FISHERY BULLETIN; VOL. 76. NO. 1 



35- 



30- 



.25- 



.20- 



.15- 



.10- 



05- 



.900 m3 



100 



200 



300 



400 



500 



m- 



FlGURE 4. — Relations between certain computed monthly 

 natural mortalities (Afj, M^) and selected values of annual pro- 

 portions of salmon maturing (m„m2, and mj) — 1961 brood of fall 

 Chinook salmon from Spring Creek hatchery. I 



SO back calculations were not possible with the 

 method of assuming a fixed value for Mj. However, 

 by assuming fixed values of m, and working from 

 the early life history of the salmon onward, it is 

 possible to calculate estimates of the various 

 parameters up to the fifth year. 



Although, as previously explained, it is not pos- 

 sible to compute M^ and F3 values (for the fifth 

 year) for the 1962 Spring Creek data, estimates of 

 the other parameters are possible. Therefore, the 

 relations between mj, m2, ma and M2, M^, for the 

 1962 brood, are shown in Figure 6; between mj, 

 m^, Wg and Fj, F^ in Figure 7; and finally, the 

 relations between m-^ and Mj are shown in Figure 

 8 for both the 1961 and 1962 broods. 



Since it is now possible to calculate estimates of 

 some of the parameters for the 1962 brood Spring 

 Creek fish, it is interesting to compare some gen- 

 eral conclusions I made (Henry 1971) with these 

 estimates. I stated that ". . . the data suggest that 

 the 1962 Spring Creek fish survived and entered 

 the ocean fishery in about the same proportions as 



S 300- 



900 1 000 



Figure 5. — Relations between computed last year of life 

 monthly natural mortality (M4) and last year of life ocean fishing 

 mortality (F3 ) for selected values of proportions of salmon matur- 

 ing the previous year (^3) — 1961 brood of fall chinook salmon 

 from Spring Creek hatchery. 



Kalama fish (Kalama 0.003, General 0.003) but in 

 much smaller proportions than the 1961 Kalama 

 brood (Kalama 0.011, Spring Creek 0.007)." In 

 other words, I indicated that the first 18 mo of 

 natural mortality after release as smolts for the 

 Spring Creek fish was higher for the 1962 brood 

 than for the 1961 brood. This tentative conclusion 

 is now supported by the data shown in Figure 8 

 where the My values for the 1961 and 1962 broods 

 of Spring Creek fish are shown. It is apparent that 

 for any given value of mi, the estimate of Mj is 

 higher for the 1962 brood and it would require a 

 considerably higher value of m^ for the 1961 

 brood, compared with 1962, to have comparable 

 estimates of M^ for the two broods. 



Another tentative conclusion made in my ear- 

 lier paper, ". . . that the ocean fishery was less 

 intense on the 1962 brood Spring Creek fish . . . ." 

 also can be examined in greater detail with these 

 new calculations. Thus, we see that when the data 

 for the two brood years are compared, for fixed 

 values of m,, m^, and m^ (Table 4), the estimated 

 fishing mortality for the 3-yr-old fish (Fj ) from the 

 1962 brood was about half that for the 1961 brood. 

 However, for the 4-yr-old fish (F2) the estimated 

 fishing mortality for the 1962 brood was about 

 twice as large as that estimated for the 1961 brood. 

 Since most of the catch was made as 3-yr-old fish 

 (Fi ) for both brood years, the overall catch ( mortal- 

 ity) was less for the 1962 brood. These relations 

 between the Fj and F^ values for the two broods 

 can be more clearly seen by comparing Figure 3 

 (the 1961 brood) with Figure 7 (the 1962 brood). 



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