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Mammals · 22 species guides

Marine Mammals: Whales, Seals & Dolphins

Marine mammals are mammals that depend on the sea for feeding, breeding or both, including whales, dolphins, porpoises, seals, sea lions, walruses, sea otters, manatees and dugongs; they evolved from land ancestors separately in several lineages and share adaptations such as streamlined bodies, insulation and, in cetaceans, the ability to hold their breath for extended dives.

Cetacean fluke and blow
Whales and dolphins surface to breathe through a blowhole. Baleen whales have two blowholes; toothed cetaceans have one. The tail fluke is horizontal, powering up-and-down strokes — unlike a fish tail, which moves side to side.
Dolphin versus porpoise
Dolphins tend to have longer beaks, curved dorsal fins and cone-shaped teeth. Porpoises have shorter faces, triangular dorsal fins and spade-shaped teeth. Porpoises are generally less acrobatic at the surface.
Seal versus sea lion
True seals — grey seal, elephant seal — have hind flippers that point backward and cannot rotate under the body; they wriggle on land. Sea lions and fur seals can walk on all fours by rotating hind flippers forward and have visible external ear flaps.
Baleen versus toothed whale
Baleen whales — blue, humpback, fin, grey — filter feed with keratin plates and lack teeth as adults. Toothed whales — sperm whale, orca, dolphins — hunt with teeth. The sperm whale has a single blowhole angled forward and to the left.

Marine mammal is a habitat grouping, not a single evolutionary branch. Whales and dolphins descended from hoofed land mammals; seals and sea lions from bear-like carnivores; manatees and dugongs from elephants; sea otters from weasel-like ancestors. What they share is a life tied to water — and the adaptations that life demands: streamlined bodies, thick blubber or dense fur for insulation, and, in cetaceans, nostrils migrated to the top of the head as a blowhole.

The identification problems in this group are practical. A dorsal fin at sea could be a dolphin, a porpoise or a shark — behaviour and shape separate them. On a beach, a seal and a sea lion look similar until you watch them move: sea lions can walk on all fours with hind flippers rotated forward; true seals wriggle and cannot rotate the hind flippers underneath. Those distinctions matter for conservation too, because the threats differ — bycatch and ship strikes for whales, entanglement and disturbance for seals, habitat loss for manatees.

Key facts

  • Marine mammals evolved from land ancestors in at least four separate lineages — cetaceans, pinnipeds, sirenians and otters.
  • Whale and dolphin tail flukes move up and down; fish tails move side to side — a reliable distinction at sea.
  • True seals cannot walk on land; sea lions and fur seals rotate their hind flippers forward and have external ear flaps.
  • Baleen whales filter feed; toothed cetaceans — including orcas and sperm whales — hunt with teeth.
  • Ship strikes, entanglement in fishing gear and ocean noise are major modern threats to cetaceans worldwide.
  • Manatees and dugongs — the sirenians — are vulnerable to boat strikes and loss of seagrass habitat in warm coastal waters.

How to recognise them

The features that separate this group in the field, in the order they are usually most useful.

Cetacean fluke and blow
Whales and dolphins surface to breathe through a blowhole. Baleen whales have two blowholes; toothed cetaceans have one. The tail fluke is horizontal, powering up-and-down strokes — unlike a fish tail, which moves side to side.
Dolphin versus porpoise
Dolphins tend to have longer beaks, curved dorsal fins and cone-shaped teeth. Porpoises have shorter faces, triangular dorsal fins and spade-shaped teeth. Porpoises are generally less acrobatic at the surface.
Seal versus sea lion
True seals — grey seal, elephant seal — have hind flippers that point backward and cannot rotate under the body; they wriggle on land. Sea lions and fur seals can walk on all fours by rotating hind flippers forward and have visible external ear flaps.
Baleen versus toothed whale
Baleen whales — blue, humpback, fin, grey — filter feed with keratin plates and lack teeth as adults. Toothed whales — sperm whale, orca, dolphins — hunt with teeth. The sperm whale has a single blowhole angled forward and to the left.
The confusion pairs
Seal versus sea lion: hind-flipper mobility and ear flaps. Dolphin versus porpoise: beak length, dorsal fin shape and teeth. Manatee versus dugong: manatees have a rounded tail paddle; dugongs have a fluked tail like a whale. Sea otter versus seal: otters have visible hind limbs and often float on their backs.

22 marine mammals guides

Search or filter by conservation status. Every guide carries sourced facts, IUCN status and FAQs.

Showing 1-22 of 22 animals

Animal group
A blue whale surfacing in open ocean, its mottled blue-grey body dwarfing the surrounding water.
Endangered

Mammals

B

Blue Whale

Balaenoptera musculus (Linnaeus, 1758)

The largest animal ever known — a colossal filter-feeder recovering from the whaling era.

All oceans — Arctic to Antarctic; migratory between feeding and breeding grounds

Open guide
A common bottlenose dolphin breaking the surface with a curved dorsal fin and intelligent dark eye.
Varies by species

Mammals

D

Dolphin

Family Delphinidae — oceanic dolphins including Tursiops truncatus (common bottlenose) and Delphinus delphis (common dolphin)

Oceanic dolphins of the open sea — social, echolocating and not river specialists.

All oceans · some rivers (separate WARN river-dolphin guides)

Open guide
A dugong grazing on a shallow seagrass meadow, its broad downturned snout pressed to the seabed and a dolphin-like fluked tail trailing behind in clear tropical water
Vulnerable globally

Mammals

D

Dugong

Dugong dugon

The gentle sea cow that mowed the seagrass meadows long before sailors mistook it for a mermaid.

Indonesia · Malaysia

Open guide
Fin whale surfacing with asymmetric jaw in cold ocean waters
Vulnerable

Mammals

F

Fin Whale

Balaenoptera physalus

The sleek greyhound of the seas

Africa · Asia

Open guide
A giant otter surfacing in a dark Amazon river, its sleek brown body and the distinctive cream-coloured throat patch visible above the water, whiskers spread and head raised alertly
Endangered

Mammals

G

Giant Otter

Pteronura brasiliensis

The Amazon's "river wolf" — the longest otter on Earth and one of its most endangered.

Brazil · Colombia

Open guide
Gray whale with mottled barnacle-covered skin surfacing at sea
Least Concern overall; the western Pacific population is Critically Endangered

Mammals

G

Gray Whale

Eschrichtius robustus (Lilljeborg, 1861) — family Eschrichtiidae

One of the longest migrations of any mammal, and a whale that feeds by rolling on the seabed.

North Pacific — eastern population from Mexico to the Arctic · Small, severely depleted western population off Russia

Open guide
Grey seal pup with white lanugo coat
Least Concern

Mammals

G

Grey Seal

Halichoerus grypus

The horse-faced seal of the Atlantic

Europe · North America

Open guide
A humpback whale breaching clear of the ocean surface, its long white-edged pectoral fins outstretched and knobbly head streaming water, against a blue sea and sky.
Least Concern globally

Mammals

H

Humpback Whale

Megaptera novaeangliae

The ocean's great singer, leaping back from the brink of whaling.

Brazil

Open guide
A live Ganges river dolphin (Platanista gangetica) surfacing in a calm, murky river, its distinctive elongated beak with visible teeth and rounded, low dorsal ridge clearly visible above the waterline; the animal's pinkish-brown skin glistens in natural light.
Endangered

Mammals

I

Indus River Dolphin

Platanista minor

A nearly blind freshwater dolphin that swims on its side through the murk of the Indus.

Pakistan

Open guide
A West Indian manatee gliding through clear shallow water with algae on its grey wrinkled skin.
Varies by species

Mammals

M

Manatee

Trichechus manatus, T. inunguis and T. senegalensis — three living species

Gentle sirenians of warm shallows — slow, plant-eating and vulnerable to boats.

Caribbean · Gulf of Mexico

Open guide
A narwhal surfacing in icy Arctic water, its long spiralled tusk visible above the surface beside mottled grey skin.
Near Threatened

Mammals

N

Narwhal

Monodon monoceros (Linnaeus, 1758)

The unicorn of the Arctic — a deep-diving whale whose tusk is a sensory tooth.

Arctic — Canada, Greenland, Russia, Svalbard

Open guide
Male elephant seal on beach with trunk-like nose
Least Concern

Mammals

N

Northern Elephant Seal

Mirounga angustirostris

The deep-diving seal giant

North America · Oceans

Open guide
A pod of orcas (Orcinus orca) swimming calmly through open coastal water, their distinctive tall black dorsal fins and black-and-white markings clearly visible at the surface
Data Deficient

Mammals

O

Orca

Orcinus orca (Linnaeus, 1758)

Apex predators of every ocean — culturally distinct pods with global reach.

Arctic · Antarctic

Open guide
A sleek otter floating on its back in clear river water, holding a small fish between its paws.
Varies by species

Mammals

O

Otter

Subfamily Lutrinae — 13 species of aquatic mustelids worldwide

River acrobats and kelp-forest hunters — mustelids built for water on every continent.

Every continent except Australia and Antarctica

Open guide
A pink-hued adult Amazon river dolphin (boto) surfacing in a tea-coloured Amazon tributary, showing its long slender beak, bulging melon forehead and low ridged back instead of a tall dorsal fin.
Endangered

Mammals

P

Pink River Dolphin

Inia geoffrensis

The blushing ghost of the flooded forest — and one of the world's most imperilled freshwater dolphins.

Brazil · Colombia

Open guide
Harbour porpoise surfacing in calm coastal water
Family page

Mammals

P

Porpoise

Family Phocoenidae — seven species, including Phocoena phocoena

Not small dolphins — a separate family, with spade-shaped teeth and no beak.

Coastal temperate and cold waters of the Northern Hemisphere and South America · Shallow seas, estuaries and some rivers

Open guide
A California sea lion balancing on a rocky haul-out, head raised and external ear flaps visible.
Varies by species

Mammals

S

Sea Lion

Family Otariidae — ~16 species of eared seals (sea lions and fur seals)

Agile eared seals of rocky coasts — vocal, social and quick on land.

Pacific coasts of Americas · Australia

Open guide
A sea otter floating on its back in kelp, using its chest as a table while eating a shellfish.
Endangered

Mammals

S

Sea Otter

Enhydra lutris (Linnaeus, 1758)

Kelp-forest gardeners with the densest fur on Earth — Endangered keystone predators.

North Pacific — California, Alaska, British Columbia, Russia, Japan

Open guide
A harbour seal resting on a rocky shore, its sleek spotted coat glistening and whiskers prominent.
Varies by species

Mammals

S

Seal

Family Phocidae — ~19 species of true (earless) seals worldwide

Streamlined mammals of ice and ocean — adapted for deep dives and harsh shores.

Arctic · North Atlantic

Open guide
A sperm whale's wrinkled head and small lower jaw break the surface before it dives, showing its distinctive profile.
Vulnerable

Mammals

S

Sperm Whale

Physeter macrocephalus (Linnaeus, 1758)

Deep-sea hunters with the largest brain on Earth — masters of the abyss.

All deep oceans — from poles to equator

Open guide
A large walrus hauled out on Arctic sea ice, its long ivory tusks and bristly whiskered snout clearly visible above a wrinkled, blubbery brown body.
Vulnerable

Mammals

W

Walrus

Odobenus rosmarus

The tusked giant of the Arctic ice.

Arctic Ocean · Bering and Chukchi Seas

Open guide
A humpback whale breaching from the ocean, its massive body arching above white spray against a deep blue sea.
Varies by species

Mammals

W

Whale

Infraorder Cetacea — ~90 species of baleen and toothed whales

Giants of the deep — baleen filter-feeders and toothed hunters of every ocean.

All oceans from Arctic to Antarctic

Open guide

Conservation: what this group faces

Marine mammals face a stack of human pressures that operate at different scales. Entanglement in fishing gear and ship strikes kill whales and manatees directly; ocean noise from shipping and seismic surveys disrupts communication and navigation in cetaceans; plastic ingestion affects species from albatrosses' marine equivalents to filter-feeding whales. River dolphins — pink and Indus — are among the most endangered mammals alive, confined to degraded river systems. Protected areas at sea help, but migratory species need safe passage along entire routes, not just reserves at one end.

Fund mammal protection Current appeals

Marine mammals: frequently asked questions

What is a marine mammal?
A mammal that depends on the sea for feeding, breeding or both. The group includes cetaceans — whales, dolphins and porpoises — pinnipeds — seals, sea lions and walruses — sirenians — manatees and dugongs — and marine otters, which feed in the ocean though they rest on land.
What is the difference between a seal and a sea lion?
True seals have hind flippers that point backward and cannot rotate under the body, so they wriggle on land. Sea lions and fur seals can walk on all fours by rotating hind flippers forward and have small external ear flaps. Sea lions are also generally more vocal and social on land.
What is the difference between a dolphin and a porpoise?
Dolphins usually have longer beaks, curved dorsal fins and cone-shaped teeth. Porpoises have shorter, blunt faces, triangular dorsal fins and spade-shaped teeth. Porpoises are generally smaller and less acrobatic at the surface.
Are whales fish?
No. Whales are mammals — they breathe air, are warm-blooded, give birth to live young and nurse them with milk. They descended from land-dwelling hoofed ancestors and retain vestigial hind limb bones inside their bodies.
What is the largest marine mammal?
The blue whale, which is also the largest animal known to have lived. Large individuals exceed the length and mass of any dinosaur. Humpback, fin and sperm whales are also among the largest mammals, though all are substantially smaller than a large blue whale.
Are marine mammals endangered?
Many are. North Atlantic right whales are Critically Endangered, with ship strikes and entanglement the main causes. Several river dolphins are at the edge of extinction. Manatees face boat strikes and habitat loss. Even relatively recovered species such as humpback whales remain vulnerable to ocean noise and climate-driven prey shifts.

Other types of mammal

All mammal guides Animals A–Z