CRONE and BOND: LIFE HISTORY OF COHO SALMON 



tagged and 38 untagged) was 13 days (range of 6 

 to 21 days). In 1967, 151 females (21 tagged and 130 

 untagged) remained an average of 11 days on the 

 spawning riffles (range of 3 to 24 days). Tagged 

 females had shorter mean redd lives than un- 

 tagged females- 12 versus 13 days in 1965 and 9 

 versus 11 days in 1967. The difference between 

 tagged and untagged fish may have been due to 

 difficulty in positively identifying untagged 

 females with short redd lives, thus biasing the 

 mean toward a greater value. Also, handling and 

 tagging might have resulted in a shorter mean 

 redd life for tagged females. 



Tagged male coho salmon in Sashin Creek and 

 both sexes in Funny Creek had shorter spawning 

 lives than tagged females in Sashin Creek. 

 Because males in Sashin Creek in 1965 were all 

 tagged with the same color and could not be 

 recognized individually on the spawning grounds 

 as they moved from female to female, their 

 spawning life could not be calculated. In 1967, 

 however, the males in Sashin Creek had a mean 

 spawning life of 9 days. The spawning life of coho 

 salmon (males and females combined) was from 3 

 to 7 days in Funny Creek in 1965 and 1967. Rapidly 

 rising and falling water levels, which caused some 

 spawners to leave the area at low flows, and 

 predation by brown bears, Ursus arctos, probably 

 contributed to the shorter spawning life in Funny 

 Creek. 



In Sashin Creek, stream life and spawning life 

 are not the same length because many coho salmon 

 enter the stream and mature in pools for a month 

 or more before they spawn. In Oregon, the mean 

 length of time that female coho salmon spent in a 

 tributary of Wilson River, Spring Creek, before 

 death was 11 days (Willis 1954). Adults migrating 

 into Spring Creek frequently begin spawning as 

 soon as they enter the tributary; apparently they 

 stay in the larger Wilson River until they are ripe 

 (Willis 1954). Koski (1966) reported mean stream 

 lives of 13.7 and 13.1 days for coho salmon that 

 spawned in two tributaries to Drift Creek, Oreg. 



Distribution and Density of Spawners 



The distribution and density of spawners on the 

 Sashin Creek spawning grounds were observed in 

 1963, 1964, 1965, and 1967 (Table 3). Distribution in 

 each study area is expressed as the percentage of 

 the total number of salmon observed spawning 

 and as total spawning effort (fish-days) observed 

 in each area. Density is the observed spawning 



effort divided by the square meters of spawning 

 area. 



In each of the 4 yr, the density of spawning coho 

 salmon was higher in the middle and lower study 

 areas than in the upper. In 1963, 1965, and 1967, the 

 middle area had the highest density of spawners; 

 in 1964 the lower area had the highest. 



In Funny Creek a few coho salmon were seen 

 spawning in 1965 and 1967. In those 2 yr about 4% 

 of the estimated escapement of coho salmon to 

 Sashin Creek spawned in Funny Creek. 



The distribution and escapement of pink and 

 coho salmon in Sashin Creek are shown in Table 5. 

 Pink salmon usually were distributed more evenly 

 throughout the creek than coho salmon. Merrell 

 (1962) and McNeil (1966) reported that spawning 

 pink salmon used the upper area extensively only 

 in years when spawning escapements were large; 

 when pink salmon escapements were small, 

 spawning was concentrated in the lower area. The 

 fact that relatively few coho salmon used Sashin 

 Creek may explain why such a small proportion 

 spawned in the upper area. In addition, ecological 

 features of that area such as steep gradient and 

 coarse bottom materials may limit its usefulness 

 for spawning. 



Table 5.-Distribution and escapement of spawning coho and 

 pink salmon in three study areas of Sashin Creek, 1963-67. 



'The weir count of coho salmon was 90 when the weir gates 

 were removed in md-September. 



Interspecific Competition 



Pink salmon are the most abundant fish in 

 Sashin Creek-the number of adult pink salmon 

 ranged from about 2,000 to 72,000, and their 

 progeny ranged from about 0.3 to 3.6 million for 

 the years of this study, 1963-72. 



Because pink salmon complete their spawning 



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