An oceanic deep-water shark with jaws like a crocodile
The Crocodile shark (Pseudocarcharias kamoharai) is a species of shark and the only extant member of the family Pseudocarchariidae. The Crocodile shark can be found worldwide in tropical waters from the surface to a depth of 1,938 feet in the mesopelagic zone. It performs a diel vertical migration, more than likely staying below a depth of 660 feet during the day and ascending into shallower water at night to feed. The Crocodile shark is the smallest living Mackerel shark. It can be distinguished by its elongated cigar-shaped body, extremely large eyes, relatively small fins, and distinctive long and slender teeth within protrusible jaws.
Family: Pseudocarchariidae – Crocodile Sharks
Common Name– Mackerel Sharks
Common Name– Crocodile Sharks
Status: IUCN Red List LEAST CONCERN
Average Size and Length: They are born around 41 cm/1.3 feet. Mature males have been measured at 74 cm/2.4 feet. Mature females have been measured from 90-110 cm/3-3.6 feet. The maximum recorded has been 3.6 feet. This is the smallest Mackerel shark.
Average Weight: They have been recorded anywhere from 9-13 pounds.
Current Rare Mythical Sightings: The Crocodile shark earned its name for its long and sharp teeth, and habit of snapping vigorously when taken out of the water. Its Latin name means “water crocodile”.
The Crocodile shark was first described as Carcharias kamoharai in a 1936 issue of Zoological Magazine (Tokyo) by ichthyologist Kiyomatsu Matsubara, based on a 73.5 cm/28.9-inch-long specimen found at the Koti Fish Market in Japan. The type specimen is a 3.3-foot-long adult male found at a fish market in Su-ao, Taiwan.
After being shuffled between the genera Carcharias and Odontaspis in the family Odontaspididae by various authors, in 1973 Leonard Compagno resurrected Jean Cadenat’s 1963 subgenus Pseudocarcharias from synonymy for this species and placed it within its own family.The morphology of the Crocodile shark suggests affinity with the Megamouth shark (Megachasmidae), Basking shark (Cetorhinidae), Thresher sharks (Alopiidae), and Mackerel sharks (Lamnidae).
Fossil Pseudocarcharias teeth dating to the Serravallian age (13.6–11.6 Ma) of the Miocene epoch have been found in Italy, and are identical to those of the modern-day Crocodile shark.
Teeth and Jaw: They have prominent long and slender teeth on a protrusible jaw. Research suggests that there are fewer than 30 tooth rows in either jaw; in the upper jaw, the first two large teeth are separated from the lateral teeth by a row of small intermediate teeth.
Head: The snout is pointed and somewhat bulbous. The eyes are very large and without nictitating membranes. The eyes have a reflective green or yellow retina and do not have an expanded iris.
Denticles: The dermal denticles are small, with a flattened crown having small ridges and backward-pointing cusps.
Tail: The caudal fin is asymmetrical with a moderately long upper lobe. The caudal peduncle is slightly compressed with weak lateral keels. It is a strong, large and muscular tail that suggests it is a strong, fast and active swimmer.
Demographic, Distribution, Habitat, Environment and Range: The Crocodile shark is an oceanic shark found worldwide in tropical waters. In the Atlantic Ocean, it has been recorded off Brazil, Cape Verde, Guinea-Bissau, Guinea, Angola, South Africa, and Saint Helena Island. In the Indian Ocean, it occurs in the Mozambique Channel and possibly the Agulhas Current and the Bay of Bengal. In the Pacific, it has been recorded from Japan, Taiwan, and the Korean Peninsula in the northwest, southward to Indonesia, Australia, and New Zealand, and eastward to the western coast of the Americas from Baja California to Chile, including the Marshall, Phoenix, Palmyra, Johnston, Marquesas, Line, and Hawaiian Islands. In New Zealand the Crocodile shark has been recorded at the Three Kings Ridge, off the coast of Northland and on the northern Kermadec Ridge. They are usually found far from land and well offshore. The average sea surface temperature is 68 °F. They can be found from the surface to at least 1,938 feet, ranging from the pelagic to the mesopelagic zone. Research suggests that they perform a diel vertical migration. They stay deeper by day (more than likely below 660 feet), and migrate vertically to the surface at night to feed.
The Crocodile shark has been found stranded on the beaches of South Africa, possibly after being stunned by upwellings of cold water. In March 2017, one Crocodile shark washed ashore dead off the coast of Devon, England in Hope Cove, the first ever seen off the coasts of the United Kingdom. Currently, it remains unknown as to why this shark was present so far north of its normal range.
Diet: More than likely they feed on pelagic bony fishes, squid and shrimp.
Ram-Suction Index: Its jaws are protrusible, with long needle-like teeth, and an active stealthy swimmer suggests that the Crocodile shark is high on the ram side of the RSI.
Aesthetic Identification: The Crocodile shark is grey to grey-brown dorsally. And lighter ventrally. On occasion there are a few dark blotches on the sides and belly with sometimes a white blotch between the corner of the mouth and the first gill slit. They have light edged fins. They have a very small, spindle-shaped, and slender body with small fins and long gill slits. The pectoral fins are small, broad and rounded. The pelvic fins are nearly as large as the pectoral fins. The first dorsal fin is small, low and angular; the second dorsal fin is smaller than the first but larger than the anal fin.
Biology and Reproduction: The Crocodile shark is ovoviviparous, having 4 pus per litter. The pups feed on the unfertilized eggs, or oophagy and possibly engage in intrauterine cannibalism. Research suggests the gestation period may be long.
The embryos have yolk sacs at 3–4 cm (1.2–1.6 in) long. Once the yolk sac is fully absorbed, they become oophagous: the mother produces large numbers of thin-walled egg capsules that contain 2–9 eggs each, which are then consumed by the unborn embryos. The abdomens of the embryos become characteristically distended with ingested yolk material, which can make up a quarter of the embryo’s total weight. It is unclear how two crocodile shark fetuses manage to share a single uterus (Fujita, K. (May 1981). “Oviphagous embryos of the pseudocarchariid shark, Pseudocarcharias kamoharai, from the central Pacific“. Japanese Journal of Ichthyology. 28 (1): 37–44.).
Males reach sexual maturity between 74–110 cm/2.4-3.6 feet and females between 89–102 cm/2.9-3.3 feet.
The Crocodile shark has a sizable squalene-rich, oily liver that allows it to maintain neutral buoyancy and its position in the water column with minimal effort.
More recent phylogenetic analyses, based on mitochondrial DNA, have suggested that the Crocodile shark is closely related to either the Megamouth shark or the Sandtiger sharks (Odontaspididae). Alternately, analysis based on dentition suggests that the closest relatives of the Crocodile shark are the Thresher sharks, followed by the Mackerel sharks.
Behavioral Traits, Sensing and Intelligence: The size and structure of its eyes suggests that it is adapted for hunting at night. They more than likely rely on sight to hunt, even picking out bioluminescent silhouettes against a black background.
It is possibly that the Crocodile shark may breach in pursuit of prey.
Speed: More than likely they are strong, active swimmers. Its tail would suggest it is also quite fast, snatching unnoticing prey.
Crocodile Shark Future and Conservation: They were considered near threatened. The population has depleted significantly and more than likely due to bycatch of pelagic longline fisheries. It is of little importance to commercial fisheries. The largest numbers are caught by the Japanese yellowfin tuna fishery and the Australian swordfish fishery, both operating in the Indian Ocean. They are also sometimes caught on squid jigs and in tuna gillnets. It is usually discarded due to its small size and low-quality meat. Today, their population trend is increasing and they are of least concern.
The Crocodile shark was responsible for damaging deep sea fiberoptic cables when the technology was first deployed in September, 1985. These cables were installed by AT&T between Gran Canaria and Tenerife in the Canary Islands. The system suffered a series of shorts that necessitated costly repairs. More than likely, the Crocodile shark was attracted to the electrical field around the cables. The problem was solved by protecting the cables with a layer of steel tape beneath a dense polyethylene coating.
Crocodile Shark Recorded Attacks on Humans: It is small, and oceanic and poses little threat to humans. Although, it has powerful jaws, so one should exercise caution.