FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 261 



inception of the commercial fishery, Karluk Lake received a large supply of chemical 

 compounds each year because practically all of each season's run of fish proceeded to 

 the lake and its tributaries to spawn and die. As soon as the commercial fishery began, 

 the spawning escapements became less, and not only were there fewer spawners avail- 

 able to deposit eggs in the gravel, but the yearly increment of chemical compounds to 

 the water was considerably decreased. 



That the productivity of bodies of fresh and salt water is controlled in part by 

 the abundance of certain inorganic salts such as phosphorus has long been known and 

 the relationship between the chemical content of the water of ponds, lakes, and the 

 ocean and their productivity has been studied by a large number of investigators. 

 Soluble phosphorus has been considered by most workers to be the chief limiting 

 factor in the productivity of aquatic organisms during the summer months, although 

 nitrogen and carbon dioxide have also been shown to be limiting factors at times. 



During the 2 or 3 years that the red-salmon fingerlings spend in fresh water, 

 prior to their sojourn in the ocean, they feed upon certain minute forms of animal life 

 existing in the lake. These animal forms, or zooplankton, are dependent upon the 

 plant forms, or phytoplankton, and they in turn are dependent upon the sunlight and 

 the inorganic salts in the lake water. Hence, fluctuations in the supply of salts in the 

 lake water can indirectly affect the growth and survival of the fish. 



In tables 21 and 22 are presented the results of temperature and chemical observa- 

 tions made on the waters of Karluk and Thumb Lakes in 1935 and 1936. Similar 

 data collected in 1927 were presented and discussed by Juday, Rich, Kemmerer, and 

 Mann (1932). 



The temperature of both Karluk and Thumb Lakes was higher in 1935 than in 

 1927 and still higher in 193G. At Station 1, in Karluk Lake (fig. 5), for example, the 

 surface temperature on August 13, 1927, was 11.1°C; on the same date in 1935 it was 

 12.2° C; and in 1936 it was 15.5° C. There was evidently a marked difference in 

 the amount of sunshine during these 3 years, and such a conclusion is confirmed by the 

 precipitation data. The June-July-Augusl precipitation at Kodiak. the nearest 

 recording station, was 22.33 inches in 1927; 13.85 in 1935; and 6.56 inches in 1936. 

 During the 47 years that June-July-August precipitation data has been tabulated at. 

 Kodiak, the average precipitation was 13.32 inches. 



Soluble phosphorus was found in the water of Karluk and Thumb Lakes in 1927 

 on the dates samples were taken, and whereas (lie surface waters of these lakes lacked 

 a measurable amount of phosphorus during the summers of 1935 and 1936, it was not 

 until September, at the end of the salmon growing season, that measurable amounts 

 of phosphorus were found. 



Silica was almost entirely absent from the surface waters of Karluk Lake during 

 1935 and 1936, whereas a small amount was present in 1927. 7 A greater amount of 

 silica occurred in the water of Thumb Lake in 1935 and 1936 than in 1927. 



7 The VJ'21 silica values should be multiplied by 1.14 to correct a change in the value used in the calculation. The method used 

 for the determination of silica is that described by 1 tienert and Wandenbulcke (1923), and Juday, Rich. Kemmerer, ami Mann (1932) 

 used Dienert and W andenbulckes value of ;<G .9 mgs. ol picric acid as being equivalent to ",0 mgs. of silica. King and Lucas 1 1928) 

 showed this value to tic in error and indicated that 25.6 mgs. of picric acid were equivalent to 50 mgs. of silica. This latter value 

 was confirmed by Robinson and Kemmerer (1930a) and was used in the present analysis. 



