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



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Figure 1 



Map of Bristol Bay, Alaska, and the location of the Kvichak and Egegik river systems. 



to ensure accurate measurements of circuli spacing. 

 The digital image was loaded in Optimas 6.5 (Media 

 Cybernetics, Inc., Silver Spring, MD) image processing 

 software to collect measurement data with a customized 

 program. The scale image was displayed on a digital 

 LCD flat panel tablet. The scale measurement axis was 

 determined by a perpendicular line drawn from a line 

 intersecting each end of the first saltwater annulus. 

 Distance (mm) between circuli was measured within 

 each growth zone (i.e., from the scale focus to the outer 

 edge of the first freshwater (FW1) annulus, between the 

 first and second freshwater (FW2) annuli, within the 

 spring plus (FWPL) growth zone, within each annual 

 saltwater (SW1. SW2, SW3) growth zone, and from the 

 last ocean annulus to the edge of the scale (i.e., the 

 saltwater plus [SWPL] growth zone). 



Data analysis 



Mean scale circuli increments (distance between adjacent 

 circuli pairs) of each age group and stock were calculated 

 for each year when 10 or more scales were available. 

 Typically, 40 to 50 scales of each age group and stock 

 were measured in a given year. To facilitate evaluation 

 of trends between odd- and even-numbered years at sea, 

 scale circuli measurements were described in terms of 

 the odd- or even-numbered year when the salmon entered 



the ocean. Thus, a salmon smolt entering the Bering Sea 

 during an even-numbered year interacted with abundant 

 odd-year Asian pink salmon during its second growing 

 season (SW2) and less abundant even-year pink salmon 

 during its third year, if it remained at sea. The number 

 of circuli pairs considered in our analysis differed by 

 growth zone, ranging from 22 circuli (SW1) to 20 cir- 

 culi (SW2) to 15 circuli (SW3) in order to represent the 

 majority of salmon. Analyses of seasonal scale growth 

 trends were based on the mean of annual mean scale 

 circuli increments, percentage change in scale circuli 

 increments during odd- versus even-numbered years, and 

 percentage change in odd- and even-year growth during 

 periods before and after the 1977 ocean regime shift. A 

 two-sample t-test was used to test for differences between 

 odd- and even-numbered year scale growth at each cir- 

 culi pair. Correlation was used to determine whether an 

 individual's growth during the second growing season 

 was related to previous growth at sea. 



Results 



First year (SW1) growth of ocean age-3 sockeye salmon 



Kvichak and Egegik river sockeye salmon scale growth 

 (distance between adjacent circuli) increased rapidly 



