Migratory Behavior and Physiological Development as Potential Determinants of Life History Diversity in Fall Chinook Salmon in the Clearwater River

Abstract

We studied the influence of behavior, water velocity, and physiological development on the downstream movement of subyearling fall‐run Chinook Salmon Oncorhynchus tshawytscha in both free‐flowing and impounded reaches of the Clearwater and Snake rivers as potential mechanisms that might explain life history diversity in this stock. Movement rates and the percentage of radio‐tagged fish that moved faster than the average current velocity were higher in the free‐flowing Clearwater River than in impounded reaches. This supports the notion that water velocity is a primary determinant of downstream movement regardless of a fish's physiological development. In contrast, movement rates slowed and detections became fewer in impounded reaches, where water velocities were much lower. The percentage of fish that moved faster than the average current velocity continued to decline and reached zero in the lowermost reach of Lower Granite Reservoir, suggesting that the behavioral disposition to move downstream was low. These findings contrast with those of a similar, previous study of Snake River subyearlings despite similarity in hydrodynamic conditions between the two studies. Physiological differences between Snake and Clearwater River migrants shed light on this disparity. Subyearlings from the Clearwater River were parr‐like in their development and never showed the increase in gill Na+/K+‐ATPase activity displayed by smolts from the Snake River. Results from this study provide evidence that behavioral and life history differences between Snake and Clearwater River subyearlings may have a physiological basis that is modified by environmental conditions.

Hydropower peaking and stalled salmon migration are linked by altered reservoir hydraulics: A multidisciplinary synthesis and hypothesis

“…Retardation of physiological smoltification, in particular, resulting in suppression of a late-migrating smolt's urge to migrate, has also been explored for delayed migration and overwintering in the reservoirs (Tiffan et al, 2018), but whether that is a cause of delay or an effect of being delayed by changes in the migratory habitat is not known.…”

“…Even if the wave structures and their effects on small-scale reservoir water velocity, direction and acceleration are fully characterized, there continues to be much uncertainty concerning fall and winter subyearling Chinook salmon habitat use, behavior, dam passage rates, routes, and survival. This is despite the many studies in this riverreservoir reach of the lower Snake River (Connor et al, 2002(Connor et al, , 2003(Connor et al, , 2005Keefer & Peery, 2008;Kock et al, 2007;McMichael et al, 2008;Tiffan et al, 2000Tiffan et al, , 2006Tiffan et al, , 2009Tiffan et al, , 2012Tiffan et al, , 2014Tiffan et al, , 2018Venditti et al, 2000). The disproportionate contribution of reservoir-type (overwintering) fish to returning adult fall Chinook salmon raises questions about the need for more data on all aspects of the fall and winter ecology of these unusual juveniles (Keefer & Peery, 2008).…”

“…Seasonal changes encountered by the latest‐arriving fish in the reservoirs may inhibit migration. Fish that have smolted by the time they reach the reservoirs in the fall have shown regression to pre‐smolt conditions during delayed migration, which may be the result of seasonal shortening daylength and declining temperature (Tiffan et al, 2018). It is unclear what is cause and effect: the loss of smoltification, which reduces the physiological cue to migrate or chaotic hydraulics with resulting delay, which would place many individuals in shorter day lengths and lower temperatures that could cause smoltification regression.…”

“…Less energetically rich food resources in the reservoirs, including non‐native prey species, was explored for contributions to differential migration timing and survival while passing through the impounded habitats (Connor & Tiffan, 2012; Tiffan et al, 2014). Retardation of physiological smoltification, in particular, resulting in suppression of a late‐migrating smolt's urge to migrate, has also been explored for delayed migration and overwintering in the reservoirs (Tiffan et al, 2018), but whether that is a cause of delay or an effect of being delayed by changes in the migratory habitat is not known.…”