12 3 4 5 6 7 



LENGTH OF WEEKLY OPEN PERIOD (DAYS) 



Figure 22. — Exploitation isopleth for the total pink salmon run 

 entering the northern part of southeastern Alaska, 1939. Tri- 

 angular entry pattern and periodic fishery assumed; n = rate of 

 exploitation or fraction of run taken In catch. 



1 2 3 4 5 6 7 



LENGTH OF WEEKLY OPEN PERIOD (DAYS) 



Figure 24. — Exploitation isopleth for the total pink salmon run 

 entering the northern part of southeastern Alaska, 1942. Tri- 

 angular entry pattern and periodic fishery assumed; /u = rate of 

 exploitation or fraction of run taken in catch. 



1.19 



12 3 4 5 6 7 



LENGTH OF WEEKLY OPEN PERIOD (DAYS) 



Figure 23. — Exploitation isopleth for the total pink salmon run 

 entering the northern part of southeastern Alaska, 1941. Tri- 

 angular entry pattern and periodic fishery assumed; /j = rate of 

 exploitation or fraction of run taken in catch. 



The computations of exploitation rates of about 

 50% are completely dependent on the assumption 

 that incomplete reporting or immediate tag loss and 

 mortality or both caused about half of the tagged fish 

 to become "unavailable." If, however, the overall 

 average F value of 0.514 computed directly from the 

 1938-42 and 1945 tagging data is correct, the average 

 rate of exploitation for these years drops to 0.32. For 

 the reasons mentioned earlier, the authors feel that 

 the higher rate of exploitation is more nearly the cor- 

 rect value. Of course, the rate of exploitation on any 

 particular stock may have been quite different than 

 the overall average. In the exploitation isopleth com- 

 putations, the fractions removed by fishing from 

 stocks in the first part of the entry triangle were con- 

 siderably higher than from stocks in the second part. 

 Approximately 7% of the fish in the entry patterns 

 used to calculate Figures 21-24 entered after the 

 season had been closed and for that reason suffered no 

 fishing mortality. 



RECOMMENDATIONS FOR THE 



DESIGN OF FUTURE TAGGING 



EXPERIMENTS 



Tagging experiments are a basic method of 

 generating knowledge needed to determine optimum 

 policies for managing the pink salmon resource of 

 southeastern Alaska. A primary objective of manage- 

 ment is to regulate the commercial fishery to allow the 

 quantity and quality of escapement that will max- 



36 



