Seasonal movements of fluvial westslope cutthroat trout in the Blackfoot River drainage, Montana

I studied the seasonal movements and habitat use of fluvial westslope cutthroat trout(Oncorhynchus clarki lewisi) from 1997 to 1999 in the Blackfoot River drainage in westernMontana to help guide restoration efforts and lead to a better understanding of this subspecies.Of 22 radio-tagged fish, 16 migrated during the spawning period (mean length, 371 mm). Ten ofthe 22 fish were tracked over a 2-year period, and 2 of these fish migrated in both 1997 and1998. Migrations to tributaries occurred during the rising limb of the hydrograph in both years andlasted for an average of 10 d (range, 1–14 d) in 1998. Migratory fish moved both upriver anddownriver to reach spawning tributaries during both years. In 1998 the mean distance traveled toaccess tributaries was 31 km (range, 3–72 km). Fish staged at the mouths of tributaries for up to14 d before entering near the peak in the hydrograph. They remained in tributaries for an averageof 27 d (range, 4–63 d), the duration varying with size of tributary and flow year. Once intributaries, fish generally remained within a 200-m reach, but frequently moved within the area. Infour tributaries to the Blackfoot River, actively spawning fish were observed in May 1998 as flowssubsided after the peak discharge. Neither of the two repeat migrants spawned within 3 km oftheir previous year\u27s spawning location, though both spawned in the same tributaries. Afterleaving tributaries, fish moved both up- and downriver to overwintering areas and did not movemore than 100 m thereafter. Fish did not exhibit fidelity to their prespawning main-stem locations.At least six fish died after spawning (38%). Westslope cutthroat trout movements, prespawningand postspawning, exhibited a plasticity not previously reported in Montana and demonstrate thelarge spatial extent to which fluvial westslope cutthroat trout utilize aquatic resources. To enablecontinued improvement of the westslope cutthroat trout population in the Blackfoot Riverdrainage, I recommend riparian timber management that continues long-term input of largewoody debris to tributaries, continued closure of the Blackfoot River watershed to angling harvest,and the use of culvert designs that will pass spawning fish under most flow conditions