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All About Dolphins for Kids: Dolphins for Children - FreeSchool

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All About Penguins for Kids: Penguins of the World for Children - FreeSchool

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All About Sharks for Children: Animal Videos for Kids - FreeSchool

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Green Turtle's Battle for Survival | Planet Earth | BBC Earth

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All About Manatees for Children: Manatee Video for Kids - FreeSchool

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Piranha facts: the (not so) deadly fish | Animal Fact Files

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Crabs Trade Shells in the Strangest Way | BBC Earth

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All About Jellyfish for Kids: Jellyfish for Children - FreeSchool

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The Dolphin | Educational Video for Kids.

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All About Whale Sharks for Children: Whale Shark video for Kids - FreeSchool

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Manatees Have Bad Breath | Life Of Mammals | BBC Earth

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Red-Bellied Piranhas 🐡 | Amazing Animals

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America's Crayfish: Crawling In Troubled Waters

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BBC: Planet Earth: Creatures of the Deep - Jellyfish

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Dolphins Herd Mullet - Blue Planet - BBC wildlife

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Emperor penguins | The Greatest Wildlife Show on Earth | BBC Earth

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The piranha (also known as the caribe) is a ferocious, schooling, fresh-water fish. It is native to warm lowland streams and lakes in South America, east of the Andes Mountains. Piranhas have been introduced to other places, including Northern Brazil, Hawaii, and parts of Central and North America. There are many species of piranha; they belong to the genera Pygocentrus and Serrasalmus. They reproduce by laying eggs.

Piranhas are opportunistic carnivores (flesh-eaters). They eat aquatic and land animals that are in the water. Some of the prey includes fish, mollusks, crustaceans, insects, birds, lizards, amphibians, rodents, and carrion (dead meat that they find). These fish are diurnal (most active during the day).

Many animals prey upon piranhas (especially young piranhas), including other piranhas, caimans, water snakes, turtles, birds, otters, and people.

Images for kids

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The piranha (also known as the caribe) is a ferocious, schooling, fresh-water fish. It is native to warm lowland streams and lakes in South America, east of the Andes Mountains. Piranhas have been introduced to other places, including Northern Brazil, Hawaii, and parts of Central and North America.

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Crayfish, also known as crawfish, crawdads, freshwater lobsters, mountain lobsters, mudbugs or yabbies, are freshwater crustaceans resembling small lobsters, to which they are related.

They breathe through feather-like gills. Some species are found in brooks and streams where there is running fresh water, while others thrive in swamps, ditches, and paddy fields. Most crayfish cannot tolerate polluted water, although some species such as are hardier. Crayfish feed on living animals and plants, and detritus. There are about 150 crayfish species in North America, and over 540 species worldwide.

The body of a decapod crustacean, such as a crab, lobster, or prawn (shrimp), is made up of twenty body segments grouped into two main body parts, the cephalothorax and the abdomen. Each segment may possess one pair of appendages, although in various groups, these may be reduced or missing. On average, crayfish grow to 17.5 cm (6.9 in) in length. Walking legs have a small claw at the end.

Geographical distribution and classification

Three families of crayfish are described, two in the Northern Hemisphere and one in the Southern Hemisphere. The Southern Hemisphere ( Gondwana-distributed) family Parastacidae, with 14 extant genera and two extinct genera, live(d) in South America, Madagascar, and Australasia. They are distinguished by the absence of the first pair of pleopods. Of the other two families, the three genera of the Astacidae live in western Eurasia and western North America, while the 15 genera of the family Cambaridae live in eastern Asia and eastern North America.

North America

The greatest diversity of crayfish species is found in southeastern North America, with over 330 species

In 1983, Louisiana designated the crayfish, or crawfish as they are commonly called, as its official state crustacean. Louisiana produces 100 million pounds of crawfish per year with the red swamp and white river crawfish being the main species harvested.

Crawfish are a part of Cajun culture dating back hundreds of years. A variety of cottage industries have developed as a result of commercialized crawfish iconology. Their products include crawfish attached to wooden plaques, T-shirts with crawfish logos, and crawfish pendants, earrings, and necklaces made of gold or silver.

Australia has over 100 species. It is home to the world's three largest freshwater crayfish:

Many of the better-known Australian crayfish are of the genus Cherax, and include the common yabby, western yabby, and red-claw crayfish.

The marron species is critically endangered, while other large Australasian crayfish are threatened or endangered.

New Zealand

In New Zealand, two species of Paranephrops are endemic, and are known by the Māori name .

Other animals

In Australia, New Zealand, and South Africa, the term "crayfish" or "cray" generally refers to a saltwater spiny lobster, of the genus Jasus that is indigenous to much of southern Oceania, while the freshwater species are usually called or , from the indigenous Australian and Māori names for the animal, respectively, or by other names specific to each species. Exceptions include western rock lobster found on the west coast of Australia; the Tasmanian giant freshwater crayfish found only in Tasmania; and the Murray crayfish found along Australia's Murray River.

In Singapore, the term crayfish typically refers to Thenus orientalis, a seawater crustacean from the slipper lobster family. True crayfish are not native to Singapore, but are commonly found as pets, or as an invasive species in the many water catchment areas, and are alternatively known as freshwater lobsters.

Fossil record

Fossil records of crayfish older than 30 million years are rare, but fossilised burrows have been found from strata as old as the late Palaeozoic or early Mesozoic. The oldest records of the Parastacidae are in Australia, and are 115 million years old and the crayfish Palaeocambarus and Cricoidoscelosus from the Yixian Formation of China are likely around 120 million years old, making them both one of, if not, the oldest known crayfish to date.

Crayfish are eaten worldwide. Like other edible crustaceans, only a small portion of the body of a crayfish is eaten. In most prepared dishes, such as soups, bisques and étouffées, only the tail portion is served. At crawfish boils or other meals where the entire body of the crayfish is presented, other portions, such as the claw meat, may be eaten. Like all crustaceans, crayfish are not kosher because they are aquatic animals that do not have both fins and scales. They are therefore not eaten by observant Jews.

As of 2005, Louisiana supplies 95% of the crayfish harvested in the U.S. In 1987, Louisiana produced 90% of the crayfish harvested in the world, 70% of which were consumed locally. In 2007, the Louisiana crawfish harvest was about 54,800 tons, almost all of it from aquaculture. About 70%-80% of crayfish produced in Louisiana are Procambarus clarkii (red swamp crawfish), with the remaining 20%-30% being Procambarus zonangulus (white river crawfish).

Crayfish are preyed upon by a variety of ray-finned fishes, and are commonly used as bait, either live or with only the tail meat. They are a popular bait for catching catfish, largemouth bass, smallmouth bass, striped bass, perch, pike and muskie. When using live crayfish as bait, anglers prefer to hook them between the eyes, piercing through their hard, pointed beak which causes them no harm; therefore, they remain more active.

Crayfish are kept as pets in freshwater aquariums. They prefer foods like shrimp pellets or various vegetables, but will also eat tropical fish food, regular fish food, algae wafers, and small fish that can be captured with their claws.

In some nations, such as the United Kingdom, United States, Australia, and New Zealand, imported alien crayfish are a danger to local rivers. Crayfish may spread into different bodies of water because specimens captured for pets in one river are often released into a different catchment. There is a potential for ecological damage when crayfish are introduced into non-native bodies of water: e.g., crayfish plague in Europe, or the introduction of the common yabby ( Cherax destructor) into drainages east of the Great Dividing Range in Australia.

Invasive species

Crayfish have been recorded as an invasive species from Louisiana to Europe to China. They have been known to consume local rice crops in China.

Images for kids

A man selling dried crayfish at an African market

In Spanish: Cangrejo de río para niños

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Army Of Spider Crabs Shed Their Shells | Blue Planet II

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Take a deep breath, gang, and join Nat Geo Kids as we learn ten fab facts about one seriously splash-tastic sea creature - in our bottlenose dolphin facts!
Facts about bottlenose dolphins

1) Bottlenose dolphins are marine mammals that live in tropical and temperate oceans (oceans with mild temperatures) around the world. This includes the waters off the UK and Ireland, where you can spot them swimming and playing in bays and river estuaries!

2) These beautiful creatures have a short thick beak (as their name suggests!) and a curved mouth, giving the appearance that they are always smiling. They are usually grey in colour, and measure around two to four metres in length.

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3) Social creatures, bottlenose dolphins travel in groups, called " pods ", of around 10-15. In these groups they play and hunt together, as well as cooperate to raise young dolphin calves and help each other.

4) Bottlenose dolphins are super swimmers, gliding through the water using their curved dorsal fin on their back, a powerful tail and pointed flippers. They can reach speeds over 30km an hour and dive as deep as 250m below the surface!

5) These cool creatures are awesome acrobats, too, and can be seen flipping (or " breaching ") out of the water. In fact, they can launch themselves up to five meters out of the water before crashing back down with a splash! There are different theories as to why they do this - it could be to get a better view of things in the distance, clean parasites off their bodies, communicate with other pods or just for good fun!

6) Although they live underwater, the bottlenose dolphin must come up to the surface to breath air. It breathes through what"s called a " blowhole ", a hole at the top of its head. These clever creatures can open this hole when inhaling and exhaling out of the water, and close it when below the ocean surface. They can hold their breath underwater for around seven minutes.

7) Bottlenose dolphins are kings of communication! They send each other messages in different ways - they squeak and whistle and also use body language, leaping out of the water, snapping their jaws and even butting heads!

8) These magnificent mammals also produce high-pitched clicks to help them navigate and find food - a process called " echolocation ". When the clicking sounds hit an object in the water - such as a rock or fish - they bounce back to the dolphin as echoes. From this, the super swimmers can work out the location, size and shape of the object. Cool, eh?

9) Carnivores, our finned friends eat mostly fish, but will also eat crustaceans such as shrimp and squid, too.

10) Thankfully, bottlenose dolphins are not classed as endangered. However, illegal hunting, fishing nets and pollution pose threats to these incredible creatures.

Love reading about sea life? Then be sure to check out our Humpback whale facts!

Image ⓒ Picture of dolphin stretched out above water: Photograph by Kjersti Joergensen, Dreamtime. Picture of a dolphin closeup in water: Photograph by Michael Price, Dreamtime. Picture of a dolphin jumping: Photograph by Avslt71, Dreamtime.

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10 facts about bottlenose dolphins - National Geographic Kids

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Take a deep breath, gang, and join Nat Geo Kids as we learn ten fab facts about one seriously splash-tastic sea creature - in our bottlenose dolphin facts! 1) Bottlenose dolphins are marine mammals that live in tropical and temperate oceans (oceans with mild temperatures) around the world.

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Emperor penguins spend their entire lives on Antarctic ice and in its waters. They survive-breeding, raising young, and eating-by relying on a number of clever adaptations.

These flightless birds breed in the winter. After a courtship of several weeks, a female emperor penguin lays one single egg then leaves! Each penguin egg's father balances it on his feet and covers it with his brood pouch, a very warm layer of feathered skin designed to keep the egg cozy. There the males stand, for about 65 days, through icy temperatures, cruel winds, and blinding storms.

Finally, after about two months, the females return from the sea, bringing food they regurgitate, or bring up, to feed the now hatched chicks. The males eagerly leave for their own fishing session at sea, and the mothers take over care of the chicks for a while.

As the young penguins grow, adults leave them in groups of chicks called crèches while they leave to fish. There is a reason for the timing of emperor penguins' hatching. By December, when the Antarctic weather has warmed somewhat, the ice the penguins occupy begins to break up, bringing open waters closer to the nesting sites. Now the chicks are old enough to take to the seas and fish for their own food.

Check out the book Penguins vs. Puffins for more about these amazing birds!

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Emperor penguins spend their entire lives on Antarctic ice and in its waters. They survive-breeding, raising young, and eating-by relying on a number of clever adaptations. These flightless birds breed in the winter. After a courtship of several weeks, a female emperor penguin lays one single egg then leaves!

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15 Amazing facts About the Great White Shark

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Sea turtles ( Chelonioidea) are turtles found in all the world's oceans except the Arctic Ocean, and some species travel between oceans. The term is US English. In British English they are simply called "turtles"; fresh-water chelonians are called " terrapins" and land chelonians are called tortoises.

There are seven types of sea turtles: Kemp's Ridley, Flatback, Green, Olive Ridley, Loggerhead, Hawksbill and the leatherback. All but the leatherback are in the family Chelonioidea. The leatherback belongs to the family Dermochelyidae and is its only member. The leatherback sea turtle is the largest, measuring six or seven feet (2 m) in length at maturity, and three to five feet (1 to 1.5 m) in width, weighing up to 2000 pounds (about 900 kg). Most other species are smaller, being two to four feet in length (0.5 to 1 m) and proportionally less wide. The Flatback turtle is found solely on the northern coast of Australia.

Description

Importantly, for each of the seven types of sea turtles, females and males are the same size, i.e. there is no sexual dimorphism.

In general, sea turtles have a more fusiform body plan than their terrestrial or freshwater counterparts. This tapering at both ends reduces volume and means that sea turtles can't, as can other turtles and tortoises, retract their head and limbs into their shells for protection. But the streamlined body plan reduces friction and drag in the water and allows sea turtles to swim more easily and swiftly.

The leatherback sea turtle is the largest sea turtle, measuring 2-3 meters (6-9 ft) in length, and 1-1.5 m (3-5 ft) in width, weighing up to 700 kilograms (1500 lb). Other sea turtle species are smaller, being mostly 60-120 cm (2-4 ft) long and proportionally narrower.

Distribution and habitat

Sea turtles can be found in all oceans except for the polar regions. The flatback sea turtle is found solely on the northern coast of Australia. The Kemp's ridley sea turtle is found solely in the Gulf of Mexico and along the East Coast of the United States.

Sea turtles are generally found in the waters over continental shelves. During the first three to five years of life, sea turtles spend most of their time in the pelagic zone floating in seaweed mats. Green sea turtles in particular are often found in mats, in which they find shelter food,and water. Once the sea turtle has reached adulthood it moves closer to the shore. Females will come ashore to lay their eggs on sandy beaches during the nesting season.

Sea turtles migrate to reach their spawning beaches, which are limited in numbers. Living in the ocean therefore means they usually migrate over large distances. All sea turtles have large body sizes, which is helpful for moving large distances. Large body sizes also offer good protection against the large predators (notably sharks) found in the ocean.

It takes decades for sea turtles to reach sexual maturity. Mature sea turtles may migrate thousands of miles to reach breeding sites. After mating at sea, adult female sea turtles return to land to lay their eggs. Different species of sea turtles exhibit various levels of philopatry. In the extreme case, females return to the same beach where they hatched. This can take place every two to four years in maturity.

The mature nesting female hauls herself onto the beach, nearly always at night, and finds suitable sand in which to create a nest. Using her hind flippers, she digs a circular hole 40 to 50 centimetres (16 to 20 in) deep. After the hole is dug, the female then starts filling the nest with her clutch of soft-shelled eggs. Depending on the species, a typical clutch may contain 50-350 eggs. After laying, she re-fills the nest with sand, re-sculpting and smoothing the surface, and then camouflaging the nest with vegetation until it is relatively undetectable visually. The whole process takes 30 to 60 minutes. She then returns to the ocean, leaving the eggs untended.

Females may lay 1-8 clutches in a single season. Female sea turtles alternate between mating in the water and laying their eggs on land. Most sea turtle species nest individually. But ridley sea turtles come ashore en masse, known as an arribada (arrival). With the Kemp's ridley sea turtle this occurs during the day.

Sea turtles have temperature-dependent sex determination, meaning the developing baby sea turtle's sex depends on the temperature it is exposed to. Warmer temperatures produce female hatchlings, while cooler temperatures produce male hatchlings. The eggs will incubate for 50-60 days. The eggs in one nest hatch together over a short period of time. The baby sea turtles break free of the egg shell, dig through the sand, and crawl into the sea. Most species of sea turtles hatch at night. However, the Kemp's ridley sea turtle commonly hatches during the day. Sea turtle nests that hatch during the day are more vulnerable to predators, and may encounter more human activity on the beach.

Larger hatchlings have a higher probability of survival than smaller individuals, which can be explained by the fact that larger offspring are faster and thus less exposed to predation. Predators can only functionally intake so much; larger individuals are not targeted as often. A study conducted on this topic shows that body size is positively correlated with speed, so larger baby sea turtles are exposed to predators for a shorter amount of time. The fact that there is size dependent predation on chelonians has led to the evolutionary development of large body sizes.

In 1987, Carr discovered that the young of green and loggerhead sea turtles spent a great deal of their pelagic lives in floating sargassum mats. Within these mats, they found ample shelter and food. In the absence of sargassum, young sea turtles feed in the vicinity of upwelling "fronts". In 2007, Reich determined that green sea turtle hatchlings spend the first three to five years of their lives in pelagic waters. In the open ocean, pre-juveniles of this particular species were found to feed on zooplankton and smaller nekton before they are recruited into inshore seagrass meadows as obligate herbivores.

Images for kids

In Spanish: Chelonioidea para niños

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Manatees are large, fully-aquatic marine mammals of the order Sirenia. They are sometimes known as sea cows. The manatees form the genus Trichechus. There are three manatee species.

The name comes from the Spanish manatí, which itself comes from a Carib word meaning " breast".

Early sightings

Christopher Columbus, who thought mermaids were real, went to the waters around Haiti, and wrote in his logbook that he had seen three mermaids. He said that they were not as beautiful as everybody said they were. Nowadays, people believe Christopher Columbus had actually seen three manatees. It is possible he saw them kissing one another, which is something they do when the meet each other in the water.

Description

Manatees have thick pads around their lips and stiff bristles that help them grab food and move it towards the mouth. A manatee eats sea grass and all kinds of sea vegetables. All its teeth are shaped like a human's molars. The eight hours of chewing each day wears down on their teeth. In fact, its first two pairs of teeth get so worn out that they simply fall out sometimes. However, manatees can grow new teeth. New teeth are always growing in the back. When front teeth fall out, the back teeth move forward to take their place. In mammals, only elephants and (quite independently) kangaroos have this kind of system.

The Sirenia are thought to have evolved from four-legged land mammals over 60 million years ago. Their closest living relatives are the Proboscidea ( elephants) and Hyracoidea ( hyraxes).

Family Trichechidae
Genus Trichechus

West Indian manatee, Trichechus manatus

Amazonian manatee, Trichechus inunguis

West African manatee, Trichechus senegalensis

Manatees live on the coasts of the Atlantic Ocean and the rivers. The West African Manatee lives on the western side of Africa, on the shores from Senegal to Angola. They also live in some rivers like the Niger River and around Lake Chad. The West Indian Manatee lives in the Gulf of Mexico and the Caribbean, and also on the shores of Brazil and Venezuela. The Amazonian Manatee lives in parts of the Amazon Basin in South America.

Manatees live in salt water and in fresh water. On the sea shores they mostly live in shallow water, like lagoons and mangroves. They also live in brackish water and rivers. Manatees like bodies of water with a temperature of over 20 °C.

They are mainly herbivores, spending most of their time grazing in shallow waters at depths of 1-2 metres (3-7 ft).

Images for kids

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Manatees are large, fully-aquatic marine mammals of the order Sirenia. They are sometimes known as sea cows. The manatees form the genus Trichechus . There are three manatee species. The name comes from the Spanish manatí, which itself comes from a Carib word meaning " breast".

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Crabs are in the subphylum Crustacea. They are decapods (having eight walking legs and two grasping claws), along with lobsters, crayfish and shrimps. Crabs form an order within the decapods, called the Brachyura. Their short body is covered by a thick exoskeleton.

They are an extremely successful group, found all over the world. They are basically heavily armoured shell-breakers. Most crabs live in sea-water, but there are some who live in fresh water, and some who live on land. The smallest are the size of a pea; the largest (the Japanese spider crab) grows to a leg span of 4 metres. About 7,000 species are known.

Structure and life-style

Crabs have short tails. A crab's tail and reduced abdomen is entirely hidden under the thorax. It is folded under its body, and may not be visible at all unless the crab is turned over. Usually they have a very hard exoskeleton. This means they are well protected against predators. Crabs are armed with a single pair of claws. Crabs can be found in all oceans. Some crabs also live in fresh water, or live completely on land.

The pincers (claws) of crabs are their most important weapons. They have at least three functions. The pincers' role in eating is to seize and subdue the prey. If the food is a shellfish ( mollusc), then the pincers can exert force to open or break the mollusc's shell. Pincers are also used in fighting between males, and for signalling to other crabs.

Crabs are omnivores, they eat almost anything they find. Often this is algae, but animal food is essential for its good health and development. They will eat molluscs, other crustaceans, worms, fungi and bacteria.

Crabs as food

Crabs are prepared and eaten all over the world. Some species are eaten whole, including the shell, such as soft-shell crab; with other species just the claws and/or legs are eaten. In some regions spices improve the culinary experience. In Asia, Masala Crab and Chilli crab are examples of heavily spiced dishes. In Maryland, blue crab is often eaten with Old Bay Seasoning.

For the British dish Cromer crab, the meat is extracted and placed inside the hard shell. One American way to prepare crab meat is by extracting it and adding a flour mix, creating a crab cake. Crabs are also used in bisque, a French soup.

True crabs appear in the fossil record in the Lower Jurassic. They are part of the ' Mesozoic marine revolution', in which a number of sea-floor predators evolved.

The closest relatives of the crabs are anomurans, a crustacean group which includes animals such as hermit crabs, king crabs and squat lobsters. They look a lot like crabs and many have the word 'crab' in their name, but are not true crabs. Anomurans can be told apart by the number of legs: crabs have eight legs, along with two claws or pincers, while the last pair of an anomuran's legs is hidden inside the shell, so that only six are visible.

Images for kids

In Spanish: Brachyura para niños

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Jellyfish are animals of the phylum Cnidaria. They are a monophyletic clade, the Medusozoa. Most of them live in the oceans, in salt water, where they eat small sea animals like plankton and little fish, and float in the sea. Only a few jellyfish live in fresh water.

They have soft bodies and long, stinging, venomous tentacles that they use to catch their prey, usually small plankton animals or small crustaceans or tiny fish. Some jellyfish hunt other jellyfish. Venom is injected by stinging cells called nematocysts. A jellyfish is 97% water.

Most jellyfish have a bell-shaped body and long tentacles at the underside of the body. Tentacles are long "arms" with special stinging cells called nematocysts. They move by contracting their bodies, but they do not have much control over where they go: most of the time, they drift with the water current. The largest type of jellyfish is the Lion's mane jellyfish, which has tentacles that can be as long as 60 meters, but most jellyfish are much smaller.

The Medusozoa are four classes of the Cnidaria:

There are many types of jellyfish. The smallest jellyfish are just a few inches across. The largest jellyfish is the Lion's mane ( Cyanea capillata), whose body can be over 3 feet (1 m) across, with much longer tentacles. Some jellyfish glow in the dark (this is called phosphorescence). Some of the most dangerous jelly fish include the box jelly (Genuses Chironex, Chiropsalmus and Carybdea) and the tiny, two-cm-across Irukandji jelly ( Carukia barnesi); the venomous sting of these jellyfish can kill a person.

Many animals eat jellyfish, including sea turtles and some fish (including the sun fish). Humans eat jellyfish too; especially in Asia jellyfish are considered a delicacy. Jellyfish spoil very quickly after they are caught. Sometimes they are dried to preserve them. There is a different process in which they are cleaned, which can take up to 40 days. They are often eaten in a kind of salad, with soy sauce or vinegar.

Most jellyfish undergo two distinct life history stages (body forms) during their life cycle. The first is the polypoid stage, when the animal takes the form of a small stalk with feeding tentacles. Very often, this polyp is attached to the sea floor, or to another hard surface; it rarely moves around. A polyp that lives that way is called sessile. In some cases, the polyp is free-floating. Polyps generally have a mouth surrounded by upward-facing tentacles. Polyps may be on their own or in groups, and some bud asexually, making more polyps. Most are very small, measured in millimeters.

In the second stage, the tiny polyps asexually produce jellyfish, each of which is known as a medusa. Tiny jellyfish swim away from the polyp and then grow and feed in the plankton. Jellyfish reproduce both sexually and asexually. Well-fed adult jellyfish spawn daily. In most species, spawning is controlled by light, so the entire population spawns at about the same time of day, often at either dusk or dawn. Jellyfish are usually either male or female (with occasional hermaphrodites). In most cases, adults release sperm and eggs into the surrounding water, where the (unprotected) eggs are fertilized and mature into new organisms.

Medusae have a radially symmetric, umbrella-shaped body called a bell, which is usually supplied with marginal tentacles that capture prey. A few species of jellyfish do not have the polyp portion of the life cycle, but go from jellyfish to the next generation of jellyfish through direct development of fertilized eggs. Jellyfish at the medusa stage usually lives only up to six months, after which it dies.

Jellyfish eat plankton and small fish, which they catch using their venomous tentacles. Jellyfish may live in symbiosis with algae. The jellyfish transports them into sunlight and get nutrients from the algae's photosynthesis. Both forms of jelly fish have small tentacles with nematocysts (stinging cells) that sting and can hurt people on contact.

A group of jellyfish is called a smack; an occurrence of many jellyfish simultaneously is sometimes called a bloom.

Images for kids

A flower hat jelly ( Olindias formosa) photographed at the Osaka Aquarium Kaiyukan

Illustration of two life stages of seven jelly species

Aurelia sp. occurs in large quantities in most of the world's coastal waters.Members of this genus are nearly identical to each other

Like many species of jellyfish, the sting of some species of Mastigias have little or no discernible effect on humans.

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Jellyfish are animals of the phylum Cnidaria. They are a monophyletic clade, the Medusozoa. Most of them live in the oceans, in salt water, where they eat small sea animals like plankton and little fish, and float in the sea. Only a few jellyfish live in fresh water.

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When a great white shark is born, along with up to a dozen siblings, it immediately swims away from its mother. Born on the east and west coasts of North America, the south of Africa and southwest Australia, baby sharks are on their own right from the start. Their mother may see them only as prey. At birth the baby shark is already about 5 feet (1.5 meters) long; as it grows it may reach a length up to four times that. The pup (which is what a baby shark is called) will live its life at the top of the ocean’s food chain. But before it grows larger, the pup must avoid predators bigger than it is—including other great white sharks. Many baby sharks do not survive their first year. Young great white sharks eat fish (including other sharks) and rays. As they grow, the sharks’ favorite prey becomes sea mammals, especially sea lions and seals. Sharks count on the element of surprise as they hunt. When they see a seal at the surface of the water, sharks will often position themselves underneath the seal. Using their tails as propellers, they swim upward at a fast sprint, burst out of the water in a leap called a breach, and fall back into the water with the seal in their mouths. They can smell a single drop of blood from up to a third of a mile (0.53 kilometers) away. Sharks don’t chew their food; they rip off chunks of meat and swallow them whole. They can last a month or two without another big meal.

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The beluga whale ( Delphinapterus leucas) is a small, toothed whale that is white as an adult. They are found in coastal areas of the Arctic Ocean, and travel south when the sea ice forms.

Mitochondrial DNA studies have shown modern cetaceans last shared a common ancestor between 30 and 34 million years ago. The family Monodontidae separated relatively early from the other odontoceti; it split from the Delphinoidea between 11 and 15 million years ago, and from the Phocoenidae, its closest relatives in evolutionary terms, more recently still.

The beluga's earliest known ancestor is the prehistoric Denebola brachycephala from the late Miocene period (9-10 million years ago). A single fossil from the Baja California Peninsula indicates the family once inhabited warmer waters. The fossil record also indicates, in comparatively recent times, the beluga's range varied with that of the polar ice packs expanding during ice ages and contracting when the ice retreated. Counter-evidence to this theory comes from the finding in 1849 of fossilised beluga bones in Vermont in the United States, 240 km (150 mi) from the Atlantic Ocean.

Description

The beluga's body is stout and has a small, blunt head with a small beak, tiny eyes and thick layers of blubber. On their head they have a round shape called the melon. This melon holds oil, and the whale is able to change its shape. Scientists believe that it has something to do with the whale's echolocation system. They have one blowhole. Beluga means white one in Russian. Its genus Delphinapterus, means "whale without fins", and the species, leucas, means " white". The beluga is also called the white whale, the white porpoise, the sea canary (because of its songs), and the squid hound (due to its diet). Unlike most other cetaceans, the beluga's seven neck vertebrae are not fused, giving it a flexible, well-defined neck.

The species presents a moderate degree of sexual dimorphism, as the males are 25% longer than the females and are sturdier. Adult male belugas can range from 3.5 to 5.5 m (11 to 18 ft), while the females measure 3 to 4.1 m (9.8 to 13.5 ft). Males weigh between 1,100 and 1,600 kg (2,430 and 3,530 lb), occasionally up to 1,900 kg (4,190 lb) while females weigh between 700 and 1,200 kg (1,540 and 2,650 lb). They rank as mid-sized species among toothed whales.

Individuals of both sexes reach their maximum size by the time they are 10 years old. The beluga's body shape is stocky and fusiform (cone-shaped with the point facing backwards), and they frequently have folds of fat, particularly along the ventral surface. Between 40% and 50% of their body weight is fat, which is a higher proportion than for cetaceans that do not inhabit the Arctic, where fat only represents 30% of body weight. The fat forms a layer that covers all of the body except the head, and it can be up to 15 cm (5.9 in) thick. It acts as insulation in waters with temperatures between 0 and 18 °C, as well as being an important reserve during periods without food.

Head and neck

Like most toothed whales, it has a compartment found at the centre of the forehead that contains an organ used for echolocation called a melon, which contains fatty tissue. The shape of the beluga's head is unlike that of any other cetacean, as the melon is extremely bulbous, lobed, and visible as a large frontal prominence. Another distinctive characteristic it possesses is the melon is malleable; its shape is changed during the emission of sounds. The beluga is able to change the shape of its head by blowing air around its sinuses to focus the emitted sounds. This organ contains fatty acids, mainly isovaleric acid (60.1%) and long-chain branched acids (16.9%), a very different composition from its body fat, and which could play a role in its echolocation system.

Belugas have a dorsal ridge, rather than a dorsal fin. The absence of the dorsal fin is reflected in the genus name of the species- apterus the Greek word for "wingless". The evolutionary preference for a dorsal ridge rather than a fin is believed to be an adaptation to under-ice conditions, or possibly as a way of preserving heat. The crest is hard and, along with the head, can be used to open holes in ice up to 8 cm (3.1 in) thick.

The beluga has a very specialized sense of hearing and its auditory cortex is highly developed. It can hear sounds within the range of 1.2 to 120 kHz, with the greatest sensitivity between 10 and 75 kHz, where the average hearing range for humans is 0.02 to 20 kHz. The majority of sounds are most probably received by the lower jaw and transmitted towards the middle ear. In the toothed whales, the lower jawbone is broad with a cavity at its base, which projects towards the place where it joins the cranium. A fatty deposit inside this small cavity connects to the middle ear. Toothed whales also possess a small external auditory hole a few centimetres behind their eyes; each hole communicates with an external auditory conduit and an eardrum. It is not known if these organs are functional or simply vestigial.

Belugas are able to see within and outside of water, but their vision is relatively poor when compared to dolphins. Their eyes are especially adapted to seeing under water, although when they come into contact with the air, the crystalline lens and the cornea adjust to overcome the associated myopia (the range of vision under water is short). A beluga's retina has cones and rods, which also suggests they can see in low light. The presence of cone cells indicates they can see colours, although this suggestion has not been confirmed. Glands located in the medial corner of their eyes secrete an oily, gelatinous substance that lubricates the eye and helps flush out foreign bodies. This substance forms a film that protects the cornea and the conjunctiva from pathogenic organisms.

Studies on captive animals show they seek frequent physical contact with other belugas. Areas in the mouth have been found that could act as chemoreceptors for different tastes, and they can detect the presence of blood in water, which causes them to react immediately by displaying typical alarm behaviour. Like the other toothed whales, their brains lack olfactory bulbs and olfactory nerves, which suggests they do not have a sense of smell.

These cetaceans are highly sociable and they regularly form small groups, or pods, that may contain between two and 25 individuals, with an average of 10 members. Pods tend to be unstable, meaning individuals tend to move from pod to pod. Radio tracking has even shown belugas can start out in one pod and within a few days be hundreds of miles away from that pod. These pods contain animals of both sexes, and are led by a dominant male. Many hundreds and even thousands of individuals can be present when the pods join together in river estuaries during the summer. This can represent a significant proportion of the total population and is when they are most vulnerable to being hunted.

They are cooperative animals and frequently hunt in coordinated groups. The animals in a pod are very sociable and often chase each other as if they are playing or fighting, and they often rub against each other.

In captivity, they can be seen to be constantly playing, vocalizing, and swimming around each other. They show a great deal of curiosity towards humans and frequently approach the windows in the tanks to observe them. Belugas may also playfully spit at humans or other whales. It is not unusual for an aquarium handler to be drenched by one of his charges. Some researchers believe spitting originated with blowing sand away from crustaceans at the sea bottom.

Belugas also show a great degree of curiosity towards humans in the wild, and frequently swim alongside boats. They also play with objects they find in the water; in the wild, they do this with wood, plants, dead fish, and bubbles they have created. During the breeding season, adults have been observed carrying objects such as plants, nets, and even the skeleton of a dead reindeer on their heads and backs. Captive females have also been observed displaying this behaviour, carrying items such as floats and buoys, after they have lost a calf; experts consider this interaction with the objects could be acting as a substitute behaviour.

Swimming and diving

Belugas are slower swimmers than the other toothed whales, such as the killer whale and the common bottlenose dolphin, because they are less hydrodynamic and have limited movement of their tailfins, which produce the greatest thrust. They frequently swim at between 3 and 9 km/h (1.9 and 5.6 mph), although they are able to maintain a speed of 22 km/h for up to 15 min. Unlike most cetaceans, they are capable of swimming backwards. Belugas swim on the surface between 5% and 10% of the time, while for the rest of the time they swim at a depth sufficient to cover their bodies. They do not jump out of the water like dolphins or killer whales.

These animals usually only dive to depths to 20 m (66 ft), although they are capable of diving to greater depths. Individual captive animals have been recorded at depths between 400 and 647 m below sea level, while animals in the wild have been recorded as diving to a depth of more than 700 m, with the greatest recorded depth being 872 m. A dive normally lasts 3 to 5 min, but can last up to 18 min. In the shallower water of the estuaries, a diving session may last around two minutes; the sequence consists of five or six rapid, shallow dives followed by a deeper dive lasting up to one minute. The average number of dives per day varies between 31 and 51.

Beluga whales often accompany bowhead whales, for curiosity and to secure polynya feasible to breathe as bowheads are capable of breaking through ice from underwater by headbutting.

Belugas play an important role in the structure and function of marine resources in the Arctic Ocean, as they are the most abundant toothed whales in the region. They are opportunistic feeders; their feeding habits depend on their locations and the season. For example, when they are in the Beaufort Sea, they mainly eat Arctic cod ( Boreogadus saida) and the stomachs of belugas caught near Greenland were found to contain rose fish ( Sebastes marinus), Greenland halibut ( Reinhardtius hippoglossoides), and northern shrimp ( Pandalus borealis), while in Alaska their staple diet is Pacific salmon ( Oncorhynchus kisutch). In general, the diets of these cetaceans consist mainly of fish; apart from those previously mentioned, other fish they feed on include capelin ( Mallotus villosus), smelt, sole, flounder, herring, sculpin, and other types of salmon. They also consume a great quantity of invertebrates, apart from shrimp, such as squid, crabs, clams, octopus, sea snails, bristle worms, and other deep-sea species. Animals in captivity eat 2.5% to 3.0% of their body weight per day, which equates to 18.2 to 27.2 kg.

Foraging on the seabed typically takes place at depths between 20 and 40 m, although they can dive to depths of 700 m in search of food. Their flexible necks provide a wide range of movement while they are searching for food on the ocean floor. Some animals have been observed to suck up water and then forcefully expel it to uncover their prey hidden in the silt on the seabed. As their teeth are neither large nor sharp, belugas must use suction to bring their prey into their mouths; it also means their prey has to be consumed whole, which in turn means it cannot be too large or the belugas run the risk of it getting stuck in their throats. They also join together into coordinated groups of five or more to feed on shoals of fish by steering the fish into shallow water, where the belugas then attack them. For example, in the estuary of the Amur River, where they mainly feed on salmon, groups of six or eight individuals join together to surround a shoal of fish and prevent their escape. Individuals then take turns feeding on the fish.

Reproduction

Estimations of the age of sexual maturity for beluga whales vary considerably; the majority of authors estimate males reach sexual maturity when they are between four and seven years old, and females reach maturity when they are between four and nine years old. The average age at which females first give birth is 8.5 years and fertility begins to decrease when they are 25, with no births recorded for females older than 41.

Female belugas typically give birth to one calf every three years. Most mating occurs usually February through May, but some mating occurs at other times of year. The beluga may have delayed implantation. Gestation has been estimated to last 12.0 to 14.5 months, but information derived from captive females suggests a longer gestation period up to 475 days (15.8 months).

The calves remain dependent on their mothers for nursing for the first year, when their teeth appear. After this, they start to supplement their diets with shrimp and small fish. The majority of the calves continue nursing until they are 20 months old, although occasionally lactation can continue for more than two years, and lactational anoestrus may not occur. Alloparenting (care by females different from the mother) has been observed in captive belugas, including spontaneous and long-term milk production. This suggests this behaviour, which is also seen in other mammals, may be present in belugas in the wild.

Communication and echolocation

Belugas use sounds and echolocation for movement, communication, to find breathing holes in the ice, and to hunt in dark or turbid waters. They produce a rapid sequence of clicks that pass through the melon, which acts as an acoustic lens to focus the sounds into a beam that is projected forward through the surrounding water. These sounds spread through the water at a speed of nearly 1.6 km per second, some four times faster than the speed of sound in the air. The sound waves rebound from objects in the water and return as echoes that are heard and interpreted by the animal. This enables them to determine the distance, speed, size, shape, and even the internal structure of the objects within the beam of sound. They also use this ability when moving around the thick ice sheets of the Arctic, to find areas of unfrozen water for breathing, or air pockets trapped under the frozen sheet ice.

These cetaceans communicate using sounds of such high frequency; their calls sometimes sound like bird songs, so belugas have been given the nickname "canaries of the sea". Like the other toothed whales, belugas do not possess vocal cords and the sounds are probably produced by the movement of air between the nasal sacks, which are located near to the blowhole.

Belugas are amongst the most vocal cetaceans. They use their vocalisations for echolocation, during mating, and in communication. They possess a large repertoire, as they can emit up to 11 different sounds, such as cackles, whistles, trills, and squawks. They also make sounds by grinding their teeth or splashing, but they rarely use body language to make visual displays with their pectoral fins or tailfins, nor do they perform somersaults or jumps in the way other species do, such as dolphins.

Distribution

Belugas have a seasonal migratory pattern. When the summer sites become blocked with ice during the autumn, they move to spend the winter in the open sea alongside the pack ice or in areas covered with ice, surviving by using polynyas to surface and breathe. In summer after the sheet ice has melted, they move to coastal areas with shallower water (1-3 m deep), although sometimes they migrate towards deeper waters (>800 m). In the summer, they occupy estuaries and the waters of the continental shelf, and on occasion, they even swim up the rivers. A number of incidents have been reported where groups or individuals have been found hundreds or even thousands of kilometres from the ocean. One such example comes from 9 June 2006, when a young beluga carcass was found in the Tanana River near Fairbanks in central Alaska, nearly 1,700 kilometers (1,100 mi) from the nearest ocean habitat. Belugas sometimes follow migrating fish, leading Alaska state biologist Tom Seaton to speculate it had followed migrating salmon up the river at some point in the previous autumn. The rivers they most often travel up include: the Northern Dvina, the Mezen, the Pechora, the Ob and the Yenisei in Asia; the Yukon and the Kuskokwim in Alaska, and the Saint Lawrence in Canada. Spending time in a river has been shown to stimulate an animal's metabolism and facilitates the seasonal renewal of the epidermal layer. In addition, the rivers represent a safe haven for newborn calves where they will not be preyed upon by killer whales. Calves often return to the same estuary as their mother in the summer, meeting her sometimes even after becoming fully mature.

The migration season is relatively predictable, as it is basically determined by the amount of daylight and not by other variable physical or biological factors, such as the condition of the sea ice. Vagrants may travel further south to areas such as Irish and Scottish waters, islands of Orkney and Hebrides, and to Japanese waters. There had been several vagrant individuals demonstrated seasonal residencies at Volcano Bay, and a unique whale were used to return annually to areas adjacent to Shibetsu in Nemuro Strait in the 2000s. On rarer occasions, individuals of vagrancy can reach the Korean Peninsula. A few other individuals have been confirmed to return to the coasts of Hokkaido, and one particular individual became a resident in brackish waters of Lake Notoro since in 2014.

Some populations are not migratory and certain resident groups will stay in well-defined areas, for example in Cook Inlet, the estuary of the Saint Lawrence River and Cumberland Sound. The population in Cook Inlet stays in the waters furthest inside the inlet during the summer and until the end of autumn, then during the winter, they disperse to the deeper water in the centre of the inlet, but without completely leaving it.

Belugas exploit a varied range of habitats; they are most commonly seen in shallow waters close to the coast, but they have also been reported to live for extended periods in deeper water, where they feed and give birth to their young.

Population

The global beluga population is made up of a number of subpopulations. The scientific committee of the International Whaling Commission recognizes these 29 subpopulations:

The estimate of population sizes is complicated because the boundaries for some of these groups overlap geographically or seasonally. The IUCN estimated the world beluga population in 2008 to be well in excess of 150,000.

The native populations of the Canadian, Alaskan, and Russian Arctic regions hunt belugas for their meat, blubber, and skin. The cured skin is the only cetacean skin that is sufficiently thick to be used as leather. Belugas were easy prey for hunters due to their predictable migration patterns and the high population density in estuaries and surrounding coastal areas during the summer.

During the 1920s, fishermen in the Saint Lawrence River estuary considered belugas to be a threat to the fishing industry, as they eat large quantities of cod, salmon, tuna, and other fish caught by the local fishermen. The presence of belugas in the estuary was, therefore, considered to be undesirable; in 1928, the Government of Quebec offered a reward of 15 dollars for each dead beluga. The Quebec Department of Fisheries launched a study into the influence of these cetaceans on local fish populations in 1938. The unrestricted killing of belugas continued into the 1950s, when the supposed voracity of the belugas was found to be overestimated and did not adversely affect fish populations. L'Isle-aux-Coudres is the setting for the classic 1963 National Film Board of Canada documentary Pour la suite du monde, which depicts a one-off resurrection of the beluga hunt.

The Arctic's native peoples still carry out subsistence hunting of belugas to obtain food and raw materials. This practice is a part of their culture, but doubts still remain whether the number of whales killed may be sustainable. The number of animals killed is about 200 to 550 in Alaska and around 1,000 in Canada. However, in areas such as Cook Inlet, Ungava Bay, and western Greenland, previous levels of commercial whaling have put the species in danger of extinction, and continued hunting by the native peoples may mean some populations will continue to decline. The Canadian sites are the focus of discussions between the local communities and the Canadian government, with the objective of permitting sustainable hunting that does not put the species at risk of extinction.

During the winter, belugas commonly become trapped in the ice without being able to escape to open water, which may be several kilometres away. Polar bears take particular advantage of these situations and are able to locate the belugas using their sense of smell. The bears swipe at the belugas and drag them onto the ice to eat them. They are able to capture large individuals in this way; in one documented incident, a bear weighing between 150 and 180 kg was able to capture an animal that weighed 935 kg.

Killer whales are able to capture both young and adult belugas. They live in all the seas of the world and share the same habitat as belugas in the sub-Arctic region. Attacks on belugas by killer whales have been reported in the waters of Greenland, Russia, Canada, and Alaska. A number of killings have been recorded in Cook Inlet, and experts are concerned the predation by killer whales will impede the recovery of this subpopulation, which has already been badly depleted by hunting. The killer whales arrive at the beginning of August, but the belugas are occasionally able to hear their presence and evade them. The groups near to or under the sea ice have a degree of protection, as the killer whale's large dorsal fin, up to 2 m in length, impedes their movement under the ice and does not allow them to get sufficiently close to the breathing holes in the ice.

Contamination

The beluga is considered an excellent sentinel species (indicator of environment health and changes), because it is long-lived, at the top of the food web, bears large amounts of fat and blubber, relatively well-studied for a cetacean, and still somewhat common.

Human pollution can be a threat to belugas' health when they congregate in river estuaries. Chemical substances such as DDT and heavy metals such as lead, mercury and cadmium have been found in individuals of the Saint Lawrence River population. Local beluga carcasses contain so many contaminants, they are treated as toxic waste. Levels of polychlorinated biphenyls between 240 and 800 ppm have been found in belugas' brains, liver and muscles, with the highest levels found in males. These levels are significantly greater than those found in Arctic populations. These substances have a proven adverse effect on these cetaceans, as they cause cancers, reproductive diseases, and the deterioration of the immune system, making individuals more susceptible to pneumonias, ulcers, cysts, tumours, and bacterial infections. Although the populations that inhabit the river estuaries run the greatest risk of contamination, high levels of zinc, cadmium, mercury, and selenium have also been found in the muscles, livers, and kidneys of animals that live in the open sea.

From a sample of 129 beluga adults from the Saint Lawrence River examined between 1983 and 1999, a total of 27% had suffered cancer. This is a higher percentage than that documented for other populations of this species and is much higher than for other cetaceans and for the majority of terrestrial mammals; in fact, the rate is only comparable to the levels found in humans and some domesticated animals. For example, the rate of intestinal cancer in the sample is much higher than for humans. This condition is thought to be directly related to environmental contamination, in this case by polycyclic aromatic hydrocarbons, and coincides with the high incidence of this disease in humans residing in the area. The prevalence of tumours suggests the contaminants identified in the animals that inhabit the estuary are having a direct carcinogenic effect or they are at least causing an immunological deterioration that is reducing the inhabitants' resistance to the disease.

Indirect human disturbance may also be a threat. While some populations tolerate small boats, most actively try to avoid ships. Whale-watching has become a booming activity in the St. Lawrence and Churchill River areas, and acoustic contamination from this activity appears to have an effect on belugas. For example, a correlation appears to exist between the passage of belugas across the mouth of the Saguenay River, which has decreased by 60%, and the increase in the use of recreational motorboats in the area. A dramatic decrease has also been recorded in the number of calls between animals (decreasing from 3.4 to 10.5 calls/min to 0 or <1) after exposure to the noise produced by ships, the effect being most persistent and pronounced with larger ships such as ferries than with smaller boats. Belugas can detect the presence of large ships (for example icebreakers) up to 50 km away, and they move rapidly in the opposite direction or perpendicular to the ship following the edge of the sea ice for distances of up to 80 km to avoid them. The presence of shipping produces avoidance behaviour, causing deeper dives for feeding, the break-up of groups, and asynchrony in dives.

Papillomaviruses have been found in the stomachs of belugas in the Saint Lawrence River. Animals in this location have also been recorded as suffering infections caused by herpesviruses and in certain cases to be suffering from encephalitis caused by the protozoan Sarcocystis. Cases have been recorded of ciliate protozoa colonising the spiracle of certain individuals, but they not thought to be pathogens or at least they are not very harmful.

The bacterium Erysipelothrix rhusiopathiae, which probably comes from eating infected fish, poses a threat to belugas kept in captivity, causing anorexia and dermal plaques and lesions that can lead to septicemia. This condition can cause death if it is not diagnosed and treated in time with antibiotics such as ciprofloxacin.

A study of infections caused by parasitic worms in a number of individuals of both sexes found the presence of larvae from a species from the Contracaecum genus in their stomachs and intestines, Anisakis simplex in their stomachs, Pharurus pallasii in their ear canals, Hadwenius seymouri in their intestines, and Leucasiella arctica in their rectums.

Relationship with humans

Belugas were among the first whale species to be kept in captivity. The first beluga was shown at Barnum's Museum in New York City in 1861. For most of the 20th century, Canada was the predominant source for belugas destined for exhibition. Until the early 1960s, they were taken from the St. Lawrence River estuary (famously captured in the film documentary Pour la suite du monde) and from 1967 from the Churchill River estuary. This continued until 1992, when the practice was banned. Since Canada ceased to be the supplier of these animals, Russia has become the largest provider. Individuals are caught in the Amur River delta and the far eastern seas of the country, and then are either transported domestically to aquaria in Moscow, St. Petersburg, and Sochi, or exported to foreign nations, including Canada.

Today, it remains one of the few whale species kept at aquaria and marine parks across North America, Europe, and Asia. As of 2006, 30 belugas were in Canada and 28 in the United States, and 42 deaths in captivity had been reported up to that time. A single specimen can reportedly fetch up to US$100,000 on the market. The beluga's popularity with visitors reflects its attractive colour and its range of facial expressions. The latter is possible because while most cetacean "smiles" are fixed, the extra movement afforded by the beluga's unfused cervical vertebrae allows a greater range of apparent expression.

To provide some enrichment while in captivity, aquaria train belugas to perform behaviours for the public and for medical exams, such as blood draws and ultrasound, provide toys, and allow the public to play recorded or live music.

In 2009 during a free-diving competition in a tank of icy water in Harbin, China, a captive beluga brought a cramp-paralyzed diver from the bottom of the pool up to the surface by holding her foot in its mouth, saving the diver's life.

Whale watching

Whale watching has become an important activity in the recovery of the economies of towns in Hudson Bay near to the Saint Lawrence and Churchill Rivers. The best time to see belugas is during the summer, when they meet in large numbers in the estuaries of the rivers and in their summer habitats. The animals are easily seen due to their high numbers and their curiosity regarding the presence of humans.

However, the boats' presence poses a threat to the animals, as it distracts them from important activities such as feeding, social interaction and reproduction. In addition, the noise produced by the motors has an adverse effect on their auditory function and reduces their ability to detect their prey, communicate, and navigate. To protect these marine animals during whale-watching activities, the US National Oceanic and Atmospheric Administration has published a "Guide for observing marine life". The guide recommends boats carrying the whale watchers keep their distance from the cetaceans and it expressly prohibits chasing, harassing, obstructing, touching, or feeding them.

Some regular migrations do occur into Russian EEZ of Sea of Japan such as to Rudnaya Bay, where diving with wild belugas became a less-known but popular attraction.

Human speech

Male belugas in captivity can mimic the pattern of human speech, several octaves lower than typical whale calls. It is not the first time a beluga has been known to sound human, and they often shout like children, in the wild. One captive beluga, after overhearing divers using an underwater communication system, caused one of the divers to surface by imitating their order to get out of the water. Subsequent recordings confirmed that the beluga had become skilled at imitating the patterns and frequency of human speech. After several years, this beluga ceased making these sounds.

Conservation status

As of 2008, the beluga is listed as "near threatened" by the IUCN due to uncertainty about threats to their numbers and the number of belugas over parts of its range (especially the Russian Arctic), and the expectation that if current conservation efforts cease, especially hunting management, the beluga population is likely to qualify for "threatened" status within five years. Prior to 2008, the beluga was listed as "vulnerable", a higher level of concern. IUCN cited the stability of the largest subpopulations and improved census methods that indicate a larger population than previously estimated.

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Images for kids

Skull of a cross between a narwhal and a beluga whale, at the Zoological Museum, Copenhagen

Front view of a Beluga whale in captivity

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The beluga whale ( Delphinapterus leucas) is a small, toothed whale that is white as an adult. They are found in coastal areas of the Arctic Ocean, and travel south when the sea ice forms. Mitochondrial DNA studies have shown modern cetaceans last shared a common ancestor between 30 and 34 million years ago.

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The whale shark ( Rhincodon typus), is a filter feeding shark. It is the largest shark in the world. It grows up to 12 metres long, and may weigh as much as 47,000 pounds.

The whale shark has a very wide distribution, found in all tropical and warm temperate seas, except in the Mediterranean.

Description

The whale shark has a streamlined body and a wide, flattened head. The mouth is transverse, very large and is nearly at the tip of the snout. The gill slits are also very large, and are designed as filtering screens. The first dorsal fin is much larger than the second dorsal fin, and is located at the back of the body. The caudal fin is semi-lunate (crescent-shaped) in adults, and with the young, the upper lobe is quite longer than the lower lobe. The whale shark has a unique "checkerboard" colour pattern of light spots and stripes on a dark background.

Whale sharks are grey, blue or brown above, with a surface pattern of creamy white spots between pale, vertical and horizontal stripes. The belly is white. The use of the strange pattern on the whale shark is unknown, although many bottom-dwelling Whale sharks use these markings as a camouflage against their backgrounds. They can be as long as 41 feet (12.3 metres) in length, and weigh as much as 47,000 pounds (21.5 tonnes). However, it is believed that there are some whale sharks which can reach lengths of up to 67 feet (20 metres). The smallest free-living individuals are around 55cm (21.7 inches) long. Whale sharks reach maturity at lengths of around 9 metres

Distribution

The whale shark has a very widespread distribution, found in all tropical and warm temperate seas, except in the Mediterranean. It is found throughout the Atlantic Ocean, from New York, through the Caribbean, to central Brazil, and from Senegal to the Gulf of Guinea. It also is found in the Indian Ocean, throughout the region, including the Red Sea and the Arabian Gulf. In the Pacific Ocean it is found from Japan to Australia, off Hawaii, and from California to Chile. Although other shark species of the order Orectolobiformes are benthic (live on or near the bottom), the whale shark lives in the pelagic zone. Studies show that this shark prefers warm waters, with surface temperatures of around 21-30 °C. It is often seen offshore but commonly comes close inshore, sometimes entering lagoons or coral atolls. Whale sharks sometimes swim deeper than 700 metres

Although the whale shark has no real predator, young Whale sharks have been found in the stomachs of Blue sharks and Blue marlin.

In spite of its large size, the whale shark is timid. Divers usually hold onto the tails of these sharks and swim with them, and the whale sharks never seem to attack. There is some risk that a diver getting too close to a whale shark could get sucked into the filtering system that the sharks use for feeding. Another risk is that they can create problems for small boats that they may accidentally knock into. For the sharks, contact with very large boats can result in severe injuries.

With the basking shark and the megamouth shark, the whale shark is one of the three known species of filter feeding sharks. It feeds mainly on plankton and nekton, small crustaceans, schooling fish, and sometimes on tuna and squids. Whale sharks may also sometimes feed on phytoplankton and macro algae. Unlike most plankton-feeding vertebrates, the whale shark does not depend on slow forward motion to operate its filtration mechanism. Instead, it relies on a versatile suction filter-feeding methodology, which allows it to draw in a larger amount of water than other filter-feeders, such as the Starfish. This allows the whale shark to capture larger amounts of plankton. Whale sharks are always seen feeding in a vertical or near vertical position with the head at or near the surface. Other food items for the whale shark can include krill, and the larvae of Christmas Island red crab.

Reproduction

There is very little information that has been documented about whale sharks mating and giving birth to young. Some whale sharks which live in captivity are studied by scientists but the whale shark is not very common in aquariums due to its large size. However, it is believed that they can have up to 300 pups at a time. This would be considerably more than other shark species, yet only a small fraction of them live to the age of maturity. It is believed that this species of shark doesn't mate until it is about 30 years old. They can live from 70 to 100 years of age.

In the past, the whale shark has been of little interest to fisheries. Now, commercial fishing for whale sharks are limited, but may expand from an increased demand for food products. In Taiwan around 100 whale sharks are caught annually. The meat of the whale shark is sold for high prices in this country, and since of this, there have been larger harvests of whale sharks over the last few years. Fishing for this shark also occurs in the Philippines, particularly in the Visayas and Mindanao areas, providing food for the local fishing communities. Whale shark fins are sold in the Orient, especially in Hong Kong. Occasionally, whale sharks are captured accidentally along the coast of India. Sometimes the flesh is eaten and the liver oil is used for waterproofing wooden fishing boats and for the manufacture of shoe polish, and it is also used as a treatment for some skin diseases. The fins of Whale sharks are also sold in India. Often, the whale shark is used as an indicator of waters which are rich in plankton-feeding fish that will, in turn, attract more valuable species, such as tuna. Whale sharks have been kept in aquaria in Japan, but their large size and their diet has made it hard to keep a whale shark in an aquarium. Some locations where the presence of whale sharks appears to be predictable, are increasingly targeted by commercial tourist operations.

Conservation

Some biological characteristics, such as the slow growth, and long time to mature, makes the whale shark vulnerable to overfishing. These characteristics also suggest that populations are slow to recover from any overfishing. The whale shark is listed as Vulnerable by the IUCN. The whale shark is listed by the AFS (American Fisheries Society) as "Conservation dependent" (meaning that the whale shark's population has reduced but it is recovering under conservation plans) in both the Atlantic waters of the U.S.A, and the Gulf of Mexico. However, it is considered not at risk in the Gulf of California. In the Maldives and Philippines there has been a ban on the fishing of whale sharks. This protection was introduced because of the serious impact that the fisheries may be making on whale shark numbers. The predictable occurrence of whale sharks in a few areas, such as western Australia, has led to the development of an expanding tourism industry. In this area the whale shark is a protected species and its tourism has been managed through a controlled system, including the licensing of a limited number of operators tours. Also, divers have been stopped from riding, chasing, or harassing any marine animal in any way, including whale sharks. Recently, some studies made on the Ningaloo Reef's whale sharks provided information that regular diving is a normal behaviour of these sharks, and there is no avoidance reaction during contact with humans.

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Images for kids

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The whale shark ( Rhincodon typus), is a filter feeding shark. It is the largest shark in the world. It grows up to 12 metres long, and may weigh as much as 47,000 pounds. The whale shark has a very wide distribution, found in all tropical and warm temperate seas, except in the Mediterranean.

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The Hammerhead sharks are a group of sharks which make up the family Sphyrnidae. Their unusual head looks like a hammer. This "hammer" on its head is also known as the "cephalofoil". Of the nine species of the Hammerhead sharks, the Winghead shark is in the genus Eusphyra, and the other eight are in the genus Sphyrna.

Description

There are nine known species of Hammerhead sharks. They range from the length of 0.9 meters to the length of 6.1 meters, and weigh from 500 pounds (225 kg) to 1000 pounds (450 kg). They are usually light grey with a tint of green, but some are more greener in colour then others, and the belly in white.

The unusual structure of the head makes the head look like a hammer, this is why they are known as "Hammerhead sharks".

Since the eyes are positioned on the ends of the cephalofoil, Hammerheads are able to see everything around them, including what is under them, and what is above them. This head helps hammerhead sharks make very tight turns in the water, and it also helps them sense prey.

Hammerhead sharks are aggressive hunters and feed on crustaceans, molluscs like octopuses and squids, and many types of fish. They also eat other types of sharks. Hammerhead Sharks favourite type of food is stingrays.

They are known to swim along the bottom of the ocean, following their prey. Hammerhead sharks use their cephalofoil as a weapon to hunt for stingrays; they hit stingrays with their cephalofoil to weaken the stingray, and then eat the stingray.

When Hammerhead Sharks can not find food, they have been known to eat each other, but Great hammerhead sharks have been known to eat their own young.

Reproduction

Hammerhead Sharks are viviparous, meaning they give live birth. Females usually give birth to 12 to 15 pups at a time, but the Great hammerhead shark gives birth to around 20 to 40 pups at a time.

Once they are born, baby Hammerhead sharks come together in groups and swim towards warmer waters. They stay together in groups until they are older and big enough to live on their own. Hammerhead shark live for around 20 to 30 years.

In 2007, the bonnethead was found to be capable of asexual reproduction, making it the first shark to be able to do this.

The hammerhead sharks are a monophyletic group. Sequence analysis shows they evolved from the Winghead shark.

Relationship with humans

Out of the nine species of Hammerhead sharks three are dangerous to humans: the Scalloped Hammerhead shark, the Great hammerhead shark, and the Smooth Hammerhead shark. The Great and Scalloped are listed as endangered by the International Union for the Conservation of Nature, while the Smalleye Hammerhead shark is listed as vulnerable. This is because of over-fishing for the fins of Hammerhead sharks, which are used in sharkfin soup. In 2010, 33 attacks were reported, but none of these attacks were fatal.

Hawaiian culture

In Hawaiian culture, sharks are considered to be gods of the seas, they are also known as aumakua, protectors of humans, and cleaners of ocean life. Some of these sharks are believed to be family members who have died and have turned into sharks. But there are some sharks which are known as niuhi, or man-eaters. These sharks include Great White Sharks, Tiger sharks, and Bull sharks. The Hammerhead sharks are known as mano kihikihi, they are not considered as man-eaters or niuhi, but are considered one of the most respected sharks in the oceans, an aumakua. Many Hawaiians believe that they have an aumakua which watches over them and protects them from the niuhi.

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The Hammerhead sharks are a group of sharks which make up the family Sphyrnidae. Their unusual head looks like a hammer. This "hammer" on its head is also known as the "cephalofoil". Of the nine species of the Hammerhead sharks, the Winghead shark is in the genus Eusphyra , and the other eight are in the genus Sphyrna.