Sei whales exhibit a greater variety in diet than, say, blue whales, but tend to feed on only one type of prey at a time. Of 21,713 stomachs examined in the North Pacific, 82.7% contained copepods only, and 12.6% contained euphausiids only; of 31,494 stomachs examined in the southern hemisphere, 54.3% contained euphausiids only, 30.5% contained copepods only, and 14.4% contained amphipods only (Nemoto and Kawamura 1977). Sei whale stomachs examined in the Northeast Atlantic contained copepods and euphausiids (Jonsgård and Darling 1977). Sei whale stomachs analysed in the North Pacific off California contained euphausiids and anchovies (Rice 1977). Sei whales are noted for their erratic appearance in specific feeding grounds, being plentiful in some years and absent (sometimes for years or even decades) in others (Horwood 1987).