Gray whales are the only baleen whales that habitually feed on the bottom. In the shallow Bering and Chukchi seas they roll to one side, press the head into soft sediment and draw in a mouthful of mud, then push the water and silt out through the baleen, retaining amphipods and other small invertebrates. The plumes of suspended sediment they leave behind are visible from the surface and from the air.
The habit leaves a physical record. Baleen on the preferred side is shorter and more worn, and most examined animals are right-sided, a rough parallel to handedness. Feeding pits scoured into the seabed can be mapped across whole shelf areas.
Bottom feeding is not exclusive. Gray whales also take krill, mysids and crab larvae in the water column, and the flexibility matters: the unusual mortality event that killed large numbers between 2019 and 2023 has been linked to changing Arctic prey, though the mechanism is still under investigation.