Population‐Specific Migration Patterns of Wild Adult Summer‐Run Chinook Salmon Passing Wells Dam, Washington

Abstract

Summer‐run Chinook Salmon Oncorhynchus tshawytscha migrating over Wells Dam, Washington, enter a habitat characterized by blocked upstream access, high tributary water temperature regimes, and robust tribal and recreational fisheries. In 2011, we initiated a 2‐year radiotelemetry study to identify population‐specific run timing, movement, and mortality of naturally produced fish passing the dam. Five hundred seventeen salmon were radio‐tagged at Wells Dam over 2 years of study. The highest proportion (44%) of tagged fish escaped to the Okanogan River, but spawning populations from the Methow River (16%), Wenatchee River (6%), Entiat River (5%), and the Columbia River upstream (14%) and downstream of Wells Dam (14%) were also represented. In general, tributary‐spawning fish had significantly earlier run timing than did main‐stem–spawning fish. We observed very little movement among spawning tributaries, but a significant proportion of fish (~30%) were detected holding in the tailrace of Chief Joseph Dam on the Columbia River prior to spawning, including fish from populations many kilometers downstream of Wells Dam. Fallback was common in each year of the study, and we calculated that passage at Wells Dam was overestimated by 27.5% in 2011 and 32.0% in 2012 due to fallback and re‐ascension. Of the fish that remained upstream, 16% in 2011 and 22% in 2012 were estimated to have died prior to spawning, excluding fish that were known or suspected to have been harvested. In 2012, warm water temperatures (>20°C) in the Okanogan River resulted in a thermal barrier that delayed migration but did not affect spawning distribution within the river compared with 2011, when no significant thermal barrier was detected. Our results highlight some of the complex migration and distribution patterns of natural‐origin Chinook Salmon passing Wells Dam and should assist managers in upstream population and fishery modeling efforts.

Identification of Summer‐Run Chinook Salmon Spawning Areas in the Main‐Stem Columbia River Upstream of Wells Dam, Washington

“…We released 255 radio‐tagged fish in 2011 and 262 radio‐tagged fish in 2012, representing 1.8% and 1.6%, respectively, of the wild summer‐run Chinook Salmon passing Wells Dam in those years. Through the subsequent radio‐tracking effort, we estimated parameters that affected postrelease distribution and escapement estimation, including tag loss, dam fallback, harvest, and prespawn mortality (see Mann and Snow ). However, most fish that were tracked upstream of Wells Dam were spatially and temporally located to suggest survival to spawning (52% of tagged fish), including a small population of Columbia River main‐stem‐spawning fish (4.8% of tagged fish).…”

“…We radio‐tagged and released 517 wild summer‐run Chinook Salmon over 2 years (2011 and 2012) as part of a study to describe stock‐specific migration timing over Wells Dam (Mann and Snow ). These fish were collected between late June and late October of each year by operating adult salmonid trapping facilities at the west‐bank and east‐bank fish passage ladders at Wells Dam.…”

“…After tagging, fish were allowed to fully recover in freshwater and then were released (upstream of the trapping facility) into the fish ladder from which they were collected. Our previous article (Mann and Snow ) provides more detail on fish collection and tagging.…”

“…After release, we monitored locations of tagged fish in the main‐stem Columbia River and in tributaries upstream and downstream of Wells Dam to identify the population of origin for fish passing the dam, consistent with the objectives of our prior work (Mann and Snow ). Summer‐run Chinook Salmon distribution upstream of Wells Dam was monitored at fixed telemetry sites or through mobile tracking to identify and quantify main‐stem Columbia River spawning areas and their relative contribution to the overall spawning escapement upstream of Wells Dam.…”

An information theory-based approach to characterize drivers of upstream salmon migration

“…At WEL, the last passable dam on the Upper Columbia, the spring run is considerably lagged relative to BON due to travel times and the fall run is nearly non-existent in some years ( Fig 2i ). At this dam, it has previously been found that fallback and re-ascension at the fish passage causes more overestimates in salmon counts relative to lower elevation dams [ 40 ]. While we do not explicitly account for this source of error, it illustrates how uncertainties can vary between dams.…”