Reservoir entrapment and dam passage mortality of juvenile Chinook salmon in the Middle Fork Willamette River

Abstract

High-head dams in Oregon's Willamette River basin inhibit seaward migration and present significant mortality risks to ESA-listed juvenile Chinook salmon (Oncorhynchus tshawytscha). Over 7 years, we passively collected 13,365 downstream-migrating juvenile salmon in rivers above and below Willamette dams. Most salmon emigrated from upstream sites in February-June, but passed dams in November-February when reservoirs were drawn down near annual lows, and access to deep-water passage routes improved. Samples collected above reservoirs were dominated by subyearlings, whereas below-dam samples were a phenotypically diverse mix of subyearling, yearling and older salmon. The life history data indicated that Willamette reservoirs seasonally entrap many salmon and some sea-ready smolts probably residualise. Annual dam-passage mortality estimates were 8-59% (mean = 26%). Individual salmon mortality risk increased significantly with body length and varied with reservoir elevation and discharge. Operational changes that allow timely volitional emigration and development of less hazardous passage routes would benefit this threatened population.

Linking Behavior, Physiology, and Survival of Atlantic Salmon Smolts During Estuary Migration

“…Migratory delay through dams (Keefer et al 2012) and physical injuries incurred during dam passage (Music et al 2011) have the potential to further promote the loss of smolt characteristics Marschall et al 2011) and impair osmoregulatory ability directly (Zydlewski et al 2010). Recent modeling suggests the possibility that dams affect smolt migrations through migratory delay and potential mismatch in the timing of estuary arrival (McCormick et al 2009;Marschall et al 2011).…”

“…Estuarine mortality that occurs naturally from causes such as predation and physiological challenges (Blackwell et al 1997;Handeland et al 1997;Halfyard et al 2013) can be exacerbated by anthropogenic influences, such as passage through dams in freshwater. These influences might occur through migratory delay (Keefer et al 2012), increased predation (Poe et al 1991;Blackwell and Juanes 1998), physical injuries (Stier and Kynard 1986;Mathur et al 2000) that can result in physiological impairment (Zydlewski et al 2010), and reduced survival during estuary passage. However, the presence and magnitude of dam-related estuary mortality (i.e., delayed or indirect effects of dams) during estuary passage by Atlantic Salmon remains uncertain ).…”

Combining Genetic, Isotopic, and Field Data to Better Describe the Influence of Dams and Diversions on Burbot Movement in the Wind River Drainage, Wyoming

“…However, these losses are often equally or more strongly dependent on reservoir level, with several studies finding higher out‐migration rates when reservoirs are low (Smith and Andersen ; Keefer et al. ). Bull Lake was relatively full during both study years.…”

Using otolith chemical and structural analysis to investigate reservoir habitat use by juvenile Chinook salmon Oncorhynchus tshawytscha

“…The WVP dams were constructed from 1941 (Fern Ridge Dam, Long Tom River) to 1969 (Blue Ridge Dam, McKenzie River). The WVP dams in basins studied here lack upstream fish passage facilities and downstream passage for juveniles is lacking or poor (Keefer et al ., ). Adults were collected at facilities below Detroit (DR), Cougar (CGR) and Dexter (DX) dams and outplanted to tributaries above the reservoirs of Detroit (North Santiam, NS), Cougar (South Fork McKenzie, SFM), Lookout Point (North Fork Middle Fork Willamette, NFMF) and Hill's Creek (Middle Fork Willamette, MFW) dams; DX is a re‐regulation dam for Lookout Point Reservoir (LOP) and the short reach between DX and LOP lacks spawning habitat.…”

“…Qualitative observations of elemental and isotopic profiles from the sampled individuals indicated stable signatures in this region. The rearing geochemical region was also consistent with expected size during first‐year rearing based on otolith–body size relationships for these populations (Bourret, ), and observed size at outmigration (Keefer et al ., ).…”