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Antibiotics can be introduced from aquaculture facilities into marine sediments, where they may affect benthic communities and generate antimicrobial resistance (AMR). Antibiotics can be used in tandem with antiparasitics, and the effects of their combined usage could affect AMR patterns and transmit antibiotic resistance genes. This study compiles patterns of antibiotic and antiparasitic drug usage from 2016 to 2021 in British Columbia, New Brunswick, Newfoundland and Labrador, and Nova Scotia (Canada) and compares them internationally. There is an overall reduction in rates of antibiotic use per fish produced in Canadian aquaculture sites from 2016 to 2021. Compared to other salmon-producing countries, Canadian antibiotic rates per tonne of fish are lower than in Chile, but higher, on average, than in Norway and Scotland. Florfenicol (FLO) and oxytetracycline (OTC) are the prevalent antibiotics used in most salmon-producing countries, including Canada. We also note that <30% of sites used two drugs per year and <18% of sites used three drugs, with most of these sites using one antibiotic and one antiparasitic. There is an increase in FLO and a decrease use in OTC use in Canada, which could be positive environmentally considering FLO's lower dose and environmental persistence. The east and west coasts show comparable antibiotic rates, with an average rate of 78 mg/kg in BC and 76 mg/kg in the Atlantic provinces; however, they have differences in the type of antibiotic (average use of OTC: BC 38 mg/kg vs. Atlantic 214 mg/kg; average use of FLO: BC 40 mg/kg vs. Atlantic 10 mg/kg). Other distinctions between coasts include variation in the timing of treatments, with seasonal use in the Atlantic provinces (May–November) and year-round use in BC. This pattern is likely influenced by differences in water temperature and, subsequently, potential susceptibility to aquatic diseases. Disease prevalence and veterinarian choice/preferred treatments are factors that, we hypothesize, may impact treatment choice; however, additional information is required to adequately comment on this point. This data compilation includes spatial descriptions that could be used for area prioritization in future studies. [ABSTRACT FROM AUTHOR]

Many Atlantic salmon (Salmo salar) populations have experienced significant declines for decades throughout North America and Europe. Mortality due to marine mammal predation during their early marine life could be an important factor contributing to these declines and limiting their population recoveries. However, quantifying predation events, and particularly the extent of marine mammal predation on Atlantic salmon, remains a challenge. In this study, we estimated the contribution of mesothermic and endothermic species predation to the mortality of Atlantic salmon post-smolts during their early marine life using acoustic telemetry. Predation events were inferred from changes in temperatures and depths experienced by acoustically tagged hatchery-reared Atlantic salmon smolts. No salmon were consumed by mesothermic predators, with most endothermic predation events being classified as marine mammals. Post-smolt mortality during the study period was low overall in both years (13.1%–16.7%), with endothermic predation accounting for 33.1%–42.9% of all marine mortality events (5.2%–5.6% mortality). Our results suggest that the current low return of adult Atlantic salmon observed in this area in recent years was not heavily influenced by endothermic predation on post-smolts in the first weeks at sea. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Ecological models are used to understand where fishing vessels operate, improving fisheries management success. The ideal free distribution (IFD) predicts equalization of catch across locations in response to distributions of fish and competing vessels. We applied the IFD as a null model to investigate the movement and catch per vessel (CPUE) of the sockeye salmon drift gillnet fleet in Bristol Bay, AK, from 1980 to 2019. The IFD prediction of equal CPUE across areas was not supported, so we explored violations of two assumptions of the theory. We categorized each vessel according to its mobility, highlighting the "free to move" assumption, and found that when we removed nonmobile vessels, some districts had fewer vessels than predicted from their high CPUE. We examined the "equal competitive ability" assumption by calculating the average CPUE, relative to success of other vessels. The underutilization of profitable districts persisted. Overall, the fleet underused high CPUE areas when considering differences in mobility and relative fishing success, indicating that unmeasured safety concerns, travel costs, knowledge of fishing grounds, or other factors could be preventing an IFD. [ABSTRACT FROM AUTHOR]

Chinook salmon (Oncorhynchus tshawytscha) in the Columbia River basin are threatened by anthropogenic changes to migratory corridors, estuaries, and natal habitats. Streams provide spatially heterogeneous natal habitats essential for salmon spawning and rearing life stages. We fit a statistical state-space model to salmon populations in Idaho's Middle Fork Salmon River (MFSR) to assess spatial variation in natal productivity and population growth. Our model integrated multiple long-term data sets to estimate variation in per-capita smolt production and smolt-to-adult (SAR) survival. Smolt production varied across stream segments, averaging 104.48 female smolts per spawning female, while SARs averaged 0.74%. Chinook salmon population growth rates exceeded replacement in 17% of segments (4 of 23). By increasing SARs to 1.8% (near the lower bound of Columbia River basin recovery targets), we predict that all 23 MFSR segments will yield positive population growth rates at contemporary (very low) spawner densities. Our analysis suggests that for Snake River basin populations within high-quality natal habitats, SAR improvements will elevate salmon population growth rates and enhance restoration of at-risk wild Chinook salmon. [ABSTRACT FROM AUTHOR]

Diadromous fish populations have incurred precipitous declines across the globe. Among many stressors, these species are threatened by anthropogenic barriers that impede movement, alter riverine habitat, and augment predator communities. In this study, we used acoustic transmitters (n = 220) with predation and temperature sensors to characterize Atlantic salmon (Salmo salar) smolt predation risk in the Penobscot River, Maine, USA. Across two seasons, we documented 79 predation events through a 170 km migratory pathway, which included three hydropower projects and a large estuary. We detected tagged smolts that were predated by fish (n = 42), marine mammals (n = 28), and birds (n = 9). Using a multistate mark-recapture framework, we estimated that 46% of smolts were predated during downstream migration, which accounted for at least 55% of all mortality. Relative predation risk was greatest through impoundments and the lower estuary, where on average, predation rates were 4.8-fold and 9.0-fold greater than free-flowing reaches, respectively. These results suggest that predation pressure on Atlantic salmon smolts is exacerbated by hydropower projects and that predation in the lower estuary may be greater than expected. [ABSTRACT FROM AUTHOR]

In response to a federal government order, the number of salmon farms operating in the Discovery Islands region declined from eight in 2020, to one in 2022. Over this period, 1627 juvenile pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon captured at sites throughout the study area were examined for sea lice. The average number of sea lice per juvenile salmon declined by 96% over the study period. Such a substantial decline was not witnessed in similar samples from the nearby Broughton Archipelago. The decline could not be attributed to chance sampling, and only a small proportion of it was associated with environmental fluctuations. [ABSTRACT FROM AUTHOR]

Managers and stakeholders increasingly ask whether predation is a driving force behind the poor status of many species, and whether predator control is likely to be a successful management action to intervene. We review existing literature on Atlantic salmon Salmo salar predation and predator control, as well as general ecological theory on the role of predation in the life cycle of this iconic fish. Many bird, mammal, and fish predators target salmon at different life stages. In healthy salmon populations, predation is likely compensated for by reduced intraspecific competition during the freshwater stage. There is little evidence that predation alone has been an underlying mechanism for driving salmon populations below conservation limits. However, depending on the predator's response to salmon abundance, predation may keep decimated populations from recovering, even when the actual causes of decline have been removed. Under such a scenario, predation control may contribute to recovery, but there are no strong examples that clearly demonstrate the efficacy of managing predators to recover threatened salmon populations, challenging further applications. [ABSTRACT FROM AUTHOR]

A new state space stock –recruitment (SR) model (XSR) was developed to treat observation errors in spawner and catch data, and nonstationarity in productivity for pink salmon (Oncorhynchus gorbuscha). Closed loop simulation was used to evaluate the management performance of XSR and compare its performance with that of a traditional SR model (TSR) and a Kalman Filter (KF). XSR produced higher expected catch than TSR and KF over a wide range of conditions. In some situations, TSR was preferred for reducing conservation concerns. However, large "outcome uncertainty" (OU) or implementation error in achieving desired management objectives can substantially reduce the management benefits of all assessment methods. Thus, OU should be considered in all management strategy evaluations, otherwise results will be misleading. Accordingly, reducing OU may better help achieve objectives. [ABSTRACT FROM AUTHOR]

During spawning migrations, adult Pacific salmon (Oncorhynchus spp.) must undergo a suite of morphological and physiological changes to prepare for spawning. Modern genomics approaches can be used to conduct nonlethal assessments of physiology and infectious agent presence in migrating salmon. We investigated gene expression changes and shifts in the prevalence and load of 18 infectious agents in the gill tissue of adult sockeye salmon (Oncorhynchus nerka) during the final 50 km of their freshwater migration. We found 77% of fish successfully migrated to spawning grounds. Fish exhibited a decrease in thermal stress gene expression following lake migration, consistent with the hypothesized benefits of thermal refugia during spawning migrations. We also found evidence of cooler water selection (∼1.5 °C) during lake migration for fish with higher infection burden, suggesting behavioural changes for fish suffering higher infection burdens and potential benefits of thermal refuges for reducing the negative impacts of infection for migrating salmon. Collectively, our findings provide further evidence that fish behaviourally regulate exposure to stressful conditions such as high temperature that may undermine survival. [ABSTRACT FROM AUTHOR]

The portfolio effect plays a critical role in population productivity and stability. Age structure of spawning salmon represents an example of portfolio effects such that the risks of experiencing unfavorable conditions are spread across time. However, the distribution of maturation ages for Pacific salmon (Oncorhynchus spp.) is increasingly concentrated into fewer and younger ages, which may impact population resilience to climate change. We explored the population dynamics of Sacramento River fall-run Chinook salmon (O. tshawytscha) under different age structure scenarios using a life-cycle model and compared two mechanisms that can underlie these changes—mortality and maturation. In addition, we tested whether age structure promotes resilience to drought. We found that high age structure diversity increased the stability of population size and harvest compared with low diversity. However, mean population size responded differently depending on the underlying mechanism. Reduced mortality of adult fish ages 4–5 increased escapement, whereas delayed maturation decreased escapement. Overall, high age structure diversity was able to buffer against the adverse effects of droughts by reducing the variability of population size and harvest compared with low diversity. Our results suggest that age structure promotes stability of salmon in an increasingly variable climate. [ABSTRACT FROM AUTHOR]

Mismatches between institutions and social–ecological systems (SESs) are one of the foremost challenges in natural resource management. However, while mismatches are often cited in the literature as a major challenge, empirical evidence of mismatches and their consequences is limited. This is particularly true for complex SESs, such as on the Pacific Coast of North America, where salmon drive interactions across multiple environments, jurisdictions, and scales. Here, I use the theoretical concept of fit to examine institutional alignment in a large-scale Pacific salmon SES, the Skeena River watershed in British Columbia, Canada. Utilizing Canadian federal environmental assessments as a proxy for colonial environmental governance institutions, I describe the common causes and consequences of mismatches between institutions and salmon SESs. This case study suggests that mismatches are threatening salmon sustainability and negatively affecting Indigenous People’s rights, livelihoods, and approaches to resource management and stewardship. I argue that improving social–ecological fit in salmon SESs will require new or revitalized forms of environmental governance that consciously fit the underlying social–ecological dynamics. While these findings are based on the Skeena River watershed, they may be generalizable to other salmon SESs in which mismatches between social and ecological processes and institutions exist.

Salmon hatcheries are management tools intended to stabilize declining abundance in salmon populations and sustain salmon fisheries. One key area of uncertainty is how hatchery release practices influence juvenile-to-adult survival. Data quality and quantity vary considerably among hatcheries making it difficult to assess the role of release practices. Using a Bayesian hierarchical approach, we analyzed releases and recoveries of Chinook (Oncorhynchus tshawytscha; 21 hatcheries) and coho (Oncorhynchus kisutch; 16 hatcheries) salmon in British Columbia from 1972 to 2017. Higher survival rates were associated with increasing weights-at-release, earlier releases of Chinook salmon, and later releases of coho salmon. The addition of environmental (sea surface temperature, Pacific Decadal Oscillation), and predator (harbour seals, killer whales) covariates did not improve model performance relative to models that used year effects to account for declines in survival and interannual variability in ocean conditions. Optimizing release practices could increase returns by 6%–245% for Chinook salmon and 5%–160% for coho salmon based on median posterior estimates for each hatchery. With these results, a large-scale adaptive management approach could be implemented to test our understanding of release practice–survival relationships and evaluate cost–benefit trade-offs. [ABSTRACT FROM AUTHOR]

Fish in all the world's oceans exhibit variable body size and growth over time, with some populations exhibiting long-term declines in size. These patterns can be caused by a range of biotic, abiotic, and anthropogenic factors and impact the productivity of harvested populations. Within a given species, individuals often exhibit a range of life history strategies that may cause some groups to be buffered against change. One of the most studied declines in size-at-age has been in populations of salmon; Chinook salmon in the Northeast Pacific Ocean are the largest-bodied salmon species and have experienced long-term declines in size. Using long-term monitoring data, we develop novel size and growth models to link observed changes in Chinook size to life history traits and environmental variability. Our results identify three distinct trends in size across the 48 stocks in our study. Differences among populations are correlated with ocean distribution, migration timing, and freshwater residence. We provide evidence that trends are driven by interannual variation in certain oceanographic processes and competition with pink salmon. [ABSTRACT FROM AUTHOR]

Hatcheries are frequently used to support or restore threatened Atlantic salmon populations. However, little is known about how rearing affects behaviour and fitness of hatchery adults that return to the river to spawn. We used acoustic telemetry to compare migration patterns exhibited by hatchery (N = 16) and wild (N = 12) Atlantic salmon spawners within a river system in Norway. Hatchery Atlantic salmon in this study were released as smolts and were identified by their missing adipose fin upon return to rivers after 1+ winters spent at sea. Hatchery-origin Atlantic salmon displayed aberrant reverse movement behaviour, by moving with frequent reversals between the river and the fjord, a behaviour that was not observed in any wild Atlantic salmon. No difference in survival and outmigration timing after spawning was found for the two groups. The observed effect of hatchery origin on behavior may have implications for stock assessments made to assess the progress of restoration in the river, particularly if behavioural differences impact catchability or detections of returning adult salmon. The consequences of different movement patterns are uncertain; however, movements are energetically costly and may ultimately impact the fitness of hatchery Atlantic salmon. [ABSTRACT FROM AUTHOR]

The growth of the net pen salmon farming industry and the concurrent decline of many wild salmon populations have generated an ongoing call for research into the potential role of infectious agents associated with salmon farming. Here, we describe a method to screen for the presence of viral nucleic acids by sampling biological waste in the vicinity of farms. We collected biological samples adjacent to 56 marine net pens from five different companies, and two farm salmon processing plants (n = 230), 70% of samples were positive for Piscine orthoreovirus-1 (PRV-1). Viral genome segments S1 (n = 68) and M2 (n = 39) were sequenced and subjected to phylogenetic analysis. Sequences were all monophyletic to the clade of PRV-1 routinely found in the region. Consistent with previous studies, samples collected near Atlantic salmon (Salmo salar) farms were related to a lineage of PRV-1a commonly detected in both farmed and wild salmon in British Columbia, while a related lineage of PRV-1a was detected near Chinook salmon (Oncorhynchus tshawytscha) farms. Similarity in sequence within companies suggests that Atlantic salmon freshwater hatcheries are a probable source of this virus to the marine environment, concordant with recent detections of PRV-1 within those hatcheries. [ABSTRACT FROM AUTHOR]

The post-smolt phase is considered a critical period for Atlantic salmon (Salmo salar). Hence, identifying migration routes used by post-smolts is needed to protect the habitats they require to successfully complete their life cycle. We used a biophysical model coupled with output from a water circulation model (FVCOM) to simulate dispersal of Atlantic salmon post-smolts in a semi-enclosed bay: Passamaquoddy Bay, New Brunswick, Canada. The model was run with nine post-smolt behaviours and six swimming speeds, and then tested against acoustic telemetry data. While no modelled behaviour entirely captured observed salmon migration routes, we identified some behaviours that could allow salmon to successfully leave the bay and resulted in predictions that matched observations reasonably well (e.g., swimming southwest, negative, or tide-varying rheotaxis). We could also rule out several behaviours as unlikely to be used by Atlantic salmon post-smolts in this area (e.g., passive dispersal, orienting based on salinity or temperature, and positive rheotaxis). Hence, with suitable behaviours and models, this approach can provide estimates of the essential habitats and migration routes of wild post-smolts. [ABSTRACT FROM AUTHOR]

In recent decades, chum salmon (Oncorhynchus keta) on the Central and North Coasts of British Columbia have experienced increasing variability and declining abundance. Chum are targeted by mixed-stock commercial fisheries despite declining trends and limited stock assessment to clarify conservation and fishery tradeoffs. We analyzed trends in chum salmon run sizes to 25 watersheds in the Central Coast region, to support co-governance of fisheries under newly ratified Fisheries Resources Reconciliation Agreement. Central Coast chum have declined by ∼90% since 1960, and only three populations did not undergo an evident decline. Bella Coola enhanced chum had an increasing trend but have experienced 29-fold variation in run sizes since 2005. Recently, Bella Coola enhanced chum comprised over 50% of Central Coast chum abundance and the contribution of this stock to overall abundance has more than tripled (from 13.8%) since enhancement began. Given concerns about the long-term health of chum salmon stocks and the social–ecological systems they support, commercial fisheries were closed on the Central Coast in 2021. If current trends continue, fishery opportunities may remain limited. [ABSTRACT FROM AUTHOR]

Extirpation of the Central Valley spring-run Chinook salmon (Oncorhynchus tshawytscha) evolutionary significant unit (ESU) from the San Joaquin River is emblematic of salmonid declines across the western seaboard of the United States. Habitat restoration and fish reintroduction efforts are ongoing, but recent telemetry studies have revealed low outmigration survival of juveniles to the ocean. Previous investigations have focused on modeling survival relative to river discharge and geographic regions, but have largely overlooked the effects of habitat variability. To evaluate the link between environmental conditions and survival of juvenile spring-run Chinook salmon, we combined high spatial resolution habitat mapping approaches with acoustic telemetry along a 150 km section of the San Joaquin River during the spring of 2019. While overall outmigration survival was low (5%), our habitat-based classification scheme described variation in survival of acoustic-tagged smolts better than other candidate models based on geography or distance. Two regional mortality sinks were evident along the longitudinal profile of the river, revealing poor survival in areas that shared warmer temperatures but that diverged in chlorophyll a, fluorescent dissolved organic matter (fDOM), turbidity, and dissolved oxygen levels. These findings demonstrate the value of integrating river habitat classification frameworks to improve our understanding of survival dynamics of imperiled fish populations. [ABSTRACT FROM AUTHOR]

Chinook salmon (Oncorhynchus tshawytscha (Walbaum, 1792)) from the upper Yukon River are highly unique, with some populations migrating nearly 3000 km to spawning habitat near the northern range limit for the species. We conducted a 4-year study to understand the behaviour of Chinook salmon in the terminal reaches of their migration by tagging salmon with acoustic and radio transmitters in Whitehorse, Yukon, Canada, ∼2800 km from the ocean. Various migration characteristics were quantified for Chinook salmon, including en route mortality, diel behaviour, migration rates, and homing patterns, and associations with salmon origin (wild vs. hatchery), sex, size, and migration timing were explored. Salmon had high survival to spawning grounds (>98%) and migrated throughout all hours of the day, with higher proportions of nighttime movements in a smaller spawning tributary than in the Yukon River mainstem. Migration rates were faster for larger salmon as well as late-arriving salmon, which was likely necessary to ensure they had sufficient time and suitable conditions on spawning grounds to reproduce. Non-direct homing movements (e.g., tributary exploration) were more common in male salmon and considerably increased migration distance through the study area. Findings from this study may help to inform the complex international and inter-nation management of these increasingly threatened Chinook salmon populations. [ABSTRACT FROM AUTHOR]

People use dietary supplements to offset nutritional deficiencies and manage metabolic dysfunction. While the beneficial effect of fish proteins on glucose homeostasis is well established, the ability of fish peptides to replicate the protein findings is less clear. With financial support from a programmatic Canadian Institutes of Health Research (CIHR) Team grant, we aimed to identify salmon peptide fractions (SPFs) with the potential to mitigate metabolic dysfunction. Additionally, the grant aims included assessing whether vitamin D, a nutrient commonly found in salmon, could potentiate the beneficial effects of salmon peptides. In parallel, technologies were developed to separate and filter the isolated peptides. We employed an integrative approach that combined nutritional interventions in animal models and human subjects to identify metabolic pathways regulated by salmon peptides and other fish nutrients. This combination of interdisciplinary expertise revealed that a SPF could be a therapeutic tool used in the prevention and management of cardiometabolic diseases. Herein, we present a perspective of our CIHR funded grant that utilized a translational approach to establish the cardiometabolic health effects and mechanisms of action of fish nutrients: from animal models to clinical trials., Competing Interests: AM and LB hold patent WO 2021/108916 A1 Peptides for regulating glucose. PLM, GP, M-CV, HJ, CG and JSW declare no conflict of interest.

Rapid climate change is altering Arctic ecosystems and significantly affecting the livelihoods and cultural traditions of Arctic Indigenous peoples. In the Inuvialuit Settlement Region (ISR), growing evidence suggests that climate change is altering marine environments. In this project we recorded and synthesized Inuvialuit knowledge of Pacific salmon. We used methods that are emergent in fisheries science to combine interview information with voluntary harvest data and better understand changes to salmon in the Arctic. We conducted 53 interviews with Inuvialuit fishers about the history of Pacific salmon harvest, how it has changed in recent decades, and concurrent changes to local environments and fish species. Our interviews show that historical, incidental salmon harvest in the ISR ranged from infrequent to common among western communities, but was rare or unprecedented among eastern communities. Participants in all six communities reported a recent increase in salmon harvest and attributed this shift to regional environmental change. Fishers were concerned that salmon would negatively affect their cultural traditions and preferred fish species. Given uncertainty about the effects of salmon on local fisheries, research on salmon in the Arctic, the likelihood of their establishment, and their potential to provide subsidies to Arctic freshwater ecosystems is vital. [ABSTRACT FROM AUTHOR]

Each year, juveniles of eight salmonid species enter the Salish Sea — the inland marine waters between northwestern Washington, USA, and British Columbia, Canada. These species vary in the proportions remaining there and migrating to feed in the Pacific Ocean. Such differential migration affects their growth rates and exposure to habitat alteration, predators, fisheries, and contaminants. We review these diverse migration patterns and present data from Puget Sound illustrating the variation in downstream migration timing, residency in the Salish Sea, and upriver return timing. Recreational catch records indicate that proportionally fewer remain in the Salish Sea than in past decades for several species, and the declines began after peaks in the late 1970s – early 1980s. These declines resist easy explanation because the factors controlling residency are poorly understood, and the Salish Sea has changed over the past decades. Regardless of the cause, the diversity of migration patterns is important to the ecology of the salmon and trout species and to the humans and other members of the Salish Sea community with which they interact. [ABSTRACT FROM AUTHOR]

Inner Bay of Fundy Atlantic salmon (Salmo salar) are endangered anadromous fish that have the potential to provide marine-derived nutrients (MDNs) to freshwater ecosystems depending on their population abundance. Salmon have been reintroduced to the Upper Salmon River, but not to the adjacent Point Wolfe River, in Fundy National Park, New Brunswick, Canada. This study determined whether stocking of adult salmon increased the productivity of the river. To examine the incorporation of MDNs, biofilm, leaf litter, Perlidae, Heptageniidae and brook trout (Salvelinus fontinalis) were sampled pre- and post-spawning in 2015–2017 from down- and upstream of a natural barrier in both rivers and analyzed for carbon (δ13C) and nitrogen (δ15N) isotopes. After salmon spawning in each year, all organisms at the downstream site of the stocked river increased in δ13C and δ15N, with the greatest enrichment in brook trout (δ13C: −23.97‰ to −21.10‰, δ15N: +6.36‰ to +10.73‰). The proportion of MDNs in brook trout after salmon spawning (2015: 23.4%, 2016: 40.7%, 2017: 37.4%) also increased with higher numbers of released adult salmon. Results support the importance of salmon restoration for increasing the proportion of MDNs and productivity in rivers in Atlantic Canada. [ABSTRACT FROM AUTHOR]

The distributional extent of Pacific salmon (Oncorhynchus spp.) in the North American Arctic is unresolved. While adult Pacific salmon have a recurring presence across the Alaskan North Slope and into the Canadian Arctic, it is uncertain if these fish are part of established Arctic populations, vagrants from outside sources reproducing unsuccessfully, or both. Here we present the first confirmed record of a juvenile chum salmon (Oncorhynchus keta) captured in the nearshore marine ecosystem in the North American Arctic. This provides the first scientific evidence of successful spawning and early marine survival of Pacific salmon in the North American Arctic. It was caught near Kaktovik, Alaska, in August 2017 with a group of similarly sized age-0 Mackenzie River Arctic cisco (Coregonus autumnalis). Stable isotope and otolith microchemistry analyses are consistent with use of the nearshore estuarine corridor from the Mackenzie River west along the northern coast. This contributes critical information needed to identify, manage, and conserve biodiversity at the northern range edge and will help to clarify the status of Pacific salmon as potentially emerging fisheries develop in the North American Arctic due to climate warming. [ABSTRACT FROM AUTHOR]

Experiments examining potential impacts of growth hormone (GH) transgenesis in fish typically use a single source strain and do not address potential differential impacts in strains of different genetic backgrounds. Here, we examine the effects of differing genetic backgrounds when reared in culture on the growth of transgenic and nontransgenic coho salmon (Oncorhynchus kisutch) produced by mating sires from different rivers with transgenic dams from a single origin. We found a significant difference in size between offspring of sires originating from various river systems in British Columbia. This difference was independent of differences between transgenotypes (i.e., transgenic vs. nontransgenic offspring). However, the effects of strain or sire were relatively small compared to the effects of the transgene, which were consistent regardless of sire origin. Thus, results derived from studies of GH transgenic fish from a single source population can provide useful information for assessments of GH transgenic salmon from other systems. This has important implications for examining potential risks from introgression of a transgene into different populations. [ABSTRACT FROM AUTHOR]

Salmonids possess straying abilities that allows them to exploit open territory and establish new populations. Atlantic salmon (Salmo salar) are expanding their distribution primarily as first-generation escapes from aquaculture, whereas Pacific salmon (Oncorhynchus spp.) are expanding their range in polar and temperate regions due to both anthropogenic and natural influences. Here we utilize artificial intergeneric reciprocal crosses to assess the ability of seven species of Pacific salmon to hybridize with Atlantic salmon. Most cross types were found to produce low numbers of hatched embryos, but none survived to sexual maturation. Survivors consisted of diploids and triploids containing both Atlantic and Pacific salmon parental genomes. Thus, introgression of DNA between Pacific and Atlantic salmon may occur to form F1 hybrids, but transmission to subsequent generations is expected to be rare and occur only over evolutionary time scales. Further, the low viability observed for the most part at early stages of development and in both reciprocal crosses indicates that intergeneric crosses in nature between Atlantic and Pacific salmon are expected to have severe fitness consequences for both dams and sires. [ABSTRACT FROM AUTHOR]

Groundwater upwellings provide warmer, stable overwinter temperatures for developing salmon embryos, which may be particularly important in cold, braided, gravel-bed sub-Arctic rivers. We used a three-year time series of aerial counts and remote sensing to estimate the distribution of low and high aggregations of spawning fall chum salmon (Oncorhynchus keta), classify approximately 0.5 km long river segments by geomorphic channel type, and map thermal variability along a 25.4 km stretch of the Teedriinjik River, Alaska. We used a dynamic multistate occupancy model to estimate detectability, occupancy, and the dynamics of spawning aggregations among river segments. Detectability was higher for large (>150) relative to smaller aggregations. Unoccupied segments were likely to remain so from year to year; low abundance spawning segments were dynamic and rarely remained in that state for multiple years, while ∼20%–35% of high abundance segments remained stable, indicating the presence of high-quality spawning habitat. Spawning habitat use was associated with warmer water temperatures likely caused by groundwater upwellings. We identified spawning habitat characteristics and trends in usage by fall chum salmon, which will inform land management decisions and assist in evaluating impacts of shifting climate conditions and resource management on Arctic salmon populations. [ABSTRACT FROM AUTHOR]

In the Pacific Northwest, USA, climate change is expected to result in a shift in average hydrologic conditions and increase variability. The relative vulnerabilities to peak flow changes among salmonid species within the same basin have not been widely evaluated. We assessed the impacts of predicted increases in peak flows on four salmonid populations in the Chehalis River basin. Coupling observations of peak flows, emissions projections, and multi-stage Beverton–Holt matrix-type life cycle models, we ran 100-year simulations of spawner abundance under baseline, mid-century, and late-century climate change scenarios. Coho (Oncorhynchus kisutch) and spring Chinook salmon (Oncorhynchus tshawytscha) shared the highest projected increase in interannual variability (SD = ±15%). Spring Chinook salmon had the greatest reduction in median spawner abundance (–13% to –15%), followed by coho and fall Chinook salmon (–7% to –9%), then steelhead (Oncorhynchus mykiss) (–4%). Our results show that interspecies and life history variability within a single basin is important to consider. Species with diverse age structures are partially buffered from population variability, which may increase population resilience to climate change. [ABSTRACT FROM AUTHOR]

Changes over time in age, sex, and length-at-age of returning Pacific salmon have been widely observed, suggesting concurrent declines in per capita reproductive output. Thus, assessment models assuming stationary reproductive output may inaccurately estimate biological reference points that inform harvest policies. We extended age-structured state-space spawner–recruit models to accommodate demographic time trends and fishery selectivity to investigate temporal changes in reference points using Kuskokwim River Chinook salmon (Oncorhynchus tshawytscha). We illustrate that observed demographic changes have likely reduced per capita reproductive output in an additive manner, for example, models including changes in both length-at-age and age composition showed larger declines than models incorporating only one time trend. Translated into biological reference points using a yield-per-recruit algorithm, we found escapement needed for maximum sustained catch has likely increased over time, but the magnitude further depended on size-selective harvest (i.e., larger increases for reference points based on larger mesh gillnets). Compared to traditional salmon assessments, our approach that acknowledges demographic time trends allows more complete use of available data and facilitates evaluating trade-offs among gear-specific harvest policies. [ABSTRACT FROM AUTHOR]

The concept of health permeates priorities and policies for managing wild Pacific salmon (Oncorynchus spp.). Regulatory agencies rely largely on salmon abundance and (or) the absence of pathogens to declare if a population is healthy. Our goal was to determine if there was a receptive policy environment within Fisheries and Oceans Canada (DFO) to adopt a cumulative effects perspective of health. We used a previously developed health model along with a multiple streams framework and a narrative review of DFO policy to see how fish health was situated in DFO’s salmon management problems, policy, and politics. We discovered that a cumulative effects perspective was consistent with policy goals and priorities. DFO’s guiding principles and responsibilities for aquatic animal health were spread across multiple policies and regulations. There were no processes or people responsible for integrating information and activities. The use of the word health in policies and planning without a consistent definition meant that DFO could not explicitly assess if it has reached its management target of healthy salmon. An option for transitioning to cumulative effects perspective is to adopt a healthy public policy perspective and processes to integrate the diverse information linked to social and environmental determinants of health.

There is increasing interest in defining optimal conditions for rearing salmon to market size in recirculating aquaculture systems (RAS). Salinity, however, as a parameter that can be potentially manipulated, has been poorly studied. To address this knowledge gap, we reared coho (Oncorhynchus kisutch (Walbaum, 1792)) and Atlantic (Salmo salar Linnaeus, 1758) salmon from smolt to market size over ∼460 days at five different salinities (0, 5, 10, 20, and 30 ppt) and examined their growth performance. We found that both species reared at intermediate salinities (5–10 ppt) started to show significantly larger body mass than fish reared either in freshwater or full-strength seawater at around days 250–300. These growth-enhancing effects were maintained until day 460. The higher growth in Atlantic salmon at intermediate salinities was associated with a reduced economic feed conversion ratio, but this was not observed in coho salmon. The all-female coho salmon showed no incidence of sexual maturation and negligible cataract formation, while the mixed-sex Atlantic salmon showed high levels of sexual maturation (up to 50%) and presence of cataracts (up to 60%). Our results indicate that all-female coho salmon may be better suited to RAS than Atlantic salmon in some aspects. However, in both species, long-term rearing at intermediate salinities improved growth in RAS. [ABSTRACT FROM AUTHOR]

Management of protected species is difficult when objectives include the recovery of both predator and its prey. Ideally, identifying trade-offs between competing objectives involves evaluating management alternatives with a quantitative model that integrates information on both species, but data are often limited. We used new predator diet data and simulation modeling to update our understanding of seal predation on juvenile Chinook (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) in the Puget Sound. Under prey size assumptions used by previous studies, estimates suggest predation could be a significant source of mortality for Chinook salmon (mean: 37% of ocean age-0 juveniles), but varied considerably among years (range of median estimates: 22%–49%). However, when we estimated prey size from otoliths recovered from seal scats, the impact (numbers of fish consumed) decreased by 71%. Predation on coho salmon was estimated to be relatively low under both scenarios (6%–8% of ocean age-0 juveniles) with a 21% decrease in consumption using otolith-derived prey size. Our analysis highlights the importance of updating model inputs and re-evaluating assumptions of multi-species models used for ecosystem-based fisheries management. [ABSTRACT FROM AUTHOR]

Understanding and quantifying migration phenology of commercially harvested Pacific salmon (Oncorhynchus spp.) is a cornerstone for managing sustainable populations. Here, we use a multidecadal data time series together with a hypothesis-driven framework to evaluate migration phenology in adult fall and winter ecotype chum salmon (O. keta) in a poorly studied but highly managed system — the South Puget Sound (SPS) of Washington State, USA. Using generalized additive mixed models that accounted for temporal autoregressive dynamics, we examined the effect of commercial harvest, climate variation, intraspecific density dependence, and predator buffering on migration timing and run duration. SPS chum salmon are migrating earlier over time, especially the winter ecotype that showed the strongest temporal shift from historical timing. Migration timing shifts were closely associated with regional marine climate regimes, local scale freshwater availability, and increasing pinniped abundance. We conclude that there is potential for the winter ecotype migration converging with that of the fall ecotype and that directional change in migration phenology may be driven by a unique combination of ecosystem factors. [ABSTRACT FROM AUTHOR]

The movement of individuals according to the availability of resources has a fundamental effect on animal distributions. In the Pacific Northwest, Bald Eagles (Haliaeetus leucocephalus (Linnaeus, 1766)) rely heavily on scavenging opportunities during the non-breeding period, and their distribution and movements are thought to be strongly influenced by the availability of post-spawning Pacific salmon (genus Oncorhynchus Suckley, 1861) carcasses. We surveyed the abundance of eagles and salmon on four adjacent rivers on Vancouver Island, British Columbia, Canada, during the 2017 fall spawning season. Salmon began to arrive in late September, peaked in abundance in mid-November, and were absent after early December. The seasonal progression of Bald Eagle abundance matched that of salmon carcass availability. The slope of proportional eagle–salmon relationship was significantly positive, though lower than the 1:1 match predicted by Ideal Free Distribution theory. The numerical response of Bald Eagles to salmon abundance was elevated on one of the rivers, potentially due to physical features such as sandbars and mudflats that increased the availability of carcasses and provided access points for eagles. [ABSTRACT FROM AUTHOR]

There is a need to explicitly consider metapopulation dynamics in the development of conservation strategies for spatially structured populations. We examined the spatial dynamics of sockeye salmon (Oncorhynchus nerka) that spawn in 36 streams of the Stuart River watershed in British Columbia, Canada, using a 69-year record of spawner abundance and a demographically based Bayesian dynamic occupancy model. We identified a set of 12 streams with good habitat conditions that were occupied >90% of years despite large year-to-year changes in abundance. Over 85% of spawners were concentrated in these streams. Many other streams with poorer habitat had small populations that were not persistent over time and were periodically recolonized by dispersers from other streams. Although it is often assumed population diversity and resiliency is maximized when all available habitats are used, for this salmon metapopulation, resiliency is due to the core streams of higher habitat quality. Currently, other streams make only small contributions to population abundance; however, some may have conservation value if their habitats become more suitable for spawning in the future. [ABSTRACT FROM AUTHOR]

Strontium isotopes (87Sr/86Sr) recorded in the otoliths of Pacific salmon (Oncorhynchus spp.) are commonly used to identify natal origin. For species that migrate at or soon after emergence, the embryonic region of the otolith provides the only record of provenance. However, maternal contribution of Sr from the yolk can confound the isotopic signature of the natal site. We experimentally quantified maternal and exogenous diet contributions to otolith 87Sr/86Sr over embryonic development in kokanee salmon (Oncorhynchus nerka). Eggs from two populations in isotopically distinct lakes were incubated and reared in a common water source. Timing of developmental events and proportional contribution from yolk to otolith 87Sr/86Sr differed significantly between the two populations. We suggest that the magnitude of difference in 87Sr/86Sr between yolk and water, the relative concentrations of Sr and Ca in these isotopic sources, and population-specific effects on otolith growth and composition contribute to this variation. Understanding how these factors affect otolith 87Sr/86Sr could extend the use of otolith geochemistry for determining provenance to species and populations in which natal site rearing is limited. [ABSTRACT FROM AUTHOR]

An array of predators that consume juvenile salmon (genus Oncorhynchus Suckley, 1861) may account for the poor returns of adult salmon to the Salish Sea. However, the Pacific Great Blue Heron (Ardea herodias fannini Chapman, 1901) is rarely listed among the known salmon predators, despite being regularly seen near salmon streams. Investigating heron predation by scanning nesting sites within 35 km of three British Columbia (Canada) rivers for fecal remains containing passive integrated transponder (PIT) tags implanted in >100 000 juvenile salmon from 2008 to 2018 yielded 1205 tags, representing a minimum annual predation rate of 0.3%–1.3% of all juvenile salmon. Most of this predation (99%) was caused by ∼420 adult Pacific Great Blue Herons from three heronries. Correcting for tags defecated outside of the heronry raised the predation rates to 0.7%–3.2%, and was as high as 6% during a year of low river flow. Predation occurs during chick-rearing in late spring and accounts for 4.1%–8.4% of the Pacific Great Blue Heron chick diet. Smaller salmon smolts were significantly more susceptible to Pacific Great Blue Heron predation than larger conspecifics. The proximity of heronries relative to salmon-bearing rivers is likely a good predictor of Pacific Great Blue Heron predation on local salmon runs, and can be monitored to assess coast-wide effects of Pacific Great Blue Herons on salmon recovery. [ABSTRACT FROM AUTHOR]

Fraser River Pacific salmon have declined in recent decades, possibly from parasitism by sea lice (Caligus clemensi and Lepeophtheirus salmonis). We describe the abundance of both louse species infesting co-migrating juvenile pink (Oncorhynchus gorbuscha), chum (Oncorhynchus keta), and sockeye (Oncorhynchus nerka) salmon over 5 years in the Discovery Islands and Johnstone Strait, British Columbia. The generalist louse, C. clemensi, was 5, 7, and 39 times more abundant than the salmonid specialist, L. salmonis, on pink, chum, and sockeye salmon, respectively. Caligus clemensi abundance was higher on pink salmon (0.45, 95% CI: 0.38–0.55) and sockeye (0.39, 95% CI: 0.33–0.47) than on chum salmon. Lepeophtheirus salmonis abundance was highest on pink salmon (0.09, 95% CI = 0.06–0.15). Caligus clemensi had higher abundances in Johnstone Strait than in the Discovery Islands. These results suggest differences in host specialization and transmission dynamics between louse species. Because both lice infest farmed salmon, but only C. clemensi infests Pacific herring (Clupea pallasii), conservation science and management regarding lice and Fraser River salmon should further consider C. clemensi and transmission from farmed salmon and wild herring. [ABSTRACT FROM AUTHOR]

Fish face many anthropogenic stressors. Authorities in marine, estuarine, and freshwater realms often share interdependent fisheries management goals, but address singular stressors independently. Here, we present a case study suggesting that coordinating stressor relief across management realms may synergize conservation efforts, especially to actualize restoration benefits. Major efforts are underway to restore juvenile salmon habitat across California's Central Valley landscape, but it is unclear how fisheries and flow management will influence juvenile salmon occupancy of restored sites. Leveraging monitoring data, we find that for juvenile salmon (<55 mm) to actualize benefits of restored habitats will likely require maintaining spawner abundances and flows at or above intermediate values, especially in less-connected portions of the landscape. Furthermore, restoration efforts may prioritize more connected regions to promote use of restored areas, considering that less connected areas are often uninhabited when water and spawners are scarcer. This ecosystem-based framework that evaluates interdependencies of management decisions may be applied to realize natural productivity and enhance conservation in many systems. [ABSTRACT FROM AUTHOR]

Coastal watersheds of the North Pacific benefit immensely from bear-mediated uploading of salmon nutrients, which increases aquatic and terrestrial productivity. To quantify the influence of spawning salmon on tree-ring signatures, we analyzed 543 rings from the heartwood of 13 old-growth Sitka spruce (Picea sitchensis (Bong.) Carrière) trees from five geographically separated watersheds in coastal British Columbia. In comparison with adjacent control trees, those receiving salmon nutrients (salmon trees) have rings that are, on average, 1.5 mm wider, 4.5‰ more enriched in isotopic nitrogen, and 0.021% more elevated in total nitrogen (P < 0.001, Mann–Whitney–Wilcoxon test). In this study, salmon nutrients enhance average stem growth by 19%. Furthermore, salmon trees show that increases in tree-ring width and nitrogen values lag sporadic, high salmon runs by 0 to 5 years. Using differences between control and salmon trees from the same site, our results collectively indicate that tree-ring width, isotopic nitrogen, and total nitrogen are valid, complementary tools for investigating historic, annual fluctuations in salmon abundance in coastal watersheds. We recommend their use in future, tree ring based reconstructions of past nutrient cycling over decadal to centennial time scales. [ABSTRACT FROM AUTHOR]

The high seas phase of Pacific salmon life history remains particularly data-limited, and the potential implications of climate impacts on ocean productivity for salmon condition and reproductive success is poorly understood. We used carbon and nitrogen stable isotopes (SI) from salmon scales to reconstruct aspects of the marine environment experienced by Rivers Inlet sockeye salmon (Oncorhynchus nerka) over the last century (1915–2016). Time series of SI compositions of salmon scales showed a greater variability after 1950, probably linked to more dynamic high seas environmental conditions. However, climate indices (e.g., Pacific Decadal Oscillation, El Niño Southern Oscillation) did not explain the SI variability. We assessed the time series with respect to changes in food web dynamics, including shifting trophic baselines, changes in prey–salmon diet, and changes in salmon foraging location. A significant correlation (r = 0.53) between sea surface temperature and δ13C enabled us to define the area of potential salmon distribution in the open ocean for approximately 9 months prior to sampling. This method shows high potential for stock-specific high seas distribution mapping that could be combined with prey isotope values to inform stock-specific foraging experience. [ABSTRACT FROM AUTHOR]

Pulses of abundance in salmon migrations can arise from single populations arriving at different times, from multiple populations with different timing characteristics, or as a combination of these. Daily observations typically record an aggregate measure of abundance passing some location rather than the abundances of the individual components. An objective method is described that partitions a compound migration into its component parts by exploiting differences in the characteristics of each pulse. Simulated data were used to demonstrate when greater model complexity may be desirable. Three case studies of increasing complexity (Chilko Lake sockeye salmon smolts (Oncorhynchus nerka), large adult Columbia River Chinook salmon (Oncorhynchus tshawytscha), Fraser River salmon test fishery) demonstrate how the model can be applied in practice. Results indicated that Chilko Lake smolts rarely emigrate to sea as a single pulse, that the dates used to distinguish the spring run of Chinook salmon in the Columbia River may be overestimating its abundance, and that pulses of sockeye salmon abundance in a Fraser River ocean test fishery in 2014 may have arisen from some factor other than population composition. [ABSTRACT FROM AUTHOR]

Predation risk and competition among conspecifics significantly affect survival of juvenile salmon, but are rarely incorporated into models that predict recruitment in salmon populations. Using densities of harbour seals (Phoca vitulina) and numbers of hatchery-released Chinook salmon (Oncorhynchus tshawytscha) smolts as covariates in spatially structured Bayesian hierarchical stock–recruitment models, we found significant negative correlations between seal densities and productivity of Chinook salmon for 14 of 20 wild Chinook populations in the Pacific Northwest. Changes in numbers of seals since the 1970s were associated with a 74% decrease (95% CI: −85%, −64%) in maximum sustainable yield in Chinook stocks. In contrast, hatchery releases were significantly correlated with Chinook productivity in only one of 20 populations. Our findings are consistent with recent research on predator diets and bioenergetics modeling that suggest there is a relationship between harbour seal predation on juvenile Chinook and reduced marine survival in parts of the eastern Pacific. Forecasting, assessment, and recovery efforts for salmon populations of high conservation concern should thus consider including biotic factors, particularly predator–prey interactions. [ABSTRACT FROM AUTHOR]

Connectivity problems in fish migration in regulated rivers have been widely studied, but few studies have rigorously compared parallel migration success between regulated and free-flowing rivers. Here, survival and migration speed of downstream migrating radio-tagged Atlantic salmon (Salmo salar) smolts were studied in two large neighboring rivers in the northern Baltic Sea area: one without and one with dams. Both rivers have a free-flowing upper section, where the survival and migration speed of salmon smolts were similar. Survival along the lower section of the free-flowing river was about six times higher than in the lower part of the regulated river with five hydropower plants. Migration speed of smolts was also significantly faster in the river without dams. These severe problems in downstream connectivity in the regulated river pose challenging tasks for restoration of salmon populations. [ABSTRACT FROM AUTHOR]

We used spatially continuous field-measured and remotely sensed aquatic habitat characteristics paired with weekly ground-based telemetry tracking and snorkel surveys to describe movements and habitat occupancy of adult rainbow trout ( Oncorhynchus mykiss) ( N = 82) in a runoff-fed, salmon-influenced southcentral Alaska river system. We found that during the ice-free feeding season (June through September) rainbow trout occurrence was associated more with fine-scale (channel unit) characteristics relative to coarse-scale (stream reach) variables. The presence of Pacific salmon ( Oncorhynchus spp., which provide an important seasonal food subsidy) and habitat size were particularly useful predictors. Weekly movement distance differed between pre- and postspawning salmon arrival, but did not vary by sex. Habitat quality, season, and the arrival of spawning salmon influenced the likelihood of rainbow trout movement, and fish moved farther to seek out higher-quality habitats. Because rainbow trout respond to habitat factors at multiple scales and seek out salmon-derived subsidies, it will be important to take a multiscale approach in protecting trout and salmon populations and managing the associated fisheries. [ABSTRACT FROM AUTHOR]

Understanding population-specific spawner-recruit relationships is necessary for sustainable salmon management. Where multiple populations are harvested together, run reconstruction methods partition mixed-stock catches and allocate recruits back to their populations of origin. Traditional run reconstruction methods often use age composition data to inform catch partitioning. However age-only methods do not account for stock-specific differences in the availability of fish to harvest within fishing areas or the incidental harvest of nontarget stocks in nearby fishing areas. Advances in molecular genetic techniques permit genetic stock identification (GSI) of both contemporary and historical catch samples. We present a statistical model for salmon run reconstruction that utilizes both age composition and GSI data to estimate differences in the availability of stocks within, and interception rates among, terminal fisheries. When applied to the commercial sockeye salmon ( Oncorhynchus nerka) fishery in Bristol Bay, Alaska, new estimates of population productivity differed from those generated using previous age-only methods by 0.1%-155.1%, with stock-specific mean absolute percent differences of 9.7%-38.7% across years, underscoring the value of genetic data for run reconstruction. With more accurate run reconstruction methods, spawner-recruit relationships can be identified more precisely, thus providing more accurate management targets for salmon fisheries. [ABSTRACT FROM AUTHOR]

Canada's Policy for Conservation of Wild Pacific Salmon has been heralded as a transformative approach to the management of wild salmon whereby conservation is the highest priority. Given that changes to the Policy are under consideration, it is timely that we understand whether our state of knowledge and the status of wild salmon in Canada have indeed improved after its adoption in 2005. To answer these questions, we used two indices of improvement: ( i) monitoring effort and ( ii) abundance of spawning adults. Our results, based on data for all species from British Columbia's north and central coasts, show that monitoring effort has continued to erode, abundance of spawning adults has significantly declined for several species, the status of many salmon Conservation Units are in zones of concern, and 42% of the Conservation Units that we assessed as Red (threatened) would have improved in status had the Canadian fishery been reduced. We conclude with recommendations to help improve our knowledge of the status of salmon and enable a robust and successfully implemented Wild Salmon Policy for the future. [ABSTRACT FROM AUTHOR]

Growth hormone (GH) is involved in the parr-smolt transformation of salmonid fishes and is known to improve salinity tolerance. This study compared the capacity for seawater acclimation of GH transgenic coho salmon ( Oncorhynchus kisutch (Walbaum, 1792)) to that of wild-type fish, allowing examination of responses to sustained (chronic) exposure to elevated GH. GH transgenic fish (GH TG) smolted 1 year in advance of wild-type salmon and showed a greater capacity to hypo-osmoregulate in seawater. As GH TG fish were much larger than the wild-type fish, a second experiment was conducted with three size-matched groups of coho salmon (a 1+-year-old wild-type group, a 1+-year-old ration-restricted GH TG group, and a 0+-year-old fully fed GH TG group). When size-matched, the effect of GH transgenesis was not as dramatic, but the feed-rationed TG1+ group exhibited smaller deviations in plasma ion and osmolality levels following seawater exposure than did the other groups, suggesting a somewhat improved hypo-osmoregulatory ability. These results support a role for GH in the development of seawater tolerance by salmonid fishes independent of fish size. [ABSTRACT FROM AUTHOR]