Hatchery practices may result in replacement of wild salmonids: adult trends in the Klamath basin,California

Appraisal of hatchery-related effects on Pacific salmonids (Oncorhynchus spp.) is a necessary component of species conservation. For example, hatchery supplementation can influence species viability by changing genetic, phenotypic and life-history diversity. We analyzed time series data for seven salmonid taxa from the Klamath River basin, California, to investigate trajectories of wild and hatchery adult populations. Linear regression coupled with randomized permutations (n?=?99,999), two- tailed t tests, and Bayesian change point analysis were used to detect trends over time. Cross correlation was also used to evaluate relationships between wild and hatchery populations. The taxa of interest were spring, fall, and late-fall Chinook Salmon (O. tshawytscha); Coho Salmon (O. kisutch); Coastal Cutthroat Trout (O. clarki clarki); and summer and hybrid Steelhead Trout (O. mykiss). Significant decreases were detected for summer and hybrid Steelhead Trout. The proportion of wild fall Chinook has also significantly decreased concurrently with increases in hatchery returns. In comparison, returns of most Chinook and coho runs to the hatcheries, and fall Chinook strays to wild spawning areas from Iron Gate Hatchery have significantly increased since the 1970s. Increases were also detected for wild late-fall Chinook and spring Chinook adults. However, both of these were significantly correlated with Chinook Salmon returns to Trinity River Hatchery, suggesting augmentation by hatchery strays. Changes in abundances appeared related to changing ocean habitat conditions and hatchery practices. Our results suggest that anadromous salmonid populations in the Klamath River basin are becoming increasingly dependent on hatchery propagation, a pattern that can threaten population persistence.     

Offshore Dolly Varden charr (<Emphasis Type="Italic">Salvelinus malma</Emphasis>) in the North Pacific

Many studies have investigated the ecology of charrs in freshwater, however, little is known about charrs in the ocean. This study examined the distribution, seasonal abundance, and some biological features of Dolly Varden (Salvelinus malma) in the Pacific Ocean. An analysis of by-catch data of Japanese offshore salmon monitoring showed that Dolly Varden were distributed across a wide range in the offshore waters of the Pacific Ocean, including the Japan Sea, Bering Sea, and Okhotsk Sea. The catch per unit effort showed a sharp increase from May to August, followed by a sharp decrease in September. Offshore areas served as an important summer habitat for anadromous Dolly Varden.     

Stable isotope evidence indicates the incorporation into Japanese catchments of marine‐derived nutrients transported by spawning Pacific Salmon

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Adult spawners: A critical period for subarctic Chinook salmon in a changing climate

Concurrent, distribution-wide abundance declines of some Pacific salmon species, including Chinook salmon (Oncorhynchus tshawytscha), highlights the need to understand how vulnerability at different life stages to climate stressors affects population dynamics and fisheries sustainability. Yukon River Chinook salmon stocks are among the largest subarctic populations, near the northernmost extent of the species range. Existing research suggests that Yukon River Chinook salmon population dynamics are largely driven by factors occurring between the adult spawner life stage and their offspring's first summer at sea (second year post-hatching). However, specific mechanisms sustaining chronic poor productivity are unknown, and there is a tremendous sense of urgency to understand causes, as declines of these stocks have taken a serious toll on commercial, recreational, and indigenous subsistence fisheries. Therefore, we leveraged multiple existing datasets spanning parent and juvenile stages of life history in freshwater and marine habitats. We analyzed environmental data in association with the production of offspring that survive to the marine juvenile stage (juveniles per spawner). These analyses suggest more than 45% of the variability in the production of juvenile Chinook salmon is associated with river temperatures or water discharge levels during the parent spawning migration. Over the past two decades, parents that experienced warmer water temperatures and lower discharge in the mainstem Yukon River produced fewer juveniles per spawning adult. We propose the adult spawner life stage as a critical period regulating population dynamics. We also propose a conceptual model that can explain associations between population dynamics and climate stressors using independent data focused on marine nutrition and freshwater heat stress. It is sobering to consider that some of the northernmost Pacific salmon habitats may already be unfavorable to these cold-water species. Our findings have immediate implications, given the common assumption that northern ranges of Pacific salmon offer refugia from climate stressors.     

Climate and ecosystem linkages explain widespread declines in North American Atlantic salmon populations

North American Atlantic salmon (Salmo salar) populations experienced substantial declines in the early 1990s, and many populations have persisted at low abundances in recent years. Abundance and productivity declined in a coherent manner across major regions of North America, and this coherence points toward a potential shift in marine survivorship, rather than local, river‐specific factors. The major declines in Atlantic salmon populations occurred against a backdrop of physical and biological shifts in Northwest Atlantic ecosystems. Analyses of changes in climate, physical, and lower trophic level biological factors provide substantial evidence that climate conditions directly and indirectly influence the abundance and productivity of North American Atlantic salmon populations. A major decline in salmon abundance after 1990 was preceded by a series of changes across multiple levels of the ecosystem, and a subsequent population change in 1997, primarily related to salmon productivity, followed an unusually low NAO event. Pairwise correlations further demonstrate that climate and physical conditions are associated with changes in plankton communities and prey availability, which are ultimately linked to Atlantic salmon populations. Results suggest that poor trophic conditions, likely due to climate‐driven environmental factors, and warmer ocean temperatures throughout their marine habitat area are constraining the productivity and recovery of North American Atlantic salmon populations.     

Flexible seaward migration of Dolly Varden <Emphasis Type="Italic">Salvelinus malma</Emphasis> in the Shiretoko Peninsula,Hokkaido, Japan

The migratory history of Dolly Varden Salvelinus malma was investigated in 30 streams in the Shiretoko Peninsula, Hokkaido, Japan, which is in the southern part of their distribution. Captured Dolly Varden were classified into two categories by their body coloration: silvery fish were thought to be an anadromous form, and non-silvery fish a fluvial form that remains in freshwater throughout its life. Forty-seven of 1,739 Dolly Varden collected in the spring and ten of 2,126 Dolly Varden collected in the autumn were silvery fish. Twenty silvery fish and 120 non-silvery fish were examined by analysis of otolith Sr:Ca ratio. Three silvery fish from autumn and 15 non-silvery fish had migrated to salt water or brackish water. The other specimens of silvery fish were regarded as smolt or pre-smolt before seaward migration. The present study suggests that Dolly Varden in the Shiretoko Peninsula have a flexible migratory history, where some of the non-silvery fish utilize marine environments while some individuals follow an anadromous life history.     

Changes in body composition associated with smoltification and premature transfer to seawater in Coho salmon (Oncorhynchus kisutch) and King salmon (O. tschawytscha)

Serum protein, glucose and fat levels were determined for Coho salmon parrs, freshwater smolts, seawater smolts, seawater stunts and freshwater desmolts. Liver and muscle glycogen, fat, protein and water concentrations were also calculated. Serum protein, glucose and fat levels were significantly lower in the freshwater smolts than in the parrs. Furthermore, both liver and muscle total fat levels were markedly decreased in the smolts, suggesting that smoltification is associated with increased catabolism. Smolts that failed to reach seawater by late summer reverted to a parr-like appearance and also regained the biochemical characteristics of parrs (high body fat and glycogen). Premature transfer of Coho presmolts into seawater caused impaired growth (stunting). Stunted Coho had higher muscle protein levels than normal smolts and parrs. Tissue water levels were not significantly different between stunts and normal seawater smolts, suggesting that the stunting phenomenon may not be caused primarily by osmoregulatory failure but may be due to shifts in metabolic patterns. In contrast to the pronounced changes seen in Coho salmon, transfer of King salmon to sea water did not result in increased catabolism of body reserves or in the production of stunts.     

Watershed‐scale climate influences productivity of Chinook salmon populations across southcentral Alaska

The ecosystems supporting Pacific salmon (Oncorhynchus spp.) are changing rapidly as a result of climate change and habitat alteration. Understanding how—and how consistently—salmon populations respond to changes at regional and watershed scales has major implications for fisheries management and habitat conservation. Chinook salmon (O. tshawytscha) populations across Alaska have declined over the past decade, resulting in fisheries closures and prolonged impacts to local communities. These declines are associated with large‐scale climate drivers, but uncertainty remains about the role of local conditions (e.g., precipitation, streamflow, and stream temperature) that vary among the watersheds where salmon spawn and rear. We estimated the effects of these and other environmental indicators on the productivity of 15 Chinook salmon populations in the Cook Inlet basin, southcentral Alaska, using a hierarchical Bayesian stock‐recruitment model. Salmon spawning during 2003–2007 produced 57% fewer recruits than the previous long‐term average, leading to declines in adult returns beginning in 2008. These declines were explained in part by density dependence, with reduced population productivity following years of high spawning abundance. Across all populations, productivity declined with increased precipitation during the fall spawning and early incubation period and increased with above‐average precipitation during juvenile rearing. Above‐average stream temperatures during spawning and rearing had variable effects, with negative relationships in many warmer streams and positive relationships in some colder streams. Productivity was also associated with regional indices of streamflow and ocean conditions, with high variability among populations. The cumulative effects of adverse conditions in freshwater, including high spawning abundance, heavy fall rains, and hot, dry summers may have contributed to the recent population declines across the region. Identifying both coherent and differential responses to environmental change underscores the importance of targeted, watershed‐specific monitoring and conservation efforts for maintaining resilient salmon runs in a warming world.     

Is isolation by adaptation driving genetic divergence among proximate Dolly Varden char populations?

Numerous studies of population genetics in salmonids and other anadromous fishes have revealed that population structure is generally organized into geographic hierarchies (isolation by distance), but significant structure can exist in proximate populations due to varying selective pressures (isolation by adaptation). In Chignik Lakes, Alaska, anadromous Dolly Varden char (Salvelinus malma) spawn in nearly all accessible streams throughout the watershed, including those draining directly to an estuary, Chignik Lagoon, into larger rivers, and into lakes. Collections of Dolly Varden fry from 13 streams throughout the system revealed low levels of population structure among streams emptying into freshwater. However, much stronger genetic differentiation was detected between streams emptying into freshwater and streams flowing directly into estuarine environments. This fine‐scale reproductive isolation without any physical barriers to migration is likely driven by differences in selection pressures across freshwater and estuarine environments. Estuary tributaries had fewer larger, older juveniles, suggesting an alternative life history of smolting and migration to the marine environment at a much smaller size than occurs in the other populations. Therefore, genetic data were consistent with a scenario where isolation by adaptation occurs between populations of Dolly Varden in the study system, and ecological data suggest that this isolation may partially be a result of a novel Dolly Varden life history of seawater tolerance at a smaller size than previously recognized.     

Perspectives on wild and hatchery salmon interactions at sea,potential climate effects on Japanese chum salmon,and the need for sustainable salmon fishery management reform in Japan

Pacific salmon (Oncorhynchus spp.) play an important role as a keystone species and provider of ecosystem services in the North Pacific ecosystem. We review our studies on recent production trends, marine carrying capacity, climate effects and biological interactions between wild and hatchery origin populations of Pacific salmon in the open sea, with a particular focus on Japanese chum salmon (O. keta). Salmon catch data indicates that the abundance of Pacific salmon increased since the 1976/77 ocean regime shift. Chum and pink salmon (O. gorbuscha) maintained high abundances with a sharp increase in hatchery-released populations since the late 1980s. Since the 1990s, the biomass contribution of hatchery returns to the total catch amounts to 50% for chum salmon, more than 10% for pink salmon, and less than 10% for sockeye salmon (O. nerka). We show evidence of density-dependence of growth and survival at sea and how it might vary across spatial scales, and we provide some new information on foraging plasticity that may offer new insight into competitive interactions. The marine carrying capacity of these three species is synchronized with long-term patterns in climate change. At the present time, global warming has positively affected growth and survival of Hokkaido populations of chum salmon. In the future, however, global warming may decrease the marine carrying capacity and the area of suitable habitat for chum salmon in the North Pacific Ocean. We outline future challenges for salmon sustainable conservation management in Japan, and recommend fishery management reform to sustain the hatchery-supported salmon fishery while conserving natural spawning populations.     

Young-of-the-year Coho Salmon <Emphasis Type="Italic">Oncorhynchus kisutch</Emphasis> recruit in fresh waters of remote Patagonian fjords in southern Chile (51°S)

Salmonid invasions are currently recognized as one of the main threats to the conservation of freshwater ecosystems in Patagonia. Although a number of salmonid species have been introduced to Patagonia over the last century not all species have succeeded at establishing widespread and large populations. To date, there are no reports of established self-sustaining Coho Salmon (Oncorhynchus kisutch) populations in southern Chile despite propagule pressure from aquaculture. Here, we assessed the natal origin of young-of-the-year Coho Salmon collected from estuaries and lakes associated with remote Patagonian fjords (51°S) by examining their otolith microchemical composition. Low strontium concentrations along a line transect from the otolith edge to its core in fish collected in one lake are consistent with freshwater residence until the moment of capture. Fish caught in estuaries displayed instead, relatively high strontium concentrations only at the otolith edge. This pattern suggests very recent movement from freshwater down to the estuary. Our findings are consistent with the hypothesis that the juvenile Coho Salmon collected in estuaries originated in the local freshwater system (lake) and provide the first ever evidence of recruitment and probable establishment of self-sustaining Coho Salmon population in Patagonia.     

Trophic ecology of Pacific salmon (<Emphasis Type="Italic">Oncorhynchus</Emphasis> spp.) in the ocean: a synthesis of stable isotope research

Increasing interest in the marine trophic dynamics of Pacific salmon has been motivated by the recognition of their sensitivity to changing climate and to the competitive effects of hatchery fish on wild stocks. It has become more common to use stable isotopes to supplement traditional diet studies of salmon in the ocean; however, there have been no integrated syntheses of these data to determine whether stable isotope analyses support the existing conventional wisdom of feeding strategies of the Pacific salmon. We performed a meta-analysis of stable isotope data to examine the extent of trophic partitioning among five species of Pacific salmon during their marine lives. Pink, sockeye, and chum salmon showed very high overlap in resource use and there was no consistent evidence for chum relying on alternative food webs dominated by gelatinous zooplankton. δ¹⁵N showed that Chinook and coho salmon fed at trophic levels higher than the other three species. In addition, these two species were distinctly enriched in ¹³C, suggesting more extensive use of coastal food webs compared to the more depleted (pelagic) signatures of pink, sockeye, and chum salmon. This paper presents the first synthesis of stable isotope work on Pacific salmon and provides δ¹⁵N and δ¹³C values applicable to research on the fate of the marine derived nutrients these organisms transport to freshwater and riparian ecosystems.     

Signals of large scale climate drivers,hatchery enhancement,and marine factors in Yukon River Chinook salmon survival revealed with a Bayesian life history model

Understanding how species might respond to climate change involves disentangling the influence of co‐occurring environmental factors on population dynamics, and is especially problematic for migratory species like Pacific salmon that move between ecosystems. To date, debate surrounding the causes of recent declines in Yukon River Chinook salmon (Oncorhynchus tshawytscha) abundance has centered on whether factors in freshwater or marine environments control variation in survival, and how these populations at the northern extremity of the species range will respond to climate change. To estimate the effect of factors in marine and freshwater environments on Chinook salmon survival, we constructed a stage‐structured assessment model that incorporates the best available data, estimates incidental marine bycatch mortality in trawl fisheries, and uses Bayesian model selection methods to quantify support for alternative hypotheses. Models fitted to two index populations of Yukon River Chinook salmon indicate that processes in the nearshore and marine environments are the most important determinants of survival. Specifically, survival declines when ice leaves the Yukon River later in the spring, increases with wintertime temperature in the Bering Sea, and declines with the abundance of globally enhanced salmon species consistent with competition at sea. In addition, we found support for density‐dependent survival limitations in freshwater but not marine portions of the life cycle, increasing average survival with ocean age, and age‐specific selectivity of bycatch mortality in the Bering Sea. This study underscores the utility of flexible estimation models capable of fitting multiple data types and evaluating mortality from both natural and anthropogenic sources in multiple habitats. Overall, these analyses suggest that mortality at sea is the primary driver of population dynamics, yet under warming climate Chinook salmon populations at the northern extent of the species’ range may be expected to fare better than southern populations, but are influenced by foreign salmon production.     

Synchronous marine pelagic regime shifts in the Northern Hemisphere

Regime shifts are characterized by sudden, substantial and temporally persistent changes in the state of an ecosystem. They involve major biological modifications and often have important implications for exploited living resources. In this study, we examine whether regime shifts observed in 11 marine systems from two oceans and three regional seas in the Northern Hemisphere (NH) are synchronous, applying the same methodology to all. We primarily infer marine pelagic regime shifts from abrupt shifts in zooplankton assemblages, with the exception of the East Pacific where ecosystem changes are inferred from fish. Our analyses provide evidence for quasi-synchronicity of marine pelagic regime shifts both within and between ocean basins, although these shifts lie embedded within considerable regional variability at both year-to-year and lower-frequency time scales. In particular, a regime shift was detected in the late 1980s in many studied marine regions, although the exact year of the observed shift varied somewhat from one basin to another. Another regime shift was also identified in the mid- to late 1970s but concerned less marine regions. We subsequently analyse the main biological signals in relation to changes in NH temperature and pressure anomalies. The results suggest that the main factor synchronizing regime shifts on large scales is NH temperature; however, changes in atmospheric circulation also appear important. We propose that this quasi-synchronous shift could represent the variably lagged biological response in each ecosystem to a large-scale, NH change of the climatic system, involving both an increase in NH temperature and a strongly positive phase of the Arctic Oscillation. Further investigation is needed to determine the relative roles of changes in temperature and atmospheric pressure patterns and their resultant teleconnections in synchronizing regime shifts at large scales.     

The Divergence of the Dolly Varden Char Salvelinus malma in the Asian Northern Pacific Populations Inferred from the PCR–RFLP Analysis of Mitochondrial DNA

Genetic differentiation of the Dolly Varden char Salvelinus malmaWalbaum was studied in five populations from the western part of the Northern Pacific. Using restriction analysis (RFLP), we examined polymorphism of three mitochondrial DNA (mtDNA) fragments amplified in polymerase chain reaction (PCR). MtDNA haplotypes were shown to fall into two phylogenetic groups, which probably reflect the existence of two previously described subspecies of Asian Dolly Varden,S. malma malma and S. malma krascheninnikovi. The divergence of mtDNA nucleotide sequences in the Dolly Varden subspecies (about 4%) corresponds to the differences between the valid char species from the genus Salvelinus.     

Ontogenetic shift to dependence on salmon-derived nutrients in Dolly Varden char from the Iliamna River,Alaska

The upstream migration, spawning, and death of anadromous, semelparous Pacific salmon brings nutrients to terrestrial and aquatic communities around the Pacific Rim. Many fishes use these resources but the relationship between fish body size and the reliance on salmon-derived nutrients might follow one of several patterns related to the onset of egg consumption with body size as fish grow, and possible shifts to alternative prey such as fishes as they grow larger still. In this study, these size-dependent hypotheses of marine subsidy use by resident Dolly Varden, Salvelinus malma, were tested using diet and stable isotope analyses. S. malma did not shift abruptly to a reliance on salmon eggs after they became large enough to eat eggs (i.e., no gape limitation). Rather, fish large enough to eat eggs but < 150 mm showed diets that blended salmon nutrients with aquatic insects, likely because they were spatially segregated from the highest concentration of spawning sockeye salmon, Oncorhynchus nerka. From intermediate through the largest sizes observed (150 to > 600 mm long) S. malma received ca. 80 % of their nutrients from salmon (eggs, flesh, and maggots that had scavenged dead salmon) based on diet analysis and stable isotope ratios despite being large enough to consume fish, as many similarly-sized salmonids do in other ecosystems. The few fish sampled in June, prior to the availability of salmon subsidies, had stable isotope signatures that also reflected heavy (ca. 90 %) reliance on marine sources, likely because they had eaten little since the end of the salmon run the previous fall. This apparent avoidance of piscivory in favor a rich yet pulsed marine subsidy highlights the importance of healthy salmon runs for the sake of not only the salmon but resident fishes that consume them.     

Comparative analysis of European wide marine ecosystem shifts: a large-scale approach for developing the basis for ecosystem-based management

Abrupt and rapid ecosystem shifts (where major reorganizations of food-web and community structures occur), commonly termed regime shifts, are changes between contrasting and persisting states of ecosystem structure and function. These shifts have been increasingly reported for exploited marine ecosystems around the world from the North Pacific to the North Atlantic. Understanding the drivers and mechanisms leading to marine ecosystem shifts is crucial in developing adaptive management strategies to achieve sustainable exploitation of marine ecosystems. An international workshop on a comparative approach to analysing these marine ecosystem shifts was held at Hamburg University, Institute for Hydrobiology and Fisheries Science, Germany on 1-3 November 2010. Twenty-seven scientists from 14 countries attended the meeting, representing specialists from seven marine regions, including the Baltic Sea, the North Sea, the Barents Sea, the Black Sea, the Mediterranean Sea, the Bay of Biscay and the Scotian Shelf off the Canadian East coast. The goal of the workshop was to conduct the first large-scale comparison of marine ecosystem regime shifts across multiple regional areas, in order to support the development of ecosystem-based management strategies.     

Differentiation of Dolly Varden char Salvelinus malma from Asia and North America inferred from PCR-RFLP analysis of mitochondrial DNA

Genetic differentiation of Dolly Varden char Salvelinus malma Walbaum from the Asian and North American Pacific coasts was studied. We examined restriction fragment length polymorphism of three mitochondrial DNA (mtDNA) fragments amplified in polymerase chain reaction, which encoded four NADH dehydrogenase subunits, the cytochrome b gene, and a D-loop segment. The mtDNA haplotypes were shown to form three phylogenetic groups, whose geographic distribution corresponded to three Dolly Varden subspecies: S. malma malma, S. malma krascheninnikovi, and S. malma lordi. The nucleotide sequence divergence between S. malma malma and S. malma krascheninnikovi was 3.8%; between S. malma malma and S. malma lordi, 3.1%; and between S. malma krascheninnikovi and S. malma lordi, 2.5%. The northern Dolly Varden S. malma malma from Asia was shown to be genetically identical to that from North America.     

Pacific Salmon,Nutrients, and the Dynamics of Freshwater and Riparian Ecosystems

Pacific salmon (Oncorhynchus spp.) accumulate substantial nutrients in their bodies as they grow to adulthood at sea. These nutrients are carried to predominantly oligotrophic lakes and streams, where they are released during and after spawning. Research over more than 3 decades has shown that the annual deposition of salmon-borne marine-derived nutrients (MD-nutrients) is important for the productivity of freshwater communities throughout the Pacific coastal region. However, the pathways and mechanisms for MD-nutrient transfer and accumulation in freshwater and riparian ecosystems remain virtually unexplored, consequently, there are many uncertainties in this area. This article addresses three related topics. First, we summarize recent advances in our understanding of the linkages among MD-nutrients, freshwater (including riparian) ecosystems, and community dynamics by addressing the importance of MD-nutrients to lakes and streams and by then reviewing large-scale and long-term processes in the atmosphere and ocean that govern variability in salmon populations. Second, we evaluate the validity of the discoveries and their implications for active ecosystem management, noting areas where extrapolation from these results still requires great caution. Finally, we outline five key research issues where additional discoveries could greatly augment our understanding of the processes shaping the structure and dynamics of salmon populations and the characteristics of their freshwater habitat and associated riparian zones. Collectively, the data suggest that the freshwater portion of the salmon production system is intimately linked to the ocean. Moreover, for the system to be sustainable, a holistic approach to management will be required. This holistic approach will need to treat climate cycles, salmon, riparian vegetation, predators, and MD-nutrient flowpaths and feedbacks as an integrated system. Received 3 July 2001; accepted 14 December 2001.     

Stream food web response to a salmon carcass analogue addition in two central Idaho, U.S.A. streams

1. Pacific salmon and steelhead once contributed large amounts of marine‐derived carbon, nitrogen and phosphorus to freshwater ecosystems in the Pacific Northwest of the United States of America (California, Oregon, Washington and Idaho). Declines in historically abundant anadromous salmonid populations represent a significant loss of returning nutrients across a large spatial scale. Recently, a manufactured salmon carcass analogue was developed and tested as a safe and effective method of delivering nutrients to freshwater and linked riparian ecosystems where marine‐derived nutrients have been reduced or eliminated. 2. We compared four streams: two reference and two treatment streams using salmon carcass analogue(s) (SCA) as a treatment. Response variables measured included: surface streamwater chemistry; nutrient limitation status; carbon and nitrogen stable isotopes; periphyton chlorophyll a and ash‐free dry mass (AFDM); macroinvertebrate density and biomass; and leaf litter decomposition rates. Within each stream, upstream reference and downstream treatment reaches were sampled 1 year before, during, and 1 year after the addition of SCA. 3. Periphyton chlorophyll a and AFDM and macroinvertebrate biomass were significantly higher in stream reaches treated with SCA. Enriched stable isotope (δ¹⁵N) signatures were observed in periphyton and macroinvertebrate samples collected from treatment reaches in both treatment streams, indicating trophic transfer from SCA to consumers. Densities of Ephemerellidae, Elmidae and Brachycentridae were significantly higher in treatment reaches. Macroinvertebrate community composition and structure, as measured by taxonomic richness and diversity, did not appear to respond significantly to SCA treatment. Leaf breakdown rates were variable among treatment streams: significantly higher in one stream treatment reach but not the other. Salmon carcass analogue treatments had no detectable effect on measured water chemistry variables. 4. Our results suggest that SCA addition successfully increased periphyton and macroinvertebrate biomass with no detectable response in streamwater nutrient concentrations. Correspondingly, no change in nutrient limitation status was detected based on dissolved inorganic nitrogen to soluble reactive phosphorus ratios (DIN/SRP) and nutrient‐diffusing substrata experiments. Salmon carcass analogues appear to increase freshwater productivity. 5. Salmon carcass analogues represent a pathogen‐free nutrient enhancement tool that mimics natural trophic transfer pathways, can be manufactured using recycled fish products, and is easily transported; however, salmon carcass analogues should not be viewed as a replacement for naturally spawning salmon and the important ecological processes they provide.