Crocodile Shark Profile
Sharks are perhaps the most fearsome animals that currently exist. Not because they particularly deserve to be feared, but because they combine two of the things that humans worry about in the deepest corners of our DNA: darkness and being eaten.
It also doesn’t help that we’re totally immobile in the sharks’ habitat. Regardless, the Japanese came up with a way of describing a shark that somehow makes it sound even more frightening. Welcome to the crocodile shark.
The crocodile shark is a species of mackerel shark that can be found in tropical waters worldwide, typically below 200m during the day before rising at night to feed.
Crocodile Shark Facts Overview
|Location:||Equatorial latitudes, worldwide|
|Weight:||Max at Around 6kg (13b)|
|Colour:||Dark grey, countershaded|
|Diet:||Mostly fish and cephalopods|
|No. of Species:||1|
|Conservation Status:||Least Concern (IUCN)|
These sharks are mostly distributed in the Atlantic Ocean near South America, as well as the Indian Ocean, and Pacific near Japan, Taiwan and Korea.
Despite the name, the crocodile sharks aren’t big enough to be dangerous to humans.
It does lurk at depths and emerge from the murk to clamp down on its prey, much like its namesake, but the teeth are designed for gripping fish, unlike its cousins with the serrated, cutting mammal-slashing teeth. It diets on bony fish, squid and shrimp.
So all in all, it’s not a threat to us. The same can’t be said for some of our infrastructure, though.
We don’t know all that much about it, and what we do know comes from the countless hundreds of lives that are wasted as bycatch from the fishing industry. Currently, they’re thought to be doing okay, but their slow reproduction and high rate of damage from tuna fisheries may soon change this.
Interesting Crocodile Shark Facts
1. Crocodile sharks are the smallest mackerel shark in the world
The crocodile shark is the smallest living mackerel shark, at about 1 m (3.3 ft) in length and weighing 4–6 kg (8.8–13.2 lb).
It is recognisable by its long spindle-shaped body, pointed snout, exceptionally huge eyes, and small fins.
2. They’re vertical migrators
We all know of the epic journey of migrating species like the Monarch butterfly or the Arctic tern; journeys that span great distances and multiple continents.
But not all migrations are so epic. Some are more localised to a few hundred kilometres between breeding and overwintering sites, some are simply daytime foraging migrations.
In the ocean, unlike on the land, there’s a much greater vertical dimension to take advantage of, and lots of animals do just that. As photosynthetic algae need to spend a lot of time up at the surface to gather sunlight, this is where the base of the oceanic food chain exists.
Zooplankton that eats these algae do so at night when there are fewer predators around to see them. In the daytime, they retreat to the protection of the cooler depths. This is called a diel vertical migration, and it’s matched by some of the larger predators too.
The crocodile shark spends the days well out of the light, down at depths of below 600 meters. As darkness descends over the ocean, it rises ominously to the shallows to feed.
3. They snap
As if a shark wasn’t snappy enough, the ferocious clapping of this shark’s jaws when it’s pulled out of the water is what has given it the nickname ‘crocodile shark’. This name is further corroborated by the long, shark teeth that are designed for gripping fish.
When snapping, much like other creepy deep-water sharks, the crocodile’s jaws protrude forward. This creates a trap-like mechanism that’s perfectly suited for ambushing small prey.
The Japanese word for this shark is mizuwani, which translates to “water crocodile”. Incidentally, this is also a popular cocktail in Japan but contains no real crocodile (or shark).
4. They attack fibre optic cables
Among the most common protestors of underwater fibre optic cables were crocodile sharks, who, presumably stimulated by the electrical current produced by the cables, were able to cause significant damage.
The exciting folks at the International Submarine Cable Protection Committee report that numerous animals like to bite underwater cables at depth, and sharks have been responsible for at least four complete failures of an underwater cable.
While the current may be responsible for the behaviour, it’s been impossible to figure out for a fact what’s going on. It might be that the sharks just don’t recognise the intrusion and want to investigate it the only way they know how. 1
5. Most of what we know comes from bycatch
This is a mixed blessing for a lot of shark species. The mix, unfortunately, is heavily skewed toward the destruction of the species involved, as well over 100,000,000 sharks are killed by by-catch each year.
But the hundreds of crocodile sharks that show up in tuna fishing boats bring us plenty of specimens to study, and for deep-sea species, this is quite exciting. It’s also quite important to figure out how to protect them.
Researchers commonly use fisheries to get their samples, and for the crocodile shark, this means visiting a tuna and swordfish longline fishery in the West Atlantic.
The tragedy of dragging hundreds of crocodile sharks out of the ocean as fishing waste means there are enough specimens of every age and reproductive stage to investigate.
Sexual maturity is attained when a crocodile shark reaches 80cm for males and 92cm for females.
The size at birth is around 42cm. It looks as though they don’t reproduce seasonally, and that mating happens over extended periods. Females give birth to around 4 pups during each cycle, if they can avoid the fishing boats.
This is a low rate of reproduction for a shark, suggesting that they are particularly vulnerable to fishing. 2
6. The babies have a weird breakfast
Crocodile sharks give birth to live young, but they don’t grow a placenta. Instead, the first meal that the young will come across will be the remaining eggs from their mother. This brutal battle royale occurs before they’re even born, and helps the surviving pups develop to full term.
There will usually only be four pups in a litter, presumably because they keep eating one another. After being born, they will likely be immediately independent and already well-trained predators.
7. Their taxonomy is still being ironed out
This almost goes without saying when it comes to deep-sea sharks. Again, little is known about these animals other than what has been gleaned from dead samples at fish markets.
It was once thought they were an elusive species of the Sand tiger shark, of which there is only one genus remaining. Then, it was thought to be a sand shark.
Currently, it’s been given its own family of “pseudo sand tiger sharks”, or Pseudocarcharias.
8. They have enormous livers
This is actually relatively common in sharks, and the reason that orcas will punt a hole in a great white and steal their livers.
The livers of crocodile sharks are particularly fatty, and this is an adaptation to having to deal with buoyancy. Liver oil acts in much the same way as a swim bladder does in bony fishes: by providing a much-needed floatation device inside the fish, allowing it to move up and down in the water column.
In crocodile sharks, the liver makes up around 20% of its body weight and may be used not only as a way of vertically migrating but as a way of remaining neutrally buoyant without using any energy. 3
8. One was found washed up on a Devon beach in the UK
While the shark is typically found in tropical waters around the equator, incredily a UK family found one washed up on the British coast.
One theory is that it followed a warm deep water current, before reaching colder waters where it couldn’t survive. Another is it was caught as bycatch in warmer waters, and discarded closer to British shores. 4
Crocodile Shark Fact-File Summary
Fact Sources & References
- Lionel Carter (2009), “Submarine cables and the oceans: Connecting the world”, Research Gate.
- P. Oliveira (2010), “Reproductive biology of the crocodile shark Pseudocarcharias kamoharai”, Wiley Online Library.
- “Biology of the Crocodile Shark (Pseudocarcharias kamoharai)”, Elasmo Research.
- Steven Morris (2017), “Crocodile shark washes up on Devon beach“, The Guardian.