Ruggerone et al.: Seasonal growth of Oncorhynchus nerka in relation to competition with O. gorbuscha 



361 



(i.e., during odd-numbered years). Initial scale growth 

 prior to the SW2 peak in spring was the same between 

 odd- and even-numbered years, although there was a ten- 

 dency for greater growth following the SW1 annulus of 

 even-year smolts (Fig. 3). Immediately after peak growth 

 near circuli 11, scale growth of even-year smolts became 

 significantly less than that of odd-year smolts (Table 1). 

 The growth differential continued through the end of the 

 SW2 growing season and it reached a maximum reduc- 

 tion of -10% to -18% near circuli 14 to 18 (Fig. 3). This 

 pattern was consistent before and after the 1977 climate 

 shift and among each stock and age group. The reduced 

 growth of even-year smolts during SW2 corresponded 

 with high abundance of pink salmon in the central North 

 Pacific Ocean during odd-numbered years. 



Scale growth during SW2 of both odd- and even-year 

 smolts tended to be greater after the 1977 climate shift 

 (Fig. 4), a period when abundance of Bristol Bay sock- 

 eye salmon and Asian pink salmon was great. This pat- 

 tern was consistent among both age groups of Kvichak 

 and Egegik River sockeye salmon. Greatest growth dif- 

 ferential between the two periods (up to 10%) occurred 

 just after peak growth (circuli 5 to 15), a pattern that 

 differed markedly from both SW1 and SW3. In contrast 

 to the relatively large increase in growth shown in 

 the central portion of SW2 after 1977, growth at the 

 beginning of SW2 was similar during both periods and 

 growth at the end of SW2 was relatively low after the 

 climate shift. 



Third year (SW3) growth of ocean age-3 sockeye salmon 



Scale growth at the beginning of the third year at sea 

 increased rapidly, peaked near circuli 5-6, then declined 



steadily through the year (Fig. 2). Peak growth during 

 SW3 was intermediate to the relatively high peak 

 growth during SW1 and relatively low peak growth 

 during SW2. 



During their third year at sea, even-year sockeye 

 smolts inhabited the North Pacific and Bering Sea when 

 relatively few Asian pink salmon were in offshore wa- 

 ters (i.e., even-numbered years). Prior to peak growth, 

 SW3 growth of even-year smolts was similar or below 

 that of odd-year smolts (Fig. 3), a pattern that contin- 

 ued from the previous season. Immediately following the 

 peak, growth of even-year smolts significantly increased 

 in relation to odd-year smolts (Table 1), and growth re- 

 mained relatively high throughout the remaining season 

 (Fig. 2). Growth of even-year smolts was approximately 

 5% to 15% greater than that of odd-year smolts from 

 circuli 8 to the annulus (Fig. 3). Differences in growth 

 during even- versus odd-numbered years tended to be 

 greater after 1976 when both pink and sockeye salmon 

 were relatively abundant. 



Peak SW3 scale growth was up to 10% greater after 

 the mid-1970 regime shift during both odd- and even- 

 numbered years (Fig. 4). However, after the peak grow- 

 ing season, scale growth was typically lower after 1976. 

 The relatively low growth after 1976 was especially 

 pronounced among odd-year smolts that inhabited the 

 ocean during odd-numbered years when Asian pink 

 salmon were abundant in offshore waters. Scale growth 

 of odd-year smolts during SW3 was as much as 10% 

 lower than that prior to 1977. 



Scale growth during both SW3 and SW2 were signifi- 

 cantly reduced during odd-numbered years at sea (Table 

 1). However, SW3 scale growth during odd- versus even- 

 years diverged immediately after the peak, whereas 



