Alaska’s nutrient-rich waters serve as a crucial summer feeding ground for several species of large whales, allowing them to build up the massive energy reserves necessary for their annual migrations. The timing of their departure is a staggered event tied closely to the diminishing availability of prey and the onset of colder temperatures. This shift signals a move from intense summer feeding to winter breeding and calving in warmer, distant waters. The precise schedule varies significantly based on the whale species.
Species-Specific Departure Schedules
Gray Whales are typically the earliest large migratory species to begin their southward journey from Alaskan feeding grounds. Their departure often starts in late September, with the peak of the migration occurring throughout October. They feed in the shallow Bering and Chukchi seas, and the southward movement of sea ice and subsequent reduction in food sources prompts this early exit. By mid-December, the main wave of Gray Whales is usually passing through the waters near Unimak Pass, marking their passage out of the Alaskan region.
Humpback Whales follow a slightly later, more prolonged departure schedule from their summer feeding areas in Southeast Alaska and the Gulf of Alaska. The main wave of North Pacific Humpbacks leaves around October and November, but individuals may continue to depart into December. This staggered movement is often described as a “trickle migration,” with different age and sex classes leaving at different times. Pregnant females may linger slightly longer to maximize energy stores before the long non-feeding migration, while juveniles and non-pregnant adults often depart first.
Bowhead Whales have a unique migration tied directly to the formation and movement of Arctic sea ice. They spend the summer in the Canadian Beaufort Sea and begin their westward migration along the northern Alaskan coast between late August and October. Their southward passage through the Bering Strait typically occurs by November, as they follow the advancing ice edge into the Bering Sea for the winter. The timing of their departure is shifting, as decreased sea ice in the Arctic has been observed to delay their fall migration.
Migration Destinations and Routes
Gray Whales undertake one of the longest migrations of any mammal, traveling between 5,000 to 7,000 miles one way. Their route follows the Pacific coastline south from the Bering Sea to the warm, protected lagoons of Baja California, Mexico, where they breed and calve.
Humpback Whales from Alaska follow separate migratory routes toward three main tropical breeding grounds. The majority of North Pacific Humpbacks travel to the Hawaiian Islands, while others head to the coast of Mexico or the western Pacific near Japan. The journey to Hawaii covers approximately 3,000 miles and is undertaken in a non-stop swim that takes several weeks.
Bowhead Whales do not migrate to distant, warm tropical waters but remain within the Arctic and Sub-Arctic region. Their movement is a seasonal shift between feeding areas in the Canadian Beaufort Sea and wintering grounds in the Bering Sea. This migration follows the expanding and receding edge of the sea ice, which provides protection from predators like Orcas.
The Biological Imperative: Why Whales Leave Alaska
The primary driver for this seasonal exodus is a combination of feeding optimization and reproductive necessity. Alaska’s cold waters offer a seasonal abundance of prey, such as krill and small fish, allowing whales to spend the summer months feeding almost constantly. During this time, they accumulate a thick layer of blubber, which serves as the energy store they rely on during migration and the winter fast. The whales leave Alaska when the food supply dwindles and fat reserves are sufficient to sustain them for the winter months.
The warm, southern waters, though low in food, provide a safer, thermally suitable environment for calving and mating. Newborn calves lack the thick insulating blubber layer needed to survive the frigid Alaskan temperatures immediately after birth. By migrating to protected tropical lagoons and bays, the mothers ensure their young can grow and develop strength before making the return journey north the following spring.
Resident and Partial Migrants
Orcas, also known as Killer Whales, are found year-round in Alaska, though their movement depends on their ecotype. Resident and transient populations have distinct feeding habits, dictated by the availability of specific prey, such as salmon or marine mammals. They often follow the retreating or advancing ice, but they do not undertake the thousands-of-miles journey of the baleen whales.
Beluga Whales remain within the Arctic and Sub-Arctic environment. The Cook Inlet population, for instance, is considered non-migratory, remaining in the inlet throughout the year. Other populations, such as those in the Eastern Chukchi and Beaufort Seas, make localized seasonal movements, often gathering in river estuaries and shallow coastal waters during the summer. These whales move between their summer areas and wintering grounds in the Bering Sea, following leads in the ice, but they do not migrate to lower latitudes.