Sawfish
Sawfish, also known as carpenter sharks, are a family of very large rays characterized by a long, narrow, flattened rostrum, or nose extension, lined with sharp transverse teeth, arranged in a way that resembles a saw. They are among the largest fish, with some species reaching lengths of about. They are found worldwide in tropical and subtropical regions in coastal marine and brackish estuarine waters, as well as freshwater rivers and lakes. All species are critically endangered.
They should not be confused with sawsharks or the extinct sclerorhynchoids which have a similar appearance, or swordfish which have a similar name but a very different appearance.
Sawfishes are relatively slow breeders and the females give birth to live young. They feed on fish and invertebrates that are detected and captured with the use of their saw. They are generally harmless to humans, but can inflict serious injuries with the saw when captured and defending themselves.
Sawfish have been known and hunted for thousands of years, and play an important mythological and spiritual role in many societies around the world.
Once common, sawfish have experienced a drastic decline in recent decades, and the only remaining strongholds are in Northern Australia and Florida, United States. All five species are rated as Critically Endangered by the International Union for Conservation of Nature. They are hunted for their fins, and for the use of other parts, including the teeth and rostrum, in traditional medicine. They also face habitat loss. Sawfish have been listed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora since 2007, restricting international trade in them and their parts. They are protected in Australia, the United States and several other countries, meaning that sawfish caught by accident have to be released and violations can be punished with hefty fines.
Taxonomy and etymology
The scientific names of the sawfish family Pristidae and its type genus Pristis are derived from the.Despite their appearance, sawfish are rays. The sawfish family has traditionally been considered the sole living member of the order Pristiformes, but recent authorities have generally subsumed it into Rhinopristiformes, an order that now includes the sawfish family, as well as families containing guitarfish, wedgefish, banjo rays and the like. Sawfish quite resemble guitarfish, except that the latter group lacks a saw, and their common ancestor likely was similar to guitarfish.
Living species
The species level taxonomy in the sawfish family has historically caused considerable confusion and was often described as chaotic. Only in 2013 was it firmly established that there are five living species in two genera.Anoxypristis contains a single living species that historically was included in Pristis, but the two genera are morphologically and genetically highly distinct. Today Pristis contains four living, valid species divided into two species groups. Three species are in the smalltooth group, and there is only a single in the largetooth group. Three poorly defined species were formerly recognized in the largetooth group, but in 2013 it was shown that P. pristis, P. microdon and P. perotteti do not differ in morphology or genetics. As a consequence, recent authorities treat P. microdon and P. perotteti as junior synonyms of P. pristis.
File:Pristidae - Pristis lathami.JPG|thumb|Extinct sawfish are often only known from their rostral teeth, here from the Eocene species Pristis lathami.
Extinct (fossil) species
In addition to the living sawfish, there are several extinct species that only are known from fossil remains found around the world in all continents. Peyeria from the Cenomanian age was once considered as the oldest known pristid, though it may represent a rhinid rather than a sawfish, or probably a junior synonym of the sclerorhynchoid Onchopristis. Indisputable sawfish genera emerged in the Cenozoic age about 60 million years ago, relatively soon after the Cretaceous–Paleogene mass extinction. Among these are Propristis, a monotypic genus only known from fossil remains, as well as several extinct Pristis species and several extinct Anoxypristis species. Historically, palaeontologists have not separated Anoxypristis from Pristis. In contrast, several additional extinct genera are occasionally listed, including Dalpiazia, Onchopristis, Oxypristis, and Mesopristis, but recent authorities generally include the first two genera within Sclerorhynchoidei and the last two are synonyms of Anoxypristis.The extinct order Sclerorhynchoidei had long rostra with large denticles similar to sawfishes and sawsharks. This feature was convergently evolved, recently proposed as 'pristification', and their closest living relatives are actually skates. While they are often called "sawfishes", the more accurate common name for sclerorhynchoids is "sawskates".
Appearance and anatomy
Sawfish are dull brownish, greyish, greenish or yellowish above, but the shade varies and dark individuals can be almost black. The underside is pale, and typically whitish.Saw
The most distinctive feature of sawfish is their saw-like rostrum with a row of whitish teeth on either side of it. The rostrum is an extension of the chondrocranium, made of cartilage and covered in skin. The rostrum length is typically about one quarter to one third of the total length of the fish, but it varies depending on species, and sometimes with age and sex. The rostral teeth are not teeth in the traditional sense, but heavily modified dermal denticles. The rostral teeth grow in size throughout the life of the sawfish and a tooth is not replaced if it is lost. In Pristis sawfish, the teeth are found along the entire length of the rostrum, but, in adult Anoxypristis, there are no teeth on the basal one-quarter of the rostrum. The number of teeth varies depending on the species and can range from 14 to 37 on each side of the rostrum. It is common for a sawfish to have slightly different tooth counts on each side of its rostrum. In some species, females on average have fewer teeth than males. Each tooth is peg-like in Pristis sawfish, and flattened and broadly triangular in Anoxypristis. A combination of features, including fins and rostrum, are typically used to separate the species, but it is possible to do it by the rostrum alone.Head, body and fins
Sawfish have a strong shark-like body, a flat underside and a flat head. Pristis sawfish have a rough sandpaper-like skin texture because of the covering of dermal denticles, but in Anoxypristis the skin is largely smooth. The mouth and nostrils are placed on the underside of the head. There are about 88–128 small, blunt-edged teeth in the upper jaw of the mouth and about 84–176 in the lower jaw. These are arranged in 10–12 rows on each jaw, and somewhat resemble a cobblestone road. They have small eyes and behind each is a spiracle, which is used to draw water past the gills. The gill slits, five on each side, are placed on the underside of the body near the base of the pectoral fins. The position of the gill openings separates them from the superficially similar yet generally much smaller sawsharks, in which the slits are on the side of the neck. Unlike sawfish, sawsharks also have a pair of long barbels on the rostrum.Sawfish have two relatively high and distinct dorsal fins, wing-like pectoral and pelvic fins, and a tail with a distinct upper lobe and a variably sized lower lobe. The position of the first dorsal fin compared to the pelvic fins varies and is a useful feature for separating some of the species. There are no anal fins.
Like other elasmobranchs, sawfish lack a swim bladder, and have a skeleton consisting of cartilage. Males have claspers, a pair of elongated structures used for mating and positioned on the underside at the pelvic fins. The claspers are small and indistinct in young males.
Their small intestines contain an internal partition shaped like a corkscrew, called a spiral valve, which increases the surface area available for food absorption.
Size
Sawfish are large to very large fish, but the maximum size of each species is generally uncertain. The smalltooth sawfish, largetooth sawfish and green sawfish are among the world's largest fish. They can certainly all reach about in total length and there are reports of individuals larger than, but these are often labeled with some uncertainty. Typically reported maximum total lengths of these three are from. Large individuals may weigh as much as, or possibly even more. Old unconfirmed and highly questionable reports of much larger individuals do exist, including one that reputedly had a length of, another that had a weight of, and a third that was long and weighed.The two remaining species, the dwarf sawfish and narrow sawfish, are considerably smaller, but are still large fish with a maximum total length of at least and respectively. In the past it was often reported that the dwarf sawfish only reaches about, but this is now known to be incorrect.
Distribution
Range
Sawfish are found worldwide in tropical and subtropical waters.Historically they ranged in the East Atlantic from Morocco to South Africa, and in the West Atlantic from New York to Uruguay, including the Caribbean and Gulf of Mexico. There are old reports from the Mediterranean and these have typically been regarded as vagrants, but a review of records strongly suggests that this sea had a breeding population. In the East Pacific they ranged from Mazatlán to northern Peru. Although the Gulf of California occasionally has been included in their range, the only known Pacific Mexican records of sawfish are from south of its mouth. They were widespread in the western and central Indo-Pacific, ranging from South Africa to the Red Sea and Persian Gulf, east and north to Korea and southern Japan, through Southeast Asia to Papua New Guinea and Australia. Today sawfish have disappeared from much of their historical range.