Genetic results confirm Blackfoot River stocks of suspected RBT to be RBT - 

 WSCT hybrids with a predominant rainbow genetic composition. For these fish, early 

 results suggest inter-annual variations in temperature and flow influence the timing of 

 migrations and spawning. Early study results also suggest spawning for "lower" River 

 RBT occurs in the lower reaches of several lower river tributaries; however a portion of 

 these lower river RBT also migrate long distances to middle River tributaries (e.g. 

 Monture Creek). In contrast, >90% of RBT telemetered upstream of the Clearwater 

 River spawned in the Monture Creek watershed. 



River movements of non-tributary spawning RBT also occurred during the normal 

 migration period. Because we tracked RBT on a daily basis during the spawning period 

 is appears unlikely these RBT entered tributaries. Rather, this movement pattern suggests 

 limited, but as yet unconfirmed, mainstem spawning. Because of WD infection levels in 

 the mainstem Blackfoot River upstream of the Clearwater River are approaching lethal 

 levels, emergent ft-y in this section of the Blackfoot River are at some heightened risk of 

 contracting WD compared to the lower river where WD is at lower levels. 



All lower tributaries used by telemetered RBT currently support a low (sub-lethal) 

 WD infection. Conversely, a majority of RBT spawning upstream of the Clearwater 

 River, including Monture Creek, support high (lethal) WD infections in lower stream 

 reaches. Mean grade WD infection in Monture Creek at stream mile 2.1 was 4.8 in July 

 2005. However, because WD infections tend to decrease in the upstream direction, it 

 appears the upper segment of emergent Monture Creek rainbow fry may be at a reduced 

 risk of exposure to lethal spore levels compared to RBT fry in lower Monture Creek. 

 Based on the Monture Creek median spawning date of April 26'*' (both years), peak 

 hatching of RBT eggs is within the first week on June, with emergence expected 2-3 

 weeks thereafter (Ron Snyder, personal communication). This post-emergence period 

 corresponds both peak period of RBT disease vulnerability (Ryce 2003), and severe 

 infectious period measured from sentinel caged RBT in Monture Creek during mid-July. 



The escalation of WD in the middle Blackfoot River and primary spawning 

 tributaries therein coincide with 1) declining juvenile densities of RBT in the lower-most 

 sampling sites of Monture Creek compared to an upstream site, 2) declining RBT 

 densities in the middle Blackfoot River, and 3) an increasing incidence of cranial 

 deformities in the Blackfoot River downstream of Monture Creek (this report). Although 

 these indices all suggest a high risk of WD in the middle river, six years of drought 

 currently confounds a clear interpretation of the influences of WD on river populations. 

 Further compounding concerns of WD, past juvenile RBT surveys identified recruitment 

 problems resulting from high juvenile (winter) mortality the middle Blackfoot River 

 (Peters and Spoon 1989). Additional telemetry work, whirling disease monitoring and 

 related research are expected to continue through 2006-07. 



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