LOWER CHATHAM STRAIT 



STEPHENS PASSAGE 



-r 



I I 



89 10 123156 



WEEK FROM BEGINNING OF SEASON I I I I I I 

 28 5 12 19 26 2 9 16 21 28 28 5 12 19 26 2 9 16 21 28 



JUNE JULY AUGUST JUNE JULY AUGUST 



DATE AT END OF WEEK 



Figure 20.— Average number of pink salmon caught per trap per 

 week in each major statistical area in 1942. The approximate 

 dates on which the catch per trap per week reached 10,000 flsh 

 and 20,000 fish are shown by the vertical lines. 



rate was 25.5 miles per day between lower Chatham 

 Strait and Frederick Sound at the 10,000-fish levels in 

 1939 and 1945. Little credence should be given to 

 these high rates. 



The rates of travel shown in Tables 12 and 13 

 should not be interpreted as representing the actual 

 rate of travel of individual fish but rather the rate of 

 movement of a certain density (not the maximum 

 density) of catchable fish. 



RATE OF TRAVEL DETERMINED 

 FROM TAGGING DATA 



Computation and interpretation of the rate of travel 

 are complicated by the extensive wandering 

 movements and also by the complex mixture of racial 

 stocks represented in a single release of tagged pink 

 salmon. In this section only the movements along the 

 main routes of travel as defined in the section entitled 

 "Migration Routes as Determined from Tag 

 Recoveries" will be considered. The objective of the 

 analysis presented here is to determine how long it 

 takes the population at a particular location in the 

 fishery to reach other locations in the fishing areas. It 

 is assumed that tagged fish continued their normal 

 migration after release. 



The rate of travel of both the center of density of a 

 group of tagged fish and also of the leading edge of the 

 tagged population are of interest. On any given day 

 after release, tagged fish were recovered in traps at 

 varying distances from the tagging station. If all 

 recoveries on a given day are ordered with respect to 

 distance, the median recovery provides a first ap- 

 proximation of the location of the center of density of 

 the group, and the second farthest recovery provides a 

 measure of the location of the leading edge of the tag- 

 ged group on the day in question. 



For each group of tagged pink salmon with suf- 

 ficient numbers of recoveries, the approximate rate of 

 travel of the center of density (called the median rate) 

 was calculated from the recoveries on the first through 

 the 14th day after release. The location in miles from 

 the tagging station of the median recovery each day 

 was regressed on the number of days out. The slope of 

 this line is an estimate of miles traveled per day. 

 There were no essential differences between the es- 

 timates obtained by weighted and unweighted regres- 

 sion lines if weights proportional to the numbers of 

 recoveries taken in the trap making the median 

 recovery were employed. Results of these com- 

 putations are given in Table 14. 



In the calculation of the rate of movement of the 

 leading edge of the distribution of tagged fish from a 

 single release, recoveries within 30 miles of the tagging 

 station were ignored. Because of the possibility that 

 reports of isolated recoveries at great distances might 

 be in error or might represent abnormal fish, the sec- 

 ond farthest rather than the most distant recovery 

 was used to estimate the rate of movement of the 

 leading edge. Recoveries on the first through the 14th 

 day after release were used. Again the rate of travel in 

 miles per day was estimated by the slope of the regres- 

 sion line. Results for releases for which four or more 

 days were available for calculating these rates are 

 shown in Table 14. 



The rate of movement of the leading edge varied 

 from 9.05 to 33.37 miles per day and averaged about 

 18 miles per day. In general, rates from different ex- 

 periments within the same major area and the same 

 year agreed with one another, with the exception of 

 the experiments in upper Chatham Strait in 1942. 

 The rate of movement of the leading edge of the dis- 

 tribution of recoveries from the release made on 9 

 August from WE-32 on the eastern shore of upper 

 Chatham Strait was 9.05 miles per day while the cor- 

 responding rate for the release from WE-24 on the 

 western shore on 18 August was 20.56 miles per day. 



The highest rate of movement of the leading edge 

 observed for releases made in Icy Strait in 1942 (13.30 

 miles per day) was considerably less than the slowest 

 rate of movement observed (18.19 miles per day) for 

 releases in Icy Strait in 1941. Thus, the 1941 and 1942 

 Icy Strait experiments showed little intraseasonal 

 variation in rate of movement of the leading edge, but 

 the rates in 1941 were consistently higher than those 



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