Early Marine Growth of Pink Salmon in Prince William Sound and the Coastal Gulf of Alaska During Years of Low and High Survival ALISON D. CROSS* AND DAVID A. BEAUCHAMP U.S. Geological Survey, Washington Cooperative Fish and Wildlife and Research Unit, School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, Washington 98195-5020, USA KATHERINE W. MYERS High Seas Salmon Research Program, School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, Washington 98195-5020, USA JAMAL H. MOSS U.S. Geological Survey, Washington Cooperative Fish and Wildlife and Research Unit, School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, Washington 98195-5020, USA, and National Marine Fisheries Service, Auke Bay Laboratory, 11305 Glacier Highway, Juneau, Alaska 99801-8626, USA Abstract.—Although early marine growth has repeatedly been correlated with overall survival in Pacific salmon Oncorhynchus spp., we currently lack a mechanistic understanding of smolt-to-adult survival. Smolt- to-adult survival of pink salmon O. gorbuscha returning to Prince William Sound was lower than average for juveniles that entered marine waters in 2001 and 2003 (3% in both years), and high for those that entered the ocean in 2002 (9%) and 2004 (8%). We used circulus patterns from scales to determine how the early marine growth of juvenile pink salmon differed (1) seasonally during May–October, the period hypothesized to be critical for survival; (2) between years of low and high survival; and (3) between hatchery and wild fish. Juvenile pink salmon exhibited larger average size, migrated onto the continental shelf and out of the sampling area more quickly, and survived better during 2002 and 2004 than during 2001 and 2003. Pink salmon were consistently larger throughout the summer and early fall during 2002 and 2004 than during 2001 and 2003, indicating that larger, faster-growing juveniles experienced higher survival. Wild juvenile pink salmon were larger than hatchery fish during low-survival years, but no difference was observed during high- survival years. Differences in size among years were determined by some combination of growing conditions and early mortality, the strength of which could vary significantly among years. Although early marine growth has repeatedly been correlated with overall survival in Pacific salmon Oncorhynchus spp. (Holtby et al. 1990; Henderson and Cass 1991; Murphy et al. 1998; Tovey 1999; Willette et al. 1999; Mortensen et al. 2000; Beamish et al. 2004), we currently lack a mechanistic understand- ing of the timing, magnitude, and source of stage- specific marine survival. Early growth and mortality of pink salmon O. gorbuscha are probably governed by some combination of prey availability, smolt quality, interspecific and intraspecific competition, predation, and ocean conditions. This study examined interannual variability in the growth performance of juvenile pink salmon among years corresponding to low marine survival (3% for adults returning to hatcheries in Prince William Sound, Alaska, during 2002 and 2004) and high marine survival (9% in 2003 and 8% in 2005; 2005; PWSAC 2005; K. Morgan, Valdez Fisheries Development Association, personal communication). This species exhibits a 2-year life cycle; therefore, adults that returned during the summers of 2002–2005 would have entered the ocean as juveniles during spring of the previous year (i.e., 2001–2004). The four Prince William Sound hatcheries that release pink salmon fry (Figure 1) collectively represent one of the largest salmon hatchery programs in the world, and the combined annual release has exceeded 600 million fry since 2001 (ADFG 2005; Table 1). These hatchery releases average over three times more fry than the natural production of approximately 190 million wild pink salmon fry migrating into Prince William Sound each year (S. Moffitt, Alaska Department of Fish and Game, personal communication). * Corresponding author: crossad@gmail.com Received January 14, 2007; accepted September 28, 2007 Published online May 1, 2008 927 Transactions of the American Fisheries Society 137:927–939, 2008 Ó Copyright by the American Fisheries Society 2008 DOI: 10.1577/T07-015.1 [Article]