Product Code Database
The crocodile shark ( Pseudocarcharias kamoharai) is a species of Lamniformes and the only extant taxon member of the family Pseudocarchariidae. A specialized inhabitant of the mesopelagic zone, the crocodile shark can be found worldwide in tropical waters from the surface to a depth of . It performs a diel vertical migration, staying below a depth of during the day and ascending into shallower water at night to feed. Typically measuring only in length, the crocodile shark is the smallest living Lamniformes. It can be distinguished by its elongated cigar-shaped body, extremely large eyes, and relatively small fins.
An active-swimming predator of pelagic , squid and shrimp, the crocodile shark has a sizable oily liver that allows it to maintain its position in the water column with minimal effort. The size and structure of its eyes suggests that it is adaptation for hunting at night. The crocodile shark is aplacental viviparous, with females typically giving birth to litters of four. The are oophagy, meaning that they feed on undeveloped eggs ovulation for this purpose by their mother. Due to its small size, the crocodile shark poses little danger to humans and is of little commercial importance. This species was responsible for damaging deep sea fiberoptic cables when the technology was first deployed in 1985.
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.Martin, R.A. Pseudocarchariidae. ReefQuest Centre for Shark Research. Retrieved on December 24, 2008. The morphology of the crocodile shark suggests affinity with the megamouth shark (Megachasmidae), basking shark (Cetorhinidae), (Alopiidae), and Lamnidae (Lamnidae). More recent phylogenetic analyses, based on mitochondrial DNA, have suggested that the crocodile shark is closely related to either the megamouth shark or the (Odontaspididae). Alternately, analysis based on dentition suggests that the closest relatives of the crocodile shark are the thresher sharks, followed by the mackerel sharks. Fossil Pseudocarcharias teeth dating to the Serravallian age (13.6–11.6 Ma) of the Miocene geological epoch have been found in Italy, and are identical to those of the modern-day crocodile shark.
The are small, broad, and rounded. The are nearly as large as the pectorals. The first dorsal fin is small, low and angular; the second dorsal fin is smaller than the first but larger than the anal fin. The caudal fin is asymmetrical with a moderately long upper lobe. The caudal peduncle is slightly compressed with weak lateral keels. The are small, with a flattened crown bearing small ridges and backward-pointing cusps It is dark brown above and paler below, sometimes with a few dark blotches on the sides and belly and/or a white blotch between the corner of the mouth and the first gill slit. The fins have thin translucent to white margins.Martin, R.A. Biology of the Crocodile Shark ( Pseudocarcharias kamoharai). ReefQuest Centre for Shark Research. Retrieved on December 24, 2008. The crocodile shark grows to a maximum length of . Most individuals are long and weigh .
From distribution records, the crocodile shark's range seems to be bound by the 37°N and 44°S, where the average sea surface temperature is . This species is not evenly distributed but is rather locally abundant in certain areas, suggesting that it is not strongly fish migration. The crocodile shark is usually found in the pelagic zone from the surface to a depth of . It is occasionally encountered inshore near the bottom and has been known to strand on the beaches of South Africa, possibly after being stunned by upwellings of cold water.Compagno, L.J.V. (2025). 9789251045435, Food and Agriculture Organization of the United Nations. ISBN 9789251045435 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. Thus far, it remains unknown as to why this particular shark was present so far north of its normal range.
The large eyes of the crocodile shark, equipped with a reflective green or yellow retina and lacking an expanded iris, suggest that it is a nocturnal hunter that relies on sight to pick out the silhouettes or bioluminescence of its prey. Little is known of the crocodile shark's feeding habits; it is thought to be an active, fast-swimming predator based on its strong musculature, large tail, and behavior when captured. On one occasion, a crocodile shark off Cape Point, South Africa, jumped out of the water in pursuit of bait. Its diet consists of small to medium-sized (including and ), squid (including Onychoteuthidae, Mastigoteuthidae, Pholidoteuthidae, and Cranchiidae) and shrimp. Crocodile sharks are not known to be preyed upon by any other species.
The crocodile shark is aplacental viviparous and typically gives birth to litters of four, two pups to each uterus. The gestation period is unknown but believed to be long. The have at long; once the yolk sac is fully absorbed they become oophagy: 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 manage to share a single uterus, when in some other oophagous mackerel sharks such as the sand tiger shark ( Carcharias taurus), only one fetus survives in each uterus. The pups are born at approximately long; males attain maturity at and females at . There is no defined reproductive season.
After AT&T installed the first deep sea fiberoptic cables between Gran Canaria and Tenerife in the Canary Islands in September 1985, the system suffered a series of shorts that necessitated costly repairs. It was discovered that attacks from the crocodile shark were responsible for most of the failures, possibly because they were attracted to the electric field around the cables. Since crocodile sharks are not benthic in nature, they were presumably biting the cables as they were being deployed. The problem was solved by protecting the cables with a layer of steel tape beneath a dense polyethylene coating.
|
|
