FISHERY BULLETIN: VOL. 70. NO. 2 



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234523452345 

 AGE (YEARS) 



Figure 8. — Calculated total ocean recoveries (in per- 

 cent) , by age, of special marked Spring Creek, Kalama, 

 and general marked Columbia River hatchery fall chi- 

 nook salmon, 1961-64 brood years. 



GRAPHIC POPULATION MODEL 



FOR COLUMBIA RIVER 



FALL CHINOOK 



To more clearly understand all the forces af- 

 fecting a stock of fish, it often is convenient to 

 depict the population in a simulated flow chart 

 or block diagram. Shapiro and Andreev (1969) 

 show such a diagram for chum salmon (0. keta) . 

 With some modification, their diagram also 

 would be applicable to Columbia River fall Chi- 

 nook salmon as shown in Figure 11. This dia- 

 gram is based on the following stock character- 

 istics. There are five age groups, four of which 

 are capable of entering the spawning groups, 

 and each brood year diminishes in numbers as 



^ 10 



MALES 



1961 BROOD 



FEMALES 



5 2 3 



AGE (YEARS) 



Figure 9. — Average weight (kilograms) by age and sex, 

 of 1961-64 brood Spring Creek and Kalama special 

 marked hatchery fall chinook salmon caught in the Co- 

 lumbia River gillnet fishery. Shaded columns represent 

 data for Kalama salmon — clear columns, Spring Creek. 

 Numbers indicate sample size. 



a result of natural mortality (M,) and ocean 

 fishing mortality {Fi). Ocean fishing mortality 

 occurs only on the 2 + , 3 + , and 4 + -year-old- 

 fish. Growth and fecundity diflFer for each age 

 group, and entry into the spawning part of the 

 population is aflfected by a probability (Pi) . The 

 spawning group is diminished by a river fishing 

 mortality (RFi) . After river fishing mortality, 

 some portion of the spawning fish (k,) are re- 

 moved for artificial propagation. Survivals to 

 recruitment resulting from artificial and natural 

 reproduction are taken to be difl"erent. The 

 number of recruits (R) is dependent on a sur- 

 vival relationship for the eflfective fecundity, i.e., 

 R/E. 



EFFECT OF TROLL FISHING ON YIELD 



A complete analysis of the Columbia River 

 fall Chinook population, as depicted in Figure 11, 

 is beyond the scope of this paper. However, I 



438 



