121 



Abstract — We tested the hypothesis 

 that larger juvenile sockeye salmon 

 [Oncorhynchus nerka) in Bristol 

 Bay, Alaska, have higher marine- 

 stage survival rates than smaller 

 juvenile salmon. We used scales 

 from returning adults (33 years of 

 data) and trawl samples of juveniles 

 (?i = 3572) collected along the east- 

 ern Bering Sea shelf during August 

 through September 2000-02. The 

 size of juvenile sockeye salmon mir- 

 rored indices of their marine-stage 

 survival rate (e.g., smaller fish 

 had lower indices of marine-stage 

 survival rate). However, there was 

 no relationship between the size of 

 sockeye salmon after their first year 

 at sea, as estimated from archived 

 scales, and brood-year survival size 

 was relatively uniform over the time 

 series, possibly indicating size-selec- 

 tive mortality on smaller individuals 

 during their marine residence. Varia- 

 tion in size, relative abundance, and 

 marine-stage survival rate of juvenile 

 sockeye salmon is likely related to 

 ocean conditions affecting their early 

 marine migratory pathways along the 

 eastern Bering Sea shelf. 



Early marine growth in relation to 



marine-stage survival rates for 



Alaska sockeye salmon iOncorhynchus nerka) 



Edward V. Farley Jr^ 



James M. Murphy* 



Milo D. Adkison^ 



Lisa B. Eisner* 



John H. Helle' 



Jamai H. Moss' 



Jennifer Nielsen^ 



Email address for E V Farley: Ed.Farley@noaa.gov 



' NOAA, Auke Bay Laboratory 

 National Marine Fisheries Service, NOAA 

 1 1305 Glacier Highway 

 Juneau, Alaska 99801 



^ Juneau Center, School of Fisheries and Ocean Sciences, 

 University of Alaska Fairbanks 

 11120 Glacier Highway 

 Juneau, Alaska 99801 



^ U.S. Geological Survey, Alaska Science Center 

 1011 East Tudor Road 

 Anchorage, Alaska 99503 



Manuscript submitted 27 March 2006 

 to the Scientific Editor. 



Manuscript approved for publication 

 5 July by the Scientific Editor. 



Fish. Bull. 105:121-130 (2007). 



Pacific salmon {Oncorhynchus spp.) 

 experience relatively high mortality 

 rates during the first few months at 

 sea (Hartt, 1980), and it is believed 

 that size plays an important role in 

 survival (Parker, 1968; Pearcy, 1992). 

 Size-dependent mortality of juvenile 

 salmon may be concentrated during 

 two specific life-history stages. The 

 first stage is thought to occur just 

 after juvenile salmon enter the marine 

 environment, where smaller individu- 

 als are believed to experience higher 

 size-selective predation (Parker, 1968; 

 Willette et al., 1999). The second stage 

 is thought to occur after the first 

 summer at sea, when smaller indi- 

 viduals may not have sufficient energy 

 reserves to survive late fall and winter 

 (Beamish and Mahnken, 2001). Thus, 

 larger individuals likely have a higher 

 probability of survival during both of 

 these stages, and size and growth 

 while salmon reside in the estuary 

 and during their first summer at sea 

 may be important for survival. 



Previous studies indicate that scale 

 radius length is proportional to fish 

 body length (Francis, 1990; Ricker, 



1992) and, in particular, incremental 

 increases in sockeye salmon (O. nerka) 

 scale radius are strongly correlated 

 with somatic growth (Fukuwaka and 

 Kaeriyama, 1997). In our study, scales 

 from adult Bristol Bay sockeye salmon 

 were examined to determine the rela- 

 tionship between size after their first 

 year at sea and survival to adulthood. 

 We compared the time series (1965-97) 

 of brood-year returns per spawner 

 with scale growth measurements 

 taken from adult sockeye salmon re- 

 turning to the Egegik and Kvichak 

 River systems in Bristol Bay, Alaska. 

 Juvenile sockeye salmon enter the 

 marine waters of the eastern Bering 

 Sea during May and June (Burgner, 

 1991) and migrate through Bristol 

 Bay to the Bering Sea and North 

 Pacific during the summer and early 

 fall months (Straty, 1981; Farley et 

 al., 2005). Two differing models of 

 seaward migration are believed to ex- 

 ist for juvenile Bristol Bay sockeye 

 salmon: in some years juvenile sock- 

 eye salmon migrate along the coastal 

 waters of the eastern Bering Sea near 

 the Alaska Peninsula, and in other 



