Whale Shark vs Blue Whale: Biggest Fish vs Biggest Animal

Key differences at a glance

The whale shark and the blue whale are the two great filter feeders of the ocean, and their names cause endless confusion. They look a little alike from a distance: both are huge, slow and gentle, and both eat tiny prey. Up close they are built in completely different ways:

• Group: the whale shark is a cartilaginous fish; the blue whale is an air-breathing mammal.
• Size: the blue whale is typically two to three times as long and five or more times heavier.
• Breathing: gills for the shark, lungs and blowholes for the whale.
• Tail: upright and swept sideways in the shark, flat and beaten up and down in the whale.
• Body surface: the shark is covered in tooth-like scales and pale spots; the whale has smooth, mottled blue-gray skin over blubber.
• Young: the shark gives birth to many small pups; the whale has one huge calf and feeds it milk.

Fish vs mammal

The whale shark is a true shark. Its skeleton is made of cartilage, its skin carries tiny tooth-like scales called dermal denticles, and its body temperature stays close to that of the water around it. Its closest relatives are carpet sharks such as nurse sharks and wobbegongs. Why it is named after whales is explained in Is a whale shark a whale?

The blue whale is a baleen whale, a mammal whose ancestors lived on land. It has a bony skeleton, breathes air, keeps a warm body temperature of about 36–37 °C (97–99 °F) and is insulated by a thick layer of blubber. Its nearest living relatives on land are hippos. The two giants last shared an ancestor more than 400 million years ago, so their similarities are a case of convergent evolution.

Which is bigger?

The blue whale wins by a wide margin. It is the largest animal known to science, living or extinct, while the whale shark is the largest fish and the largest animal that is not a whale.

Few whale sharks have ever been weighed, so their weights are estimates. A newborn blue whale calf is already about as long as many of the young whale sharks seen at coastal feeding sites. For bus and dinosaur comparisons, see How big is a blue whale?, and for other record-holders, the largest animals in the world.

Gills vs lungs: breathing and diving

A whale shark takes oxygen from the water passing over its five pairs of gills, so it never needs to surface for air. Tagged whale sharks spend days in deep water and have dived to 1,928 m (6,325 ft).

A blue whale must hold its breath underwater and return to the surface to breathe through its two blowholes, sending up a tall spout of spray up to 9–12 m (30–39 ft) high. Its feeding dives off California average about 10 minutes and reach around 200 m (660 ft); the deepest dive recorded from a tagged blue whale was 315 m (1,033 ft). How whales manage this is covered in How do whales breathe?

So the fish, not the whale, is the deeper diver.

Tails, speed and swimming

You can often tell a shark from a whale by its tail. Like other fish, the whale shark has an upright tail fin that sweeps from side to side. The blue whale has broad, flat flukes that beat up and down, a movement inherited from running land mammals whose backbones flex up and down.

Both are usually slow. Whale sharks typically cruise at about 2–5 km/h (1–3 mph). Blue whales usually travel at 2–8 km/h (1–5 mph) but can sprint in short bursts of about 30 km/h (19 mph).

Two ways to filter feed

Both animals strain small prey from seawater, but with different equipment. The whale shark has 20 spongy filter pads in its throat, probably modified gill rakers. It swims forward with its mouth open, sucks in water while almost stationary, or hangs vertically at the surface, and it eats plankton, krill, fish and coral eggs, crab larvae, small fish and squid.

The blue whale has several hundred baleen plates made of keratin hanging from its upper jaw. It lunges into a dense swarm of krill, opens its mouth and lets its pleated throat balloon out, taking in a mouthful of water and prey that can weigh about as much as the whale itself. It then pushes the water out through the baleen and swallows the krill. A 2021 study estimated that eastern North Pacific blue whales eat about 16 tonnes of krill a day in the feeding season, while a 6 m (20 ft) whale shark feeding at the surface off Mexico was estimated to take in about 21 kg (46 lb) of plankton a day.

Babies and lifespan

Whale sharks give birth to live young, but there is no milk and no parental care. The eggs hatch inside the mother, and one female carried about 300 embryos. Pups are born at about 40–60 cm (16–24 in) and must survive alone. Whale sharks grow slowly, and males take about 25 years to mature.

A blue whale mother gives birth to a single calf after a pregnancy of 10–12 months and nurses it on rich milk, on which it gains about 90 kg (200 lb) a day until weaning at around 6–8 months. Females usually calve every 2–3 years.

Both are long-lived. Blue whales are thought to live about 80–90 years, and whale shark lifespan estimates range from about 80 to 130 years.

Where they live and where they meet

Whale sharks stay in tropical and warm-temperate seas, mostly between about 30° N and 35° S. Blue whales live in every ocean except the Arctic, and many migrate between cold, krill-rich feeding grounds near the poles and warmer waters where they breed.

Their ranges overlap in some warm and temperate waters. Both can be seen in Mexico’s Gulf of California, where whale sharks gather near La Paz and Bahía de los Ángeles and blue whales arrive in late winter, and off Western Australia, where pygmy blue whales migrate past the coast near Ningaloo Reef.

Conservation: two endangered giants

Both species are listed as Endangered on the IUCN Red List. Commercial whaling killed hundreds of thousands of blue whales in the 20th century, until hunting was banned in 1966. Today their numbers are slowly rising, and the main threats are ship strikes, entanglement and underwater noise.

Whale sharks were never hunted on the same industrial scale, but fishing for their meat, fins and oil, bycatch and collisions with ships caused a decline of more than half over about 75 years, and the trend is still downward. Ship strikes are a shared threat, since both feed near the surface in busy waters.