It is a very popular dolphin that is one of the highlights of the aquarium show! The sight of them swimming around in the water is beautiful, and the sight of them playing ball is cute.
Dolphins have a gentle personality, but did you know that they actually have great power?
Let’s take a peek at the world of dolphins you didn’t know!

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～ Basic information. ～

Mammalia-Cetartiodactyla-Cetacea-Odontoceti.

Length:1.3m～10m weight:30～300kg.

Dolphins mainly live in the sea, but there are also species that live in freshwater rivers. The well-known bottlenose dolphin lives in seas other than the Antarctic and Arctic regions, as well as in temperate or subtropical seas.

Dolphins are basically animals that move in groups. The reasons for forming groups include making it easier to breed, making it easier to find food, and making it easier to find predators such as killer whales so that they can escape quickly if necessary. The number of groups varies in size from a few to several thousand.

You cannot clearly distinguish between male and female dolphins by appearance alone. To determine the sex of a dolphin, you need to look for the genitalia under the navel while it is lying on its back.

In the case of males, the “groove” where the genitalia is located and the “anus” are arranged vertically and can also look like an “exclamation mark”. On the other hand, in the case of females, the groove is in the same place, but it is characteristic that it looks like the kanji character “small” when viewed closely.

Breeding periods vary depending on the species, so there is no specific time. The length of pregnancy also varies. On average, it seems to be between 10 and 15 months. Dolphins usually give birth to one offspring at a time.

The lifespan of dolphins is said to be 30-35 years, but some dolphins have lived for as long as 50 years.

They mainly eat fish and crustaceans such as shrimp. They swallow fish whole without chewing, but they always put the head in first when doing so. This is because there is a risk that fish scales or fins will get stuck in their throats if they don’t.

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Dolphin’s Q&A.

Is it true that dolphins communicate with ultrasound?

The fact is that dolphins have almost no sense of smell and their eyesight is not very good.

Instead, their hearing function has evolved to specialize. When communicating with each other, they began to use ultrasound. This ultrasound is called “echolocation.” By using this echolocation, they can always grasp the location of their food and the surrounding conditions.

Dolphins have a unique communication method. First, there is a part called the “blowhole” on their head. When it vibrates, it produces a sound called a “click.”

There is also a fatty tissue called the “melon organ” in their head, which collects the clicks. Ultrasound emitted from there hits objects and returns as an “echo.” Finally, they catch and confirm the echo with their lower jaw bone.

To put it simply, they catch the echo with their bones by bone conduction. This is how echolocation works.

※Bone conduction is a technique for listening to bone-conducted sound. By transmitting vibrations to the bones, you can hear sounds. The characteristic of this sound is that only you can hear it.

Why is the dolphin’s body slippery?

If you have ever touched a dolphin at an aquarium, you might know that their skin is smooth and rubbery to the touch and has elasticity.

The first reason is that it is said that the body became smooth to swim faster in the sea. Water has a property that when something moves in the water, a “vortex” of air and other things is generated on the surface of the object.

Normally, it becomes a resistance and you can’t move as you want, but the dolphin’s body is smooth and elastic, so it hardly receives such resistance.

The second reason is that the dolphin’s skin has a very fast metabolism cycle. It is always in a state of wearing new skin, so its body is smooth. The human metabolism cycle is 28 to 40 days, but dolphins create new skin every two hours.

※Metabolism refers to the process of replacing old things with new ones one after another.

Is it true that dolphins are smart?

Jumping while checking the trainer’s instructions and playing with balls in dolphin shows is a very impressive sight.

Since they accurately follow the given instructions, many people think that they are also intelligent.

In conclusion, it has been confirmed that dolphins have excellent brains after humans. There is data that shows the ratio of brain weight to body weight called the encephalization quotient. Dogs have 0.14, humans have 0.89, and dolphins have 0.64, which is a number close to humans.

Although there are still some unknowns that have not been clarified by simply expressing them in numbers, when you see the many techniques performed in dolphin shows, it is probably because they understand the content as well as being intelligent.

Where does the dolphin get its name?

In English, the animal is called “dolphin”, in fact, in the case of Japanese, it is named “iruka”. This time, why did they come to be called iruka in Japanese? We will introduce its origin.

There are several theories about the origin of the name, and to introduce a famous one, it seems that in the past, the word “io” was used to represent fish.

Furthermore, there is a theory that the food beast is called “ka”, and because it resembles a fish, it is thought that “io” and the edible beast “ka” became “iwoka” and then “iruka”, and there is also a theory that “irue” became “iruka” because they often came to a place called “Irie”.

There are many other stories that became “iku = yurki = iruka”, and that when fishing for dolphins, the boat was filled with the smell of blood, so it became “chinoka = iruka”.

How do dolphins sleep?

I think we often see dolphins swimming in pools or the ocean. We have never seen them resting on land, have we?

So how do dolphins sleep? They sleep by resting one side of their brain at a time. This is called “Unihemispheric slow-wave sleep.” For example, when the left brain is resting, the right eye is closed and when the right brain is resting, the left eye is closed.

The reason why we sleep this way is that when we rest both the right and left brains, the brain goes into a deep sleep.

When the brain is completely at rest, there is a risk of not being able to move quickly when you wake up, which can prevent you from escaping immediately when you are found by an enemy or cause you to drown while drowsy. To prevent this from happening, they sleep with one side of their brain resting at a time.

This way, half of our brain is awake and we can always check for external enemies and watch over babies to make sure they don’t go anywhere. When we sleep, we are in the water, but when we breathe, we come up to the surface.

Is it true that there are dolphins that eat dolphins?

It’s true.

First of all, the most famous is the orca, which is a member of the delphinidae belonging.In addition, it seems that the delphinidae false killer whale and pygmy killer whale also prey on dolphins.

Is it true that you fish for dolphins in Japan?

It’s true.

Some people may have heard this story on the news, but Japan has been a country where dolphin hunting has been popular since ancient times. Although the number of areas where dolphin hunting is practiced has decreased significantly, there are still places where dolphin hunting is practiced. As of 2023, the most famous dolphin hunting area is in Taiji-cho, Wakayama Prefecture.

Dolphin hunting has been practiced not only in Japan but also in Western countries in the past. However, since the post-war period, countries that have stopped dolphin hunting have emerged one after another. As a result, criticism of Japan, which still practices dolphin hunting, has increased due to its coverage in the news and its use as a subject for movies.

However, we follow the law so that we do not overfish unnecessarily, and it is one of the fisheries that has supported the development of this area since ancient times. Isn’t it discrimination to say that you can eat cows and pigs, but you can’t eat dolphins because they’re friendly and cute? There is also an opinion.

It is quite a difficult problem, but it may be one of the issues that we humans must solve in a gentle manner.

Is it true that dolphins are stronger than sharks?

Dolphins are popular at aquariums and even perform in shows due to their high intelligence and gentle image. On the other hand, sharks are often seen as very aggressive and scary animals due to their image of attacking people in movies. Although dolphins and sharks have almost opposite personalities, dolphins are actually quite strong animals.

Here is an example of a bottlenose dolphin that is often seen at aquariums. Large sharks sometimes try to eat the young of bottlenose dolphins, but adult dolphins have been known to ram the sharks to drive them away.

It is surprising that the impact of a dolphin can have enough power to rupture and kill a shark’s internal organs if it is hit directly.

This is due to the difference in body structure between sharks and dolphins. Sharks have no ribs to protect their internal organs because their bodies are made of cartilage. On the other hand, dolphins have ribs and sturdy skeletons, so it is not surprising that sharks die when they are hit by dolphins.

In addition, dolphins are smart, so they understand that attacking any part of the shark will kill them. It is said that. In some cases, sharks were attacked by groups of dolphins due to brain play.

And the swimming speed is quite fast, with large sharks reaching 35km~50km, while dolphins have a maximum speed of 70km. If you spot a shark in the distance, it can be said that it is fast enough to escape.

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Type of dolphin.

・Bottlenose Dolphin
・Indian Ocean Bottlenose Dolphin
・Common Dolphin
・Long-Beaked Common Dolphin
・Atlantic Humpback Dolphin
・Indo-Pacific Humpback Dolphin
・Indian Humpback Dolphin
・Pantropical Spotted Dolphin
・Atlantic Spotted Dolphin
・Spinner Dolphin
・Clymene Dolphin
・Striped Dolphin
・Fraser’s Dolphin
・Rough-toothed Dolphin
・Tucuxi
・Northern Right Whale Dolphin
・Southern Right Whale Dolphin
・Commerson’s Dolphin
・Chilean Dolphin
・Heaviside’s Dolphin
・Hector’s Dolphin
・Orca
・Irrawaddy Dolphin
・Risso’s Dolphin
・False Killer Whale
・Pygmy Killer Whale
・Melon-headed Whale
・Long-finned Pilot Whale
・Short-Finned Pilot Whale
・Hourglass Dolphin
・Peale’s Dolphin
・Pacific White-Sided Dolphin
・Atlantic White-Sided Dolphin
・White-Beaked Dolphin
・Australian Snubfin Dolphin
・Dall’s Porpoise(dalli type)
・Dall’s Porpoise(truei type)
・Dall’s Porpoise
・Finless Porpoise
・Burmeister’s Porpoise
・Harbour Porpoise
・Vaquita
・Spectacled Porpoise
・Boto
・La Plata Dolphin
・Baiji
・Ganges River Dolphin
・Indus River Dolphin
・Narwhal
・Beluga

Bibliography.

大日本百科全書（ニッポニカ）

Petpedia
https://petpedia.net/article/623/dolphin

pepy
https://pepy.xsrv.jp/29172

和歌山県
https://www.pref.wakayama.lg.jp/prefg/071500/iruka/index.html

イルカはかせになろう！
https://dolphinkids.heteml.net/

国立科学博物館
https://www.kahaku.go.jp/research/db/zoology/marmam/pictorial_book/index.html

伊豆シュノーケリングクラブ
https://izu-snorkeling.info/category/イルカと泳ぐ/

ペットのなまえ
https://pet-name.com/dolphin/

新江ノ島水族館
https://www.enosui.com/diaryentry.php?eid=02306#:~:text=イルカ

万物の寿命まるわかり事典
http://www.lance4.net/banbutuno-jumyo/z0044.html

アイキャッチ画像
https://pixabay.com/images/id-1974975/