HENfRY: NATURAL AND FISHING MORTAUTIES OF CfflNOOK SALMON 



40n .40-1 



.SO- 



SO- 



20- 



,10- 



.007 



.008 

 .009 

 .010 



100 



200 



-r 



300 



600N^°° 



400 



500 



600 



Figure 6. — Relations between certain computed monthly 

 natural mortalities (Afj, A/3) and selected values of annual pro- 

 portions of salmon maturing (m 1 , m2, and m^ ) — 1 962 brood of fall 

 Chinook salmon from Spring Creek hatchery. 



.20- 



.10- 



1962 



.002 



.004 



.006 



.008 



.010 



m, 



Figure 8. — Relations between computed monthly natural mor- 

 tality (Ml) during the first 18 mo after release as smolts and 

 selected values of proportions of salmon maturing after 18 mo 

 (mj) — 1961 and 1962 broods of fall chinook salmon from Spring 

 Creek hatchery. 



Table 4. — Comparison of estimates of fishing mortality (F) for 

 the 1961 and 1962 broods of marked fall chinook salmon from 

 Spring Creek hatchery for fixed values of proportion of salmon 

 maturing annually im). 



1961 brood 1962 brood 



1961 brood 1962 brood 





0.001 

 .300 

 .051 



0001 

 ,300 

 .026 



600 

 .037 



0600 

 .078 



.120 



roos 



^003 



. — 001 



Thus, for a given value of mj, the generally higher 

 Fj values compared with F^ for the 1961 brood is 

 quite different from the generally higher F<i val- 

 ues compared with F-^ for the 1962 brood data 

 shown in Figure 7. 



A general comparison between the calculated 

 Mg and Mg values can be obtained by comparing 

 Figure 4 with Figure 6. There is considerable simi- 

 larity between the pattern of mortality estimates 

 for these two broods. In both cases, as m^ in- 

 creases, Mg increases and M^ decreases. However, 

 for a given 7772 and m^, the estimates of M3 are 

 slightly higher for the 1962 brood, whereas for a 

 given 1712 and mj, the estimates of M^ are very 

 similar for the two broods. 



ACKNOWLEDGMENTS 



Figure 7. — Relations between certain computed monthly ocean 

 fishing mortalities (Fj, F^) and selected values of proportions of 

 salmon maturing annually (mj, m.^, and m^ — 1962 brood of fall 

 chinook salmon from Spring Creek hatchery. 



I thank S. Hoag of the International Pacific 

 Halibut Commission as well as R. A. Fredin and G. 

 Hirschhorn for their many helpful suggestions in 

 reviewing my manuscript. 



53 



