Knifetooth sawfish

Knifetooth sawfish
Temporal range: 56–0 Ma
Eocene to Present[1]
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Order: Pristiformes
Family: Pristidae
Genus: Anoxypristis
Species: A. cuspidata
Binomial name
Anoxypristis cuspidata
(Latham, 1794)
Synonyms

Pristis cuspidatus

The knifetooth sawfish (Anoxypristis cuspidata), also known as the pointed sawfish or narrow sawfish, is a species of sawfish in the family Pristidae, part of the Batoidea, a superorder of cartilaginous fish that includes the rays and skates. The sawfishes are characterised by the long, narrow, flattened rostrum or extension on their snout. This is lined with sharp transverse teeth, arranged in a way that resembles the teeth of a saw. It is found in the shallow coastal waters and estuaries of the Indo-West Pacific, ranging from the Red Sea and the Persian Gulf to southern Japan, Papua New Guinea and northern Australia. It is the only living member of the genus Anoxypristis, but was previously included in the genus Pristis. Compared to that genus, Anoxypristis has a narrower rostral saw with numerous teeth on the distal part and no teeth on the basal one-quarter (toothless section about one-sixth in juveniles).[3] This endangered species reaches a length of up to 3.5 metres (11 ft).[4]

In addition to the living Anoxypristis cuspidata, this genus includes a few extinct species that only known from fossil remains.[5][6]

Description

The knifetooth sawfish grows to a maximum length of about 3.5 metres (11 ft), although there are highly questionable and unconfirmed claims of much larger individuals.[4] Its body is generally shark-like but its most obvious feature is the flattened head which is extended forward in a blade-like bony snout with, in Australian waters, 18 to 22 pairs of sideways-facing teeth, though elsewhere there may be as many as 25.[4] These teeth are short and flat and are roughly triangular in shape. The blade does not taper towards its point and in adults the basal one-quarter is devoid of teeth. In juveniles about one-sixth of the base is toothless.[3] The nostrils are narrow and partially concealed by nasal flaps. The skin of young sawfish is smooth but on older individuals it is sparsely covered in dermal denticles.[7] The dorsal (upper) side of the fish is greyish and the ventral (lower) side a rather paler grey colour and the fins are also pale. The rostrum is grey with white teeth and sometimes has a chocolate-brown base portion.[4]

Distribution and habitat

The knifetooth sawfish is distributed across a broad swathe of the Indo-Pacific Ocean. At its westernmost extreme, it is present in the Gulf of Arabia and may extend as far as Somalia. It is present in the waters off Iran, India, Sri Lanka, Bangladesh, Malaysia, Burma, Indonesia and Papua New Guinea. Its northernmost limit is the Gulf of Chihli, China, South Korea and the most southerly parts of Japan and its southern limit is the northern Australian states of Western Australia, Northern Territory and Queensland. This is a bentho-pelagic fish which is found at depths down to about 40 metres (130 ft). It tolerates low salinity levels and is found in inshore waters including bays and estuaries.[2]

Behaviour

The knifetooth sawfish feeds on small fish, squid and invertebrates such as crabs and shrimps. It uses its rostrum in a side-to-side thrashing action to stir up the sediment and uncover concealed prey and also among schools of fish to incapacitate or stun individual fish. It is itself prey to various sharks such as the hammerhead shark (Sphyrna spp.), the bull shark (Carcharhinus leucas) and the copper shark (Carcharhinus brachyurus) and also the saltwater crocodile (Crocodylus porosus).[4]

The breeding behaviour of the knifetooth sawfish has been little studied. Fertilisation is internal and a number of young develop at one time in the oviduct, each one being nourished from a yolk sac. They are born, probably after a gestational period of about five months, and litter sizes of 6 to 23 young have been recorded. The pups are probably 0.5 to 0.8 metres (1 ft 8 in to 2 ft 7 in) long at birth and their rostral teeth are not fully developed, being covered by a membrane, and this prevents them from damaging the mother's tissues.[4]

Status

Pregnant females and juvenile knifetooth sawfish are particularly susceptible to entrapment in fishing gear and this is the major threat faced by this fish. Overfishing and habitat degradation through urbanisation of the coastline also put this species at risk and the population trend is downward. For these reasons, the IUCN have listed this fish as "Endangered" in its Red List of Threatened Species.[2]

See also

References

  1. ↑ Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (Chondrichthyes entry)". Bulletins of American Paleontology. 364: 560. Archived from the original on 2011-09-30. Retrieved 2008-01-09.
  2. 1 2 3 D'Anastasi, B.; Simpfendorfer, C. & van Herwerden, L. (2013). "Anoxypristis cuspidata". The IUCN Red List of Threatened Species. IUCN. 2013: e.T39389A18620409. doi:10.2305/IUCN.UK.2013-1.RLTS.T39389A18620409.en. Retrieved 3 January 2018.
  3. 1 2 Marine Fisheries Service; National Oceanic and Atmospheric Administration (12 December 2014). "Endangered and Threatened Wildlife and Plants; Final Endangered Listing of Five Species of Sawfish Under the Endangered Species Act". Federal Register. pp. 73977–74005. Retrieved 17 November 2017.
  4. 1 2 3 4 5 6 "Knifetooth sawfish". Ichthyology. Florida Museum of Natural History. Retrieved 2013-09-24.
  5. ↑ Wueringer, B.E.; L. Squire Jr. & Collin, S.P. (2009). "The biology of extinct and extant sawfish (Batoidea: Sclerorhynchidae and Pristidae)". Rev Fish Biol Fisheries. 19: 445–464. doi:10.1007/s11160-009-9112-7.
  6. ↑ "Introduction". Fossil Sawfish. Retrieved 29 November 2017.
  7. ↑ Sa-a, Pascualita. " Anoxypristis cuspidata (Latham, 1794): Pointed sawfish". FishBase. Retrieved 2013-09-24.
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