PROGRESS IN BIOLOGICAL INQUIRIES, 193 3 375 



heavy winds. Teini)eratures were found to bo j^iiituble everywliere, 

 probably caused by high altitude and cold nights. Since all other 

 conditions appear to be favorable, the explanation may be found 

 in winter oxygen deficiency. 



Scofcld Reservoir. — Reports of poor catclies at this lake, together 

 with rumors of heavy winter losses, resulted in a request by the 

 department for this study. Sets with the graded size gill net indi- 

 cated a reasonable abundance of trout in a portion of the reservoir 

 and thereby reassured guides and fishermen in that locality. Sub- 

 sequent improvement in the catches confirmed our findings. Food 

 eamples showed a fair amount of plankton and bottom forms. Oxy- 

 gen determinations during August at 6 scattered stations indicated 

 a marked deficiency over about half of the area in spite of the fact 

 that a maximum depth of only 21 feet was found. This indicates 

 that there may be a decided winter deficiency which would cause a 

 considerable loss of trout. Recommendations that heavy plantings 

 here be avoided and that a study of winter oxygen conditions be 

 made are being followed. 



Bear Lake. — At the request of the Bureau's Division of Fish Cul- 

 ture, a study of Bear Lake, Utah-Idaho, was made possible by the 

 defrayment of expenses by that division. 



Chemical analyses made during a former study by the Bureau, 

 and confirmed in part by this investigation, show an abundance of 

 oxygen at all deptiis. The water is highly alkaline and, according 

 to previous studies, contains considerable zinc. Temperatures were 

 found to be entirely suitable for trout. A study of the food supply, 

 however, indicated a decided deficiency. Plankton was found to be 

 scarce. The Bureau's earlier workers also remarked the scarcity of 

 phytoplankton and suggested that the high zinc content might be 

 a cause. Bottom samples were poor in both the deeps and the shal- 

 lows, the sand beaches being almost devoid of life. Limited areas 

 of gravel and rocky shore supported a goodly number of organisms, 

 including shrimp. Aquatic vegetation appeared to be limited to a 

 few small patches of Potamogeton. Permanent lowering of the lake 

 level by power development has resulted in a littoral zone composed 

 almost entirel}' of sand, leaving stranded the original gravel and 

 cobble beaches. This has undoubtedly eliminated a rich productive 

 area and thereby decreased the lake's food supply. Sets with the 

 graded size gill net indicated a scarcity of fish. 



01)servations following several plantings of fingerling trout and 

 salmon indicated that heavy losses may be sustained due to the dep- 

 redations of gulls, chub C^igoma), and adult trout. A period of 

 approximately 48 hours seems necessary for young trout and salmon 

 to lose their conspicuous dark color and to acquire the strength 

 and agility necessary to escape their enemies. Experiments in 

 adaptation will be conducted by the Division of Fish Culture at this 

 lake during the coming season in an attempt to overcome this loss 

 in planting. 



MUSSEL INVESTIGATIONS AND POLLUTION STUDIES IN INTERIOR 



WATERS 



The various activities carried on by the staff under the direction of 

 Dr. M. M. Ellis with headquarters and laboratories furnished by the 



3—34 5 



