CRONE and BOND: LIFE HISTORY OF COHO SALMON 



1,500 - 



l.fOO 



1,300 



1,200 



1,100 



1,000 



100 - 



POTENTIAL ECC DEPOSITION 



T — I—I — I — I — I — I — I — I — I 1 — I — I — r 



ASONDJFMAMJJAS 



PREEMERCED ALEVINS 



FRY 



YEARLINGS 



1961 BROOD ^o. 



1 — I — I — I — I — I — I — I — r"T — 



~r I I I I I I I I I I I I I I I I I I r 

 OCT. NDJ FMAMJJA SONDJ FMAMJ JAS 



MONTH 



Figure lO.-Estimated populations of juvenile coho salmon of 

 three brood years, Sashin Creek, from potential egg deposition to 

 late summer of second year. (Arithmetic plot.) 



for each of the three brood years, instantaneous 

 mortality coefficients (Ricker 1958) were computed 

 to compare mortality for the periods and years 

 (Table 20). The equation for determining the 

 instantaneous mortality coefficient, 



M,, = 



-In (^„ ) 



follows the notation of McNeil (1966), where t, the 

 interval of time, is in months (one unit is equal to 1 

 mo); the symbol In represents the natural loga- 

 rithm; j is the brood year; and n is the study period. 



2,000 - 



1,000 

 800 



600 

 500 



too 



, 300 



=> 



= 200 



I- 

 < 



a. 

 O 



0. 



< 



I- 



100 

 80 



60 

 50 

 W 

 30 



20 



, POTENTIAL ECC DEPOSITION 



1965 

 '\ ^'^°°°\ PREEMERCED ALEVINS 



1961 \ 



2 - 



YEARLINCS 



-I I I L 



SEPT 



ONDJ FMAMJ J ASONDJ FMAMJ J AS 

 MONTH 



Figure 11. -Estimated populations of juvenile coho salmon of 

 three brood years, Sashin Creek, from potential egg deposition to 

 late summer of second year. (Semilogarithmic plot to indicate 

 mortality rate.) 



Table 20.-Instantaneous mortality coefficients during five 

 periods^ in the freshwater life of three brood years of coho 

 salmon in Sashin Creek. 



Brood 

 year 



Instantaneous mortality coefficient in period 



1 



1963 

 1964 

 1965 



0.37 

 0.27 

 0.25 



0,38 

 0.30 

 0.32 



1.23 

 1.88 

 0.87 



0.12 0.25 



0.05 0.55 



0.14 — 



'See text for explanation of time covered in each period. 



S,, is the survival within the nth period and is 

 calculated from the formula, 



Si-52* . . -'^ = S, 



S 



or 



Sn = 



Si'S2' . . .'S(n - U 



where S is survival through n study periods ex- 

 pressed as a percentage of potential egg deposi- 

 tion (Table 19). 



Instantaneous mortality was higher through 



919 



