Interannual and Spatial Feeding Patterns of Hatchery and Wild Juvenile Pink Salmon in the Gulf of Alaska in Years of Low and High Survival JANET L. ARMSTRONG,* KATHERINE W. MYERS,DAVID A. BEAUCHAMP,NANCY D. DAVIS, ROBERT V. WALKER, AND JENNIFER L. BOLDT School of Aquatic and Fishery Sciences, University of Washington, Box 355020, 1122 Northeast Boat Street, Seattle, Washington 98195-5020, USA JOHN J. PICCOLO AND LEWIS J. HALDORSON School of Fisheries and Ocean Sciences, University of Alaska–Fairbanks, 11120 Glacier Highway, Juneau, Alaska 99801, USA JAMAL H. MOSS National Oceanographic and Atmospheric Administration–Fisheries, Auke Bay Laboratory, 11305 Glacier Highway, Juneau, Alaska 99108, USA Abstract.—To improve understanding of the mechanisms affecting growth and survival, we evaluated the summer diets and feeding patterns (prey composition, energy density, and stomach fullness) of hatchery and wild juvenile pink salmon Oncorhynchus gorbuscha in Prince William Sound (PWS) and the northern coastal Gulf of Alaska (CGOA). Our study (1999–2004) included 2 years of low (;3%), mid (;5%), and high (;8–9%) survival of PWS hatchery pink salmon. Because variations in diet should affect growth and ultimately survival, we expected that the variations in diet, growth, and survival would be correlated. During August in the CGOA, pteropod-dominated diets and higher gut fullness corresponded to high survival (5–9%), and copepod-dominated diets and lower gut fullness corresponded to low survival (3%). Within years, no significant differences were found in diet composition or gut fullness between hatchery and wild fish or among the four PWS hatchery stocks. Diets varied by water mass (habitat) as juveniles moved from PWS to more saline habitats in the CGOA. In July, when juveniles were most abundant in PWS, their diets were dominated by pteropods and hyperiid amphipods. The diets of fish that moved to inner-shelf (i.e., the least- saline) habitat in the CGOA in July were dominated by larvaceans in low-survival years and pteropods in high-survival years. Diet quality was higher in CGOA habitats than in PWS in July. In August, fish moved to the more productive, more saline water masses in the CGOA, where large copepods and pteropods were dominant prey and diet quality was better than in PWS. Our results indicate that spatial variation in the diets of juvenile pink salmon in July and the timing of migration to the CGOA play a critical role in marine growth and survival. The Northeast Pacific Global Ocean Ecosystems Dynamics (NEP–GLOBEC) Program was designed to investigate how two continental shelf ecosystems, the California Current System and the coastal Gulf of Alaska (CGOA), respond to large-scale climate change (U.S. GLOBEC 1996; Weingartner et al. 2002). One core hypothesis of NEP–GLOBEC is that ocean survival of Pacific salmon Oncorhynchus spp. is primarily determined by survival of juveniles in coastal regions, and is affected by interannual and interdecadal changes in physical forcing and by changes in food web dynamics. Pink salmon O. gorbuscha were selected as the target species to address this hypothesis in the CGOA shelf ecosystem because they are highly abundant zooplanktivores that spend little or no time rearing in freshwater as juveniles and support valuable commercial fisheries as adults (Clark et al. 2006). In addition, they have a shorter lifespan (2 years) than other Pacific salmon species, which provides a more direct link between short-term climatic change and forcing mechanisms that drive marine food web dynamics. Numerous studies reviewed by Ruggerone and Nielsen (2004) have documented that pink salmon seem to have a competitive advantage over other salmonid species in the North Pacific Ocean owing to their high abundance, high consumption rates, rapid growth, and ability to use a wide variety of prey species, including those of lower trophic levels. Run strength of pink salmon is thought to be determined * Corresponding author: janeta@u.washington.edu Received September 17, 2007; accepted February 19, 2008 Published online August 21, 2008 1299 Transactions of the American Fisheries Society 137:1299–1316, 2008 Ó Copyright by the American Fisheries Society 2008 DOI: 10.1577/T07-196.1 [Article]