How Many Species of Sawfish Are There in the World Today?

Jason sawfishSawfishes are large highly modified and elongate rays that swim like a shark and have a long snout with laterally-placed spines.  The snout (called a ‘rostrum’) is actually an extension of the skull (known as a ‘chondrocranium’) and the lateral spines are called ‘rostral teeth’ by scientists.  Like the rest of the skeleton of the sawfish, the rostrum is composed of cartilage, albeit reinforced with extra calcium.  The rostrum and rostral teeth are used in food gathering.  The sawfish uses the rostrum to stun fishes and to a lesser extent, invertebrates, which it then sucks into its mouth positioned under the head.  There is no cutting or tearing and sawfish can only consume fish and invertebrates that fit into the mouth whole.  The longest species of sawfish, the green sawfish (Pristis zijsron), is reported to reach a length of 23.9 feet according to Last and Stevens (1994).

Sawfishes can be distinguished from saw sharks (Pristiophurus spp. and Pliotrema warreni) by the lack of barbels, ventrally located gills (versus laterally located), dorso-laterally compressed body, and uniformly sized rostral teeth.  Sawfishes grow much larger than do saw sharks.  Further, sawfishes prefer warm coastal waters while saw sharks inhabit deeper cooler offshore waters.

Living sawfish species are globally distributed in tropical and sub-tropical coastal marine and estuarine waters, and sometimes inhabit rivers and associated freshwater bodies such as Lake Nicaragua.  The center of distribution is the western Pacific including northern Australia and Papua New Guinea. 

All modern sawfish species are considered imperiled and regarded by the International Union for the Conservation of Nature (IUCN) as ‘critically endangered’ with declining populations (www.iucnredlist.org).  Unfortunately, the IUCN is not a regulatory agency and thus no protection is afforded by this group.  Only two species currently have protection under the endangered species act of 1972, and only in waters of the United States.  The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) has protected all species of sawfish from international trade of sawfish parts since 2007 (www.cites.org).  However, the confusing taxonomy of modern sawfishes has hampered conservation efforts and such efforts are further disadvantaged by the poorly known geographical population structure.

Until very recently, there were six valid living species worldwide. The Knifetooth Complex of sawfish currently consists of one species:

Anoxypristis cuspidata (knifetooth sawfish [western Pacific and Indian oceans])

 The Smalltooth Complex of sawfish consists of three species:

Pristis clavata (dwarf sawfish [western Pacific Ocean])

Pristis pectinata (smalltooth sawfish [eastern and western Atlantic Ocean])

Pristis zijsron (green sawfish [western Pacific and Indian oceans])

 The Largetooth Complex of sawfish consisted of two species:

Pristis microdon (freshwater sawfish [western Pacific and Indian oceans])

Pristis perotteti (largetooth sawfish [eastern and western Atlantic Ocean, eastern Pacific Ocean])

Some researchers also considered the species Pristis pristis to be a valid member of the Largetooth Complex, although most considered it as an invalid synonym due to problems relating to its original description and lack of voucher specimens in museums (Faria 2007).  Also, the eastern Pacific population of the largetooth sawfish was considered to be a separate species (Pristis zephyreus) by some researchers following molecular phylogenetic work by Faria (2007), although no reliable morphological differences have been found between the eastern Pacific population and largetooth sawfish from the western Atlantic.

The freshwater sawfish and the largetooth sawfish have been problematic for researchers because the two species cannot be reliably differentiated by morphology and thus, these species were differentiated solely by region.  For specimens lacking collection data, this presents a challenge as the species may not be reliably determined at all.  Molecular work has shown that these species group closely together in terms of genetic background (Naylor et al. 2012).

Because of the fact that the largetooth sawfish and the freshwater sawfish are indistinguishable by morphology and share similar genetic backgrounds, it has been very recently proposed by researchers that these two species should be combined.  In a paper published in early 2013 and authored by Faria et al. (2013), all the Largetooth Complex species have been combined into a composite species under the resurrected name of Pristis pristis.  The resurrection of the formerly invalid name of Pristis pristis was based on Rule 23.1 (principle of priority) of the International Code of Zoological Nomenclature, which states that ‘the valid name of a taxon is the oldest available name applied to it’ (International Commission on Zoological Nomenclature 1999).  Since the species name Pristis pristis was published in 1758 (as Squalus pristis by Carl Linnaeus), it precedes the naming of all other Largetooth Complex species.  For this reason and because this name was used as a valid species after 1899, Pristis pristis is proposed by Faria et al. (2013) for use in place of Pristis microdon, Pristis perotteti, and the species of questionable validity, Pristis zephyreus.

Based on Faria et al. (2013), there are now a total of five valid sawfish species:

The Knifetooth complex (one species):

Anoxypristis cuspidata (knifetooth sawfish [western Pacific and Indian oceans])

The Smalltooth complex (three species):

Pristis clavata (dwarf sawfish [western Pacific Ocean])

Pristis pectinata (smalltooth sawfish [eastern and western Atlantic Ocean])

Pristis zijsron (green sawfish [western Pacific and Indian oceans])

The Largetooth complex of sawfish now consists of only one species:

Pristis pristis (largetooth sawfish [eastern and western Atlantic, eastern and western Pacific, and Indian oceans])

It is possible that in the future, changes may occur within the taxonomy of the knifetooth sawfish.  Gene flow between Indian Ocean and western Pacific specimens was found to be very low in a study by Faria et al. (2013).  Specimens from the Indian Ocean were found to have a higher average number of rostral teeth per side (average of 25.6) versus western Pacific specimens (average of 21.2) (faria et al. 2013).  Results of the Faria et al. (2013) study suggest that the knifetooth sawfish may actually represent multiple species.  In fact, a DNA-sequencing based analysis by Naylor et al. (2012) showed that knifetooth sawfish had considerable genetic differences from all other living members of the sawfish family.  This suggests that in the future the knifetooth sawfish may even be placed into a separate family distinct from the other sawfishes.

It is clear that there is still a lot to learn about sawfishes.  Although it is uncertain what changes will occur in sawfish taxonomy, or what new information will come to light from future scientific research, it remains clear that this interesting group of animals will continue to captivate scientists and layman alike for many years to come.

Sources Cited: Faria, V.V.  2007.  Taxonomic Review, Phylogeny, and Geographical Population Structure of the Sawfishes (Chondrichthyes, Pristiformes).  PhD dissertation, Iowa State University, Ames, IA.

Faria, V.V., M.T. McDavitt, P. Charvet, T.R. Wiley, C.A. Simpfendorfer, and G.J.P. Naylor.  2013. Species delineation and global population structure of critically endangered sawfishes (Pristidae).  Zoological Journal of the Linnean Society 167(1):136–164.

International Commission on Zoological Nomenclature.  1999.  International Code of Zoological Nomenclature. The International Trust for Zoological Nomenclature, The Natural History Museum, London, UK.

Last, P.R. and J.D. Stevens.  1994. Sharks and Rays of Australia.  CSIRO Division of Fisheries, Victoria, Australia.

Naylor, G.J.P., J.N. Caira, K. Jensen, K.A.M., Rosana, W.T. White, and P.R. Last.  2012. A DNA sequence-based approach to the identification of shark and ray species and its implications for global elasmobranch diversity and parasitology. Bulletin of the American Museum of Natural History 2012(367):1–262.

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