| Sawfishes Temporal range: Upper Cretaceous–Recent | |
|---|---|
 | |
| Smalltooth sawfish (Pristis pectinata) | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Superorder: | Batoidea |
| Order: | Pristiformes |
| Family: | Pristidae Bonaparte, 1838 |
| Genera | |
| Anoxypristis Pristis | |
Sawfish, also known as the Carpenter Shark, are a family of rays, characterized by a long, toothy nose extension snout. Several species can grow to approximately 7 metres or 23 feet.[2][3][4] The family as a whole is largely unknown and little studied. They are members of the sole living family Pristidae within the order Pristiformes, from the Ancient Greek pristēs (πρίστης) meaning "a sawyer" or "a saw".
They are not to be confused with sawsharks (order Pristiophoriformes), which have a similar appearance.
All species of sawfish are considered Critically Endangered by the IUCN,[5] and the only legal international trade involves live Pristis microdon to appropriate aquaria for primarily conservation purposes.[6]
Description
The sawfish's most distinctive feature is the saw-like rostrum. The rostrum is covered with sensitive pores that allow the sawfish to detect movement of prey hiding under the ocean floor. The rostrum serves as a digging tool to unearth buried crustaceans. When a suitable prey swims by, the normally lethargic sawfish springs from the bottom and slashes at it with its saw. This generally stuns or injures the prey sufficiently for the sawfish to devour it. Sawfish also defend themselves with their rostrum, against intruding divers and predators such as sharks. The "teeth" protruding from the rostrum are not real teeth, but modified tooth-like structures called denticles.
The body and head of a sawfish are flat, and they spend most of their time lying on the sea floor. Like rays, sawfish's mouth and nostrils are on their flat undersides. The mouth is lined with small, dome-shaped teeth for eating small fish and crustaceans; sometimes the fish swallows them whole. Sawfish breathe with two spiracles just behind the eyes that draw water to the gills. The skin is covered with tiny dermal denticles that gives the fish a rough texture. Sawfish are usually light grey or brown; the smalltooth sawfish, Pristis pectinata, appears olive green.
Like other elasmobranchs, sawfish lack a swim bladder and use a large, oil-filled liver to control buoyancy. Their skeleton is made of cartilage.
The eyes of the sawfish are undeveloped due to their muddy habitat. The rostrum is the main sensory device.
The intestines are shaped like a corkscrew, called a spiral-valve.
The smallest sawfish is the dwarf sawfish (P. clavata), which can be as long as 1.4 metres (4.6 ft),[7] much smaller than the others. The largest species seem to be the largetooth sawfish (P. microdon), the Leichhardt's sawfish (P. perotteti), and the common sawfish (P. pristis), which all can reach approximately 7 m (23 ft) in length.[2][3][4] One southern sawfish was recorded as weighing 2.455 tonnes (5,410 lb).[8]
Distribution and habitat
Sawfish are found in tropical and sub-tropical areas in the Atlantic and Indo-Pacific. They inhabit coastal areas such as bays and estuaries, but frequently penetrate far into rivers and major lakes such as Lake Nicaragua.
Sawfish live only in shallow, muddy water and can be found in both freshwater and saltwater. All sawfish have the ability to traverse between fresh and saltwater.
Behavior
Sawfish are nocturnal, usually sleeping during the day, hunting at night. Despite fearsome appearances, they do not attack people unless provoked or surprised. The smalltooth sawfish is well known by fishermen as a prize game fish because of the fight it puts up once hooked. Capturing sawfish is illegal in the USA and Australia.
Reproduction
Little is known about the reproduction habits of the sawfish. They reach sexual maturity at 10 years (at least in species where data is available).
The sawfish is estimated to mate once every two years, with an average litter of around eight. They mature very slowly; it is estimated that the larger species do not reach sexual maturity until they are 3.5 to 4 metres (11 to 13 ft) long and 10 to 12 years old. They reproduce at lower rates than most fish. This makes the animals especially slow to recover from overfishing.[9]
Females are viviparous, bearing live pups, whose semi-hardened rostrum is covered with a membrane. This prevents the pup from injuring its mother during birth. The membrane eventually disintegrates and falls off.
Taxonomy and species
The sawfish has seven species in two genera.[1] This scheme has been described as chaotic,[10] possibly omitting undescribed species including synonyms remains. The Pristis pristis species complex, which also includes P. microdon and P. perotteti, is in need of a taxonomic review.
Family Pristidae Bonaparte, 1838
- Genus Anoxypristis E. I. White and Moy-Thomas, 1941
- Anoxypristis cuspidata (Latham, 1794) (Knifetooth sawfish)
- Also known as the narrow or pointed sawfish. Lives in muddy areas of the Indo-West Pacific. Appears grey. Has been included in the genus Pristis, but has a narrower rostral saw with numerous teeth on the distal part and no teeth in the quarter nearest the head.
- Anoxypristis cuspidata (Latham, 1794) (Knifetooth sawfish)
- Genus Pristis H. F. Linck, 1790
- Pristis clavata Garman, 1906 (Dwarf sawfish)
- Also known as the Queensland sawfish. Inhabits muddy bays and estuaries along the northern coast of Australia. Relatively small, reaching only around 1.4 m (4.6 ft).
- Pristis microdon Latham, 1794 (Leichhardt's sawfish)
- Also known as the Largetooth sawfish (however this can lead to confusion with P. perotteti when the two are considered to be separate species) or Freshwater sawfish. Typically restricted to coastal regions of the Indo-Pacific, but has sometimes been considered synonymous with P. perotteti, and uncertainty exists over what species the scientific name P. microdon really belongs to, since the original description lacked a type locality.
- Pristis pectinata Latham, 1794 (Smalltooth sawfish)
- Also known as the wide sawfish. Appears green or bluish-grey. Restricted to coastal parts of the Atlantic Ocean, including the Mediterranean. Reports from elsewhere are believed to be misidentifications.[11]
- Pristis perotteti J. P. Müller & Henle, 1841 (Large-tooth sawfish)
- Typically restricted to coastal parts of the tropical and subtropical Atlantic and east Pacific, but with records far inland (e.g., Santarém and Lake Nicaragua). See P. microdon.
- Pristis pristis (Linnaeus, 1758) (Common sawfish)
- Lives in the coastal parts of the tropical and subtropical Atlantic, Mediterranean, eastern Pacific and in northern Australia. As suggested by its name, once plentiful, but has declined drastically along with the other sawfishes.
- Pristis zijsron Bleeker, 1851 (Longcomb sawfish)
- Found in the Indo-West Pacific. Prefers muddy bays and estuaries.
Conservation
While fins from many shark species are utilized in the trade, certain shark species have been identified over the centuries as supplying the tastiest and most succulent fins. The shark-like rays (the sawfishes and shovelnose rays) supply the highest quality fin. As observed by one of the leading treatises on shark trade, "The ... fins ... from the white-spotted guitarfish [Rhynchobatus spp.] are considered to be most valuable. The preferred shark species for fins are tiger, mako, sawfish, sandbar, bull, hammerhead, blacktip, porbeagle, thresher and blue shark."[12] The fins from the critically endangered sawfishes "are highly favored in Asian markets and are some of the most valuable shark fins."[13] Sawfishes are now protected under the highest protection level of the Convention on International Trade in Endangered Species (CITES), Appendix I,[14] but given the great volume of the shark fin trade, and that detached shark fins are difficult to identify, it is unlikely that CITES protection will prevent sawfish fins from entering the trade.
Capturing sawfish is illegal in the United States and in Australia. The sale of smalltooth sawfish rostra is also prohibited in the United States under the Endangered Species Act (ESA); the sale of other sawfish rostra remains legal.[citation needed] However, most rostra on the American market are from the smalltooth sawfish, partly because few laymen can differentiate the species from which the rostra originated.
Habitat destruction is another threat to sawfish.
While popular in public aquaria, sawfishes are difficult to maintain because of their size. They likely require a variety of habitats, including both seawater and freshwater to complete their life cycle. Consequently, captive breeding has resulted in very little success, so far limited to a single species (P. pectinata)[15] at a single aquarium (Atlantis Paradise Island).[16]
The international trade of sawfish was banned by the CITES convention in June 2007.[17] At the 14th CITES Conference the Australian delegation proposed an annotation to all species from the family Pristidae to Appendix I. The annotation was supported by the required two-thirds majority, and allowed P. microdon to be treated as Appendix II “for the exclusive purpose of allowing international trade in live animals to appropriate and acceptable aquaria for primarily conservation purposes.”[6] The annotation was accepted on the basis that Australian populations of P. microdon are robust relative to other populations in the species' range; and that the capture of individuals for aquaria is likely to be detrimental to the population in any other country than Australia. All trade must be accompanied by an agreement between the exporter, importer and the Australian CITES Management Authority ensuring that the receiving aquarium has the capacity to house and care for the animal and that display is accompanied by comprehensive educational material. Since the implementation of the annotation, a sawfish research association has been established in northern Australia to facilitate accelerated research effort in P. microdon and other euryhaline elasmobranchs in rivers that drain to the Gulf of Carpentaria.
Source: http://wikipedia.org
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