Steelhead Populations Research Articles

Effects of Entrainment and Bypass at Screened Irrigation Canals on Juvenile Steelhead

AbstractExpensive bypass screens have been installed throughout the western United States to prevent the entrainment of valuable anadromous salmonids into irrigation canals. However, few studies have quantified the annual extent and variability of entrainment and bypass success for anadromous salmonids emigrating through screened irrigation diversion networks in a basinwide context. By monitoring the movement of hatchery steelhead Oncorhynchus mykiss surrogates marked with passive integrated transponder tags through three irrigation canals, we estimated canal entrainment, bypass success, and survival for threatened juvenile steelhead emigrating from the Umatilla River in northeast Oregon. Annual entrainment of steelhead was positively related to the days of canal operation and negatively related to mean seasonal river flow. The relationship between flow and entrainment differed by canal; as a result, steelhead entrainment was not always greatest at canals with the largest water diversion rates. Binary models (steelhead entrainment or no entrainment) that best described daily entrainment depicted the influence of annual differences in river flows on canal entrainment and indicated that this relationship can change under different values of thermal experience (sum of daily mean temperatures). Most of the entrained hatchery steelhead (range = 97–100%) were returned to the river by screened bypasses, even when large percentages of the steelhead population were entrained. Based on similarities in movement, hatchery steelhead were good surrogates for the entrainment of naturally reared steelhead. We estimated that the three fish screens in the Umatilla River basin prevented losses of up to 25% of the steelhead population to irrigation canals over 5 years. Interannual variability in fish entrainment should be considered when monitoring irrigation canals, and managers should not necessarily limit entrainment monitoring or screening projects to canals that divert the most water.

Population Structure and Run Timing of Steelhead in the Skeena River, British Columbia

Identification of population-specific run timing is an important component of salmonid fisheries management and was a major focus of our study. Population structure of steelhead Oncorhynchus mykiss was examined in the Skeena River of northern British Columbia. Variation at 14 microsatellites was surveyed in 3,062 steelhead sampled from 17 populations in the drainage. During 1998–2010, 6,691 individuals were sampled in a lower river test fishery to obtain information on relative abundance and time of arrival of specific populations near the river mouth. The genetic differentiation index F ST calculated over all populations and loci was 0.021; individual locus values ranged from 0.017 to 0.045. Differentiation in steelhead allele frequencies among populations was approximately 14 times the differentiation observed among years within populations. A regional structuring of populations was the general pattern observed, with steelhead populations from the upper portion of the drainage clustering together in 87% of dendrograms evaluated and those in the lower portion of the drainage clustering together in 100% of dendrograms. The 17 populations sampled were arranged in nine reporting groups for genetic stock identification applications. The estimated stock composition of a simulated known-origin mixture was within 2% of the correct estimate for seven of the nine reporting groups present in the mixture. The stock composition of an actual known-origin sample was estimated within 2% of the correct estimate for eight of the nine reporting groups present. Application to actual samples from the test fishery indicated that upper drainage populations generally migrated through the lower river earlier than other populations, whereas lower river populations typically migrated later. Genetic mixed-stock analysis can assist managers in regulating fisheries to maintain productivity of Skeena River steelhead. Received July 25, 2011; accepted December 15, 2011

Movement of Resident Rainbow Trout Transplanted below a Barrier to Anadromy

AbstractWe tracked the movement of resident coastal rainbow trout Oncorhynchus mykiss irideus that were experimentally transplanted below a migration barrier in a northern California stream. In 2005 and 2006, age‐1 and older rainbow trout were captured above a 5‐m‐high waterfall in Freshwater Creek and individually marked with passive integrated transponder tags. Otolith microchemistry confirmed that the above‐barrier trout were the progeny of resident rather than anadromous parents, and genetic analysis indicated that the rainbow trout were introgressed with cutthroat trout O. clarkii. At each of three sampling events, half of the tagged individuals (n = 22 and 43 trout in 2005 and 2006, respectively) were released 5 km downstream from the waterfall (approximately 10 km upstream from tidewater), and an equal number of tagged individuals were released above the barrier. Tagged individuals were subsequently relocated with stationary and mobile antennae or recaptured in downstream migrant traps, or both, until tracking ceased in October 2007. Most transplanted individuals remained within a few hundred meters of their release location. Three individuals, including one rainbow trout released above the waterfall, were last detected in the tidally influenced lower creek. Two additional tagged individuals released above the barrier were found alive in below‐barrier reaches and had presumably washed over the falls. Two of seven tagged rainbow trout captured in downstream migrant traps had smolted and one was a presmolt. The smoltification of at least some individuals, coupled with above‐barrier “leakage” of fish downstream, suggests that above‐barrier resident trout have the potential to exhibit migratory behavior and to enter breeding populations of steelhead (anadromous rainbow trout) within the basin.

Fine‐Scale Population Genetic Structure and Dispersal of Juvenile Steelhead in the Bulkley‐Morice River, British Columbia

AbstractA knowledge of fine‐scale population genetic structure and patterns of dispersal is an essential component of any action to conserve genetic diversity and maintain population viability. We genotyped 417 juvenile steelhead Oncorhynchus mykiss from the main stem and tributaries of the Bulkley–Morice River, British Columbia, at 10 microsatellite loci to assess fine‐scale population structure and the patterns and magnitude of juvenile dispersal and mixing. We detected significant genetic structuring among juvenile steelhead from seven tributaries of the Bulkley–Morice River (pairwise FST: 0.008–0.156) and found significant isolation by distance among the tributary populations (R2 = 0.198, P = 0.038). These results reflect the homing behavior of spawning adults as well as the temporal stability of those populations. Genotype assignment of tributary‐caught juveniles showed that rates of juvenile dispersal varied among tributaries. The assignment of juveniles sampled from the main stem of the river to source tributary populations suggested that long‐distance movement in juvenile steelhead is common and that juveniles are well mixed in the main stem. Dispersal and fine‐scale genetic structure in pristine steelhead populations are more complex than previously thought. Therefore, actions to conserve Bulkley–Morice River steelhead must strive to maintain the genetic diversity of tributary populations.

Smoltification in an Impounded, Adfluvial Redband Trout Population Upstream from an Impassable Dam: Does It Persist?

AbstractThis study evaluated whether a population of adfluvial redband trout Oncorhynchus mykiss gairdnerii (a subspecies of rainbow trout) in Mann Creek and Reservoir, southwestern Idaho, continues to undergo smoltification. This population had an anadromous component before the construction of main‐stem and tributary dams in 1958 and 1967, respectively. Smoltification was assessed by quantifying the proportion of juvenile migrants that displayed high skin reflectance, comparing mean gill Na+,K+‐ATPase activity among migrants, and examining migration timing compared with that of neighboring steelhead (anadromous rainbow trout) populations. Approximately one‐quarter of the 1,502 juvenile migrants trapped and examined displayed the intermediate or high skin reflectance (nonbanded silvery coloration) characteristic of smolts; the other fish maintained a banded coloration more typical of resident fish. For 78 samples of gill filaments over the course of the migration season (18 March to 3 June), Na+,K+‐ATPase activity varied considerably among fish (0.95–5.81 μmol Pi · h−1 · mg protein−1) and doubled in nonbanded fish over the course of the migration period. ATPase activity was significantly higher for nonbanded fish than for banded fish at the end of the migration period (21 May – 4 June). Juvenile adfluvial redband trout migrated from Mann Creek in approximate synchrony with neighboring steelhead populations. These results suggest the possibility that in areas in the Snake River drainage where steelhead have been extirpated as a result of artificial barriers, remnant populations retain the potential for anadromy.

Resilience and Water Governance: Adaptive Governance in the Columbia River Basin

The 1964 Columbia River Treaty between the United States and Canada is currently under review. Under the treaty, the river is jointly operated by the two countries for hydropower and is the largest producer of hydropower in the western hemisphere. In considering the next phase of international river governance, the degree of uncertainty surrounding the drivers of change complicates efforts to predict and manage under traditional approaches that rely on historical ecosystem responses.At the same time, changes in social values have focused attention on ecosystem health, the decline of which has led to the listing of seven salmon and four steelhead populations under the U.S. Endangered Species Act. Although adaptive management is considered one approach to resource management in the face of uncertainty, an early attempt at its implementation in the U.S. portion of the basin failed. We explore these issues in the context of resilience, taking the position that while adaptive management may foster ecological resilience, it is only one factor in the institutional changes needed to foster social-ecological resilience captured in the concept of adaptive governance.

Simulating Effects of Nonintrogressive Hybridization with a Stocked Hatchery Strain of Rainbow Trout on the Sustainability and Recovery of Naturalized Steelhead Populations in Minnesota Waters of Lake Superior

AbstractA model was developed to explore the impacts of nonintrogressive hybridization with a stocked hatchery strain of rainbow trout Oncorhynchus mykiss (Kamloops strain [KAM]) on the sustainability and recovery of naturalized steelhead (anadromous rainbow trout) populations in Minnesota tributaries of Lake Superior. The model was used to assess the extinction risk of Lake Superior steelhead over a 50‐year period based on multiple KAM stocking scenarios, initial population sizes, and levels of assortative mating. No extinctions occurred in simulated steelhead populations regardless of initial size after a one‐time introduction of KAM; however, the risk of extinction due to nonintrogressive hybridization increased dramatically for scenarios involving annual stocking of KAM. The level of assortative mating among KAM and steelhead greatly influenced the risk of steelhead population decline or extinction for all scenarios. Results of the model support the contention that nonintrogressive hybridization could be an impediment to the sustainability and recovery of the steelhead population in Lake Superior.Received June 14, 2010; accepted July 20, 2011

Resilience and Water Governance: Adaptive Governance in the Columbia River Basin

The 1964 Columbia River Treaty between the United States and Canada is currently under review. Under the treaty, the river is jointly operated by the two countries for hydropower and is the largest producer of hydropower in the western hemisphere. In considering the next phase of international river governance, the degree of uncertainty surrounding the drivers of change complicates efforts to predict and manage under traditional approaches that rely on historical ecosystem responses.At the same time, changes in social values have focused attention on ecosystem health, the decline of which has led to the listing of seven salmon and four steelhead populations under the U.S. Endangered Species Act. Although adaptive management is considered one approach to resource management in the face of uncertainty, an early attempt at its implementation in the U.S. portion of the basin failed. We explore these issues in the context of resilience, taking the position that while adaptive management may foster ecological resilience, it is only one factor in the institutional changes needed to foster social-ecological resilience captured in the concept of adaptive governance.

Human Influence on the Spatial Structure of Threatened Pacific Salmon Metapopulations

To remain viable, populations must be resilient to both natural and human-caused environmental changes. We evaluated anthropogenic effects on spatial connections among populations of Chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss) (designated as threatened under the U.S. Endangered Species Act) in the lower Columbia and Willamette rivers. For several anthropogenic-effects scenarios, we used graph theory to characterize the spatial relation among populations. We plotted variance in population size against connectivity among populations. In our scenarios, reduced habitat quality decreased the size of populations and hydropower dams on rivers led to the extirpation of several populations, both of which decreased connectivity. Operation of fish hatcheries increased connectivity among populations and led to patchy or panmictic populations. On the basis of our results, we believe recolonization of the upper Cowlitz River by fall and spring Chinook and winter steelhead would best restore metapopulation structure to near-historical conditions. Extant populations that would best conserve connectivity would be those inhabiting the Molalla (spring Chinook), lower Cowlitz, or Clackamas (fall Chinook) rivers and the south Santiam (winter steelhead) and north fork Lewis rivers (summer steelhead). Populations in these rivers were putative sources; however, they were not always the most abundant or centrally located populations. This result would not have been obvious if we had not considered relations among populations in a metapopulation context. Our results suggest that dispersal rate strongly controls interactions among the populations that comprise salmon metapopulations. Thus, monitoring efforts could lead to understanding of the true rates at which wild and hatchery fish disperse. Our application of graph theory allowed us to visualize how metapopulation structure might respond to human activity. The method could be easily extended to evaluations of anthropogenic effects on other stream-dwelling populations and communities and could help prioritize among competing conservation measures.

Effectiveness and Trade‐Offs Associated with Hydraulic Egg Collections from Natural Salmon and Steelhead Redds for Conservation Hatchery Programs

AbstractMaintaining a large genetically effective number of breeders (Nb) in supplemented salmon populations is considered vital to their long‐term sustainability, yet may be difficult to consistently achieve in practice, especially in conservation hatchery programs that require small numbers of eggs for captive rearing. We evaluated efforts to hydraulically collect eggs from naturally produced redds, as implemented by conservation hatchery programs for Endangered Species Act listed populations of Snake River Chinook salmon Oncorhynchus tshawytscha and Hood Canal steelhead O. mykiss; we then compared the estimated Nb represented in the hydraulically collected captive populations with the Nb obtained by the more conventional approach (i.e., adult collection and artificial spawning). Egg collection goals in the steelhead and Chinook salmon conservation hatchery programs were met in most cases and were never exceeded. The embryo viability and egg‐to‐fry survival consistently exceeded 90% and were no less than would be expected through artificial spawning. Demographic estimates suggested that a greater Nb in the captive population would be obtained by hydraulic redd sampling than by artificial spawning of captured adults to produce a specific, limited number of eggs. Hydraulic redd sampling allows sexual selection to occur naturally on the spawning grounds and does not require barrier weirs, handling of adults, or the removal of a female's entire fecundity from natural production. The high rate of survival to emergence for hydraulically collected eggs (>95%) suggests that eggs are not damaged by the collection process, but the fate of uncollected eggs that are disturbed during the process is unknown. Hydraulic redd sampling requires fairly frequent redd surveys to time collections at the proper stage of embryonic development, and access to some redds in remote areas can be difficult. Hydraulic sampling of eyed eggs appears to have largely accomplished the goals of these small‐ to moderately‐sized conservation hatchery programs.

A Microsatellite Genome Screen Identifies Chromosomal Regions under Differential Selection in Steelhead and Rainbow Trout

AbstractNovel genetic resources now make it possible to directly assess the effects of natural selection on specific regions of the salmonid genome. Natural selection on specific genetic loci will also affect the variation in linked flanking regions through “hitchhiking” effects, causing greater differentiation between populations than would be expected from purely neutral processes. Here we identify candidate genomic regions for the effects of differential natural selection in two closely related populations of steelhead–rainbow trout Oncorhynchus mykiss separated for the last century following anthropogenic introduction above a barrier waterfall in a coastal California stream. A set of 110 expressed sequence tag (EST)‐linked and 188 anonymous microsatellite loci, most of which are mapped, were chosen to provide distributed coverage of all linkage groups in the O. mykiss genome. A genome screen was then performed to identify genomic regions under divergent selection. Multiple complementary statistical methods were used to detect outlier loci, and loci identified by more than one method were considered strong candidates for genomic regions affected by recent natural selection and genomic adaptation to the environment above the waterfall. We identified six strongly supported outlier loci, including one linked to an EST and two located in a genomic region that contains quantitative trait loci associated with egg development, spawning time, and other life history variation. Identification of regions in the genome that are potentially under selection provides valuable information about the genetic basis of selection in novel habitats and the genetic architecture of salmonid life history variation.

Factors influencing density, distribution, and mesohabitat selection of juvenile wild salmonids and residual hatchery winter steelhead

To best manage Eagle Creek National Fish Hatchery, negative interactions between hatchery salmonids and Endangered Species Act listed wild salmonids in the Eagle Creek Basin need to be minimized. Our objectives were: 1) to compare summer rearing densities in two similar streams, where one stream received a release of hatchery salmonids and one stream did not receive a release of hatchery salmonids, 2) to determine if residual hatchery winter steelhead were present in the Eagle Creek Basin, and 3) if so, determine how their presence and density relates to mesohabitat selection and distribution of naturally produced salmonids. A comprehensive snorkel survey identified significantly higher densities of juvenile coho salmon rearing in North Fork Eagle Creek, compared to upper and lower Eagle Creek. We found age 0 winter steelhead in significantly higher densities in upper Eagle Creek as opposed to lower Eagle Creek and North Fork Eagle Creek. Residual hatchery steelhead were located only in Eagle Creek and were rearing in the same 15 mesohabitat units that contained the estimated majority of wild fish populations. In Eagle Creek, the probability of occurrence for all species, regardless of origin, was highest in the vicinity of the hatchery. Residual hatchery winter steelhead density indicated a negative relationship with age 0 winter steelhead density. Due to residual hatchery winter steelhead being present in only 15 sampled habitat units we recommend future sampling effort be focused in areas with known populations of residual hatchery winter steelhead to determine if a distinct relationship between these population densities exists. From these data it is unclear if residual hatchery steelhead are affecting densities, distributions, and mesohabitat selection of wild salmonids in the basin. However, while we were unable to detect any direct impacts of residual hatchery fish on the wild population, these results do suggest the potential exists for competitive ecological interactions between hatchery and wild populations.

Development of natural growth regimes for hatchery-reared steelhead to reduce residualism, fitness loss, and negative ecological interactions

Wild steelhead (Oncorhynchus mykiss) typically spend two or more years in freshwater before migrating to sea, but hatchery steelhead are almost ubiquitously released as yearlings. Their large size at release coupled with life history pathways that include both male and female maturation in freshwater present ecological risks different from those posed by hatchery populations of Pacific salmon. Yearling hatchery reared steelhead that fail to attain minimum thresholds for smoltification or exceed thresholds for male maturation tend to ‘residualize’ (i.e., remain in freshwater). Residuals pose ecological risks including size-biased interference competition and predation on juvenile salmon and trout. Three hatchery populations of steelhead in Hood Canal, WA were reared under growth regimes designed to produce a more natural age at smoltification (age-2) to aid in rebuilding their respective natural populations. Mean smolt sizes and size variability at age-2 were within the range of wild smolts for two of the three populations. The third population reared at a different facility under similar temperatures exhibited high growth rate variability and high male maturation rates (20% of all released fish). Experimentally comparing age-1 and age-2 smolt programs will help identify optimal rearing strategies to reduce the genetic risk of domestication selection and reduce residualism rates and associated negative ecological effects on natural populations. Investigations of Winthrop National Fish Hatchery summer-run steelhead will measure a) selection on correlated behavioral traits (‘behavioral syndromes’), b) degree of smoltification, c) changes in hormones that regulate gonad growth at key developmental stages, and d) conduct extensive post-release monitoring of fish reared under each growth regime.

Comparative Evaluation of Molecular Diagnostic Tests for Nucleospora salmonis and Prevalence in Migrating Juvenile Salmonids from the Snake River, USA

Nucleospora salmonis is an intranuclear microsporidian that primarily infects lymphoblast cells and contributes to chronic lymphoblastosis and a leukemia-like condition in a range of salmonid species. The primary goal of this study was to evaluate the prevalence of N. salmonis in out-migrating juvenile hatchery and wild Chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss from the Snake River in the U.S. Pacific Northwest. To achieve this goal, we first addressed the following concerns about current molecular diagnostic tests for N. salmonis: (1) nonspecific amplification patterns by the published nested polymerase chain reaction (nPCR) test, (2) incomplete validation of the published quantitative PCR (qPCR) test, and (3) whether N. salmonis can be detected reliably from nonlethal samples. Here, we present an optimized nPCR protocol that eliminates nonspecific amplification. During validation of the published qPCR test, our laboratory developed a second qPCR test that targeted a different gene sequence and used different probe chemistry for comparison purposes. We simultaneously evaluated the two different qPCR tests for N. salmonis and foundthat both assays were highly specific, sensitive, and repeatable. The nPCR and qPCR tests had good overall concordance when DNA samples derived from both apparently healthy and clinically diseased hatchery rainbow trout were tested. Finally, we demonstrated that gill snips were a suitable tissue for nonlethal detection of N. salmonis DNA in juvenile salmonids. Monitoring of juvenile salmonid fish in the Snake River over a 3-year period revealed low prevalence of N. salmonis in hatchery and wild Chinook salmon and wild steelhead but significantly higher prevalence in hatchery-derived steelhead. Routine monitoring of N. salmonis is not performed for all hatchery steelhead populations. At present, the possible contribution of this pathogen to delayed mortality of steelhead has not been determined.

Discovery and characterization of single‐nucleotide polymorphisms in steelhead/rainbow trout, Oncorhynchus mykiss

Single-nucleotide polymorphisms (SNPs) have several advantages over other genetic markers, including lower mutation and genotyping error rates, ease of inter-laboratory standardization, and the prospect of high-throughput, low-cost genotyping. Nevertheless, their development and use has only recently moved beyond model organisms to groups such as salmonid fishes. Oncorhynchus mykiss is a salmonid native to the North Pacific rim that has now been introduced throughout the world for fisheries and aquaculture. The anadromous form of the species is known as steelhead. Native steelhead populations on the west coast of the United States have declined and many now have protected status. The nonanadromous, or resident, form of the species is termed rainbow, redband or golden trout. Additional life history and morphological variation, and interactions between the forms, make the species challenging to study, monitor and evaluate. Here, we describe the discovery, characterization and assay development for 139 SNP loci in steelhead/rainbow trout. We used EST sequences from existing genomic databases to design primers for 480 genes. Sanger-sequencing products from these genes provided 130 KB of consensus sequence in which variation was surveyed for 22 individuals from steelhead, rainbow and redband trout groups. The resulting TaqMan assays were surveyed in five steelhead populations and three rainbow trout stocks, where they had a mean minor allele frequency of 0.15-0.26 and observed heterozygosity of 0.18-0.35. Mean F(ST) was 0.204. The development of SNPs for O. mykiss will help to provide highly informative genetic tools for individual and stock identification, pedigree reconstruction, phylogeography and ecological investigation.

Disruption of historical patterns of isolation by distance in coastal steelhead

When natural populations exchange migrants at a rate proportional to their geographic distance, population genetics theory leads to the expectation of a pattern of isolation-by-distance (IBD), whereby geographic and genetic distance are correlated. However, the presence or absence of such patterns in modern populations may not fully reflect the historical relationships among those populations. Thus, historical samples, collected prior to modern human impacts, can often provide a critical baseline for comparison with modern populations. Steelhead, the anadromous form of rainbow trout, Oncorhynchus mykiss, are native to western North America and are endangered or threatened throughout most of California, near the southern extent of their native range. Population samples of steelhead collected in 1897 and 1909 in Central California rivers provided the opportunity to evaluate the historical genetic composition and population structure of these threatened fish. Here we show that these steelhead populations had a historically strong correlation between genetic and geographic distance that has been virtually erased in modern populations, suggesting that current relationships among modern steelhead populations are no longer reflective of natural migratory pathways. This demonstrates the critical role of migration in maintaining population relationships of threatened species and highlights the importance of natural history museums in providing historical baseline information.

Smolt Transformation in Two California Steelhead Populations: Effects of Temporal Variability in Growth

AbstractWe tested the effect of temporal patterns in food supply on life history decisions in coastal steelhead Oncorhynchus mykiss irideus from a Central California coastal (CCC) population (Scott Creek) and a Northern California Central Valley (NCCV) population (upper Sacramento River basin). We manipulated growth through feeding experiments conducted from May to the following March using warm (2006 cohort) and cool (2007 cohort) temperature regimes. Survival in seawater challenges just before the time of typical juvenile emigration provided an index of steelhead smolt versus nonsmolt life history pathways. Survival varied significantly with fish size (with larger fish being more likely to survive than smaller fish) and by source population (with CCC steelhead being more likely to survive than NCCV steelhead of the same size). The timing of increased food supply (treatment group) did not significantly affect seawater survival rates in either NCCV or CCC steelhead. For both strains, the eventual survivors of seawater challenges (putative smolts) diverged from the eventual mortalities (putative nonsmolts) in both size and growth rate by June in both years, suggesting that the initial growth advantages were maintained throughout the experiments. A significant divergence in condition factor between smolts and nonsmolts by December matched the expected morphological transition of smolts, which showed faster growth in length than weight compared with nonsmolts. The apparent timing of the decision window, several months before the typical period of smolt emigration, matches the patterns observed for other salmonids. In coastal California, this decision must occur before fish have had the opportunity to take advantage of improved winter–early spring feeding conditions. These results support the role of early growth opportunity in life history decisions and provide insight into the applicability of life history models for managing California steelhead.

Growth, Condition Factor, and Bioenergetics Modeling Link Warmer Stream Temperatures Below a Small Dam to Reduced Performance of Juvenile Steelhead

Abstract We investigated the growth and feeding performance of juvenile steelhead Oncorhynchus mykiss using field measures and bioenergetics modeling. Juvenile steelhead populations were sampled from mid-June through August 2004 at study sites upstream and downstream of Hemlock Dam. The growth and diet of juvenile steelhead were determined for a warm (summer) and subsequent (late summer) transitional period at each study site. Empirical data on the growth and diet of juvenile steelhead and mean daily temperatures were used in a bioenergetics model to estimate the proportion of maximum consumption achieved by juvenile steelhead by site and period. Modeled estimates of feeding performance were better for juvenile steelhead at the upstream compared to the downstream site during both periods. The median condition factor of juvenile steelhead did not change over the summer at the upstream site, but showed a significant decline over time at the downstream site. A negative trend in median condition factor at the...

Seasonal foraging and piscivory by sympatric wild and hatchery-reared steelhead from an integrated hatchery program

We compared the diet of hatchery-reared steelhead produced from an integrated hatchery program as emigrating spring smolts and non-migrating hatchery residuals to their sympatric wild counterparts. Our results suggest that there is a potential for hatchery fish to affect wild steelhead populations due to dietary overlap and subyearling salmonid predation; however, relative ecological risk did not increase as steelhead delayed or forwent emigration. Predation by hatchery smolts was related to release timing, but not experience with native fish. Diet composition appears to be more strongly affected by seasonal and yearly differences in prey abundance and presence rather than differences in rearing environments. Hatchery and wild steelhead showed small but important foraging differences. Hatchery smolts did not consume as many salmonids as wild fish and hatchery residuals showed relatively stronger surface oriented feeding behavior than wild parr. Because most hatchery smolts emigrated shortly after release and the overall number of residuals in the study creek was low, we speculate that in this case there is low dietary and predatory-based risk of hatchery steelhead in Abernathy Creek negatively impacting wild salmonids.

Ecotype Distinctions among Steelhead in Hood River, Oregon, Allow Real‐Time Genetic Assignment of Conservation Broodstocks

AbstractEfforts to rehabilitate threatened summer‐run (SR) and winter‐run (WR) populations of steelhead Oncorhynchus mykiss in the Hood River, Oregon, include operation of two conservation hatchery programs. Annual collection of discrete broodstocks relies on identification of SR and WR fish based on return time, reproductive state, and other physical and behavioral characteristics. An increased likelihood of misidentification occurs in the spring, when SR and WR return times overlap. The resulting interbreeding between ecotypes in the hatchery imposes serious genetic risks to wild SR and WR steelhead populations. We characterized life history differences between Hood River SR and WR steelhead and evaluated genetic structure using a suite of microsatellite loci. Significant differences in life history, including age at return and fork length, were corroborated by spatially influenced genetic structure among SR and WR fish; SR fish spawn in the west fork of the Hood River, while WR fish spawn in the east and middle forks. Temporal and spatial distinctions persist among Hood River steelhead ecotypes despite past operation of segregated hatchery programs utilizing out‐of‐basin stocks. We evaluated the feasibility of using real‐time genetic assignment tests to differentiate SR from WR among candidate broodstock fish captured downstream of spawning grounds. Among adult steelhead of known origin, we observed 91.5% assignment accuracy for WR fish and 77.7% accuracy for SR fish. A rapid‐response protocol was subsequently developed that provides hatchery managers with genetic assignment of broodstock to ecotypes within 24 h after interrogation of returning fish.