1092 tJ. S. BUREAU OF FISHERIES 



experiment avus begun, which involved the marking of 50,000 sea- 

 ward migrants during June, 1929. The seaward migration this 

 season appeared to be extraordinarily heavy. It was derived chiefly 

 from the unusually large spawning escapement of 1926, when a total 

 of approximately two and a half million adults passed through the 

 counting weir. The returns from this experiment will therefore 

 be awaited with great interest. The run of adult red salmon at 

 Karluk in 1929 was exceedingly poor — a condition that had been an- 

 ticipated and discussed in a report published in 19<27.^ As a result 

 of this poor run, the commercial fishing operations at Karluk were 

 so restricted during the past season that it was impossible to secure 

 I'eliable data as to the number of marked fish in the run from pre- 

 vious marking experiments, nor was it possible to satisfactorily 

 sample the run for a study of the age groups and other related 

 problems. 



A second report dealing with the red-salmon runs of the Karluk 

 River has been nearly completed. It includes the presentation of 

 all data accumulated since 1926, especially the results of the mark- 

 ings experiment begun in 1926. 



Of the 46,700 fish marked in 1926, between 25 and 30 per cent 

 returned as mature fish. This is a much higher return than was ex- 

 pected a priori and on the basis of the returns from similar mark- 

 ing experiments conducted at the hatcheries on the Columbia River. 



In addition to estimating the survival, there was a second and 

 corollary purpose in instituting these marking experiments. This 

 was to determine the total number of seaward migrants and the age 

 groups represented. The 46,700 migrants marked in 1926 made up 

 an unknown proportion of the total number, but it was a proportion 

 which could be exj^ected to remain constant until the fish returned 

 at maturity, provided that there was no differential mortality 

 between marked and unmarked fish. In controlled experiments 

 conducted on the Columbia River it has been shown that there 

 is practically no increased loss following marking. Our computa- 

 tions show the total number of seaward migrants in 1926 to be 

 approximately 7,500,000. 



This is the first attempt to calculate the size of the seaward migra- 

 tion at Karluk by means of marking experiments combined with 

 careful and extensive sampling of the runs for marked fish. The 

 results are interesting and it is believed that they are fairly reliable, 

 but it will necessarily be several years before we can have data that 

 will enable us to determine the relative accuracy with which we can 

 calculate the total number of migrants produced by a given spawning 

 escapement. 



In connection with the annual weir count of the spawning fish we 

 have, then, the means of determining the following variables in- 

 volved in the productivity of the stream: (1) The number of fish 

 in the spawning escapement, (2) the number of migrants produced 

 by each spawning escapement, and (3) the number of fish from each 

 niigration which survive to maturity. The value of such data ac- 

 cumulated over a series of years can scarcely be overestimated. It 



• Investigations conceiiring the red-salmon runs to the Karluk River, Alaska. By Charles 

 H. Gilbert and Willis H. Rich. Bulletin U. S. B. F. XLIII, 1927 (1928). Part II, pp. 1-69. 

 Document No. 1021. 



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