Native Salmon Research Articles

Use of environmental DNA for early detection of invasive Elodea species in interior Alaska

Abstract Invasive Canadian waterweed Elodea canadensis and western waterweed E. nuttallii are a threat to native salmon Onchorhynchus spp. in Alaska. Early detection is important to stop or mitigate spread. We evaluated detection of environmental DNA (eDNA) as a tool for early detection of these invasive species in Alaska. First, we evaluated four quantitative real-time PCR assays, one for each species, and two targeting either species, using samples taken at known infestations in Chena Lakes and Potter Marsh, Alaska. We also deployed E. nuttallii in screened containers at the Small Arms Complex Pond, Fort Wainwright, Alaska (Test Pond) in 2018 and 2019 to evaluate the detection of eDNA as a function of distance from the containers. At the known infestations, we detected the eDNA of both species in water samples. However, in our Test Pond, we only detected Elodea eDNA in 2 of 126 samples collected in 2019. Both detections were from samples collected within 10 cm of the containers. There were no detections in 60 samples collected in 2018 at the Test Pond. While there are potential uses for the eDNA markers we developed (e.g., species identification), we found no evidence to support their use as an early detection tool for Elodea in Alaska.

A Review of Pacific Salmon Hatcheries in British Columbia, Canada, and Interactions With Natural Populations

Pacific salmon Oncorhynchus spp. hatcheries in British Columbia (BC) have been the major activity of the Salmonid Enhancement Program since 1977. However, the present diminished abundance of Pacific salmon and loss of fisheries in BC called for a review of hatchery effectiveness. The Pacific Salmon Foundation conducted a review resulting in 15 reports publicly available on the Pacific Salmon Foundation marine science website. The review includes evaluations of effectiveness of hatchery production, evidence of interactions with natural salmon populations (including rebuilding natural populations with hatchery‐produced salmon), and future opportunities via genomics. Beyond the estimation of juvenile production and contribution to catches and spawning escapements, the ability to assess effectiveness was limited. The assessments of interactions provided a few examples of positive outcomes, but most were negative. The lack of comparative assessments in purely wild populations seriously limits interpretations of hatchery–wild interactions. Future evaluations of the hatchery effectiveness require more quantitative and integrated assessments of hatchery and wild salmon, open data sharing for public review or research, and related studies could benefit from application of new genomic technologies. This paper presents recommendations to address these needs and calls for regularized reviews of the Salmonid Enhancement Program and its net value to sustainability of BC's Pacific salmon.

Experiences from targeted removal of farmed Atlantic salmon from Norwegian rivers

Abstract Farmed salmon escaping from aquaculture and interbreeding with wild conspecifics pose a significant threat to the genetic integrity of natural salmon populations. Despite advancements in aquaculture security, escape incidents persist, prompting the need for effective mitigation strategies. This study summarizes experiences from efforts to remove escaped farmed salmon over a 12-year period in 63 western Norwegian rivers, using either (1) spearfishing during snorkelling by trained personnel or (2) traditional fishing methods employed by local groups. Recaptured farmed salmon ranged widely in size and included both spawners as well as immature fish, demonstrating that farmed fish entering rivers comprise fish of different ages and escape histories. Traditional fishing by locals recaptured the highest number of farmed fish, while removal during snorkelling in general captured larger and mature fish. On average, 53% of the farmed salmon observed during snorkelling were recaptured. This efficacy was influenced by the number of farmed fish present and the size of the farmed fish. In addition, efficacy increased over time, indicating that the removal team became more efficient. The study underscores that active removal, when executed judiciously, contributes to reducing the ecological risks associated with escaped farmed fish, complementing broader strategies for sustainable aquaculture.

Most of the escaped farmed salmon entering a river during a 5-year period were infected with one or more viruses.

Disease interactions between farmed and wild populations have been poorly documented for most aquaculture species, in part due to the complexities to study this. Here, we tested 567 farmed Atlantic salmon escapees, captured in a Norwegian river during 2014-2018, for five viral infections that are prevalent in global salmonid aquaculture. Over 90% of the escapees were infected with one or more viruses. Overall prevalences were: 75.7% for piscine orthoreovirus (PRV-1), 43.6% for salmonid alphavirus (SAV), 31.2% for piscine myocarditis virus (PMCV), 1.2% for infectious pancreatic necrosis virus (IPNV) and 0.4% for salmon anaemia virus (ISAV). A significantly higher prevalence of PMCV infection was observed in immature compared to mature individuals. The prevalence of both SAV and PMCV infections was higher in fish determined by fatty acid profiling to be 'recent' as opposed to 'early' escapees that had been in the wild for a longer period of time. This is the first study to establish a time-series of viral infection status of escapees entering a river with a native salmon population. Our results demonstrate that farmed escapees represent a continuous source of infectious agents which could potentially be transmitted to wild fish populations.

Aulukluki neqkat: Centering care of salmon and relational research in Indigenous fisheries in the Kuskokwim River, Alaska

This Indigenous-led project aims to better understand historical and contemporary ways in which Alaska Native Peoples steward salmon and the values connected to salmon stewardship. Indigenous Peoples have stewarded Alaska lands and waters for thousands of years yet have been largely excluded from western science and management systems. In this project we utilize a participatory approach that allows for the equitable valuing of ideas and knowledges to document the breadth and depth of Yup’ik and Athabascan knowledge and governance systems in southwestern Alaska. We reshape research methodologies by centering Indigenous frameworks and research methodologies including circle dialogues and multi-generational interviews led by Indigenous scholars and students in their home communities and regions. In this paper, we share the Yup’ik and Athabascan values, knowledge, management, and governance mechanisms that can improve the long-term sustainability and equity of Alaska salmon systems. This research elevates the voices of Alaska Native salmon stewards and experts from the Kuskokwim Bay and the Kuskokwim River. We elaborate on five key themes that emerged from this research including: traditional Indigenous ways of life, Indigenous stewardship, self-determination, food and livelihood sovereignty, and ecosystem changes, and identify a more equitable and sustainable path forward for salmon and people in Alaska.

Recreational anglers in Norway report widespread dislike of invasive pink salmon

Abstract Pink salmon have returned to Norwegian rivers at high abundance in recent odd‐numbered years (2017, 2019, 2021, 2023), presenting potential threats to native biodiversity and ecosystem services, including major sport fishing tourism for Atlantic salmon and sea‐run brown trout in Norway. Presently, there exists a knowledge gap on angler perceptions and attitudes towards the presence of pink salmon in Norwegian rivers, resulting in difficulty assessing the socioeconomic repercussions of their invasion. We distributed an online questionnaire to anglers who purchased the national salmon fishing licence in Norway in 2020 to assess their perceptions of pink salmon and the intentions of anglers to modify their fishing practices. There were widespread negative perceptions of pink salmon in Norway. Perceptions were matched with intentions to modify fishing behaviour among some of the anglers, with 41% saying that they would modify fishing to increase the catch of pink salmon to help remove them before they spawned in the rivers. However, anglers were more prone to say they would decrease fishing effort if both pink salmon catches and fishing licence costs were to increase or if pink salmon were to dominate their catch. Salmon anglers in Norway were strongly oriented towards their chosen recreational activity and do not plan to stop fishing their preferred rivers. They also do not want pink salmon to become established in Norway and are prepared to volunteer for stewardship roles that intervene against pink salmon. However, they overwhelmingly reported not wanting to eat pink salmon. Fisheries managers must take into account the widespread desire for management intervention against pink salmon, even though eradication is not likely no matter how intensive removal efforts become. Efforts to change narratives about pink salmon to encourage fishers to harvest pink salmon from the fjords and rivers for consumption might lead to effective population control, relieving native salmon, trout and charr from potential negative impacts of this prolific colonizer. Read the free Plain Language Summary for this article on the Journal blog.

Экологическое и эпигенетическое воздействие на искусственно разводимых тихоокеанских лососей рода Oncorhynchus

The fundamental reasons for the decline in the number of natural salmon herds in the countries of the northern Pacific basin and in the southern waters of the Russian Far East are given. It is shown how the scientifically unjustified creation of a system of salmon hatcheries caused the formation of negative ecosystem, social and economic consequences from large-scale artificial cultivation of all types of Pacific salmon. The colossal influence of ecological and epigenetic influence on the transformation of ontogenesis, reduction of vitality and reproduction of healthy offspring, loss of navigation-innate instinct (homing) in artificially raised Pacific salmon of the genus Oncorhynchus is considered.

Knowledge Shared by Alaska Native Commercial Salmon Set Gillnetters in Norton Sound to Reduce Marine Fatalities

ABSTRACT Objectives The goal of this exploratory pilot study was to reduce marine fatalities in Norton Sound using knowledge shared from Alaska Native salmon set gillnetters in Unalakleet, AK. The following objectives to address this goal were: 1) identify factors that influence safety for Alaska Native commercial set gillnetters in Norton Sound; 2) use findings from objective 1 to improve commercial fishing training, education, and resources; and 3) disseminate and communicate results from objective 1 to commercial fishers in the Norton Sound fleet, commercial fishing safety partners, and the Alaska Native injury prevention community. Methods Ten semi-structured interviews were conducted with Alaska Native commercial set gillnetters in Unalakleet, AK. We utilized knowledge shared to identify factors that influence safety for their fleet. Using an Interpretative Phenomenological Analysis Methodology, 10 interviews were recommended for a homogenous sample. Results Most participants learned to fish at a young age from the family, with safety lessons passed on by family members. Fishing is a lifestyle and interconnected with harvesting and a way of living. Set gillnetters in Norton Sound use open skiffs and have limited access to workable Personal Flotation Devices (PFDs) and safety training. Participants reported health benefits but also negative long term physical effects, financial stress, and difficulty fishing with age. Respect and awareness of the ocean was reported as the most important strategy to reduce risk. Stories were shared of falls overboard, capsizing, and local fatalities and hazards, such as being overloaded with fish, entanglement, and maneuvering a small boat in large waves. Stronger winds and shifting weather patterns were experienced from climate change. Conclusion This exploratory pilot study identified factors that influence safety for Alaska Native commercial set gillnetters. Findings should be used to 1) determine best methods to influence behaviors to reduce risks in this hazardous fishery; 2) increase awareness and promote expanded application of best practices, equipment, and resources; 3) encourage and promote outreach initiatives targeted for this unique population; and 4) develop tailored training programs for commercial fishing in an open skiff. Research with Alaska Native fishing communities will require value and respect of indigenous knowledge, collaboration with local people, and follow-up to bring findings back to the community.

Genomic divergence of hatchery- and natural-origin Chinook salmon (Oncorhynchus tshawytscha) in two supplemented populations

Captive propagation is widely used for the conservation of imperiled populations. There have been concerns about the genetic effects of such propagation, but few studies have measured this directly at a genomic level. Here, we use moderate-coverage (10X) genome sequences from 80 individuals to evaluate the genomic distribution of variation of several paired groups of Chinook salmon (Oncorhynchus tshawytscha). These include (1) captive- and natural-origin fish separated by at least one generation, (2) fish within the same generation having high fitness in captivity compared to those with high fitness in the wild, and (3) fish listed as different Evolutionarily Significant Units (ESUs) under the US Endangered Species Act. The distribution of variation between high-fitness captive and high-fitness natural fish was nearly identical to that expected from random sampling, indicating that differential selection in the two environments did not create large allele frequency differences within a single generation. In contrast, the samples from distinct ESUs were clearly more divergent than expected by chance, including a peak of divergence near the GREB1L gene on chromosome 28, a gene previously associated with variation in time of return to fresh water. Comparison of hatchery- and natural-origin fish within a population fell between these extremes, but the maximum value of FST was similar to the maximum between ESUs, including a peak of divergence on chromosome 8 near the slc7a2 and pdgfrl genes. These results suggest that efforts at limiting genetic divergence between captive and natural fish in these populations have successfully kept the average divergence low across the genome, but at a small portion of their genomes, hatchery and natural salmon were as distinct as individuals from different ESUs.

Glacier runoff influences biogeochemistry and resource availability in coastal temperate rainforest streams: Implications for juvenile salmon growth

AbstractMeltwater contributions to watersheds are shrinking as glaciers disappear, altering the flow, temperature, and biogeochemistry of freshwaters. A potential consequence of this landscape change is that streamflow patterns within glacierized watersheds will become more homogenous, potentially altering the capacity of watersheds to support Pacific salmon. To assess heterogeneity in stream habitat quality for juvenile salmon in a watershed in the Alaska Coast Mountains, we collected organic matter and invertebrate drift and measured streamwater physical and biogeochemical properties over the main runoff season in two adjacent tributaries, one fed mainly by rain and the other partially by glacier ice/snowmelt. We then used bioenergetic modeling to evaluate how temporal patterns in water temperature and invertebrate drift in each tributary influence juvenile salmon growth potential. Across the study period, average invertebrate drift concentrations were similar in non‐glacierized Montana (0.33 mg m−3) and glacier‐influenced McGinnis Creeks (0.38 mg m−3). However, seasonal patterns of invertebrate drift were temporally asynchronous between the two streams. Invertebrate drift and modeled fish growth were generally higher in McGinnis Creek in the spring and Montana Creek in the Summer. For juvenile salmon, tracking these resource asynchronies by moving between tributaries resulted in 20% greater growth than could be obtained within either stream alone. These results suggest that hydrologic heterogeneity within watersheds may enhance the diversity of foraging and growth opportunities for mobile aquatic organisms, which may be essential for supporting productive and resilient natural salmon runs.

Обнаружение особо опасных вирусных болезней рыб семейства лососёвых (Salmo salar) с применением полимеразной цепной реакции

Significant economic damage to aquaculture facilities and marine aquatic organisms is caused by viral diseases of fish, almost a quarter of the detected viruses cause diseases. Pathogens mainly fall during the transportation of infected fish from disadvantaged farms to "clean" aquatic farms, as well as from "escaped" fish from cages to the sea, where contamination of natural salmon and other aquatic organisms occurs. When delivering fish planting material to Russia from countries with different epizootological situations, constant monitoring and forecasting of possible risks is necessary. To prevent the spread of viral infections of fish, diagnostics and prevention occupy a leading place. Laboratory diagnostics of fish diseases of viral etiology is based on the isolation of the pathogen and its identification by serological methods that require a long time and research in specialized specialized laboratories of large research institutes. More effective and highly sensitive are molecular diagnostic methods, in particular, polymerase chain reaction (PCR) with reverse transcription to detect a number of particularly dangerous viral diseases of fish. Infectious necrosis of hematopoietic tissue, infectious pancreatic necrosis, viral hemorrhagic septicemia and infectious anemia of salmon were identified by highly specific and sensitive diagnostic PCR method. The improved technique of PCR with reverse transcription makes it possible to detect pathogens in salmon and other fish both with obvious clinical signs and with hidden virus carrier.

Spatiotemporal distribution of Ceratonova shasta in the lower Columbia River Basin and effects of exposure on survival of juvenile chum salmon Oncorhynchus keta.

In the Columbia River Basin (CRB), USA, anthropogenic factors ranging from dam construction to land use changes have modified riverine flow and temperature regimes and degraded salmon habitat. These factors are directly implicated in native salmon and steelhead (Oncorhynchus species) population declines and also indirectly cause mortality by altering outcomes of ecological interactions. For example, attenuated flows and warmer water temperatures drive increased parasite densities and in turn, overwhelm salmonid resistance thresholds, resulting in high disease and mortality. Outcomes of interactions between the freshwater myxozoan parasite, Ceratonova shasta, and its salmonid hosts (e.g., coho O. kisutch and Chinook salmon O. tshawytscha) are well-described, but less is known about effects on chum salmon O. keta, which have a comparatively brief freshwater residency. The goal of this study was to describe the distribution of C. shasta relative to chum salmon habitat in the CRB and assess its potential to cause mortality in juvenile chum salmon (listed as threatened in the CRB under the U.S. Endangered Species Act). We measured C. shasta densities in water samples collected from chum salmon habitat throughout the lower CRB during the period of juvenile chum salmon outmigration, 2018–2020. In 2019, we exposed caged chum salmon fry from two hatchery stocks at three C. shasta-positive sites to assess infection prevalence and survival. Results demonstrated: (1) C. shasta was detected in spawning streams from which chum salmon have been extirpated but was not detected in contemporary spawning habitat while juvenile chum salmon were present, (2) spatiotemporal overlap occurs between C. shasta and juvenile chum salmon in the Columbia River mainstem, and (3) low densities of C. shasta caused lethal infection in chum salmon fry from both hatchery stocks. Collectively, our results suggest C. shasta may limit recovery of chum salmon now and in the future.

Predatory ability and abundance forecast the ecological impacts of two aquatic invasive species

Characterising interspecific interaction strengths, combined with population abundances of prey and their novel predators, is critical to develop predictive invasion ecology. This is especially true of aquatic invasive species, which can pose a significant threat to the structure and stability of the ecosystems to which they are introduced. Here, we investigated consumer-resource dynamics of two globally-established aquatic invasive species, European green crab (Carcinus maenas) and brown trout (Salmo trutta). We explored the mediating effect of prey density on predatory impact in these invaders relative to functionally analogous native rock crab (Cancer irroratus) and Atlantic salmon (Salmo salar), respectively, feeding on shared prey (Mytilus sp. and Tenebrio molitor, respectively). We subsequently combined feeding rates with each predator’s regional abundance to forecast relative ecological impacts. All predators demonstrated potentially destabilising Type II functional responses towards prey, with native rock crab and invasive brown trout exhibiting greater per capita impacts relative to their trophic analogues. Functional Response Ratios (attack rates divided by handling times) were higher for both invasive species, reflecting greater overall per capita effects compared to natives. Impact projections that incorporated predator abundances with per capita effects predicted severe impacts by European green crabs. However, brown trout, despite possessing higher per capita effects than Atlantic salmon, are projected to have low impact owing to currently low abundances in the sampled watershed. Should brown trout density increase sixfold, we predict it would exert higher impact than Atlantic salmon. Such impact-forecasting metrics and methods are thus vital tools to assist in the determination of current and future adverse impacts associated with aquatic invasive species.

Black bear colour polymorphism through a fragmented Snell’s window

Abstract The white colour morph of the black bear (Ursus americanus kermodei) occurring on islands on the coast of British Columbia, western Canada, captures more salmon (Oncorhynchus spp.) than does the black morph and is hypothesized to have reduced contrast against the sky from the visual perspective of the salmon. We tested this hypothesis in a natural salmon stream by recording the number and proximity of chum salmon (Oncorhynchus keta) approaches (N = 1617 fish, 91 trials) towards life-size bear models differing in body and leg coloration under a mixed forest-sky canopy. Although salmon approached the white models at a much higher rate than black models, consistent with camouflage, we found greater abrupt evasions to the black models, largely independent of their contrast against the above-surface or below-surface backgrounds. Upward-facing sub-surface video-imaging through the rippled water-air interface indicated major visual fragmentation of the model’s integrity. We suggest that increased evasiveness to black models reflects an evolutionary response due to 3+ million years of trophic interaction between salmon and bears, and that the major differences between calm vs. rippled conditions through the optical cone (Snell’s window) at the water-air interface remains a largely unexplored theme in assessing foraging preferences and adaptive coloration within and among species using the water-air interface.

Bias in hatchery-origin coho salmon survival estimates due to underestimated prerelease mortality

The widely accepted belief that hatchery-origin salmon survive less well than natural-origin or wild salmon can be, at least in part, an artifact of the way hatchery salmon survival is estimated. Hatchery salmon are often marked several months before release, while natural salmon are marked during their seaward migration. Underestimated prerelease mortalities result in biased low survival estimates. In British Columbia, although hatchery rearing practices have been modified to reduce unrecorded mortalities, experimental evidence indicates that coho salmon (Oncorhynchus kisutch) smolt survivals continue to be underestimated by ∼13%. Better reporting and incorporation of survival bias in data sets and analyses as well as additional work to evaluate bias for other regions and species over time is needed.

Can we identify wild-born salmon from parentage assignment data? A case study in the Garonne-Dordogne rivers salmon restoration programme in France

Parentage assignment with genomic markers provides an opportunity to monitor salmon restocking programs. Most of the time, it is used to study the fate of hatchery-born fish in those programs, as well as the genetic impacts of restocking. In such analyses, only fish that are assigned to their parents are considered. In the Garonne-Dordogne river basin in France, native salmon have disappeared, and supportive breeding is being used to try to reinstate a self-sustained population. It is therefore of primary importance to assess the numbers of wild-born returning salmon, which could appear as wrongly assigned or not assigned, depending on the power of the marker set and on the size of the mating plan. We used the genotypes at nine microsatellites of the 5800 hatchery broodstock which were used from 2008 to 2014, and of 884 upstream migrating fish collected from 2008 to 2016, to assess our ability to identify wild-born salmon. We simulated genotypes of hatchery fish and wild-born fish and assessed how they were identified by the parentage assignment software Accurassign. We showed that 98.7% of the fish assigned within the recorded mating plan could be considered hatchery fish, while 93.3% of the fish in other assignment categories (assigned out of the mating plan, assigned to several parent pairs, not assigned) could be considered wild-born. Using a Bayesian approach, we showed that 31.3% of the 457 upstream migrating fish sampled from 2014 to 2016 were wild-born. This approach is thus efficient to identify wild-born fish in a restoration program. It remains dependent on the quality of the recording of the mating plan, which we showed was rather good (<5% mistakes) in this program. To limit this potential dependence, an increase in the number of markers genotyped (17 instead of 9) is now being implemented.

Differential sensitivity to warming and hypoxia during development and long-term effects of developmental exposure in early life stage Chinook salmon.

Warming and hypoxia are two stressors commonly found within natural salmon redds that are likely to co-occur. Warming and hypoxia can interact physiologically, but their combined effects during fish development remain poorly studied, particularly stage-specific effects and potential carry-over effects. To test the impacts of warm water temperature and hypoxia as individual and combined developmental stressors, late fall-run Chinook salmon embryos were reared in 10 treatments from fertilization through hatching with two temperatures [10°C (ambient) and 14°C (warm)], two dissolved oxygen saturation levels [normoxia (100% air saturation, 10.4-11.4mg O2/l) and hypoxia (50% saturation, 5.5mg O2/l)] and three exposure times (early [eyed stage], late [silver-eyed stage] and chronic [fertilization through hatching]). After hatching, all treatments were transferred to control conditions (10°C and 100% air saturation) through the fry stage. To study stage-specific effects of stressor exposure we measured routine metabolic rate (RMR) at two embryonic stages, hatching success and growth. To evaluate carry-over effects, where conditions during one life stage influence performance in a later stage, RMR of all treatments was measured in control conditions at two post-hatch stages and acute stress tolerance was measured at the fry stage. We found evidence of stage-specific effects of both stressors during exposure and carry-over effects on physiological performance. Both individual stressors affected RMR, growth and developmental rate while multiple stressors late in development reduced hatching success. RMR post-hatch showed persistent effects of embryonic stressor exposure that may underlie differences observed in developmental timing and acute stress tolerance. The responses to stressors that varied by stage during development suggest that stage-specific management efforts could support salmon embryo survival. The persistent carry-over effects also indicate that considering sub-lethal effects of developmental stressor exposure may be important to understanding how climate change influences the performance of salmon across life stages.

Формы существования предкавказской кумжи - Strutta caucasicus (Дорофеева, 1967) Каспийского бассейна

A morphological analysis of brooks trout in Dagestan showed that each spawning herd is morphologically unique and differs from the rest in a certain set of characters. However, all of them, when comparing the age composition, spawning conditions, the extent of spawning migrations in rivers, etc. have a lot in common. All of them meet the definition of a population as a group of individuals united by panmixia, a single territory and isolated to one degree or another from similar groups within the species. The morphological characteristics of trout in the upper of rivers Avar, Andi, and Kara-Koysu further confirms the validity of this approach. Presumably, the structure of trout populations is in continuous change and the differences in morphological indicators are phenotypic in nature and reflect the biotic and abiotic conditions prevailing in this region. The interaction of variability and selection in the population maintains a mobile equilibrium of biological properties forms the passing (brown trout) and residential (trout) forms.
 The trout of Sulakriver breaks up into several local herds (trout of Avar Koysu, Andi Koysu, Kara-Koysu, etc.) with a specific and limited range of its migrations. To a certain extent, differing from neighboring ones, each of the herds maintains its integrity and does not mix with the rest. Thus, the brooks trout of Dagestan seem to combine two functions - the self-reproduction of local settled populations and generating migrant individuals in the Caspian trout (Terek, Samur, Kara-Su rivers, etc.).
 In the rivers of the Kara-Su system, regardless of the place of fishing and the season, trout is represented by almost 100% males. Naturally, the question arises: who ensures the reproduction of trout herds in the absence of females? At the same time, the Salmo truttacis caucasicus (Dorofeyeva, 1967) comes to spawn in these rivers, and its livestock is represented exclusively by females (70-80%). Therefore, brooks trout of the Kara-Su system rivers and the Salmo truttacis caucasicus, coming here to spawn, should be considered as a single reproduction fund. Eggs, laid by either a brown trout female or a trout female, can leave individuals, that roll into the sea and turn into a passing trout, and individuals that remain in the river will be called brooks trout.
 The total reproductive potential of small rivers of the Dagestan coast of the Caspian Sea is currently no less than in native salmon rivers (Terek, Samur). That is why small rivers play an important role in the natural reproduction of trout and brown trout. Among the small salmon rivers of Dagestan, the greatest fishery value have tributaries of the Sulak river, rivers of the Kara-Su system, Shura-ozen, Manas-ozen, etc. Significant differences in the climatic features of these areas inevitably affect the biology of trout inhabiting them.

Individual‐based simulations suggest mixed impacts of warmer temperatures and a nonnative predator on Chinook salmon

AbstractAs the climate changes, warmer water temperatures may stress populations of native coldwater fishes. Simultaneously, nonnative warmwater predators may expand their ranges and interact with already at‐risk native fish populations. To explore the independent and combined effects of these two stressors on threatened salmon, we present a case study of simulated Chinook salmon Oncorhynchus tshawytscha and largemouth bass Micropterus salmoides interacting under two thermal regimes in the Snoqualmie River, Washington, USA. We applied an individual‐based and spatially explicit model that tracks fish movement and growth. We evaluated changes in Chinook salmon emergence date, outmigration date, mass, and survival. We ran simulations for four scenarios: (1) Baseline, run without either stressor, (2) Warm, run with warmer temperatures, (3) Predator, run with largemouth bass, and (4) Warm‐Predator, run with both stressors. We assessed outcome metrics relative to the Baseline scenario. In the Warm scenario, salmon emerged 37 d and outmigrated 55 d earlier. There were 61% more subyearling migrants that were 31% smaller, and 72% fewer yearlings. In the Predator scenario, salmon survival decreased 64% for subyearlings and 69% for yearlings, and subyearlings were 7% smaller. In the Warm‐Predator scenario, salmon emerged 39 d and outmigrated 59 d earlier, subyearling survival increased 22%, subyearling mass decreased 37%, and 93% fewer yearlings survived. Our results suggest that warmer temperatures shift emergence and outmigration; predation by nonnative species is a threat to salmon survival; and life history strategies experience these stressors in different ways. Whereas subyearling production benefited from warmer temperatures more than it was hurt by predation, yearling production was depressed by both stressors independently and combined. Managers can use our individual‐based and spatially explicit approach to identify key times and areas to address exposure to extreme temperatures, overlap with nonnative species, and their interactive effects on threatened salmon. Our case study addressed three pressing needs identified in the literature: investigate impacts of nonnative species on threatened native salmon, build tools to evaluate management options where bass and salmon overlap, and explore how freshwater fishes will contend with multiple interactive stressors.

Consequences of Piscine orthoreovirus genotype 1 (PRV-1) infections in Chinook salmon (Oncorhynchus tshawytscha), coho salmon (O.kisutch) and rainbow trout (O.mykiss).

Piscine orthoreovirus genotype 1 (PRV‐1) is the causative agent of heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon (Salmo salar L.). The virus has also been found in Pacific salmonids in western North America, raising concerns about the risk to native salmon and trout. Here, we report the results of laboratory challenges using juvenile Chinook salmon, coho salmon and rainbow trout injected with tissue homogenates from Atlantic salmon testing positive for PRV‐1 or with control material. Fish were sampled at intervals to assess viral RNA transcript levels, haematocrit, erythrocytic inclusions and histopathology. While PRV‐1 replicated in all species, there was negligible mortality in any group. We observed a few erythrocytic inclusion bodies in fish from the PRV‐1‐infected groups. At a few time points, haematocrits were significantly lower in the PRV‐1‐infected groups relative to controls, but in no case was anaemia noted. The most common histopathological finding was mild, focal myocarditis in both the non‐infected controls and PRV‐1‐infected fish. All cardiac lesions were judged mild, and none were consistent with those of HSMI. Together, these results suggest all three species are susceptible to PRV‐1 infection, but in no case did infection cause notable disease in these experiments.