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Fishery Bulletin 103(2) 



2002). Increased growth of Bristol Bay sockeye salmon 

 during the first two years at sea was associated with 

 greater adult returns, but high abundance apparently 

 led to increased competition and reduced growth during 

 the third year. 



The potential for competition for food between Asian 

 pink salmon and Bristol Bay sockeye salmon stocks is 

 great in the North Pacific Ocean and Bering Sea. Tro- 

 phic level, diet, and feeding behavior of pink salmon 

 overlap significantly with sockeye salmon (Welch and 

 Parsons, 1993; Davis et al., 2000; Kaeriyama et al., 

 2004). Asian pink salmon are highly abundant, averag- 

 ing approximately 162 million adults in odd-numbered 

 years and 104 million adults in even-numbered years, 

 1955 to 2000 (Rogers 1 ). Bristol Bay sockeye salmon and 

 Asian pink salmon overlap in the central North Pacific 

 Ocean and the Bering Sea. Greatest overlap is with 

 pink salmon from the eastern Kamchatka Peninsula 

 and Sakhalin Island (French et al., 1976; Takagi et al., 

 1981; Myers et al. 3 ), which are especially abundant, as 

 shown by average harvests of 79,000 metric tons (t) in 

 odd-numbered years and 33,000 t in even-numbered 

 years, 1955-99 (Sinyakov, 1998; Anonymous 4 ). 



Evidence for competition between Asian pink and 

 Bristol Bay sockeye salmon was provided in a recent in- 

 vestigation by Ruggerone et al. (2003). During 1955-97, 

 annual sockeye salmon scale growth during the second 

 and third years at sea was significantly reduced during 

 odd- compared to even-numbered years. Adult sockeye 

 salmon length was relatively low when sockeye salmon 

 overlapped with abundant odd-year pink salmon during 

 the year prior to homeward migration. Furthermore, 

 smolt-to-adult survival of Bristol Bay sockeye salmon 

 was significantly lower when they encountered odd-year 

 pink salmon during the second year at sea. However, 

 Bristol Bay sockeye salmon encountered relatively few 

 pink salmon during their first year at sea and no com- 

 petition effect was observed during this early marine 

 period. 



In our study we examined the seasonal growth of 

 Bristol Bay sockeye salmon scales in an effort to deter- 

 mine the approximate timing and duration of reduced 

 growth during odd-numbered years at sea that was 

 observed by Ruggerone et al. (2003). Scale circuli in- 

 crements and annuli are correlated with salmon body 

 size (Clutter and Whitesel, 1956; Fukuwaka and Kaeri- 

 yama, 1997; Fukuwaka, 1998). We compared seasonal 

 scale growth before and after 1977 to examine seasonal 

 growth trends associated with the twofold increase in 

 Bristol Bay sockeye salmon abundance and the 1977 



:) Myers, K. W., K. Y. Aydin, R. V. Walker, S. Fowler, and M. L. 

 Dahlberg. 1996. Known ocean ranges of stocks of Pacific 

 salmon and steelhead as shown by tagging experiments, 

 1956-1995. Report FRI-UW-9614, 159 p. School of Aquatic 

 and Fishery Sciences, Univ. Washington, Seattle, WA 



4 Anonymous. 2002. Biostatistical information on salmon 

 catches, escapement, outmigrants number, and enhancement 

 production in Russia in 2001. Doc. no. 646, 14 p. NPAFC, 

 889 Pender Street, Vancouver, Canada. 



ocean regime shift (Rogers, 1984; Beamish and Bouil- 

 lon, 1993; Rogers 1 ). We also examined the hypothesis 

 that seasonal growth during the second growing sea- 

 son was dependent on previous marine growth (Aydin, 

 2000). These hypotheses were tested by using scales 

 from Kvichak River and Egegik River sockeye salmon, 

 which averaged approximately 16 million fish per year 

 or approximately 57% of the annual sockeye salmon run 

 to Bristol Bay, 1955-2000. 



Methods 



For our study, we used scales from four age groups of 

 Kvichak River sockeye salmon and three age groups of 

 Egegik River sockeye salmon collected from the late 

 1950s through 2000 (Fig. 1). Adult salmon scales were 

 obtained from the Alaska Department of Fish and Game 

 (ADFG) archive in Anchorage, Alaska, and from the 

 School of Aquatic and Fishery Sciences, University of 

 Washington. Scales have been collected annually for 

 measuring and quantifying age composition for manage- 

 ment of the fisheries in Alaska. We selected scales from 

 salmon sampled in the Kvichak and Egegik rivers rather 

 than in the ocean fisheries to reduce the possibility of 

 mixed stocks in the scale collection. Scale collections 

 from the Kvichak River began in 1955, whereas collec- 

 tions from Egegik River began in 1960. Major freshwater 

 and ocean age groups from Kvichak (ages 1.2, 1.3, 2.2, 

 2.3) and Egegik (ages 1.3, 2.2, 2.3) sockeye salmon were 

 measured. Age was designated by European notation, 

 i.e. the number of winters spent in freshwater before 

 going to sea (1 winter=age-l. or two winters = age-2.) 

 followed by the number of winters spent at sea (two 

 winters = age-.2 or 3 winters = age-.3.l. Nearly all Bristol 

 Bay sockeye salmon mature after spending two or three 

 winters at sea. 



Scales were selected for measurement in this study 

 only when 1) we agreed with the age determination 

 previously made by ADFG, 2) the scale shape indi- 

 cated that the scale was removed from the "preferred 

 area" (Koo. 1962), and 3) circuli and annuli were clearly 

 defined and not affected by scale regeneration or sig- 

 nificant resorption along the measurement axis. We 

 measured up to 50 scales per year, representing equal 

 numbers of male and female salmon from each age 

 group within each stock. 



Scale measurements followed procedures described 

 by Davis et al. (1990) and Hagen et al. 5 After select- 

 ing a scale for measurement, the scale was scanned 

 from a microfiche reader and its image was stored as a 

 high resolution digital file. High resolution (3352x4425 

 pixels) allowed the entire scale to be viewed and pro- 

 vided enough pixels to be seen between narrow circuli 



5 Hagen, P. T., D. S. Oxman, and B. A. Agler. 2001. Devel- 

 oping and deploying a high resolution imaging approach for 

 scale analysis. Doc. 567, 11 p. North Pacific Anadromous 

 Fish Commision, 889 Pender Street, Vancouver, Canada. 



