FORTY-FIRST BIENNIAL REPORT 109 



1947 eggs (marked dorsal and adipose) and spring-spawned from 1948 eggs (marked 

 adipose) . In addition, two 1948 summer plants of fingerling brown trout (4,000) and 

 rainbow trout (4,000) were made for an additional carryover test. During the 1948 

 season, 8,384 anglers fished 31,962 hours for a total of 20,379 wild and planted fish. 

 Marked hatchery fish contributed 93.6 percent of total catch. Out of the 19,945 

 catchable rainbow trout planted, 18,362 (92.1 percent) were caught. Only 72 (3.8 

 percent) of the fall-spawned 1947 carryover plant and 175 (8.8 percent) of the 

 spring-spawned 1947 carryover plant showed in 1948 creels. No 1947 carryover fish 

 were taken after August 14. Wild fish contributed 6.4 percent of total 1948 catch : 

 1,131 (87.6 percent) were brown trout, 140 (10.8 percent) were rainbow trout, and 

 21 (1.6 percent) were eastern brook. Average angler catch per hour for the season 

 was 0.63. Sixty percent of the right ventral fish were taken in only 20 fishing days 

 (4-day samplings following the post-planting closures). 



Additional treatment of aquatic plant beds at Twin Lakes, Mammoth, Mono 

 County, California. Submitted December 28, 1948. 6 pp., 1 figure. 



Abstract : An area of 2.8 acres between center and lower Twin Lakes, in the 

 Mammoth Lake Recreation Area, choked by dense growths of chiefly Anacharis, was 

 treated with 885 pounds of sodium arsenite powder (75 percent arsenious oxide) 

 giving an initial concentration of 21.2 p. p.m. arsenious oxide ; partial collapse and 

 a "burn" of plant growth down to a depth of 6 inches was observed a week later. 

 The high concentration used forms a test of sodium arsenite in a disturbed water 

 situation where wave action, stream flow, and ground seepages might easily nullify 

 caustic action of the poison at lower concentration. Control of plants in the interlake 

 area will restore the area to angling, interlake boat travel, and to recreational use 

 of hundreds of vacationers using the Twin Lakes camp grounds. 



Creel inventory at Rush Creek Test Stream, Mono County, California, 1949. 

 Submitted December 19, 1949. 13 pp., 2 figures, 4 tables. 



Abstract : The creel inventory was conducted for 179 fishing days. From April 

 29 to August 29, 19,975 rainbow trout averaging 7^ inches long (marked VV) were 

 planted at six intervals. Two special summer plants of fingerling browns (3,003) 

 and rainbow (3,000) were made for a further carryover test. During the 1949 season, 

 10,004 anglers fished 36,417 hours for a total of 18,020 wild and planted fish. Marked 

 hatchery fish contributed 90.8 percent of the total. Out of 19,975 catchable rainbow 

 (marked VV) planted, 15,995 (80.0 percent) were taken. Only 54 of the fall-spawned 



1948 cari-yover plant and 114 of the spring-spawned 1948 carryover plant (2.2 

 percent combined) were taken in 1949 creels. Wild fish contributed 9.2 percent of the 



1949 total catch ; 1,373 (83.0 pereeent) were brown, 279 (16.7 percent) were rainbow 

 and 5 (0.3 percent) were eastern brook. Average catch per angler hour for the 

 season was 0.49 with the catch per angler day at 1.8. 



Chemical treatment of Upper Twin Lake, Robinson Creek, Mono County, Cali- 

 fornia. Submitted April 15, 1950. 41 pp., including 14 figures, 9 photos, 3 maps, 

 6 tables, 2 graphs. 



Abstract : Upper Twin Lake, Robinson Creek, Mono County, 14 miles south- 

 west of Bridgeport, was treated September 8, 1949, with 16,835 pounds of cube, 

 rotenone averaging about 5 percent, to remove a large population of chubs, sandbar 

 suckers, shiners, and sculpins. The lake at spill has 265 surface acres with a maxi- 

 mum depth of 112 feet ; maximum temperature is 65° F., and there is unusually high 

 oxygen deep into the hypolimnion. Plan of the project is described and embodied in 

 Figure 5, p. 8A. Only 194 trout were reported from the lake, while over 100,000 

 rough fish were killed. End concentration of cube used was approximately 0.68 

 p. p.m. ; 15,200 pounds of cube was used in lake treatment and 1,635 pounds in treat- 

 ment of about 4 miles of tributaries. Spill from the lake was nontoxic to trout and 

 whitefish 75 days after treatment. Restocking and proposed management program 

 is discussed and recommendations presented. 



Chemical treatment of Tamarack Lake, Mono County, California, 1949. Sub- 

 mitted January 26, 1950. 8 pp., 2 figures. 



Abstract : Tamarack Lake, 12.7 acres at an elevation of 9,700 feet near 

 Bridgeport, Mono County, California, was infested with sand-bar suckers (Catosto- 

 mus arenarius ) , introduced about 1879 by pioneers of the Bridgeport Valley as for- 

 age for trout in the lake. Elimination of the sucker population was accomplished 

 September 21-23, 1949, with 535 pounds of cube (rotenone 3.9 percent) as a necessary 

 step in preparation for the proposed chemical treatment of Lower Twin Lake as 

 well as for restoration of Tamarack Lake as a trout water. 



