Anadromous Salmon Research Articles

Effects of ocean warming with stable and fluctuating ocean acidification on seawater transition in Chinook salmon smolts

Anadromous salmon populations are declining in the Pacific Northwest, with high mortality during the transition from fresh- to seawater as smolts, a stage particularly vulnerable to adverse environmental conditions. This study seeks to explore the impacts of warming and ocean acidification on the transition of life in freshwater to life at sea in Chinook salmon smolts. In a fully factorial experiment, we transitioned Chinook salmon from fresh- to seawater at current and future conditions of temperature (13 °C and 16 °C, respectively) and ocean acidification (400 and 1400 atm CO2), including a fluctuating CO2 treatment (between control and high CO2) that may be more representative of natural environmental conditions associated with upwelling and tidal cycling. We hypothesized that constant elevated CO2 levels would impair smoltification success immediately following seawater transfer, but that fluctuating conditions would be even more physiologically challenging. We predicted that elevated temperatures would exacerbate these effects. To test this, we measured plasma ion concentrations, gill Na+/K+-ATPase (NKA) isoform mRNA and protein expression, as well as condition indices in freshwater and following 1, 3, 6, and 18 days in seawater at the respective treatments. We confirmed the existence of gill freshwater and seawater isoforms of NKA (α1a and α1b, respectively) in Chinook salmon for the first time, and found an upregulation of both isoforms in the fluctuating CO2 treatment but a reduction of the number of NKA α1b cells 3-days post seawater transfer at 13 °C. At 16 °C, NKA α1b was upregulated in high CO2 levels, with an elevated hematocrit indicating fish were likely stressed. Taken together, plasma ions, gill NKA and condition indices revealed a complex response to interacting warming and acidification during the first few days in seawater, however there were no longer-term adverse physiological responses. Thus, Chinook salmon appear to be relatively resilient to near-future climate change.

Adaptation in landlocked Atlantic salmon links genetics in wild and farmed salmon to smoltification

Increased knowledge of heritable traits in Atlantic Salmon (Salmo salar) is important to overcome bottlenecks in salmonid aquaculture. Atlantic salmonid populations, both landlocked and anadromous, represent an interesting model to gain insight into anadromy related traits, most notably, the probability to smoltify. While a previous study has identified several genomic regions diverging between anadromous and landlocked populations across the species range, the present study explores these data further with the aim to uncover if some of these genomic regions are linked to beneficial genetic traits associated with smoltification. In this study 17 of these loci were monitored in 669 anadromous salmon originating from 36 full-sibling families that had been reared under common garden conditions. The Smolt Index was calculated, using multiple visual markers, and provided a means of assessing smoltification stage. One SNP, located in Ssa04, showed a significant association with probability to smoltify, where individuals homozygous for the landlocked variant (LL) displayed a decrease in probability of smoltifying after one winter when compared with the homozygous for the anadromous variant (AA). This effect was independent of individual fish size. A separate common garden study comprising 200 individuals from either anadromous or landlocked strains showed that expression levels of ncor1, a thyroid mediator hormone located on the same chromosomal region (Ssa04), were significantly reduced in landlocked individuals post smoltification but remained constant in their anadromous counterparts. This study therefore suggests that while size is still the most important trigger for the induction of smoltification, there may also be an additional genetic component or trigger that has been ‘lost’ during the years deprived of SW transfer. In conclusion, the LL genotype identified here could potentially be used by the industry to delay smoltification and may also represent one of the first clues to the genetic regulation of smoltification in Atlantic salmon.

Climate‐driven straying dynamics in anadromous salmon and steelhead: Research agenda for conservation

Climate‐driven straying dynamics in anadromous salmon and steelhead: Research agenda for conservation

An evaluation of tradeoffs in restoring ephemeral vs. perennial habitats to conserve animal populations

IntroductionHabitat loss and degradation pose significant threats to global fish and wildlife populations, prompting substantial investments in habitat creation and restoration efforts. Not all habitats provide equal benefits, leading to challenges in prioritizing restoration actions. For example, juvenile anadromous salmonids require high quality rearing aquatic habitats to achieve the physiological requirements needed to successfully migrate to the ocean. However, there are profound disagreements among anadromous salmon restoration managers whether it is best to focus efforts on restoring in-channel habitats that are available for the entire rearing period or floodplain habitats that, while facilitating greater growth and survival than in-channel habitats, are only available for a few weeks at a time and are typically only activated every two-to-three years.MethodsWe used an existing fall-run Chinook salmon decision-support model to evaluate under what conditions floodplain restoration would provide greater benefits than in-channel habitat restoration. The simulations included a wide range of floodplain inundation frequencies and durations and floodplain benefits in the form of increased survival and growth relative to in-channel habitats.ResultsThe simulations results indicated that in-channel habitat restoration was always the best habitat restoration action when there was no existing in-channel habitat despite simulating a wide range of flood frequency, duration, and growth and survival benefits. Floodplain restoration was generally best when there was sufficient in-channel habitat available to successfully rear most of the juveniles produced by the returning adult salmon.DiscussionWe hypothesize that in-channel and floodplain habitats have different roles in salmon population maintenance with in-channel habitats regulating the overall population size and floodplains acting as recurrent resource pulses. Our study provides a quantitative framework to evaluate the benefit of these two habitat types and provides generalizable rulesets that can be used by managers when implementing habitat restoration strategies for species that inhabit both in-channel and floodplain habitats.

Correction: Predicting favourable streams for anadromous salmon spawning and natal rearing under climate change

Correction: Predicting favourable streams for anadromous salmon spawning and natal rearing under climate change

The estuarine growth and residency of juvenile Pacific salmon in North America: a compilation of empirical data

The value of estuaries as nursery habitat for juvenile anadromous salmon is likely variable across estuaries and species. Here, we compiled published empirical data on juvenile salmon estuarine growth and residency. We aimed to quantify the range and variability of these aspects for five species of Pacific salmon across estuaries, methodologies, and life histories. The majority of studies focused on Chinook and coho salmon, largely from their southern range. While there is some evidence of higher growth in wild-origin fish relative to hatchery-origin fish, the wide range of metrics employed made identification of trends among life histories challenging, and unification of reporting could strengthen future research. Different salmon life histories exhibited different residencies, with natural-origin subyearling coho exhibiting the longest mean residency (∼3 months) and 1+ sockeye salmon exhibiting the shortest (3.7 days). Across life histories, hatchery fish exhibited much shorter estuary residencies than wild fish. Collectively, our review highlights key patterns in salmon estuary ecology, identifies knowledge gaps, and lays the foundation for future studies to quantify the importance of estuaries for specific salmon.

Predicting favourable streams for anadromous salmon spawning and natal rearing under climate change

Successful management of imperilled anadromous salmon stocks requires understanding how salmon will respond to a changing climate across their extensive ranges. Though largely unused for anadromous salmon to date, environmental niche models (ENMs) can provide a strong foundation for estimating where and how much habitat will likely remain favourable. We applied a comprehensive suite of ENM statistical approaches to five Pacific salmon species, focusing on freshwater spawning and natal rearing habitat as not only critical for population survival, but also highly susceptible to a changing climate. We developed ENMs for spawning ranges across British Columbia (BC), Canada, and western US, and projected future scenarios for BC. Projections indicated net expansion of favourable spawning habitat across species in BC, with the most change occurring by 2060. However, shifts in favourable habitat varied greatly geographically and by species, with notable reductions in coastal and southern interior streams. Our results provide a basis for identifying important changes in spawning and natal rearing habitat conditions to help inform priorities for restoration and protection actions.

Emergence of persistent institutionalized inequality at the Bridge River site, British Columbia: the roles of managerial mutualism and coercion.

Persistent institutionalized inequality (PII) emerged at the Bridge River site by ca 1200-1300 years ago. Research confirms that PII developed at a time of population packing associated with unstable fluctuations in a critical food resource (anadromous salmon) and persisted across multiple generations. While we understand the demographic and ecological conditions under which this history unfolded, we have yet to address details of the underlying social process. In this paper, we draw on Bridge River's Housepit 54 to examine two alternative hypotheses. Hypothesis 1, mutualism, suggests that household heads signalled to maintain and attract new members as a means of supporting the demographic viability of the house. Inequality is indicated by variation in prestige markers but less obviously in economic fundamentals. Hypothesis 2, coercion, asserts that the more successful households developed control over access to critical food resources, forcing others into the choice between emigration and subjugation. Inequality is indicated by inter-family differences in prestige markers and economic fundamentals. Results suggest that inequality emerged under a mutualism scenario but persisted for subsequent generations under more coercive conditions. This article is part of the theme issue 'Evolutionary ecology of inequality'.

Genomic footprints of bottleneck in landlocked salmon population

At the end of the last ice age, several Atlantic salmon populations got caught up in the lakes and ponds of the Northern Hemisphere. Occasionally, the populations also got locked when the flow of rivers terminated from reaching the sea due to land upheaval. Therefore, the pattern of evolution shaping the landlocked salmon populations is different from the other anadromous salmons, which migrate between the sea and rivers. According to the theories of population genetics, the effect of genetic drift is expected to be more pronounced in the former compared to the latter. Here we examined this using the whole genome data of landlocked and anadromous salmon populations of Norway. Our results showed a 50–80% reduction in the genomic heterozygosity in the landlocked compared to anadromous salmon populations. The number and total size of the runs of homozygosity (RoH) segments of landlocked salmons were two to eightfold higher than those of their anadromous counterparts. We found the former had a higher ratio of nonsynonymous-to-synonymous diversities than the latter. The investigation also revealed a significant elevation of homozygous deleterious Single Nucleotide Variants (SNVs) in the landlocked salmon compared to the anadromous populations. All these results point to a significant reduction in the population size of the landlocked salmons. This process of reduction might have started recently as the phylogeny revealed a recent separation of the landlocked from the anadromous population. Previous studies on terrestrial vertebrates observed similar signatures of a bottleneck when the populations from Island and the mainland were compared. Since landlocked waterbody such as ponds and lakes are geographically analogous to Islands for fish populations, the findings of this study suggest the similarity in the patterns of evolution between the two.

Colonization of a temperate river by mobile fish following habitat reconnection

AbstractMobile species are particularly affected by artificial barriers requiring large investments to restore connectivity. However, few large‐scale, long‐term studies have investigated the ecological outcomes of restoring connectivity for these species. Our study, spanning 15–20 years, quantified response trajectories, which represent temporal trends following disturbance, of three native salmonids colonizing 20 km of protected habitat following restoration of fish passage at Landsburg Dam, Cedar River, WA, in 2003. Built in 1901, the dam blocked the upriver movement of native anadromous coho and Chinook salmon and nonanadromous mountain whitefish for 102 years. Restoration effectiveness was also assessed by comparing temporal trends in freshwater productivity of juvenile coho and Chinook salmon in the Cedar River after restoration to a nearby undammed subbasin. We also compared summer densities of juvenile coho and Chinook salmon, and mountain whitefish above the dam measured a decade after restoration to undammed reference systems. Anadromous salmon and nonanadromous mountain whitefish populations increased linearly or nonlinearly following restoration. The positive, asymptotic response represented by adult Chinook salmon counts indicates a slowing in population recovery rate, plateauing a decade after restoration. In contrast, annual abundance of adult coho salmon increased at a constant rate, indicating additional capacity 15 years post‐restoration. Salmonid compositional diversity, driven largely by juvenile coho salmon, also increased nonlinearly, plateauing in a decade. We observed substantial spatial variation in the temporal response, as juvenile coho salmon and mountain whitefish population expansion slowed linearly with upstream distance from the restoration site. There was evidence that some of the annual variation in salmonid biomass in summer was a result of discharge variability in winter and spring, with biomass declining as flow variability increased. Species reintroduction and establishment had no discernible effect on stream‐rearing salmonids living above the dam before restoration, while increasing coho freshwater productivity at the subbasin scale. Results from our study showed recolonization by three mobile species, each with a unique life history, takes at least a decade or more and was dependent on species and life stage, size of the spawning population, distance from restoration site, and annual variability in streamflow.

Postrelease exploration and stress tolerance of landlocked and anadromous Atlantic salmon and their hybrids

AbstractThreatened fish populations worldwide are relying on stock supplementation by hatchery‐reared fish. Although stocking with non‐native fish may lead to hybridization, thereby disrupting local adaptations, it could also improve the adaptive potential of small populations by increasing variability in essential behavioral traits. In this study, we crossbred the critically endangered Finnish landlocked salmon with a geographically close Baltic anadromous salmon population to compare boldness‐related behavioral traits among the crossing groups. We studied postrelease exploration in seminatural streams and tested stress tolerance of the fish, as reflected by their response during swimming trials and commencement of feeding after the trials. In the stress tolerance experiments, we compared fish with different rearing backgrounds to gain insight into environmentally induced variability in stress tolerance. When compared with the anadromous salmon, the landlocked salmon showed more active postrelease exploration and higher stress tolerance. The hybrids displayed intermediate behaviors compared with the purebred salmon, indicating heritability of these traits. The landlocked salmon showed less variable exploration than the hybrids with anadromous salmon as the maternal strain, but we did not find rearing‐dependent responses in stress tolerance. In summary, our findings suggest that hybridization could help in reversing likely domestication‐related negative behavioral traits in the landlocked salmon.

British Columbia freshwater salmon hatcheries demonstrate minimal contribution to piscine orthoreovirus (PRV) regional occurrence with no evidence for nonendemic strain introductions

Piscine orthoreovirus genotype 1 (PRV-1) is a common virus in farmed and wild salmon in the northeastern Pacific Ocean. Its regional occurrence in freshwater is far less clear. From 2019 to 2021, tissues of 5619 juvenile anadromous salmon (primarily Atlantic, Chinook, and coho) sampled from 12 commercial and 27 enhancement British Columbia hatcheries during 83 sampling events were screened for PRV-1 prior to seawater entry. More than 2200 (∼40%) were also screened using a Pan-PRV assay targeting all known PRV genotypes. PRV-1 was detected in four coho salmon at two freshwater enhancement facilities and in one Chinook salmon at a commercial facility. Partial (S1 segment) genome sequencing identified detections to be of the PRV-1 subgenotype endemic to the northeastern Pacific. PRV-1 was not detected (5611 individuals; 99.9%) or test results were inconclusive (3 individuals; 0.05%) for all remaining samples screened for PRV-1. PRV-2 and PRV-3 were not detected using the Pan-PRV assay. It is concluded that commercial and enhancement freshwater hatcheries of British Columbia contribute minimally to the prevalence and persistence of PRV-1 in anadromous salmon of the northeastern Pacific, and these hatcheries appear not to have contracted or participated in the distribution of nonendemic forms of PRV in recent years.

Tough places and safe spaces: Can refuges save salmon from a warming climate?

The importance of thermal refuges in a rapidly warming world is particularly evident for migratory species, where individuals encounter a wide range of conditions throughout their lives. In this study, we used a spatially explicit, individual-based simulation model to evaluate the buffering potential of cold-water thermal refuges for anadromous salmon and trout (Oncorhynchus spp.) migrating upstream through a warm river corridor that can expose individuals to physiologically stressful temperatures. We considered upstream migration in relation to migratory phenotypes that were defined in terms of migration timing, spawn timing, swim speed, and use of cold-water thermal refuges. Individuals with different migratory phenotypes migrated upstream through riverine corridors with variable availability of cold-water thermal refuges and mainstem temperatures. Use of cold-water refuges (CWRs) decreased accumulated sublethal exposures to physiologically stressful temperatures when measured in degree-days above 20, 21, and 22°C. The availability of CWRs was an order of magnitude more effective in lowering accumulated sublethal exposures under current and future mainstem temperatures for summer steelhead than fall Chinook Salmon. We considered two emergent model outcomes, survival and percent of available energy used, in relation to thermal heterogeneity and migratory phenotype. Mean percent energy loss attributed to future warmer mainstem temperatures was at least two times larger than the difference in energy used in simulations without CWRs for steelhead and salmon. We also found that loss of CWRs reduced the diversity of energy-conserving migratory phenotypes when we examined the variability in entry timing and travel time outside of CWRs in relation to energy loss. Energy-conserving phenotypic space contracted by 7%-23% when CWRs were unavailable under the current thermal regime. Our simulations suggest that, while CWRs do not entirely mitigate for stressful thermal exposures in mainstem rivers, these features are important for maintaining a diversity of migration phenotypes. Our study suggests that the maintenance of diverse portfolios of migratory phenotypes and cool- and cold-water refuges might be added to the suite of policies and management actions presently being deployed to improve the likelihood of Pacific salmonid persistence into a future characterized by climate change.

A life cycle model for evaluating estuary residency and recovery potential in Chinook salmon

Understanding the spatial and temporal habitat use of a population is a necessary step for recovery planning. For Chinook salmon (Oncorhynchus tshawytscha), variation in their migration and habitat use complicate predicting how restoring habitats could impact total recruitment. To evaluate how juvenile life history variation affects a population’s response to potential restoration, we developed a stage-structured model for a Chinook salmon population in a northern California river with a seasonally closed estuary. We modeled the timing of juvenile migration and estuarine use as a function of freshwater conditions and fish abundance. We used the model to evaluate the sensitivity of the population to different estuary and freshwater restoration scenarios that could affect population parameters at different life stages. The population’s run size increased most in response to freshwater restoration that enhanced spawning productivity (egg and fry survival), followed by spawner capacity. In contrast, estuary restoration scenarios affected only a subset of Chinook salmon (average 15%), and as a result, did not have a large impact on the total recruitment of a cohort. Under current condition, estuary rearing fish were over six times less likely to survive than fish that migrate to the ocean in the spring or early summer before estuary closure. Because estuary residents experienced low survival in the estuary and in the ocean, improvements to both estuary survival and growth would be needed to increase their total survival. When life cycle monitoring data is available, life cycle models such as ours generate predictions at scales relevant to conservation and are an advantageous approach to managing and conserving anadromous salmon that use multiple habitats throughout their life cycle.

Hatchery propagation did not reduce natural steelhead productivity relative to habitat conditions and predation in a mid-Columbia River subbasin

For over 150 years, hatchery-origin anadromous salmon and trout have been reared and released throughout the Pacific Northwest to mitigate for lost habitat and sustain harvest opportunity. Some studies demonstrate that introgression of hatchery and naturally produced fish may constrain conservation efforts through maladaptive genetic processes. However, empirical demonstrations of the influence of these genetic interactions on population productivity are lacking, making it difficult to assess their importance relative to other drivers of productivity. We estimated the effect of the proportion of hatchery-origin spawners (pHOS), proportionate natural influence (PNI), and hatchery fish releases on natural adult winter steelhead recruitment in the Hood River, Oregon, over a 27-year period of record. Adult winter steelhead productivity was not associated with pHOS and PNI. However, natural winter steelhead productivity was positively associated with ocean conditions, stream flow, and hatchery fish release numbers, while negatively associated with pinniped abundance. Our analysis highlights the importance of quantifying the influence of hatchery programs on fish production relative to environmental factors known to affect natural-origin anadromous fish recruitment.

Gene expression levels of synaptic exocytosis regulator synaptophysin in the brain and the olfactory organ of anadromous salmon.

Anadromous Pacific salmon (genus Oncorhynchus) are known for their homing behavior based on olfactory imprinting, which is formed during their seaward migration. Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE/Snare) complex is a minimum unit of vesicle exocytosis from the pre-synaptic membrane. Its component genes (synaptosome-associated protein 25, syntaxin 1, and vesicle-associated membrane protein 2) are more strongly expressed in the olfactory nervous system (olfactory epithelium, olfactory bulb, and telencephalon) at the migration stages related to olfactory imprinting and/or retrieval in salmon. This study focused on the mRNA synthesis of synaptophysin (Syp), one of the Snare regulatory factors. syp is strongly expressed in chum salmon (Oncorhynchus keta) olfactory nervous system during the seaward migration and temporarily increased during the homeward migration. In reference to our previous studies, these expression changes were similar to the snare genes in the chum salmon. Therefore, syp and Snare component genes were synchronously expressed reflecting the development and short-term plasticity of the olfactory nervous system that is essential for olfactory imprinting.

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.

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.

Atlantic Salmon Movement Patterns and Habitat Use during Colonization of Novel Habitat

AbstractAllowing reproductive individuals to colonize novel habitat or recolonize previously occupied habitat is increasingly being considered as a tool for recovery of depleted populations of anadromous salmon. Successful application of these techniques requires thorough understanding of how adults use the riverscape during colonization to ensure that programs achieve desired outcomes. We examined the movements and habitat use of adult Atlantic SalmonSalmo salarduring colonization of novel habitat in an eastern Canadian river using a novel combination of acoustic telemetry, remote sensing, ground surveys, and continuous records of river temperature and discharge. Females moved less than males, regardless of river temperature or discharge, whereas males engaged in more extensive movements except at elevated temperature and discharge. Probability of movement was lower during the summer, coincident with individuals holding in pools during high‐heat/low‐discharge events. River temperature, discharge, and day of year were influential in predicting whether salmon held in pools, and size was the most important physical characteristic identifying “suitable” holding pools. Observed movement patterns may reflect different evolutionary strategies employed by each sex to maximize reproductive fitness. Because spawning behavior is highly conserved within salmonids, these findings may (1) provide a generalized picture of how Atlantic Salmon use space during colonization of unoccupied habitat and (2) be used to optimize future reintroduction and assisted migration programs.

All Fish, All the Time: A Good General Objective for Fish Passage Projects?

Better understanding of the degree of “passability” needed to sustain robust sub‐populations upstream of barriers could help address and perhaps eliminate perceived trade‐offs between fish passage and other resource management goals. We used spatially explicit, individual‐based modeling to explore the population‐level consequences of various levels of upstream passability by (1) adult resident trout, and (2) juvenile salmon. In simulations of a stream network with widespread barriers, adult trout allowed to move upstream during only the highest 4% of streamflows sustained the distribution and abundance of the population to the same extent as in a no‐barrier scenario. In simulations of salmon production in a reach fully accessible to spawning adults, the number of barriers to upstream movement by juvenile salmon did not affect the production of large outmigrants. Passage objectives less ambitious than “all the fish, all the time” may sometimes suffice to maintain populations of resident trout and anadromous salmon.