The waters of the oceans are fraught with a huge variety of inhabitants that differ from each other in appearance, interesting shapes, and unusual names. In some cases, it was the peculiar appearance of the inhabitants of the ocean and their similarity with any objects, tools that allowed them to get their names. The sawfish is one of these inhabitants of the ocean.
Origin of the species and description
The sawfish as a species is an inhabitant of the oceans that has survived to this day since the Cretaceous period. Sawfish belong to the class of cartilaginous fish, which, in addition to it, includes sharks, rays and skates. A distinctive feature of this group is that the fish belonging to it have a skeleton made of cartilaginous tissue, and not bone. In this group, the sawfish is included in the stingray family, although it does not have a spike characteristic of representatives of this subspecies in its structure.
Interesting fact: Previously, the image of the sawfish was used by many cultures as a symbol of a tribe, such as the Aztecs.
The sawfish got its name due to the presence on the head of a wide bone outgrowth with notches, similar to a double-sided saw. Its scientific name is rostrum. Some species of sharks and rays have this feature. However, the term “sawfish” has stuck with stingrays, whose biological name from the Latin name “Pristidae” sounds like “common sawfish” or “sawfish ray”.
The differences between the sawfish and the sawfish, with which often confused even by the most experienced researchers, are:
- The saw shark is significantly smaller in size than the saw fish. The first most often reaches only 1.5 meters, the second – 6 meters or more;
- Different shapes of fins. The fins of the saw sharks are clearly defined and separated from the body. In sawfish rays, they smoothly merge into the lines of the body;
- In sawfish rays, gill slits are located on the belly, in sharks – on the sides;
- The so-called “saw” — the growth on the head is more accurate and even in width in sawfish rays, and the notches have the same shape. In sharks, the outgrowth is narrowed towards its end, long whiskers grow on it, and teeth of various sizes.
- The movement of the shark occurs due to the tail fin, when it makes sudden movements. The sawfish, on the other hand, moves smoothly, with wavy body movements.
The sawfish is considered little studied, therefore the specific number of its species is unknown. However, scientists have identified 7 species of sawn rays: green, Atlantic, European (of all the largest – up to 7 meters in length), fine-toothed, Australian (or Queensland), Asian and comb.
Interesting fact: Sawfish is edible, but not considered commercial. When catching fish, it is more like a trophy, because its meat is very hard.
All sawfly rays are conditionally divided into two groups depending on the size of the notches: one has large, while the other is small. In the oral cavity, the sawfish also has teeth, much smaller, but the same in size. Depending on the species, sawfish have between 14 and 34 pairs of teeth.
Interesting fact: The life expectancy of sawfish is quite high – sawfish can live up to 80 years.
Appearance and Features
The body of the sawfly ray is elongated, similar in shape to the body of a shark, but flatter. It is covered by placoid scales. The color of the body of the sawfish from the back is dark, olive-gray. Her belly is light, almost white. The tail part is practically not separated from the body of the sawfish, externally merges with it, being its continuation.
The sawfish has a flat snout with a characteristic long outgrowth in the shape of a rectangle, slightly narrowed from the base to the end, and notches are located on its sides. In reality, the saw teeth are transformed spikes that are covered with scales. The length of the growth, according to various sources, is from 20% to 25% of the total length of the entire sawfish, which is about 1.2 meters in adults.
On the ventral part of the body of the sawfly ray, in front of each pectoral fin, gill slits are located in two rows on the right and left. The nostrils in the form of gill slits, which are often mistaken for the eyes, and the mouth opening together are very similar to the face. In fact, the eyes of the sawfish are small and they are located on the dorsal part of the body. Behind them are sprinklers, with the help of which water is pumped through the gills. This allows the sawfish to be almost motionless on the bottom.
The sawfish has only 7 fins:
- two lateral fins on each side. Those closer to the head, — wide. They fused with the head, gradually tapering towards it. Large fins are of great importance when swimming sawfish, making waves;
- two high dorsal;
- din caudal, which in some individuals is divided into two lobes. The spike, which is located on the caudal fin of many rays, is absent.
Sawfish rays are quite large: their length, according to ichthyologists, is about 5 meters, and sometimes up to 6-7.5 meters . The average weight is 300-325 kg.
Where does the sawfish live?
Sawfish have an extensive habitat: most often it is tropical and subtropical waters of all oceans, with the exception of the Arctic Ocean. More often they can be found in the western part of the Atlantic Ocean from Brazil to Florida, and sometimes in the Mediterranean Sea.
Ichthyologists explain this by seasonal migrations: in summer, sawfish move from southern to northern waters, and in autumn they return to the south. In Florida, they can be seen in estuaries and bays almost always during the warmer months. Most of its species (five out of seven) live off the coast of Australia.
If we talk about the location of certain species of sawfish, we can distinguish that:
- European sawfish are found in the tropical and subtropical zones of the Atlantic Ocean and the Indo-Pacific region, in addition, they are found in the coastal region of Santarena and in Lake Nicaragua;
- green sawfish live, as a rule, in the tropical coastal zones of the Indo-Pacific region ;
- Atlantic sawfish are found in the tropical and subtropical zones of the Pacific and Indian Oceans;
- Small-toothed and Asian sawfishes are located in the tropical coastal zones of the Indian and Pacific Oceans;
- Australian – in the coastal waters of Australia and the rivers of this continent;
- crested – in the Mediterranean Sea, as well as in the tropics and subtropics of the Atlantic Ocean.
Sawfish prefer coastal waters as a habitat, so it is very difficult to meet them in the open ocean in practice. Quite often they swim in shallow water, where the water level is low. Therefore, a large dorsal fin can be seen above the water.
Sawfish, meeting in sea and fresh water, sometimes swims into rivers. In Australia, he prefers to live in the rivers all the time, feeling quite comfortable. Sawfish cannot tolerate human-polluted water. Habitat fish-saw more often chooses artificial reefs, mud bottom, algae, sandy soils. It can also be found near sunken ships, bridges, estuaries and piers.
What does the sawfish eat?
Sawfish is a predator, so it feeds on the inhabitants of sea waters. Most often, its food is invertebrates living in sand and silt on the seabed: crabs, shrimps and others. The sawfly earns its own food by loosening the bottom soil with its unusual nose, digging them out, and then eating them.
In addition, the sawfish prefers to feed on small fish such as mullet and members of the herring family. In this case, he breaks into a flock of fish and for some time begins to swing his rostrum in different directions. Thus, the fish stumbles upon its notches, like a saber, and falls to the bottom. The sawfly then slowly collects and eats its prey. Sometimes sawfish prey on larger fish, using their notches on the rostrum, pulling out pieces of meat from them. The larger the school of fish, the more likely it is to stun or spear more fish.
The so-called “saw” helps the sawfly in search of prey, as it is endowed with electroreceptors. Due to this, the sawfly is sensitive to the movement of marine life, catching the slightest movements of probable prey that swims in the water or burrows at the bottom. This makes it possible to see a three-dimensional image of the surrounding space even in muddy waters and use your growth at all stages of the hunt. Sawfish can easily detect their prey, even on a different water layer.
Experiments on sawmills confirm this. Sources of weak electrical discharges were placed in various places. It was these places that the sawfish attacked in order to catch prey.
Character and lifestyle features
Due to the fact that the sawfly is a hunter, it is quite aggressive. It looks especially intimidating in combination with the similarity to a shark. However, for humans, it does not pose a danger, rather, on the contrary, it is quite harmless. As a rule, when meeting with a person, the saw-nosed stingray tries to hide faster. However, when approaching him, a person should be careful and not anger him. Otherwise, sensing danger, the sawfish can use its rostrum as a defense and injure a person.
Only once was an unprovoked attack of a sawfly on a person recorded. It happened on the southern coast of the Atlantic Ocean: he hurt a man's leg. The individual was small in size – less than a meter long. The remaining few cases that occurred in the Gulf of Panama were provoked. In addition, there is an unconfirmed fact of attacks by sawfish off the coast of India.
There is an opinion about the clumsiness of the sawfish due to its rather long rostrum. However, in reality, the speed of her movements is simply elusive. This is noticeable by the dexterity of actions, the way of hunting the prey and its prey.
Most of the time, sawfish prefer to be near the seabed. They choose muddy water as a place to rest and hunt. Adult sawfishes give preference to a rather large depth – 40 m, where their cubs do not swim. Most often, the day for sawfish is a time of rest, but they are awake at night.
Social structure and reproduction
The sawfish differs from other types of fish not only in its unusual outgrowth, there are also differences in matters of reproduction. Sawfish do not lay eggs, but reproduce by carrying them inside the female, as do sharks and rays. Fertilization takes place in the womb of the female. How long are the cubs in the body of the female — unknown. For example, in the most studied small-toothed sawfish, the cubs stay in the body of the female for about 5 months.
There is no placental connection. However, in the tissue cells connected to the embryo, there is a yolk, which feeds on the sawfly cubs. During intrauterine development, their serrations are soft, completely covered with skin. This is inherent in nature, so as not to injure the mother. Teeth become stiff only with time.
Interesting fact: There is a species of sawfish whose females can breed without the participation of males, thus replenishing their numbers in nature. Moreover, at birth, their appearance has an exact copy of the mother.
Sawfish are born, shrouded in a skin membrane. At a time, a female sawfish produces about 15-20 cubs. The onset of puberty of the cubs comes slowly, the period depends on belonging to a particular species. For example, in small-toothed sawfish, this period is 10-12 years, on average & # 8212; about 20 years old.
If we talk about the correspondence of size and sexual maturity, then the studied small-toothed sawfish in Lake Nicaragua reached it at a length of 3 meters. The details of the sawfish reproductive cycle are not known because they have been little studied.
Natural enemies of sawfish
The natural enemies of sawfish are aquatic mammals and sharks. Since some sawfish swim in rivers, and there are species that are constantly in them, sawfish also have freshwater enemies – crocodiles.
To protect against them, the sawfish uses its long rostrum. The sawn stingray successfully defends itself, swinging this piercing and cutting tool in different directions. In addition, with the help of endowed electroreceptors, which are located on the rostrum, it is possible for the sawmill to obtain a three-dimensional image of the surrounding space. This allows you to navigate even in troubled water to protect yourself from enemies, and when danger approaches, hide from their field of vision. Observations in the aquarium of the contained sawfish rays also indicate the use of their “saw” to protect them.
Scientists from the Australian University of Newcastle, while studying the mechanism of using the rostrum, discovered another function that sawfish use to protect themselves from enemies. For this purpose, 3D models of sawn rays were created, which became participants in a computer simulation.
During the study, it was found that the sawmill, when moving, cuts through the water with its rostrum, like a knife, making smooth movements without vibrations and turbulent eddies. This feature allows you to move in the water unnoticed by your enemies and prey, who could determine its location by the vibration of the water.
Population and species status
Earlier, at the end of the 19th and beginning of the 20th centuries, the sawfish population was widespread, so it was not difficult to meet representatives of this species of rays. Evidence of this is a report by a fisherman in the late 1800s that he netted approximately 300 individuals in one fishing season in the coastal waters of Florida. Also, some fishermen said that they met sawfish of different sizes in the coastal waters of the western part of the peninsula.
There were no studies to measure the sawfish population that could be published during this period. However, sawmill population declines have been documented. It is believed that this is due to commercial fishing, namely the use of fishing gear: nets, fishing trawls and seines. Sawfish are quite easily entangled in them, due to their shape and long rostrum. Most of the caught sawfish suffocated or were killed.
Sawfish have little commercial value, as their meat is not used by humans for food due to its rather coarse structure. Previously, they were caught because of the fins, from which it was possible to make soup, and their parts were also distributed in the rare goods trade. In addition, liver fat was in demand in folk medicine. The rostrum of the sawfly is the most valuable: its cost exceeds $1,000.
The second half of the 20th century saw a significant decline in the number of sawfish in Florida. This happened just because of their catch and limited reproductive abilities. Therefore, since 1992, their capture has been banned in Florida. On April 1, 2003, the sawfish was recognized as an endangered species in the USA, and a little later it was listed in the International Red Book. In addition to fishing, the reason for this was human pollution of coastal waters, which led to the fact that sawfish cannot live in them.
Interesting fact: Poaching has taken a toll on sawfish populations. For this reason, as well as the deteriorating environmental situation, the Asian sawfish has been given the status of “Endangered” by the International Union for Conservation of Nature.
Nature itself and its evolutionary mechanism – parthenogenesis (or virgin reproduction) entered into the solution of the problem of the threat of extinction of the species of sawfish. This conclusion was made by scientists from Stony Brook University in New York. They discovered cases of parthenogenesis in the small-toothed sawfish, which is an endangered species.
From 2004 to 2013, scientists observed a group of small-toothed sawfish, which were located off the coast of Charlotte Harbor. As a result, 7 cases of virgin breeding were identified, which is 3% of the total number of mature sawfish in this group.
Saw fish protection
Due to a significant decline in the population, since 1992, the capture of sawfish rays has been banned in Florida. According to the endangered species status given in the USA on April 1, 2003, they are under federal protection. Since 2007, it has been illegal to trade in the body parts of sawfish rays, namely fins, rostrums, their teeth, skin, meat and internal organs at the international level.
Currently, the sawfish is listed in the International Red Book. Therefore, sawmills are subject to strict protection. In order to preserve the species, only the catch of small-toothed sawfish is allowed, which are subsequently kept in aquariums. In 2018, the EDGE ranking of the most endangered species among the most evolutionarily isolated was compiled. The sawfish came first on this list.
In this regard, scientists have proposed the following measures to protect the sawfish:
- use of the CITES ban (“Convention on International Trade in Wild Species endangered fauna and flora”);
- reducing the amount of unintentional harvesting of sawfish rays;
- maintaining and reviving the natural habitats of sawfish.
In some cases, unintentional catching is associated with sawfish hunting for prey. Because, chasing her, the sawfish can get into fishing nets. For this reason, scientists from the Australian University of Queensland, led by Barbara Wueringer, while studying the process of their hunting, are trying to find a way so that they do not fall into the nets of fishermen.
Sawfish as a species is a species that has survived to this day inhabitant of the oceans since the Cretaceous period. Quite common earlier, about 100 years ago, at the moment it has the status of an endangered species. The reason for this is man. Even though the sawfish is harmless to humans and is not a commercial fish, it is caught for the sale of some parts, and also pollutes its habitats.
Currently, the sawfish will be listed in the International Red Book, and therefore subject to strict protection. Moreover, nature itself and its evolutionary mechanism – parthenogenesis – entered into the solution of the problem of the threat of extinction of the sawfish species. The saw fish has every chance of preserving and reviving the population.