Salmon Recovery Research Articles

Sex-specific diet differences in harbor seals (Phoca vitulina) via spatial assortment.

The lack of recovery of Chinook salmon (Oncorhynchus tshawytscha) in the Pacific Northwest has been blamed in part on predation by pinnipeds, particularly the harbor seal (Phoca vitulina). Previous work at a limited number of locations has shown that male seal diet contains more salmon than that of female seals and that sex ratios at haul-out sites differ spatiotemporally. This intrapopulation variation in predation may result in greater effects on salmon than suggested by models assuming equal spatial distribution and diet proportion. To address the generality of these patterns, we examined the sex ratios and diet of male and female harbor seals from 13 haul-out sites in the inland waters of Washington State and the province of British Columbia during 2012-2018. DNA metabarcoding was conducted to determine prey species proportions of individual scat samples. The sex of harbor seals was then determined from each scat matrix sample with the use of quantitative polymerase chain reaction (qPCR). We analyzed 2405 harbor seal scat samples using generalized linear mixed models (GLMMs) to examine the factors influencing harbor seal sex ratio at haul-out sites and permutational multivariate analysis of variance (PERMANOVA) to examine the influence of sex and haul-out site on harbor seal diet composition. We found that the overall sex ratio was 1:1.02 (female:male) with notable spatiotemporal variation. Salmoniformes were about 2.6 times more abundant in the diet of males than in the diet of females, and Chinook salmon comprised ca. three times more of the average male harbor seal's diet than the average female's diet. Based on site-specific sex ratios and diet data, we identified three haul-out sites where Chinook salmon appear to be under high predation pressure by male harbor seals: Cowichan Bay, Cutts Area, and Fraser River. Our study indicates that combining sex-specific pinniped diet data with the sex ratio of haul-out sites can help identify priority sites of conservation concern.

Population recovery of a migratory anadromous fish in a small forest stream following restoration of longitudinal connectivity

Restoration of movement corridors is a key management action used to address threats to migratory and other mobile species. Yet, we lack restoration effectiveness studies that allow for species to reestablish naturally (i.e. without supplementation) following habitat reconnection that capture all phases (dispersal, growth, and regulation) of recovery, and that takes an ecosystems approach. We investigated the natural recovery of migratory anadromous Coho salmon following habitat reconnection across a 5‐km section of Rock Creek, a forested tributary of the Cedar River, Washington, United States, 3 km upstream of Landsburg Dam. The dam blocked upstream fish movement for 102 years until the completion of a fish ladder in 2003. We also evaluated the response of non‐migratory trout, which are closely related to Coho salmon. Juvenile Coho salmon natal to the Cedar River dispersed into Rock Creek for rearing until spawning there in 2007. After restoration, juvenile Coho salmon density (fish/m2) increased 18‐fold, approaching an asymptote (i.e. regulation phase) a decade later. Coho salmon recovery in Rock Creek was spatially variable, however, slowing with distance from the site of restoration. Trout density was also higher after restoration relative to before, likely due to several mechanisms, including increased capacity resulting from the reestablishment of marine organic matter subsidies delivered by spawning anadromous fish. Our study demonstrates that migratory species can recover naturally after the restoration of habitat connectivity and associated movement corridors. Furthermore, our results suggest that such actions can also benefit nontarget species by reestablishing key ecosystem links driven by the target species.

A Review of the Multi-Stakeholder Process for Salmon Recovery and Scenario Mapping onto Stability Landscapes

A Review of the Multi-Stakeholder Process for Salmon Recovery and Scenario Mapping onto Stability Landscapes

Survival implications of diversion entrainment for out‐migrating juvenile Chinook Salmon and steelhead

AbstractObjectiveEfforts to ameliorate the negative effects of diversion dams on aquatic species of concern are important in rivers where water withdrawal supports agricultural economies, and they are likely to become increasingly important with impending climate change. A multi‐year study was conducted to evaluate the survival consequences of diversion dam passage for juvenile Chinook Salmon Oncorhynchus tshawytscha and steelhead O. mykiss in the highly managed Yakima River, Washington. Canal entrainment and passage were evaluated at four diversion dams in the lower Yakima River where seaward‐migrating juvenile salmon and steelhead either pass dams via spill bays or enter canals with downstream fish‐screening facilities designed to collect entrained fish and return them to the main‐stem river.MethodsWe used acoustic telemetry to monitor the downstream migration behavior of 4403 juvenile Chinook Salmon and steelhead during 2018–2021.ResultPercent entrainment into canals was substantial (6–59%) at three of the four diversion dams studied, and entrainment probability was positively associated with the proportion of streamflow diverted into canals. Survival probability estimates for groups of tagged fish that were entrained into canals were lower than survival probability estimates for tagged fish that passed through spill bays on the dams. Absolute differences in survival probabilities between routes ranged from 0.099 to 0.369, demonstrating that canal entrainment reduced the survival of outmigrating juvenile Chinook Salmon and steelhead. We also found that entrainment resulted in migration delays, which could further affect survival because fish are increasingly exposed to predation and decreased water quality as water temperature increases throughout the migration season.ConclusionCanal entrainment resulted in increased mortality and travel time through the study area, highlighting the need to limit the entrainment of juvenile salmon and steelhead at diversion dams in rivers where salmon recovery is important.

Juvenile Pacific salmonid habitat use in two Puget Sound lowland rivers

AbstractObjectiveLarge rivers are complex, productive environments that support numerous species. However, humans have extensively modified these ecosystems, contributing to the decline of Pacific salmonid Oncorhynchus spp. populations. Salmon recovery efforts rely upon an understanding of salmonid habitat needs at different life stages, but data on juvenile salmonid habitat use within large rivers are rare due to the challenges of sampling in large rivers. To help fill this information need, we used a cataraft‐mounted electrofisher to evaluate juvenile salmonid use of natural (bar, backwater, side channel, and unarmored bank) and human‐modified (riprap‐armored bank and biorevetment bank [armored banks with added wood]) channel edge habitats in the Snoqualmie and Green rivers within the Puget Sound region of Washington State.MethodsWe electrofished over 1000 25‐m transects across seven spring rearing seasons (2016–2022) and measured transect water depths and widths of low‐velocity habitat (≤0.45 m/s).ResultBars, backwaters, and side channels were shallower and had wider low‐velocity habitat than armored banks. River flow also influenced water depth and low‐velocity width, but the relationship varied depending on the habitat type. Subyearling Chinook Salmon O. tshawytscha and subyearling Coho Salmon O. kisutch occurred more frequently and were more abundant along natural edge habitats than along armored banks, while their use of biorevetment banks was intermediate between their use of natural edge habitats and armored banks. In contrast, yearling Coho Salmon and trout occurred more frequently and were more abundant along armored, biorevetment, and unarmored banks than along bars and backwaters, but they also used side channels extensively. Habitat use shifted throughout the spring, but specific shifts varied by species or life history stage.ConclusionThese results emphasize the importance of conserving natural edge habitats, removing bank armoring, and reconnecting or restoring side channels. Additionally, our results highlight that a diversity of habitat types and conditions is necessary to support multiple species and life history stages.

Expansion of smallmouth bass distribution and habitat overlap with juvenile Chinook salmon in the Willamette River, Oregon

AbstractSmallmouth bass populations have expanded far beyond their native range and these predatory fish present a pervasive threat to native aquatic species throughout North America. In the western United States, smallmouth bass are now present in river and reservoir habitats where Pacific salmon are found and are considered a potential threat to salmon recovery in many locations. We conducted a study to determine if smallmouth bass are expanding their range in the mainstem Willamette River, Oregon, and developed a model to assess habitat overlap between smallmouth bass and juvenile Chinook salmon. Sampling during 2011–2022 revealed that the distribution of smallmouth bass had expanded throughout that timeframe to encompass the entire mainstem Willamette River, including important rearing habitats for juvenile Chinook salmon. The model predicted that smallmouth bass and juvenile Chinook salmon habitat overlap was substantial, highlighting the need for additional research to evaluate for potential negative impacts to salmon recovery in the basin. The model was also used to evaluate the efficacy of using flow management to reduce interactions between these two species, but the scenarios we examined suggested that this was not a viable option. These results highlight the need for continued research to assess interactions between smallmouth bass and juvenile salmon, and other native species of concern, in the Willamette River Basin. The development of the model is useful for resource managers to understand interactions between these species to prioritize locations for sampling in the future.

Leading the charge: A qualitative case-study of leadership conditions in collaborative environmental governance structures

Collaborative governance structures are increasingly common among natural resource managers. While studies have assessed the conditions under which collaborative action occurs, little emphasis has been placed on the role leadership may play in joint-jurisdictional systems. Management of species under the Endangered Species Act offers an opportunity to assess the collaboration of federal, state, and tribal resource agencies. The Gulf of Maine Distinct Population Segment of Atlantic salmon (Salmo salar) was managed under a structure called the Atlantic Salmon Recovery Framework (ASRF) from 2011 to 2019. Using the ASRF as a case study, we examined the influence of leadership approaches on perceived program efficacy, member buy-in, and experience through semi-structured interviews. Participant reflections revealed three major leadership themes that participants found inadequate: (1) shared goals, (2) transparency, and (3) trust. Collaborative approaches that foster these leadership conditions may increase adaptive capacity and the likelihood of sustained success in this, and other, environmental governance structures.

Why Aren't Salmon Responding to Habitat Restoration in the Pacific Northwest?

Declines in populations of Pacific salmon Oncorhynchus spp. in the Pacific Northwest have led to listings under the Endangered Species Act. One objective of current recovery efforts is the restoration of freshwater and estuarine habitats, which had been occurring prior to Endangered Species Act listing but increased dramatically afterwards. However, few listed populations are improving. We believe that there are five factors contributing to the lack of population response to habitat restoration: Not enough restoration has been done. We are not doing the right things in the right places at the right times. Ongoing habitat degradation is offsetting restoration benefits. Not enough time has passed. Monitoring has been inadequate to detect changes in Pacific salmon abundance. All factors contribute to the disappointing progress on Pacific salmon recovery, although their importance varies. Two factors are more consistently significant than the others. Resources available to address habitat damage remain insufficient. The scale of the problem is large, so the response needs to be correspondingly large to yield desired outcomes. Of equal significance is the failure of restoration programs to identify elements controlling fish production. Implementing the right projects in the right places is key to improving the outcomes of restoration.

A Resilience History of the Columbia River Basin and Salmonid Species: Regimes and Policies

We view the history of the Columbia River Basin through a resilience lens from the point of view of salmonids, as keystone species for the river basin ecosystems and social systems. We rely on the concept of multiple stable states as depicted in a stability landscape, as a scientific theory, but equally as a metaphor and a mental model. Using evidence-based plausibility arguments concerning the existence, creation, and potential critical transitions between regimes, we describe change over centuries. We argue that a critical transition occurred taking the state of the system from its historic regime into a novel regime stabilized by new social feedbacks and institutional configurations. By using a state space defined by four variables used in policy deliberations for salmon recovery we tie our results to historical and contemporary management issues. Knowledge of (a) which regime is currently occupied and (b) which critical transitions between regimes are possible are both crucial to effective policy formation. We draw distinctions between positions held by federal agencies, tribal agencies, and civil society organizations as to the current state of affairs and policy recommendations, raising questions about the appropriate use of decision support systems in the public process for decision making.

Pacific Coastal Salmon Recovery and IIJA Funds (DOC)

Federal Grants & ContractsVolume 47, Issue 5 p. 4-4 Grants Alerts Pacific Coastal Salmon Recovery and IIJA Funds (DOC) First published: 31 January 2023 https://doi.org/10.1002/fgc.32833Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume47, Issue52 February 2023Pages 4-4 RelatedInformation

Incorporating Evidence into Collaborative Ecosystem Restoration: A Content Analysis of Bibliographic References and their Use in Salmon Recovery Plans.

Collaborative environmental management draws on a wide range of information, from a variety of stakeholders, to inform policy. Scientific information is particularly relevant for ecosystem restoration plans, such as those created for recovering species on the brink of extinction. This study examines use of evidence in salmon recovery plans in Puget Sound, USA. Across 12 plans, coders characterized 1104 references to identify their source, recency, domain, and context. Subsequently, 11 plans were analyzed in-depth to identify how each reference was used to support particular kinds of claims. Results indicate the most frequent source of information cited in salmon recovery plans is government agencies, especially from national and state governments, followed by peer reviewed journal articles and scientific books. Journal articles come predominantly from high impact (top quartile) journals, although these articles are on average 15 years old. Sources are almost exclusively from the domain of natural sciences (97%), with just 1% social sciences and 2% non-scientific. More references come from beyond than within the local watershed. Different reference sources are used to support different kinds of claims, with government agency sources positively associated with claims about species status/trends, and peer reviewed journal articles positively associated with claims about causes of species decline. Overall, the lack of social science references, and lack of references to support claims about levels of community support, reduce managers' abilities to incorporate features of social systems into species recovery planning.

Density Dependence in Three Snake River Sockeye Salmon Nursery Lakes in Central Idaho

AbstractSnake River Sockeye Salmon Oncorhynchus nerka, listed as an endangered species in 1991, currently inhabit three nursery lakes (Redfish, Pettit, and Alturas lakes) in the Sawtooth Valley, Idaho. Conspecific kokanee (lacustrine Sockeye Salmon) are also present in the lakes. Snake River Sockeye Salmon recovery efforts, initially focused on genetic conservation, are now attempting to rebuild naturally spawning populations using hatchery supplementation. However, in Sockeye Salmon nursery lakes, density dependence is frequently observed when elevated O. nerka abundance leads to declines in zooplankton biomass, body size, and shifts in community composition. In turn, these changes lead to reductions in juvenile O. nerka growth rates, survival, and adult returns. We examined a long‐term data set of O. nerka population metrics and associated zooplankton community metrics. We found evidence of density dependence within and among nursery lakes. We detected differences in zooplankton biomass, lengths of preferred zooplankton prey (Daphnia spp. and cyclopoid copepods), parr growth rates, and age‐1 smolt size among the three lakes. We found negative relationships between O. nerka density and zooplankton biomass and size. We identified positive relationships between zooplankton biomass and two response variables: smolt size at migration and growth rates of hatchery parr. The relationships were generally similar among lakes. Variable outcomes were a result of differences in O. nerka density (or zooplankton biomass), controlled primarily by the relative proportion of spawning and rearing habitat in each lake. Understanding unique lake habitats, ecological interactions, and the role of density dependence is germane to management of Snake River Sockeye Salmon populations.

Ceratonova shasta: a cnidarian parasite of annelids and salmonids.

The myxozoan Ceratonova shasta was described from hatchery rainbow trout over 70 years ago. The parasite continues to cause severe disease in salmon and trout, and is recognized as a barrier to salmon recovery in some rivers. This review incorporates changes in our knowledge of the parasite's life cycle, taxonomy and biology and examines how this information has expanded our understanding of the interactions between C. shasta and its salmonid and annelid hosts, and how overarching environmental factors affect this host–parasite system. Development of molecular diagnostic techniques has allowed discrimination of differences in parasite genotypes, which have differing host affinities, and enabled the measurement of the spatio-temporal abundance of these different genotypes. Establishment of the C. shasta life cycle in the laboratory has enabled studies on host–parasite interactions and the availability of transcriptomic data has informed our understanding of parasite virulence factors and host defences. Together, these advances have informed the development of models and management actions to mitigate disease.

Spatiotemporal distribution of Ceratonova shasta in the lower Columbia River Basin and effects of exposure on survival of juvenile chum salmon Oncorhynchus keta.

In the Columbia River Basin (CRB), USA, anthropogenic factors ranging from dam construction to land use changes have modified riverine flow and temperature regimes and degraded salmon habitat. These factors are directly implicated in native salmon and steelhead (Oncorhynchus species) population declines and also indirectly cause mortality by altering outcomes of ecological interactions. For example, attenuated flows and warmer water temperatures drive increased parasite densities and in turn, overwhelm salmonid resistance thresholds, resulting in high disease and mortality. Outcomes of interactions between the freshwater myxozoan parasite, Ceratonova shasta, and its salmonid hosts (e.g., coho O. kisutch and Chinook salmon O. tshawytscha) are well-described, but less is known about effects on chum salmon O. keta, which have a comparatively brief freshwater residency. The goal of this study was to describe the distribution of C. shasta relative to chum salmon habitat in the CRB and assess its potential to cause mortality in juvenile chum salmon (listed as threatened in the CRB under the U.S. Endangered Species Act). We measured C. shasta densities in water samples collected from chum salmon habitat throughout the lower CRB during the period of juvenile chum salmon outmigration, 2018–2020. In 2019, we exposed caged chum salmon fry from two hatchery stocks at three C. shasta-positive sites to assess infection prevalence and survival. Results demonstrated: (1) C. shasta was detected in spawning streams from which chum salmon have been extirpated but was not detected in contemporary spawning habitat while juvenile chum salmon were present, (2) spatiotemporal overlap occurs between C. shasta and juvenile chum salmon in the Columbia River mainstem, and (3) low densities of C. shasta caused lethal infection in chum salmon fry from both hatchery stocks. Collectively, our results suggest C. shasta may limit recovery of chum salmon now and in the future.

Integrating Ecosystem Models with Long‐Term Monitoring to Support Salmon Recovery

AbstractOkanogan summer‐run Chinook Salmon Oncorhynchus tshawytscha holding in the Similkameen River near Oroville, Washington. Photo credit: Brian Miller, Confederated Tribes of the Colville Reservation.The Ecosystem Diagnosis and Treatment model (EDT) is a deterministic, life cycle‐based habitat model developed to support the conservation and recovery of declining Pacific salmon Oncorhynchus spp. and steelhead Oncorhynchus mykiss in the Pacific Northwest. Originally conceived in the 1990s, the current generation of EDT is proving its value as a data synthesis and analysis platform, capable of transforming complex environmental data into useful quantitative metrics to guide decision making. Here we describe the integration of EDT with long‐term research, monitoring, and evaluation in the Okanogan River in the state of Washington to support the ongoing conservation and recovery of steelhead listed under the Endangered Species Act. The lessons learned in this important Columbia River subbasin demonstrate the value of EDT as an adaptive management tool that is both effective and transferable. Modeling tools like EDT are one of many technological advances that will help resource managers identify priority habitats for conservation and restoration.

Ups and downs of non‐native and native stream‐dwelling salmonids: Lessons from two contrasting rivers

AbstractFreshwater rivers and lakes are particularly vulnerable to anthropogenic disturbance because of their proximity to human occupation. Anthropogenic impacts in fresh water include those caused by dams, water pollution, channelization, and invasive species. One common action to conserve freshwater biodiversity involves supplementing or reintroducing extirpated species, though the benefits of these efforts are controversial. Installation of fishways to dams and removal of invasive alien species has also resulted in recovery of native species. Herein results of long‐term monitoring of salmonids in two rivers in Japan are presented. The first case involves a river above a dam where native white‐spotted charr Salvelinus leucomaenis and masu salmon Oncorhynchus masou declined rapidly in number following dam construction, where non‐native rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta increased in number, and where stocking of native masu salmon was unsuccessful. The second case involves a river formerly dominated by non‐native rainbow trout, in which native Dolly Varden charr Salvelinus curilus and masu salmon increased in numbers following removal of non‐native species and fishway installation. Results reveal natural recovery of masu salmon in a river within which they were once completely extirpated, without stocking. Because salmonids are migratory fish and return to natal rivers, when locally extinct, human intervention to stock or reintroduce them has often been deemed necessary. However, restoration of wildlife would not require stocking or reintroduction if factors that impede the self‐recovery capability of species are removed.

Cultural and educational releases of salmon in areas blocked by major hydroelectric projects on the Columbia River

Abstract Salmon are revered by Pacific Northwest Tribes as a central figure in their cultural and spiritual identity and have been a critical food resource for millennia. Historic commercial overfishing and hydropower development on the Columbia River have devastated salmon runs and altered tribal communities. Before European settlement of North America, most Pacific Northwest Tribal economies were based on obtaining salmon for food and bartering for other commodities. Despite extensive efforts to promote salmon recovery in downstream areas, most salmon populations continue to struggle throughout the Columbia River Basin. Over 1,800 km of historical salmon habitat remain inaccessible upstream of Chief Joseph and Grand Coulee dams due to lack of fish passage at these facilities. The Indian Tribes of the upper Columbia Basin are working collectively on salmon reintroduction efforts through both a long-term scientific phased approach and near-term cultural and educational releases. This paper will briefly outline the Phased approach and provide detail on the initial results of some recent cultural and educational releases of salmon in the blocked area. The cultural and educational releases had a goal of reconnecting the people with the salmon and the salmon with historic habitats. These salmon release events were diverse and included school children releasing juvenile fish they raised in the classroom, releasing adult salmon to swim free and reproduce, and tribal members harvesting salmon from their ancestral waters. Ceremonies were held to celebrate the significance of salmon to the tribal cultures and the salmon's return home. In addition to the ceremonies, some fish were tagged to evaluate survival and behavior and to begin to document the effectiveness of trap and haul efforts. The effort resulted in anadromous salmon reintroduction to their traditional waters for the first time in 60 to 110 years. These efforts have generated tremendous interest from the press and given the people of the region a glimpse at what is possible, building momentum for the larger Phased reintroduction effort.

Effects of Livestock Exclusion on Stream Banks and Riparian Vegetation in Washington and Oregon

Livestock exclusion is a widespread restoration technique in the Pacific Northwest to protect and improve riparian and stream habitats. To assess stream restoration outcomes from excluding livestock, the Washington State Salmon Recovery Funding Board and the Oregon Watershed Enhancement Board evaluated 12 livestock exclusion projects from 2004 to 2017 using a before-after control-impact design. Paired treatment and control reaches were monitored once before restoration implementation (year 0) and several years after implementation (years 1, 3, 5, and 10) to assess bank erosion, bank canopy cover, riparian vegetation structure, pool tail fine sediment, and exclosure fencing function. Livestock exclusion significantly reduced bank erosion and bare ground. Bank erosion in treatment reaches decreased from 44% pre-project to 11% by year 10. In treatment reaches, bare ground was over 1.5 times lower in year 10 than pre-project. Most treatment reaches had intact fencing at the conclusion of the ten-year monitoring period, but there were instances where fencing did not fully function as intended, allowing livestock to access riparian areas inside the exclosure. Several metrics did not respond over time, which may be the result of several factors, including limitations of the sampling protocols, evidence of livestock grazing in treatment reaches, lack of site stratification, control reaches that were not well matched with treatment reaches, and short-duration of pre-project data collection. Despite these limitations, we still detected significant decreases in bank erosion and bare ground within treatment reaches. Future livestock exclusion monitoring should consider focus on ensuring fence maintenance, improved monitoring oversight, and the use of more quantitative monitoring protocols.

Considering intervention intensity in habitat restoration planning: An application to Pacific salmon

Habitat restoration is a key strategy for recovering imperiled species, and planning habitat restoration activities cost effectively can help advance recovery objectives. Habitat restoration planning involves decisions about where and when to undertake restoration, and what type of restoration to undertake. This article focuses on decisions about the amount of restoration to undertake for a given type, location, and time, termed intervention intensity. A return on investment framework is developed for incorporating intervention intensity into habitat restoration planning. The framework is then applied in the context of planning habitat restoration for Pacific salmon recovery as a case study. Results showed that no single intervention type or location dominated, and several returns to scale relationships emerged across the candidate interventions. Scenarios that considered interventions across multiple intensities outperformed single-intensity scenarios in terms of total benefits and cost effectiveness. These findings highlight the usefulness of exploratory return on investment analysis for prioritizing habitat restoration interventions, and underscore the importance of systematically considering how much restoration to undertake, in addition to what to do and where.

Piscine predation on juvenile salmon in sub‐arctic Alaskan rivers: Associations with season, habitat, predator size and streamflow

AbstractPredation on anadromous salmon can have important consequences for both predators and prey. Salmon provide large seasonal pulses of energy and nutrients via carcasses, eggs and juveniles to many freshwater consumers, and conversely, predation can represent a significant source of mortality for juvenile salmon. Recent declines of Chinook salmon (Oncorhynchus tshawytscha) populations in Alaska have raised concern that predation might inhibit their recovery. Here, we quantify patterns of predation by freshwater fishes on juvenile salmon across seasons, habitats, predator sizes and streamflow levels in the Arctic‐Yukon‐Kuskokwim region of Alaska. We analysed piscivore stomach contents and identified prey using DNA sequence “barcoding.” In coastal rivers, juvenile pink (O. gorbuscha) and chum (O. keta) salmon contributed heavily to Arctic grayling (Thymallus arcticus) and Dolly Varden char (Salvelinus malma) diets, coho salmon (O. kisutch) prey were rare, and Chinook salmon were not detected. In interior rivers, Arctic grayling, burbot (Lota lota) and northern pike (Esox lucius) consumed small numbers of Chinook salmon. Predation on Chinook salmon was documented disproportionately in sloughs during a summer of exceptionally high streamflow. Dietary and distributional patterns suggested northern pike and burbot may exclude salmon from sloughs in low‐gradient river reaches that would otherwise provide suitable rearing habitat. The data also provided tentative support for the hypothesis that high streamflow induces juvenile Chinook salmon to move from mainstem habitats into sloughs, where they face an increased risk of mortality. Incorporating predation risk into climate adaptation, fisheries management and habitat restoration decisions may help to facilitate Chinook salmon recovery.