
Whale sharks: Atomic tests solve age puzzle of world's largest fish - willvarfar
https://www.bbc.com/news/science-environment-52155008
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pvaldes
In my experience, bony fishes are not easy to date by counting rings. I tried
it and discarded the whole work. If you find 20 rings, you can assume that the
fish would have 10 years (one opaque ring in summer and other hyaline ring for
winter), but unfortunately there are also bifurcated rings, disease's rings,
fused and duplicated rings so your animal could have several false duplicated
rings, and have only 7 years. In 200 thin rings your error can be awful.

To know the sex of the animals is also important, because females will produce
extra hyaline spawn rings starting somewhere in their adult phase. And
males... well, nobody nows. They obviously do not get pregnant but do the male
whale sharks fight and stop eating?. Not to mention than some fishes can
change its sex perfectly.

This with bony fishes, that have true bones. Big sharks are cartilaginous
fishes. Cartilaginous tissue dyes badly and rings in its vertebra are less
clearly marked. This animals migrate (vertically and horizontally). This means
that would probably starve for long periods and then feast and that their
vertebras would be subject to a wide range of pressure that could erase rings.

> So any animal that was alive then incorporated that spike in Carbon-14 into
> their hard parts

The key of the phrase is _hard_ parts. They are looking at cartilage, that is
not hard and is a very slow growing and inert structure (what if most of all
carbone went to the muscle instead?). The only hard part in whale sharks is
the tooth (1-5 milimeters long if I remember correctly). Those teeth are lost
and replaced continuously so can't be used to age the animal. Even more, they
are releasing carbon-14 at a unknown rate. I would like to see how they
address this fact as source of error in their models.

I remain still sceptical when I read this kind of results. Tagging or
photoidentification could help, but our best chance is with captive animals.

~~~
x3n0ph3n3
> I tried it and discarded the whole work.

Why wouldn't you publish on how it can't be done reliably?

~~~
pvaldes
It just didn't pass the cut. I had plenty of other interesting questions to
chew, and moved on. There is not reason anymore to revisit it. Most of those
bones would be unreadable today in any case.

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walkingolof
A method like this was used to determine the age of the Greenland shark, a
large shark living in cold waters.

"In 2016, a study based on 28 specimens that ranged from 81 to 502 cm
(2.7–16.5 ft) in length determined by radiocarbon dating of crystals within
the lens of their eyes, that the oldest of the animals that they sampled,
which also was the largest, had lived for 392 ± 120 years and was consequently
born between 1504 and 1744"

[https://en.wikipedia.org/wiki/Greenland_shark](https://en.wikipedia.org/wiki/Greenland_shark)

~~~
pvaldes
> had lived for 392 ± 120 years

Is the same problem, I personally (is just my opinion) wouldn't discard that
where 392 solid meals instead, one seal or reindeer at a time boosting grow
periods between nape and nape, minus an unknown number of pregnancy events.

Scientists are forced to publish something, anything, in short periods of
time, so here we are. And is getting worse.

~~~
bpodgursky
Radiocarbon dating wouldn't be affected by meal frequency, unless I'm missing
something. It's just identifying the oldest material in the specimen.

~~~
pvaldes
We have two main different ways to attack the problem of age, and both have
issues

> But as scientists know the rate at which this isotope decays, it is a very
> useful marker in determining age... The older the creature, the less
> Carbon-14 you'd expect to find.

They are registering decay in the level of carbon-14.

The clock is adjusted for bone (storing this isotope as a more or less
permanent crystalline mix of carbone and calcium). This is cartilage.

And teeth in sharks last only for some period ranging between, lets say, two
weeks and two years (100 days for a white shark or so). Somewhere inside this
period, those pieces storing carbon-14 will fall and will need to be replaced
in a few days. If the reserves are mobilised from vertebra to tooth, then you
would expect to find much less carbon-14 than usual.

Therefore you could conclude than the fish is much older than it really is.

Counting the number and type of rings on vertebra is a different problem, and
is affected by fasting and starving periods.

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hprotagonist
You can play a similar radiocarbon dating trick with the lenses of greenland
sharks. They live to about 390 +/\- 120 years old, and are estimated to reach
sexual maturity at 150 years old.

A specimen analysed in 2016 was born somewhere between 1500 and 1740.

[https://science.sciencemag.org/content/353/6300/702.full](https://science.sciencemag.org/content/353/6300/702.full)

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Zenst
"Over time, every living thing on the planet has absorbed this extra Carbon-14
which still persists."

Is that as consistent in absorption? More so animals that feed upon different
levels and maybe more so - do plankton absorb more or less and any animal
feeding upon them would see a higher rate perhaps. I'm still looking into
these aspects - fun google time. #1

Another train of thought I have from reading this is: We may well read in the
future about plastic pollution being used to measure metrics in life forms.
[EDIT ADD]

#1

[https://en.wikipedia.org/wiki/Carbon-14](https://en.wikipedia.org/wiki/Carbon-14)

It is naturally formed by cosmic rays, it has also been measured as highers in
area's that atomic testing happened (so near Australia) and with that,
Southern hemisphere. Given that, one would expect, any life form that was
located near area's near the poles or southern oceans would be more exposed to
the natural and atomic unnatural sources and whilst the unnatural sources
would dissipate - anything exposed during the early times would also have
higher levels than such a lifeform in those same area's today due to decay and
dispersion.

~~~
gus_massa
I think you can assume they didn't change the diet too much, so before 1945,
measuring the carbon in the bones(?) you should get a nice smooth exponential
curve, and then a jump in 1945 [Is there a small delay?]. More details in
[https://en.wikipedia.org/wiki/Bomb_pulse](https://en.wikipedia.org/wiki/Bomb_pulse)

~~~
Zenst
Whilst their food would not of changed in source, the content would of had
spikes above global average it periods of time due to the atomic spike, also
how that dispersed and how long until equilibrium would all be factors that
come into play. Let alone natural hotspots from solar radiation increase near
the poles.

But then the error +/\- rate would seem to accommodate those kind of margins,
but always nice if there is a way of narrowing those margins, so may be a
field of research that has some headroom and also help learn many other
tangents and maybe another data point for historical solar radiation.

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pjc50
It is rather remarkable that nuclear weapons have left a legacy written at the
atomic level in every living creature.

~~~
jmiskovic
And not just in living creatures. Ships sunk before atomic tests are valuable
source of "low-background steel".

[https://en.wikipedia.org/wiki/Low-
background_steel](https://en.wikipedia.org/wiki/Low-background_steel)

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skoskie
100-150 years old.

