FISHERY BULLETIN: VOL. 74, NO. 4 



Table 3.-Distribution and density of spawning coho salmon in three areas of Sashin Creeit in 1963-65 and 1967. 



Distribution 



% of total salmon observed 



Spawning effort (fish-days) 



Density of spawning 

 (fish-days per square meter) 



'W. J. McNeil, unpublished notes on 1963 coho studies. On file at Auke Bay Fisheries Laboratory, Auke Bay, 

 AK 99821. 



Table 4.— Estimates of coho salmon escapements to Sashin 

 Creek, 1963-65 and 1967, based on three methods of estimation. 



'Based on observations in 1965 and 1967 that spawning ground 

 counts and redd life estimates were about one-half the estimates 

 based on marked-to-unmarked ratios of spawners. 



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SPAWNERS 



STREAM DISCHARGE 



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Figure 4.— Spawning ground counts of coho salmon in relation to 

 stream discharge, Sashin Creek, 1967. 



We believe that the best estimates of abundance 

 of spawners are those based on tagging and 

 observing marked-to-unmarked ratios, but such 

 estimates are not available for 1963 and 1964. 

 Therefore, because the estimates derived from 

 spawning effort and redd life in 1965 and 1967 



902 



were approximately one-half the estimate from 

 marked-to-unmarked ratios, the assumption was 

 made that in 1963 and 1964, only 50% of the 

 spawners in Sashin Creek were estimated from 

 spawning effort and redd life. Our best estimates 

 of the numbers of coho salmon spawners are 916 in 

 1963. 162 in 1964, 221 in 1965, and 370 in 1967 (Table 

 4). These values are used in the remainder of this 

 report. 



The population estimates of coho salmon 

 spawners in Sashin Creek do not include jack coho 

 salmon (precocious males of various freshwater 

 ages but only one summer of marine life) because 

 none were tagged; without tags, their presence on 

 the spawning riffles would have been difficult to 

 detect. Apparently, only a few jack coho salmon 

 enter Sashin Creek; none were seen during the 

 1965 surveys of the spawning grounds, and only 

 five were seen during underwater observations in 

 1967. 



Redd Life 



The estimates of mean redd life used in our 

 calculations of escapement size were based on 

 experiments with marked females in Sashin Creek 

 in 1965 and 1967. Many untagged females that 

 could be identified from natural markings, such as 

 wounds, fungused areas, color, and size, were used 

 along with the tagged females. A female had to be 

 observed at the same location on two consecutive 

 days before she was considered to have selected a 

 permanent spawning site. One day was added to 

 the observed redd life for females, on the assump- 

 tion that they began to construct a redd an aver- 

 age of one-half day before first being observed and 

 remained on the redd for an average of one-half 

 day after last being observed. 



The mean redd life of female coho salmon varied 

 between tagged and untagged (identified from 

 natural markings) females in both 1965 and 1967. 

 In 1965 the mean redd life for 56 females (18 



