Blue Whale vs. Gray Whale: What’s the Difference?
Key Takeaways
- Size is the biggest difference. Blue whales can reach about 100 feet and more than 150 tons. Gray whales top out around 49 feet and 45 tons.
- They eat in different ways. Gray whales are bottom feeders that suck up amphipods and other small invertebrates from the sea floor. Blue whales lunge through open water to gulp huge swarms of krill.
- They live in different places. Gray whales stay close to shore in shallow coastal waters. Blue whales prefer deep offshore waters.
- They visit San Diego at different times. Gray whales pass by in winter and spring during their migration. Blue whales feed off Southern California in summer and early fall.
- Both are protected. Blue whales are listed as endangered. The eastern North Pacific gray whale recovered after whaling, but the western population remains critically endangered.
- You can see both from San Diego, which makes it one of the best places in the world for whale watching.
Whales are some of the most impressive animals on the planet. They’re intelligent, graceful, and enormous, and they’ve been swimming Earth’s oceans for millions of years. That’s a big part of why whale watching is such an exciting experience.
Two of the most famous whales off the California coast are the blue whale and the gray whale. Both are baleen whales and both migrate along the Pacific coast, but they live remarkably different lives. They differ in size, diet, habitat, and appearance, and they visit San Diego in different seasons.
In this guide, we’ll compare blue whales and gray whales side by side so you know what makes each one special, and how to see both on a San Diego whale watching tour. For the latest sightings, check out our whale watching report.
Blue Whale vs. Gray Whale at a Glance
| Feature | Blue Whale | Gray Whale |
| Adult length | Up to ~100 ft | Up to ~49 ft |
| Adult weight | Up to 150+ tons (300,000+ lb) | ~30–45 tons (60,000–90,000 lb) |
| Newborn calf | ~20–25 ft, up to ~3 tons | ~14–16 ft, ~2,000 lb |
| Main diet | Krill | Amphipods, mysids, and other small invertebrates |
| Feeding style | Lunge feeding in open water | Bottom feeding on the sea floor |
| Habitat | Deep offshore waters worldwide | Shallow coastal waters of the North Pacific |
| Dorsal fin | Small, set far back | None (low hump and “knuckles” instead) |
| Color | Blue-gray with light mottling | Mottled gray with white barnacle patches |
| Blow | Tall, straight column up to ~30 ft | Lower, bushy, often heart-shaped |
| Lifespan | ~80–90 years | ~50–70+ years |
| Best time in San Diego | Summer to early fall | Winter to spring |
| Conservation status | Endangered | Eastern population recovered; western population critically endangered |
Size: The Biggest Difference Between Blue and Gray Whales
Size is the most obvious difference between these two whales.
How Big Are Blue Whales?
The blue whale is the largest animal known to have ever lived. Adults can grow to about 100 feet long and weigh more than 150 tons, which is heavier than any dinosaur ever discovered. As in many baleen whales, females are generally larger than males.
Blue whales are huge from the very beginning. A newborn calf is about 20 to 25 feet long and can weigh up to about 3 tons. While nursing on its mother’s rich, fatty milk, a blue whale calf can gain about 200 pounds a day. That’s one of the fastest growth rates in the animal kingdom. Learn more in our guide to how big baby whales really are.
How Big Are Gray Whales?
The gray whale is still a very large animal, even if it’s about half the length of a blue whale. Adults usually weigh 60,000 to 70,000 pounds, and the largest can reach about 90,000 pounds and 49 feet long.
Gray whale calves are big too. A newborn is about 14 to 16 feet long and weighs around 2,000 pounds. Calves grow quickly on their mother’s milk, building up the blubber they’ll need for their first long migration north to the Arctic.
Feeding Habits: How Blue and Gray Whales Eat
Both species are baleen whales, meaning they filter food through baleen plates instead of chewing it with teeth. But their feeding styles couldn’t be more different. For a closer look, see our guide to what whales eat.
What Do Gray Whales Eat?
Gray whales are the only large whales known to feed mainly on the sea floor. They roll onto their sides, suck up mouthfuls of sediment, and push the mud and water back out through their short, stiff baleen, trapping the food inside. They often leave feeding pits on the ocean floor and trails of mud behind them.
Their favorite foods are amphipods and mysids, tiny shrimp-like crustaceans, along with tube worms, crab larvae, and other small invertebrates. Gray whales are also opportunistic, so they’ll feed on whatever is available in the area.
Gray whales do most of their eating during the summer in Arctic waters. During that season, a gray whale may eat about 2,400 pounds of food a day, gaining roughly 16 to 30 percent of its body weight. Those fat reserves carry it through the rest of the year, because gray whales eat very little during their long migration and while breeding in Mexico.
What Do Blue Whales Eat?
Blue whales eat almost nothing but krill, small shrimp-like animals only a couple of inches long. To catch enough of them, blue whales lunge through dense krill swarms with their mouths wide open, taking in a huge volume of water. The pleated throat expands like a balloon, and the whale then pushes the water out through its baleen, keeping the krill.
Like gray whales, blue whales do most of their feeding during a few months of the year. During that time, a single blue whale can eat several tons of krill a day. The commonly cited figure is about 8,000 pounds, and some research suggests it can be even more. That enormous appetite is how blue whales grow so big.
Habitat: Coastal Gray Whales vs. Deep-Water Blue Whales
Where Do Gray Whales Live?
Gray whales are coastal whales. As shallow-water bottom feeders, they stay close to shore, often just outside the surf line. That’s why gray whales are one of the easiest large whales to see from a boat, and sometimes even from shore.
Today, gray whales live only in the North Pacific Ocean. The best-known population is the eastern North Pacific gray whale, which migrates along the West Coast between Alaska and Mexico. A much smaller western North Pacific population lives off the coasts of Russia and Asia.
Where Do Blue Whales Live?
Blue whales are found in every ocean in the world, from the tropics to the poles. They prefer deep offshore waters, especially areas where cold, nutrient-rich water rises to the surface and fuels krill swarms.
Off Southern California, blue whales are often found along the edges of deep underwater canyons and ridges, where krill gather in huge numbers. That makes San Diego one of the best places to see the largest animal on Earth.
Migration Patterns: How Far Do Blue and Gray Whales Travel?
Gray Whale Migration
Gray whales make one of the longest migrations of any mammal, traveling roughly 10,000 to 12,000 miles round trip every year.
- Summer: Feeding in the cold Arctic waters of the Bering, Chukchi, and Beaufort Seas
- Fall and early winter: Swimming south along the West Coast, past San Diego
- Winter: Mating and giving birth in the warm, protected lagoons of Baja California, Mexico
- Late winter and spring: Heading back north, often with newborn calves swimming beside their mothers
Because they migrate so close to shore, gray whales are a highlight of gray whale watching season in San Diego. Learn more in our guide to gray whale migration facts.
Blue Whale Migration
Blue whale migration is harder to track, since these whales spend much of their time far offshore. Research shows that in general, blue whales:
- Spend summer and fall in cooler, food-rich waters, feeding on krill
- Spend winter and spring in warmer, lower-latitude waters, where they’re thought to breed and give birth
The eastern North Pacific blue whale population, the one we see off California, feeds off the West Coast in summer and fall. In winter it moves south toward the waters off Mexico and Central America. Read more about blue whale watching season in California.
Appearance: How to Tell Blue and Gray Whales Apart
If you’re out on the water, here’s how to tell the difference.
Gray Whale Appearance
- Color: Dark to medium gray, heavily mottled with white and light gray patches
- Barnacles and whale lice: Gray whales carry more barnacles than almost any other whale, which gives them a rough, textured look
- No dorsal fin: Instead, they have a low hump followed by a row of small bumps, or “knuckles,” along the back
- Head: Relatively small and slightly arched
- Blow: Lower and bushier than a blue whale’s, and often heart-shaped when seen from behind
Blue Whale Appearance
- Color: Blue-gray with light mottling. Just under the water they can look bright blue or turquoise, and at the surface they look darker blue-gray.
- Underside: Blue whales sometimes have a yellowish belly caused by tiny organisms called diatoms, which earned them the nickname “sulphur-bottom”
- Dorsal fin: Very small for their size and set far back on the body
- Head: Broad and flat, shaped like a U from above
- Blow: A tall, straight column of spray that can reach about 30 feet high
Reproduction: How Blue and Gray Whales Raise Their Calves
As mammals, both species give birth to live young and nurse them with milk. Mothers usually have one calf at a time, and the calf receives nutrients through an umbilical cord during gestation.
Gray whales:
- Reach maturity at around 8 to 9 years old on average
- Gestation lasts about 12 to 13 months
- Calves are born in the warm lagoons of Baja California
- Mothers and calves stay close together during the northbound migration, when you can often see them passing San Diego
Blue whales:
- Reach maturity at around 5 to 15 years old
- Gestation lasts about 11 to 12 months
- Calves are born in warmer waters during the winter months
- Calves nurse for about 6 to 7 months, gaining weight at an incredible rate
Lifespan: How Long Do Blue and Gray Whales Live?
Scientists estimate the age of baleen whales by counting the layers in their waxy earplugs, which build up over time a little like tree rings.
- Gray whales usually live about 50 to 70 years, and some may live longer.
- Blue whales usually live about 80 to 90 years, possibly more.
Adult whales have few natural predators. Killer whales (orcas) are known to hunt gray whale calves, especially during migration, and sharks may target young, sick, or injured whales. Today, the biggest threats to both species come from humans, including ship strikes, fishing gear entanglement, and changes to their ocean habitat.
Population and Conservation
Gray Whale Population
Gray whales are one of the great conservation success stories. Whaling nearly wiped out the eastern North Pacific gray whale, but after it was protected, the population recovered to tens of thousands of whales. The population has declined in recent years during a series of unusual deaths first recorded in 2019, and scientists continue to monitor it closely.
The western North Pacific gray whale is a different story. Only a few hundred remain, and it’s considered critically endangered. Learn more about gray whale conservation and how we can protect gray whales.
Blue Whale Population
Blue whales were hunted heavily in the 20th century, which reduced their numbers dramatically. Today they’re protected worldwide but still listed as endangered. The eastern North Pacific population, which feeds off California, is thought to be one of the largest remaining blue whale populations in the world. That’s another reason San Diego is so special for whale watching.
You can help protect both species by learning about ways to protect our oceans and choosing responsible whale watching operators.
When Can You See Blue and Gray Whales in San Diego?
One of the best things about San Diego is that you can see both of these incredible whales, just at different times of year.
Seeing Gray Whales in San Diego
- Best season: Winter and spring
- Southbound migration: Gray whales head south toward Baja in winter
- Northbound migration: They return north in late winter and spring, often with calves
- Where: Close to the coast, often within a few miles of shore
Gray whale season is one of the most popular times of year for whale watching. Plan your trip with our guide to San Diego whale watching in January, and discover more with these 10 interesting facts about gray whales.
Seeing Blue Whales in San Diego
- Best season: Summer to early fall
- Why: Blue whales come to feed on the krill that gathers off Southern California
- Where: Usually farther offshore in deeper water
Summer is the time to look for the largest animal on Earth. Learn more about blue whale watching in San Diego and San Diego whale watching in July.
On any trip, you may also see humpback whales, fin whales, minke whales, dolphins, sea lions, and seabirds. Curious about other species? Read about the types of toothed whales seen off San Diego and what we see on our tours.
FAQs About Blue Whales and Gray Whales
What is the main difference between a blue whale and a gray whale?
The main difference is size. Blue whales can grow to about 100 feet long and weigh more than 150 tons, while gray whales reach about 49 feet and 45 tons. They also feed differently: blue whales eat krill in open water, and gray whales feed on the sea floor.
Which is bigger, a blue whale or a gray whale?
The blue whale is much bigger. It’s about twice as long as a gray whale and can weigh three to four times as much or more.
Is a blue whale bigger than a gray whale at birth?
Yes. A newborn blue whale is about 20 to 25 feet long and up to about 3 tons, while a newborn gray whale is about 14 to 16 feet long and around 2,000 pounds.
Do blue whales and gray whales eat the same thing?
No. Blue whales eat almost only krill. Gray whales mostly eat amphipods, mysids, and other small invertebrates that they suck up from the sea floor.
Do gray whales have a dorsal fin?
No. Gray whales don’t have a dorsal fin. Instead, they have a low hump and a row of small knuckle-like bumps along their back. Blue whales have a small dorsal fin set far back on the body.
Why are gray whales covered in barnacles?
Gray whales swim slowly and spend a lot of time in coastal waters, which makes them easy for barnacles and whale lice to attach to. These hitchhikers create the white and orange patches that make each gray whale’s pattern unique.
Why is the blue whale called “blue”?
Blue whales look bright blue or turquoise underwater. At the surface, they appear more blue-gray with light mottling.
When is the best time to see gray whales in San Diego?
Winter and spring, during their annual migration between the Arctic and Baja California.
When is the best time to see blue whales in San Diego?
Summer and early fall, when blue whales come to Southern California to feed on krill.
Can you see blue whales and gray whales on the same trip?
It’s uncommon, since they usually visit San Diego in different seasons. Gray whales are here in winter and spring, and blue whales are here in summer and fall. There can be some overlap at the edges of each season.
How far do gray whales migrate?
Gray whales travel roughly 10,000 to 12,000 miles round trip each year between their Arctic feeding grounds and their breeding lagoons in Mexico, one of the longest migrations of any mammal.
How long do blue whales and gray whales live?
Blue whales typically live about 80 to 90 years, and gray whales about 50 to 70 years or more.
Are blue whales endangered?
Yes. Blue whales are listed as endangered. They were heavily hunted in the 20th century and are now protected worldwide.
Are gray whales endangered?
The eastern North Pacific gray whale, the population we see off California, recovered after whaling and is not listed as endangered. The western North Pacific gray whale is critically endangered.
Is whale watching safe for blue and gray whales?
Yes, when it’s done responsibly. Next Level Sailing follows responsible whale watching practices and gives whales plenty of space. Learn how to keep ocean wildlife safe when visiting San Diego’s hot spots.
See Blue Whales and Gray Whales With Next Level Sailing
Whether you want to watch a gray whale mother and calf glide past the coast in spring, or feel the thrill of seeing the largest animal on Earth surface in summer, San Diego is one of the best places in the world to do it.
Join Next Level Sailing aboard the historic Yacht America for an unforgettable whale watching adventure.
Why sail with Next Level Sailing?
- A one-of-a-kind vessel. Sail aboard the Yacht America, a stunning sailing yacht with plenty of deck space for wildlife viewing.
- Eco-friendly whale watching. Wind-powered sailing means a quieter, more sustainable way to see marine life.
- Expert crew. Learn about whale behavior, migration, and conservation on every trip.
- Year-round tours. From gray whale season to blue whale season, there’s always something to see.
- Great for groups. Plan a corporate event or celebrate a special occasion on the water.