CRONE and BOND: LIFE HISTORY OF COHO SALMON 



the estuary from Sashin Creek each year, 1956-68; 

 2) the migration of fry to the estuary and their 

 ability to survive in salt water; 3) age and growth 

 of juveniles in the stream; 4) survival through 

 various life stages (potential egg deposition to fry 

 emergence and as juveniles in the stream); and 5) 

 mortality in fresh water. 



Juveniles Entering the Estuary 



In Sashin Creek the emergence of coho salmon 

 fry from the gravel usually begins in April and is 

 completed by the end of May, although in 

 especially cold years emergence may not start 

 until June or July. Juvenile coho salmon usually 

 live in Sashin Creek for 1 to 3 yr before migrating 

 to salt water as smolts, but some migrate to the 

 estuary during their first spring or summer as fry. 

 The migration of fry to salt water soon after they 

 emerge has been reported in several other streams 

 (Chamberlain 1907; Gilbert 1913; Pritchard 1940; 

 Wickett 1951; Foerster 1955), but none of these 

 authors reported a substantial return of adult 

 salmon from such early-migrating fry. All of the 

 scale samples from adult coho salmon at Sashin 

 Creek indicated that the fish had spent at least 1 yr 

 in fresh water. The absence of adults originating 

 from early-migrating fry suggests very poor 

 survival of fry entering the estuary at a small size 

 (usually <35 mm from Sashin Creek), which could 

 be the result of heavy predation or some failure to 

 adapt physiologically to the marine environment. 

 We have assumed that we can identify adults 

 derived from early-migrating fry on the basis of 

 the pattern of circuli on their scales. However, if 



fry surviving in the estuary developed scale pat- 

 terns indistinguishable from those of fry spending 

 a year or more in fresh water, our assumption that 

 age emigrants did not contribute to the adult run 

 could be incorrect. 



Numbers of Fry and Smolts 



Counts and estimates of the numbers of juvenile 

 coho salmon migrating from Sashin Creek ranged 

 from 218 to 44,023 fry and 928 to 2,865 smolts 

 between 1956 and 1968 (Table 10). In 1964, 44,023 

 fry left the stream between 19 April and 28 

 August, and most migrated in a 2-wk period in 

 mid-June-the greatest migration was 3,528 fry on 

 15 June. The smolt migration in Sashin Creek 

 varied about threefold from 1956 through 1968 

 (excluding 1965-66-Table 10). The relatively low 

 counts of smolts in 1964 probably resulted from a 

 change in the trapping procedures at the weir. 

 Before 1964, all fish migrating from Sashin Creek 

 were captured. The procedures used in 1964 were 

 designed to capture a portion of the emigrating 

 fry and did not retain smolts well. Because of high 

 water and ice damage to the weir, complete counts 

 of emigrating fry and smolts were not made for 

 1965-67. In 1965 and 1967, estimates of fry and 

 smolts were based on catches in fyke nets that 

 sampled the migrants at the weir site. No es- 

 timates were obtained in 1966. 



A comparison of the time of smolt migration 

 from Sashin Creek with the time of migration 

 from streams and lakes along the eastern Pacific 

 coast from south-central Alaska to central coastal 

 California indicates that there is a tendency 



Table lO.-Numbers and times of migration of coho salmon frj' and smolts past the Sashin Creek weir and yield of smolts, 



1956-68.' 



'The year 1966 is not included because the weir was damaged and substitute sampling was not conducted. 



^Daily counts for 1956-64, available from Olson and McNeil (1967). 



^Counting procedure changed from total to partial counts; holding facilities were inadequate for retaining all smolts cap- 

 tured. J I. t H 



"Weir not functional; fyke net(s) fished to sample a portion of the spring emigration. Numbers of fry and smolts presenteo 

 are estimates made from fyke net catches. 



907 



