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



363 



smolts. Growth of even- and odd-year smolts during 

 the first growing season was not significantly different 

 but even-year smolts tended to have somewhat greater 

 growth immediately following peak growth (circuli 7-13) 

 and at the end of the growing season (circuli 19-22) 

 (Fig. 6). 



SW1 growth was markedly greater after 1976 when 

 salmon abundance was relatively high compared with 

 the growth during 1952-1976 (Fig. 7). Greater growth 

 during the recent time period was most pronounced 

 immediately after entry to Bristol Bay and after peak 

 growth (circuli 13-18), but it was relatively low at the 

 end of the growing season (circuli 20-22). These pat- 

 terns were generally consistent between odd- and even- 

 year smolt years. 



r (SW2) growth of ocean age-2 sockeye 



Second yea 

 salmon 



SW2 scale growth patterns of ocean age-2 sockeye 

 salmon were similar to SW2 patterns of ocean age-3 

 sockeye salmon. Scale growth of odd- and even-year 

 smolts was similar until scale growth of even-year smolts 

 significantly declined approximately three circuli after 

 peak growth (Fig. 5, Table 1). Lower growth of even-year 

 smolts continued to the end of the growing season. Scale 

 growth of even-year migrants during their second year 

 at sea was approximately 107c to 15% less than that of 

 odd-year migrants (Fig. 6). Low growth of even-year 

 migrants was associated with odd-numbered years at 

 sea — a trend that was observed among SW2 and SW3 

 growth periods of ocean age-3 sockeye salmon. 



Scale growth during SW2 was greater after 1976 when 

 salmon abundance was relatively high compared with 

 the growth before 1977, especially during the middle of 

 the growing season (Fig. 7). However, after 1976, growth 

 near the end of the growing season (circuli 17-20) tend- 

 ed to be below average. These patterns were consistent 

 among the two stocks and three age groups. 



Late season growth of ocean age-2 sockeye salmon 

 during the second year at sea differed from that of 

 ocean age-3 sockeye salmon (Figs. 2 and 5). Growth 

 after circuli 8 of SW2 was significantly greater among 

 ocean age-2 compared with ocean age-3 sockeye salm- 

 on (df=283, £=12.81, P<0.001), averaging 11% greater 

 growth. 



Growth during homeward migration (SWPL) of ocean 

 age-2 sockeye salmon 



Scale growth of ocean age-2 sockeye salmon during the 

 homeward migration peaked at circuli 4, then declined. 

 Prior to peak growth, even-year migrants experienced 

 approximately 57c less growth than odd-year migrants, 

 a pattern that was similar prior to and after the climate 

 shift (Fig. 6). Low initial growth during SWPL appeared 

 to be a continuation of relatively low growth during 

 SW2. No difference in peak growth between odd- and 

 even-years was apparent. Growth tended to be higher 

 after the mid-1970s (Fig. 7). 



10 13 16 19 22 



Circuli pair 



Figure 7 



Percent change in ocean age-2 sockeye salmon (O. nerka) 

 scale growth entering ocean during 1977 to 1998 com- 

 pared with 1952-1976. Growth patterns represent smolts 



entering ocean during odd- I ) and even-numbered 



years ( ). Even-year smolts encountered odd-year 



pink salmon (O. gorbuscha) during the second year at 

 sea (SW2). 



Relationship between early marine and late SW2 

 scale growth 



We examined correlations between early marine scale 

 (SW1 growth through the first eight circuli of SW2) and 

 late SW2 growth (circuli 11 to annulus), corresponding 

 with periods before and after the divergent scale growth 

 pattern observed between odd- and even-numbered years. 

 Negative correlations between early marine and late SW2 

 scale growth were observed among each stock and age 

 group, before and after the 1977 regime shift, and among 

 fish inhabiting the ocean during odd- or even-numbered 

 years (Table 2). Only one of the 28 correlations (Egegik 

 age-2. 2, early period, odd SW2 year) was statistically 

 insignificant. Thus, individual sockeye salmon that expe- 

 rienced somewhat low growth during early marine life 

 tended to have somewhat high growth during later por- 

 tions of their second year at sea, regardless of whether 

 they competed with pink salmon. The strength of the 



