Salmon Runs Research Articles

Review: Where the Salmon Run: The Life and Legacy of Billy Frank Jr, by Trova Heffernan

Review: <i>Where the Salmon Run: The Life and Legacy of Billy Frank Jr</i>, by Trova Heffernan

Network for success

It's 7:40 am on a Monday morning, the bell has just rung and our first period horticultural science class is about to start. As the freshman students settle down to their work on this crisp September morning, it becomes glaringly apparent that the school year is fully under way. Today's topic is an introduction to FFA, led off by the reading of the FFA Creed. As the hands of today's volunteers go up, paragraphs are assigned, we begin to absorb this timeless piece. As the first student recites the opening paragraph so eloquently written by E.M. Tiffany, our year's perspective comes into full view. I believe in the future of agriculture, with a faith born not of words, but of deeds. Achievements won by present and past generations of agriculturists, in the promise of better days through better ways, even as the better things we now enjoy have been brought to us through the struggles of former years. Contained in that one paragraph is the bridge of technology and science from one era to next, but also contained is the past and future of agricultural education. As class continues in our suburban classroom setting, we are reminded of how. different agricultural education is today than it has ever been in the past. We have long since passed the days of the traditional agriculture 1,2,3,4 curriculum and have moved into a world of aquaculture, natural resources, veterinary science, horticultural science, and biotechnology. A curriculum area once only offered in rural agricultural communities is now a mainstay in not only rural school districts, but suburban, and urban as well. And yet the question of our freshman students remains, how does this relate to me? Fortunately, we have curriculum that inherently offers an answer. As we continually align our curriculum with state standards, national skill standards, and maintain cross-accreditation within our school districts, the one worry we never have to entertain is the worthwhile nature of our curriculum. A plentiful food source and interest in preservation of the environment have become increasing areas of interest to all citizens, not just those involved in the field of agriculture. This interest continues into all secondary science classrooms, and the diversification continues of traditional science programs to more closely emulate the practical, hands-on characteristics of the agriculture classroom. While the traditional classes race to catch up, we continue to forge ahead into the new frontier of teaching and the fast changing field of agriculture. Whether we are working on raising native plant species in the greenhouse to help restore a native salmon run in a stream restoration project the class has undertaken, or studying the skeletal structure of a canine specimen at the local veterinary clinic, the intrigue of science is alive in our classrooms. As students come to us with an elementary knowledge of genetics and DNA, gleaned from their favorite crime fighting television show, we introduce the spooling of wheat germ DNA and the process of DNA electrophoresis into the classroom. Students are finding it easier to make the connection of chemistry and math from a theoretical approach to applying and using it first hand. As science and technology continue to advance, our curriculum stays in step by offering students current laboratory applications and insight into the changing face of the agriculture industry. As the final student volunteer recites the closing paragraph of the FFA Creed, it rings loud and clear that each student can exert influence in their home and community. It will be our mission this year to open new doors for this student in the FFA and in the classroom that allow them to reach this full potential with the skills and abilities necessary to be a skilled and knowledgeable leader for the next generation. …

Modeling a shape memory alloy actuator using an evolvable recursive black-box and hybrid heuristic algorithms inspired based on the annual migration of salmons in nature

The purpose of current investigation is to engage two efficient evolvable neuro-evolutionary machines to identify a nonlinear dynamic model for a shape memory alloy (SMA) actuator. SMA materials are kind of smart materials capable of compensating any undergo plastic deformations and return to their memorized shape. This fascinating trait gives them versatility to be applied on different engineering applications such as smart actuators and sensors. As a result, modeling and analyzing of their response is an essential task to researchers. Nevertheless, these materials have intricate behaviors that incorporate the modeling with major dilemma and obstacles. In this research, two novel evolvable machines comprised recurrent neural network (RNN) and two novel hybrid heuristic methods nominally cellular automate and Kohonen map assisted versions of The Great Salmon Run (CTGSR and KTGSR respectively) optimization algorithm are developed to find a robust, representative and reliable recursive identification framework capable of modeling the proposed SMA actuator. To elaborate on the acceptable performance of proposed systems, several experimental tests are carried out. Obtained results reveal the promising potential of the evolvable frameworks for modeling the behavior of SMA as a complex real world engineering system. Furthermore, by executing some comparative tests, the authors indicate that both of their proposed hybrid heuristic algorithms outperform the sole version of TGSR as well as some other well-known evolutionary algorithms.

Effects of spawning Pacific salmon on the isotopic composition of biota differ among southeast Alaska streams

Summary1. Adult Pacific salmon (Oncorhynchus spp.) transport marine nutrients to fresh waters and disturb sediments during spawning. The relative importance of nutrient fertilisation and benthic disturbance by salmon spawners can be modulated by environmental conditions (e.g. biological, chemical and physical conditions in the catchment, including human land use).2. To determine the importance of the environmental context in modifying the uptake and incorporation of salmon‐derived material into stream biota, we measured the nitrogen (δ15N) and carbon (δ13C) isotopic composition of benthic algae (i.e. epilithon) and juvenile coho salmon (Oncorhynchus kisutch) in seven streams across a timber‐harvest gradient (8–69% catchment area harvested), both before and during the salmon run. Conditional bootstrap modelling simulations were used to assess variability in the response of epilithon and juvenile coho salmon to spawning salmon.3. In response to spawning salmon, epilithon exhibited enrichment in both δ15N (mean: 1.5‰) and δ13C (2.3‰). Juvenile coho were also enriched in both δ15N (0.7‰) and δ13C (1.4‰). Conditional bootstrap models indicate decreased variation in data as spatial replication increases, suggesting that the number of study sites can influence the results of Pacific salmon isotope studies.4. Epilithon isotopic enrichment was predicted by environmental conditions, with δ15N enrichment predicted by stream temperature and timber harvest (R2 = 0.87) and δ13C enrichment by discharge, sediment size, timber harvest and spawner density (R2 = 0.96). Furthermore, we found evidence for a legacy effect of salmon spawners, with pre‐spawner δ15N and δ13C of both epilithon and juvenile coho predicted by salmon run size in the previous year.5. Our results show that the degree of incorporation of salmon‐derived nitrogen and carbon differs among streams. Furthermore, the environmental context, including putative legacy effects of spawning salmon, can influence background isotopic concentrations and utilisation of salmon‐derived materials in southeast Alaska salmon streams. Future studies should consider the variation in isotopic composition of stream biota when deciding on the number of study sites and samples needed to generate meaningful results.

"There's Something in the Water": Salmon Runs and Settler Colonialism on the Columbia River

This paper seeks to decentralize the human and interrogate the ways in which settler colonialism shapes the land itself by engaging with indigenous epistemologies that take seriously notions of place, relationship with the land, and the spatially located lifeways of non-human beings. Analyzing public discourse around the ongoing lawsuit filed by the Humane Society against the states of Oregon and Washington and the Columbia River Indian tribes over the "humane" trapping and euthanizing of sea lions that endanger salmon populations, I reveal that the dominant rubric for human/"nature" relationships in the Northwest—shared natural resource management—has become ossified. By deconstructing the hegemonic notions of "nature" and the commons and to whom they belong that are encoded within the lawsuit, this paper demonstrates that the conquest of Native peoples and conquest of the land are co-constitutive, and that processes of settler colonialism must be considered in light of their geographically specific locations.

Where the Salmon Run: The Life and Legacy of Billy Frank, Jr by Trova Heffernan

Where the Salmon Run: The Life and Legacy of Billy Frank, Jr by Trova Heffernan

Bio-inspired methods for fast and robust arrangement of thermoelectric modulus

This paper aims to evaluate the ability of some well-known bio-inspired metaheuristics for optimal arrangement of thermoelectric cells mounted in a thermal component. In real life applications, proper arrangement of thermoelectric modules plays a pivotal role by maximising the generated electricity. However, some defects such as the increase in total maintenance cost is often associated with the use of thermoelectric cells. Hence, it is mandatory to contrive a policy which guarantees the maximum electricity generation while keeps the maintenance cost in lowest level. Here, authors use both adaptive neuro-fuzzy inference system (ANFIS) and experimental data to model the power generation and maintenance cost of thermoelectric cells. At the next step, they engage some famous bio-inspired metaheuristic algorithms, i.e., bee algorithm (BA), particle swarm optimisation (PSO) and the great salmon run (TGSR) to arrange the thermoelectric cells in a cost effective manner. The gained results indicate that the proposed algorithms are highly capable to find an efficient arrangement for thermoelectric cells within a rational duration. Besides, through independent runs, it is observed that metaheuristics show acceptable robustness for the current case study.

Whole-Stream Metabolism Responds to Spawning Pacific Salmon in Their Native and Introduced Ranges

Pacific salmon (Oncorhynchus spp.) perform important ecological roles in stream ecosystems by provisioning nutrients as resource subsidies and modifying their physical habitat as ecosystem engineers. These contrasting roles result in concurrent nutrient enrichment and benthic disturbance, where local environmental characteristics potentially determine which effect predominates. Whole-stream metabolism quantifies the functional response to salmon and may identify patterns in enrichment and disturbance not apparent from structural measurements alone. We measured ecosystem respiration (ER) and gross primary production (GPP), along with chemical and physical characteristics, in seven Southeast Alaska streams and two Michigan streams, before and during the salmon run. These streams in the native and introduced ranges of salmon differed in environmental characteristics, from geomorphology at the reach scale to climate at the biome scale. Salmon consistently increased ER across streams and biomes, from an average (±SE) of 1.92 ± 0.23 g O2 m−2 d−1 before salmon to 6.30 ± 1.08 g O2 m−2 d−1 during the run. In the cobble-bottom streams of Southeast Alaska, GPP doubled from 0.29 ± 0.05 g O2 m−2 d−1 before salmon to 0.66 ± 0.16 g O2 m−2 d−1 during the run. In contrast, GPP responded inconsistently to salmon in the sand-bottom Michigan streams, increasing in one and decreasing in the other. Patterns in ER and GPP among streams and time periods were predicted by stream water nutrients (for example, ammonium, soluble reactive phosphorus) rather than by physical characteristics (for example, light, sediment size, and so on). This study demonstrates that salmon can periodically override physical controls on ER and GPP and enhance whole-stream metabolism via their dual ecological roles as both resource subsidies and ecosystem engineers.

Migration Strategies of Adult Chinook Salmon Runs in Response to Diverse Environmental Conditions in the Klamath River Basin

AbstractBiotelemetry and body temperature records of 130 adult Chinook salmon Oncorhynchus tshawytscha tagged over multiple years were used to investigate migration behaviors in response to diverse riverine conditions within the context of run timing strategies in a single river system. Four distinct runs were identified: Klamath–Trinity spring run, Trinity summer run, Klamath fall run, and Trinity fall run. Only the timing of Klamath–Trinity spring‐run and Trinity fall‐run Chinook salmon tended to prevent fish exposure to adversely high river temperatures. Faster migration rates reduced the accumulation of thermal units regardless of river temperature, especially at migration rates ≥10 km/d. Behavioral thermoregulation was minimal for all run groups (8% of all migrants), typically brief (&lt;12 h) during summer months at nonnatal tributary confluences. Spring‐run fish migrating on the descending limb of the snowmelt peak experienced increased accumulated thermal units due to slow migration rates, resulting in more elevated relative disease risk with lower apparent migration success than rapidly migrating summer‐run fish. Klamath fall‐run fish held extensively in the lower Klamath River regardless of date or river condition, resulting in the highest cumulative thermal experience of all run groups with moderate thermal stress. Trinity fall‐run fish experienced minimal thermal stress due to their later run timing. Results demonstrate the need to comprehensively investigate fish migrations in order to detect potentially subtle but important context‐sensitive dynamics between migration behaviors and environmental conditions that can impact the viability of salmon populations. This study's findings highlight concerns regarding global warming and vulnerability runs of salmon that migrate in the late spring and early fall in the absence of adaptive shifts in run timing or appropriate human intervention. Conversely, these results also demonstrate the unexpected ability of adult Chinook salmon to migrate successfully through surprisingly warm temperatures and endure acute thermal stress if sufficiently large volumes of cold water await them at their destination.

Biogeochemical transformation of a nutrient subsidy: salmon, streams, and nitrification

Migratory animals can alter ecosystem function via the provision of nutrient subsidies. These subsidies are heterogeneous in space and time, which may create hot spots or hot moments in biogeochemical transformations, in turn altering the ecosystem effect of the subsidy by changing the form of the nutrients. Annual migrations of Pacific salmon (Oncorhynchus spp.) transport nutrients from the marine environment to their natal freshwater ecosystems. Salmon subsidies provide high quality nutrients (e.g., nitrogen, phosphorus, carbon) that may also be large in quantity where salmon migrations are near historic levels. We hypothesized that the nutrient subsidy provided via the excretion of ammonium (NH4 +) by live salmon would stimulate microbially mediated nitrification rates in stream sediments and increase streamwater nitrate (NO3 −) concentrations. We quantified sediment nitrification in seven streams in Southeast Alaska before and during the salmon run in 2007 and 2008. Nitrification rates increased 3-fold from before to during the salmon run (mean ± SE = 0.07 ± 0.01 to 0.24 ± 0.02 mgN gAFDM−1 d−1, respectively). The variation in nitrification was explained by both streamwater and exchangeable NH4 + concentrations (R 2 = 0.50 and 0.71, respectively), which were low before salmon and increased relative to the size of the salmon run. To experimentally test the effect of salmon subsidies on nitrification rates, we staked senesced salmon carcasses on stream sediments for 3 weeks during the salmon run and then measured nitrification rates directly under the carcasses. Sediment nitrification was 2–5 times higher under the carcasses compared to nearby sediments without the direct carcass influence. Our results confirm that biogeochemical transformations alter the form of salmon-derived nitrogen, representing an overlooked aspect in the dynamics of this subsidy. Therefore, animal-derived nutrient subsidies are not passively retained or exported in recipient ecosystems, but also transformed, thereby influencing the form and incorporation of these nutrient subsidies.

Spatial and Temporal Variability of Macroinvertebrates in Spawning and Non-Spawning Habitats during a Salmon Run in Southeast Alaska

Spawning salmon create patches of disturbance through redd digging which can reduce macroinvertebrate abundance and biomass in spawning habitat. We asked whether displaced invertebrates use non-spawning habitats as refugia in streams. Our study explored how the spatial and temporal distribution of macroinvertebrates changed during a pink salmon (Oncorhynchus gorbuscha) spawning run and compared macroinvertebrates in spawning (riffle) and non-spawning (refugia) habitats in an Alaskan stream. Potential refugia included: pools, stream margins and the hyporheic zone, and we also sampled invertebrate drift. We predicted that macroinvertebrates would decline in riffles and increase in drift and refugia habitats during salmon spawning. We observed a reduction in the density, biomass and taxonomic richness of macroinvertebrates in riffles during spawning. There was no change in pool and margin invertebrate communities, except insect biomass declined in pools during the spawning period. Macroinvertebrate density was greater in the hyporheic zone and macroinvertebrate density and richness increased in the drift during spawning. We observed significant invertebrate declines within spawning habitat; however in non-spawning habitat, there were less pronounced changes in invertebrate density and richness. The results observed may be due to spawning-related disturbances, insect phenology, or other variables. We propose that certain in-stream habitats could be important for the persistence of macroinvertebrates during salmon spawning in a Southeast Alaskan stream.

A century of hydrological variability and trends in the Fraser River Basin

This study examines the 1911–2010 variability and trends in annual streamflow at 139 sites across the Fraser River Basin (FRB) of British Columbia (BC), Canada. The Fraser River is the largest Canadian waterway flowing to the Pacific Ocean and is one of the world’s greatest salmon rivers. Our analyses reveal high runoff rates and low interannual variability in alpine and coastal rivers, and low runoff rates and high interannual variability in most streams in BC’s interior. The interannual variability in streamflow is also low in rivers such as the Adams, Chilko, Quesnel and Stuart where the principal salmon runs of the Fraser River occur. A trend analysis shows a spatially coherent signal with increasing interannual variability in streamflow across the FRB in recent decades, most notably in spring and summer. The upward trend in the coefficient of variation in annual runoff coincides with a period of near-normal annual runoff for the Fraser River at Hope. The interannual variability in streamflow is greater in regulated rather than natural systems; however, it is unclear whether it is predominantly flow regulation that leads to these observed differences. Environmental changes such as rising air temperatures, more frequent polarity changes in large-scale climate teleconnections such as El Niño-Southern Oscillation and Pacific Decadal Oscillation, and retreating glaciers may be contributing to the greater range in annual runoff fluctuations across the FRB. This has implications for ecological processes throughout the basin, for example affecting migrating and spawning salmon, a keystone species vital to First Nations communities as well as to commercial and recreational fisheries. To exemplify this linkage between variable flows and biological responses, the unusual FRB runoff anomalies observed in 2010 are discussed in the context of that year’s sockeye salmon run. As the climate continues to warm, greater variability in annual streamflow, and hence in hydrological extremes, may influence ecological processes and human usage throughout the FRB in the 21st century.

Identifying the behaviour of laser solid freeform fabrication system using aggregated neural network and the great salmon run optimisation algorithm

Bio inspiration is a branch of artificial simulation science that shows pervasive contributions to variety of engineering fields such as automated pattern recognition, systematic fault detection, machine learning and applied optimisation. In this paper, a new bio-inspired optimisation algorithm which is the simulation of 'the great salmon run' (TGSR) is developed. Thereafter, it has been used to predict the efficient structure of an aggregated artificial neural network (AANN) to identify the behaviour of laser solid freeform fabrication (LSFF) system. Our experiments show that the combination of AANN and an appropriate supervised method is best suit for modelling cited engineering process. To prove the superiority of TGSR in both robustness and quality, it has been compared with most of the state-of-the-art optimisation techniques such as fast simulated annealing (FSA), parallel migrating genetic algorithm (PMGA), differential evolutionary with parent centric crossover (DEPCX), unified particle swarm optimisation (UPSO), shuffle frog leaping algorithm (SFLA), artificial bee colony (ABC), firefly algorithm (FA) and cuckoo search (CS). The obtained results confirm the acceptable potential of the proposed method to be applied on complex engineering systems.

The great salmon run: a novel bio-inspired algorithm for artificial system design and optimisation

The major application of stochastic intelligent methods in optimisation, control and management of complex systems is transparent. Many researchers try to develop collective intelligent techniques and hybrid meta-heuristic models for improving the reliability of such optimisation algorithms. In this paper, a new optimisation method that is the simulation of 'the great salmon run' (TGSR) is developed. This simulation provides a powerful tool for optimising complex multi-dimensional and multi-modal problems. For demonstrating the high robustness and acceptable quality of TGSR, it is compared with most of the well-known proposed optimisation techniques such as parallel migrating genetic algorithm (PMGA), simulate annealing (SA), differential evolutionary algorithm (DEA), particle swarm optimisation (PSO), bee algorithm (BA), artificial bee colony (ABC), firefly algorithm (FA) and cuckoo search (CS). The obtained results confirm the predominance of the proposed method in both robustness and quality in different optimisation problems.

Environmental variability and the ecological effects of spawning Pacific salmon on stream biofilm

Summary1. Variation in resource subsidies can create or reinforce heterogeneity in recipient ecosystems. Related activities of organisms delivering resource subsidies, such as ecosystem engineering by Pacific salmon spawners (Oncorhynchus spp.), also alter heterogeneity. We studied whether heterogeneity in stream environmental conditions and spawner abundances were reflected in the net ecological effects of salmon (i.e. enrichment by resource subsidies and disturbance by ecosystem engineering) on benthic biofilm.2. We sampled seven Southeast Alaska streams over 3 years, both before and during the salmon run. In each stream and year, stream environmental characteristics and their influence on responses of benthic biofilm [mean and coefficient of variation of chlorophyll a (chl a), ash‐free dry mass (AFDM) and autotrophic index (AFDM:chl a)] to spawners were assessed.3. Streams and periods before and during the salmon run were distinct based on their environmental characteristics. The responses of most biofilm metrics to spawners were stream‐ and year‐specific, suggesting that the ecological effect of spawners ranged from net enrichment to net disturbance depending on the stream or year studied. The environmental context, especially temperature, large wood, and sediment size, explained &gt;50% of biofilm variability during the run, but &lt;30% over the entire study, suggesting that salmon can alter environmental constraints.4. Precision of biofilm estimates improved by increasing either the number of streams or the number of years sampled (i.e. spatial or temporal replication). However, combining data from different North Pacific Rim ecoregions inflated the confidence interval as compared with a single ecoregion, indicating the importance of regional environmental contexts for net salmon effects.5. Our results suggest that biofilm responses to salmon can vary greatly, even within a single ecoregion, and that environmental conditions can modify net salmon effects. Consequently, generalisations about biofilm responses across the native range of salmon may be challenging.

Does timber harvest influence the dynamics of marine-derived nutrients in Southeast Alaska streams?

Streams often rely on nutrient subsidies, and variation in nutrient delivery may alter the ecosystem response. Pacific salmon (Oncorhynchus spp.) provide marine-derived nutrients to their natal streams but also cause benthic disturbance, with the net effect determined by watershed and stream characteristics. To understand the factors contributing to variation in salmon-derived nutrients (SDN), we studied nutrient concentration and export in seven streams with varying physical characteristics due to timber harvest (e.g., channel complexity) over three years in Southeast Alaska, USA. Salmon increased concentrations and export of dissolved and particulate nitrogen, phosphorus, and carbon, but the magnitude of increase varied up to 41-fold among streams. The density of live salmon best predicted the increase in nutrient concentration and export, whereas the density of carcasses had a negligible effect. Nutrient export was predicted by transient storage before and after the salmon run. Streams in harvested watersheds with simplified channels had greater nutrient export than those in pristine watersheds with complex channels. However, enrichment from salmon overrode the effect of timber harvest on export during the run. Our study demonstrates that enrichment via SDN is short-lived and related to run size, whereas timber harvest and carcasses exert little influence on SDN dynamics.

Ecological Effects of Live Salmon Exceed Those of Carcasses During an Annual Spawning Migration

We tested the hypothesis that the carcasses of anadromous Pacific salmon (Oncorhynchus spp.) constitute a significant source of nutrients in the nutrient-poor freshwaters where these fish migrate, spawn, senesce, and die. In a 110 m-long stream reach in Southeast Alaska, we retained nearly 3000 salmon carcasses and compared streamwater nitrogen (N), phosphorus (P), and the biomass of benthic biofilm in this reach with an upstream reference reach. The study spanned 5 months, bracketed the entire salmon run, and encompassed significant seasonal variation in abiotic stream conditions. Concentrations of dissolved and particulate N and P followed distinctly unimodal patterns through time, which tracked the abundance of live salmon, and we observed strong predictive relationships between live-salmon abundance and streamwater-nutrient concentrations. In contrast, we did not observe clear relationships between salmon carcasses and streamwater nutrients. Biofilm biomass within our study reaches seemed to more closely track the abundance of live salmon than the abundance of carcasses. The experimental retention of carcasses had a minor or undetectable influence on nutrient concentrations and biofilm within the study reach as compared to the reference reach. We conclude that physical factors such as temperature, discharge, nutrient limitation, and irradiance vary seasonally in ways that maximize the influence of nutrients provisioned by live salmon and minimize the influence of carcass-derived nutrients on the aspects of stream ecosystems that we examined. Overall, our results promote a new perspective on the ecological role of salmon in freshwaters, and contribute to a more mechanistic understanding of how migratory fishes can influence aquatic ecosystems.

Increasing Regional Temperatures Associated with Delays in Atlantic Salmon Sea‐Run Timing at the Southern Edge of the European Distribution

AbstractPopulations of Atlantic salmon Salmo salar at the edge of the species’ distribution are the most vulnerable to environmental changes. Those inhabiting southern European rivers are expected to be particularly affected by global warming. However, they are exploited as a very valuable resource for the region, attracting tourism and generating substantial income. In the central part of northern Spain (Asturias), there is a long tradition of sport fisheries (angling). The first salmon caught in a river each year is called the “campanu.” Analysis of a 50‐year time series demonstrates that the run timing of the Asturian Atlantic salmon has changed over this period, as inferred from significant delays in the date of capture of the campanu. Average campanu weight has experienced a parallel significant decrease but age has not changed, indicating diminution of salmon condition. These changes are statistically associated with an increase in regional temperature, there being a minor effect of the global climate North Atlantic Oscillation index. Negative effects of high temperatures on salmon run and feeding, together with long migratory routes, may explain these results.

Timber harvest intensifies spawning-salmon disturbance of macroinvertebrates in southeastern Alaskan streams

We addressed how timber harvest can interact with salmon (Oncorhynchus spp.) spawning activities to influence benthic macroinvertebrate communities in streams on Prince of Wales Island, Alaska. We predicted that spawning salmon would cause greater disturbance to macroinvertebrates in streams in watersheds with high than with low timber-harvest intensity because finer sediments that accumulate in streams after timber harvesting would be readily dislodged by spawning salmon and lower volumes of large wood in the streams would decrease availability of macroinvertebrate refugia from salmon activity. We used a modified Hess sampler to collect benthic macroinvertebrates from 6 riffles in each of 7 streams before and during the annual salmon run. Diptera biomass was lower and Plecoptera biomass was higher during the salmon run than before it. During the run, insect biomass, scraper biomass, and Ephemeroptera biomass were higher in streams with low than with high timber-harvest intensity, possibly because the finer sediments in the high timber-harvest intensity streams were more readily dislodged by salmon. Macroinvertebrate community structure (density and biomass) differed between before and during the run. Epeorus longimanus, Baetis, Seratella tibialis, Suwallia, Chironomidae, and Simuliidae were significant indicators of before-salmon benthic communities, whereas Sweltsa and Zapada cinctipes typified during-salmon communities. Some taxa probably are more tolerant of salmon disturbance than others, and their life histories might be adapted to the autumn salmon run. Overall, our results indicate that strong interactive effects can occur between anthropogenic activities and natural disturbance and that timber-harvest activity can intensify the effects of spawning-salmon disturbance on macroinvertebrates.

Marine-derived nutrients, bioturbation, and ecosystem metabolism: reconsidering the role of salmon in streams

In coastal areas of the North Pacific Ocean, annual returns of spawning salmon provide a substantial influx of nutrients and organic matter to streams and are generally believed to enhance the productivity of recipient ecosystems. Loss of this subsidy from areas with diminished salmon runs has been hypothesized to limit ecosystem productivity in juvenile salmon rearing habitats (lakes and streams), thereby reinforcing population declines. Using five to seven years of data from an Alaskan stream supporting moderate salmon densities, we show that salmon predictably increased stream water nutrient concentrations, which were on average 190% (nitrogen) and 390% (phosphorus) pre-salmon values, and that primary producers incorporated some of these nutrients into tissues. However, benthic algal biomass declined by an order of magnitude despite increased nutrients. We also measured changes in stream ecosystem metabolic properties, including gross primary productivity (GPP) and ecosystem respiration (ER), from three salmon streams by analyzing diel measurements of oxygen concentrations and stable isotopic ratios (delta O-O2) within a Bayesian statistical model of oxygen dynamics. Our results do not support a shift toward higher primary productivity with the return of salmon, as is expected from a nutrient fertilization mechanism. Rather, net ecosystem metabolism switched from approximately net autotrophic (GPP > or = ER) to a strongly net heterotrophic state (GPP << ER) in response to bioturbation of benthic habitats by salmon. Following the seasonal arrival of salmon, GPP declined to <12% of pre-salmon rates, while ER increased by over threefold. Metabolism by live salmon could not account for the observed increase in ER early in the salmon run, suggesting salmon nutrients and disturbance enhanced in situ heterotrophic respiration. Salmon also changed the physical properties of the stream, increasing air-water gas exchange by nearly 10-fold during peak spawning. We suggest that management efforts to restore salmon ecosystems should consider effects on ecosystem metabolic properties and how salmon disturbance affects the incorporation of marine-derived nutrients into food webs.