50 per cent of the stocked trout. In 1962, the plant 

 was reduced by one-fourth and the creel census will 

 be continued to evaluate this change in the planting 

 schedule. 



Observations were made on the spawning, 

 growth, distribution, harvest and movement of trout 

 in Willow Creek Reservoir from March through No- 

 vember, 1960. Successful reproduction was observed 

 only in Willow Creek. Rainbow trout taken in 1960 

 showed a decline in average size and slower growth 

 rate than the same species taken in previous years. 

 Distribution of trout in the reservoir appeared to be 

 correlated with water temperatures. Rainbow trout 

 were most evenly distributed in the reservoir when 

 water temperatures were warmest, but were con- 

 centrated near the surface when temperatures were 

 cool. Brown trout were always more abundant near 

 the bottom, and when water was warmest were re- 

 stricted to deeper areas. Brown trout made up thirty 

 per cent of the game fish in gill net catch but only 

 2'/2 per cent of the estimated harvest, indicating that 

 present fishing methods are not effective on this 

 species. Marking studies indicated that the hatchery 

 fish as well as fish marked in the spawning runs 

 distributed themselves throughout the reservoir. The 

 estimated harvest of rainbow trout was less than 

 15,000 fish during the fishing season. These fish were 

 mostly from the 1959 and 1960 plants of 55,000 fish 

 per year. In 1961, the plant was reduced and the 

 season was liberalized. The evaluation of angler 

 harvest is being continued to determine the effect of 

 this change in management. 



A population study was continued on Canyon 

 Ferry Reservoir during 1960. Gill net sets were made 

 duplicating the sets of 1955 and 1958. Comparison 

 indicated that the fish population of this reservoir 

 had more or less stabilized by 1958. Growth rates 

 increased during the early years of impoundment but 

 decreased to pre-impoundment levels by 1958. 

 Fingerling rainbow trout stocking was successful 

 only during the early years of impoundment. A 

 change to planting trout seven inches long or more 

 has maintained the fishery but it is possible that a 

 comparable fishery could be maintained with smaller 

 size fish. If this proves true, a considerably greater 

 number of smaller fish could be planted for the 

 same cost as the present plants. A creel census is 

 now underway to evaluate the success of various 

 sizes of planted trout. The U. S. Bureau of Sport 

 Fisheries and Wildlife is assisting in this study. 



During 1960 the U. S. Forest Service sprayed DDT 

 in a portion of the Gallatin Drainage in an effort to 

 control spruce budworms. Observations were mode 



in the area to determine the effect of this project on 

 trout streams. Spray concentrations were reduced 

 along the streams but sampling with fine-mesh nets 

 indicated that stream insects were killed in all of the 

 tributaries and throughout the Gallatin River within 

 and below the spray area. The only trout mortality 

 was in Rat Lake where the spray caused an exten- 

 sive kill. 



An investigation was begun on the water temper- 

 atures of the Madison River and the influence of the 

 three lakes on the river. Due to the thermal waters 

 of the Firehole River, the upper Madison River is 

 unusually warm for a headwater stream. It appears 

 that Hebgen and Earthquake Lakes cool the stream 

 during the critical early summer weeks while Mea- 

 dow Lake warms the stream during the same period. 

 Summer stream temperatures reached highs of 80° 

 F. above Hebgen and 83" F. below Meadow Lake. 

 These temperatures are approaching critical levels 

 for trout. Any further developments of reservoirs or 

 diversions which would increase water temperatures 

 may seriously affect trout production in the Madison 

 River. 



Hebgen Reservoir (15,000 acres) in southern Gal- 

 latin County on the Madison River was drawn slowly 

 for inspection and repair following the August 1959 

 earthquake in the area. The reservoir was treated 

 with toxaphene at the rate of 0.025 parts per million 

 in an attempt to kill off Utah chubs. The toxaphene 

 was applied by spray plane to the lower portion of 

 the reservoir pool and the upper portion through 

 drip stations located on the tributaries. Although 

 water that seeped through the closed control gates 

 was toxic to fish for a distance of one-half mile below 

 the dam, very few fish were killed in the upper 

 portion of the reservoir. It is possible that high 

 turbidity in the upper portion of the reservoir pool 

 was responsible for the rather poor results. Fish 

 stocking, since the reservoir refilled with water, has 

 provided excellent fishing. 



CENTRAL FISHERIES DISTRICT 



Eleven lakes and impoundments were surveyed 

 during the biennium. Several of these were studied 

 in order to evaluate the success of different periods 

 and rates of stocking fish following rehabilitation. 

 Information from this continuing study thus far shows 

 that a better return of planted fish is being realized 

 from plants made later in the season. Other infor- 

 mation recorded on lakes and impoundments in- 

 cluded size, volume and fish numbers for use in 

 future management. 



25 



