THIRTY-Sl!;VENTII BIENNIAL REPORT 21 



powders. In very dilute concentrations (1:2,000,000) this kills fish 

 without being injurious to plant life, to many forms of fish food, or to 

 human beinsfs and other mammals. Six bodies of water in California have 

 been subjected to this treatment by the Bureau of Fish Conservation in 

 the last two years, and are listed below. 



Gull Lake, Mono County. This 70-acre lake, once an excellent trout 

 fishery, had become'overrun with lake chubs. The lake was poisoned with 

 timbo on September 11, 1940. An estimated 500,000 eliubs were killed, 

 of which all but 100,000 were over two inches Ion*?. Only 254 trout were 

 found in the lake. It was restocked November 1st to 4th, some 50 days 

 after the treatement, with 76,000 eastern brook trout five inches lonfj. The 

 catch the following season (1941) is estimated at over 10,000 trout. 



Hume Lake, Fresno County. Deterioration of trout fishing in this 

 94-acre reservoir had been ascribed to the number of minnows present 

 and had led to requests for remedial measures. Draining of the water by 

 the United States Forest Service in early October, 3940, in order to repair 

 the dam removed a large proportion of the rough fish, and on October 10th 

 poisoning with timbo of the remaining pools and springs on the lake bot- 

 tom, and of the tributary streams, was undertaken. The complexity of the 

 operation made estimates difficult, but it is reported that great numbers 

 of the minnow Lavinia exilicauda were destroyed. The lake was restocked 

 in late November with four-inch rainbow and satisfactory fishing was 

 reported the following season. 



TJiompsons Lake, Plumas County. This two-acre lake lies 500 feet 

 above and one-quarter mile from Bucks Lake, an excellent trout fishing 

 water. Black bass placed therein by unauthorized persons constituted a 

 menace to trout due to the possibility of their migrating down into Bucks 

 Lake in the overflow from Thompson 's which occurs after heavy winters. 

 The lake was poisoned with timbo October 16, 1940, and 1,000 large- 

 mouthed black bass and 27 Lock Leven trout were destroyed. This lake 

 was not restocked; serving as domestic water supply for local cabin 

 owners, the presence of fishermen on its shores was not desired. 



Lake Almanor, Plumas County. Carp present in this lake had been 

 blamed by fishermen for deterioration in the rainbow fishing. Although 

 no positive evidence of this exists, it was decided to experiment with carp 

 control during May and June of 1941. At this season the carp come into 

 the shallow bays to spawn. It was found that the best results were 

 obtained by spreading a strong solution of timbo across the mouth of a 

 bay which carp had entered, and then working back toward the head of 

 the bay. As the fish tried to escape they were killed passing through the 

 timbo barrier, and it is estimated that from 10,000 to 12,000 were disposed 

 of in this way in the course of the season. Some minnows were killed but, 

 so far as is known, only one small trout. Trout do not frequent the warm 

 shallows where the carp spa^vn. 



Hot Creek Hatchery Water Supply, Mono County. Infections of 

 rainbow trout at this hatchery with Ichthyopthyrius having caused con- 

 siderable losses in the past, it was decided to try to destroy all fish in the 

 springs which form the water supply in the hope that elimination of 

 these hosts for the parasite would do away with the disease. A great 

 difficulty lay in the fact that the water issues from caves which extend 

 far back under the ground, thus making it impossible to poison the actual 



