Coopers Lake and Nevada Reservoir Fisheries Assessments {from Berg 2003) 



Nevada and Coopers Lakes arc located near the middle portions of the Blackfoot 

 River watershed. Nevada Lake, formed by an earthen dam in 1941, is located in the 

 middle reaches of the Nevada Creek. At an elevation of 4,615', the lake has a surface 

 area of approximately 337 acres. Coopers Lake is a natural glacial trough lake with a 

 surface area of -196 acres at an elevation of 4,490'. McDermott Creek flows out of the 

 Scapegoat wilderness into the north end Coopers Lake. Salmon Creek is the outlet 

 stream. 



Methods 



Fish sampling surveys were conducted June 21-24, 2003 on Nevada Lake and July 

 12-16, 2003 on Coopers Lake. We used standard "Montana" experimental floating and 

 sinking nylon or monofilament gill nets, measuring 6' x 125' with graduated mesh 

 ranging from 0.75 to 2.0" square measure. Overnight stationary gill net sets were equally 

 distributed around the entire perimeter of each lake to produce a representative catch. 

 The size and complexity of each lake dictated the number of gill nets set used. During 

 the surveys, 16 floating and 4 sinking gill net sets were placed on the Nevada Lake and 19 

 floating and 6 sinking gill net sets on Coopers Lake. Locations coordinates for each gill 

 net set were recorded using GPS. Locations were also marked on USGS topographic 

 maps. Sampling recorded sex, total length to the nearest millimeter and weighed to the 

 nearest 10 grams for all species. 



Results 



Our overnight stationary gill net survey on Nevada Lake handled 1,871 fish (Table 

 1 1). Yellow perch, illegally introduced into Nevada Reservoir, accounted for 55% of the 

 total catch, followed by longnose suckers (13%), and red-side shiners (9%), largescale 

 suckers (9 %), rainbow trout (8%) and westslope cutthroat trout (8%). 



Coopers Lake survey produced 632 fish. Northern pikeminnow comprised 71% 

 of the total catch, followed by longnose suckers (28%) and low densities of WSCT 

 (0.6%) and brook trout (0.6%). 



Discussion 



Sampling and stocking of Coopers Lake has been inconsistent. Coopers Lake 

 supported bull trout in the 1970s; however, in 2003, we detected no bull trout and very 

 low densities of other game fish (WSCT and brook trout). Recent tributary sampling 

 indicates weak recruitment of wild fish to the reservoir (Pierce et al. 2002). Based on 

 recent angler interviews, satisfaction with the fishery also appears low. In addition. 

 Coopers Lake has also had a long history of perceived over-population problems with 

 non-game species. The sum of these variables makes Coopers Lake a likely location for 

 an illegal fish introduction. 



Beginning in 2003, we initiated increased plants of WSCT into Coopers Lake. 

 Sampling in 2003 did not detect the recently introduced hatchery fish. This may be the 

 result of an ineffective net mesh size (too large) for these fish, planting location or other 



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