Sawfish

Source: Wikipedia, the free encyclopedia.
For other uses, see Sawfish (disambiguation).
Not to be confused with sawshark.

Sawfish
Temporal range: Late Cretaceous - Recent[1] (see article for discussion)
Green sawfish
, Pristis zijsron (below)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Superorder: Batoidea
Order: Rhinopristiformes
Family: Pristidae
Bonaparte, 1838
Genera

Sawfish, also known as carpenter sharks, are a

estuarine waters, as well as freshwater rivers and lakes. All species are endangered.[3]

They should not be confused with sawsharks (order Pristiophoriformes) or the extinct sclerorhynchoids (order Rajiformes) which have a similar appearance, or swordfish (family Xiphiidae) which have a similar name but a very different appearance.[1][4]

Sawfishes are relatively slow breeders and the females give birth to live young.[2] They feed on fish and invertebrates that are detected and captured with the use of their saw.[5] They are generally harmless to humans, but can inflict serious injuries with the saw when captured and defending themselves.[6]

Sawfish have been known and hunted for thousands of years,

mythological and spiritual role in many societies around the world.[8]

Once common, sawfish have experienced a drastic decline in recent decades, and the only remaining strongholds are in

habitat loss.[4] Sawfish have been listed by CITES since 2007, restricting international trade in them and their parts.[11][12] 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.[13][14]

Taxonomy and etymology

The scientific names of the sawfish

romanized: prístēs, lit. 'saw, sawyer'.[15][16]

Despite their appearance, sawfish are rays (superorder Batoidea). 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.[17][18] Sawfish quite resemble guitarfish, except that the latter group lacks a saw, and their common ancestor likely was similar to guitarfish.[5]

Living species

The species level

genera.[4][19]

junior synonyms of P. pristis.[3][21][22][23][24][25]

Genus and species group Image Scientific name Common names[10][22] (most frequently used listed first)[4]
IUCN status[10]
 Distribution[10] Main habitats[10]
Anoxypristis
Anoxypristis cuspidata
(Latham
, 1794)
Narrow sawfish
,
knifetooth sawfish, pointed sawfish 		Critically endangered Indo-Pacific Marine waters, estuaries
Pristis Smalltooths
Pristis clavata
Garman
, 1906 		Dwarf sawfish,
Queensland sawfish 		Critically endangered Indo-Pacific Marine waters, estuaries
Pristis pectinata
Latham
, 1794 		Smalltooth sawfish Critically endangered Atlantic Marine waters, estuaries
Pristis zijsron
Bleeker
, 1851
Green sawfish
,
longcomb sawfish, narrowsnout sawfish, olive sawfish 		Critically endangered Indo-Pacific Marine waters, estuaries
Largetooths
Pristis pristis
(Linnaeus, 1758
) 		Largetooth sawfish,
common sawfish, wide sawfish, freshwater sawfish, river sawfish, Leichhardt's sawfish, northern sawfish 		Critically endangered Atlantic,
Indo-Pacific,
East Pacific 		Marine waters, estuaries, rivers, lakes

Extinct (fossil) species

Extinct sawfish are often only known from their rostral teeth, here from the Eocene species Pristis lathami.[26]

In addition to the living sawfish, there are several

Sclerorhynchidae and the last two are synonyms of Anoxypristis.[1][30] Fossils of sawfish have been found around the world in all continents.[29]

The extinct family Sclerorhynchidae resemble sawfish. They are known only from Cretaceous fossils,

polyphyletic.[27]

Appearance and anatomy

Sawfish are dull brownish, greyish, greenish or yellowish above,

shade varies and dark individuals can be almost black.[32] The underside is pale,[32] and typically whitish.[2]

Saw

green sawfish below. Notice difference in tooth shape and absence/presence of teeth on basal quarter of rostrum
(each red or black section on ruler is 10 cm or 3.9 in)

The most distinctive feature of sawfish is their saw-like

dermal denticles.[34] The rostral teeth grow in size throughout the life of the sawfish and a tooth is not replaced if it is lost.[34][35] 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 (about one-sixth in juvenile Anoxypristis).[36][37] The number of teeth varies depending on the species and can range from 14 to 37 on each side of the rostrum.[2][38][note 1] It is common for a sawfish to have slightly different tooth counts on each side of its rostrum (difference typically does not surpass three).[39][40] In some species, females on average have fewer teeth than males.[1][39] Each tooth is peg-like in Pristis sawfish, and flattened and broadly triangular in Anoxypristis.[2] A combination of features, including fins and rostrum, are typically used to separate the species,[2][38] but it is possible to do it by the rostrum alone.[41]

Head, body and fins

pectoral fin
)
narrow sawfish (bottom). Notice especially the structure of the saw, tail and pectoral fins, and the position of the first dorsal fin compared to the pelvic 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.

pectoral fins.[43] The position of the gill openings separates them from the superficially similar yet generally much smaller (up to c. 1.5 m or 5 ft long) sawsharks, in which the slits are on the side of the neck.[1][45] Unlike sawfish, sawsharks also have a pair of long barbels on the rostrum ("saw").[1][45]

Sawfish have two relatively high and distinct

anal fins.[42]

Like other

elasmobranches, sawfish lack a swim bladder (instead controlling their buoyancy with a large oil-rich liver), and have a skeleton consisting of cartilage.[46] Males have claspers, a pair of elongated structures used for mating and positioned on the underside at the pelvic fins.[42] The claspers are small and indistinct in young males.[38]

Their

corkscrew, called a spiral valve, which increases the surface area available for food absorption.[citation needed
]

Size

Green sawfish (top) and Dwarf sawfish
(bottom).

Sawfish are large to very large fish, but the maximum size of each species is generally uncertain. The

largest fish. They can certainly all reach about 6 m (20 ft) in total length and there are reports of individuals larger than 7 m (23 ft), but these are often labeled with some uncertainty.[2] Typically reported maximum total lengths of these three are from 7 to 7.6 m (23–25 ft).[2] Large individuals may weigh as much as 500–600 kg (1,102–1,323 lb),[47] or possibly even more.[48][49] Old unconfirmed and highly questionable reports of much larger individuals do exist, including one that reputedly had a length of 9.14 m (30 ft), another that had a weight of 2,400 kg (5,300 lb), and a third that was 9.45 m (31 ft) long and weighed 2,591 kg (5,712 lb).[48]

The two remaining species, the

narrow sawfish, are considerably smaller, but are still large fish with a maximum total length of at least 3.2 m (10.5 ft) and 3.5 m (11.5 ft) respectively.[2][50] In the past it was often reported that the dwarf sawfish only reaches about 1.4 m (4.6 ft), but this is now known to be incorrect.[51]

Distribution

The smalltooth sawfish is the only species found strictly in the Atlantic region and the only that survives in the United States.[3]

Range

Sawfish are found worldwide in tropical and

subtropical waters.[3]

Historically they ranged in the East Atlantic from

Mediterranean and these have typically been regarded as vagrants,[3] but a review of records strongly suggests that this sea had a breeding population.[53] In the East Pacific they ranged from Mazatlán (Mexico) to northern Peru.[54] 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.[54] 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.[3] Today sawfish have disappeared from much of their historical range.[3]

Habitat

A smalltooth sawfish in shallow water at Bimini, the Bahamas

Sawfish are primarily found in coastal marine and

salinities) and also found in freshwater.[2] The largetooth sawfish, alternatively called the freshwater sawfish, has the greatest affinity for freshwater.[55] For example, it has been reported as far as 1,340 km (830 mi) up the Amazon River and in Lake Nicaragua, and its young spend the first years of their life in freshwater.[21] In contrast, the smalltooth, green and dwarf sawfish typically avoid pure freshwater, but may occasionally move far up rivers, especially during periods when there is an increased salinity.[51][56][57] There are reports of narrow sawfish seen far upriver, but these need confirmation and may involve misidentifications of other species of sawfish.[58]

Sawfish are mostly found in relatively shallow waters, typically at depths less than 10 m (33 ft),[3] and occasionally less than 1 m (3.3 ft).[56] Young prefer very shallow places and are often found in water only 25 cm (10 in) deep.[4] Sawfish can occur offshore, but are rare deeper than 100 m (330 ft).[3] An unidentified sawfish (either a largetooth or smalltooth sawfish) was captured off Central America at a depth in excess of 175 m (575 ft).[59]

The dwarf and largetooth sawfish are strictly warm-water species that generally live in waters that are 25–32 °C (77–90 °F) and 24–32 °C (75–90 °F) respectively.[51][55] The green and smalltooth sawfish also occur in colder waters, in the latter down to 16–18 °C (61–64 °F), as illustrated by their (original) distributions that ranged further north and south of the strictly warm-water species.[55][60] Sawfish are bottom-dwellers, but in captivity it has been noted that at least the largetooth and green sawfish readily take food from the water surface.[55] Sawfish are mostly found in places with soft bottoms such as mud or sand, but may also occur over hard rocky bottoms or at coral reefs.[61] They are often found in areas with seagrass or mangrove.[3]

Sawsharks are typically found much deeper, often at depths in excess of 200 m (660 ft), and when shallower mostly in colder subtropical or temperate waters than sawfish.[1][45]

Behavior

Breeding and life cycle

A juvenile smalltooth sawfish being released

Relatively little is known about the reproductive habits of the sawfish, but all species are

ovoviviparous with the adult females giving birth to live young once a year or every second year.[3] In general, males appear to reach sexual maturity at a slightly younger age and smaller size than females.[3] As far as known, sexual maturity is reached at an age of 7–12 years in Pristis and 2–3 years in Anoxypristis. In the smalltooth and green sawfish this equals a total length of 3.7–4.15 m (12.1–13.6 ft), in the largetooth sawfish at 2.8–3 m (9.2–9.8 ft), in the dwarf sawfish about 2.55–2.6 m (8.4–8.5 ft), and in the narrow sawfish at 2–2.25 m (6.6–7.4 ft).[3] This means that the generation length is about 4.6 years in the narrow sawfish and 14.6–17.2 years in the remaining species.[3]

Mating involves the male inserting a

elasmobranchs, the mating appears to be rough, with the sawfish often sustaining lacerations from its partner's saw.[62] However, through genetic testing it has been shown that at least the smalltooth sawfish also can reproduce by parthenogenesis where no male is involved and the offspring are clones of their mother.[63][64] In Florida, United States, it appears that about 3% of the smalltooth sawfish offspring are the result of parthenogenesis.[65] It is speculated that this may be in response to being unable to find a partner, allowing the females to reproduce anyway.[64][65]

The

site fidelity, generally staying in the same fairly small area in the first part of their lives.[69] In the green and dwarf sawfish there are indications that both sexes remain in the same overall region throughout their lives with little mixing between the subpopulations. In the largetooth sawfish the males appear to move more freely between the subpopulations, while mothers return to the region where they were born to give birth to their own young.[70][71]

The length of the full lifespan of sawfish is labeled with considerable uncertainty. A green sawfish caught as a juvenile lived for 35 years in captivity,[55] and a smalltooth sawfish lived for more than 42 years in captivity.[72] In the narrow sawfish it has been estimated that the lifespan is about 9 years, and in the Pristis sawfish it has been estimated that it varies from about 30 to more than 50 years depending on the exact species.[3]

Electrolocation

Further information: Electroreception and electrogenesis

The rostrum (saw), unique among

Electroreception is found in all cartilaginous fishes and some bony fishes. In sawfish the sensory organs are packed most densely on the upper- and underside of the rostrum, varying in position and numbers depending on the species.[75][73] Utilizing their saw as an extended sensing device, sawfish are able to examine their entire surroundings from a position close to the seafloor.[1] It appears that sawfish can detect potential prey by electroreception from a distance of about 40 cm (16 in).[5] Some waters where sawfish live are very murky, limiting the possibility of hunting by sight.[71]

Feeding

Two largetooth sawfish at the Shanghai Ocean Aquarium

Sawfish are predators that feed on fish,

molluscs.[2] Old stories of sawfish attacking large prey such as whales and dolphins by cutting out pieces of flesh are now considered to be wholly unsubstantiated.[1][60] Humans are far too large to be considered potential prey.[76] In captivity they are typically fed ad libitum or in set amounts that (per week) equal 1–4% of the total weight of the sawfish, but there are indications that captives grow considerably faster than their wild counterparts.[55]

Exactly how they use their saw after the prey has been located has been debated, and some scholarship on the subject has been based on speculations rather than real observations.[5][74] In 2012 it was shown that there are three primary techniques, informally called "saw in water", "saw on substrate" and "pin".[74] If a prey item such as a fish is located in the open water, the sawfish uses the first method, making a rapid swipe at the prey with its saw to incapacitate it. It is then brought to the seabed and eaten.[5][55][74] The "saw on substrate" is similar, but used on prey at the seabed.[5][74] The saw is highly streamlined and when swiped it causes very little water movement.[77] The final method involves pinning the prey against the seabed with the underside of the saw, in a manner similar to that seen in guitarfish.[5][74] The "pin" is also used to manipulate the position of the prey, allowing fish to be swallowed head-first and thus without engaging any possible fin spines.[5][74] The spines of catfish, a common prey, have been found imbedded in the rostrum of sawfish.[33] Schools of mullets have been observed trying to escape sawfish.[78] Prey fish are typically swallowed whole and not cut into small pieces with the saw,[33] although on occasion one may be split in half during capture by the slashing motion.[5] Prey choice is therefore limited by the size of the mouth.[27] A 1.3 m (4.3 ft) sawfish had a 33 cm (13 in) catfish in its stomach.[71]

It had been suggested that sawfish use their saw to dig/rake in the bottom for prey,

hydrodynamic studies.[77] Large sawfish often have rostral teeth with tips that are notably worn.[35]

Saw and self-defense

Old stories often describe sawfish as highly dangerous to humans, sinking ships and cutting people in half, but today these are considered myths and not factual.[1][60] Sawfish are actually docile and harmless to humans, except when captured; they can inflict serious injuries when defending themselves, by thrashing the saw from side to side.[6][16][55] The saw is also used in self-defense against predators, such as sharks, that may eat sawfish.[33] In captivity, they have been seen using their saws during fights over hierarchy or food.[71]

Relationship with humans

In history, culture and mythology

Engraving showing a whale and several fish, including a sawfish, in China (Johan Nieuhof: Het gezantschap der Neêrlandtsche Oost-Indische Compagnie, 1665)

The largetooth sawfish was among the species formally described by Carl Linnaeus (as "Squalus pristis") in Systema Naturae in 1758,[21] but sawfish were already known thousands of years earlier.[7]

Sawfish were occasionally mentioned in antiquity, in works such as

Pliny's Natural History (77–79 AD).[4] Pristis, the scientific name formalised for sawfish by Linnaeus in 1758, was also in use as a name even before his publication. For example, sawfish or "priste" were included in Libri de piscibus marinis in quibus verae piscium effigies expressae sunt by Guillaume Rondelet in 1554, and "pristi" were included in De piscibus libri V, et De cetis lib. vnus by Ulisse Aldrovandi in 1613. Outside Europe, sawfish are mentioned in old Persian texts, such as 13th century writings by Zakariya al-Qazwini.[4]

Sawfish have been found among archaeological remains in several parts of the world, including the Persian Gulf region, the Pacific coast of Panama, coastal Brazil and elsewhere.[4][80]

A mask with a sawfish rostrum from Sepik, Papua New Guinea, now housed at the Ethnological Museum of Berlin

The cultural significance of sawfish varies significantly. The

Kuna people on the Caribbean coast of Panama and Colombia consider sawfish as rescuers of drowning people, and protectors against dangerous sea creatures.[8] Also in Panama, sawfish were recognized as containing powerful spirits that could protect humans against supernatural enemies.[8]

In the

Gambia, the saws indicate courage; the more saws are on display in a house, the more courageous the owner is seen to be.[84] In Senegal, the Lebu people believe the saw can protect their family, house and livestock. In the same general region, they are recognized as ancestral spirits who use the saw as a magic weapon. The Akan people of Ghana see sawfish as an authority symbol. There are proverbs with sawfish in the African language Duala.[85] In some other parts of coastal Africa, sawfish are considered extremely dangerous and supernatural, but their powers can be used by humans, as their saw is seen to retain powers against disease, bad luck and evil.[85] Among most African groups, consumption of sawfish meat is entirely acceptable, but among some (the Fula, Serer and Wolof people) it is taboo.[84] In the Niger Delta region of southern Nigeria, the saws of sawfish (known as oki in Ijaw and neighbouring languages) are often used in masquerades.[86]

In Asia, sawfish are a powerful symbol in many cultures. Asian shamans [

Carmine Maggiore in Naples.[4]

Kampfabzeichen der Kleinkampfverbände
(Battle Badge of Small Combat Units)
10000 CFA franc Banknote showing a form of sawfish imagery

Sawfish have been used as symbols in recent history. During

Kampfabzeichen der Kleinkampfverbände
 (Battle Badge of Small Combat Units) depicted a sawfish.

In cartoons and humorous popular culture, the sawfish—particularly its rostrum ("nose")—has been employed as a sort of living tool. Examples of this can be found in Vicke Viking and Fighting Fantasy volume "Demons of the Deep".[citation needed]

A stylized sawfish was chosen by the

Baoule bronze weight, used for exchanges in the trade of gold powder.[84]

In aquariums

Atlantis Paradise Island became the world's first place to breed a member of this family in captivity, when smalltooth sawfish pups were born in 2012.[89][90]

Sawfish are popular in

photoperiod are necessary to encourage breeding.[55] Artificial insemination, as already practiced with a few captive sharks, is also being considered.[93] Tracking studies indicate that if sawfish are released to the wild after spending a period in captivity (for example, if they outgrow their exhibit), they rapidly adopt a movement pattern similar to that of fully wild sawfish.[94]

Among the five sawfish species, only the four Pristis species are known to be kept in public aquariums. The most common is the largetooth sawfish, with

studbooks including 16 individuals in North America in 2014, 5 individuals in Europe in 2013 and 13 individuals in Australia in 2017; this was followed by the green sawfish, with 13 individuals in North America, and 6 in Europe.[55] Both of these species are also kept at public aquariums in Asia, and the only captive dwarf sawfish are in Japan.[95] In 2014, studbooks included 12 smalltooth sawfish in North America,[55] and the only ones kept elsewhere are at a public aquarium in Colombia.[95]

Decline and conservation

narrow sawfish caught by a local fisherman almost 100 years ago in the Dutch East Indies
(now Indonesia)

Sawfish were once common, with habitat found along the coastline of 90 countries,[96] locally even abundant,[4][7] but they have declined drastically and are now among the most threatened groups of marine fish.[3]

Fishing for various uses

Sawfish and their parts have been used for numerous things. In approximate order of impact, the four most serious threats today are use in

US$5,000 in Kenya and in 2014 a single rostral tooth sold as cockfighting spurs in Peru or Ecuador had a value of up to US$220.[4] Secondary uses are the meat for consumption and the skin for leather.[4] Historically the saws were used as weapons (large saws) and combs (small saws).[88] Oil from the liver was prized for use in boat repairs and street lights,[98] and as recent as the 1920s in Florida it was regarded as the best fish oil for consumption.[4]

Sawfish fishing goes back several thousand years,

gill nets.[99] In an attempt of lowering this, a guide to sawfish release has been published.[102]

Habitat destruction and vulnerability to predators

Although fishing is the main cause of the drastic decline in sawfish, another serious problem is habitat destruction. Coastal and estuarine habitats, including mangrove and seagrass meadows, are often degraded by human developments and pollution, and these are important habitats for sawfish, especially their young.[4][103] In a study of juvenile sawfish in Western Australia's Fitzroy River about 60% had bite marks from bull sharks or crocodiles.[104] Changes to river flows, such as by dams or droughts, can increase the risk faced by sawfish young by bringing them into more contact with predators.[69][105][106]

21st century status

The combined range of the five sawfish species encompassed 90 countries, but today they have certainly disappeared entirely from 20 of these and possibly disappeared from several others.[3] Many more have lost at least one of their species, leaving only one or two remaining.[3] Of the five species of sawfish, three are critically endangered and two are endangered according to the International Union for Conservation of Nature's Red List of Threatened Species.[107] The sawfish is now presumed extinct in 55 nations (including China, Iraq, Haiti, Japan, Timor-Leste, El Salvador, Taiwan, Djibouti and Brunei), with 18 countries with at least one species of sawfish missing and 28 countries with at least two.[107] The United States and Australia appear to be the last strongholds of the species, where sawfish are better protected.[107] Science Advances identifies Cuba, Tanzania, Colombia, Madagascar, Panama, Brazil, Mexico and Sri Lanka as the nations where urgent action could make a big contribution to saving the species.[107]

Australia
A largetooth sawfish in Northern Australia, which is the only remaining stronghold for four of the five species.[4][71]

The only remaining stronghold of the four species in the Indo-Pacific region (narrow, dwarf, largetooth and green sawfish) is in

AU$121,900.[13] The narrow sawfish does not receive the same level of protection as the Pristis sawfish.[103][109] Under CITES regulations, Australia was the only country that could export wild-caught sawfish for the aquarium trade from 2007 to 2013 (no country afterwards).[21] This strictly involved the largetooth sawfish where the Australian population remains relatively robust, and only living individuals "to appropriate and acceptable aquaria for primarily conservation purposes".[21] Numbers traded were very low (eight between 2007 and 2011),[4] and following a review Australia did not export any after 2011.[21]

Largetooth sawfish have been monitored in

the Kimberley.[110]

A study by

Indigenous rangers, which captured more than 500 sawfish between 2002 and 2018, concluded that the survival of the sawfish could be at risk from dams or major water diversions on the Fitzroy River. It found that the fish are completely reliant on the Kimberley's wet season floods to complete their breeding cycle; in recent drier years, the population has suffered. There has been debate about using water from the river for agriculture and to grow fodder crops for cattle in the region.[111]

Sharks and Rays Australia (SARA) are conducting a citizen science investigation to understand the sawfish's historical habitats. Citizen can report their sawfish sighting online.[112]

Rest of the world

Except for Australia, sawfish have been extirpated or only survive in very low numbers in the Indo-Pacific region. For example, among the four species only two (narrow and largetooth sawfish) certainly survive in South Asia, and only two (narrow and green sawfish) certainly survive in Southeast Asia.[3]

Sign for the protection of smalltooth sawfish in Florida, USA

The status of the two species of the Atlantic region, the smalltooth and largetooth sawfish, is comparable to the Indo-Pacific. For example, sawfish have been entirely extirpated from most of the Atlantic coast of Africa (only survives for certain in

power saw to remove a smalltooth sawfish's rostrum and then released the maimed fish; he received a fine, community service and probation.[120]

A smalltooth sawfish briefly captured for tagging as part of a conservation project

Since 2007, all sawfish species have been listed on

IUCN.[3] The other rated as Endangered is the dwarf sawfish, but this primarily reflects that its main decline happened at least 100 years ago and IUCN ratings are based on the time period of the last three generations (estimated about 49 years in dwarf sawfish).[3][99]

There are several research projects aimed at sawfish in Australia and North America, but also a few in other continents.[126] The Florida Museum of Natural History maintains the International Sawfish Encounter Database where people worldwide are encouraged to report any sawfish encounters, whether it was living or a rostrum seen for sale in a shop/online.[4][14][82] Its data is used by biologists and conservationists for evaluating the habitat, range and abundance of sawfish around the world.[4] In an attempt of increasing the knowledge of their plight the first "Sawfish Day" was held on 17 October 2017,[83][127] and this was repeated on the same date in 2018.[128]

See also

  • Threatened rays

Notes

  1. ^ Correct rostral tooth count refers to visible teeth and alveoli ("tooth sockets") from lost teeth.[1]

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Further reading

External links

Wikimedia Commons has media related to Pristidae.
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