Gray whale foraging on ghost shrimp (Callianassa californiensis) in littoral sand flats of Puget Sound, U.S.A.

Gray whales (Eschrichtius robustus) residing in Puget Sound, Washington, U.S.A., in 1990 and 1991 created feeding pits on littoral sand flats dominated by ghost shrimp (Callianassa californiensis). The whales removed an extensive biomass of shrimp from the pits. Ghost shrimp standing stock was 2–5 times lower inside than outside feeding pits, equivalent to a removal of 3–6 kg of shrimp per pit. An estimated 2700–3200 feeding pits were present on 19 km of sand flat in 1990, while 19 000 feeding pits were documented over the same region in spring and summer, 1991. We estimated that 10–12 and 75 t of shrimp were removed from the pits in 1990 and 1991, respectively. Ghost shrimp represent an energetically valuable prey for gray whales, providing 2–15 times higher standing stocks than any other reported prey. We discuss our results in the context of conflicts with human activity, impacts on the littoral community, and the significance of an expanding gray whale population.