SYKES and BOTSFORD: CHINOOK SALMON SPAWNING ESCAPEMENT 



ture of an individual whose previous bottom capture 

 was ignored was considered to be a bottom capture, 

 as movement was probably the result of the previous 

 capture event. 



RESULTS 



Total escapement estimates for the three methods 

 and the weir count of fish moving into the spawn- 

 ing area are presented in Table 1. All three methods 

 result in escapement estimates that are close to the 

 weir count. The third method is the most efficient 



Table 1.— Estimates of total escapement and the estimates used 

 to compute them for each of the three methods. 



'Estimate of these standard errors are not available. 



in the sense that it requires the least sampling effort. 



For the third method, Jolly-Seber estimates and 

 associated estimated standard errors, computed 

 from the survey data along with the average value, 

 standard errors, and 95% confidence limits obtained 

 from simulation, are presented in Table 2. Esti- 

 mated standard errors and simulated standard 

 errors are in close agreement, except that the distri- 

 bution of estimates around the mean value is clear- 

 ly asymmetrical. Since they are based on simulation 

 of the actual process rather than approximate 

 analytical expressions, confidence limits obtained 

 from simulation are presumably more realistic than 

 those estimated by the methods of Jolly and Seber. 



The sum of the estimated escapement by time 

 i + 2 is plotted with the sum of the weir count at 

 time i in Figure 2. Since the numbers of fish which 

 migrated through the weir correlates well with the 

 estimated number of fish that died 2 wk later, most 

 salmon probably spawned and died within 2 wk of 

 having entered the stream. Since the estimate of 

 immigration during the last sampling interval seems 

 to fit the known number of fish immigrating, the 

 assumption of constant survival seems to be a good 

 one. It is clear that our criteria for stopping sam- 

 pling when most spawning activity had ceased 

 resulted in an estimate of the complete run. Sam- 

 pling for another week would have removed the 

 need to make any assumptions in estimating B 4 , 

 but since this value will always be small in relation 

 to the total escapement, the increase in accuracy 

 does not seem worth the additional effort. 



Data regarding the condition of carcasses at the 

 time of capture reflect a declining trend in catch- 



Table 2.— Estimates of escapement (E), population size (W), immigration (S), survival 

 (O), and associated standard errors obtained from a Jolly-Seber analysis of data for 

 method three. Also shown are the computed mean, standard error, and 95% con- 

 fidence intervals obtained by simulation. 



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