Grey whales, scientifically known as Eschrichtius robustus, are a type of baleen whale inhabiting the Pacific Ocean. These large marine mammals are recognized for undertaking one of the longest annual migrations of any mammal, traveling thousands of miles between their feeding and breeding grounds. Their diet and distinct feeding methods are central to their biology, offering insight into their ecological role and connection to marine environments.
Primary Prey and Diet Composition
Grey whales primarily consume small invertebrates found on the seafloor, making them bottom-feeders. Their main food source is amphipods, tiny, shrimp-like crustaceans, often found in dense concentrations of 12,000 to 20,000 individuals per square yard. Their diet also includes other benthic organisms such as marine worms (polychaetes), small crustaceans like mysids and ghost shrimp, and mollusk larvae.
While their diet is predominantly seafloor invertebrates, grey whales are also generalist feeders. They opportunistically consume pelagic zooplankton, such as krill, and occasionally small fish like Pacific herring eggs or anchovies. During summer feeding periods, an adult grey whale can consume approximately 1.3 tons of food daily. Over a five to six-month feeding season, a single whale may ingest around 70 metric tons of prey to build essential fat reserves.
Specialized Feeding Behavior
Grey whales possess a unique feeding technique called “bottom-feeding” or “suction feeding.” To feed, they roll onto one side, often their right side, near the ocean floor. They use their powerful muscular tongue to suck in large mouthfuls of sediment, water, and the small invertebrates within.
Once the sediment and water are inside their mouths, the whales use their baleen plates to filter out their prey. These baleen plates are coarse, off-white structures, measuring between 2 to 10 inches long, and number between 130 to 180 on each side of their upper jaw. The water and mud are expelled, leaving the trapped food to be swallowed. This process creates plumes of mud seen rising to the surface and leaves oblong, bowl-shaped pits, roughly three by six feet in size, on the seafloor. This method contrasts with “lunge feeding” or “skim feeding” strategies employed by other baleen whales.
Feeding Grounds and Migration
The primary feeding grounds for grey whales are located in the shallow, nutrient-rich Arctic waters, particularly the Bering and Chukchi Seas. These northern regions offer an abundant supply of benthic invertebrates. Whales spend summer months intensely feeding to accumulate significant fat reserves.
Their renowned long migration, which can span 16,000 to 23,000 kilometers round trip, is directly linked to the availability of these food resources. After building up sufficient energy reserves in the Arctic, they undertake their journey south to warmer waters, such as the lagoons of Baja California, Mexico, where they breed and calve during the winter months. Grey whales generally feed very little, if at all, during their migration or while in their winter breeding grounds, relying instead on the fat reserves accumulated during the productive Arctic summer. Recent changes in ocean conditions, including the loss of sea ice, have begun to affect the abundance of their traditional prey in these critical Arctic feeding grounds.