Pristiophoriformes

(Sawsharks)

Class Chondrichthyes

Order Pristiophoriformes

Number of families 1

Evolution and systematics

Sawsharks first appear in the fossil record during the late Cretaceous period (some 85 million years ago [mya]) in Lebanon in the form of more or less complete fossils, but almost all sawshark fossils consist of isolated remains of rostral spines from the Tertiary period (from between 65 and 5 mya). Sawshark fossils are not very common, but indicate that they were once more widespread, at least in the Pacific, southern and northeastern Atlantic, as remains have been found in Japan, Africa, Europe, New Zealand, and North and South America.

Sawsharks are closely related to the cow and frilled sharks (Hexanchiformes), the dogfishes and allies (Squaliformes), the angelsharks (Squatiniformes), and the rays (or batoids). Together these groups comprise the Squalea, as all members have complete hemal arches (ventral projections arising from the vertebral column) in the trunk region anterior to the tail, among other unique anatomical features. Within the Squalea, the sawsharks are most closely related to the rays. All sawsharks are classified in the family Pristiophoridae.

There are two genera of living sawsharks, Pliotrema and Pristiophorus. Pristiophorus has four included species, but Pliotrema is monotypic (that is, only a single species, P. warreni, is recognized). The phylogenic relationships among sawshark species have not been investigated. Their taxonomy is still poorly known, mainly as a result of the paucity of specimens available for study from many regions. Two putatively new species of sawsharks have been reported from Australia. Their general biology is also inadequately known.

Physical characteristics

Sawsharks are readily identified by their slender, slightly depressed body, which is preceded by a very elongated toothed "saw." The saw (or "rostral saw") is an anterior, hypertrophied extension of the snout region (rostrum). The saw has large, sharp, lateral rostral spines, which are replaced continuously through life, as well as a pair of long, ventrally extending barbels that are well anterior to the nostrils. The mouth and nostrils are entirely on the ventral surface. Sawsharks lack an anal fin, have relatively large pectoral and spineless dorsal fins, and a low, long caudal fin. The eyes and spiracles are large.

Sawsharks are sometimes confused with the sawfishes (Pristidae), a group of rays that also have elongated rostral saws. However, both groups are easily distinguished, as sawfishes (rays) do not present rostral barbels, have rostral teeth of equal size that grow continuously (as opposed to sawshark rostral spines which are replaced when broken off, and vary in size), and have ventral gill slits. There are numerous other anatomical differences, such as the arrangement of canals for the passage of vessels and nerves within the rostral saw, and the mode of attachment of rostral spines (which are not embedded in the saw in sawsharks, as they are in sawfishes).

The genera of sawsharks (Pliotrema and Pristiophorus) are easily distinguished. Pliotrema has six gill slits, whereas Pristiophorus has five (gills slits in all sawsharks are lateral, just anterior to the pectoral fins), and the rostral spines of Pliotrema bear small serrations on their posterior margins. Most species of sawsharks are drab and gray colored, with the exception of the more ornately colored P. cirratus.

Sawsharks are small to average in size, reaching about 55 in (140 cm) in length. Most species are born at about 9.8–13.8 in (25–35 cm). The size at sexual maturity is poorly known, but has been established to be around 32.7 in (83 cm) for males for at least one species, P. warreni, and slightly larger for females.

Distribution

As far as is known, sawsharks have a restricted distribution in tropical and warm-temperate waters, occurring in the western Pacific Ocean (Philippines, Japan, and China; P. japonicus), western Indian Ocean (southeastern Africa; P. warreni), southern, western, and eastern Australia (P. nudipinnis and P. cirratus), and also in the western North Atlantic, around the Bahamas, and between Cuba and Florida (P. schroederi).

Habitat

Most sawshark species inhabit the continental shelf region, but some species are also present along the continental slope in waters as deep as 3,002 ft (915 m), and one species, P. schroederi, is known only from deep waters. Some species present great depth variation, occurring in shallow bays but also along the upper slope. Sawsharks are generally found on soft gravely or sandy bottoms.

Behavior

Sawsharks, similar to the sawfishes (rays), utilize their saw to stun and kill fish by swinging it from side to side, and also to stir up bottom sediments when hunting. The rostral barbels may contain taste buds, and the saw is heavily endowed with sensory receptors (ampullary pores, which detect electrical fields, and lateral-line pores, which detect physical perturbations in the water). Some species are rather abundant, occurring in large groups, perhaps for feeding purposes, and may also present segregation of individuals according to age.

Feeding ecology and diet

Sawsharks feed mostly on fishes, but also on invertebrates such as squid and crustaceans.

Reproductive biology

All sawsharks have internal fertilization (as do all chondrichthyans), are ovoviviparous (or aplacentally viviparous), giving birth to from seven to 17 young, but little is known about the length of their gestation periods. Young feed on yolk from the yolk sac until birth. The rostral spines are concealed in embryonic sawsharks, oriented backward so as to not harm the mother (but still very sharp), and become perpendicularly oriented only after birth. Fetal individuals present elongated rostral barbels, proportionally much longer than adults.

Conservation status

The common sawshark (P. cirratus) is listed as Lower Risk/Near Threatened by the IUCN.

Significance to humans

Sawsharks are consumed locally as food at least in the western Pacific (P. japonicus), and in Australia (P. cirratus), being caught as bycatch during bottom trawls. They are not usually kept in aquaria. Sawsharks pose little threat to humans, due primarily to their more obscure habits and depth distribution, but the rostral spines are quite sharp even in late-term embryos or juveniles, and may easily cause injury if handled.

Species accounts

List of Species

Common sawshark

Pristiophorus cirratus

family

Pristiophoridae

taxonomy

Pristis cirratus Latham, 1794, Australia (Port Jackson, New South Wales).

other common names

English: Longnose sawshark; French: Requin scie à long nez; Spanish: Tiburòn sierra trompudo.

physical characteristics

Common sawsharks are uniquely pigmented, with a reddish brown background pattern; numerous irregular darker brown saddles along the trunk, fins, and head; dark brown stripes across rostral saw; as well as numerous small spots (smaller than the eye) scattered on body; the rostral spines have dark margins. Ventrally uniform creamy white. Rostral saw is relatively long and slender when compared to the other Australian species, P. nudipinnis, and the rostral barbels are located at about the center of the rostral saw, as opposed to slightly closer to the eyes as in the latter species.

distribution

Common sawsharks occur off southern and western Australia (reaching to about 30°S), including around Tasmania.

habitat

These sharks are found on the continental shelf and upper slope, from 131–1,017 ft (40–310 m), usually on sandy bottoms. They are also reported to occur in bays and estuaries, but are believed to be more abundant from 121–479 ft (37–146m). Although present in the same general area as P. nudipinnis, P. cirratus apparently occupies deeper waters.

behavior

Common sawsharks are believed to form schools (perhaps for feeding) and are abundant in trawls for benthic fishes. This species has been filmed swinging its saw from side to side in an attempt to injure small fishes. They commonly rest on the bottom, with the rostral saw slightly elevated and supported in a tripodlike stance by the rostral barbels. Common sawsharks are not frequently observed in the wild.

feeding ecology and diet

These sharks feed on fishes, including cornetfishes (Fistulariidae), and on invertebrates, particularly crustaceans.

reproductive biology

Mostly unknown, but they are reported to breed during winter months. Their size at birth is about 15 in (38 cm), and males are sexually mature at about 3.3 ft (1 m) in length.

conservation status

These fishes are listed as Lower Risk/Near Threatened by the IUCN.

significance to humans

Common sawsharks are captured as bycatch by trawlers and are available regularly in fish markets. The flesh is reported to be very good. The elongated rostral saw is sometimes coveted for its value as an ornament. ◆

Sixgill sawshark

Pliotrema warreni

family

Pristiophoridae

taxonomy

Pliotrema warreni Regan, 1906, South Africa (Natal and False Bay).

other common names

English: Sawshark; French: Requin scie flutian; Spanish: Tiburòn sierra del cabo.

physical characteristics

Sixgill sawsharks are unique in having six gill slits. The rostral saw is relatively elongated, and the rostral barbels are much closer to the mouth than to the rostral tip. The sharks are pale brown dorsally. At birth they measure 13.8 in (35 cm). They reach about 55 in (140 cm), the males maturing at about 32.7 in (83 cm), and the females at 43.3 in (110 cm).

distribution

Southeastern Africa, from Cape Agulhas (South Africa) to Mozambique and Madagascar. P. warreni is the only sawshark species in the western Indian Ocean.

habitat

These sharks are found on the continental shelf and upper slope, from 197–1,481 ft (60–430 m). Reported to occur in deeper depths (below 361 ft/110 m) off Natal, South Africa.

behavior

The behavior of these sharks is not well known, but they presumably use their rostral saw like other sawsharks—to stun, dig out, and kill prey. The adults are partially segregated from the young by occupying deeper waters in at least one area (off Natal).

feeding ecology and diet

Sixgill sawsharks feed on a variety of fishes (eels, hake, and gapers) as well as shrimp and squid.

reproductive biology

The litter size is five to seven per gestation, but much is yet to be learned about its reproductive biology.

conservation status

Not threatened.

significance to humans

Sixgill sawsharks are occasionally captured as bycatch and consumed locally.

Resources

Books

Cappetta, H. Chondrichthyes II, Mesozoic and Cenozoic Elasmobranchii. Stuttgart: Gustav Fischer Verlag, 1987.

Compagno, L. J. V. "Part 1: Hexanchiformes to Lamniformes." In Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known To Date. FAO fisheries synopsis, no. 125; Vol. 4, part 1. Rome: United Nations Development Programme, 1984.

Hennemann, R. M. Sharks and Rays, Elasmobranch Guide of the World. Frankfurt: Ikan, 2001.

Last, P. R., and J. D. Stevens. Sharks and Rays of Australia. Melbourne, Australia: CSIRO, 1994.

Nelson, J. Fishes of the World. 3rd ed. New York: John Wiley & Sons, 1994.

Springer, V. G., and J. P. Gold. Sharks in Question. The Smithsonian Answer Book. Washington, DC: Smithsonian Institution Press, 1989.

Whitley, G. P. The Fishes of Australia. Part 1. The Sharks, Rays, Devil-Fish, and Other Primitive Fishes of Australia and New Zealand. Sydney, Australia: Royal Zoological Society of New South Wales, 1940.

Periodicals

Compagno, L. J. V. "Phyletic Relationships of Living Sharks and Rays." American Zoologist 17 (1977): 303–322.

Luer, C. A., and P. W. Gilbert. "Elasmobranch Fish. Oviparous, Viviparous, and Ovoviviparous." Oceanus Magazine 34, no. 3 (1991): 47–53.

Slaughter, B. H., and S. Springer. "Replacement of Rostral Teeth in Sawfishes and Sawsharks." Copeia 1968, no. 3 (1968): 499–506.

Springer, S., and H. R. Bullis, Jr. "A New Species of Sawshark, Pristiophorus schroederi, from the Bahamas." Bulletin of Marine Science of the Gulf and Caribbean 10, no. 2 (1960): 241–254.

Organizations

American Elasmobranch Society, Florida Museum of Natural History. Gainesville, FL 32611 USA. Web site: http://www.flmnh.ufl.edu/fish/Organizations/aes/aes.htm

Other

FishBase. August 8, 2002 (cited October 10, 2002). <http://www.fishbase.org>

The Catalog of Fishes On-Line. February 15, 2002 (cited October 17, 2002). <http://www.calacademy.org/research/ichthyology/catalog/fishcatsearch.html>

Marcelo Carvalho, PhD