Anadromous Salmon Research Articles

Differential expression of olfactory genes in Atlantic salmon (Salmo salar) during the parr-smolt transformation.

The anadromous salmon life cycle includes two migratory events, downstream smolt migration and adult homing migration, during which they must navigate with high precision. During homing migration, olfactory cues are used for navigation in coastal and freshwater areas, and studies have suggested that the parr–smolt transformation has a sensitive period for imprinting. Accordingly, we hypothesized that there would be significant changes in gene expression in the olfactory epithelium specifically related to smoltification and sampled olfactory rosettes from hatchery‐reared upper growth modal juvenile Atlantic salmon at 3‐week intervals from January to June, using lower growth modal nonsmolting siblings as controls. A suite of olfactory receptors and receptor‐specific proteins involved in functional aspects of olfaction and peripheral odor memorization was analyzed by qPCR. Gene expression in juveniles was compared with mature adult salmon of the same genetic strain caught in the river Gudenaa. All mRNAs displayed significant variation over time in both modal groups. Furthermore, five receptor genes (olfc13.1, olfc15.1, sorb, ora2, and asor1) and four olfactory‐specific genes (soig, ependymin, gst, and omp2) were differentially regulated between modal groups, suggesting altered olfactory function during smoltification. Several genes were differentially regulated in mature salmon compared with juveniles, suggesting that homing and odor recollection involve a different set of genes than during imprinting. Thyroid hormone receptors thrα and thrβ mRNAs were elevated during smolting, suggesting increased sensitivity to thyroid hormones. Treatment of presmolts with triiodothyronine in vivo and ex vivo had, however, only subtle effects on the investigated olfactory targets, questioning the hypothesis that thyroid hormones directly regulate gene expression in the olfactory epithelium.

Life histories of anadromous salmon males reveal a trade-off between primary and secondary sexual traits

Abstract The life-history trade-off between investment in somatic growth and gonadal tissue is caused by individual energy limitations and results in individuals that adopt specific tactics to achieve reproduction. Allocation in primary and secondary sexual traits in Atlantic salmon males was studied by assessing life history traits (smolt size, sea age, growth rate) based on back-calculation of scales, ejaculate energy content (sperm ATP content, mass and density) and the size of secondary sexual traits. We found that males investing less in secondary sexual traits produce ejaculates with a higher energy content. Differences were found in the investment into primary and secondary sexual traits between fish that spent one year in the sea before returning to their spawning grounds (grilse) and multi-sea-winter adults, suggesting that different energy allocation patterns in reproductive effort reflect alternative developmental pathways. These findings are consistent with the pattern where multi-sea-winter male ejaculate investment relies principally on the resource acquisition in the ocean, whereas grilse ejaculate investment relies chiefly on the resource allocation of available surplus energy, thus representing alternative male reproductive tactics.

Bridging the Gap Between Salmon Spawner Abundance and Marine Nutrient Assimilation by Juvenile Salmon: Seasonal Cycles and Landscape Effects at the Watershed Scale

Anadromous Pacific salmon are semelparous, and resource subsidies from spawning adults (marine-derived nutrients, or MDN) benefit juvenile salmonids rearing in freshwater. However, it remains unclear how MDN assimilation relates to spawner abundance within a watershed. To address this, we examined seasonal, watershed-scale patterns of MDN assimilation in rearing coho (Oncorhynchus kisutch) and Chinook (O. tshawytscha) salmon and compared it with spawner biomass and landscape features in a western Alaska watershed with contrasting structural complexity in two sub-drainages. Adult salmon biomass density was estimated from escapement and spawner distribution data, and MDN assimilation in juvenile salmon was estimated via stable isotopes. In the North River, MDN assimilation was lowest in early summer, prior to annual spawning migrations, increased after spawning, and peaked in late winter. In the more complex mainstem Unalakleet River, MDN assimilation was higher but varied minimally from summer through fall before increasing in late fall and winter. Summer MDN assimilation, prior to salmon spawning, was primarily a function of habitat complexity, where MDN was highest in sloughs and the more complex mainstem river. After salmon spawned, fall MDN assimilation was a function of adult pink and Chinook salmon biomass as well as MDN assimilation that occurred prior to spawning (that is, summer MDN), but unrelated to total summer biomass (all salmon species biomass combined). Thus, MDN assimilation by juvenile salmon in the fall was a function of species-specific adult spawner abundance but seasonal patterns of MDN assimilation were masked in complex habitat where summer MDN assimilation remained high.

Individual Based Modelling of Fish Migration in a 2-D River System: Model Description and Case Study.

Diadromous fish populations in the Pacific Northwest face challenges along their migratory routes from declining habitat quality, harvest, and barriers to longitudinal connectivity. These stressors complicate the prioritization of proposed management actions intended to improve conditions for migratory fishes including anadromous salmon and trout. We describe a multi-scale hybrid mechanistic-probabilistic simulation model linking migration corridor conditions to fish fitness outcomes. We demonstrate the model's utility using a case study of salmon and steelhead adults in the Columbia River migration corridor exposed to spatially- and temporally-varying stressors. The migration corridor simulation model is based on a behavioral decision tree that governs individual interactions with the environment, and an energetic submodel that estimates the hourly costs of migration. Emergent properties of the migration corridor simulation model include passage time, energy use, and survival. We observed that the simulated fishes' initial energy density, the migration corridor temperatures they experienced, and their history of behavioral thermoregulation were the primary determinants of their fitness outcomes. Insights gained from use of the model might be exploited to identify management interventions that increase successful migration outcomes. This paper describes new methods that extend the suite of tools available to aquatic biologists and conservation practitioners. We have developed a 2-dimensional spatially-explicit behavioral and physiological model and illustrated how it can be used to simulate fish migration within a river system. Our model can be used to evaluate trade-offs between behavioral thermoregulation and fish fitness at population scales.

The evolutionary consequences for seawater performance and its hormonal control when anadromous Atlantic salmon become landlocked

Populations of anadromous fish have become landlocked in relatively recent geological history (<14,000 years), but the evolutionary impacts of this altered lifecycle on traits underlying seawater performance have not been established. In order to examine the effects of relaxed selection on seawater traits, anadromous and landlocked Atlantic salmon were reared under identical conditions and examined for differences in seawater performance and its underlying physiological and endocrine control during the time of spring downstream migration. Salinity tolerance, survival and initial growth in seawater were greater in anadromous than in landlocked salmon. Abundance of the seawater isoform of gill Na+/K+-ATPase increased in spring in both strains but was greater in anadromous salmon. Hormones associated with seawater acclimation (adrenocorticotropic hormone, cortisol and growth hormone) increased in spring in both strains but were higher in anadromous salmon, whereas plasma thyroid hormones did not differ. Hypothalamic urotensin I mRNA levels also increased in spring and were higher in the anadromous strain. The results provide evidence that salinity tolerance and associated physiological traits are regulated by seasonal stimulation of the hypothalamic-pituitary-interrenal axis, and that relaxed selection on seawater entry traits has decreased this stimulation in landlocked salmon.

Comparing abundance‐based and tag‐based estimates of coho salmon marine survival

AbstractObtaining reliable estimates of marine survival is essential for understanding anadromous salmon population dynamics. Two common approaches to estimating marine survival are (a) dividing abundance of returning adult salmon abundance by abundance of smolts from the same cohort, or (b) tagging a portion of the migrating smolts and estimating the return rate of tagged adults. This study compared these two approaches to estimating marine survival for coho salmon, Oncorhynchus kisutch (Walbaum), across multiple years in three California streams. Abundance‐based survival estimates were higher than tag‐based estimates; average estimates for the two techniques differed from 1.5‐fold to 7.4‐fold across streams. One likely cause for these divergent estimates is migration of juveniles from natal habitat before smolt trapping begins, resulting in an underestimate of smolt abundance and an overestimate of marine survival rate for the abundance‐based method. Estimates of marine survival obtained from abundance estimates and tag returns are not directly comparable.

Characteristics of a Naturalized Kokanee Salmon Oncorhynchus nerka Population in Atypical Habitat

Kokanee salmon are a dwarf freshwater form of the anadromous sockeye salmon (Oncorhynchus nerka) native to the Pacific coast of North America and Asia and widely introduced in western North America as a sport and prey fish. Few kokanee salmon introductions have succeeded in eastern North America. A naturalized population of kokanee salmon has persisted for over 50 yr in Florence Lake, Wisconsin, an unlikely location given its relatively small size (21.4 ha), shallow maximum depth (7.6 m), low elevation (381 m), and southerly latitude (45.12°N). Kokanee salmon completed their entire life cycle within the lake and rarely entered an accessible coldwater inlet stream. Spawning occurred during late October and early November along the lake shoreline. Spawning redds with defending males were observed in 1–2 m of water on sand/gravel/ cobble substrate. Kokanee salmon growth in the lake was relatively rapid, and fish had a mean total length of 117 mm after their first growing season (age 0+), 212 mm after their second (age 1+), begin to mature and spawn after their third (age 2+) at 317 mm for females and 324 mm for males, and were at 344 mm for females and 354 mm for males after their fourth (age 3+). Few fish reproduced at age 4+. Despite limited oxy-thermal habitat during summer, kokanee salmon appear to thrive in Florence Lake, perhaps because of cold inflows from the inlet and springs within the lake.

Sediment-associated organopollutants, metals and nutrients in the Nechako River, British Columbia: a current study with a synthesis of historical data

The flow-diverted Nechako River is the second largest tributary of the Fraser River which drains 25% of mainland British Columbia, Canada. The watershed provides critical reproductive habitats for anadromous chinook salmon (Oncorhynchus tshawytscha) and sockeye salmon (O. nerka) and year-round habitat for the endangered Nechako white sturgeon (Acipenser transmontanus) population. In this study, the chemical quality of sediment in the upper Nechako River and its major tributaries was examined for polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), legacy organochlorine (OC) pesticides, polycyclic aromatic hydrocarbons (PAHs), organophosphorus and phenoxy acid herbicides, polychlorinated dibenzo-p-dioxins (PCDDs) and furans (PCDFs), labile (exchangeable) metals/metalloids, and major nutrients (N and P). ΣPCB and ΣPBDE were detected in channel bottom sediments at all Nechako River and tributary sites; hexachlorobenzene (HCB) and 4,4′-DDE (dichlorodiphenyldichloroethylene) were also detected at most sites. Organophosphorus and phenoxy acid herbicides were not detected in any samples. While ΣPCB, ΣPBDE, HCB, and 4,4′-DDE concentrations in bottom sediments were always well below provincial and federal guidelines for the protection of aquatic life, concentrations of total labile As (AsT), CrT, CuT, FeT, MnT, NiT, and ZnT in suspended and/or bottom sediments often exceeded provincial threshold effect levels (TEL) and, in some cases, approached or exceeded probable effect levels. Distinct CuT, NiT, PbT and ZnT concentration maxima in suspended sediments were linked to road and urban densities. Historical PCDD, PCDF and PAH data show that concentrations in bottom sediment samples were highest at a site in the lower Nechako River between Miworth and the City of Prince George where PCDD and PCDF concentrations exceeded the interim federal TEL. Nitrogen and P concentrations in bottom sediments were negatively correlated with water velocity and sediment texture; the evidence suggests that reductions in velocity resulting from the 1952 diversion of the Nechako River have increased the nutrient content of bottom substrates.

Global dataset for carbon and nitrogen stable isotope ratios of lotic periphyton

Carbon and nitrogen stable isotope ratios (δ13C and δ15N) have been widely employed in food web analysis. In lotic environments, periphyton is a major primary producer that makes a large contribution to food web production as well as carbon and nitrogen cycling. While the δ13C and δ15N values have many advantages as a natural tracer, the controls over their high spatial and temporal variability in stream periphyton are not well known. Here, we present the global dataset of δ13C and δ15N values of lotic periphyton from 54 published and two unpublished sources, including 978 observations from 148 streams/rivers in 38 regions around the world, from arctic to tropical sites. The 54 published sources were articles recorded during the period of 1994–2016 in 25 academic journals. The two unpublished sources were from the authors’ own data. The dataset showed that δ13C and δ15N values of periphyton ranged from −47.3 to −9.3‰ and from −5.6 to + 22.6‰, respectively. The dataset also includes physicochemical factors (altitude, coordinates, catchment area, width, depth, geology, vegetation, canopy coverage, biome, season, presence of anadromous salmon, temperature, pH, current velocity, and discharge), nutrient data (nitrate and ammonium concentrations), and algal attributes (chlorophyll a concentration, algal species compositions, and carbonates removal) in streams/rivers studied, all of which may help interpret the δ13C and δ15N values of periphyton. The metadata file outlines structure of all the data and with references for data sources, providing a resource for future food web studies in stream and river ecosystems.

Millennial-scale decline in coho salmon abundance since the middle Holocene in a coastal Oregon watershed, USA

ABSTRACTThe population size of anadromous salmon in the Pacific Northwest is strongly influenced by decadal variation in watershed and oceanographic conditions and therefore should also be influenced by larger magnitude millennial-scale variations in these conditions. We studied δ15N of bulk organic matter in lake sediment from Woahink Lake, Oregon, as a proxy of marine-derived nutrients (MDN) from spawning coho salmon. We compared this site to a control lake with a natural barrier to salmon migration. From 7.5 to 5.4 ka, a dune was emplaced, breached, and emplaced again, forming Woahink Lake in a former estuary. δ15N decreased steadily since 5.4 ka at Woahink but not at the control lake. δ15N reached a minimum just prior to anthropogenic nutrient loading, which caused an increase in δ15N, thus precluding a comparison with the historical decline in salmon abundance. A mixing model of lake-water nitrate, developed to explore alternate scenarios for the observed range of δ15N, could not explain these results without invoking MDN input from at least several hundred salmon annually. Our results show a previously unreported pattern of a millennial-scale decline in salmon that has plausible linkages to parallel changes in ocean circulation and productivity.

Enhanced invertebrate prey production following estuarine restoration supports foraging for multiple species of juvenile salmonids (Oncorhynchus spp.)

Estuaries provide crucial foraging resources and nursery habitat for threatened populations of anadromous salmon. As such, there has been a global undertaking to restore habitat and tidal processes in modified estuaries. The foraging capacity of these ecosystems to support various species of out‐migrating juvenile salmon can be quantified by monitoring benthic, terrestrial, and pelagic invertebrate prey communities. Here, we present notable trends in the availability of invertebrate prey at several sites within a restoring large river delta in Puget Sound, Washington, U.S.A. Three years after the system was returned to tidal influence, we observed substantial additions to amphipod, copepod, and cumacean abundances in newly accessible marsh channels (from 0 to roughly 5,000–75,000 individuals/m2). In the restoration area, terrestrial invertebrate colonization was dependent upon vegetative cover, with dipteran and hymenopteran biomass increasing 3‐fold between 1 and 3 years post‐restoration. While the overall biodiversity within the restoration area was lower than in the reference marsh, estimated biomass was comparable to or greater than that found within the other study sites. This additional prey biomass likely provided foraging benefits for juvenile Chinook, chum, and coho salmon. Primary physical drivers differed for benthic, terrestrial, and pelagic invertebrates, and these invertebrate communities are expected to respond differentially depending on organic matter exchange and vegetative colonization. Restoring estuaries may take decades to meet certain success criteria, but our study demonstrates rapid enhancements in foraging resources understood to be used for estuary‐dependent wildlife.

Polyphyletic ancestry of expanding Patagonian Chinook salmon populations

Chinook salmon native to North America are spreading through South America’s Patagonia and have become the most widespread anadromous salmon invasion ever documented. To better understand the colonization history and role that genetic diversity might have played in the founding and radiation of these new populations, we characterized ancestry and genetic diversity across latitude (39–48°S). Samples from four distant basins in Chile were genotyped for 13 microsatellite loci, and allocated, through probabilistic mixture models, to 148 potential donor populations in North America representing 46 distinct genetic lineages. Patagonian Chinook salmon clearly had a diverse and heterogeneous ancestry. Lineages from the Lower Columbia River were introduced for salmon open-ocean ranching in the late 1970s and 1980s, and were prevalent south of 43°S. In the north, however, a diverse assembly of lineages was found, associated with net-pen aquaculture during the 1990s. Finally, we showed that possible lineage admixture in the introduced range can confound allocations inferred from mixture models, a caveat previously overlooked in studies of this kind. While we documented high genetic and lineage diversity in expanding Patagonian populations, the degree to which diversity drives adaptive potential remains unclear. Our new understanding of diversity across latitude will guide future research.

Evaluating Evidence for Historical Anadromous Salmon Runs in Eklutna Lake, Alaska

We assessed historical presence of sockeye salmon in Eklutna Lake, Alaska, prior to construction of a diversion dam on the downstream Eklutna River in 1929, using nitrogen stable isotopes measured in a lacustrine core 93 cm long. Sediments in the core were dated using varve counts, verified by 210Pb and 137Cs measurements. The basal date of the core was AD 1859, and varves became slightly thinner and less distinct after 1929. Sediments were primarily clastic with carbon content below 1%. Nitrogen isotope values were generally low and stable throughout the core, ranging from 1.5‰ to 2.5‰. There is no statistical evidence for a change in isotopic composition after emplacement of the dam. In light of published evidence from oral history, cultural records, and habitat relationships that suggest sockeye salmon could have been present in the lake before 1929, we conducted a simple sensitivity test to assess the possibility that a small salmon run may have gone undetected by our technique. We found that a salmon run of up to 1000/year, and potentially as many as 15 000/year, would be possible without noticeably altering the measured isotopic composition of the sediments in Eklutna Lake. Our results provide no evidence that such runs occurred, but do not preclude the possible existence of a relatively small sockeye fishery in Eklutna Lake before 1929.

Incremental analysis of vertebral centra can reconstruct the stable isotope chronology of teleost fishes

Abstract Isotope analysis has high potential for understanding fish ecology and food‐web structure in aquatic ecosystems. The utility of isotope analysis will be greatly improved if we can reconstruct the chronology of several isotopes at multiple growth stages of individual fish. However, no practical methods exist for reconstructing the chronology of light‐element isotopes (e.g. δ13C, δ15N, δ34S, and Δ14C) in teleost fishes. Here, we present and test a new analytical approach for reconstructing the isotopic ratios of light isotopes at multiple life‐stages in teleost fishes. We sampled an anadromous salmon species, masu salmon Oncorhynchus masou (n = 3), along with water from its natal stream and from the ocean. We subdivided the vertebral centra of the salmon equally into 10 sections and extracted bone collagen from each sample. We then measured the stable sulphur isotope ratios of each vertebral section and compared them with δ34S values of the river water and sea water. We also measured the 87Sr/86Sr ratios of otoliths as a reference indicator of salmon migration between fresh water and the ocean. In all samples, the bone section closest to the centre of the centrum had the lowest δ34S values, which were similar to those of fresh water. The δ34S values gradually increased from the centre to marginal sections, finally reaching constant values similar to those of seawater. The 87Sr/86Sr ratios of sagittal otolith sections had significant inter‐individual differences and were consistent with the patterns of variation of the δ34S values of the vertebral sections. Our results show that the vertebral centra of teleost fishes record isotopic information from juvenile to adult life stages. We suggest that our method can provide reproducible isotopic chronology, even in teleost fishes smaller than 50 cm. This method can be used in isoscape studies and in studies of the ecology of marine teleost fishes.

Upscaling site‐scale ecohydraulic models to inform salmonid population‐level life cycle modeling and restoration actions – Lessons from the Columbia River Basin

AbstractWith high‐resolution topography and imagery in fluvial environments, the potential to quantify physical fish habitat at the reach scale has never been better. Increased availability of hydraulic, temperature and food availability data and models have given rise to a host of species and life stage specific ecohydraulic fish habitat models ranging from simple, empirical habitat suitability curve driven models, to fuzzy inference systems to fully mechanistic bioenergetic models. However, few examples exist where such information has been upscaled appropriately to evaluate entire fish populations. We present a framework for applying such ecohydraulic models from over 905 sites in 12 sub‐watersheds of the Columbia River Basin (USA), to assess status and trends in anadromous salmon populations. We automated the simulation of computational engines to drive the hydraulics, and subsequent ecohydraulic models using cloud computing for over 2075 visits from 2011 to 2015 at 905 sites. We also characterize each site's geomorphic reach type, habitat condition, geomorphic unit assemblage, primary production potential and thermal regime. We then independently produce drainage network‐scale models to estimate these same parameters from coarser, remotely sensed data available across entire populations within the Columbia River Basin. These variables give us a basis for imputation of reach‐scale capacity estimates across drainage networks. Combining capacity estimates with survival estimates from mark–recapture monitoring allows a more robust quantification of capacity for freshwater life stages (i.e. adult spawning, juvenile rearing) of the anadromous life cycle. We use these data to drive life cycle models of populations, which not only include the freshwater life stages but also the marine and migration life stages through the hydropower system. More fundamentally, we can begin to look at more realistic, spatially explicit, tributary habitat restoration scenarios to examine whether the enormous financial investment on such restoration actions can help recover these populations or prevent their extinction. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Interactions of baseflow habitat constraints: Macroinvertebrate drift, stream temperature, and physical habitat for anadromous salmon in the Calapooia River, Oregon

Abstract The Calapooia River in western Oregon supports a small winter steelhead trout (Oncorhynchus mykiss) population and historically supported spring Chinook salmon (Oncorhynchus tshawytscha). Early timber harvesting removed the riparian forest, and log transportation practices simplified the channel. Those disturbance legacies continue to affect fish habitat by limiting shade and channel complexity, complicating conservation efforts. To evaluate juvenile salmonid rearing potential, macroinvertebrate drift, thermal regime and physical habitat were measured at eight sites in 24 km of the upper river during late summer baseflow. Overall physical habitat was simple, with few functioning instream structures or pools. During the 22‐day drift study, flows declined and maximum site stream temperatures ranged from 23.1°C at the lower end to 16.4°C 24 km upstream. Macroinvertebrate drift concentrations ranged from 0.7–13.7 ind. m−3 with biomasses from 0.02–1.23 mg m−3. Drift concentration biomass was higher upstream (P = 0.006) than downstream and declined overall (P &lt; 0.001) during the study. Drift biomass was dominated by five taxon groups – Baetis tricaudatus, Calineuria californica, Hesperoperla pacifica, Simulium spp., and Chironomidae, which were 65% of total biomass. During twilight, total biomass and biomass of B. tricaudatus, Simulium spp., and Chironomidae (both larvae and adults) were higher. Total drift declined dramatically over the study period owing to decreases in drift concentration and a 58% decline in discharge, greatly reducing overall drift and available food resources for juvenile‐rearing salmonids. The upper catchment, both with cooler temperatures and higher food availability, provided the best conditions for juvenile anadromous salmonids to survive late summer conditions. Conservation consequences of climate change‐induced alterations in flow and temperature may further affect habitat quality for juvenile salmonids in this catchment in the coming decades.

Carnation Creek watershed experiment—long‐term responses of coho salmon populations to historic forest practices

AbstractThe Carnation Creek project is a long‐term study of the effects of forestry practices on a small coastal watershed (11 km2) located in southwestern Vancouver Island. Initiated in 1970, this pretreatment versus post‐treatment case study consists of 5 years of preharvest, 6 years of during‐harvest, and now, 34 years of postharvest research. Forty‐one percent of the watershed was clearcut from 1976 to 1981. One tributary sub‐basin (1.1 km2) was left as an unharvested reference drainage. Riparian treatments varied from clearcuts to a variable‐width buffer. Fish population responses to logging have been complex, and specific to species and life stages. Stream warming due partly to riparian harvest increased the growth and survival of juvenile coho salmon and elevated smolt production by 65% for nearly three decades. These relatively short‐term thermal benefits offset the effects of riparian clearcutting which included accelerated bank erosion, streambed scour, loss of stable in‐stream wood, and sediment movement downstream. Landslides in 1984 greatly amplified these effects but took more than 20 years to propagate downstream to reduce fish habitat complexity and increase streambed instability and sediment transport over the entire portion inhabited by anadromous salmon. These delayed impacts have surpassed the thermal‐related benefits for coho salmon. Fry‐to‐smolt overwinter survival has declined from a mean of 50% between 1982 and 2004 to 15% since 2005. Coho salmon smolt production has consequently been reduced to below prelogging levels. Results show that forestry‐related alterations may take decades to fully develop and persist for decades longer without watershed and stream channel restoration.

Nutrient dynamics in a highly managed reservoir system: considering anadromous sockeye salmon (Oncorhynchus nerka) and nutrient restoration

ABSTRACTScott DC, Harris SL, Hebert AS, van Poorten BT. 2017. Nutrient dynamics in a highly managed reservoir system: considering anadromous sockeye salmon (Oncorhynchus nerka) and nutrient restoration. Lake Reserve Manage. 33:14–22.Modeling nutrient flux in Alouette Reservoir, British Columbia, allowed us to (1) determine the relative importance of key factors that influence its nutrient dynamics and (2) evaluate the potential value of returning anadromous salmon to this highly altered reservoir. Annual surface water releases over the dam spillway have facilitated out-migration of juvenile sockeye salmon (Oncorhynchus nerka) produced by resident kokanee parents since 2005, and these juveniles have returned as adult sockeye annually since 2007, thus restoring an anadromous run lost for nearly 90 years. This re-anadromization program may have an effect on the nutrient restoration program, which includes annual additions of nitrogen and phosphorus designed to enhance the recreational kokanee fishery within the reservoir. High flow release to facilitate juvenile out-migration resulted in a net export of nutrients because few adults returned, and a portion of nutrients added to the reservoir were flushed downstream. If only anadromous sockeye are considered, however, nutrient flux was positive in 5 of 6 years for nitrogen (average 2.30 kg; range −1.06 to 5.97), and in 4 of 6 years for phosphorus (average 0.24 kg; range −0.15 to 0.62). Overall, our results show the export of nutrients by the anadromy restoration project represents an average of just 1.54 and 0.60%, respectively, of the seasonal nitrogen and phosphorus budget for the system. Therefore, although the anadromy restoration results in a net loss of nutrients from the system, its effect on the nutrient restoration project is minimal.

Stable isotope (δ13C, δ15N, δ34S) analysis of sediment cores suggests sockeye salmon (Oncorhynchus nerka) did not historically spawn in Lake Roberta, Washington (USA)

Historically, the Sanpoil River, Washington (USA) produced spawning runs of chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (O. mykiss). Lake Roberta is connected to the Sanpoil River and local oral history suggests it may have supported anadromous sockeye salmon (O. nerka) until the completion of Grand Coulee Dam in the 1940s. Post-spawning mortality of anadromous salmon provides large pulses of marine-derived nutrients to aquatic and terrestrial ecosystems in the vicinity of spawning sites. Unique isotopic ratios of these marine-derived nutrients are often transferred to freshwater algae and archived in lake sediments. However, marine-derived isotope signatures may be overpowered by large inputs of other nutrient sources such as agricultural fertilizers, reactive nitrogen deposition, nitrogen fixation, or poor trophic transfer to freshwater algae. We compared nitrogen and sulfur isotope compositions for pre-1940 and post-1940 sediments to those collected from a control lake with no history of anadromy to investigate the possible historic presence of anadromous salmon in Lake Roberta. We also analyzed carbon isotopes, carbon:nitrogen ratios, and sediment accumulation rates to determine if changes in the lake sediments resulted from eutrophication rather than salmon exclusion. If sockeye did spawn in Lake Roberta historically, and if excessive nitrogen inputs did not overpower the marine-derived signal, we would expect pre-1940 sediment organic matter isotope compositions indicative of the large pulses of marine nutrients from decomposing salmon carcasses. Isotope results and land use in the Lake Roberta watershed present no conclusive evidence to support anecdotal accounts of anadromy. There is some evidence to suggest that marine-derived nutrients transferred to riparian communities within the lake’s watershed may have moved downstream to the lake. However, most of the evidence suggests eutrophication and a switch to increased autochthonous productivity are the main causes of changes in the lake sediment isotope composition.

Effects of multiple stresses hydropower, acid deposition and climate change on water chemistry and salmon populations in the River Otra, Norway

Many surface waters in Europe suffer from the adverse effects of multiple stresses. The Otra River, southernmost Norway, is impacted by acid deposition, hydropower development and increasingly by climate change. The river holds a unique population of land-locked salmon and anadromous salmon in the lower reaches. Both populations have been severely affected by acidification. The decrease in acid deposition since the 1980s has led to partial recovery of both populations. Climate change with higher temperatures and altered precipitation can potentially further impact fish populations. We used a linked set of process-oriented models to simulate future climate, discharge, and water chemistry at five sub-catchments in the Otra river basin. Projections to year 2100 indicate that future climate change will give a small but measureable improvement in water quality, but that additional reductions in acid deposition are needed to promote full restoration of the fish communities. These results can help guide management decisions to sustain key salmon habitats and carry out effective long-term mitigation strategies such as liming. The Otra River is typical of many rivers in Europe in that it fails to achieve the good ecological status target of the EU Water Framework Directive. The programme of measures needed in the river basin management plan necessarily must consider the multiple stressors of acid deposition, hydropower, and climate change. This is difficult, however, as the synergistic and antagonistic effects are complex and challenging to address with modelling tools currently available.