Sockeye Salmon Populations Research Articles

Evolution of age and length at maturation of Alaskan salmon under size‐selective harvest

Spatial and temporal trends and variation in life-history traits, including age and length at maturation, can be influenced by environmental and anthropogenic processes, including size-selective exploitation. Spawning adults in many wild Alaskan sockeye salmon populations have become shorter at a given age over the past half-century, but their age composition has not changed. These fish have been exploited by a gillnet fishery since the late 1800s that has tended to remove the larger fish. Using a rare, long-term dataset, we estimated probabilistic maturation reaction norms (PMRNs) for males and females in nine populations in two basins and correlated these changes with fishery size selection and intensity to determine whether such selection contributed to microevolutionary changes in maturation length. PMRN midpoints decreased in six of nine populations for both sexes, consistent with the harvest. These results support the hypothesis that environmental changes in the ocean (likely from competition) combined with adaptive microevolution (decreased PMRNs) have produced the observed life-history patterns. PMRNs did not decrease in all populations, and we documented differences in magnitude and consistency of size selection and exploitation rates among populations. Incorporating evolutionary considerations and tracking further changes in life-history traits can support continued sustainable exploitation and productivity in these and other exploited natural resources.

Alterations to dam‐spill discharge influence sex‐specific activity, behaviour and passage success of migrating adult sockeye salmon

ABSTRACTDelays in the freshwater spawning migrations of anadromous fishes at upstream barriers are well documented, but underlying mechanisms causing slowed migrations are seldom known. Using acoustic accelerometer transmitters and generalized linear models, we investigated how alterations in flow at a diversion dam in British Columbia, Canada, affected the activity, behaviour and passage success of a Fraser River sockeye salmon population (Oncorhynchus nerka). Spilling excess water through the radial gate of the dam decreased the attraction efficiency of a vertical‐slot fishway by 90% and increased delay below the dam by 2 h, which had adverse effects on passage. Relative to males, female sockeye salmon had significantly lower passage success (73% vs 94%), attraction efficiency (79% vs 100%) and passage efficiency (89% vs 94%) at a fishway, delayed longer in the dam tailrace (mean ± standard error (SE): 20·8 ± 4·1 h vs 14·6 ± 3·2 h), and resorted to anaerobic swimming efforts for a greater percentage of time (0–61·3% vs 0·7–2·7%). Given that the persistence of Pacific salmon populations relies on the spawning success of females, understanding how males and females vary in their response to modified flow regimes will improve the management of complex fish‐passage problems. Copyright © 2013 John Wiley & Sons, Ltd.

Cardiorespiratory performance and blood chemistry during swimming and recovery in three populations of elite swimmers: Adult sockeye salmon

Every year, millions of adult sockeye salmon (Oncorhynchus nerka) perform an arduous, once-in-a-lifetime migration up the Fraser River (BC, Canada) to return to their natal stream to spawn. The changes in heart rate, stroke volume, and arterio-venous oxygen extraction (i.e., factors determining rates of oxygen delivery to the tissues by the cardiovascular system) have never been directly and simultaneously measured along with whole animal oxygen uptake in a maximally swimming fish. Here, such measurements were made using three sockeye salmon populations (Early Stuart, Chilko and Quesnel), which each performed two consecutive critical swimming speed (Ucrit) challenges to provide a comprehensive quantification of cardiovascular physiology, oxygen status and blood chemistry associated with swimming and recovery. Swim performance, oxygen uptake, cardiac output, heart rate and stroke volume did not significantly vary at rest, during swimming or during recovery between populations or sexes. Despite incomplete metabolic recovery between swim challenges, all fish repeated their swim performance and similar quantitative changes in the cardiorespiratory variables were observed for each swim challenge. The high maximum cardiorespiratory performance and excellent repeat swim performance are clearly beneficial in allowing the salmon to maintain steady ground speeds and reach the distant spawning grounds in a timely manner.

Selecting for the phenotypic optimum: size‐related trade‐offs between mortality risk and reproductive output in female sockeye salmon

Summary Selection drives evolutionary changes but is often difficult to quantify and tightly link to phenotypic trait distributions in wild populations. Sampling a single population of sockeye salmon (Oncorhynchus nerka) for over a decade, we calculated the expected spawning success for females resulting from: (i) increased fecundity with body length, (ii) the mortality cost of prolonged marine residency necessary to achieve large size, (iii) size‐selective natural mortality on the spawning grounds from biotic (bear and gull predation) and abiotic (stranding) processes and (iv) exploitation by a size‐selective commercial fishery. We quantified the size‐specific probability of different modes of death and the resultant potential for successful spawning, and then modelled the theoretical relationship between female length and fitness (spawning success) in the population. This optimal distribution closely matched the observed length distribution of the focal population, when removals by the size‐selective commercial fishery were included. We then used a likelihood‐based approach to compare competing model predictions to length distributions from other populations in the watershed with different levels of size‐selective freshwater mortality, as determined by the physical characteristics of the spawning grounds. This study provides a quantitative framework for assessing female spawning success in wild populations, as represented by the expected number of eggs deposited per spawning female. These results advance previous analyses of natural selection in that predictions for phenotypic distributions were generated and then compared to those observed in situ, rather than assuming the adaptive nature of observed distributions.

Evaluating alternative methods for monitoring and estimating responses of salmon productivity in the North Pacific to future climatic change and other processes: A simulation study

We used empirically based simulation modelling of 48 sockeye salmon (O. nerka) populations to examine how reliably alternative monitoring designs and fish stock assessment methods can distinguish between changes in density-dependent versus density-independent components of productivity and identify the relative contribution of a climate-driven covariate. We explored a wide range of scenarios for ocean and freshwater conditions and the response of salmon productivity (adult recruits per spawner) to those conditions. Our results show that stock assessments based on historical relationships between salmon productivity and climate-driven oceanographic conditions will likely perform poorly when those relationships change, even when such changes are anticipated and incorporated into stock assessment models in a timely manner. Estimating the relative importance of climate-driven oceanographic influences as a driver of sockeye productivity will be difficult, especially if climatic changes occur rapidly and concurrently with other disturbances. Thus, better understanding of the mechanisms by which climatic changes and other drivers influence salmon productivity may be essential to avoid undesirable management outcomes. As well, an expansion of monitoring of juvenile salmon abundances on more salmon stocks is needed to help distinguish the effects of different drivers.

Low cardiac and aerobic scope in a coastal population of sockeye salmon Oncorhynchus nerka with a short upriver migration

This study showed that a coastal population (Harrison) of Fraser River sockeye salmon Oncorhynchus nerka had a lower aerobic and cardiac scope compared with interior populations with more challenging upriver spawning migrations, providing additional support to the idea that Fraser River O. nerka populations have adapted physiologically to their local migratory environment.

Maternal and environmental influences on egg size and juvenile life‐history traits in Pacific salmon

Life-history traits such as fecundity and offspring size are shaped by investment trade-offs faced by mothers and mediated by environmental conditions. We use a 21-year time series for three populations of wild sockeye salmon (Oncorhynchus nerka) to test predictions for such trade-offs and responses to conditions faced by females during migration, and offspring during incubation. In years when their 1100 km upstream migration was challenged by high water discharges, females that reached spawning streams had invested less in gonads by producing smaller but not fewer eggs. These smaller eggs produced lighter juveniles, and this effect was further amplified in years when the incubation water was warm. This latter result suggests that there should be selection for larger eggs to compensate in populations that consistently experience warm incubation temperatures. A comparison among 16 populations, with matching migration and rearing environments but different incubation environments (i.e., separate spawning streams), confirmed this prediction; smaller females produced larger eggs for their size in warmer creeks. Taken together, these results reveal how maternal phenotype and environmental conditions can shape patterns of reproductive investment and consequently juvenile fitness-related traits within and among populations.

Optimum and maximum temperatures of sockeye salmon (Oncorhynchus nerka) populations hatched at different temperatures

Temperature tolerance and heart rates were compared among nine sockeye salmon (Oncorhynchus nerka (Walbaum in Artedi, 1792)) populations, whose eggs were incubated at 10, 14, and 16 °C before rearing all hatchlings at a common temperature. Critical thermal maximum (CTmax) significantly differed among populations and temperature treatments. Populations with shorter migration distance and a lower migration and spawning temperature tended to have higher CTmax at 90 days posthatch. However, the relationship was reversed when fish of similar size were compared at 135–214 days posthatch. CTmax at 90 days posthatch was also positively related to body mass, which differed appreciably among populations at this development stage. With growth, the population differences in CTmax diminished from 3.1 to 1 °C. Elevated incubation temperature also decreased CTmax. Arrhenius breakpoint temperature (ABT) for maximum heart rate differed among populations incubated at 14 °C. The Chilko Lake population, which rear at 1.2 km above sea level, had the highest heart rate across all temperatures when incubated at 14 °C, but the lowest ABT among populations. This study provides clear evidence for the local adaptation among sockeye salmon populations with respect to temperature tolerance and cardiac capacity, information that adds to the debate on whether intraspecific variance is adaptive, or a constraint, or both.

Exploiting genetic diversity to balance conservation and harvest of migratory salmon

Population-based management is central to the conservation of highly exploited species. Managing to sustain population diversity is especially challenging for migratory species. The aggregate of populations of sockeye salmon (Oncorhynchus nerka) that spawn in drainages of Bristol Bay, Alaska, is the most abundant in the world and supports the largest high-value salmon fishery in North America. We applied molecular tools (genetic data from 38 single nucleotide polymorphisms, assayed in 96 populations) to detect migratory trends in stock composition of sockeye salmon returning to Bristol Bay and to inform fisheries management in real time. We reliably and repeatedly detected abundances that were unanticipated based upon preseason forecasts, fishing effort was shifted accordingly, and the fleet and local economies benefited while the risk of overharvesting weaker stocks was minimized. This approach is being developed for other species and fisheries and provides a useful model for conservation wherever migrating species are intensely managed.

Transcriptome-wide comparison of sequence variation in divergent ecotypes of kokanee salmon

BackgroundHigh throughput next-generation sequencing technology has enabled the collection of genome-wide sequence data and revolutionized single nucleotide polymorphism (SNP) discovery in a broad range of species. When analyzed within a population genomics framework, SNP-based genotypic data may be used to investigate questions of evolutionary, ecological, and conservation significance in natural populations of non-model organisms. Kokanee salmon are recently diverged freshwater populations of sockeye salmon (Oncorhynchus nerka) that exhibit reproductive ecotypes (stream-spawning and shore-spawning) in lakes throughout western North America and northeast Asia. Current conservation and management strategies may treat these ecotypes as discrete stocks, however their recent divergence and low levels of gene flow make in-season genetic stock identification a challenge. The development of genome-wide SNP markers is an essential step towards fine-scale stock identification, and may enable a direct investigation of the genetic basis of ecotype divergence.ResultsWe used pooled cDNA samples from both ecotypes of kokanee to generate 750 million base pairs of transcriptome sequence data. These raw data were assembled into 11,074 high coverage contigs from which we identified 32,699 novel single nucleotide polymorphisms. A subset of these putative SNPs was validated using high-resolution melt analysis and Sanger resequencing to genotype independent samples of kokanee and anadromous sockeye salmon. We also identified a number of contigs that were composed entirely of reads from a single ecotype, which may indicate regions of differential gene expression between the two reproductive ecotypes. In addition, we found some evidence for greater pathogen load among the kokanee sampled in stream-spawning habitats, suggesting a possible evolutionary advantage to shore-spawning that warrants further study.ConclusionsThis study provides novel genomic resources to support population genetic and genomic studies of both kokanee and anadromous sockeye salmon, and has the potential to produce markers capable of fine-scale stock assessment. While this RNAseq approach was successful at identifying a large number of new SNP loci, we found that the frequency of alleles present in the pooled transcriptome data was not an accurate predictor of population allele frequencies.

Landscape heterogeneity and local adaptation define the spatial genetic structure of Pacific salmon in a pristine environment

Identifying the spatial distribution of genetic variation across the landscape is an essential step in informing species conservation. Comparison of closely related and geographically overlapping species can be particularly useful in cases where landscape may similarly influence genetic structure. Congruent patterns among species highlight the importance that landscape heterogeneity plays in determining genetic structure whereas contrasting patterns emphasize differences in species-specific ecology and life-history or the importance of species-specific adaptation to local environments. We examined the interacting roles of demography and adaptation in determining spatial genetic structure in two closely related and geographically overlapping species in a pristine environment. Using single nucleotide polymorphism (SNP) loci exhibiting both neutral and putative adaptive variation, we evaluated the genetic structure of sockeye salmon in the Copper River, Alaska; these data were compared to existing data for Chinook salmon from the same region. Overall, both species exhibited patterns of isolation by distance; the spatial distribution of populations largely determined the distribution of genetic variation across the landscape. Further, both species exhibited largely congruent patterns of within- and among-population genetic diversity, highlighting the role that landscape heterogeneity and historical processes play in determining spatial genetic structure. Potential adaptive differences among geographically proximate sockeye salmon populations were observed when high FST outlier SNPs were evaluated in a landscape genetics context. Results were evaluated in the context of conservation efforts with an emphasis on reproductive isolation, historical processes, and local adaptation.

Early marine growth of juvenile Fraser River sockeye salmon (Oncorhynchus nerka) in relation to juvenile pink (Oncorhynchus gorbuscha) and sockeye salmon abundance

Mortality of salmon in the ocean is considered to be greatest during the first few months and that its magnitude is an inverse of growth. First year marine growth (M1) in two Fraser River sockeye salmon ( Oncorhynchus nerka ) populations was positively correlated, reflecting a shared oceanic experience as postsmolts. M1 declined abruptly in both populations after 1977, corresponding to a well-documented change in climate. The reduction in average M1 was not accompanied by a detectable reduction in average survival. In both populations, M1 was significantly greater in even years when juvenile pink salmon ( Oncorhynchus gorbuscha ) are abundant in the Strait of Georgia, suggesting that interspecific competition there has little effect on M1. All correlations of M1 with regional pink salmon or sockeye salmon abundances, lagged to align ocean entry years, were negative, but few (pink) or none (sockeye) were statistically significant. The negative correlations were due to the long-term changes (pink salmon abundance increasing, sockeye M1 smaller). Odd year dominance of juvenile pink salmon in northern British Columbia, Canada, is persistent and corresponds with the biennial pattern of M1 variation in Fraser River sockeye salmon and may be the source of the significant odd–even year line effect on M1.

Reliability of Indicators of Decline in Abundance

Although there are many indicators of endangerment (i.e., whether populations or species meet criteria that justify conservation action), their reliability has rarely been tested. Such indicators may fail to identify that a population or species meets criteria for conservation action (false negative) or may incorrectly show that such criteria have been met (false positive). To quantify the rate of both types of error for 20 commonly used indicators of declining abundance (threat indicators), we used receiver operating characteristic curves derived from historical (1938-2007) data for 18 sockeye salmon (Oncorhynchus nerka) populations in the Fraser River, British Columbia, Canada. We retrospectively determined each population's yearly status (reflected by change in abundance over time) on the basis of each indicator. We then compared that population's status in a given year with the status in subsequent years (determined by the magnitude of decline in abundance across those years). For each sockeye population, we calculated how often each indicator of past status matched subsequent status. No single threat indicator provided error-free estimates of status, but indicators that reflected the extent (i.e., magnitude) of past decline in abundance (through comparison of current abundance with some historical baseline abundance) tended to better reflect status in subsequent years than the rate of decline over the previous 3 generations (a widely used indicator). We recommend that when possible, the reliability of various threat indicators be evaluated with empirical analyses before such indicators are used to determine the need for conservation action. These indicators should include estimates from the entire data set to take into account a historical baseline.

The Efficacy of Reservoir Flow Regulation for Cooling Migration Temperature for Sockeye Salmon in the Nechako River Watershed of British Columbia

AbstractSince the early 1980s, a water temperature management program has been in existence on the Nechako River system in central British Columbia, Canada. The program releases water based on anticipated meteorological conditions in an attempt to prevent temperature from exceeding a specified threshold of 20°C downstream during a period when spawning migrations of sockeye salmon Oncorhynchus nerka are in the Nechako River. Since the inception of the program, this threshold has been exceeded only rarely; however, the variables that influence water temperature and that are used to manage water releases in the Nechako River watershed have not been subject to an independent analysis. Increasing demand for water at other times of year and a desire to restore a more natural hydrograph to the river to meet other ecological demands have impelled this analysis. A principal components analysis that examined the factors contributing to river temperature demonstrated that the summer controlled flow releases accounted for 24% of the temperature variability and were probably a factor in maintaining compliance with the program's temperature threshold. Furthermore, during most summers, the Nechako River provided a cooling influence to input from the Stuart River tributary in a downstream reach that is used by the majority of the migrating sockeye salmon. Water temperature has a modest influence on prespawning mortality (up to 22% of the variability), suggesting that attempts to reduce summer water temperatures through releases in the upper Nechako River watershed can mitigate against poor spawning success of sockeye salmon populations that migrate through the lower reaches of the system.Received April 19, 2011; accepted December 9, 2011

Population-Specific Consequences of Fisheries-Related Stressors on Adult Sockeye Salmon

The objective of this study was to determine whether fisheries-related stressors differently influence two populations of adult sockeye salmon (Oncorhynchus nerka) with shared migration timing and location but where one population (i.e., Harrison) spawns 1 mo after the other (i.e., Weaver). Four stressor treatments were used following beach seine capture: (1) immediate release, (2) release after 10-15 min in the beach seine, (3) an additional 3-min gill net entanglement and 1-min air exposure, and (4) an additional 3-min tangle net simulation and 1-min air exposure. A comprehensive acoustic telemetry array and manual tracking revealed that survival was low overall, with more Weaver fish (34.2% of 38 tagged) reaching spawning areas compared to Harrison fish (17.8% of 78 tagged). For the Harrison population but not the Weaver, the gill net treatment influenced immediate (i.e., survived treatment) and short-term (i.e., 5-d postrelease) survival as well as survival to reach spawning areas. Harrison fish were more likely to be injured by the treatment, and reflex impairment predicted their short-term and long-term survival. Physiological condition did not differ between populations at the time of release, although both populations showed signs of severe physiological disturbances from the gill and tangle net simulations. These results suggest that even short durations of gill or tangle net entanglement can result in profound population-specific physiological disturbances and mortality. The notion that there can be population-specific variation in response to fisheries encounters adds complexity to management and provides further evidence for intraspecific differences in migration success.

Multi‐century reconstructions of Pacific salmon abundance from climate‐sensitive tree rings in west central British Columbia, Canada

ABSTRACTShort records of naturally fluctuating Pacific salmon (Oncorhynchus spp.) populations elicit challenges for the long‐term management of North American fisheries. A dendrochronologic approach was used to reconstruct long proxy histories of regional Pacific salmon populations returning to streams along west central British Columbia coastlines. Tree rings from five tree species collected at 18 sites were found to be sensitive to interannual fluctuations in large‐scale ocean and atmospheric circulation patterns. Using a regional network of climate‐sensitive ring‐width and ring‐density tree‐ring chronologies in linear regression models, multi‐century long‐term abundance records for populations of sockeye, chinook, chum and pink salmon were generated. Models explained between 27% and 39% of the variability in escapement records and were more proficient at capturing trends than annual magnitudes. The reconstructions vary in length, dating from 1400, 1536 and 1638 ad and extending to 2009 ad. Notable fluctuations in salmon abundance over the past six centuries are described, with significant population collapses shown to occur during the early 1400s, the late 1500s, the mid‐1600s, the early 1700s, the early 1800s and parts of the 1900s. These models are the first to utilize climate‐sensitive tree‐ring records to reconstruct regional abundance histories and thus contribute potentially valuable information for salmon fisheries managers. Copyright © 2012 John Wiley & Sons, Ltd.

Resurrecting an extinct salmon evolutionarily significant unit: archived scales, historical DNA and implications for restoration

Archival scales from 603 sockeye salmon (Oncorhynchus nerka), sampled from May to July 1924 in the lower Columbia River, were analysed for genetic variability at 12 microsatellite loci and compared to 17 present-day O.nerka populations-exhibiting either anadromous (sockeye salmon) or nonanadromous (kokanee) life histories-from throughout the Columbia River Basin, including areas upstream of impassable dams built subsequent to 1924. Statistical analyses identified four major genetic assemblages of sockeye salmon in the 1924 samples. Two of these putative historical groupings were found to be genetically similar to extant evolutionarily significant units (ESUs) in the Okanogan and Wenatchee Rivers (pairwise F(ST) = 0.004 and 0.002, respectively), and assignment tests were able to allocate 77% of the fish in these two historical groupings to the contemporary Okanogan River and Lake Wenatchee ESUs. A third historical genetic grouping was most closely aligned with contemporary sockeye salmon in Redfish Lake, Idaho, although the association was less robust (pairwise F(ST) = 0.060). However, a fourth genetic grouping did not appear to be related to any contemporary sockeye salmon or kokanee population, assigned poorly to the O.nerka baseline, and had distinctive early return migration timing, suggesting that this group represents a historical ESU originating in headwater lakes in British Columbia that was probably extirpated sometime after 1924. The lack of a contemporary O.nerka population possessing the genetic legacy of this extinct ESU indicates that efforts to reestablish early-migrating sockeye salmon to the headwater lakes region of the Columbia River will be difficult.

Some consequences of Pacific salmon hatchery production in Kamchatka: changes in age structure and contributions to natural spawning populations

Aggregate hatchery production of Pacific salmon in the Kamchatka region of the Russian Federation is very low (< 0.5% of total harvest, with five hatcheries releasing approximately 41 M juvenile salmon annually), but contributions in certain rivers can be substantial. Enhancement programs in these rivers may strongly influence fitness and production of wild salmon. In this paper we document significant divergence in demographic traits in hatchery salmon populations in the Bolshaya River and we estimate the proportion of hatchery chum salmon in the total run in the Paratunka River to demonstrate the magnitude of enhancement in this system. We observed a reduction in the expression of life history types in hatchery populations (ranging from 1 to 9 types) compared to wild populations (17 types) of sockeye salmon in the Bolshaya River. We found similar trends in Chinook salmon in the same river system. This reduced life history diversity may make these fish less resilient to changes in habitat and climate. We estimate hatchery chum salmon currently contribute 17-45% to the natural spawning population in the Paratunka River. As hatchery fish increase in numbers at natural spawning sites, this hatchery production may affect wild salmon production. It is important to investigate the risk of introgression between hatchery and wild salmon that can lead to reduction in salmon fitness in Kamchatka rivers, as well as the potential of ecological interactions that can have consequences on status of wild salmon and overall salmon production in this region.

Survival of Endangered Snake River Sockeye Salmon Smolts from Three Idaho Lakes: Relationships with Parr Size at Release, Parr Growth Rate, Smolt Size, Discharge, and Travel Time

AbstractIn 1991, Snake River sockeye salmon Oncorhynchus nerka were listed as endangered. The Sawtooth Valley Project was initiated to conserve and rebuild sockeye salmon populations that historically spawned and reared in five Sawtooth Valley lakes designated as critical habitat in central Idaho. We evaluated smolt survival of sockeye salmon that were stocked as parr into Redfish, Pettit, and Alturas lakes. Smolt travel time, residuals of Salmon River discharge and smolt travel time, and specific growth rate of parr explained 58% of the variation in smolt survival in a multiple‐regression model. Smolt survival was inversely related to smolt travel time, and travel time was negatively correlated with mean May discharge in the Salmon River at Salmon, Idaho. We were particularly interested in the relationships between smolt survival and parr size at release, smolt size at migration, and parr growth rate. Smolt survival from nursery lakes to Lower Granite Dam was negatively correlated with mean parr size at release and mean smolt size at emigration. Smaller parr and smolts survived better. Smolt survival to the dam was correlated with parr growth rates in the three lakes combined; the relationship was nonlinear. Smolt survival increased as specific growth rate increased up to 0.06% per day, but further increases in growth rate were associated with reductions in survival. Absolute growth rates of parr were negatively related to parr weight at release. Smaller individuals grew faster than larger individuals, apparently as a result of size‐dependent metabolic demand and prey availability. The relationships between smolt survival and parr size, smolt size, and parr growth rate differed among lakes. These data suggest that successful migrants must at least maintain weight during the winter preceding migration and that the stocking of smaller parr with lower metabolic demand may be preferable to stocking larger parr when forage is limited.Received November 18, 2010; accepted June 1, 2011

Analysis of gene origin in the first adult returns to the Cultus sockeye salmon captive breeding program

Rigorous evaluation of the utility of captive breeding for the restoration of depleted wild salmonid fish populations has not been undertaken. In particular, little is known about the reproductive success of captively-bred individuals that are released back into an extant population and their capacity to assist in long-term population persistence. For the endangered Cultus Lake sockeye salmon population, we examined the potential genetic contribution of the first juvenile fish released from a captive breeding program upon their maturity in the natural Cultus Lake environment. Genetic analysis of 792 Cultus sockeye salmon that were spawned in captivity in 2004 and their adult progeny of 2007 and 2008 revealed a genetic bottleneck originating from 20 wild sockeye salmon hatchery-spawned at Cultus Lake in the previous generation. Pedigree analysis revealed that six of the 20 sockeye salmon spawned in 2001 (grandparents) gave rise to a majority of the hatchery spawners in 2004 (parents) and provided more than 30% of the genes in the progeny that survived to maturity in the wild. Allele frequencies and genetic diversity of the age three progeny that returned to Cultus Lake from their marine migration in 2007 reflected the bottleneck, but its genetic signature was faint among the more genetically diverse age four fish that returned in 2008. Two-generation analysis of gene origin among fish resulting from 2004 hatchery production indicated that they contained the genetic diversity expected from 36 effective ancestors.