PROGRESS IN BIOLOGICAL INQUIRIES, 1937 31 



Little increase in local spawning escapements has been noted in 

 recent years and a considerable decrease in the commercial catch 

 has been evident. Since local popnlations mature almost exclusively 

 in the third year, the coming- season should demonstrate the effect on 

 this species of the removal of fixed fishing gear from these waters in 

 1935. Unless the beneficial results of this reduction in gear are con- 

 siderably greater than is anticipated, more stringent measures for 

 securing an adequate spawning reserve of this species must be adopted 

 if a continued decline in numbers is to be avoided. 



KARLUK RIVER RED SALMON 



The investigation to determine the extent and causes of the fluctua- 

 tions in the size of red salmon runs in Karluk River, Alaska, was 

 continued in 1937 by J. T. Barnaby and A. C. DeLacy. 



Operation of a counting weir in the river provides data on the 

 inunber of adult fish escaping to the spawning grounds. This es- 

 capement, together with the daily catches of salmon made by the 

 companies fishing in the Karluk district, is used to determine the 

 total run into the river. The age group composition of the 1937 run 

 was calculated from an analysis of 14,000 scale samples taken through- 

 out the season. This study of the salmon populations spawning in 

 Karluk River is furnishing valuable data on fluctuations in the size 

 of the runs and also on variations in the ratio of return to escapement. 



Studies of the relation between the growth rate of young salmon 

 in fresh water and their survival both in the fresh water and in the 

 sea were continued. Samples of seaward migrant young were col- 

 lected for the purpose of determining the age and length frequencies 

 of the 1937 population. Results thus far obtained from this study 

 indicate a positive correlation between fresh water growth rate and 

 survival. 



During the season an examination of 434,000 adult salmon dis- 

 closed more than 2,100 marked individuals returning from previous 

 years' marking experiments. The numbers and ages of these marked 

 fish indicates that the mortality rate of salmon while in the ocean 

 is fairly constant. The slight variations which occur in it from year 

 to year are not of sufficient degree to account for the great variations 

 in the total survival of these fish from one generation to another. 

 It is evident that the wide fluctuations in the ratio of return to es- 

 capement are due primarily to variations in the natural conditions 

 affecting survival in fresh water. 



Studies of the food available for young salmon in fresh water 

 entailed a chemical analysis of the waters of Karluk Lake and its 

 tributary streams as well as the sampling of these Avaters for plank- 

 ton content. The phosphorous, nitrate, silica, oxygen, and carbonate 

 content of these waters was determined a number of times during 

 the season. As noted in previous years, phosphorous and silica were 

 the chief limiting factors in the growth of plankton and the asso- 

 ciated growth of young salmon which depend upon the plankton 

 for their food supply. 



Predatoi^ species. — The Dolly Varden trout is considered the chief 

 predator of the salmon during their stay in fresh water. Although 

 a considerable amount of money is expended every year by the Terri- 



76022—38 5 



