A radiotelemetry evaluation was conducted during April–October 2011 to describe movement patterns, forebay behavior, and passage of juvenile steelhead, coho salmon, and Chinook salmon at Cowlitz Falls Dam, Washington. The primary focus of the study was to describe fish behavior near a behavioral guidance structure (BGS) and floating surface collector (FSC) deployed upstream of Cowlitz Falls Dam. A secondary focus was to determine the proportion of tagged fish that were detected near spillbays 2 and 3 on the dam, because this location has been proposed for deploying weir boxes as an additional dam-based collection alternative in the future. Juvenile steelhead (Oncorhynchus mykiss), coho salmon (Oncorhynchus kisutch), and Chinook salmon (Oncorhynchus tshawytscha) were collected and tagged at the Cowlitz Falls Fish Collection Facility and transported upstream where they were released into the Cowlitz and Cispus Rivers. We radio-tagged and released 110 juvenile steelhead, 110 juvenile coho salmon, and 110 juvenile Chinook salmon and monitored their movements in and around the BGS/FSC complex, at the dam, and downstream of the dam. We used detection records and a Markov chain model to calculate probabilities of movement between specific areas in the forebay of Cowlitz Falls Dam. These areas are referred to as states and the Markov chain model was used to create a series of tables, called transition matrices, that contained estimated probabilities of movement between states. These probabilities were insightful for understanding how radio-tagged fish moved near the BGS, FSC, and spillbays.

Most tagged fish (89–91 percent) moved downstream of release sites (9 or 22 rkm upstream of the dam) and were detected in the dam forebay during the study period. Tagged fish that encountered the BGS on their first approach to the dam were distributed across the forebay, which supports the concept of using a BGS to concentrate fish near a collector entrance in the dam forebay. We found that 14 percent of the steelhead, 18 percent of the coho salmon, and 17 percent of the Chinook salmon encountered the FSC discovery area without BGS guidance on their first trip through the forebay. The BGS guided 36 percent of the steelhead, 22 percent of the coho salmon, and 46 percent of the Chinook salmon to the FSC discovery area when fish first entered the forebay, which resulted in 40–63 percent (by species) of the tagged fish arriving at the FSC discovery area. Movement patterns along the BGS showed that fish were likely to guide along the device, but also demonstrated the tendency of fish to move under the BGS and downstream to Cowlitz Falls Dam.

Differential distribution among sucker species within the Williamson River Delta and between the delta and adjacent lakes indicated that shortnose suckers likely benefited more from the restored Williamson River Delta than Lost River or Klamath largescale suckers (Catostomus snyderi). Catch rates in shallow-water habitats within the delta were higher for shortnose and Klamath largescale sucker larvae than for larval Lost River suckers in 2008, 2009, and 2010. Shortnose suckers also comprised the greatest portion of age-0 suckers captured in the Williamson River Delta in all 3 years of the study. The relative abundance of age-1 shortnose suckers was high in our catches compared to age-1 Lost River suckers in 2009 and 2010.

Tagged fish that arrived at Cowlitz Falls Dam were distributed across the dam face but a high percentage of each species (65 percent of steelhead; 61 percent of coho salmon; 71 percent of Chinook salmon) arrived on the northern side of the dam. Movement probabilities near spillbays 1 and 4 showed a strong preference for tagged fish to move from the outer edges of the dam towards the center of the dam where they were detected at the debris barrier (range of probabilities = 0.690–0.841). We found that 76 percent of the steelhead, 61 percent of the coho salmon, and 92 percent of the Chinook salmon were detected at spillbays 2 or 3 during the study. This behavior supports the strategy of weir box deployments in spillbays 2 and 3 for future dam-based collection options. Tagged fish that arrived at the dam commonly moved upstream and were detected at the BGS or FSC discovery area. This behavior provided a secondary opportunity for fish to encounter the FSC discovery area and we found that in total, 72 percent of the steelhead, 48 percent of the coho salmon, and 92 percent of the Chinook salmon were detected near the FSC while residing in the forebay. Overall, 88 percent of the steelhead, 76 percent of the coho salmon, and 95 percent of the Chinook salmon that entered the forebay were detected near the FSC or in spillbays 2 and 3.

Turbine passage was the most common passage route for tagged fish at Cowlitz Falls Dam during 2011. We found that 40 percent of the steelhead, 52 percent of the coho salmon, and 33 percent of the Chinook salmon passed through turbines. An additional 22 percent of the steelhead and 32 percent of the coho salmon passed through turbines or spillways when both passage routes were available. Fish collection numbers were relatively low during 2011 compared to long-term averages. In total, 37 percent of the steelhead, 14 percent of the coho salmon, and 23 percent of the Chinook salmon that entered the forebay were collected, primarily through collection flumes. The FSC collected a single radio-tagged fish (a Chinook salmon) in 2011.