Populations Of Fall Chinook Salmon Research Articles

The incorporation of environmentally derived 87Sr/86Sr and Sr/Ca in early otolith formation of Chinook salmon

AbstractEffective species management often requires understanding patterns of movement and habitat use. A common approach in identifying where individuals reside relies upon chemical tracers from the environment that are incorporated into an individual's tissues. For fish, isotopes in their otoliths, specifically the portion of their otolith formed during their larval stage, have been used to identify the natal origin. Complicating this work, however, is the fact that during this life stage, there is a shift in the source of isotopes deposited onto the growing otolith from maternally to environmentally derived. The objective of this study was to identify the portion of the otolith representing this transition to environmentally derived isotopes so as to accurately investigate questions of natal origin for a threatened population of fall Chinook salmon (Oncorhynchus tshawytscha). We exposed developing larvae to four treatments that differed in terms of their water strontium isotope ratio (87Sr/86Sr) and used change‐point analysis of otolith 87Sr/86Sr and strontium to calcium ratio (Sr/Ca) to identify the otolith radius corresponding to the transition to environmentally derived isotopes. Our results indicated this transition occurred, on average, at 132 μm (87Sr/86Sr; ±50 μm standard deviation) and 127 μm (Sr/Ca; ±29 μm) from the otolith core, which corresponded to the developmental time between hatching and exogenous feeding. A substantial proportion of our otoliths (i.e., 61%) did not show convergence between otolith and water 87Sr/86Sr by the end of the 113‐day experiment, which was likely due to the dietary contribution of marine‐based feed. Therefore, we were unable to recommend an otolith radius to target for the purposes of reconstructing natal origin apart from being beyond approximately 130 μm.

Juvenile river residence and performance of Snake River fall Chinook salmon

AbstractAn animal's performance during its early life stage can greatly influence its survival to adulthood. Therefore, understanding aspects of early life history can be informative, particularly when designing management plans to rebuild a population. For a threatened population of fall Chinook salmon (Oncorhynchus tshawytscha) in the Snake River of Idaho, we reconstructed the early life history for 124 returning wild and hatchery adults using information recorded in their otoliths. Of our sampled wild adults (n = 61), 43% and 49% reared within the Snake River and Clearwater/Salmon rivers. We also found that only 21% of our sampled wild adults exhibited the historically common subyearling out‐migration strategy, in which juveniles exit freshwater shortly after hatching, while the remaining wild adults exhibited the yearling out‐migration strategy (i.e., individuals delay their freshwater exit). As expected, yearlings had, on average, a significantly larger body size than subyearlings at ocean entry. However, 35% of wild yearlings overlapped in size with wild subyearlings suggesting that spending more time in freshwater might not necessarily result in a larger body size. Lastly, we observed that variability in fork length at Snake River egress and ocean entry were best explained by migration strategy and where it reared, followed by hatch year and sex. Results from this study highlight the utility of adult otoliths in providing details about early life history, an understanding of which is critical to the conservation of Snake River fall Chinook salmon.

Effect of hydroelectric dam operations on the freshwater productivity of a Columbia River fall Chinook salmon population

Altering the timing and magnitude of discharge fluctuations can minimize the adverse effects of operating hydroelectric dams on the productivity of downstream salmon populations. Hydroelectric operations at Priest Rapids Dam during the mid-1970s resulted in dewatering of fall Chinook salmon (Oncorhynchus tshawytscha) redds, causing mortality of intragravel life stages. Since then, a series of operational constraints have been implemented at Priest Rapids Dam to reduce the effects of discharge fluctuations on the population of fall Chinook salmon that spawns and rears downstream from the dam. Initial protections that focused on preventing redd dewatering were subsequently increased to include postemergence life stages. We used stock–recruit analyses to identify changes to the population’s freshwater productivity that occurred over a 30-year period and coincided with changes to dam operations. We observed a 217% increase in productivity that corresponded with constraints enacted to prevent redd dewatering and an additional 130% increase that coincided with enactment of constraints to limit stranding and entrapment of juveniles. The information gained from this study may be used to guide efforts elsewhere to mitigate the effects of hydroelectric dam operations on downstream fish populations.

Spatial structuring of an evolving life-history strategy under altered environmental conditions

Human disturbances to ecosystems have created challenges to populations worldwide, forcing them to respond phenotypically in ways that increase their fitness under current conditions. One approach to examining population responses to disturbance in species with complex life histories is to study species that exhibit spatial patterns in their phenotypic response across populations or demes. In this study, we investigate a threatened population of fall chinook salmon (Oncorhynchus tshawytscha) in the Snake River of Idaho, in which a significant fraction of the juvenile population have been shown to exhibit a yearling out-migration strategy which had not previously been thought to exist. It has been suggested that dam-related environmental changes may have altered the selective pressures experienced by out-migrating fall chinook, driving evolution of a later and more selectively advantageous migration strategy. Using isotopic analysis of otoliths from returning adult spawners, we reconstructed the locations of individual fish at three major juvenile life stages to determine if the representation of the yearling life history was geographically structured within the population. We reconstructed juvenile locations for natal, rearing and overwintering life stages in each of the major spawning areas in the basin. Our results indicate that the yearling life-history strategy is predominantly represented within one of the main spawning regions, the Clearwater River, rather than being distributed throughout the basin. Previous studies have shown the Clearwater River to have cooler temperatures, later hatch dates, and later outmigration of juveniles, indicating a link between environment and expression of the yearling life history. Our data suggest that this new yearling life history may be disproportionally represented in returning adult spawners, indicating selection for this life history within the population.

Implications of Mark‐Selective Fishing for Ocean Harvests and Escapements of Sacramento River Fall Chinook Salmon Populations

AbstractThe need to protect imperiled salmon stocks along the Pacific coast of North America has led to an increasing use of mark‐selective fisheries (MSFs) as a management strategy to reduce harvest mortality of wild salmon while allowing harvest of abundant hatchery salmon. However, MSFs remain untested in ocean fisheries for Chinook salmon Oncorhynchus tshawytscha off the coasts of California and Oregon, where hatchery fish have been estimated to compose the majority of Chinook salmon but where harvests have been restricted to protect several imperiled stocks. We developed a quantitative framework based on conventional cohort models to examine how aggregate ocean harvest and in‐river escapement of Sacramento River fall‐run Chinook salmon, the numerically dominant stock in the region, would have differed under MSF scenarios compared with the historic, traditional fishery. At historic contact rates (fishing effort) for 1988–2007, we estimated that annual in‐river escapement of natural‐origin fish would have increased by 119% on average under MSF scenarios, while reductions in harvest would have been inversely proportional to the fraction of hatchery‐origin fish. During the more recent period of constrained fishing (2001–2007), we estimated MSF outcomes for a range of plausible contact rates (40–60% of age‐4 fish) and hatchery fractions (40–80% of Chinook salmon). The combination of these factors determined the magnitude of estimated harvest reductions or gains under MSFs, with total MSF harvest (2001–2007) ranging from 46% lower to 48% higher than historic harvest. Increases in total escapement of natural‐origin fish (2001–2007) under MSFs ranged from 24% to 48% depending on the contact rate. Comparisons between the traditional fishery and simulated MSF outcomes were robust to a wide range of cohort parameter values, suggesting that our aggregate results provide useful insights into potential MSF outcomes and the effects of key uncertainties.Received November 1, 2010; accepted December 19, 2011

Evaluation of Early Life Stage Fall Chinook Salmon Exposed to Hexavalent Chromium from a Contaminated Groundwater Source

We conducted a laboratory evaluation to assess the risk to early life stage (i.e., eyed egg to swim up) fall Chinook salmon (Oncorhynchus tshawytscha) for exposure to hexavalent chromium from a contaminated groundwater source. Local populations of fall Chinook salmon were exposed to Hanford Site source groundwater that was diluted with Columbia River water. Specific endpoints included survival, development rate, and growth. Tissue burdens of fish were also measured to estimate uptake and elimination rates of chromium. Survival, development, and growth of early life stage fall Chinook salmon were not adversely affected by extended exposures (i.e., 98 day) to hexavalent chromium ranging from 0.79 to 260 microg/l. Survival for all treatment levels and controls exceeded 98% at termination of the test. In addition, there were no differences among the mean lengths and weights of fish among all treatment groups. Whole-body concentrations of chromium in early life stage fall Chinook salmon had a typical dose-response pattern; i.e., those subjected to highest exposure concentrations and longest exposure intervals had higher tissue concentrations. Given the spatial extent of chromium concentrations at the Hanford Site, and the dynamics of the groundwater-river water interface, the current cleanup criterion of 10 microg/l chromium appear adequate to protect early life stage fall Chinook salmon. These findings, together with previous research indicate low risk to these populations.

Upstream Migration of Minijack (Age‐2) Chinook Salmon in the Columbia River: Behavior, Abundance, Distribution, and Origin

AbstractIt has recently been demonstrated that a large percentage of yearling Chinook salmon Oncorhynchus tshawytscha smolts released from a production‐scale hatchery on the Yakima River display an underappreciated life history strategy. Instead of migrating to the ocean for long‐term rearing and growth, males may instead undertake a short‐term migration downstream, turn around, and migrate back upstream where they reproductively mature at age 2. Following local hatchery traditions, these fish are referred to as “minijacks.” We used information produced from (1) large‐scale passive integrated transponder (PIT)‐tagging programs at hatcheries in the Columbia and Snake River basins and (2) the installation of PIT tag detectors in the fish passage ladders built into dams on these rivers to investigate the occurrence, behavior, distribution, and origin of minijacks. A minijack was operationally defined as a fish detected in a ladder after 1 June in the same year it was released. Minijacks were found in every hatchery release group of more than 7,500 PIT‐tagged Chinook salmon smolts reported (2002, 13 groups; 2003, 15 groups). Minijack population migration upstream past Bonneville Dam peaked in late June and July. This lagged migrations of age‐4 adults (from the same populations) by approximately 2 months. However, minijacks also displayed population‐specific variation in timing of upstream migrations past Bonneville Dam; minijacks from spring Chinook salmon populations appeared before fall Chinook salmon populations. Detection rates of minijacks at all dams ranged from 0.02% to 0.33% of the total smolts released for different hatchery groups. Expansion of this rate, based on the relation between minijack estimates at Cle Elum Hatchery (before release) and detections at Bonneville Dam (after release), suggests that minijack abundance in the Columbia and Snake River basins exceed hundreds of thousands of fish.

Habitat quality of historic Snake River fall Chinook salmon spawning locations and implications for incubation survival. Part 2: intra-gravel water quality

Reintroduction of fall Chinook salmon into the Swan Falls Reach of the Snake River is of regional interest; however, water quality has been considerably degraded. We examined the quality of the incubation environment within historic spawning sites by monitoring temperature, dissolved oxygen (DO) and the presence of hydrogen sulphide (H2S) within the water column, the undisturbed hyporheic zone, and simulated redds, during two annual periods representative of fall through spring incubation periods. The hydrographs of the two years differed, with year one representative of high flows and year two of low flows. The thermal regime during the two years also differed: year one was warmer overall than year two. Water column DO remained near saturation throughout both years. Within the undisturbed hyporheic, DO was lower than in the water column during both years, and quickly decreased to relatively anoxic conditions. During both years, the DO within simulated redds remained sufficiently high (> 7.0 mg l−1) to support fall Chinook incubation through the hatch phase of development. However, as each incubation season progressed, conditions in simulated redds decreased to less than 6.0 mg l−1 prior to the estimated beginning of emergence, and tended toward levels less than 4.0 mg l−1 prior to the estimated completion of emergence. Hydrogen sulphide was detected at highly toxic levels in the hyporheic zone and within some simulated redds during both years. Depressed DO conditions and the presence of H2S within simulated redds prior to, and throughout the period of estimated emergence suggest that survival of incubating salmon in the Swan Falls reach would be variable and low, and that relative survival would not be sufficient to support the reintroduction and sustainability of a viable population of fall Chinook salmon to that reach. Copyright © 2005 John Wiley & Sons, Ltd.

Comparison of mainstem spawning habitats for two populations of fall chinook salmon in the Columbia River basin

Comparison of mainstem spawning habitats for two populations of fall chinook salmon in the Columbia River basin

Comparison of mainstem spawning habitats for two populations of fall chinook salmon in the Columbia River basin

Extensive hydroelectric development in the Columbia River system has eliminated most mainstem riverine habitat available for spawning by fall chinook salmon (Oncorhynchus tshawytscha). The two remaining populations, Hanford Reach, Columbia River and Hells Canyon Reach, Snake River, are separated geographically and their status is markedly different. Annual escapements to Hanford Reach have averaged approximately 80 000 adults, while the Snake River run size has declined to <1500 adults over the past 10 years. We compared their spawning habitat characteristics over a range of measurement scales, as a means to identify strategies for rebuilding the weak Snake River population. Physical habitat characteristics of redds were similar for both study areas. Redd locations were correlated with channel characteristics, such as braiding and sinuosity. Several differences between the two spawning areas were identified at the watershed scale: the Hells Canyon Reach had a much steeper longitudinal gradient, was largely confined by bedrock, and had a more variable flow regime. These features are controlling variables that operate at the reach-scale to limit the availability and size of substrate and other conditions that influence egg deposition and incubation survival. Geomorphological characteristics of the two study sites are sufficiently different to indicate that the production potential of the Hells Canyon Reach population is markedly lower than that of the Hanford Reach population. Copyright © 2000 John Wiley & Sons, Ltd.

Status of Fall Chinook Salmon Populations in the Mid-Columbia River, 1948–1992

Abstract Historically, fall Chinook salmon Oncorhynchus tshawytscha spawned in the main-stem Columbia River over a distance of approximately 900 km. However, because of hydroelectric development and other human activities, most natural production of upriver stocks of fall Chinook salmon (upriver bright, URB) is now restricted to a 90-km-long section of river known as the Hanford Reach. The adjacent Hanford Nuclear Reservation was managed for production of nuclear materials from 1943 to 1971, which restricted many development activities, including additional hydroelectric projects. Aerial counts of fall Chinook salmon redds since 1948 at the Hanford Reach provide an index of relative abundance among spawning areas and years. Redd counts during peak spawning were less than 1,000 annually from 1948 to 1961, but they increased to as high as 8,800 in 1989 following construction of several main-stem dams on both the Columbia and Snake rivers. Escapement of adult fall Chinook salmon to the Hanford Reach averaged...

Social Interaction Between Juvenile Coho (Oncorhynchus kisutch) and Fall Chinook Salmon (O. tshawytscha) in Sixes River, Oregon

Spawning and emergence of coho and fall chinook salmon overlapped in timing and location in Sixes River, Oregon. In early spring both species were distributed throughout most of the river system. Underwater observations during this period indicated that both species occupied the same habitat. As temperatures increased, coho disappeared from the main river, but continued to occupy cool tributaries. Fall chinook were found primarily in the main river until early summer, when they moved to the estuary.In flowing-water observation troughs coho assumed social dominance and defended space near the source of incoming food. In allopatry in the troughs, both grew at similar rates, but coho maintained lower population densities than did chinook. In sympatry in the troughs or in cool tributary streams, coho grew faster than chinook. Coho had brighter fin and body colors, greater fin development, deeper bodies, and were heavier than fall chinook of the same length.Our study suggests that the population of fall chinook salmon in Sixes River might be adversely affected by an increase in numbers of coho. Our evidence suggests that ecology of native fishes should be examined closely before widespread manipulation of fish stocks is encouraged.