Dwarf SawfishPristis clavata
Although sawfish look somewhat like sharks, they are modified rays, with rows of specialized denticles like teeth along their rostrum (snout). These dwarf sawfish are much smaller than average, only growing to around 10 feet long, and have a more pronounced pectoral disk appearance like rays. Sawfish swipe their rostrum back and forth in schools of fish to stun them before eating them, but little else is known about their behavior. They are no harm to humans, and are only used for food when accidentally caught in commercial fishing nets or by artisanal fishers.
Order - Pristiformes
Family - Pristidae
Genus - Pristis
Species - clavata
Another common name for the dwarf sawfish is Queensland sawfish. Non-English vernaculars referring to the knifetooth sawfish include dwergzaagrog (Dutch) and piloun trpaslici (Czech).
Importance to Humans
Landings of the dwarf sawfish are probably accidental, as they are caught in commercial gillnet and trawl fisheries targeting other species. There is currently no evidence of this species being targeted in any known fishery. Like all sawfishes, dwarf sawfish can be utilized as meat for human consumption, their fins sold into the Asian 'shark fin' market, their livers processed for oil, and their skins made into leather. The eggs, liver oil, and bile of sawfishes are used in Chinese traditional medicine, and their rostra may be used in traditional medicine, as religious offerings, and sold as curios. There is no indication of utilization of this species as food in Australia.
This species is probably not sought after as a game fish, due to its relatively small size and its inability to put up a significant fight on hook and line.
Danger to Humans
The dwarf sawfish, like all sawfishes, is harmless to humans if left undisturbed. Humans are too large to be viewed as potential prey. Care must be taken when handling or approaching a sawfish of any size, as they may defend themselves when they feel threatened, using their rostrum to strike from side to side with considerable force.
The status of the dwarf sawfish populations are currently unknown, and no effective legislation exists to protect this species. However, The World Conservation Union (IUCN) Red List of Threatened Species categorizes this species as "Endangered". This is due to its very limited known distribution and significant bycatch in commercial gillnet and trawl fisheries throughout its range. This species is also vulnerable to near-shore hook and line fisheries within its restricted range. Other impacts may include human-induced habitat loss and pollution of inshore coastal waters, estuaries, and the lower reaches of rivers.
Geographical DistributionThe dwarf sawfish occurs in tropical Australia from Cairns on the Queensland coastline to the Kimberley coastline of Western Australia. However, the distribution may be larger than is presently known and may also include New Guinea, Indonesia, and Malaysia. A record of the dwarf sawfish from the Canary Islands is based on a dried rostrum having tooth counts within the range of this species, but it may be from another sawfish species.
The habitat preferences of this species is not well known. The dwarf sawfish occur only in coastal and estuarine habitats. This species is known to occur miles up rivers and appears to be uncommon in the Gulf of Carpentaria, preferring sand and mud flats, along with estuarine habitats. The dwarf sawfish has been found in the Pentecost River, Western Australia, as far as 6.2 miles (10 km) upstream, and in the adjacent estuary. It has not been documented in freshwater habitats.
All sawfishes are highly modified and elongate rays having a shark-like body and a blade-like snout (termed 'rostrum') that has lateral, tooth-like denticles (termed 'rostral teeth') set into sockets. The presence of a rostrum having laterally protruding teeth separates sawfishes from all other batoids (skates and rays).
The dwarf sawfish can be distinguished from sawsharks (Pristiophorus spp.) by its lack of barbels, ventrally located gills (versus laterally), and its similar-sized rostral teeth.
The dwarf sawfish is distinguished from the knifetooth sawfish (Anoxypristis cuspidata) by its sharply pointed rostral teeth (versus blade-like), the location of the first pair of rostral teeth near the rostral base, its unicuspidate dermal denticles along the body (versus tricuspidate or lack of denticles), its tapering and broad rostrum, and the lack of a well-developed lower caudal fin lobe.
The dwarf sawfish is distinguished from the freshwater sawfish (Pristis microdon) by the more posterior first dorsal fin position, the lack of a lower caudal fin lobe, and the spacing of the rostral teeth being slightly closer to each other towards the rostral tip (versus evenly spaced).
The dwarf sawfish is distinguished from the largetooth sawfish (Pristis perotteti) by its geographic range, and by the same characteristics that separate it from the freshwater sawfish (see above).
The dwarf sawfish is distinguished from the smalltooth sawfish (Pristis pectinata) by the fewer average number of rostral teeth per side (18-23, versus 20-34 per side), and the position of the first dorsal fin origin posterior to the pelvic fins.
The dwarf sawfish is distinguished from the green sawfish (Pristis zijsron) by the fewer number of rostral teeth per side (typically 18-23, versus 23-37 per side), the forward location of the first dorsal fin, and the second dorsal fin being smaller than the first dorsal fin. The dwarf sawfish also has a tapered rostrum and its inter-tooth space between the last two teeth is less than two times the inter-tooth space of the first two teeth.
In addition to the above characteristics, the dwarf sawfish is significantly smaller, on average, than any other sawfish species.
The dorsal body surface of the dwarf sawfish is olive-brown in color, darker on the head, and fading to a whitish or yellowish ventrally. The fins of this species are often lighter in color than the dorsal body surface.
Oral dentition of the dwarf sawfish is similar in both jaws, exhibiting many rows of blunt teeth with rounded cusps and smooth surfaces. The oral teeth of the dwarf sawfish sometimes show wear from use, which may be particularly noticeable towards the symphysis (medial junction of each jaw) along the front series of tooth rows.
Dermal denticles of this species cover the body, fins, and rostrum. These denticles have a flat, oval-shaped or rounded crown. Denticles are similar in all development stages, although larger individuals exhibit a more pronounced crown than do young. Denticles along the posterior portion of the body are more elongate and convex. Denticles along the ventral body surface are smaller and are positioned in a pavement-like pattern.
Size, Age & Growth
The largest specimen ever recorded was a mature male that measured 10.03 feet (3.06 m) in total length. A female measuring 6.89 feet (2.1 m) was found to be immature. This is significantly smaller than the maximum size of any other living sawfish species, lending this species its common name of dwarf sawfish.
Despite the dwarf sawfish's interesting mode of food gathering, using its rostrum in a side-to-side slashing motion to dislodge invertebrates from substrate and to stun schooling fishes, little is known about the feeding habits of this species. Food items for the dwarf sawfish have not yet been recorded. Probable food items include small fishes and crustaceans, such as crabs and shrimps.
Little is known about the reproduction of the dwarf sawfish, and no mature females of this species have yet been recorded. Male dwarf sawfish mature by about 10 feet (3.0 m) or less. Like sharks, skates, and rays, the dwarf sawfish utilizes internal fertilization. Like all rays, this species utilizes a strategy of embryo nourishment called aplacental yolk sac viviparity. With this strategy, the embryos are nourished only by their yolk sac, which provides energy for them to develop into fully functional young sawfish in utero. The yolk sac is connected to the embryo by a yolk stalk and both of these structures are fully absorbed before the young sawfish are born. The gestation period of the dwarf sawfish is not known, but the largetooth sawfish has a gestation period of about five months. Young dwarf sawfish have not yet been captured and litter sizes of this species have not yet been reported. The young are probably born tail-first. The saw teeth of young sawfish do not fully erupt, and are covered in a sheath of tissue, until after birth so as not to injure the mother. Young dwarf sawfish rostral teeth reach their full size proportionate to the size of the rostrum soon after birth. The reproductive cycle of the dwarf sawfish has not yet been documented, but the largetooth sawfish has been reported to produce litters every other year.
Predator attacks on dwarf sawfish have not been documented, but likely predators include hammerhead sharks (Sphyrna spp.), bull sharks (Carcharhinus leucas), copper sharks (Carcharhinus brachyurus), and saltwater crocodiles (Crocodylus porosus).
The newly described parasite species Neoheterocotyle darwinensis n. sp. lives within the gills of the dwarf sawfish, and is known to occur near Darwin, Australia. Other species likely to use the dwarf sawfish as a host include Nonacotyle pristis, a species known to inhabit the gills of the freshwater sawfish, monogenean helminths such asErpocotyle caribbensis and Pristonchocotyle intermedia, both inhabiting the gills of largetooth sawfish in Central America, and the cestode helminths Phyllobothrium pristis and Anthobothrium pristis, both inhabiting the spiral valve of largetooth sawfish in Central America. Other potential parasites include copepods, nematodes, protozoans, and trematodes. Areas of parasite inhabitation may include the skin, gills, and digestive tract.
The dwarf sawfish was first described in 1906 by Samuel Garman, a legendary anatomist and the first official curator of fishes, amphibians, and reptiles at the Museum of Comparative Zoölogy (MCZ) at Harvard. A male dwarf sawfish measuring 24.4 inches (61.9 cm) in total length from Queensland, Australia was deposited and cataloged at the MCZ in October of 1877. This specimen remains as a representative example (termed 'type specimen') of the species. Due to copper staining, this specimen is slightly green in color. This discoloration may have caused Garman to describe his new species as olive-green in color (sawfishes are normally brown or tan in color). Garman later illustrated this specimen in his famous 1913 monograph entitled The Plagiostomia. The valid scientific name for the dwarf sawfish is Pristis clavataGarman, 1906. Synonyms include Pristis pectinata Latham, 1794 and Pristis pristis (Linnaeus, 1758), both are misidentifications. The generic name Pristis is Greek for "saw". The specific name clavata is derived from the Latin wordclava meaning "club".
Prepared by: Jason C. Seitz