We sampled the nestling diets of tufted puffins (Fratercula cirrhata) and horned puffins (F. corniculata) in 3 years at colonies from the north-central Gulf of Alaska to the eastern Aleutian Islands, Alaska, USA. Overall, tufted puffins consumed (by weight) 41% sandlance (Ammodytes hexapterus), 22% capelin (Mallotus villosus), 19% walleye pollock (Theragra chalcogramma), 13% other fish, and 5% invertebrates, whereas horned puffins took 85% sandlance, 4% capelin, 2% pollock, 8% other fish, and <1 % invertebrates. All of the pollock consumed were young of the year, whereas 4 year-classes of capelin were present, from young of the year through spawning adults. Puffins took mostly first-year sandlance, but fish in their second year or older were also common at colonies near Kodiak, Alaska. The importance of juvenile pollock in the diet of tufted puffins varied geographically from little or no use in the north-central Gulf and Kodiak areas to moderate use (5 to 20%) in the Semidi and Shumagin Islands to heavy use (25 to 75%) in the Sandman Reefs and eastern Aleutians. An estimated 11 billion pollock were consumed by tufted puffins throughout the region in 1986. The proportion of pollock in puffin diets at the Semidi Islands was strongly correlated with independent estimates of cohort strength in 3 years. Puffins may thus provide a useful index of distribution and year class abundance of first-year pollock, a species that currently supports an important commercial fishery in the Gulf of Alaska.
