Table 12. --Time difference (In days) between average weekly catches of 10,000 and 20,000 fish In 

 traps in outer Icy Strait and four inner areas and miles traveled per day (M/D) calculated from 

 the time difference. 



Miles per day not computed for outer Icy Strait-lower Chatham Strait route. 

 Twenty thousand fish per week not reached in outer Icy Strait. 



Ten thousand fish per week not reached. 



in 1942. In 1941 the rate of movement decreased from 

 July to August for releases in upper Chatham Strait 

 and increased from July to August for releases in mid- 

 dle Chatham Strait. In other years rates for August 

 releases in middle Chatham Strait remained high. In 

 1941, the year with the best distribution of tagging ex- 

 periments, the rate of movement of the leading edge 

 was greatest for releases in Icy Strait, intermediate for 

 releases in upper and lower Chatham Strait, and least 

 for releases in middle Chatham Strait. 



The rate of travel of the median tag recoveries 

 varied from 0.52 to 15.35 miles per day; the overall 

 average was about 8 miles per day. Differences 

 between the rates of movements of leading edges and 

 of medians varied from 0.39 to 30.93 miles per day. 

 For most experiments the difference ranged between 5 

 and 15 miles per day. As the season progressed in 

 1939, the median rates decreased for fish tagged in 

 lower Chatham Strait and the rates of movement of 

 the leading edges of the populations increased. For 

 those experiments for which both rates were 

 calculated, the rate of movement of the leading edge 

 averaged 29.06 miles per day and the rate of travel of 

 the median averaged 7.88. 



Knowledge of the rate of movement of the leading 

 edge of a population and also of rate of drift of the 

 center of density should be useful in formulating 

 fishing regulations and in allocating recovery effort in 

 future tagging experiments. The data indicate that 

 the leading edges of the tagged populations moved at 

 rates somewhat less than 25 miles per day and that 

 the centers of density drifted at an average rate of 

 about 8 miles per day but that these rates varied con- 

 siderably from year to year and from area to area. The 

 significance of these seasonal as well as the areal and 

 annual variations should be included as an objective 

 of future tagging experiments. 



MORTALITY RATES 



For a given release the decrease in number of tags 

 recovered per unit time during successive time periods 

 provides a measure of the rate at which the tagged 

 population vanishes from the fishing area. It is con- 

 venient for management purposes to work in terms of 

 survival rates. Factors contributing to the dis- 

 appearance of both tagged and untagged fish from the 

 fishing area are fishing mortality, natural mortality, 



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