The Grey Whale (Eschrichtius robustus) undertakes one of the longest annual migrations of any mammal, traveling between its northern feeding grounds and the warmer lagoons of Mexico. This remarkable journey requires immense energy, and the whale acquires its fuel using a method unlike most other baleen species. The Grey Whale’s unique diet and specialized feeding technique, which involves foraging directly on the seafloor, distinguishes it within the order Cetacea.
Primary Prey of the Grey Whale
The Grey Whale is a benthic feeder, meaning its diet consists of small organisms living in or on the soft, muddy sediments of the ocean floor. The bulk of their energy intake comes from tiny crustaceans, particularly amphipods, which reside in high densities in Arctic and sub-Arctic waters. Amphipods form the foundation of the Grey Whale’s summer diet, providing the fat and protein stores necessary for the rest of the year.
While amphipods are the main target, the diet also includes other benthic organisms, such as cumaceans, ghost shrimp, and polychaete worms extracted from the sediment. The whales must locate areas with extremely high concentrations of prey to make foraging energetically worthwhile. In productive feeding areas, high feeding activity is associated with amphipod biomass reaching approximately 160 grams of wet weight per square meter of seafloor.
Foraging focuses on dense patches of these invertebrates, often found in shallow continental shelf waters. Although the Grey Whale primarily consumes bottom-dwelling invertebrates, some populations, particularly the Pacific Coast Feeding Group, display a more varied diet. These whales may opportunistically consume swarms of epibenthic mysid shrimp, crab larvae, or schools of small fish like anchovies, showcasing flexibility based on local prey availability.
Benthic Suction Feeding
The method by which the Grey Whale captures its prey is known as benthic suction feeding. This technique is distinct from the lunge-feeding of humpbacks or the skimming of right whales. To feed, the whale descends to the seafloor and rolls onto its side, often showing a preference for its right side.
The whale swims horizontally along the bottom, scooping up large amounts of sediment, water, and prey. It uses its powerful, muscular tongue as a piston to generate a strong vacuum, effectively sucking the infauna out of the substrate. The large volume of water and mud is then expelled through the mouth, leaving a visible plume of sediment, known as “sediment streaming,” in the whale’s wake.
The Grey Whale’s baleen plates are uniquely adapted for this process; they are relatively short and coarse compared to the finer, longer baleen of other filter feeders. These robust bristles act as a sieve, trapping the small invertebrates while the mud and seawater are pushed out. The repetitive action of scraping the seafloor creates distinct, excavated pits, typically ranging from 2 to 20 square meters in size.
Dietary Requirements and Migration Fasting
The Grey Whale’s intensive feeding season in the northern waters of the Bering and Chukchi Seas is connected to its life cycle of seasonal fasting. During the summer and early autumn, the whales engage in hyperphagia, or excessive feeding, to accumulate massive blubber reserves. These thick layers of blubber fuel the nearly 10,000 to 14,000-mile round-trip migration and the subsequent months spent in the warm, food-poor breeding lagoons off Baja California.
Once the whales begin their southward journey in the late autumn, they largely cease feeding, relying on stored fat for energy. This fasting period continues through the winter breeding season, where females give birth and nurse their calves in sheltered lagoons. The energy demands of migration, mating, and lactation are met entirely by metabolizing the blubber built up during the previous summer.
This “feast and fast” strategy requires the availability of high-density benthic prey in the Arctic feeding grounds. Insufficient feeding during the summer months leads to poor body condition, which has been linked to increased mortality during migration and reduced reproductive success. The ability to successfully build and maintain these energy reserves dictates the whale’s capacity to complete its annual cycle.