FISHERY BULLETIN: VOL. 72. NO. 1 



of marked fish are summarized in Tables 6a and 

 6b by region of recovery, fishery, brood year, 

 and mark. The marks from the Uppermost 

 River section (Appendix Table 5a) are com- 

 bined in Table 6b. The total estimated catch of 

 marked fish from both broods was 179,096. A 

 total of 33,910 marked coho salmon returned 

 to the study hatcheries during the 3 yr of sam- 

 pling. 



Bias Associated with Marks 



To proceed from the estimated catch of 

 marked fish to the total catch of hatchery fish, 

 we must be sure that our assumptions (see 

 "EXPERIMENTAL DESIGN") are satisfied. 

 Some elements (e.g., loss of maxillary bones 

 due to hooking, loss of fins due to injury) cannot 

 be evaluated; others (e.g., mark regeneration, 

 natural marks, relative survival of marked fish) 

 can be appraised more adequately. 



Mark Regeneration (Assumption 1) and Quality 

 of Marking 



We have three indications of the permanence 

 of fin and maxillary marks. First, about 550 

 marked coho salmon of the 1966 brood were 

 held for 2 yr at the Klickitat station for fin 

 regeneration studies. We examined these fish 

 periodically throughout the retention period and 

 observed no adipose regeneration. However, we 

 noted a 4.5% complete maxillary regenei'ation. 

 Second, the appearance of D-Ad marks in the 

 releases of the 1966-brood coho from Leaven- 

 worth National Fish Hatchery indicated maxil- 

 lary regeneration; the maxillary bone was 

 clipped from all 1966-brood Leavenworth coho 

 marked, vet 5% of the marked coho released had 



only a D-Ad finclip. During marking of the 

 Leavenworth coho, 100 marked fish per marker 

 were examined at irregular periods each day to 

 check mark quality. No undipped maxillaries 

 were observed. This caused us to disregard fail- 

 ure to clip maxillaries as a reason for the 

 appearance of the D-Ad marks. Therefore, we 

 believe the D-Ad marks occurred mainly be- 

 cause of maxillary regeneration. Finally, the 

 percentage of D-Ad-only marks in the 1969 

 lower Columbia River commercial catch of 

 1966-brood Leavenworth Hatchery marked 

 fish was 6.5% . This is very close to the percen- 

 tage of D-Ad-only marks in the release. Because 

 of these indications, we are assuming that mark 

 regeneration caused little bias in this study. 



Natural Marks (Assumption 2) 



The catch of hatchery fish would be over- 

 estimated if marks identical to those used in this 

 study occurred naturally. To ensure that no 

 natural marks existed in hatchery stocks, coho 

 salmon returns at most Columbia River and 

 some Puget Sound hatcheries were examined 

 for 2 yr before the study. Approximately 35,000 

 returns were examined and no marks identical 

 to those we planned to use were observed. Also, 

 fish markers at all participating hatcheries ex- 

 amined approximately 3.5 million coho for 

 naturally missing fins and maxillary bones. Only 

 26 were found to have naturally missing adipose 

 fins and none had naturally missing dorsal fins 

 or maxillary bones. 



The possible occurrence of natural marks 

 from other river systems is more difficult to 

 evaluate. Comparisons of the percentage of 

 each mark caught in the lower Columbia River 



Table 4. — Estimated catches of coho sahnon and number ot fish 

 examined for marks, 1967-69.1 



1/ From all areas sampled (Table 3)» 



148 



