CRONE and BOND: LIFE HISTORY OF COHO SALMON 



Most coho salmon fry (age 0) collected in June 

 were under 40 mm in fork length and had not 

 formed scales. Gribanov (1948) found that the 

 scale covering usually appeared on young coho 

 salmon from Kamchatka at 40 mm long. 



Growth and Age Characteristics 



Growth of juvenile coho salmon in Sashin Creek 

 was determined from fork lengths (measured to 

 the nearest millimeter) of samples of fry and 

 fingerlings. Fry were collected periodically during 

 summer 1964, and fry and fingerlings were cap- 

 tured during each of several population estimates 

 of juveniles in Sashin Creek during 1965-67. An 

 additional 50 fry from each of the three study 

 areas of Sashin Creek were measured in mid-July 

 1966 and mid-August 1967. Samples of fingerlings 



SEPTEMBER 



Figure 6.-Mean and range of fork lengths of fry (age 0) and 

 fingerling (ages I and II) coho salmon, Sashin Creek, 1964-68. 

 Lengths were measured from live fish. 



from the three study areas were measured in early 

 July, early August, and mid-September 1968. 



There was no consistent difference in the mean 

 fork lengths of corresponding age groups of 

 juvenile coho salmon captured in the upper, mid- 

 dle, or lower areas in any sampling period (Table 

 14). Juveniles from Funny Creek were usually 

 slightly smaller than those from Sashin Creek 

 during a corresponding period. 



The length data for juvenile coho salmon sam- 

 pled in Sashin Creek for 1964-68 have been com- 

 bined by month for fry and fingerlings (Figure 6). 

 The difference between the fork length of fry and 

 fingerlings was pronounced in early summer, but 

 by July the lengths of fast-growing fry and 

 slow-growing fingerlings overlapped (Figure 6). 

 Occasionally it was difficult to assign the proper 

 age-group to juveniles in the overlapping sizes, 

 although they could usually be separated by the 

 brightly colored and proportionally longer fins and 

 smaller eyes of the fry. 



The average fork length of coho salmon fry in 

 Sashin Creek in October is about 60 mm. The 

 average length of those that do not become smolts 

 the following spring but remain in the stream a 

 second year is usually 65-75 mm by July. In the 

 1968 migration, age I smolts averaged 83 mm, age 

 II smolts 105 mm, and age III smolts 104 mm 

 (Figure 7). In comparison, in 1968 coho salmon 

 from Hood Bay Creek in southeastern Alaska 

 averaged 83 mm fork length as age I smolts and 96 

 mm as age II smolts; in 1969 age I smolts averaged 

 79 mm and age II smolts 91 mm (Armstrong 1970). 

 For the years 1956, 1965, and 1968, coho salmon 

 smolts migrating from Karluk Lake, Kodiak Is- 

 land, Alaska, averaged HI mm as age I smolts, 139 



60 



70 



.X. 



80 



_l_ 



90 



_i_ 



-L 



100 



_L. 



-L. 



FORK LENCTH (mm ) 



110 



120 



.i- 



mo 



1 



Figure 7.- Length frequencies of ages 

 I, II, and III coho salmon smolts, Sashin 

 Creek, 1968. Total sample was 256 fish, 

 of which 37% were age 1, 56% age II, and 

 4% age III. Ages were determined by 

 analysis of scale samples, and lengths 

 were measured on live fish. 



911 



