Did you know that there is a crocodile shark? Despite its name (due to its teeth) it is a small shark (just 3.3 ft -1 m- long) that is not considered dangerous to humans –  except if captured (it fights vigorously and snaps strongly) or in vicinity of deep-sea communications cables (the before-mentioned AT&T cables were repeatedly damaged by its bites).

Pseudocarcharias kamoharai.jpg
By NOAA Observer Program, Public Domain

Which is odd, since the crocodile shark doesn’t live at the bottom of the sea (where the cables were placed), but can be found from the surface to a depth of 1,940 ft -590 m- in tropical waters all over the world. It has a very large oily liver (up to 20% of its total weight), which provides near neutral buoyancy and allows it to hover to preserve energy while waiting on its prey. Then it has to swim fast to actively catch small bony fishes, shrimp and squid, it even jumped out of the water once in pursuit of bait. The crocodile shark may be a vertical migrator, ascending near the surface at night and returning to the depths before dawn. It has very large eyes, equipped with a reflective green or yellow retina and lacking a nictating membrane (protective third eyelid) and an expanded iris, which suggests that it is a visual hunter despite the dark environment.

Male crocodile sharks mature at a length of about 29 in – 74 cm -, females at 35 in – 89 cm. They are ovoviviparous, where four 16 in -40 cm- long pups are usually born per litter, two per uterus. The embryos are oophagous, meaning that they feed first off a yolk sac and later use undeveloped eggs ovulated for this purpose by their mother. They replenish their yolk sac, too, which can make up a quarter of the embryo’s total weight.

Due to its small size, the crocodile shark is of little commercial importance (perhaps in the future for the squalene in its large liver). However, substantial numbers are caught as bycatch even now, leading it to be assessed as Near Threatened by the IUCN.

Sources: here and here

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