First, Mysis feed on the same small organisms (zooplankton) that kokanee prefer. Because 

 kokanee feed mainly near "thermocline" (generally 15 to 45 feet below the surface) during 

 daylight hours, the kokanee rarely got opportunities to feed on Mysis. Not only were the Mysis 

 not being eaten by the kokanee, they were competing successfully for the same zooplankton on 

 which kokanee fed. 



The second outcome of Mysis introduction to McGregor Lake was related to lake trout. Prior to 

 Mysis intrcxlucticHis, lake trout existed at lower densities. Lake trout tend to live near the bottom 

 of the lake especially as fry and fingerlings. Young lake trout that were too small to begin feeding 

 on fish had to survive on the relatively small numbers of aquatic invertebrates and zooplankton 

 that existed near the bottom of the lake. In effect, there was a "bottleneck" that allowed only a 

 small number of young lake trout to survive to grow large enough to feed on fish (i.e. kokanee, 

 rainbow trout, redside shiners). When Mysis were introduced, the bottleneck no longer existed 

 for young lake trout. Many more young lake trout could survive on this new food source that 

 existed at the bottom of the lake during the daytime, they survived in much larger numbers to a 

 size that could eat kokanee, which they did. 



The combined result of the Mysis introduction was that food supplies dwindled for kokanee; this 

 made them more susceptible to predation because they had to spend more time foraging. In 

 addition, the lake trout were in such high densities that a "predator trap" was created that greatly 

 reduced kokanee survival. Future stocking of kokanee was no longer feasible and in 1985, FWP 

 discontinued stocking kokanee in McGregor Lake. In addition, the lake trout became stunted as 

 numbers increased and kokanee disappeared. 



Curraitly, FWP manages McGregor Lake as a lake trout/rainbow trout fishery. Most anglers now 

 fish for lake trout which are popular due to high catch rates (both in summer and winter). The 

 flesh of lake trout in McGregor Lake is "pink" due to Mysis in their diet. Lake trout less than 

 eight pounds taid to have this pink flesh and are excellent tasting. Fifty thousand rainbow trout 

 are stocked annually because there is no significant natural reproduction in the lake. Rainbow 

 trout provide a reasonable spring and winter fishery mostly along the shoreline, but their 

 abundance is limited by lake trout predation. Catches range from 8" to 18" and 3 to 5 pound trout 

 are sometimes caught. In addition, yellow perch provide a limited, self-sustaining fishery with 

 very few large fish. 



Manflgftment Concerns: 



1. FWP is not sure if rainbow trout can exist in McGregor Lake at levels greater than what 

 currently exist due to high predator (lake trout) densities. 



2. The population of lake trout is comprised mostly of smaller fish. 



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