Discussion 



We found general movement patterns of westslope cutthroat trout and bull trout 

 were similar to fish captured in the Blackfoot river in downstream reaches (Swanberg 

 1997, Schmetterling 2001, 2003), but also noteworthy differences. 



Bull trout: movements and habitat use 



While the bull trout in the Blackfoot River downstream of the North Fork have 

 been studied (Swanberg 1997; Schmetterling 2003), upper river fluvial bull trout (above 

 the North Fork) have not been adequately evaluated, with the exception of a limited 

 telemetry study upstream of Lincoln (Swanberg and Bums 1997). Early telemetry studies 

 reported an upper and lower component to Blackfoot River fluvial bull trout population 

 (Swanberg 1997; Swanberg and Bums 1997). 



Nine of 10 telemetered adult bull trout in the upper Blackfoot River migrated and 

 presumably spawned. Spawners utilized localized areas in only two spawning streams, 

 the North Fork and Copper Creek. This and early studies (Swanberg 1 997, Swanberg and 

 Bums 1 997) showed that these fish behave differently, hi this study, bull trout spawners 

 entered in the North Fork between late May and mid-July and exited between late 

 September and mid-November, consistent with movements in lower river (Swanberg 

 1997). By contrast, bull trout spawners in Copper Creek entered later (mid-June through 

 late July) and remained in Copper Creek longer than the North Fork bull trout, and than 

 Copper Creek bull trout described in earlier studies (Swanberg 1997; Swanberg and 

 Bums 1997). 



This study identified upper river use (upstream of the North Fork Blackfoot) by 

 bull trout that spawn and presumably rear in the North Fork Blackfoot. This use involved 

 the down-river movement of bull trout captured near Nevada Creek before ascending the 

 North Fork, and the up-river retum to wintering areas of the Blackfoot River (near 

 Nevada Creek) shortly after spawning. For these fish, the high fidelity to spawning and 

 wintering sites observed in our study conforms to movement pattems in the lower basin 

 (Swanberg 1997). 



This mainstem over-wintering use provides the first FWP documented presence of 

 bull trout in the Blackfoot River between Nevada Creek and the North Fork. This reach 

 of the Blackfoot River suffers water quality problems including elevated summer water 

 temperatures (Peters and Spoon 1988; Ingman et al 1990; Results Part FV). Densities of 

 bull trout are extremely low based on population surveys conducted during spring 2002. 

 Based on the thermal tolerances of bull trout (and small sample size), use near Nevada 

 Creek appears to be seasonal and likely limited to over-wintering. All telemetered bull 

 trout using this reach exited by mid-June, and retumed to previous wintering areas by 

 November. 



In contrast to a 1996 bull trout telemetry study (n=5) upstream of Lincoln 

 (Swanberg and Bums 1997), bull trout that spawned in Copper Creek attained larger 

 mean size (23.7" compared with 20.9"; t-test, P = 0.11), occupied a much larger mean 

 home range size (42.2 river miles compared with 1 1.0), exhibited tributary wintering and 

 displayed more diverse migratory traits. Unlike this early study that found post-spawning 

 tributary out-movement, three post-spawning Copper Creek bull trout made no attempt to 

 leave and instead wintered in Copper Creek. These inter-annual differences in movement 



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