Figure 9.— Weir site at West Fork, Olsen Creek. 



were completed in the second week of Septem- 

 ber. High water forced temporary removal of 

 both weirs on several occasions. One such 

 occasion, August 22-24, coincided with a 

 known migration of salmon (fig. 7). Upstream 

 migrants were first counted through both 

 weirs on June 26. The total numbers counted 

 were: East Fork weir, 18,870 pink and 256 

 chum salmon; West Fork weir, 16,888 pink 

 and 290 chum salmon. As in 1960, a few coho 

 salmon were counted through the weirs. 



Magnitude of Intertidal Migration 



Because of periodic inundation of the area 

 by tidewater, weirs could not be used to 

 measure numbers of intertidal spawners. 

 Moreover, because two techniques for popu- 

 lation censusing would have to be used as 

 long as weirs were in operation and also 

 because of their high operational costs and 

 possible detrimental effects on fish migration. 



a single method that could be used to esti- 

 mate numbers of both intertidal and fresh- 

 water spawners was needed. Therefore, in 

 1961 a system of sample tag ratios was used 

 in addition to weir counts to estimate the 

 spawning populations. 



The method of estimating animal populations 

 from the ratio of marked to \inmarked mem- 

 bers has been employedbynnany investigators. 

 Howard (1948) and Schaefer (1951) thoroughly 

 discuss the theory and procedures involved in 

 an enunneration problem of this type. Both of 

 these investigators demonstrated that a high 

 degree of precision could be obtained if live 

 fish were tagged close to the site of recovery. 

 One of the basic assumptions in an emumera- 

 tion problem of this type is that tagged fish 

 are distributed randomly in the population. 

 According to Howard, this need not be so if 

 the dead fish are sampled thoroughly enough 

 to obtain an accurate account of the overall 

 tag ratio. 



11 



