There have been many legends and rumors about this giant fish that lives in the southern seas for a long time. People, frightened by its appearance and size, described the whale shark as a terrible lone monster from the ocean depths. Only after a lot of time it became clear that this predator, despite its intimidating appearance, is not at all dangerous. However, the whale shark remains one of the most mysterious fish on the planet to this day.
Origin of the species and description
The whale shark has long eluded researchers, and the few descriptions available have been more speculation than truth. For the first time, an animal (4.5-meter specimen obtained from South Africa) was described by E. Smith in 1828. Currently, a stuffed animal of this whale shark is located in Paris. The biospecies has been given the name Rhincodon types. The fish belongs to the shark family. In terms of dimensions, it surpasses not only the largest brothers, but also other types of fish.
The name “whale” fish received due to its huge size and way of feeding. According to the structure of the jaws, the animal is more reminiscent of cetaceans than shark relatives. As for the history of the biospecies, the most ancient ancestors of the whale shark lived in the Silurian period, approximately 440-410 million years ago. According to the most common hypothesis, the direct ancestor of shark-like fish was placoderms: marine or freshwater.
Appearance and Features
The whale shark is difficult to confuse with other representatives of the animal kingdom. The reason is that, in addition to its colossal dimensions, it has other external features:
- A powerful body covered with thick skin with tiny spiky scales. The skin in the belly area is somewhat thinner, so in a dangerous situation, the fish tries to hide a weak spot by turning its back to the enemy.
- Relatively small, somewhat flattened head, which turns into a flat muzzle with a wide (about one and a half meters) mouth. The mouth is in the center of the snout. This is another specific feature that distinguishes this shark from other members of the family (their mouth is located in the lower half of the muzzle).
- Behind the head, on the sides of the body, there are five gill slits. They serve as a kind of sieve that allows water to pass through. Through the gills comes out what the fish cannot swallow.
- The eyes are small, deep set. Even in large individuals, the diameter of the eyeball does not exceed 50 mm. They are located almost at the edges of the mouth. Whale sharks do not have nictitating membranes. However, in case of danger, their eyes are drawn deep into the orbits and tightly closed by a skin fold.
- The maximum width of the body is directly behind the head. It gradually tapers towards the tail.
- Whale sharks have 2 dorsal fins, slightly offset back. The first is slightly larger and higher than the second, in the form of an almost regular triangle. The tail fin of twelve meter sharks reaches 5 m, and the pectorals – 2.5 m.
- The teeth are very small. Even in the largest fish, they do not exceed 0.6 cm. But the number of teeth is very large (about 15 thousand). Hence the Latin name of the animal – Rhincodon, the translation of which means “grinding teeth.”
For a long time it was believed that the largest length of representatives of this species is about 12.7 m. However, according to some sources, animals reach large sizes. By the end of the last century, officially recorded information appeared about individual 20-meter individuals, whose weight reaches 34 tons. However, such colossi are rare even among whale sharks. On average, their length is about 9.7 m, with a mass of about 9 tons. Among all the fish on the planet, they are champions in size.
The color of the fish is very characteristic. The back and lateral surfaces of the body are dark gray. This background is mottled with yellowish or off-white longitudinal and transverse stripes. Between them are marks of the same shade of a rounded shape. The head and pectoral fins have the same spots, often and chaotically located. The belly is light grey. On the skin of the fins and body there are characteristic grooves-scratches that merge into a single pattern. The nature of the “pattern” for each individual is unique. It does not change with age, and you can recognize one or another fish by the look of the pattern.
Where does the whale shark live?
Whale sharks live in tropical seas, with a surface water temperature of 21-26 degrees. You will not meet slow giants above the fortieth parallel. This is due not so much to the thermophilicity of sea colossi as to their food preferences. After all, it is in warm waters that a lot of plankton is found – the favorite food of these fish.
The range of the whale shark extends to the following territories:
- Ocean waters near the Seychelles.
- Populations of whale sharks are found near Australia, Chile, the Philippine Islands and in the Gulf of Mexico.
Regions adjacent to Madagascar and the southeastern part of the African continent. It is estimated that about 20% of the total number of these fish lives in the waters of the Indian Ocean near Mozambique.
What does a whale shark eat?
Like other types of sharks, this fish belongs to the category of predators. However, you cannot blame her for bloodthirstiness. Despite the formidable appearance and no less frightening Latin name, the “gnashing teeth” whale shark feeds on zooplankton and small schooling fish (small tuna, mackerel, sardines, anchovies). This fish uses its teeth not to chew its prey, but to prevent it from slipping out of its giant mouth. In other words, these are not millstones for grinding food, but a kind of “locks” for locking it.
Like baleen whales, the shark “grazes” for a long time. Taking water in her mouth, she strains the plankton. The fish closes its mouth, and the water comes out through the gills-filters. Thus, only those inhabitants of the ocean who are able to penetrate the narrow esophagus of the fish (its diameter reaches only 100 mm) remain in the mouth of the fish. To get enough, a whale shark must spend about 8-9 hours daily on food. In an hour, she passes through the gills about 6 thousand cubic meters of ocean water. Sometimes small animals clog filters. To clean them, the fish “clears their throat”. At the same time, the stuck food literally flies out of the animal's mouth.
The stomach capacity of whale sharks is about 0.3 m3. Part of the prey fish spends on maintaining the energy balance. Some food is stored in a special compartment of the stomach as a reserve. Part of the useful substances is deposited in the animal's liver – a kind of energy pantry. You could call it a rainy day stock. The liver of a whale shark is relatively small, and is not suitable as a “float” for holding a large, heavy body in the water column. These fish do not have a swim bladder. For better buoyancy, the animal swallows air, releasing it when diving into the ocean depths.
According to recent studies conducted by Japanese zoologists, the diet of whale sharks turned out to be somewhat more diverse than originally thought. In addition to animal food, which undoubtedly forms the basis of the menu, they also feed on algae, and, if necessary, they can starve. Fish “fast” mainly during migration from one food base to another. When there is a shortage of basic food, the whale shark is content with a vegetarian “diet” for some time.
Character and lifestyle features
Most ichthyologists tend to consider whale sharks to be calm, peaceful and very slow creatures. As a rule, the animal keeps closer to the water surface, but sometimes goes to a depth of 700 meters. The fish swims at a low speed – about 5 km/h, and sometimes even less. She is active almost around the clock, with short breaks for sleep.
This species of sharks is completely safe for humans. Divers take advantage of this and not only get close to the fish, but also climb on them. However, wounded individuals can be dangerous. A single blow of the tail is enough to kill a person or damage a small vessel.
Social Structure and Reproduction
Whale sharks are kept alone or live in small groups. Large aggregations of hundreds of individuals are rare. The record-breaking herd of sea giants (420 individuals) was recorded in August 2009 near the Yucatan Peninsula. Most likely, they were attracted by freshly baked mackerel caviar, which the giants enjoy eating. The puberty period for a whale shark is quite long. With a life expectancy of 70-100 years, it is ready for reproduction at the age of 30-35, sometimes at 50 years. The length of a mature individual ranges from 4.5 to 5.6 m (according to other sources, 8-9 m). The body length of sexually mature males is about 9 m.
There is no exact information on the ratio between the number of females and males in the population. Studying a herd of fish off the western coast of Australia (Ningaloo Reef Marine Reserve), scientists found that the number of females in the total number of observed animals does not exceed 17%. However, this information cannot be called absolutely reliable, since whale sharks use this region not for bearing offspring, but for feeding. The animal belongs to the category of ovoviviparous cartilaginous fish. For some time, the whale shark was called oviparous, since eggs with embryos were found in the womb of a female caught off the coast of Ceylon. The length and width of one embryo in the capsule are 0.6 and 0.4 m, respectively.
A 12-meter female can carry up to 300 embryos at the same time. Each embryo is enclosed in an ovoid capsule. A newborn baby shark is 0.4-0.5 m long. After the birth, the baby is completely independent and viable. He leaves the mother's body with a sufficient supply of substances that allow him to not look for food for a long time. There is a known case when a live cub was extracted from the womb of a captured female. Placed in an aquarium, he felt quite well, and began to take food only on the 17th day. The duration of pregnancy is 1.5-2 years. The female is kept alone during the gestation period.
Natural enemies of whale sharks
In addition to the main enemy – man – these giants are attacked by marlin and blue sharks. The great white sharks are not far behind. As a rule, young individuals are the most vulnerable to predators, but there are attacks on quite adult fish. In essence, the whale shark is completely defenseless against predators. Thick skin with spiked scales is not always effective in saving from enemies. This colossus simply has no other means of defense. Whale sharks are also saved by the fact that the skin has a unique ability to regenerate. Fish are unusually tenacious, wounds heal very quickly. This is one of the reasons why the giants were able to survive to this day, practically unchanged for 60 million years.
Population and species status
The number of whale sharks is small. According to some reports, the total number of these fish on the planet is about 1 thousand individuals. The main reason for the sharp decline in animals is their uncontrolled commercial capture in the Philippine Islands and Taiwan, where the meat, liver and fins of the whale shark are at a high price. These fish are also exterminated because of the shark oil rich in useful substances. The reduction in the number of animals is also facilitated by the fact that fishers are trying to catch the largest individuals (and these are mainly females). These calm predators are very easy prey, catching them is quite simple. Sometimes a slow animal, almost unable to maneuver, gets under the blades of moving ships.
According to the international status, the whale shark belongs to the status of endangered species (since 2016, it was previously defined as “vulnerable”). Until 2000, the status of the animals was listed as “uncertain” because there was not enough information about the biospecies. Since the 90s of the last century, a number of countries have imposed a ban on catching these fish.
Whale shark conservation
Despite the small number, the giant fish has found distribution in the culture of the eastern peoples. For example, Japanese and Vietnamese fishermen are convinced that a meeting with a whale shark – a good sea deity – is a good omen. Despite the fact that seafood is the basis of the diet for the population of these countries, the Japanese and Vietnamese do not eat whale shark meat. The Vietnamese name of this animal has a literal translation: “Lord-Fish”.
Whale sharks are of great importance for the tourism business. Excursions are very popular, when tourists can watch these slow-moving beauties from the ship. And some daredevils swim up to them with scuba gear. Such diving tours are popular in Mexico, Seychelles, Caribbean and Maldives, Australia. Of course, such increased attention from people does not contribute to the growth of the population of these fish, which are becoming less and less. Tourists should keep their distance from them, not only for safety reasons, but also in order not to damage the outer mucous layer that protects the skin of animals from small parasites. Attempts are being made to keep these sharks in captivity.
The first experience dates back to 1934. The fish was not placed in an aquarium. A specially fenced off part of the bay (Japanese Islands) served as an aviary for her. The fish lived for 122 days. In the period 1980-1996, the maximum number of these animals was kept in captivity in Japan – 16. Of these, 2 females and 14 males. Currently, on The Okinawa Aquarium is home to a 4.6-meter male whale shark, the largest of the whale sharks that have been in captivity.The basis of the diet of fish caught near Okinawa is sea shrimp (krill), small squid and small fish.
Since 2007, 2 sharks (3.7 and 4.5 m) caught near Taiwan have been kept in the Georgia Aquarium in Atlanta (USA). The capacity of the aquarium for these fish is more than 23.8 thousand m3. An individual that was previously kept in this aquarium died in 2007. The experience of Taiwanese scientists in keeping whale sharks in captivity is not so successful. Twice sharks died shortly after being placed in the aquarium, and only in 2005 the attempt was successful. To date, there are 2 whale sharks in the Taiwan Aquarium. One of them, a 4.2-meter female, is devoid of a dorsal fin. In all likelihood, she suffered from fishermen or from the teeth of a predator. Since the summer of 2008, a 4-meter individual has been kept in the aquarium in Dubai (the volume of the tank is 11 thousand m3). The fish are fed with krill, that is, its diet does not differ from the “menu” of baleen whales.
Unfortunately, the number of whale sharks on Earth is declining. The main reason is poaching, despite the ban on fishing in many countries. In addition, these are not only the largest, but perhaps the least studied fish on the planet. Most of their life passes far from the coast, so the study of these animals causes certain difficulties. The whale shark needs our help. Improving the understanding of their behavioral characteristics, the specifics of nutrition and biology will allow us to develop effective measures for the conservation of these majestic creatures as a biospecies.