The Blue Whale: Larger Than the Megalodon

Since the era of woolly mammoths, humans have been captivated by enormous mammals. In the ocean, the blue whale (Balaenoptera musculus) reigns supreme as the largest animal to have ever existed on Earth.

So Exactly How Big Are Blue Whales?

Adam Ratner, a marine scientist at The Marine Mammal Center, states, "Blue whales are the largest animals on Earth and the biggest creatures ever known to exist." No evidence suggests any other animal, including the largest dinosaurs, exceeded the blue whale in size. But what about the Megalodon, the ancient shark species thought to be the largest fish ever (famously featured in the 2018 film The Meg)? Scientists estimate the Megalodon reached only about 58 feet (18 meters), though some argue it could grow up to 82 feet (25 meters). In comparison, blue whales can exceed 100 feet (30 meters) in length, with most averaging between 75-90 feet (23-27 meters). The largest blue whales are found in the Southern Ocean near Antarctica.

Can you guess how much this massive creature weighs? 5 tons? Too low. 50 or 100 tons? Closer, but still not there. A blue whale weighs around 400,000 pounds (181,437 kilograms), or 200 tons.

Ratner reveals more astonishing facts about the blue whale's immense size.

While these numbers are staggering, what do blue whales actually look like? They have a blue-gray hue, which gives them their name, though they are also called "sulfur-bottom whales" due to their yellowish underside. Their skin features lighter gray patches that look like paint splotches. As part of the baleen whale family, they lack teeth and instead have up to 800 plates of black baleen with coarse bristles for filtering food. Interestingly, female blue whales are typically larger than males.

What Do Blue Whales Eat?

Given their colossal size, one might assume blue whales feast on large prey, but this isn't true. Despite their immense bodies, blue whales primarily feed on tiny, two-inch crustaceans called krill. And they consume enormous amounts of it.

Ratner explains, "Due to their size, blue whales require massive amounts of food. They use baleen plates to filter small zooplankton from the water, consuming up to six tons (12,000 pounds or 5,443 kilograms) of krill daily." He adds, "In a single gulp, a blue whale can ingest 125 percent of its body weight in water and krill (250 tons), equating to half a million calories!"

Blue Whale Behavior and Communication

Despite their massive size, little is known about blue whales' social behavior, though they are not considered aggressive. "Blue whale social structures remain largely a mystery. They are often seen alone or in small groups," says Ratner. "In the wild, they are generally non-confrontational, focusing on feeding or migrating. However, their behavior during breeding seasons may differ and requires further study." Marine biologists are currently exploring how blue whales communicate through sound.

"Blue whales generate some of the loudest sounds in the animal kingdom, emitting low-frequency rumbles that can travel hundreds, and sometimes even thousands, of miles underwater," explains Ratner. "While researchers are still deciphering the purpose of these vocalizations, they believe it may relate to finding mates or signaling feeding opportunities."

Jeff Jacobsen, a marine biologist at the Noyo Center for Marine Science, elaborates on blue whale sounds, which scientists use to estimate population sizes and other factors. These repeated calls, known as songs, are produced exclusively by male blue whales. "Their songs vary by ocean basin and region. The low-frequency calls can travel vast distances, depending on ocean conditions," Jacobsen notes in an email.

The frequency of blue whale songs is influenced by noise from sources like ships. According to a study by researchers at Oregon State University, published in August 2017, blue whales adjust their song frequency by altering the rate at which air passes through their vocal cords. This study observed a gradual decline in call frequencies, but the exact purpose of these songs remains unclear. Since only males sing, it is speculated that these songs play a role in mating and courtship.

If you're interested, you can listen to blue whale sounds at Blue Whale Vocalization.

Blue Whale Mating and Offspring

Ratner explains that female blue whales give birth to one calf every two to three years after an 11-month gestation period. These calves are born around 25 feet (8 meters) long and weigh 7,000 pounds (3,175 kilograms), heavier than a mid-size SUV. "The mother's milk is so rich that calves gain 200 pounds (90 kilograms) daily while nursing," Ratner adds.

Details about blue whale mating remain scarce. "Mating behavior is still under study, but it appears males compete to protect females from rivals. We observe dramatic surface behaviors in the fall, with males 'fighting' over a female," says Jacobsen.

John Calambokidis, co-founder of the nonprofit Cascadia Research and a research biologist, provides insights into blue whale mating habits. "Blue whales produce extremely loud calls, recently discovered to be made only by males, suggesting a role in mating or male competition," he explains. During mating season, blue whales form male-female pairs, with the female leading. Competition among males can escalate, involving high-speed chases when multiple males are present.

How Many Are There and Are They Endangered?

Blue whales live an average of 80-90 years, but their survival is increasingly threatened. Listed as endangered under the Endangered Species Act, their population plummeted from 250,000 before commercial whaling to an estimated 10,000-25,000 today, according to Ratner.

Calambokidis notes that "the blue whale population remains below 5 percent of its pre-whaling numbers, with the most significant decline occurring in the Southern Hemisphere, where they were once most abundant."

Jacobsen concurs, stating, "Blue whales along the California coast were less affected by whaling, with at least 2,000 individuals still present. However, populations near Antarctica are still recovering." He highlights the ongoing threat of ship collisions, which claimed the life of the Noyo blue whale, now being restored at the Noyo Center. "For instance, higher krill concentrations in shipping lanes correlate with increased whale strikes," Jacobsen explains, referencing an article by Oregon State University's Whale Telemetry Group.

Blue whales also face challenges like fishing gear entanglements and climate change impacts on their food supply. Efforts are underway to improve their habitats. Ratner mentions that the Marine Mammal Center has advocated for shifting shipping lanes in San Francisco Bay to reduce whale strikes. He also emphasizes that individuals can help by reducing their carbon footprint, cutting fossil fuel use, and minimizing single-use plastics, which often endanger marine life through entanglement or ingestion.

Migratory Habits

Blue whales, like many marine mammals, migrate seasonally and are found globally. Ratner explains, "Blue whales inhabit all oceans except the Arctic, residing in both coastal and deep oceanic waters." They typically move toward polar regions in summer to feed and return to warmer equatorial waters in winter to breed. Calambokidis adds that blue whales have more flexible migration patterns compared to other baleen whales, such as gray whales, as their movements are driven by the need to locate abundant food sources rather than strict migratory routes.

Blue whales can be broadly categorized into Northern and Southern Hemisphere populations. One of the largest groups in the Northern Hemisphere consists of approximately 2,000 blue whales that feed near California and migrate to Costa Rica and Mexico, as noted on the Marine Mammal Center's website.

"Despite their enormous size, much about blue whales' specific movements and behaviors remains a mystery," says Ratner. Tracking them is challenging because satellite tags, commonly used on other marine mammals like sea lions, can cause skin infections in whales. Instead, scientists rely on photo identification to monitor individual blue whales globally. "Blue whales, like many other whales, have unique skin markings that allow researchers to identify them and study their migration patterns and life history," Ratner explains.

In positive news, the IUCN Red List of Threatened Species indicates that blue whale populations have likely increased in recent decades, offering hope for the future of these ocean giants.