Movement Patterns of Adult Bull Trout and Fish Passage Implications at Albeni Falls Dam, Idaho

The bull trout population (Salvelinus confluentus) in the Pend Oreille Basin of northern Idaho and northeastern Washington is listed as threatened under the U.S. Endangered Species Act. A series of hydropower dams without fish passage, including Albeni Falls Dam (AFD) in northern Idaho, block historic upstream and downstream migrations of bull trout. The USFWS has required research to evaluate feasibility of restoring fish passage at AFD, necessitating study of bull trout behavior at the dam to determine potential use and advantageous siting. Study objectives were to verify origins of bull trout downstream of AFD to confirm entrainment, quantify spatial and temporal movement of bull trout at the dam, and to determine if discharge operations affect bull trout ability to access potential powerhouse or spillway passage locations. The behavior and movements of twelve bull trout and seventeen westslope cutthroat trout (Oncorhynchus clarki lewisi) at AFD were monitored from 2008 to 2010. Two macro and four micro radio telemetry detection zones were delineated to determine large and fine scale movements in the tailraces of the powerhouse and spillway; micro detection zones delineated regions near the dam where a fish passage structure entrance may be constructed. All bull trout captured downstream were genetically determined to be from upstream tributaries of Lake Pend Oreille. Both bull trout and cutthroat trout were detected in each of the six zones every year and were detected more frequently (over 70% of the time) in the powerhouse macro zone in most seasons. An approximately equal amount of time was spent between the two micro zones within each macro zone. Bull trout transitioned more between powerhouse micro zones than spillway micro zones or between the macro zones. Bull trout were detected at the powerhouse during all operational discharge regimes, but were detected most when all three turbines were in operation. This study determined that bull trout were able to swim throughout the tailrace and exhibit active searching behavior suggesting they would discover potential fish passage entrances at any of the four micro zone locations along the dam face. Results clarified bull trout movement in the tailrace which will guide decisions for upstream fish passage. Reconnecting this historical bull trout migration corridor will be critical to the recovery of bull trout in the Pend Oreille and Clark Fork watersheds.