Wildlife Spotlight: Blue Whale (Balaenoptera musculus)

Blue whale fluke. Credit: Robert Schwemmer

Right in your ocean backyard this month and in September, you can see the world’s largest population of the earth’s largest animals: blue whales.

Approximately 2,000 blue whales live off the California Coast and migrate to warmer waters in Mexico and Costa Rica during the winter. These giants come to the waters around the Farallon Islands to feed on their favorite food, the shrimp-like krill. Krill are abundant in the area in late summer and early fall because of upwelling, the process of deeper, cold, nutrient-rich waters moving upward to the ocean surface due to the offshore movement of surface waters. Blue whales must eat 2-4 tons of krill a day during the feeding season.

Some blue whales are more than 100 feet (30.5 m) long, but 70-90 feet (23-27 m) is typical — about as long as three school buses. An average weight for an adult is 200,000 to 300,000 pounds (100-150 tons). Its heart alone is as large as a small car.

Appearance

Blue whales are mostly blue-gray, mottled with light gray. Cold water diatoms adhere to their skin and sometimes give their bellies a yellowish tinge, giving the blue whale its nickname of "sulfur bottom." Blue whales are long and streamlined. Their dorsal fins are extremely small, and their pectoral flippers are long and thin.

Blue whales are rorqual whales, a family of baleen whales with pleated throat grooves that expand when the animal takes in water while feeding. In blue whales, 55-68 throat grooves extend from the throat to the navel. Blue whale baleen is black with over 800 plates.

These majestic mammals have been found in every ocean of the world. They swim individually or in small groups. Often pairs are observed.

Mating and Breeding

Females give birth to calves every two to three years. Pregnancy lasts for about one year. A newborn calf is about 23 feet (7 m) long and weighs 5,000 to 6,000 pounds (2,700 kg). A nursing mother produces over 50 gallons (200 liters) of milk a day. The milk contains 35% to 50% fat and allows the calf to gain weight at a rate of up to 10 pounds an hour or over 250 pounds (44 kg) a day! At six months and an average length of about 52 feet (16 m), the calf is weaned. The blue whale reaches sexual maturity in 10 years.

Status

The blue whale was too swift and powerful for the 19th century whalers to hunt, but with the arrival of harpoon cannons, they became a much sought after species for their large amounts of blubber. The killing reached a peak in 1931 when 29,649 blue whales were taken. By 1966, blues were so scarce that the International Whaling Commission declared them protected throughout the world. Today, there are probably fewer than 15,000 blue whales in the oceans, and they are considered an endangered species.

For a chance to see these beautiful giants, join us on a FMSA Whale Watching Trip to the Farallones on Sundays, August 19 and September 16, or Saturday, September 22.