What kind of animal is the Finless Porpoise? The latest information on its characteristics, ecology, and habitat. Dolphins you can see at the aquarium.

What kind of animal is a finless porpoise? We will explain its characteristics, ecology, and habitat (fish that can be seen in the Seto Inland Sea region and aquariums). Finless porpoises are very small and cute dolphins. They live widely in the Indian Ocean, from the Persian Gulf to Pakistan, India, and Bangladesh.

What is a finless porpoise? About basic status

The finless porpoise is a small dolphin that belongs to the porpoise family, genus Porpoise. The scientific name is Neophocaena phocaenoides, and the kanji is Sunname. The total length is 1.5-2m and the weight is 50-60kg. The list of information is as follows.

Japanese（和名）	スナメリ
English（英名）	Finless porpoise
scientific name(学名)	Neophocaena phocaenoides
classification（分類）	Mammalia、Cetacea、 Hylobatidae、Symphalangus  哺乳綱、クジラ目、ネズミイルカ科、スナメリ属
IUCN Status(保全状況)	ENDANGERED
Length（体長）	1.5-2m
Weight（体重）	50-60kg

What are the roots and origins of the finless porpoise?

The roots of the finless porpoise (Neophocaena asiaeorientalis) lie in the cetacean lineage, which evolved from mammals that lived on land approximately 50 million years ago. Modern finless porpoises belong to the family Phocoenidae (porpoises), a group within the order Cetacea (whales and dolphins) that retains ancient characteristics.

Ancestors were land-dwelling mammals

Whale evolution began during the Eocene epoch, about 50 million years ago.

Evolutionary timeline:

Approx. 50 million years ago
Mammals related to land-dwelling ungulates (hoofed mammals)
↓
Early primitive whales (Pakicetids)
↓
Cetaceans adapted to aquatic life
↓
Odontocetes (toothed whales, such as dolphins and orcas)
↓
Phocoenidae (porpoise family)
↓
Finless porpoise

Their ancestors are believed to have branched off from a group closely related to modern cattle and hippopotamuses.

The finless porpoise’s direct lineage: Phocoenidae

The finless porpoise is classified as follows:

Order: Cetartiodactyla

Infraorder: Cetacea

Suborder: Odontoceti

Family: Phocoenidae

Related species include:

Harbor porpoise

Dall’s porpoise

Vaquita (one of the world’s smallest dolphins)

…and others.

When did the finless porpoise’s ancestors emerge?

The family Phocoenidae is believed to have diverged from the dolphin lineage approximately 20 to 15 million years ago (during the Miocene epoch).

Subsequently, a lineage adapted to the shallow waters of East Asia developed, eventually leading to the modern finless porpoise.

Why do they lack a dorsal fin?

The most distinctive feature of the finless porpoise is

“the absence of a dorsal fin.”

This is a result of evolution. Habitat:

Coastal waters

Estuaries

Shallow waters

Inner bays

In these environments, a dorsal fin is not necessarily required.

Conversely,

Rocks

Fishing nets

Shallow areas

…pose a risk of snagging.

Therefore,

It is believed that they evolved to lose the dorsal fin

…resulting in a smooth back.

scientific classification

• 界：動物界 (Animalia)
• 門：脊索動物門 (Chordata)
• 綱：哺乳綱 (Mammalia)
• 目：クジラ目 (Cetacea)
• 亜目：ハクジラ亜目 (Odontoceti) – 歯のあるクジラ類
• 科：ネズミイルカ科 (Phocoenidae)
• 属：スナメリ属 (Neophocaena)
• 種：Neophocaena phocaenoides（スナメリ）

About habitat

Finless porpoises are mainly distributed in ocean areas such as the Indian Ocean. Currently, they can be seen in places such as Ise Bay, Sendai Bay, and the Seto Inland Sea in Japan. You can see photos of the heads, backs, and bumps of creatures on the internet. There is a lot of material available and research is progressing.

1. Geographic Distribution

Distribution Area: Western Indian Ocean to Southeast Asia and East Asia coasts

Coastal China, Yellow Sea, East China Sea, Gulf of Vietnam, Gulf of Thailand, etc.

In Japan, they have been spotted in coastal areas such as the Seto Inland Sea and Tokyo Bay.

2. Water Characteristics

Prefers shallow coastal areas

Shallow waters and bays with depths of 10-50m

Also found in estuaries and inland bays

Can adapt to low-salinity brackish waters

3. Movement and Schooling

Travels in small schools (a few to a dozen individuals)

Migrates along the coast in search of food, but rarely ventures into the open sea

4. Environmental Conditions

Water Temperature: Prefers warm coastal areas

Shallow waters with abundant food are key to survival

Habitat is affected by overfishing and development

feature is? What kind of creature is it?

The finless porpoise has a silvery-white body color and a rounded head. The tail fin is crescent-shaped. Finless porpoises have no dorsal fin, making them very distinctive and conspicuous. They are rarely seen in the open ocean, so humans rarely see them. Finless porpoises usually live in shallow waters up to 50 meters deep and can be seen at river mouths.

1. Physical Characteristics

Body Type: Small, rounded toothed whale

Body Length: Approximately 1.4-2.0 m in adults

Weight: 50-70 kg

Dorsal Fin: Small, triangular, and inconspicuous

Face: Rounded snout, lacking a long beak like a dolphin’s

Color: Gray back, whitish underside, and generally solid, smooth body

2. Movement/Behavior

Swim in shallow coastal waters, moving in small groups (a few to a dozen individuals)

Rarely exhibiting sharp jumps or flashy movements, they tend to swim calmly

Move slowly while searching for food

3. Diet

Carnivorous (mainly fish-eating)

Preys on small fish, shrimp, squid, etc.

Preys in shallow waters, moving quickly near the seabed or underwater

4. Sociality

Live in small groups

Communicate calmly within the group

Shy of humans, tending to avoid boats and noise

What is your personality like?

Finless porpoises are highly social animals that value discipline. They are usually seen in groups. They often act alone.

1. Gentle and Timid

Generally docile and calm in nature

Sensitive to sounds and activity from humans and boats, and will immediately flee when approached

Rarely exhibits flashy jumps or aggressive behavior

2. Sociality

Live in small groups (a few to a dozen individuals)

Swim and forage cooperatively within the group

Rarely engage in territorial disputes or fierce competition, coexisting peacefully

3. Highly Cautious

Swim slowly near the surface, but will quickly dive if they sense danger

As a coastal fish, they are sensitive to environmental changes and human presence

4. Feeding and Behavioral Characteristics

Feeding is calm and planned

Cooperative group behavior is observed to efficiently catch small fish and shrimp

What does the ecology look like?

Finless porpoises live on fish, crustaceans, and invertebrates. The breeding season is uneven and the gestation period is about 10 months. In the wild, they can live up to 23 years.

1. Habitat

Living in coastal areas, estuaries, and bays

Mainly active in shallow waters 10-50m deep

Can live in brackish waters of bays and estuaries

Rarely ventures into the open ocean

Prefers shallow waters and coastal areas with abundant feeding grounds

2. Diet

Carnivorous (mainly fish-eating)

Preys on small fish, shrimp, squid, etc.

Catches prey by swimming quickly through the water

Forages while moving along food-rich coastal areas

3. Sociality/School Structure

Live in small schools (several to a dozen individuals)

Swim cooperatively within the school to search for feeding grounds

Rarely engages in social conflict, coexisting peacefully

4. Behavior

Diurnal, active during the day

Swim slowly near the surface, searching for food

Swim quickly to avoid danger

Disperse and search for food while moving in schools

5. Reproduction

Sexual maturity: 2-4 years

Gestation period: Approximately 10-11 months

Litter size: Usually one pup

Rearing: Carried by the mother and nursing for several months

Pups are dependent on their mother for survival and follow their parents on the surface and in shallow waters.

Are there any natural enemies?

Sharks are the biggest threat to finless porpoises.

About Diving

The diving capabilities of the finless porpoise (Neophocaena asiaeorientalis) evolved not for deep-sea diving, but for rapid and frequent movement within shallow coastal waters.

Diving Depth

Finless porpoises primarily inhabit areas such as:

The Seto Inland Sea

Inner bays

Estuaries

Shallow coastal waters

Consequently, their typical dives are relatively shallow:

Ranging from a few meters to about 20 meters

Reaching a maximum of around 50 meters

Unlike sperm whales (which dive thousands of meters) or bottlenose dolphins (hundreds of meters), they are diving animals specialized for shallow waters.

Dive Duration

Typical dive times:

Normal: Approximately 30 seconds to 2 minutes

Longer dives: A few minutes

Rather than staying submerged for long periods to chase prey, finless porpoises repeat a cycle of:

“Short dive → Surface → Breathe → Dive again”

Physiological Changes During Diving

Like other cetaceans, finless porpoises are adapted for life underwater.

① Efficient Oxygen Use

When diving, they:

Lower their heart rate

Concentrate blood flow to vital organs

Store oxygen using myoglobin in their muscles

② Flexible Ribcage

When subjected to water pressure:

Their ribs deform flexibly

Air in the lungs is compressed

While these adaptations are more pronounced in animals that dive to great depths, finless porpoises also possess these fundamental diving adaptations.

About Their Vocalizations

The vocalizations of the finless porpoise (Neophocaena asiaeorientalis) are distinctive among cetaceans; they are a species that relies primarily on ultrasonic “echolocation” for their daily activities. They frequently use high-frequency sounds that are largely inaudible to the human ear.

Characteristic Sound: “Clicks”

The sounds finless porpoises produce most often are

“click-click” or “snap-snap”

short clicking sounds.

However, rather than serving as conversation, these sounds are used for:

checking their surroundings

searching for prey

determining the location of other individuals

The frequencies are extremely high, centering on the ultrasonic range (tens of kHz to over 100 kHz), which humans cannot hear.

Echolocation

Finless porpoises emit sound from an organ in their head,

projecting ultrasonic waves

that bounce off fish or the sea floor

and receiving the echoes

to assess distance, shape, and movement.

This allows them to hunt in:

murky rivers

the ocean at night

shallow waters with poor visibility

Sounds for Communication with Others

Finless porpoises do not often use the complex “whistles” seen in bottlenose dolphins.

Main sounds:

① Clicks

Uses:

locating other individuals

searching for prey

perceiving surroundings

② Burst-pulse sounds

Rapid, continuous clicking sounds.

Uses:

short-range information exchange

approaching prey

alerting/warning

③ Low-frequency sounds / Contact sounds

These are believed to be used between individuals for:

mother-calf recognition

maintaining the pod (group)

Sounds Made by Calves

Because finless porpoise calves stay close to their mothers,

they produce high-frequency clicks

and short contact sounds.

The mother relies on these sounds to track:

the calf’s location

distance

condition

Seasonal Activities

The finless porpoise (Neophocaena asiaeorientalis) does not hibernate or undertake large-scale migrations. While active year-round in the coastal waters and bays near Japan, its behavioral patterns shift depending on water temperature, prey availability, breeding cycles, and sea conditions.

Spring (March–May)

Activity Characteristics

Water temperatures begin to rise

Increased activity among fish and crustaceans

Heightened foraging activity

Behavior

More frequent movement into shallow waters

Moving within bays while chasing small fish

Increased social interaction with other porpoises

Spring is a period of increased activity due to the abundance of food resources.

Summer (June–August)

Activity Characteristics

Water temperatures rise

Fish become abundant

Breeding and rearing season in some regions

Behavior

Active foraging during morning and evening hours

Activity in shallow waters continues during the day

Mother-calf interactions are frequently observed

Calves born in summer learn the following while swimming alongside their mothers:

Swimming techniques

Breathing timing

How to locate prey

Autumn (September–November)

Activity Characteristics

Changes in fish species composition

A time to secure food reserves for the winter

Behavior

Increased time spent foraging

Wide-ranging movement along the coast

Occasional movement in groups

As water temperatures become moderate, this is also a favorable season for observation.

Winter (December–February)

Activity Characteristics

Water temperatures drop

Changes in the distribution of prey species

Behavior

Occasional movement to warmer waters or the inner reaches of bays

Changes in diving duration and activity levels

Conservation of energy

However, finless porpoises are not migratory animals that travel to cold regions; they generally remain within the same coastal areas.

Regarding Swimming Speed

The finless porpoise (Neophocaena asiaeorientalis) is not built for high-speed, long-distance travel; instead, its swimming style prioritizes maneuverability, allowing it to thoroughly explore shallow coastal waters.

Typical Swimming Speeds

Estimates:

Normal swimming: Approx. 2–5 km/h

Foraging: Approx. 3–6 km/h

Avoiding danger: Approx. 10–20 km/h

While they do not reach the high speeds of bottlenose dolphins (which can exceed 30 km/h), they possess ample maneuverability for shallow waters.

Why aren’t they built for high speed?

Finless porpoises inhabit:

Inner bays

Estuaries

Coastal areas

Shallow waters

In these environments:

There is little need for high-speed, long-distance travel.

Agility (the ability to make tight turns) is crucial.

The ability to explore near the seabed is important.

Consequently, their evolution favored:

“Turning and exploration capabilities” over speed.

Physical Characteristics and Swimming Style

① Lack of a dorsal fin

This is the finless porpoise’s most distinctive feature.

Advantages:

Easier to move in shallow water

Easier to swim near the seabed

Less likely to get caught in fishing nets

The absence of a dorsal fin also reduces underwater drag.

② Rounded body shape

Finless porpoises have a rounder physique than dolphins.

This body shape is well-suited for:

Sharp turns

Precise changes in direction

Navigating shallow areas

③ Propulsion from the tail fluke

Like other cetaceans:

They move their tail flukes up and down.

They generate propulsion using powerful muscles.

Unlike fish, which move their tails from side to side, this is a swimming style unique to mammals.

About Finless Porpoise Baby

This article explains the baby finless porpoise (Neophocaena phocaenoides). As a small, coastal toothed whale, it is highly dependent on its mother.

1. Birth and Physical Characteristics

Birth Weight: Approximately 5-10 kg

Body Length: Approximately 70-90 cm

Appearance: Approximately the same body shape as an adult, but smaller and with softer skin

Dorsal Fin: A small, prominent triangular dorsal fin develops as the baby grows

Snout: Short and rounded, without a dolphin-like beak

2. Dependence on Mother

Swim alongside their mother for the first few months of life

Nursing period: Approximately 6-12 months

They cling to their mother’s back or nearby, and are protected by their mother in times of danger

3. Growth and Development

Acquiring the Ability to Swim Unassisted: Begins to swim alongside their mother within a few weeks of birth

Acquiring Foraging: Learns by watching small fish caught by their mother

Social Learning: Learns by observing school movements and danger avoidance

4. Behavioral Characteristics

Develops motor skills while playing alongside their mother

Learns to dive and change direction underwater

Sensitive to danger and stimuli, and is dependent on their mother’s instructions and movements

5. Protection from predators

Because they cannot defend themselves against predators on their own, the protection of their mother and herd is essential.

Early learning diving skills increases survival rates.

Are finless porpoises an endangered species?

The finless porpoise is listed as an endangered species. This species is particularly endangered in China’s Yangtze River basin, where it is endangered. Since it can only be seen in clean oceans, marine pollution by humans is the biggest threat, and we are in a critical situation due to the destruction of the environment by humans.

1. IUCN Assessment

Classification: Vulnerable (VU)

Reason for Assessment:

Limited to coastal areas, its distribution is limited.

Significant impacts from human activities.

2. Threat of Extinction

Conflict with Fisheries

Frequent deaths occur as bycatch (entanglement) in bottom trawls and set nets.

Hits are particularly severe in areas with heavy coastal fishing.

Habitat Degradation

Habitat decline due to reclamation at estuaries and coastal areas, industrial development, and pollution.

Water pollution and noise are also sources of stress.

Decreased prey.

A decline in coastal prey such as small fish and shrimp affects survival.

3. Conservation Status

Habitat protection is being promoted under coastal protected areas and international regulations.

International trade is restricted by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

Preventing bycatch from fishing and development is important.

Can finless porpoises be kept as pets?

Finless porpoises are an endangered species and cannot be kept by the general public. We recommend viewing them at an aquarium and having them show you around at events.

1. Difficulty in Breeding
   ① Unique Habitat

Marine mammals that live in shallow coastal and estuary waters

Requires specific environmental conditions, such as water depth, current, and salinity.

Cannot be reproduced in a home aquarium or small pool.

② Sociality and Stress

They are social creatures that live in small groups, making solitary breeding unsuitable.

Highly intelligent, they can become stressed and aggressive in a cramped environment, leading to health problems and aggression.

③ Difficult to manage their diet

They prey on small fish, shrimp, squid, etc.

It is impossible to properly manage the freshness and variety of seawater and food at home.

④ Difficult to manage health

Lack of seawater environment, disease prevention, and exercise space can damage their health.

Wild individuals are highly susceptible to stress.

2. Legal Restrictions

Finally, finless porpoises are subject to wildlife protection laws and the CITES Convention in many countries.

Capturing, importing, and breeding are illegal and subject to penalties.

In Japan, breeding is prohibited without special permission.

3. Safety Issues

Wild finless porpoises are not accustomed to humans and are at high risk of stress and aggression.

They are also at risk of diseases and parasites specific to marine mammals.