Figure 10. — Weir site at East Fork, Olsen Creek. 



In our studies, pink salmon for tagging were 

 captured with a seine in the stream at the 3- 

 to 5-foot tide level at low tide and were sub- 

 sequently recovered dead on the spawning 

 grounds. Tagging was done at 4-day intervals 

 with Petersen disk tags. Different color com- 

 binations were used for each sample. The 

 number tagged each time varied from 11 to 

 191, depending on availability of the fish. The 

 first sample was tagged on July 4 and the 

 last on September 11. The intertidal area was 

 patrolled daily for tagged and untagged car- 

 casses. To prevent duplication of counts each 

 dead fish was cut in half. Tags were removed 

 from carcasses only during these daily sur- 

 veys. 



Tag ratios of fresh-water carcasses ob- 

 tained on weekly stream surveys were used 

 rather than ratios from the daily removal of 

 carcasses off the weirs. Pink salmon spawned 

 more than a mile above each weir site, and 

 hence carcasses that drifted against the weirs 



were probably not representative of the total 

 fresh-water population. 



Twelve pink salmon streams in Port Gravina 

 in addition to Olsen Creek were surveyed 

 once a week to check for emigrant tags (fig. 11). 

 A summary of the recovery data is given in 

 table 4. Tagged fish taken in the commercial 

 fishery and those found in the Port Gravina 

 streams were considered emigrants and were 

 subtracted from the total tagged to correct 

 population estimates. 



The following formula was used to estimate 

 the total spawning population from the ratio 

 of tagged to untagged carcasses: 



N 



nt 



s 



N = total number in population 



n = number of carcasses sampled 



t = number of fish tagged 



s = number of tagged carcasses in sample 



12 



