Sharks. They are one of the most mysterious kinds of animals.
Hardly any other creatures in our oceans are as fascinating to us as
as they are.
However, despite sharks being one of the most diverse
animals on the planet, with more than 400 different species,
only a handful of them
seem to be appreciated, or even noticed by the broader public.
So, today, I want to talk about one of the lesser known groups of sharks.
Sleeper sharks.
More specifically, about the Greenland Shark, found in the North Atlantic and Arctic ocean,
and the Pacific Sleeper Shark,
found in the North Pacific.
These two species are morphologically so similar
that some scientists still take into consideration
the possibility that they are all the same species.
The only major difference between the two
is their distinctive ranges.
So what makes these sharks so special?
First of all, they are one of the largest living species of sharks,
with an average size of just under 4 meters, or 30 feet,
and a speculated maximum size of 6-7 meters, or 23 feet,
based on video evidence,
they are comparable to the Great White Shark in size.
That not many people have heard of them, despite their huge size,
is mainly due to the fact that very little is known about them,
and they are very rarely observed,
which in turn is due to their unique lifestyle
While most sharks live somewhat close to the surface,
Sleeper sharks instead spend most of their lives
in the deep cold waters, near continental shelves
and slopes.
They are in fact one of the deepest diving fish.
Rare sightings by cameras of underwater robots or oil rigs
document this astonishing ability.
Greenland Sharks have been found at depths of up to 2600 meters,
or 8500 feet.
Only the Portuguese Dogfish,
a different species of Sleeper Shark, and the deepest living shark known,
has been found deeper than that,
at a depth of 3600 meters, or 12000 feet.
Adapted to living in frigid waters
between minus 2 to 10 degrees celsius,
you can only find them close to the surface in places where
shallow water is cold enough for them,
primarily, in the Arctic.
This makes them not only the biggest fish you can find there,
but also the only shark that can tolerate Arctic temperatures year round.
As a result, they were long thought of as purely polar animals,
but the continuous sightings of individuals in further south regions
suggests that they are a lot more common than previously thought.
To find out more about these understudied animals,
researches examine the contents of the stomachs of sharks accidentally caught
by commercial fishermen.
Originally, it was suspected that these sharks were scavengers
that feed primarily off carrion.
But these new studies confirm their much broader food spectrum.
It seems Sleeper Sharks are opportunistic apex predators that will eat
just about anything that comes across their path.
Nearly every animal that shares a habitat with these sharks
could be found in their stomachs.
Most of it is fairly unspectacular,
like a variety of small and medium sized fish
crustaceans, octopuses, jellyfish,
and gastropods.
However, other findings baffle the researchers.
Many Greenland Sharks have been found with seemingly fresh meat of
seals inside their stomachs, suggesting that they're actively hunting.
Other notable finds include
the remains of small whales, other sharks, dogs,
horses, reindeer, and moose
A similar study done for pacific sleeper sharks
revealed countless squid beaks of colossal and giant squids
in their stomachs
which suggests that they must be a big part of their regular diet.
This makes sleeper sharks only the second animal known to science that hunts these squids for food besides
the sperm whale.
Some researchers also suspect that greenland sharks
are responsible for a series of yearly seal killings
of the coast of Nova scotia.
This strange phenomenon became commonplace in recent years.
as every year, hundreds of mutilated seals
are washed up on the shore of Sable Island.
The wounds these bodies bear are extremely unusual.
Most of them are long, clean edge corkscrew-like
wounds that appear to have been made with a sharp instrument.
But whether or not the Greenland shark is actually the corkscrew killer of Sable Island
is still, to this day, not solved.
Other potential suspects are killer whales, and boat propellers.
How sleeper sharks could ever catch living prey,
is also still a mystery.
For one thing, they are absurdly slow - as the name might suggest.
A satellite tagging study found that Greenland sharks are only cruising at a mere
1.1 kilometres per hour through the ocean -
roughly at the speed of a crawling baby.
This makes them slower than any other shark.
Pacific sleeper sharks aren't much faster either.
And although both species are capable of quick bursts of speed
in order to hunt
even then, they are far to slow to catch a swimming seal
or many of the other things they might want to eat.
This lead scientists to believe that these sharks are primarily ambush predators.
that use the darkness of the deep sea
and the ability to glide silently through the ocean
to sneak up on their prey
It is also suspected that they hunt seals while
they're sleeping, or carelessly poking their heads through
ice holes to breathe. Still with
Still, with nobody directly observing them actively catching prey
The question, how they hunt, remains mostly unresolved
Also, because many sleeper sharks appear to be
almost blind.
The huge majority both pacific sleeper sharks and Greenland Sharks
are colonized by a parasitic copepod that attached itself to the front of the shark's eyes
and eats its cornea tissue.
It was hypothesised that the parasite might be bioluminescent, attracting prey for the shark
and making it a mutualism rather than parasitism.
However, there was never any scientific evidence for this theory
and it has been debunked multiple times by now.
Overall, this parasites don't appear to affect this sharks too severely.
Adapted to life in the deep sea,
ice site isn't mandatory for their survival.
instead, they lackly rely on their other senses
particularly on their sense of smell which is highly developed.
Another topic we know very little about is their reproduction.
As neither mating, no birth has been ever observed so far.
However, we do know that Greenland Sharks are ovoviviparous.
Like the Great White and many other sharks.
This means, that they don't lay eggs but instead give births to life young
after the eggs have hatched inside the universe.
Additionally, new research from the University of Copenhagen revealed
that they only reach sexual maturity at about age of 150.
This has likely to do with their very slow metabolism.
And the cold waters that they inhabit.
Which results in this sharks having a very slow growth rate
of only between 0.5 to 1 cm per year.
This was calculated through radiocarbon dating of certain metabolicly inert proteins
from the shark's eye lenses.
These proteins are not renewed after being synthesised in the body when the shark was apart.
Which allowed the researchers to estimate when the 28 individual examine were born.
Using this technique, they established that the largest shark, a 5 meter long female
was between 270 and 512 years old.
Where the actual value most likely being somewhere in the middle.
This means that the Greenland Shark has the longest known lifespan of all vertebrate species.
Unfortunately, the long enter wall between birth and sexual maturity
might make them vulnerable to over fishing and environmental change.
To what extend they endangered and how the warming of the ocean is impacting these sharks
is however not known
As no accurate global population numbers are available.
Luckily, today there isn't any large-scaled commercial fishery for them anymore.
However, in the first half of the twentieth century, Greenland shark was commercially fished for its liver.
This were used for lamp and machine oil and because of it,
the sharks were killed in great numbers before