Salmon Management Research Articles

Invasive species management: The case of pink salmon in Iceland

The combination of warming waters and increased human activity in the Arctic creates increasingly favorable conditions for the arrival of invasive species to Arctic and sub-Arctic aquatic ecosystems. Invasive species threaten biodiversity and can impact local communities and industries that rely on healthy ecosystems. In Iceland, the pink salmon (Oncorhynchus gorbuscha), native to Pacific waters, has been found in rapidly increasing numbers since 2017. This research aimed to explore the institutional response to the arrival of pink salmon in Iceland. Documents such as international agreements and Icelandic laws and policies were analyzed for similarities, differences, and knowledge gaps related to pink salmon management. In addition, semi-structured interviews (n=10) explored experiences, knowledge, and opinions of individuals in different levels of decision-making, biological research, angling tourism, and nature conservation. Results show that reactions to the arrival of pink salmon are limited to registration of catches. No widespread research has been initiated and knowledge of basic ecology and potential impacts are lacking. Furthermore, no organized coordinated management responses are in place. Because of the growing importance of invasive species management around the world, this research adds novel insight into opportunities for improvement of invasive species management in Iceland through the development of recommendations for formalized procedures and risk assessments.

Accounting for Salmon Body Size Declines in Fishery Management Can Reduce Conservation Risks

ABSTRACTChanges in population demographic structure can have tangible but unknown effects on management effectiveness. Fishery management of Pacific salmon is often informed by estimates of the number of spawners expected to produce maximum sustainable yield (SMSY), implicitly assuming that reproductive output per spawner does not change over time. However, many salmon populations have experienced long‐term trends in age, sex and length compositions that have resulted in smaller body sizes of mature fish. We present an empirically based simulation approach for evaluating management implications of declining reproductive output resulting from shifting demographics. We simulated populations with or without demographic trends, selective or unselective harvests, and harvest policies based on assessment methods that did or did not account explicitly for demographic trends when estimating SMSY. A management strategy evaluation showed reduced expected harvests and run sizes when populations exhibited negative demographic trends. Reduced abundances and increased conservation risks (higher probability of falling below an abundance threshold) could be partially mitigated by using stock‐recruitment analyses based on total egg mass instead of spawner abundance, or via precautionary management where target escapements were higher than SMSY, especially in fisheries that selectively removed large fish. Explicit accounting of demographic trends in stock‐recruit analyses resulted in up to 25% higher run sizes and up to 20% lower conservation risks compared to traditional methods when trends toward smaller, younger and male‐biased runs were present in the population. Conservation of population demographic structure may be critical for sustaining productive fish populations and their benefits to ecosystems and people.

Adapting management of Pacific salmon to a warming and more crowded ocean

Abstract The North Pacific Ocean is warming and overall Pacific salmon abundance is higher now than at any other time in the past century. This increase in abundance is in large part due to warming-related changes in marine ecosystems at northern latitudes that primarily benefit pink salmon, and industrial-scale hatchery production to support commercial fisheries. A large body of evidence indicates that increasing and more variable ocean temperatures, as well as competition among salmon at sea, are associated with shifts in salmon productivity, body size, and age at maturation. However, these relationships vary by species, location, and time, resulting in increased harvest opportunities in some regions and exacerbated conservation concerns in others. The weight-of-evidence suggests North Pacific salmon nations should, as a minimum, limit further increases in hatchery salmon production until there is a better scientific understanding of hatchery and wild salmon distribution at sea, how they interact, and how the consequences of these interactions are influenced by broader climate and ecosystem conditions. Coordinated research to overcome knowledge gaps and develop strategies to reduce unintended interactions between hatchery and wild salmon could be funded (in part) by a tax placed on industrial-scale hatchery salmon releases. A tax would formalize recognition that there are finite prey resources to support salmon in the ocean and that both prey and wild salmon represent a “common property” whose use should not be without cost to those that seek to benefit from them. We highlight additional approaches salmon nations can take to adapt to changing conditions and suggest that improved communication and collaboration among North Pacific salmon research and management agencies will be key to balancing the benefits and risks of a warming and more crowded ocean.

The 1999 Pacific Salmon Agreement: An Essay in Honor of Ted L. McDorman

In 1999 an agreement was concluded between Canada and the United States on amendments to the 1985 Pacific Salmon Treaty which brought to an end a period of prolonged dispute and hostility over the management of salmon by the two countries and paved the way for a period of amicable relations on the issue that has lasted to this day. The negotiation of the agreement and the outcome were marked by two important characteristics: The negotiating process deviated from traditional state-to-state negotiations, and the ultimate agreement expressed the obligations of the parties not in simple verbal form but rather as the outcome of complex formulae designed to determine abundance and the sharing consequences. The key to the negotiation was fisheries scientists agreeing on the appropriate formula. This article seeks to reflect on two aspects of the negotiation of the 1999 agreement identified by Ted McDorman: first, the process as a mechanism for negotiating international agreements; and second, the broader implications of the “scientific complexity” of the agreement—the integration of law, science, and technology.

The state of spawning grounds, a study of the biology and population dynamics of pacific salmon on Kunashir Island (Southern Kuril Islands) in 2023

The purpose: formation of scientific foundations for improving the efficiency of salmon management on Kunashir Island (South Kuril zone) to ensure the sustainable exploitation of the commercial stock of Pacific salmon, maintain the necessary level of their reproduction, preserve the habitat, as well as improve scientific approaches to forecasting commercial catches.Methods used: the work was carried out in accordance with the methods generally accepted in fisheries research.Result: information was obtained on the dynamics of Pacific salmon entry, the filling of spawning grounds and the state of reservoirs on Kunashir Island. The collection of materials characterizing the biological indicators of chum salmon producers was carried out. Statistical information was obtained on catches of chum salmon and artificial reproduction of salmon fish on Kunashir Island.Practical significance: information on the filling of the spawning grounds of Pacific salmon on Kunashir Island and the quality indicators of their producers will be used to substantiate fishing regulation measures. Data on the state of artificial and natural reproduction of Pacific salmon are intended to develop a strategy for the development of artificial reproduction on Kunashir Island.

Effects of acclimation temperature and feed restriction on the metabolic performance of green sturgeon.

Green sturgeon (Acipenser medirostris) are an anadromous threatened species of sturgeon found along the Pacific coast of North America. The southern distinct population segment only spawns in the Sacramento River and is exposed to water temperatures kept artificially cold for the conservation and management of winter-run Chinook salmon (Oncorhynchus tshawytscha). Past research has demonstrated costs of cold-water rearing including reduced growth rates, condition and survivorship of juvenile green sturgeon. Our research investigates how the stressors of water temperature and food limitation influence the metabolic performance of green sturgeon. We reared green sturgeon at two acclimation temperatures (13 and 19°C) and two ration amounts (100% and 40% of optimal feed). We then measured the routine and maximum metabolic rates (RMR and MMR, respectively) of sturgeon acclimated to these rearing conditions across a range of acute temperature exposures (11 to 31°C). Among both temperature acclimation treatments (13 or 19°C), we found that feed restriction reduced RMR across a range of acute temperatures. The influence of feed restriction on RMR and MMR interacted with acclimation temperature. Fish reared at 13°C preserved their MMR and aerobic scope (AS) despite feed restriction, while fish fed reduced rations and acclimated to 19°C showed reduced MMR and AS capacity primarily at temperatures below 16°C. The sympatry of threatened green sturgeon with endangered salmonids produces a conservation conflict, such that cold-water releases for the conservation of at-risk salmonids may constrain the metabolic performance of juvenile green sturgeon. Understanding the impacts of environmental conditions (e.g. temperature, dissolved oxygen) on ecological interactions of green sturgeon will be necessary to determine the influence of salmonid-focused management.

The impact of post-ovulatory ageing on the development of diploid and triploid Atlantic salmon (Salmo salar L.)

This study is the first to investigate the effects of post-ovulatory ageing (POA) on both diploid and triploid Atlantic salmon (Salmo salar L.). Following ovulation, female broodstock were partially stripped periodically (at 0, 5, 10, 15 and 20 days post-ovulation, DPO), creating five groups of ova with differing durations held in the body cavity. Survival and bone architecture were negatively impacted by increasing POA, irrespective of ploidy, and an increase in individual growth variation was observed, particularly in triploids. Several ovarian fluid and egg quality parameters were screened to determine potential prospective biomarkers that may predict the future success of an egg batch. Ovarian fluid osmolality and egg lipid composition, vitamin E concentration and TBARS emerged as good candidates. Furthermore, significant changes in abundance of 19 proteins involved in cell organisation, metabolism and reproduction were observed at different stages of POA. Also, a suite of genes involved in energy metabolism, apoptosis and cell cycle regulation showed significantly reduced expression in eggs at 20 DPO compared to 0 DPO. The data show that increasing POA negatively impacts egg survival and future growth and increases deformity prevalence. Several potential biomarkers show promise and should be investigated further. Although egg quality appears to remain stable up to 10 DPO, the data suggests that fertilising eggs within 5 DPO would reduce the variation in growth, thus improving future performance potential and further benefitting stock management of both diploid and triploid Atlantic salmon.

Ecosystem-based sustainable management of chum salmon in Japan’s warming climate

Pacific salmon (Oncorhynchus spp.) play two important roles in the North Pacific ecosystem: as a keystone species and as providers of an ecosystem service that offers human food resources for countries of the North Pacific rim. In a climate that has been rapidly warming since the late 2000 s, the return of Japanese chum salmon (O. keta), most of which reproduce through an artificial hatchery program, has reduced. This study reviews the following issues: 1) the impacts of warming climate on production dynamics and the life history of Pacific salmon; 2) the importance of wild salmon on the sea-terrestrial ecosystem linkage; 3) biological and genetic issues of hatchery-produced salmon such as population dynamics (density-dependent effects) and genetic disturbance (seed transplantation and domestication); and 4) the establishment of ecosystem-based sustainable management for Pacific salmon in the warming climate.

Modeling the interaction between salmon management and consumption by coastal brown bears

AbstractHarvest management policy for species with strong trophic connections can reverberate through food webs and cause unintended consequences, such as altering the abundance of a harvested species' predators or prey. Pacific salmon (Oncorhynchus spp.), a key food for many predators and an economically valuable harvested species, is generally managed for maximum sustained harvests without explicit consideration for the freshwater and terrestrial food webs that they support. The density of brown bear (Ursus arctos) populations in Alaska, USA, is correlated with the amount of salmon they can access and consume, so it seems likely their populations are inadvertently affected by salmon management. We simulated the effect of salmon management policy on brown bears by customizing a general bear–salmon model using empirical data from three watersheds in southwest Kodiak, Alaska. Our goal was to quantify the effect of current salmon management policy (i.e., escapement goals and early/late run allocations) on salmon consumption by brown bears. Bears in the individually‐based model evaluated the value of each foraging site based on salmon abundance, salmon vulnerability, and competition with other bears and made movement decisions (among salmon spawning sites) accordingly. A validation of the model based on empirical brown bear foraging data revealed that simulated bears selected the same salmon spawning locations but visited more sites and fished for more days compared to real bears. In simulations across variables (salmon abundance, phenological variation, bear competition, and bear density), consumption of salmon by bears was remarkably resilient to changes in salmon abundance within the range of current high and low escapement goals, as long as all run‐timing variation and salmon sub‐populations were preserved. Mean salmon consumption increased by ~20% as escapement approximately doubled from the regional lower escapement goal of 625,000 to the upper goal of 1,270,000, but rapidly declined if salmon abundance decreased below the minimum escapement goal. In this system, salmon management policy, designed to achieve maximum sustained yield, also provides adequate salmon for the current bear population. This model creates a potentially useful tool for assessing the knock‐on effects of future changes to salmon management policy.

Reproductive success of jack and full-size males in a wild coho salmon population.

Despite the wealth of research on Pacific salmon Oncorhynchus spp. life histories there is limited understanding of the lifetime reproductive success of males that spend less time at sea and mature at a smaller size (jacks) than full-size males. Over half of returning male spawners can be jacks in some populations, so it is crucial to understand their contribution to population productivity. We quantified adult-to-adult reproductive success (RS) of jacks and their relative reproductive success (RRS) compared to full-size males in a wild population of coho salmon in the Auke Creek watershed, Juneau, Alaska. We used genetic data from nearly all individuals (approx. 8000) returning to spawn over a decade (2009-2019) to conduct parentage analysis and calculate individual RS. The average adult-to-adult RS of jacks (mean = 0.7 and s.e. = 0.1) was less than that of full-size males (mean = 1.1 and s.e. = 0.1). Jack RRS was consistently below 1.0 but ranged widely (0.23 to 0.96). Despite their lower average success, jacks contributed substantially to the population by siring 23% of the total returning adult offspring (1033 of 4456) produced between 2009 and 2015. Our results imply that jacks can affect evolutionary and population dynamics, and are relevant to the conservation and management of Pacific salmon.

Status of a stocked Atlantic salmon population in Lake Huron

In 2011, the Michigan Department of Natural Resources (MDNR) expanded stocking of Atlantic salmon (Salmo salar) in Lake Huron to enhance fishing opportunities following Chinook salmon (Oncorhynchus tshawytscha) abundance declines. Currently, little is known about the population produced from this stocking. We fit an assessment model to harvest data from Michigan jurisdictional waters to estimate Atlantic salmon population dynamics and abundance. Because of potential biases in MDNR creel survey harvest estimates, a survey was e-mailed to online purchasers of a 2019 Michigan fishing license asking about where and when Atlantic salmon were harvested to correct creel harvest estimates. Anglers were also asked about catch-and-release angling and tested on their ability to identify Lake Huron salmonids. Creel harvest estimates overlapped spatially and temporally with 42% of survey reported Atlantic salmon harvest. After correcting creel harvest estimates, total abundance of Atlantic salmon in 2019 was estimated at approximately 392,000 fish with a peak abundance of approximately 406,000 fish. Anglers released 27% of caught fish and correctly identified Atlantic salmon 28% of the time. To assess the occurrence of food resource competition, differences in condition (i.e., expected weight at length) were evaluated. Condition was higher in later years than in earlier years despite abundance increases. Our results suggested that past stocking established a population of approximately 400,000 Atlantic salmon with evidence suggesting that fish were finding sufficient food resources. Future Atlantic salmon management efforts may be improved by quantifying post-stocking survival rates and other sources (e.g., charter, Canadian) of harvest.

Incorporating conservation limit variability and stock risk assessment in precautionary salmon catch advice at the river scale

Abstract International wild Atlantic salmon management priorities have moved from exploitation to conservation since the 1990s, recognizing the need to protect diversity and abundance at individual river levels amid widespread declines. Here we review international salmon-stock assessments and describe a simple, transferable catch-advice framework, established for management of fisheries that conforms to international obligations. The risk assessment approach, applied at the river scale, jointly incorporates uncertainty in estimated and forecasted returning salmon numbers with the level of uncertainty around spawning requirements (Conservation Limits). Outputs include quantification of risk of stocks not attaining conservation limits (CL) and surpluses above CL on stocks able to support sustainable exploitation via total allowable catches (TAC), with monitoring by rod catch or fish counter. Since management implementation and cessation of at-sea mixed-stock fisheries, there has been a deterioration in the performance of many individual stocks, without any sustained increase in fisheries open to harvest. Given declines in mid-latitude Atlantic salmon populations over 30 years, the novel framework presented provides an approach to protect stocks failing to meet spawning thresholds while supporting sustainable exploitation of those achieving them. On-going management policy of adopting scientific advice and allowing exploitation only on stocks exceeding CLs is central to the objective of protecting salmon stocks.

Population variability in thermal performance of pre-spawning adult Chinook salmon.

Climate change is causing large declines in many Pacific salmon populations. In particular, warm rivers are associated with high levels of premature mortality in migrating adults. The Fraser River watershed in British Columbia, Canada, supports some of the largest Chinook salmon (Oncorhynchus tshawytscha) runs in the world. However, the Fraser River is warming at a rate that threatens these populations at critical freshwater life stages. A growing body of literature suggests salmonids are locally adapted to their thermal migratory experience, and thus, population-specific thermal performance information can aid in management decisions. We compared the thermal performance of pre-spawning adult Chinook salmon from two populations, a coastal fall-run from the Chilliwack River (125km cooler migration) and an interior summer-run from the Shuswap River (565km warmer migration). We acutely exposed fish to temperatures reflecting current (12°C, 18°C) and future projected temperatures (21°C, 24°C) in the Fraser River and assessed survival, aerobic capacity (resting and maximum metabolic rates, absolute aerobic scope (AAS), muscle and ventricle citrate synthase), anaerobic capacity (muscle and ventricle lactate dehydrogenase) and recovery capacity (post-exercise metabolism, blood physiology, tissue lactate). Chilliwack Chinook salmon performed worse at high temperatures, indicated by elevated mortality, reduced breadth in AAS, enhanced plasma lactate and potassium levels and elevated tissue lactate concentrations compared with Shuswap Chinook salmon. At water temperatures exceeding the upper pejus temperatures (Tpejus, defined here as 80% of maximum AAS) of Chilliwack (18.7°C) and Shuswap (20.2°C) Chinook salmon populations, physiological performance will decline and affect migration and survival to spawn. Our results reveal population differences in pre-spawning Chinook salmon performance across scales of biological organization at ecologically relevant temperatures. Given the rapid warming of rivers, we show that it is critical to consider the intra-specific variation in thermal physiology to assist in the conservation and management of Pacific salmon.

Evaluating the importance of accurate sex ratios on egg deposition targets and conservation limit compliance for Atlantic salmon (Salmo salarL.) in the River Tamar, south‐west England

AbstractEffective management of Atlantic salmon requires a suite of metrics that are fed into stock assessment models to assess stock compliance within individual rivers in relation to estimated conservation limits. Key among metrics required to assess compliance are the number of adult female spawners within each adult sea age class and their corresponding egg deposition rates. Owing to the current need to conserve salmon stocks, adult sex ratios used to calculate egg deposition estimates often depend on data derived from historic lethal sampling. Using non‐invasive sampling and an accurate genetic sex test, we determined the proportion of female fish in two adult life history stages (one sea winter and two sea winter) of Atlantic salmon from the River Tamar, an Environment Agency (England) Monitored River. Our results suggested that phenotypic‐based sexing of Tamar salmon was unreliable, especially for early run fish and that the proportion of female salmon has been under‐estimated, thereby leading to consistent under‐estimation of egg deposition rates.

Should we adapt nature to climate change? Weighing the risks of selective breeding in Pacific salmon

ABSTRACT This paper uses the case of genomics-assisted selective breeding in Pacific salmon hatcheries to investigate how people weigh the risks of adapting nature to changing climate conditions. Drawing on 105 interviews with people involved in salmon management, this study embeds risk assessments of selective breeding in the context of present interventions into salmon life cycles. While responses to novel technologies are frequently plotted along a support-opposition continuum, the debate over selective breeding Pacific salmon is multivalent, with respondents supporting selective breeding in some contexts while opposing it in others. Nearly half of respondents supported selective breeding to fix the mistakes of past interventions and rewild salmon. Given that past problems have stemmed from technological responses, these findings paradoxically suggest that further interventions may not necessarily be perceived as violating values of naturalness or wildness. Genomic technologies offer new pathways for climate adaptation. In doing so, they expand ethical debates about the role of humans and novel technologies in conserving and managing wildlife.

Using Merged Pre-Fishery Abundance as a Parameter Evaluating the Status of Atlantic Salmon and Anadromous Brown Trout Populations: A Norwegian Case Study

Methods used to monitor variation in population sizes in both Atlantic salmon and anadromous brown trout (sea trout) have been widely used in Norway the last 20 years. However, a national management regime, based on population data, has only been established for one of the two species, the Atlantic salmon. One prerequisite for using this “one species” model is that there is negligible interspecific competition between salmon and trout in the rivers. This may, however, be an oversimplification of the real situation. The pre-fishery abundance (PFA), monitored with combination of underwater video systems, snorkelling counts, and catch statistics will, in most rivers, include both salmon and Sea Trout. In the present study, we estimated a total PFA for rivers, or groups of rivers, in eight regions in Norway in 2019. The total size of each river system was measured by abiotic factors such as river area, river length, annual mean water flow, and size of precipitation field; additionally, one biotic factor, smolt age, was used to standardise PFA data across regions. A comparison shows that the standardised total PFA of salmon and trout varies across regions where the highest estimated PFA was four times higher than the lowest. Compared to the traditional one-species approach, the merged PFA data show a different population status in the eight regions. The difference in the two approaches was mainly linked to the variation in size in anadromous brown trout populations. Merging data from salmon and trout populations in defined regions may be a better input in a management model than the current model used by the Norwegian Scientific Committee for Salmon Management (VRL).

Attitudes and behaviors for understanding compliance in Greenland's Atlantic salmon (Salmo salar) fishery

AbstractNoncompliance is a central challenge for conservation, but in settings with limited access to behavioral data, it can be difficult to evaluate what drives compliance. Conservationists can measure and evaluate resource users' attitudes, and in so doing, leverage a complementary, nonbehavioral measure for evaluating compliance. In Greenland, wild Atlantic salmon (Salmo salar) fishers are under increasing regulatory pressure to report salmon catch because the majority of North Atlantic salmon stocks are classified as suffering. The objective of this study is to measure salmon catch reporting compliance, reporting behavior, and attitudes toward Greenland's salmon management. We surveyed Greenland's licensed salmon fishers, used an unmatched count technique to estimate the incidence of underreporting salmon catch, and linked salmon fishers' actual catch reports to their survey responses. In 2019, more than 84% of salmon fishers reported their catch and demonstrating high levels of compliance. We also found that salmon fishers did not indicate strong instrumental motivations for reporting, but exhibited moral obligations and normative, legitimacy‐based motivations to report catch. Salmon fishers found regulations to be fair, and that regulatory authorities were professional and acted honestly. Catch underreporting was also remarkably low, with 90–94% of respondents stating that they report all their catch. Joining together individuals' attitudinal and behavioral responses to conservation rules illustrates the benefits and limitations of expanding actor‐based theories of compliance. This case of already high levels of compliance offers empirical evidence for further improving fisheries compliance, and it also illustrates the limitations that fishery managers face when conserving a highly migratory species.

The likely suspects framework: the need for a life cycle approach for managing Atlantic salmon (Salmo salar) stocks across multiple scales

Abstract The ongoing declines in Atlantic salmon populations across its range underscore the need for co-ordinated scientific-based knowledge to support management and decisions for their conservation. Current salmon management actions remain largely focused on addressing bottlenecks to production in the freshwater phase of the life-cycle, whereas the continued declines observed in the recent decades are thought to be driven primarily by constraints on the marine phase. The challenges brought by global warming and other emerging stressors require immediate actions, requiring us to re-think the methods behind stock assessment and forge stronger linkages between data, models and policies to promote more effective management actions. We outline a scientific framework that takes a wider ecosystem view, designed to evaluate holistically a suite of indicators and potential drivers of salmon mortality at key phases of the life cycle. The aims of the proposed “Likely Suspects Framework” are to enhance cross-fertilisation of ideas between assessment processes at the stock-complex scale and stock-specific focused management activities, and to develop new decision support tools to improve management efficiencies and scenario testing. Adopting such an approach provides a new way to catalyse the acquisition and deployment of both existing and new data and models that are urgently needed for assisting the conservation and future stewardship of salmon stocks on both sides of the Atlantic.

Fitness consequences of hybridization between wild Newfoundland and farmed European and North American Atlantic salmon

Selection due to multi-generational domestication and genetically distinct origins raises concerns about potential fitness consequences of hybridization between farmed and wild Atlantic salmon. In Newfoundland (NF), Canada, the aquaculture industry uses the North American (NA) Saint John River strain, though site-specific permission has been granted to farm a European origin (EO) strain. We used complementary experiments to investigate differences in (1) dominance status and (2) growth and survival in allopatry (NF wild fish) versus sympatry (NF wild fish with NA/EO farmed individuals and related F1 hybrids) in contrasting tank and semi-natural stream environments. NA farmed salmon were more dominant than NF wild individuals, with hybrids being intermediate in expression and not differing from wild fish. EO farmed salmon also tended to dominate NF wild individuals, but not significantly. Competition with farmed fish and hybrids did not affect the growth of wild fish in sympatry versus allopatry in the tank environment. However, that was not the case in one instance in the stream environment where wild fish in sympatry with NA farmed fish and hybrids outgrew those in allopatry. Within sympatric treatments, both EO and NA farmed salmon outgrew wild individuals in the tank environment, but not always in the stream environment (exception: NA farmed). Hybrids tended to display intermediate growth performance relative to farmed and wild fish in both environments. Survival did not differ among cross types in either environment. These findings suggest that irrespective of distinct origins, both EO and NA farmed salmon displayed greater dominance and growth than NF wild salmon in the tank environment. However, in the stream environment, competition imposed by NA farmed fish and related hybrids on wild fish appeared less than that imposed by the EO strain and related hybrids, as evident in growth performance. Findings thus provide valuable insight into the effects of hybridization and, consequently, fitness-related trait differences among divergent EO and NA farmed, NF wild, and F1 hybrid populations of importance for the conservation and management of Atlantic salmon.

Non‐stationary and interactive effects of climate and competition on pink salmon productivity

Pacific salmon (Oncorhynchus spp.) are exposed to increased environmental change and multiple human stressors. To anticipate future impacts of global change and to improve sustainable resource management, it is critical to understand how wild salmon populations respond to stressors associated with human‐caused changes such as climate warming and ocean acidification, as well as competition in the ocean, which is intensified by the large‐scale production and release of hatchery reared salmon. Pink salmon (O. gorbuscha) are a keystone species in the North Pacific Ocean and support highly valuable commercial fisheries. We investigated the joint effects of changes in ocean conditions and salmon abundances on the productivity of wild pink salmon. Our analysis focused on Prince William Sound in Alaska, because the region accounts for ~50% of the global production of hatchery pink salmon with local hatcheries releasing 600–700 million pink salmon fry annually. Using 60 years of data on wild pink salmon abundances, hatchery releases, and ecological conditions in the ocean, we find evidence that hatchery pink salmon releases negatively affect wild pink salmon productivity, likely through competition between wild and hatchery juveniles in nearshore marine habitats. We find no evidence for effects of ocean acidification on pink salmon productivity. However, a change in the leading mode of North Pacific climate in 1988–1989 weakened the temperature–productivity relationship and altered the strength of intraspecific density dependence. Therefore, our results suggest non‐stationary (i.e., time varying) and interactive effects of ocean climate and competition on pink salmon productivity. Our findings further highlight the need for salmon management to consider potential adverse effects of large‐scale hatchery production within the context of ocean change.