Salmon River Research Articles

Regional estimation of river water temperature at ungauged locations

River water temperature measurement networks suffer from an inadequate spatial coverage and a lack of data. No methods exist for the regional estimation of river water temperature at ungauged sites based on data series from gauged sites. The development of such methods is hence of significant importance. It is proposed in this study to develop a Temperature-Duration-Curve (TDC) based method to estimate river water temperature at ungauged sites on a real-time basis. A Generalised Additive Model (GAM) based method is used to estimate TDCs at ungauged sites. The estimated TDCs are then used in combination with a spatial interpolation method to obtain daily temperature estimates at ungauged sites. Results are compared with a simple method based on the geographical distance weighted average of neighboring stations. The approaches are applied to 126 river thermal stations located on Atlantic salmon rivers in eastern Canada. Leave-one-out cross validation results indicate that the TDC based methods are robust and outperform the geographical distance weighted method.

Importance-performance analysis of the fishing tourism service structure: Recreational anglers’ preferences on the remote salmon river of Teno in Finland

Fishing tourism is an important means of livelihood in the northern peripheries. Along the River Teno on the northern border of Norway and Finland, which has had the largest wild Atlantic salmon stock complex in the world, fishing tourism is threatened. The salmon population has declined, challenging fishing tourism as a livelihood. For the future development and continuation of fishing tourism, understanding the preferences of fishing tourists is increasingly important. We apply importance-performance analysis to examine the contribution of the perceived importance and the performance of attributes to the overall satisfaction of fishing tourists with their trips to the River Teno. Overall satisfaction was most affected by the perceived performance of the catch and the fishing permits. The results support fishing tourism actors in identifying potential key areas for development and assessing the potential of non-fishing-related services that may contribute to the future livelihood of the area.

Changes in the smoltification age of Atlantic salmon (<i>Salmo salar </i>L.) of the Yokanga, Kharlovka and Vostochnaya Litsa Rivers (the Murmansk Region)

Throughout the world, in recent decades, there has been a decrease in the abundance of Atlantic salmon, the main reason for which is a decrease in its survival rate during life at sea. Its value has a direct dependence on the length and, accordingly, the age of the smolts. Foreign researchers have found that the nature of long-term changes in the age structure of smolts can vary significantly by region. At the same time, the age of Atlantic salmon in Russian rivers, which account for a significant part of the area of the range of this species, was not considered. In this regard, the analysis of long-term data characterizing the age composition of salmon smolts of some rivers of the Murmansk region has been carried out. It has found been that in the first years of the period 2000-2018, the age structure of Atlantic salmon smolts was transformed in the rivers Yokanga, Kharlovka and Vostochnaya Litsa. As a result, fish at the age of 6 ceased to occur among them, the abundance of fish at the age of 5+ significantly decreased and the abundance of fish in the age groups of 3+ or 4+ significantly increased. The most likely reason for this is the change in the temperature regime of rivers since the mid-1990s, as a result of which the life time in the rivers of juvenile salmon has been reduced. Rejuvenation of the smolt population may have ambiguous consequences for the abundance of adult salmon, which are determined by the cumulative effect of reducing natural mortality at the stage from eggs to smolts, increasing their abundance and reducing their length, and reducing the survival rate during salmon life in the sea.

Climate and human exploitation have regulated Atlantic salmon populations in the River Spey, Scotland, over the last 2000 years

Historical salmon catch records suggest that climatic variability, and more recently human exploitation, control patterns of abundance in Atlantic salmon populations. We present the first long-term (2000-year) reconstruction of Atlantic Salmon population variations based on a Marine Derived Nutrient (MDN) lake sediment record. Our record is constructed from nitrogen isotopes (δ15N) measured from a lake sediment core, which we compare with an escapement index (EI) derived from historic net catch data on major Scottish salmon rivers. We used an isotope mixing model to demonstrate that the N isotope values are likely enriched with MDN and demonstrate that Loch Insh sediments are enriched compared with a control site (Loch Vaa) that has never had exposure to salmon. We demonstrate that current adult spawner returns are around half that of historic values prior to major human exploitation. Before the onset of widespread human exploitation and habitat degradation, large fluctuations in salmon abundance are attributed to variations in North Atlantic sea surface temperature. While our data support published reconstructions of declining Atlantic salmon stocks in Northwest European rivers over the last 1000 years, rather than point to a solely human cause, the human impact appears to be overprinted on larger-scale changes in marine habitat occurring at the transition from the warmer Medieval Climatic Anomaly (MCA) to the cooler Little Ice Age (LIA).

Increased Mercury and Reduced Insect Diversity in Linked Stream-Riparian Food Webs Downstream of a Historical Mercury Mine.

Historical mining left a legacy of abandoned mines and waste rock in remote headwaters of major river systems in the western United States. Understanding the influence of these legacy mines on culturally and ecologically important downstream ecosystems is not always straightforward because of elevated natural levels of mineralization in mining-impacted watersheds. To test the ecological effects of historic mining in the headwaters of the upper Salmon River watershed in Idaho (USA), we measured multiple community and chemical endpoints in downstream linked aquatic-terrestrial food webs. Mining inputs impacted downstream food webs through increased mercury accumulation and decreased insect biodiversity. Total mercury (THg) in seston, aquatic insect larvae, adult aquatic insects, riparian spiders, and fish at sites up to 7.6 km downstream of mining was found at much higher concentrations (1.3-11.3-fold) and was isotopically distinct compared with sites immediately upstream of mining inputs. Methylmercury concentrations in bull trout and riparian spiders were sufficiently high (732-918 and 347-1140 ng MeHg g-1 dry wt, respectively) to affect humans, birds, and piscivorous fish. Furthermore, the alpha-diversity of benthic insects was locally depressed by 12%-20% within 4.3-5.7 km downstream from the mine. However, because total insect biomass was not affected by mine inputs, the mass of mercury in benthic insects at a site (i.e., ng Hg m-2 ) was extremely elevated downstream (10-1778-fold) compared with directly upstream of mining inputs. Downstream adult aquatic insect-mediated fluxes of THg were also high (~16 ng THg m-2 day-1 ). Abandoned mines can have ecologically important effects on downstream communities, including reduced biodiversity and increased mercury flux to higher order consumers, including fish, birds, and humans. Environ Toxicol Chem 2022;41:1696-1710. Published 2022. This article is a U.S. Government work and is in the public domain in the USA.

Natural and anthropogenic drivers of escaped farmed salmon occurrence and introgression into wild Norwegian Atlantic salmon populations

Abstract Marine aquaculture of Atlantic salmon (Salmo salar) is a relatively new industry where breeding programs have led to rapid genetic change in the captive populations that were built up alongside conspecific wild individuals. Throughout its 50-years history, marine aquaculture of Atlantic salmon has been associated with escapes, and studies have shown that escapees may enter rivers, spawn successfully, and this may lead to farmed-to-wild genetic introgression and maladaptation in wild populations. Yet, an open question is what factors can best explain the variability in the proportion of farmed escapees in wild populations, and when present, which additional factors lead to introgression. Here, we combine two large-scale data sets from monitoring escaped farmed salmon and introgression in Norwegian rivers between 2006 and 2018 to model how anthropogenic, environmental, and population factors influence proportion of escapees and level of introgression. We found that increasing farming intensity and river discharge increase the expected proportions of escaped farmed salmon in rivers, whereas a larger wild salmon population size reduces the expected proportion of escapees despite increasing the expected absolute numbers of escaped farmed salmon. On a large scale, introgression is primarily a function of proportions of escaped farmed salmon, and only to a minor extent a function of local environmental factors or salmon population characteristics. This suggests that as long as salmon aquaculture is based on technologies where non-sterile fish can escape, all anadromous wild Atlantic salmon populations are at risk. Large marine protected areas without salmon aquaculture may slow down the rate of intrusion and introgression by increasing the distance between intensive aquaculture and wild populations.

A Fish Out of Basin: Increased Stress Physiology and Reduced Performance of Salmon River Hatchery Chinook Salmon

AbstractVariation in rearing conditions across hatcheries and basins can affect the performance of hatchery salmonids in the wild. In 2008, the Shoshone‐Bannock Tribes began planning an out‐of‐basin hatchery facility on the eastern Snake River Plain for rearing threatened Chinook Salmon Oncorhynchus tshawytscha for release in tributaries of the upper Salmon River, Idaho, USA. To help determine the viability of the planned out‐of‐basin hatchery, we reared 100,000 juvenile Chinook Salmon from the same genetic stock at one in‐basin (Sawtooth Fish Hatchery on the Salmon River) and one out‐of‐basin (Springfield Fish Hatchery on the Snake River Plain) site in Idaho that are characterized by significant differences in water hardness and temperature regime. In October 2018 and April 2019, we tested whether fish condition, stress physiology, acute mortality, and downstream survival differed between the two groups at the parr and smolt life stages upon release in the Yankee Fork Salmon River, which is characterized by low water hardness. For both release groups, parr experienced low acute mortality during the 48 h after release; however, the out‐of‐basin group had a downstream survival rate through an unimpounded portion of the migration corridor that was an order of magnitude lower than that for the in‐basin group. During the smolt release, the out‐of‐basin group showed signs of extreme physiological stress, acute mortality rates of 40–80%, and low survival in the unimpounded portion of the migratory corridor. The in‐basin group recovered from the stress of transport and release, had no acute mortality, and survived through the unimpounded migratory corridor at a rate comparable to that of previous years’ releases. Based on the results of this comparative study, comanagers are evaluating alternatives to the proposed out‐of‐basin hatchery program. This case study highlights the effects of differences between rearing and release conditions on salmon physiology and survival as well as the value of conducting preliminary evaluations prior to implementing large‐scale hatchery supplementation programs.

Nutrient limitation in Atlantic salmon rivers and streams: Causes, consequences, and management strategies.

Freshwater catchments can experience nutrient deficits that result in reduced primary and secondary productivity. The most commonly limiting nutrients are nitrogen and phosphorus, either separately or together. This review considers the impact of increasing nutrient limitation in temperate basin stream and river systems, focusing on upland areas that currently or previously supported wild Atlantic salmon ( Salmo salar ) populations.Anthropogenic changes to land use and increases in river barriers have altered upland nutrient dynamics, with particular impacts on salmon and other migratory fish species which may be net importers of nutrients to upland streams. Declining salmon populations may further reduce nutrient sources, reducing ecosystem and fisheries productivity below desired levels.Experimental manipulations of nutrient levels have examined the impacts of this cultural oligotrophication. There is evidence that growth and biomass of juvenile salmon can be increased via appropriate additions of nutrients, offering potential as a conservation tool. However, further research is required to understand the long‐term effects of these additions on salmon populations and stream ecosystems, and to assess the vulnerability of downstream habitats to eutrophication as a result.Although purposeful nutrient addition with the aim of enhancing and conserving salmonid populations may be justified in some cases, it should be undertaken in an adaptive management framework. In addition, nutrient addition should be linked to nutrient retention and processing, and integrated into large‐scale habitat restoration and recovery efforts.Both the scientific and the management community should recognize that the ecological costs and benefits associated with adding nutrients to salmon streams may change in a non‐stationary world.

Retracted: Monitoring Hatchery Broodstock Composition and Genetic Variation of Spring/Summer Chinook Salmon in the Columbia River Basin with Multigeneration Pedigrees

AbstractHatchery production of Chinook Salmon Oncorhynchus tshawytscha in the Columbia River basin comprises most of the anadromous salmonid production in this region. Hatchery facilities and programs serve to mitigate for impacts to salmonids due to the construction and operation of hydropower dams and habitat impacts from development in addition to the conservation and restoration of natural populations. A genetic method referred to as parentage‐based tagging (PBT) enables highly reliable detection of hatchery‐origin fish and inference of multigeneration pedigrees. This study compiles 11 years of PBT data from nearly 125,000 interior stream‐type Chinook Salmon from 24 spawning hatcheries located in tributaries of the mid‐ and upper Columbia River as well as the Salmon, Clearwater, and Grande Ronde River subbasins. Multigenerational pedigrees allowed investigation of the proportion of natural‐ and hatchery‐origin broodstock (pNOB and pHOB, respectively) for each hatchery and enumeration of the scale of production between segregated and integrated programs. We then compared how pHOB and the scale of production influenced the number of stray fish observed, genetic diversity, relatedness, and age‐class compositions within broodstocks. Over 91.0% of hatchery broodstock could be assigned back to their parents, and there was an overall rate of less than 1.0% of broodstock that were unintentionally incorporated into nonnatal hatchery programs. We evaluated 14 segregated programs with 0.0–10.0% pNOB, 7 intermediate programs (10.1–50.0% pNOB), and 3 integrated programs (>50.0% pNOB). There was no correlation between the scale of production or pNOB with the level of genetic diversity, but as production size increased, so did the effective number of breeders. This study demonstrates the utility of PBT as a monitoring tool for hatchery broodstocks, and results suggest that segregated and integrated programs have tradeoffs that generally align with their intended broodstock management purpose of providing fish for harvest and/or fish for supplementation or reintroduction.

The endangered freshwater pearl mussel Margaritifera margaritifera shows adaptation to a local salmonid host in Finland

Abstract The freshwater pearl mussel Margaritifera margaritifera (FPM) is an endangered unionid which has a glochidium larva that attaches to the gills of Atlantic salmon Salmo salar or brown trout S. trutta, although some FPM populations have been shown to exclusively attach to only one of these species. The origin of host fish populations may be crucial for conservation actions for this mussel species, but the relative suitability of local (sympatric) and non‐local (allopatric) salmonid populations as the hosts for FPM has been studied only rarely. We hypothesised that FPM glochidia would show adaptation to local salmonid strains and, therefore, that they would be more successful (abundant, larger) attached to sympatric than to allopatric fish. Here, we investigated the infection success (abundance and growth of encysted larvae in fish) of FPM in local versus non‐local fish by caging different strains of brown trout and Atlantic salmon in rivers where FPM populations are present. Higher abundances of glochidia in local fish were observed in three brown trout streams, and larger glochidia were found in sympatric hosts in one brown trout stream and in one salmon river. Furthermore, non‐local allopatric fish were not better hosts than local fish in any of the FPM populations tested, neither in brown trout or salmon rivers and neither in abundance nor size of larvae. Therefore, the results supported the hypothesis that glochidia show local adaptation by being more successful when attached to local fish strains. Thus, the local, sympatric fish strain should be preferred in FPM conservation programmes that involve captive breeding of juvenile mussels and introduction of host fish, but the regional assessment of local host dependency of FPM also would be important outside the current study area. The results also indicate the importance of restoration of original salmonid populations in FPM rivers to enable the natural, effective reproduction cycle of FPM in their original, sympatric hosts, and thus to promote the recovery of endangered FPM populations.

Количественные характеристики зообентоса бассейна озера Удыль (заказник «Удыль», Хабаровский край)

The article reports the results of the study on zoobenthos in the wetlands of Lake Udyl and its 12 tributaries (the Lower Amur, Udyl Nature Reserve) during the 2021 summer flood. Except for the Bichi River, benthic communities of the rivers and streams in the Lake Udyl basin were studied for the first time. The study found that the composition, structure and quantitative characteristics of the bottom communities of Udyl Lake and the Bichi salmon river differed from the previous results obtained in the 1930s–1940s and the 1990s. The results revealed a rich taxonomic composition of invertebrates (19 groups), low values of density and biomass in the water bodies of the reserve. The zoobenthos was dominated by amphibiotic insects (57% of the total density and 43% of the total biomass). We established that oligochaetes and chironomids in the Udyl Lake basin differed in the highest quantitative indicators. The quality of water was determined using classical (GW, TBI, IB, ND/Nex, NCh/Nex) and modified (IPM, TBIM) bioindicative indices and metrics. The results show that, in general, the ecosystem of Lake Udyl and the watercourses flowing into it is in a relatively satisfactory condition.

Details of artificial reproduction of Atlantic salmon (Semga) at the Umba fish hatchery

The world's demand for fish products for food and industrial purposes has already significantly exceeded the reproduction capacity of wild fish. Further increasing exploitation of natural fish populations leads to a sharp reduction in their numbers and degradation of population biodiversity. The only way to solve the problem is to develop artificial reproduction of fish. This applies primarily to salmon, which are the most valuable and popular types of fish. In the Murmansk region, there are three fish hatcheries that carry out artificial reproduction of Atlantic salmon. Factory reproduction at the Umba Fish Hatchery (URZ) is currently an important and necessary process, since the plant is the only fish hatchery for reproductive purposes in the Tersk district. The article reveals the peculiarities of reproduction of Atlantic salmon (salmon) in the URZ. A brief description of the Umba River is given. The main fish-breeding activities are covered: catching and keeping of producers, collection of sexual products and fertilization, incubation of eggs, keeping of larvae and their transfer to external nutrition, factory tagging of juveniles, release of juveniles in the Umba River and its tributaries. The peculiarity of the Umba plant in contrast to the other two fish hatcheries of the Kola Peninsula is shown. The question of the necessity of the existence of the Umba fish hatchery and the prospects for its development is highlighted. The reasons for the decline in the number of salmon in Umba are listed. Recommendations for restoring the abundance and preserving the intraspecific biodiversity of the Umba River salmon are provided.

Classification of hydropeaking impacts on Atlantic salmon populations in regulated rivers

AbstractThis article proposes and demonstrates a new classification system of fish population level effects of hydropeaking operations in rivers. The classification of impacts is developed along two axes; first, the hydromorphological effect axis assesses the ecohydraulic alterations in rivers introduced by rapid and frequent variations in flow and water level, second the vulnerability axis assesses the site‐specific vulnerability of the fish population. Finally, the population level impact is classified into four classes from small to very large by combining the two axes. The system was tested in four rivers in Norway exposed to hydropeaking, and they displayed a range of outcomes from small to very large impacts on the salmon populations. The river with a relatively high base flow and ramping restrictions scored better than rivers with the lower base flow or limited ramping restrictions, indicating that hydropeaking effects can be mitigated while maintaining high hydropower flexibility. Most effect factors could easily be calculated from timeseries of discharge and water level, whereas the use of hydraulic models to estimate potential stranding areas may require more work. The vulnerability factors are mainly qualitative and depend more heavily on expert judgments and are thus more uncertain. The system was deemed suitable for the purpose of supporting management decisions for rivers exposed to hydropeaking operations. It evaluates the severity of the additional pressures due to hydropeaking operations and proved useful to identify mitigating measures. While the system was developed for Atlantic salmon river systems, it could be adapted to other species or systems.

Genomic Evaluation of the Genus Coltivirus Indicates Genetic Diversity among Colorado Tick Fever Virus Strains and Demarcation of a New Species.

The type species of the genus Coltivirus, Colorado tick fever virus (CTFV), was discovered in 1943 and is the most common tick-borne viral infection in the Western US. Despite its long history, very little is known about the molecular diversity of viruses classified within the species Colorado tick fever coltivirus. Previous studies have suggested genetic variants and potential serotypes of CTFV, but limited genetic sequence information is available for CTFV strains. To address this knowledge gap, we report herein the full-length genomes of five strains of CTFV, including Salmon River virus and California hare coltivirus (CTFV-Ca). The sequence from the full-length genome of Salmon River virus identified a high genetic identity to the CTFV prototype strain with >90% amino acid identity in all the segments except segment four, suggesting Salmon River virus is a strain of the species Colorado tick fever coltivirus. Additionally, analysis suggests that segment four has been associated with reassortment in at least one strain. The CTFV-Ca full-length genomic sequence was highly variable from the prototype CTFV in all the segments. The genome of CTFV-Ca was most similar to the Eyach virus, including similar segments six and seven. These data suggest that CTFV-Ca is not a strain of CTFV but a unique species. Additional sequence information of CTFV strains will improve the molecular surveillance tools and provide additional taxonomic resolution to this understudied virus.

TESTING OF A NEST-INCUBATOR OF CAVIAR OF SALMON SPECIES OF FISH OF THE GENUS SALMO "SALMO-3000" IN THE CONDITIONS OF THE ARCTIC RIVER INDYORA (KOLA PENINSULA)

The article presents the results of approbation of the artificial nest-incubator of eggs "Salmo-3000" for the reproduction of salmon species of fish of the genus Salmo, tests were carried out in the r. Inder (White Seabasin). An original device was used, installed at the bottom of the river's threshold section. The nest design includes: the main body - a streamlined oval flattened container formed by three layered incubation trays and a lid; remote water intake / filter; connecting branch pipe with accessories for water distribution and discharge; elements fastening to the ground and a device for driving fasteners into the ground. The nest allows you to incubate fertilized eggs of Atlantic salmon or brown trout during autumn, winter and spring (autonomy for at least 8 months) and in summer (June) to obtain viable larvae that independently settle in the river threshold or are forcibly removed from rearing devices in the basins. During the test, the following advantages were revealed (increased capacity for incubated eggs up to 3,000 salmon / brown trout eggs per device, effective water distributor, grates that limit the eggs from washing out during laying, fixing rods made of fiberglass reinforcement that do not give oxidation, water intake / filter effectively cleaning and supplying water to caviar), and the disadvantage - the complexity and duration of the installation of the device, up to 60 minutes per device. In general, the hatching efficiency of larvae was 97.2% at partial load. The output of fry into the river was 96.0%. The device can be used to restore the abundance of Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) in small rivers where hatchery reproduction is unprofitable for various reasons.

Comment on “Salmon lice-induced mortality of Atlantic salmon post-smolt during migration in Norway” by Johnsen et al. (2021)

Abstract Johnsen et al. (2021) present a model that predicts lice-induced mortality of virtual post-smolt (VPS) Atlantic salmon migrating from 401 Norwegian salmon rivers. An important feature of this model is that the source of lice is farmed salmon. The model predicts lice-induced mortalities exceeding 30% for VPS from 82 rivers, 10–30% for 140 rivers, and less than 10% for 179 rivers. These are high numbers and have contributed to mandatory reductions in the production of farmed salmon in two of the 13 management areas in Norway. In this comment, the model used by Johnsen et al. (2021) is evaluated. Mortality estimates from observed lice numbers on post-smolts caught by trawling in outer fjord areas are compared with the model predicted mortalities for VPS migrating from rivers draining into the corresponding fjords. It is found that Johnsen et al. (2021) systematically overestimates lice-induced mortality for VPS compared to estimates from trawled smolt from corresponding fjords. The present analysis thus contradicts the concluding remark in Johnsen et al. (2021), that: “The estimated lice level on modelled post-smolts is shown to coincide with the level observed on captured wild post-smolt”.

Indigenous sex-selective salmon harvesting demonstrates pre-contact marine resource management in Burrard Inlet, British Columbia, Canada

To gain insight into pre-contact Coast Salish fishing practices, we used new palaeogenetic analytical techniques to assign sex identifications to salmonid bones from four archaeological sites in Burrard Inlet (Tsleil-Waut), British Columbia, Canada, dating between about 2300–1000 BP (ca. 400 BCE–CE 1200). Our results indicate that male chum salmon (Oncorhynchus keta) were preferentially targeted at two of the four sampled archaeological sites. Because a single male salmon can mate with several females, selectively harvesting male salmon can increase a fishery’s maximum sustainable harvest. We suggest such selective harvesting of visually distinctive male spawning chum salmon was a common practice, most effectively undertaken at wooden weirs spanning small salmon rivers and streams. We argue that this selective harvesting of males is indicative of an ancient and probably geographically widespread practice for ensuring sustainable salmon populations. The archaeological data presented here confirms earlier ethnographic accounts describing the selective harvest of male salmon.

Food web incorporation of marine-derived nutrients after the reintroduction of endangered inner Bay of Fundy Atlantic salmon (Salmo salar)

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

Effects of early-life stage and environmental factors on the freshwater and marine survival of Chinook salmon (Oncorhynchus tshawytscha) in rivers of Southeast Alaska

Effects of early-life stage and environmental factors on the freshwater and marine survival of Chinook salmon (Oncorhynchus tshawytscha) in rivers of Southeast Alaska

Using landscape ecology principles to prioritize habitat restoration projects across the Columbia River Estuary

To increase survival of diverse Columbia River salmon populations and life history types, we developed a landscape framework for habitat restoration to assess and reduce habitat fragmentation, and thereby improve habitat functions. For the last two decades, aquatic habitat has been restored in the Columbia River Estuary (U.S.A.) to aid salmon and steelhead (Oncorhynchus spp.) listed under the Endangered Species Act. The 234‐km long estuary exhibits tidal to fluvial gradients in hydrology, sedimentology, and ecology, punctuated by large tributary rivers, cities, and land uses; it has lost two‐thirds of its historical floodplains and wetlands to development. Since 2009, an expert panel has assessed potential benefits of proposed restoration projects based on habitat “opportunity” (accessibility to juvenile salmon) and “capacity” (attributes supporting salmon production). These criteria favored large restoration projects located near the mainstem river, but they were insufficient for assessing a project's benefits due to geographic location relative to existing habitat. Our landscape framework applies the concept of restoring and conserving habitat “stepping stones” of appropriate size and location to benefit juvenile salmon growth and survival throughout their estuary residency and migration. We also compared contemporary and historical landscape conditions to identify restoration priorities. We improved our restoration project assessments by evaluating each project's benefits to juvenile salmon according to its location in the estuary relative to other habitat. Our approach operationalizes landscape ecology‐based decisions within the Columbia River Estuary for migratory salmon and is applicable to other large estuary systems with migratory aquatic species.