The Longest Marine Migration: Gray Whales’ Epic Journey

Baleen whales are some of the most unique and breathtaking animals. These huge marine mammals are some of the biggest to have ever existed and are found all over the world.  Despite their size, baleen whales are gentle giants known for undertaking some of the longest migrations of any animal. Continue reading to discover why baleen whales migrate and where they travel.

Baleen Whales: Overview

Baleen whales (Mysticeti) have baleen plates instead of teeth. Made of keratin, the substance of human hair and nails, and growing in rows on each side of their mouths, baleen plates trap the microscopic prey on which these behemoths feed. The baleen plates have bristles on them that act as filters when the whale is feeding. Baleen whales have two blowholes and are typically much larger than their toothed counterparts. The blue whale (Balaenoptera musculus), a baleen species, is the largest animal to have ever lived, with the largest specimen recorded in 1909 as a whopping 110 feet long.

Baleen whales feed on krill, plankton, and small fish. Called filter feeding, they feed by taking in great mouthfuls of water, which are filtered through their baleen plates. The baleen plates catch the krill or fish, which the whale then swallows.

Baleen whales are usually solitary or travel in small groups rather than large, social pods. Even though they are solitary animals, they are usually within range of other members of their species. They communicate using low-frequency sounds known as songs, which can travel great distances. These communication songs are thought to be used to warn of danger and for mating.

Baleen Whale Migration

Many species of baleen whales migrate each year from their cold water feeding grounds where they summer, to their warm water breeding grounds for the winter.  Their feeding grounds are higher latitude areas closer to the poles where the water is colder and the food is much more abundant, while the breeding grounds are closer to the equator.

Baleen whales spend between four and six months during summer in the rich feeding grounds of polar waters, including the Northern Pacific, around the Gulf of Alaska. During this time, they eat around 4% of their body weight each day, which is much more than they require. This overeating behavior, called hyperphagia, allows baleen whales to store energy in the form of blubber, which sustains them on their journey.

When the temperatures start to fall, baleen whales begin their six-to-eight-month migration to tropical waters to give birth. Throughout this time, baleen whales eat much less or even not at all, depending on food availability, relying on the fat (blubber) that they stored.

Why Baleen Whales Migrate

Baleen whales migrate to give birth in the warmer tropical waters. When baleen whale calves are born, they have underdeveloped blubber, which is the layer of fat that keeps them warm. As their blubber isn’t fully developed, it isn’t thick enough to keep them warm in colder waters. Giving birth in the warmer waters allows calves time to develop a thick layer of blubber before migrating back to their cold water feeding grounds.

Another reason baleen whales migrate is to protect their calves from killer whales. Killer whales, apex predators that hunt in packs, are one of the main predators of baleen whale calves. Although they are sometimes found in tropical waters, they prefer colder water, making tropical waters safer for baleen whale calves.

Calves nurse for between 4 and 11 months, sticking close to their mothers during this period. Nursing calves quickly grow from their mother’s milk, which has a fat content of almost 50%. Calves are usually weaned in their first summer spent in the feeding grounds and return to the tropical waters alone the following winter.

Length of Baleen Whale Migration

Most baleen whales travel between 1,800 and 3,000 miles twice per year. Southern populations of humpback whales leave their Antarctic feeding grounds in January each year and spend three months traveling 3,000 miles to their breeding grounds in the waters off the coast of Australia. Other baleen whales migrate shorter distances, while some populations of Bryde’s whales are considered resident whales because they don’t migrate, remaining in one area year-round.

Gray Whale Migration: The Longest Migration of Any Animal in the World

Depending on the species and where they are located, whale migrations can be extremely long.The gray whale has the longest recorded migration of any marine mammal. 

Scientists recorded a gray whale migration in 2015 using GPS and were astonished that a 9-year-old gray whale named Varvara logged a 13,887-mile journey! Almost as amazing, gray whales give birth in only three calving lagoons, all of which are located in California’s Baja Peninsula.

Baleen Whales: Endangered

Sadly, several species of baleen whale are under threat. Blue, right, humpback, and sei whales are classified as endangered. Many of these populations were hunted almost to extinction by commercial whaling operations. Although large-scale whaling is now a thing of the past, there are still many hazards for these magnificent whales.

Collisions with ships are a major factor for some species, particularly blue whales, which are unable to get out of the way quickly enough due to their huge size.  An increase in the speed of modern vessels in already busy shipping lanes also adds to this risk.  In addition to ship strikes, baleen whales face threats from pollution, disease, and entanglement in fishing gear.