FISHERY BULLETIN VOL. 76, NO. 1 



Grays River, Cascade, Klickitat, Bonneville, and 

 Little White) had too few special mark returns to 

 obtain reliable estimates of marked to unmarked 

 ratios at return. Thus returns to only three hatch- 

 eries (Spring Creek, Kalama, and Big Creek), hav- 

 ing sufficient special mark returns, were used to 

 calculate average special mark relative survivals 

 for each brood. However, if special marked fish 

 from the other seven hatcheries had lower relative 

 survivals than the average, the contributions of 

 these hatcheries would be underestimated using 

 this method. 



Relative survivals of special marks to common 

 marks were first calculated using the formula: 



Special mark return/Common mark return 

 Special mark release/Common mark release " 



The relative survivals are: 



Table 4. — Mark percentages at release for common and special 

 marked fall chinook salmon by brood year and hatchery. 



'Special marks not included. 



^Common marks included with unmarked releases. 



^Includes Big White Salmon pond releases. 



The potential contributions of the hatchery fall 

 chinook salmon were calculated by dividing the 

 estimated catch of marks by the marked fish rela- 

 tive survival times the mark proportion at release. 

 The formula for calculating the potential con- 

 tributions of Spring Creek, Kalama River, and 

 other special mark hatcheries is: 



Estimated catch of spec, marks 



(Spec, mark relative survival)! Spec, mark proper, at rel.) • 



From these values we concluded that special 

 marked fish survived between 50 and 80% as well 

 as common marked fish. Multiplying the common 

 mark relative survivals by 50 and 80% for each 

 brood year yielded the following average special 

 mark relative survivals: 



Brood 

 1961 

 1962 

 1963 

 1964 



Survival 

 0.395 

 0.310 

 0.242 

 0.291 



The next step was to determine the mark pro- 

 portions at release for common and special marks 

 for each brood year. Special marks were excluded 

 from the calculation of the common mark propor- 

 tions. This was done for two reasons: special 

 marked fish had a lower relative survival than the 

 common or unmarked fish, and the special marks 

 could be identified in the fisheries and related back 

 to specific hatcheries. The common marked fish 

 had to be treated as unmarked fish in calculating 

 the special mark proportions at release because 

 common mark catches could not be related to spe- 

 cific hatcheries. These mark porportions at release 

 are presented in Table 4. 



The potential contribution of all study facilities 

 was calculated with the formula: 



Estimated catch of common marks 



(Common mark relative survival )( Common mark proper, at rel. ) 



+ Potential catch of spec, marks. 



The potential catch of special marks is an esti- 

 mate of the special marks that would have been 

 caught if marking had not caused differential 

 mortality. The formula used to calculate this po- 

 tential catch is: 



Estimated catch of special marks 

 Special mark relative survival 



Value of Hatchery Contribution 



With estimates of the potential contribution of 

 Columbia River hatchery fall chinook salmon, the 

 potential value of the catches could be calculated 

 from average weight and unit price data. The av- 

 erage weights for the commercially caught fish 

 were obtained from common marked fish. Total 

 weights of hatchery fish caught in the commercial 

 fisheries are underestimated with this method be- 



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