Sawfish

Sawfishes Fossil range: Upper Cretaceous–Recent PreЄ Є O S D C P T J K Pg N [1]
Smalltooth sawfish, Pristis pectinataLargetooth sawfish, "Pristis microdon"
Conservation status
Critically Endangered (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Superorder:	Batoidea
Order:	Pristiformes
Family:	Pristidae
Genera
Anoxypristis Pristis

Sawfishes (or carpenter sharks) are a family of marine animals related to rays. Their most stunning attribute is a long, toothy snout. Several species can attain massive sizes (up to approximately 7 metres or 23 ft),^[2][3][4] but 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 Greek pristēs (πρίστης) meaning "a sawyer" or "a saw". The sawfishes are part of the ray family even though they look more like sharks than typical rays.

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

All species of sawfishes 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 most eye-catching feature of a sawfish is the saw-like 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 as the sawfish hovers over the bottom. 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. Sawfish have also been known to defend themselves with their rostrum, against predators such as sharks, and against intruding divers. The "teeth" protruding from the rostrum are not real teeth, but modified tooth-like structures called denticles.

A plate sketching of a sawfish

The body and head of a sawfish are flat, and they spend most of their time lying on the sea floor. Like rays, the mouth and nostrils of sawfishes are located on their flat undersides. 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 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 the sawfishes 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 metres (4.6 ft) dwarf sawfish (P. clavata),^[7] a species much smaller than the other sawfishes. The largest species seem to be the largetooth sawfish (P. microdon), the southern 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, whose length for some reason went unmeasured, was said to have weighed 2.455 tonnes (5,410 lb).^[8]

In 1927, the English writer T. C. Bridges wrote in his book Heroes of Modern Adventure that he captured a very large sawfish on a fishing expedition off the coast of Panama. He claimed that the fish was 9.4 m (31 ft) in length, 6.4 m (21 ft) in girth, and 2.585 t (5,700 lb) in weight, a half-tone photograph of the fish being presented on page 151. This claim has not been scientifically verified and is not considered reliable.

Distribution and habitat

Sawfishes 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 ascend far into rivers and are even known from major lakes such as Lake Nicaragua.

Sawfishes live only in shallow, muddy water and can be found in both freshwater and saltwater. All sawfishes have the ability to traverse between fresh and saltwater.

Behavior

Sawfishes are nocturnal, usually sleeping during the day, hunting at night. Despite fearsome appearances, they are gentle fish 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.

Reproduction

Little is known about the reproduction habits of the sawfishes. Each individual lives around 25 to 30 years, and matures at 10 years (at least in the species where data is available).

Females give live birth to 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.

The sawfish is estimated to mate once every two years, with an average litter of around eight pups. 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 also reproduce at lower rates than most other fish do. This makes the animals especially slow to recover from overfishing.^[9]

Taxonomy and species

There are seven species of sawfishes in two genera,^[1] but considerable taxonomic confusion exists (to the extent that it even has been described as chaotic),^[10] and the possibility that undescribed species exist or some of the below should be considered synonyms remains. Especially the Pristis pristis species complex, which also includes P. microdon and P. perotteti, is in need of a taxonomic review.

Family Pristidae

• Genus Anoxypristis
  • Knifetooth sawfish, Anoxypristis cuspidata (Latham, 1794).

    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 of the quarter nearest the head.

• Genus Pristis
  • Dwarf sawfish, Pristis clavata Garman, 1906.

    Also known as the Queensland sawfish. Inhabits muddy bays and estuaries along the northern coast of Australia. Relatively small compared to other species, maximum length only around 1.4 m (4.6 ft).

  • Largetooth sawfish, Pristis microdon Latham, 1794.

    Also known as the Leichhardt's sawfish. As typically recognised, 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 (the original description lacked a type locality).

  • Smalltooth sawfish, Pristis pectinata Latham, 1794.

    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 now believed to be misidentifications of other species.^[11]

  • Large-tooth sawfish, Pristis perotteti Müller & Henle, 1841.

    As typically recognised, 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.

  • Common sawfish, Pristis pristis (Linnaeus, 1758).

    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 as the other sawfishes.

  • Longcomb sawfish, Pristis zijsron Bleeker, 1851.

    Found in the Indo-West Pacific. Prefers muddy bays and estuaries.

Conservation

Sawfish seen from below, from 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), and their liver oil for use as medicine.

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) are known to supply the highest quality fin—the "caviar" of shark 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] It is well known that 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 as detached shark fins are difficult to identify, it is unlikely that CITES protection will prevent highly valued sawfish fins from entering the trade.

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.

While popular in public aquaria, sawfishes are difficult to maintain because of their size. They likely require a variety of habitats, and both salt- and freshwater to complete their life cycle. Consequently, attempts of captive breeding have resulted in very little success, and so far limited to a single species (P. pectinata)^[15] at a single aquarium (Atlantis Paradise Island).^[16]

As of June 2007 the international trade of sawfish has been banned by the CITES convention.^[17] At the 14th Conference of the Parties to CITES an annotation to listing all species from the family Pristidae to Appendix I was made by the Australian delegation. The annotation, which was supported by the required two thirds majority, was for 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.

The annotation means that people visiting public aquaria may gain awareness of this species and the issues that have endangered its survival through much of the species range. 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.

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.^[9] The sawfish also notably served as the emblem of German submarine U-96, known for its portrayal in Das Boot, and later the symbol of the 9th U-Boat Flotilla.

In cartoons and humorous popular culture, the sawfish - particularly its nose - can be employed as a sort of living tool. Examples of this can be found in Vicke Viking and Fighting Fantasy volume "Demons of the Deep".

References

• Unique Australian Animals - Sawfish
• The Ocean Conservancy: Sawfish