Migration Strategies of Adult Chinook Salmon Runs in Response to Diverse Environmental Conditions in the Klamath River Basin

Abstract

Biotelemetry and body temperature records of 130 adult Chinook salmon Oncorhynchus tshawytscha tagged over multiple years were used to investigate migration behaviors in response to diverse riverine conditions within the context of run timing strategies in a single river system. Four distinct runs were identified: Klamath–Trinity spring run, Trinity summer run, Klamath fall run, and Trinity fall run. Only the timing of Klamath–Trinity spring‐run and Trinity fall‐run Chinook salmon tended to prevent fish exposure to adversely high river temperatures. Faster migration rates reduced the accumulation of thermal units regardless of river temperature, especially at migration rates ≥10 km/d. Behavioral thermoregulation was minimal for all run groups (8% of all migrants), typically brief (<12 h) during summer months at nonnatal tributary confluences. Spring‐run fish migrating on the descending limb of the snowmelt peak experienced increased accumulated thermal units due to slow migration rates, resulting in more elevated relative disease risk with lower apparent migration success than rapidly migrating summer‐run fish. Klamath fall‐run fish held extensively in the lower Klamath River regardless of date or river condition, resulting in the highest cumulative thermal experience of all run groups with moderate thermal stress. Trinity fall‐run fish experienced minimal thermal stress due to their later run timing. Results demonstrate the need to comprehensively investigate fish migrations in order to detect potentially subtle but important context‐sensitive dynamics between migration behaviors and environmental conditions that can impact the viability of salmon populations. This study's findings highlight concerns regarding global warming and vulnerability runs of salmon that migrate in the late spring and early fall in the absence of adaptive shifts in run timing or appropriate human intervention. Conversely, these results also demonstrate the unexpected ability of adult Chinook salmon to migrate successfully through surprisingly warm temperatures and endure acute thermal stress if sufficiently large volumes of cold water await them at their destination.

Thermal exposure of adult Chinook salmon in the Willamette River basin

“…The protocol resulted in overestimates of maximum encountered temperatures and of warm water exposure duration in the samples relative to the overall runs. The duration component may have been offset somewhat by faster salmon migration rates in the main stem at warmer temperatures, as observed in several other adult Chinook salmon studies (Keefer et al, 2004a;Salinger and Anderson, 2006;Strange, 2012). This offset was presumably not enough to compensate for the selection bias.…”

“…However, more recent research suggests that thermal migration barriers may occur at higher thresholds in some southern populations. Just south of the Willamette basin, for example, many radio-tagged Klamath River Chinook salmon (stream-and ocean-type) initiated or continued to migrate in water temperatures Z23°C (Strange, 2010(Strange, , 2012. Just northeast of the Willamette, many Chinook salmon rapidly migrate through Columbia and Snake River reservoirs at temperatures 421°C (stream-type, Keefer et al, 2004a;ocean-type, Goniea et al, 2006).…”

“…The logger data were also used to estimate the total time that salmon were exposed to temperature Z18°C and Z20°C, two thresholds associated with thermoregulatory behaviors in adult Chinook salmon (e.g., Goniea et al, 2006;Strange, 2012) and stress responses in several adult salmon studies (e.g., McCullough et al, 2001;Eliason et al, 2011;Martins et al, 2012). Most salmon had bi-modal or otherwise non-normally distributed temperature histories and so beanplots (Kampstra, 2008) were created to visually present the data.…”

“…Temperatures in this range have been linked to a variety of stress responses and sublethal effects in adult Pacific salmon (reviews by Richter and Kolmes, 2005 ;McCullough et al, 2009;Hinch et al, 2012). Behavioral responses include migration delay or cessation (Yates et al, 2008;Caudill et al, 2013) and the use of cool-water refuges (Berman and Quinn, 1991;Goniea et al, 2006;Strange, 2012). Physiological responses include accelerated maturation (Berman, 1990;McCullough et al, 2001), depletion of energetic reserves needed to complete migration and reproduction (Brett, 1995;Lee et al, 2003;Rand et al, 2006), and increased susceptibility to several pathogens (Kocan et al, 2004;Wagner et al, 2005;Kent et al, 2013).…”

“…In this study, we reconstructed Willamette basin Chinook salmon temperature histories with radio transmitters and internal temperature loggers, a biotelemetry combination that has been used to evaluate several thermally at-risk salmon populations (e.g., Donaldson et al, 2009;Hasler et al, 2012;Strange, 2012;Caudill et al, 2013). Our first objective was to identify the location and duration of exposure to potentially stressful temperatures, defined as Z18 or Z 20°C, from values in McCullough et al (2001) and Richter and Kolmes (2005).…”