Instruct: Given a question, retrieve relevant documents that can help answer the question.
Query: What do sawfishes eat?
Sawfish are predators that feed on fish, crustaceans and 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 myths and not factual.[1][59] Humans are also far too large to be considered potential prey.[71]
Harranahynchus is an extinct genus of sclerorhynchid (Family Sclerorhynchidae) sawfish from the late Maastrichtian deposits of the Muwaqqar Chalk Marl Formation of Harrana in Jordan. The genus is so far represented by a single species, "Harranahynchus minutadens" and named after its minute rostral and dental battery teeth that do not exceed two millimeters in length, a size that is significantly smaller than the rostral teeth of any other modern or extinct sawfish species. Harranahynchids were medium-sized benthic predators around 2-2.5 meters in length and lived in the shallow offshore subtropical marine waters of the southern Tethys Ocean alongside other sclerohynchid sawfishes such as "Schizorhiza stromeri" Weiler, 1930.
The longcomb sawfish, narrowsnout sawfish or green sawfish ("Pristis zijsron") is a species of sawfish in the family Pristidae, found in tropical and subtropical waters of the Indo-West Pacific. It has declined drastically and is now considered a critically endangered species.
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 3.1m (10ft) and 3.5m (11ft) respectively.[2] In the past it was often reported that the dwarf sawfish only reaches about 1.4m (4.6ft), but this is now known to be incorrect.[50]
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 6m (20ft) in total length and there are reports of individuals larger than 7m (23ft), but these are often labeled with some uncertainty.[2] Typically reported maximum total lengths of these three are from 7to 7.6m (23–25ft).[2] Large individuals may weigh as much as 500–600kg (1,102–1,323lb),[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 9.14m (30ft), another that had a weight of 2,400kg (5,300lb), and a third that was 9.45m (31ft) long and weighed 2,591kg (5,712lb).[48]
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]
The most distinctive feature of sawfish is their saw-like rostrum with a row of whitish teeth (rostral teeth) on either side of it. The rostrum is an extension of the chondrocranium ("skull"),[27] made of cartilage and covered in skin.[33] The rostrum length is typically about one-quarter to one-third of the total length of the fish,[5] but it varies depending on species, and sometimes with age and sex.[1] The rostral teeth are not teeth in the traditional sense, but heavily modified 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]
The dwarf sawfish is protected in Australian waters, but elsewhere in the world, sawfishes are harvested for their meat, fins, rostrums and oil. The main threat facing the dwarf sawfish is being caught as bycatch in gillnets and trawl nets. That this is the cause of declining numbers is demonstrated by the fact that populations are declining fastest in heavily fished areas. The International Union for Conservation of Nature has assessed the conservation status of this fish as "endangered". There is a need for education of fishermen about safe release practices and how to manage their fisheries. However, the threats are continuing, and there is no reason to believe that the population of dwarf sawfish is recovering from previous declines.5. (Sensory Systems in Sawfishes. 1. The Ampullae of Lorenzini) https://www.researchgate.net/profile/Barbara_Wueringer/publication/51559323_Sensory_systems_in_sawfishes._1._The_ampullae_of_Lorenzini/links/09e415091dacec5f51000000.pdf
In the Bissagos Islands off West Africa dancing dressed as sawfish and other sea creatures is part of men's coming-of-age ceremonies.[80][83] In Gambia the saws indicate courage; the more on display at a house the more courageous the owner.[83] 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 with 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.[84] 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 retains the powers against disease, bad luck and evil.[84] Among most African groups consumption of meat from sawfish is entirely acceptable, but in a few (in West Africa the Fula, Serer and Wolof people) it is taboo.[83] In Asia sawfish are a powerful symbol in many cultures. Asian shamans use sawfish rostrums for exorcisms and in other ceremonies to repel demons and disease.[85] They are believed to protect houses from ghosts when hung over doorways.[4] Illustrations of sawfish are often found at Buddhist temples in Thailand.[81] In the Sepik region of New Guinea locals admire sawfish, but also see them as punishers that will unleash heavy rainstorms on anyone breaking fishing taboos.[8] Among the Warnindhilyagwa, a group of Indigenous Australians, the ancestral sawfish Yukwurrirrindangwa and rays created the land. The ancestral sawfish carved out the river of Groote Eylandt with their saw.[8][86] Among European sailors sawfish were often feared as animals that could sink ships by piercing/sawing in the hull with their saw (claims now known to be entirely untrue),[59] but there are also stories of them saving people. In one case it was described how a ship almost sank during a storm in Italy in 1573. The sailors prayed and made it safely ashore where they discovered a sawfish that had "plugged" a hole in the ship with its saw. A sawfish rostrum said to be from this miraculous event is kept at the Sanctuary of Carmine Maggiore in Naples.[4]
The dwarf sawfish or Queensland sawfish, "Pristis clavata", is a sawfish of the family Pristidae, found in tropical Australia. This endangered species is by far the smallest species in its family.
There are several research projects aimed at sawfish in Australia and North America, but also a few in other continents.[116] 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][81] 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.[82][117]
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,[54] and a smalltooth sawfish lived for more than 42 years in captivity.[70] 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]
Sawfish are primarily found in coastal marine and estuarine brackish waters, but they are euryhaline (can adapt to various salinities) and also found in freshwater.[2] The largetooth sawfish, alternatively called the freshwater sawfish, has the greatest affinity for freshwater.[54] For example, it has been reported as far as 1,340km (830mi) 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.[50][55][56] There are reports of narrow sawfish seen far upriver, but these need confirmation and may involve misidentifications of other species of sawfish.[57]
The cultural significance of sawfish varies significantly. The Aztecs in what is currently Mexico often included depictions of sawfish rostra (saws), notably as the striker/sword of the monster Cipactli.[80] Numerous sawfish rostra have been found buried at the Templo Mayor and two locations in coastal Veracruz had Aztec names referring to sawfish.[4] In the same general region, sawfish teeth have been found in Mayan graves.[81] The saw of sawfish is part of the dancing masks of the Huave and Zapotecs in Oaxaca, Mexico.[4][82] The Kuna people on the Caribbean coast of Panama and Colombia considers 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]
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, followed by the green sawfish with 13 individuals in North America and 6 in Europe.[54] Both these species are also kept at public aquariums in Asia and the only captive dwarf sawfish are in Japan.[93] In 2014, studbooks included 12 smalltooth sawfish in North America,[54] and the only kept elsewhere are at a public aquarium in Colombia.[93]
Relatively little is known about the reproductive habits of the sawfish, but all species are ovoviviparous with the adults 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 3.7–4.15m (12.1–13.6ft), in the largetooth sawfish at 2.8–3m (9.2–9.8ft), in the dwarf sawfish about 2.55–2.6m (8.4–8.5ft), and in the narrow sawfish at 2–2.25m (6.6–7.4ft).[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]
Adults are primarily found in estuaries and marine waters to a depth of , but mostly less than . Nevertheless, the species does appear to have a greater affinity for freshwater habitats than the smalltooth sawfish ("P. pectinata"), green sawfish ("P. zijsron"), and dwarf sawfish ("P. clavata"). Largetooth sawfish from the population in Lake Nicaragua appear to spend most, if not all, of their life in freshwater, but tagging surveys indicate that at least some do move between this lake and the sea. Captive studies show that this euryhaline species can thrive long-term in both salt and freshwater, regardless of its age, and that an acclimation from salt to freshwater is faster than the opposite. In captivity they are known to be agile (even swimming backwards), have an unusual ability to "climb" with the use of the pectoral fins and they can jump far out of the water; a individual jumped to a height of . It has been suggested that this may be adaptions for traversing medium-sized waterfalls and rapids when moving upriver. They are generally found in areas with a bottom consisting of sand, mud or silt. The preferred water temperature is between , and or colder is lethal.
The only remaining stronghold of the four species in the Indo-Pacific region (narrow, dwarf, largetooth and green sawfish) is in Northern Australia, but they have also experienced a declined there.[4][69] Pristis sawfish are protected in Australia and only Indigenous Australians can legally catch them.[100][103] Violations can result in a fine of up to AU$121,900.[13] The narrow sawfish does not receive the same level of protection as the Pristis sawfish.[100][104] 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] 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]
A range of English names have been used for the species, or populations now part of the species, including common sawfish (despite it being far from common today), wide sawfish, freshwater sawfish, river sawfish (less frequently, other sawfish species also occur in freshwater and rivers), Leichhardt's sawfish (after explorer and naturalist Ludwig Leichhardt) and northern sawfish.
Unlike the largetooth sawfish ("P. pristis"), the only other sawfish in the Atlantic, the smalltooth sawfish has a leading edge of the dorsal fin that is placed roughly above the leading edge of the pelvic fins (when the sawfish is seen from above or the side), relatively short pectoral fins and lack of a distinct lower lobe to the tail (lower lobe very small or absent). It can be separated from the more similar dwarf sawfish ("P. clavata") and green sawfish ("P. zijsron") by the distribution (both are only found in the Indo-Pacific) and the dorsal fin (its leading edge is placed slightly or clearly behind the leading edge of the pelvic fins in the dwarf and green sawfish). The smalltooth sawfish has a relatively narrow rostrum ("saw") with 20–32 teeth on each side.
The smalltooth sawfish ("Pristis pectinata") is a species of sawfish in the family Pristidae. It is found in shallow tropical and subtropical waters in coastal and estuarine parts of the Atlantic. Reports from elsewhere are now believed to be misidentifications of other species of sawfish. It is a critically endangered species that has disappeared from much of its historical range.
Vertebrate biologist Barbara Wueringer, of the University of Queensland, demonstrated that sawfish use their extended rostrum to detect and manipulate prey. She observed the animals' reaction to food already at the bottom of the tank, food falling from the water's surface, and introduced electric dipoles. When the sawfish came across scraps of fish resting on the bottom of the tank, it used its rostrum to pin the "prey" down as it swam over and engulfed it. When food was identified as it fell through the water, the sawfish would approach its "prey" from the side and swiftly strike to impale the victim with the teeth of its saw. Both of these cases support the respective digging and attacking behaviors expected from feeding sawfish in the wild. In order to show that sawfish use their beak to sense their surroundings, Wueringer placed electric dipoles throughout the tank to simulate the electrical signals that surround moving prey. Just as the sawfish displayed different aggressive behaviors towards the "prey," they also responded differently based on the electrical signals they received by either avoiding or approaching the signal source. With this evidence, the sawfish is now regarded as the only jawed fish to use its rostrum for both prey detection and manipulation.
Sawfish are mostly found in relatively shallow waters, typically at depths less than 10m (33ft),[3] and occasionally less than 1m (3.3ft).[55] Young prefer very shallow places and are often found in water only 25cm (10in) deep.[4] Sawfish can occur offshore, but are rare deeper than 100m (330ft).[3] An unidentified sawfish (either a largetooth or smalltooth sawfish) was captured off Central America at a depth in excess of 175m (575ft).[58]
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][59] Sawfish are actually docile and harmless to humans, except when captured where they can inflict serious injuries when defending themselves by thrashing the saw from side-to-side.[6][16][54] The saw is also used in self-defense against predators such as sharks that potentially may eat sawfish.[33] In captivity they have been seen using their saws during fights over hierarchy or food.[69]
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][100] In a study of juvenile sawfish in Western Australia's Fitzroy River about 60% had bite marks from bull sharks or crocodiles.[101] Changes to river flows, such as by dams, can increase the risk faced by sawfish young by bringing them into more contact with predators.[67][102]