sured from scales from 2,054 unmarked coho salm- 

 on (Table 1). In all scale readings only scales 

 that had one or more ocean annuli were read. 

 Fewer than 0.5% of the fish were age 2.1, and the 

 scales indicated that the fish grew slowly in their 

 first year of life.' These scales were assumed to be 

 from wild fish. 



Wild and hatchery fish were assumed to have 

 similar numbers of regenerated scales, most of 

 which were regrown because of scale loss during 

 freshwater rearing. If wild fish tend to lose more 

 scales because of their more rigorous rearing envi- 

 ronment in freshwater, the numbers of wild fish 

 are slightly underestimated, since those samples 

 taken from unmarked salmon that were discarded 

 for lack of useable scales would have been biased 

 toward being wild fish. 



Once we had classified scales from unmarked 

 fish as hatchery or wild we weighted the number of 

 unmarked fish that were landed at each port dur- 

 ing 2-wk periods (sampling strata) for the season 

 by our estimated percentages of hatchery and wild 

 fish for that stratum. The estimated catch of 

 known marked fish was then added to the un- 



'Most adult coho salmon caught off Oregon are age 1.1, where 

 numbers left and right of the decimal indicate number of fresh- 

 water and marine annuli on the scales, respectively. Age 1 . 1 fish 

 are in their third year of life. 



FISHERY BULLETIN VOL 77. NO ;l 



marked hatchery fish to find the total number of 

 hatchery fish caught in that stratum (Table 5). 



Because of the small number of scales available 

 from unmarked fish for several strata, we com- 

 bined 2-wk periods for a given port where neces- 

 sary to obtain a sample of at least 50 fish. Small 

 sample sizes necessitated combining samples for 

 Brookings and Gold Beach. 



The observed percentage of hatchery coho salm- 

 on in the unmarked sample was corrected for wild 

 fish incorrectly classified as hatchery fish, and 

 hatchery fish incorrectly classified as wild fish. 

 Confidence levels were also computed. Both proce- 

 dures are described by Worlund and Fredin ( 1962 ). 



RESULTS 



The percentages of hatchery fish contributing to 

 Oregon's sport fishery were highest near the Co- 

 lumbia River and decreased steadily southward 

 (Table 6). The percentages of wild fish in the catch 

 were highest late in the season at Garibaldi, 

 Depoe Bay, Newport, and Winchester Bay and 

 near midseason at Hammond. Total estimated 

 percentages of hatchery fish landed at each port 

 from mid-June to mid-September 1977 were 85 at 

 Hammond, 83 at Garibaldi, 79 at Depoe Bay, 77 at 

 Newport, 61 at Winchester Bay, 65 at Coos Bay, 



Table 5. — Estimated number of coho salmon landed 

 Oregon sport fishery by port in 1977. Data are for 



and the catch per angler day (in parentheses) by 

 2-wk periods from 16 June to 15 September. 



Table 6. — Estimated percentages and 95% confidence intervals of hatchety-reared coho salmon in the total 

 catch landed in 1977 by the Oregon sport fishery. 



620 



