Greenland sharks are some of the slowest-swimming sharks, which attain a maximum swimming speed about half the maximum swimming speed of a typical seal. Therefore, biologists have wondered how the sharks are able to prey on the seals. Greenland sharks apparently search out seals and ambush them while they sleep. Greenland sharks have also been found with remains of polar bear, horses, moose, and reindeer (in one case an entire reindeer body) in their stomachs. The Greenland shark is also known to be a scavenger, but to what extent carrion (almost certainly the origin of the reindeer) figures into the slow-moving fish’s stomach contents is unknown. It is known that the species is attracted by the smell of rotting meat in the water.
It’s been reported from mark-release-recapture studies that the sharks grow only about 1 cm per year (due, no doubt, to their cold habitat), so their large size suggested to some scientists that they might be very old. This suggestion was supported by a new paper in Science by Julius Nielsen et al. (reference below, access probably not free). Using a unique method of dating these sharks, they found that they could be up to 500 years old, attaining sexual maturity only after 150 years. That makes them the longest-lived vertebrate on record, far longer-lived than the previous recordholders, Aldabra tortoises and bowhead whales—a bit more than 200 years each. (See the bottom for the longest lived animals that we know about.)
The way that Nielsen et al. aged the sharks (they sampled 28 females between 2011 and 2013) was to use radiocarbon dating on the proteins in the eye nucleus, whose center forms when the shark is still a fetus. (Note: the sharks weren’t killed for this study: they were “by-catch”, accidentally caught in fishing nets.)
It turns out that nuclear bomb testing in the 1950s and 1960s created a spike in radioactive carbon (carbon 14) that was absorbed into the marine environment, and then into animal proteins, so you can see a spike in the amount of radioactive carbon occurring in specimens caught beginning around 1960 (figure from the paper):
The authors found that the highest amounts of radioactive carbon were found in the eye nuclei of smallest sharks, which were presumably born about 50 years ago. They also did radiometric dating of the eye nuclei of the other sharks, which were born before the pulse and could be dated using conventional methods. Because once the eye nuclei are formed in utero the proteins (and the carbon they contain, derived from the environment at that time) do not change further, forming in effect, biological artifacts that can be dated just like ancient wooden artifacts.
The analysis was a bit more complicated than this, but you can read the paper and its references for details. The upshot is that there’s opportunity for error—not only in the radiocarbon dating itself, but in their use of Bayesian statistics, which requires prior assumptions about age and growth rate.
Given this, the authors are still confident that their estimates are pretty accurate within the error limits shown. The figures that everyone wants to know are in bold (my emphasis):
The model estimated asymptotical total length to be 546 ± 42 cm (mean ± SD), a size matching the largest records for Greenland sharks, and the age estimates (reported as midpoint and extent of the 95.4% probability range) of the two largest Greenland sharks to be 335 ± 75 years (no. 27, 493 cm) and 392 ± 120 years (no. 28, 502 cm). Moreover, because females are reported to reach sexual maturity at lengths >400 cm , the corresponding age would be at least 156 ± 22 years (no. 19, 392 cm) (table S2). Amodel was 109.6%, demonstrating that samples are in good internal agreement, implying that the age estimates are reliable.
The error limits put the upper age limit of the biggest shark as 512 years and the lower limit at 272 years, with the point estimate at 392 years. That means the shark was estimated to have been born in 1624, and could have been born as early as 1504 (that’s 60 years before Shakespeare was baptized). The Guardian says this about the point estimate of the oldest female:
But not everyone is convinced that Greenland sharks can live for four centuries. “I am convinced by the idea of there being long lifespans for these kinds of sharks, [but] I take the absolute numbers with a pinch of salt,” said Clive Trueman, associate professor in marine ecology at the University of Southampton.
Trueman agrees that it is possible to get a record of the early life of a vertebrate from eye lens proteins. However, the fact that the proteins in the centre of the eye lenses, and hence the carbon-14 within them, came from nutrients taken in by the shark’s mother adds a number of uncertainties to the calculations, he says.
Campana says while the approach taken by the researchers is sound, he remains unconvinced that Greenland sharks live for almost 400 years. But, he adds, “future research should be able to nail the age down with greater certainty.”
2.) Is this the longest lived animal? No, not by a long shot. Sponges and corals, which are animals, can live millennia, with some Antarctic sponges estimated at 10,000 years old. However, for animals we’re more familiar with, the record longevity known with reasonable certainty is held by a clam. As I mentioned in 2013, a specimen of the ocean quahog Arctica islandica—a clam nicknamed “Ming”—was snatched from the sea floor off Iceland and dated at 507 years old using growth rings. Pity that the heartless scientists killed it, for who knows how long it might have lived? Like the shark above, this is a cold-water organism. Cold environments can put physiological limits on growth rates by slowing down metabolism, and that might have something to do with extreme longevity. Who knows?
To close, here’s an email exchange I had with Matthew about this paper:
Matthew: And why don’t most vertebrates live for a long time anyway, Mr Professor?
Me: Antagonistic pleiotropy? How the hell do I know?
Matthew: He he. The more you know, the more you realise we know nothing about anything.
Me: Nothing about anything? Not how many hydrogen atoms in a normal water molecule? Not when we split off from the ancestors of chimps? Not how old the universe or the Earth are?
Matthew: You know what I mean. Don’t be a curmudgeon
Excellent! Thank you. My son will be interested in this.
Amazing to me how small that quahog is, for 500 years old. Much slower growth that a tre(e.g. sequoia, redwood, etc.)
Me: Me know nothing. But article good.
They are very beautiful – they look as if they are carved out of granite…
Subscribe. I did read all of this science post.
I also read it all and I would like all subsequent science posts to end with a brief, slightly terse exchange between Curmudgeon Coyne and Merry Matthew.
Cool.
The pictures of that shark indicate recent studies are true: you do get happier with age.
Amazing. What stories she could tell.
I’m picturing a Forrest Gump style movie with great moments in history that somehow involve a Greenland shark.
Lyndon B. Johnson: [Putting medal on Greenland shark] America owes you a debt of gratitude, son. Now I understand you were wounded. Where were you hit?
Greenland shark: In the pelvic fin
Interesting post, more in-depth than where I’ve seen it posted elsewhere.
So, I assume this it THE shark, made into kæstur hákarl, that the Icelanders are famous for eating after letting it ferment, that tastes strongly of ammonia, and is the required gross-out on every travel show to Iceland, where the host is shown a plate of little white cubes, supplied with local booze, Brennivín, then takes a bit and a swig, gags, makes a face, the server admits they can’t stand it either, and everyone is happily nauseous. Bit worrisome, that. I can’t say that I trust any government catch quotas for any species that takes 150 years to reach maturity. Ain’t it grand to slaughter such a beast for televised novelties?
Ha, I would assume so. It is “håkäring” in Sweden. (From “håskärding” = shark (“haj”) to cut up. An easy catch? [ https://sv.wikipedia.org/wiki/H%C3%A5k%C3%A4ring ])
Of course we can’t, but now we can change them:
“The researchers say this has consequences for future conservation of the animals.
Because of their extreme longevity, Greenland sharks may still be recovering from being over-fished before WW2.
The sharks’ livers were once used for machine oil, and they were killed in great numbers before a synthetic alternative was found and the demand fell.
“When you evaluate the size distribution all over the North Atlantic, it is quite rare that you see sexually mature females, and quite rare that you find newborn pups or juveniles,” Mr Nielsen explained.
“It seems most are sub-adults. That makes sense: if you have had this very high fishing pressure, all the old animals – they are not there any more. And there are not that many to give birth to new ones.
“There is, though, still a very large amount of ‘teenagers’, but it will take another 100 years for them to become sexually active.”
[ http://www.bbc.com/news/science-environment-37047168 ]
Reblogged this on My Garden Biodiversity and commented:
The path of a never ending learning curve is also the path to never ending discoveries
That is one long swim.
Very interesting. I wonder if there are techniques for calibrating or corroborating eye nuclei dating? For instance wasn’t foxtail pine tree ring data used to calibrate early radiocarbon dating efforts?
Somehow that shark looks very intimidating. The eyes, I guess. But they are also quite beautiful in their way. I can imagine that polar bears, seals, and other mammals, die and sink at a fairly constant rate. You could think of it as a slow-motion rain of protean falling to the bottom of the sea. What a feast for sharks such as these.
CBS Morning News ran a spot on this today, and actually got the science parts pretty well correct despite teasers like “How do the scientists tell how old they are? By looking deeply into their eyes,” which they then went on to explain in the full report.
Also noted, the study was done in part at VIMS – the VA Institute of Marine Science – which is part of Wm&Mary.
Amazing discovery. Here’s a link to the paper for those of us not in the U of C: http://science.sciencemag.org/content/353/6300/702
So ‘Ming’ the clam’s sobriquet ?
And not Edna, that specific boater’s wife ?
or, say, her husband Noah’s grandpappy,
the patriarchal Methuselah himself ?
Blue
“attaining sexual maturity only after 150 years”
How the hell would such a species evolve? There are plenty of opportunities for a small, slow shark to die. How could it possibly pay any gene to wait that long before having a *chance* at being transmitted?
More info on their reproduction would be nice.
“How the hell would such a species evolve?”
Veeryyy slooowlyyy.
More seriously, it would evolve as anything else: as long as it works.
That’s the point: it looks like it oughtn’t to work.
I can imagine any number of just-so stories for it to work, of course, but that’s not enough.
Whales take 5 to 10 years. Elephants 14. Generally speaking humans are (tied for) the slowest to reach maturity among the species I know that are even vaguely comparable to us.
I consider 150 years to reach sexual maturity (!!!!!!) a *very extraordinary claim*, based on what little knowledge of biology I have, and would require much more evidence before I dare repeat it.
Who is to say that they evolved for a great length of time as cold water, slow growing animals? Their present Methuselah life history could have emerged recently, only a million or so years ago.
Possibly. And it helps that they’re apex predators. And that sharks are slow, generally (I get 10 to 33 years depending on sources for GWS maturity).
But still… how are they not wiped out by diseases and stuff? Red Queen and all that.
My point is, “X lives 500 years” is a nice bit of polite after-dinner trivia. A good 6/10 on the surprise-o-meter. “X hits sexual maturity at 150”, otoh, is a solid 9.75/10. It seriously knocks my socks off.
I’d at least expect them to be virtually disease-free and highly cancer-resistant (notions that are popular, but seem debunked, unless *that* species is very different somehow), or to mutate very fast. Or are shark pathogens very slow to mutate too? WTH is going on here?
Thanks for the great science post. My favorite science posts are usually ones like these that target a specific species and an unusual trait. I am reminded of the post on the Opah being the only homeothermic fish.
Very interesting to learn that the Pacific nuclear bomb tests affected all the sea life at the time. Now that is pretty unnerving. It’s amazing how one small species can cause such immense damage to such a large planet and its inhabitants.
I’m with you on the “we know nothing” meme. In fact, I really dislike it. Firstly, it’s not true, we know loads about the Universe, just not everything.
Secondly, anti-science and whoo believing types try to use it as a stick to beat us with:
“My whoo idea is definitely true”
“There’s not the slightest evidence it works”
“But scientists admit they don’t know anything therefore I’m right”.
Great science post as usual. Still my favourite type of piece on your website (alongside Hili updates and readers’ photos) and still hugely appreciated. Thank you as ever for the effort involved in producing these.
I love this post. That’s one gorgeous creature.
Long live curmudgeons!
Very interesting!
“Sponges and corals, which are animals, can live millennia…”
I wonder whether the appearance of mesoderm, i.e. cells that cannot directly dump their waste into surrounding water, somehow hinders longevity.
For anyone interested in knowing a little more about the radiocarbon dating method that utilizes the lens crystalline proteins, here’s a link to an article in an open access journal, PLoS One:
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0001529
Just as a comparison, the primary lens fibers of the eye lens nucleus form between weeks 5 and 7 of human prenatal development, so quite early in the course of a 9-month gestation. The PloS One article indicates that there’s no remodeling of/metabolic additions to these lens fibers and no removal of degraded fibers, once the primary lens capsule has formed during embryonic development.
This seems a reasonable effort to me, given the other tests on dating core lens proteins are a positive control that demonstrates the method is feasible.
It would be extra good to use a parallel test with a different isotope, to see if that gives a similar result. I cannot find a suitable one that would be direct components of proteins (sulfur for example is in proteins, but radioisotopes of sulphur have short half lives). But proteins often use metal atoms as a prosthetic group, and maybe there is a suitable radioisotope among those.
“They have poisonous flesh, laced with neurotoxins” — you know people are going to want to lick them now!
Also, I like their eyes!
The longevity question? I do not find it a surprise given that sharks have been swimming our ancient seas for some 420 millions years, if there is some advantage to be made or somewhere to ‘niche oneself’ that is a lot of time relatively speaking for the species to find it and make use of it’s environment.
The post keeps me in check though as science should do and WEIT does..
I despair at the rate in which we are killing them off and a lot of it as by catch, it is obscene and careless. The gun we are using to shoot ourselves in the foot is getting bigger, diversity is what makes our lives richer, like global warming we are slow to ‘get it’
Love the shark. This lady, Christina Zenato, has dedicated her life to these beautiful creatures. She specialises in removing fishing hooks that have become embedded in their mouths. Both of these videos are on https://www.youtube.com/ etc
Here she reaches into the sharks mouth to remove a hook.
watch?v=xDKNUG2fwRA
According to a documentary on UK TV last week the same shark (I think) visits her regularly. It doesn’t seem to mind being touched. She said she can feel the vibration as water is forced through the gills. Maybe better than a cat’s purring?
watch?v=Fdtj19LrIPU
Fascinating! I’d heard about this, but wanted more information, and here you have dropped it in my lap. Thanks for sharing!
I didn’t see it mentioned here, but most Greenland sharks are functionally blind because of the copepod Ommatokoita elongate that attack themselves to the sharks cornea. You can see some of these parasites in some photos (e.g. the white streak).
attack => attach
Damn autocorrect! Although in this case the former word also nearly works.