What kind of animal is a Risso’s Dolphin? We will explain its characteristics, ecology, and habitat. This dolphin is a rare animal that is hard to see even in aquariums. It grows to a huge size of about 3m in length, so it is difficult to keep it as a pet, but it puts on a very flashy performance in dolphin shows.
What is a Risso’s Dolphin? Basic Stats
Risso’s dolphins are marine mammals belonging to the Delphinidae family and the Risso’s genus. They are large dolphins that can grow to 3-4m in length and weigh 300-600kg. Their kanji characters are flower giant heads, their scientific name is Grampus griseus, and their English name is Risso’s dolphin. The list of information is as follows:
| Japanese（和名） | ハナゴンドウ |
| English（英名） | Risso’s dolphin |
| scientific name(学名) | Grampus griseus |
| classification（分類） | Mammalia、Odontoceti、 Delphinidae、Grampus 哺乳綱、ハクジラ亜目、マイルカ科、ハナゴンドウ属 |
| IUCN Status(保全状況) | LEAST CONCERN |
| Length（体長） | 3-4m |
| Weight（体重） | 300－600kg |
ハナゴンドウの分類学
- 界（Kingdom）: 動物界 (Animalia)
- 門（Phylum）: 脊索動物門 (Chordata)
- 綱（Class）: 哺乳綱 (Mammalia)
- 目（Order）: 鯨偶蹄目 / 鯨目 (Cetacea)
- 亜目（Suborder）: 歯鯨亜目 (Odontoceti)
- 科（Family）: ハクジラ科 (Delphinidae)
- 属（Genus）: ハナゴンドウ属 (Feresa)
- 種（Species）: ハナゴンドウ (Feresa attenuata)
Habitat
Risso’s whales live in temperate and tropical seas around the world, so they are distributed worldwide. They seem to like warm seas, and prefer the open ocean rather than coastal waters. The minimum water temperature is 10°C, and they tend to prefer 15°C or higher.
- Main Habitat
Tropical to subtropical open ocean
Warm waters of the Pacific, Indian, and Atlantic Oceans
Around Japan, they can be found in the waters south of Okinawa and the Ogasawara Islands.
Pelagic
Most often live in the open ocean rather than nearshore waters.
Most often travel to deep waters and along ocean currents.
- Habitat Characteristics
Water Temperature: Prefers warm waters between 20-30°C.
Depth: Lives in a wide range of depths, from deep waters to mid-depths in the open ocean.
Schooling: Usually travels in small schools of 10-30 individuals.
Migratory Behavior: Moves according to food resources and seasons.
- Points of Interest
Rarely enters rivers or shallow waters; they are entirely marine.
Sightings are rare; they often dive in the open ocean to catch food.
They sometimes work together in schools to hunt for fish and squid.
What are its characteristics? What kind of creature is it?
Risso’s whales have a sturdy upper body that tapers toward the caudal peduncle. They have a round head and no beak. They have a high, sickle-shaped dorsal fin, long pectoral fins, and a body color that ranges from gray-white to dark gray. They turn white with age. They are actually quite different from pilot whales, as they have no teeth on their upper jaw. They have many scratches on their bodies that make them look like they have lots of flowers in bloom, hence the name “flower” pilot whales.
- Physical Characteristics
Body Color: Blackish throughout, with a lighter color around the chest and mouth
Body Length and Weight:
Adults are approximately 2.5 m long
Weight: Approximately 150-200 kg
Dorsal Fin: Triangular, slightly curved
Snout (Beak): Short, rounded, and well-formed for a toothed whale
Body Type: Muscular and sturdy. Adapted for high-speed swimming in the open ocean
- Behavior and Personality
School Life
Live in small shoals (approximately 10-30 individuals)
Sometimes work together to catch prey
Agile and active
Able to swim at high speeds and migrate in the open ocean
Mysterious and rarely observed
Often diving deep in the open ocean, it is little known
- Ecological Characteristics
Diet: Preys on fish and squid
Reproduction: Gives birth to a single offspring
Peco-adapted: Can migrate across wide ocean areas and swim in deep waters
What is their personality like?
Risso’s whales are very social animals that value discipline. They are usually seen in groups, but often act alone.
- Sociable
Live in small groups (approximately 10-30 individuals)
They sometimes cooperate within the group to catch prey
They are thought to communicate with others through clicking sounds and calls
- Active and agile
Swimming at high speeds, they migrate through the open ocean
They have excellent diving abilities and can catch prey in deep waters
- They can also be mysterious and timid
They often dive deep into the open ocean, and observations have been rare
They are highly wary of ships and humans and often avoid approaching them
- They may be playful
They have been observed jumping and using their tails in groups
Like ocean-going dolphins, they may learn social skills through play.
What is their ecology like?
Risso’s whales live by eating fish, crustaceans, invertebrates, etc. Their lifespan is about 40 years.
- Habitat
Live mainly in the open ocean and deep seas
Distributed in the tropical to subtropical Pacific, Indian, and Atlantic Oceans
Mostly active in the open ocean deeper than near the coast
Water Temperature: Prefers warm waters of 20-30°C
Depth: Capable of diving from mid- to deep-sea depths
School Life: Lives in small schools of 10-30 individuals
Migratory Behavior: Travels long distances depending on food resources and the season
- Diet
Preys primarily on fish and squid
Dives to pursue prey and sometimes cooperates in schools
- Reproduction and Rearing
Gestation Period: 10-12 months
Birth: One baby at a time
Chubby animals learn hunting and pack life while playing alongside their mothers
- Society & Behavior
They live in groups and communicate with others through clicking and calls.
They are skilled at high-speed swimming and have excellent diving abilities.
They are adapted to life in the open ocean, and although difficult to observe, they are active and agile.
- Adaptability
Muscular and slender bodies → adapted to high-speed swimming and open-ocean life.
Adapted to hunting and schooling in the open ocean and deep sea.
They have developed cooperation within groups and the ability to dive.
Do they have any natural predators?
Killer whales are the biggest threat to Risso’s whales.
About Risso’s Dolphin Baby
Risso’s Dolphin baby (Feresa attenuata) dolphins (young) differ slightly in appearance and behavior from adult dolphins, and are characterized by a strong dependency on their mother and herd.
- Physical Characteristics
Body Length: Approximately 1 m at birth
Weight: Approximately 15–20 kg
Body Color: Gray to black throughout, becoming dark black like an adult as it matures
Dorsal Fin/Snout: Same shape as an adult, but smaller and rounder
- Behavior/Personality
Dependent on Mother
For the first few months of life, they swim close to their mother, protecting them from food and danger.
Playful
They may play on the water surface using their tail fin or body.
They learn social skills by chasing each other around in their school.
Learning Behavior
They learn hunting and migratory behavior by observing the behavior of their mother and school.
- Biological Features
Diet: Breastfed for the first few months
Weaning: Begins eating fish, squid, and other prey within a few months to a year
Growth: Reaches adult size within 1–2 years and begins participating in school activities
Dangers: Young are sensitive to predators, ships, and food shortages in the open ocean.
Are Risso’s dolphins endangered?
Risso’s dolphins are not endangered when viewed as a whole. They are kept in aquariums around the world and occasionally appear in dolphin shows. The population is said to be 60,000 along the coast of the United States, 170,000 in the eastern Pacific, and 80,000 in the western Pacific.
- International Union for Conservation of Nature (IUCN) Assessment
The IUCN Red List classifies it as “Least Concern (LC).”
It is distributed widely across tropical and subtropical waters, and its population is considered relatively stable.
- Why it is not endangered
Distributed widely across tropical and subtropical open oceans
It lives in groups and has a relatively stable reproductive rate
Its only natural predators are killer whales and large sharks
- Caution
Fisheries and bycatch: It may be accidentally caught in purse seines
Environmental change: Marine pollution and climate change may affect its prey resources and habitat
Can Risso’s dolphins be kept as pets?
Risso’s dolphins are too large for ordinary people to keep as pets. If you’re looking for one, we recommend visiting an aquarium or other place to view them and getting guided or guided by events.
- Legal and Conservation Issues
Rossi’s dolphins are internationally protected marine mammals.
Capturing and selling wild specimens is prohibited in most countries.
Even in Japan, keeping wild specimens as pets is illegal.
Only aquariums and research facilities with special permission can keep them in captivity.
- Ecological and Breeding Environment Issues
Pelagic: Their migration habits over large ocean areas in schools make this impossible to replicate at home.
Highly social: Keeping them alone is stressful.
Unique diet: They require large quantities of fish and squid, and their feeding behaviors must be learned.
Water temperature control is difficult: They require warm tropical to subtropical waters.
- Aquarium Breeding
Very few examples of captivity exist worldwide.
Even in Japan, captivity is limited to a limited number of facilities.
Care requires large aquariums, specialized staff, and a veterinarian.
コメント