California Sea Grant College Program

We collated information on population size, diet composition, energy requirements, energy densities of prey species, and assimilation efficiency from the literature to estimate annual prey consumption by Common Murres (Uria aalge) between Cape Blanco, Oregon and Point Conception, California in 2004. We estimated that the population consumed approximately 242,250 metric tons of prey, including 70,500 metric tons consumed by breeding adults, 51,920 metric tons consumed by nonbreeding adults and subadults during the breeding season (March-August), 119,620 metric tons consumed by all birds during the wintering period (September –February), and 214 metric tons consumed by dependent chicks prior to leaving breeding colonies. Pacific hake (Merluccius productus) and market squid (Loligo opalescens) each made up over 20% of annual prey consumption. Other species making up at least 10% of annual consumption included shiner surfperch (Cymatogaster aggregata), northern anchovy (Engraulis mordax), and rockfish (Sebastes spp.). Chick diet was dominated by anchovy/sardine (Sardinops sagax; 63%), rockfish (21%), and smelt (Osmeridae spp.; 7%). Understanding these prey requirements is important for understanding the dynamics of predator and prey populations and for effective management of ocean resources.