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Dolphins on Mikurashima Island

Minami bottlenose dolphin, a resident of Mikurashima


Mikurajima, the island where dolphins live

Currently, about 130 to 150 wild dolphins called the Southern bottlenose dolphins live around Mikurashima.


Bottlenose dolphins (bottlenose dolphins) used to be divided into open-ocean Tranquitus type and coastal Adancus type, but in 2001, Adancus type dolphins living in the seas near Mikurashima and Ogasawara were classified as a different species from "Minami bottlenose dolphins". was defined as Compared to the bottlenose dolphin, it is slightly smaller and has a longer beak.


Mikurashima is now known as an “island where you can play with dolphins,” but that doesn’t mean that they started playing with us.

Dolphins have lived on Mikurashima for a long time, but I first met them in the late 1980s.

Originally, dolphins were cautious wild animals. At that time, although they would swim with the boat, they would quickly run away even if they entered the sea, and they could not see their shadows or shapes in the water. It wasn't until the 90's that I started to feel like I could swim with them.


I am often asked, "When can I see dolphins?", but dolphins live on Mikurashima all year round.

However, the dolphin swim season is limited to April to November. Because the sea is rough in winter, most Tokai Kisen ships to Mikurashima do not arrive, and even dolphin swim ships cannot depart.
Mikurashima rules stipulate 3/15 to 11/15.


individual identificationHow many dolphins live on Mikurashima?

Individual identification (ID) is the process of identifying each animal based on its physical characteristics and scars.

On Mikurashima, individuals are identified based on clues such as missing tail fins, dorsal fins, and pectoral fins, large scratches, and body characteristics. Newborn pups are clean and unblemished, so they cannot be identified, but they stay with their mothers for 2 to 3 years, so if they can make some kind of landmark during that time, they will be able to identify the pups even after they leave the herd. .


Most of the dolphins on Mikurashima have been individually identified, and the overall population count is fairly accurate.

There were years when nearly 20 to 30 dolphins disappeared at one time, and there were concerns about the impact of dolphin swimming, but is this a mass migration? has been reported in other sea areas, and the cause is unknown. Each year, some are born and some move or die, so there are some pluses and minuses.

life of dolphins

Mikurashima is the place where dolphins give birth, raise their children, and live.

They live in groups rather than families.In the case of Mikurashima, there are small groups of 3-4 animals and large groups of 20-30 animals. Males form groups with males and females with females, but there are cases where females mix with male groups as a group of close friends.The swarm itself is also in a state of flux, as it regroups and disperses, mixing in and out of other swarms.


Females often form large groups to protect their parents and their babies, while males form groups with relatively few dolphins.Most females spend their entire lives on Mikurashima, but males leave Mikurashima when they reach a certain age and migrate somewhere else. This is why there are no elderly males on Mikurashima.

Animals have an optimal population in their breeding areas. It is said that the main reason for this is that if the number of dolphins increases too much, they will run out of food.


According to observations on Mikurashima, females reach the age of primiparous at around 10 years old. By the way, dolphins have a gestation period of about 12 months. Babies snuggle close to their mother dolphins and are breastfed for about 2 to 3 years, spend an average of about 3 years together, and eventually separate from their parents. Dolphins other than mothers are often babysitters, so being with dolphins does not necessarily mean that they are parent and child.


Dolphins do not always play with us. They also have their own rhythms, so play time, rest time, meal time, travel time for something, other conveniences? And it feels like the mood at that time, and it's just playing or just passing by. When the sea is rough, there are times when boats cannot approach the waters where dolphins live.

Quietly see off the passing dolphins. Even if you chase after them, they will only get tired and won't turn around, and you may end up giving them unnecessary stress.

The dolphins who play with us will approach from the other side. Let's swim with dolphins when you meet them!

People who can dive will be more likely to approach from the other side if you wait in the water.

For those who are not good at diving, you can have a lot of fun just by swimming with dolphins on the surface of the water.



A large group of females. You can also see baby dolphins.

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