WAHLE. VREELAND. and LANDER: BIOECONOMIC CONTRIBUTION 



marked 1964-brood coho from Big Creek 

 Hatchery (Figure 1) contained only 3% age 2 

 coho. This available evidence indicates that 

 Assumption 3 (all coho in ocean fisheries are 

 in their third and final year of life) is reasonably 

 satisfied. 



A comparison was made of marked and un- 

 marked returns (Appendix Tables 2a and 2b) 

 to hatcheries in the same river section where 

 released to test Assumption 4 (marked and un- 

 marked fish have the same maturity schedules). 

 Appendix Table 3 shows the percent of 2-yr-old 

 coho salmon in the marked and unmarked re- 

 turns by river section and brood year. Un- 

 marked strays to other river sections could not 

 be identified by origin, so it was necessary to 

 assume that straying was the same for marked 

 and unmarked returns. The D-Ad comparison 

 (Leavenworth Hatchery) was not made because 

 passage difficulties at John Day Dam in 1969 

 led to no returns of adults to Leavenworth 

 Hatchery. The nearly equal percentages of 2-yr- 

 olds in the marked and unmarked returns by 

 river section and brood year indicate that 

 Assumption 4 is satisfied. 



Marked Proportions at Release and Capture 

 (Assumptions 5 and 6) 



Inspection of mark proportion data in 

 Appendix Tables la and lb shows the variabil- 

 ity between hatcheries to be small enough to 

 consider Assumption 5 (same proportion of 

 releases marked at each hatchery in a given 

 river section) reasonably well satisfied. At pre- 

 sent, no data exist to support Assumption 6 

 (equal vulnerability to capture for marked and 

 unmarked fish from a given river section), but 

 it is intuitively satisfied. Fish marked by clip- 

 ping maxillary bones and/or the adipose fin 

 would not seem to be more vulnerable to cap- 

 ture by fishing gear than unmarked fish. 



Relative Survival of Marked Fish 



Worlund, Wahle, and Zimmer (1969) found 

 that marked fall chinook salmon did not survive 

 as well as unmarked chinook. We also found 

 this for coho salmon. To determine the un- 

 marked catch of hatchery fish, we must account 

 'for the lower survival of marked fish. The rela- 

 tive survival values for both broods and each 

 mark type of coho were calculated as explained 



under "Estimating Procedures." Oxytetracy- 

 cline (TM-50) was used to mark both broods of 

 coho at Eagle Creek and Big Creek hatcheries 

 to obtain survival values for Ad and Ad-RM 

 marked coho, respectively. Returns to three 

 hatcheries. Little White Salmon, Cascade, and 

 Klaskanine, on streams having no wild spawn- 

 ing populations were used to obtain relative 

 survival values for both broods of Ad-LM and 

 Ad-RM marked coho. Finally, the marked to 

 unmarked ratios at release and return for each 

 river section were combined to obtain survival 

 values for each mark type in both brood years. 



The relative survival estimates are in Appen- 

 dix Table 6. Marked coho salmon that strayed 

 to sections other than where they were released 

 (Appendix Tables 2a and 2b) were excluded from 

 the marked returns in computing relative sur- 

 vival (see "Bias Associated with Marks"). There- 

 fore, the median value for each of the mark 

 types for both brood years combined was arbi- 

 trarily used to obtain reasonable approxima- 

 tions for relative survival. The same value was 

 used for Ad-LM and Ad-RM marked coho. The 

 median va'ues for the Ad-only and Ad-maxillary 

 marked coho were 89 and 72%, respectively. 



The relative survival of D-Ad marked 1965- 

 brood coho salmon from Leavenworth National 

 Fish Hatchery (Uppermost section) was obtained 

 from TM-50 marking data. In 1967 and 1968, 

 a total of 174 D-Ad-TM-50 marked and 1,305 

 TM-50-only marked 1965-brood coho returned 

 to Leavenworth. From these values, the marked 

 to unmarked relative survival of 1965-bi-ood 

 D-Ad marked coho was calculated to be 53% . 

 Few hatchery returns of 1966-brood Leaven- 

 worth coho were obtained because of passage 

 difficulties at John Day Dam due to construc- 

 tion of fish ladders and mortalities caused by 

 trapping at Priest Rapids Dam. Hence, a rela- 

 tive survival estimate for the D-Ad-RM and D- 

 Ad-LM marks could not be calculated. The value 

 for the D-Ad marked 1965-brood coho (53%) 

 was therefore used to estimate the 1966-brood 

 Leavenworth catch of unmarked fish. 



Final Estimates Corrected for Marking 



One marked fish represented about 9 un- 

 marked ones at release but about 11-20 (depend- 

 ing on the mark) at return (Tables 2, 6a, and 6b). 

 The foregoing estimates of relative survival for 

 unmarked fish were applied (see "Estimating 



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