Sawfish

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Sawfishes
Smalltooth sawfish, Pristis pectinata
Smalltooth sawfish, Pristis pectinata
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Superorder: Batoidea
Order: Pristiformes
Family: Pristidae
Genera

Anoxypristis
Pristis
See text for species.
For other uses, see Sawfish (disambiguation).

Sawfishes are a family of marine animals related to sharks and rays. Their most striking appearance is a long, toothy snout. They are members of the sole family Pristidae within the order Pristiformes, from the Greek pristēs meaning "a sawyer" or "a saw".

They are not to be confused with sawsharks (order Pristiophoriformes), which have a similar physical appearance.

All species of sawfish are considered critically endangered and international trade is banned.[2]

Contents

[edit] Description

The most eye-catching feature of the sawfish is their saw-like snout, called a rostrum. The rostrum is covered with motion- and electro-sensitive pores that allow sawfish to detect movement and even heartbeats of buried prey in the ocean floor. The rostrum acts like a metal detector as the sawfish hovers over the bottom, looking for hidden food. It is also used as a digging tool to unearth buried crustaceans. When a suitable prey swims by, the normally lethargic sawfish will spring from the bottom and slash at it furiously with its saw. This generally stuns or injures the prey sufficiently for the sawfish to devour it without much resistance. Sawfishes have also been known to defend themselves with their rostrum, against predators (like sharks) and intruding divers. The "teeth" protruding from the rostrum are not real teeth, but modified denticle scales. (The scales of a sawfish have a similar structure to its teeth, confusing the distinction somewhat.)

A plate sketching of a sawfish.
A plate sketching of a sawfish.

The body and head of a sawfish is flat as they spend most of their time lying on the sea floor. Like rays, the sawfish's mouth and nares are located on its flat underside. The mouth is lined with small, dome-shaped teeth for eating small fish and crustaceans; though sometimes the fish swallows them whole. Sawfishes breathe with two spiracles just behind the eyes that draw water to the gills. The skin is covered with tiny dermal denticles (skin-teeth) that gives the fish a rough texture. Sawfishes are usually light grey or brown; the smalltooth sawfish, Pristis pectinata, appears olive green.

Like other elasmobranchs, sawfishes lack a swim bladder and use a large, oil-filled liver instead to keep them buoyant. Their skeleton is made of cartilage.

The eyes of 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 1.4 m (4.6 foot) dwarf sawfish, Pristis clavata, a species much smaller than most other sawfish. The largest species seem to be the largetooth sawfish, Pristis microdon and the southern sawfish, Pristis perotteti, both of which can exceed 7 m (23 feet) in length. One southern sawfish, whose length for some reason went unmeasured, was said to have weighed 2,455 kg (5,400 lb).[citation needed]

[edit] Distribution and habitat

Sawfish are found in tropical and sub-tropical areas around Africa and Australia and in the Caribbean, and frequently ascend far into rivers. They are also found in bays and estuaries.

Sawfish live only in shallow, muddy water and can be found in both freshwater and saltwater. Most prefer river mouths and freshwater systems. All sawfish have the ability to traverse between fresh and saltwater, and often do so.

[edit] Behavior

Sawfish are nocturnal, usually sleeping during the day, hunting at night. Despite fearsome appearances, they are gentle fishes and will not attack humans 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 United States and Australia.

[edit] Reproduction

Little is known about the reproduction habits of the sawfish. Each individual lives around 25 to 30 years, and matures at 10 years.

Females give live birth to pups, whose semi-hardened rostrum is covered with a rubbery envelope. This prevents the pup from injuring its mother during birth. The rubbery envelope eventually disintegrates and falls off.

The sawfish is estimated to mate once every two years, with an average litter of around eight pups. They mature slowly - it is estimated that they don't reproduce until they're 3.5 to 4 meters long and 10 to 12 years old - and reproduce at immensely lower rates than most fish do. This makes the animals especially slow to recover from overfishing.[3]

[edit] Species

[edit] Conservation

Sawfish seen from below, inside an underwater tunnel at Atlantis Paradise Island, Nassau, Bahamas.
Sawfish seen from below, inside an underwater tunnel at Atlantis Paradise Island, Nassau, Bahamas.

All species of sawfish are considered critically endangered. As well as being accidentally caught in fishing nets sawfish are also hunted for their rostrum (which is prized as a curiosity by some), their fins (which are eaten as a delicacy), their liver oil and for use as medicine.

It is illegal to capture Sawfish 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. However, due to the fact that most rostra on the American market are from the smalltooth sawfish and very few laymen can differentiate the species from which the rostra originated, it is therefore generally advised not to purchase sawfish rostra at all.

Habitat destruction is another threat to sawfish conservation.

Sawfishes are difficult to conserve in aquaria because it appears they may require a blend of saltwater and freshwater to stay healthy. However, the amount and duration of exposure are uncertain.

As of June 2007 the international trade of sawfish has been banned by the CITES convention.[4] An exception is made to Australia to export live specimens for use in aquaria. It is believed that exhibiting sawfish will raise awareness and therefore help with conservation. Some feel Australia requested this right for financial motives and that it will be detrimental for the survival of sawfish.[2]

[edit] Cultural perception

Sawfish became a powerful symbol in many cultures. Aztecs revered sawfish as an "Earth monster." Its rostrum is used by some Asian shamans for exorcisms and other ceremonies to repel demons and disease, which has contributed to its demise.[3]

[edit] References

Wikimedia Commons has media related to:
  1. ^ 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 June 2007
  2. ^ a b BBC NEWS | Science/Nature | Sawfish protection acquires teeth
  3. ^ a b Raloff, Janet (2007). Hammered Saws, Science News vol. 172, pp. 90-92.
  4. ^ (3-15 June 2007) "Convention on International Trade in Endangered Species of Wild Fauna and Flora".: CoP14 Prop. 17, The Hague: Fourteenth meeting of the Conference of the Parties. 
v • d • e
Extant chondrichthyes orders by superorder
Kingdom: Animalia · Phylum: Chordata · Subphylum: Vertebrata · Infraphylum: Gnathostomata
Batoidea
Rajiformes · Pristiformes · Torpediniformes
Selachimorpha
Holocephali