction."
"I think the fact that these animals are the swimming old-growth forests of the sea is very important," said Harvey-Clark.
Some 'monster sharks' yet to be found
There are still a lot of unknowns, including how many Greenland sharks there are and how big can they actually get.
"They swim very slowly in a deep, dark black abyss most of the time," said Harvey-Clark.
The largest Greenland shark ever recorded, said Harvey-Clark, measured 6.8 metres and there could be even bigger specimens.
He said during one research expedition in a fjord on the east side of Greenland he found multiple large Greenland sharks on one fishing line that had been "severely cannibalized" by even larger sharks.
"You haul the line back later and often what you'll find are the heads of three or four sharks and then two or three sharks that have large pieces missing and one or two intact sharks," said Harvey-Clark.
"The astounding thing about that when we would haul the line back from these deep, dark depths would be the size of the bites. I mean, we were pulling up sharks that were four metres and the bites were considerably larger. There were some monster sharks at the bottom of this fjord."
In terms of population, he said the local Inuit fishing for halibut reported a bycatch of about 2,000 Greenland sharks in one year.
Occasionally Nova Scotia fishermen capture Greenland sharks as bycatch but not nearly as often.
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With files from CBC's Mainstreet