Diadromous Fish Species Research Articles

Environmental DNA metabarcoding reveals the effect of river slope on diadromous fish communities in island rivers

Understanding the natural factors that influence diadromous fish communities in river ecosystems is crucial for effective biodiversity management. However, this remains an unexplored and challenging task. Here, the relationship between river morphology and diadromous fish communities within rivers was explored. We focused on river slope and estuary size, as these may constrain their upstream migration and affect the availability of important nursery grounds for some species. Using environmental DNA metabarcoding, we investigated the diadromous fish communities within 12 rivers of subtropical Yakushima Island, southern Japan, and compared the community differences among rivers with different river slopes and estuary sizes. Fewer diadromous fish species were detected in rivers with steeper slopes and smaller estuaries. Additionally, the community similarity was greater among rivers with analogous gradients and estuary sizes. These results indicate that river slopes exert a species-selective effect on diadromous fish communities by affecting their upstream migration and estuarine habitat availability, thereby playing a crucial role in shaping the composition of these communities within rivers. Conserving gentle-gradient rivers with large estuaries would be crucial for preserving the diversity of diadromous fish species, which play a crucial role in shaping biodiversity especially in rivers of subtropical and tropical oceanic islands.

Challenges in downstream dam passage and the effect of dam removal on Atlantic salmon (Salmo salar) smolt migrations.

Migration is critical for life-cycle completion in diadromous fish species. River connectivity is vital in facilitating these large-scale movement events, but the extent of present-day river fragmentation can interfere with these migrations. Fish passage solutions (FPSs) are commonly implemented with the aim of improving river connectivity. In our study, we investigated the performance of two types of FPSs, spill regimes and complete dam removal, on Atlantic salmon (Salmo salar) smolt migrations. We used acoustic telemetry to monitor migration behavior and passage success of 120 wild smolts released in three different groups/sites: one group with two dams to pass to reach the river mouth, a second group with one dam to pass, and a control group without any barriers to pass (upstream of a recently removed hydroelectric dam). Smolt passage probabilities were similar for the two studied dams (87% and 86%) but showed variation in path choice, delay times, and loss rates. Passage success was influenced by several factors, such as body size, diel period, and water temperature, but not flow. Cumulative passage success to the river mouth was 61%, with most individuals being lost within lentic river stretches, either in the forebays of hydroelectric power stations or in naturally wide river stretches. Within the recently rehabilitated river sections (post dam removal), passage speeds were significantly faster than all other sections of the river (post-rehabilitation x¯ = 56.1 km/day) with significantly faster speeds compared to pre-rehabilitation (pre-x¯ = 28.0 km/day). Our findings provide valuable information on the benefits of dam removal and highlight the need for further rehabilitation measures in upriver reaches where barriers still affect downstream passage.

Diadromous fish run assessment: a double-observer model using acoustic cameras to correct imperfect detection and improve population abundance estimates

IntroductionDiadromous fish populations have strongly declined over decades, and many species are protected through national and international regulations. They account for less than 1% of fish biodiversity worldwide, but they are among the most perceptible linkages between freshwater and marine ecosystems. During their migration back and forth, diadromous fish species are subjected to many anthropogenic threats, among which river damming can severely limit access to vital freshwater habitats and jeopardize population sustainability. Here, we developed a method based on a double-observer modeling approach for estimating the abundance of diadromous fish during their migration in rivers.MethodsThe method relies on two independent and synchronous records of fish counts that were analyzed jointly thanks to a hierarchical Bayesian model to estimate detection efficiencies and daily fish passage. We used simulated data to test model robustness and identify conditions under which the developed approach can be used. The approach was then applied to empirical data to estimate the annual silver eel run in the Touques River, France.ResultsThe analysis of simulated datasets and the study case gives evidence that the model can provide robust,accurate, and precise estimates of detection probabilities and total fish abundance in a set of conditions dependent on the information provided in the data (annual distribution of fish passage, annual number of observation, pairing period, etc.).DiscussionThen, the method can be applied to various species and counting systems, including nomad acoustic camera devices. We discuss its relevance for programs on river continuity restoration, notably to quantify population restoration associated with dam removals.

Connecting population functionality with distribution model predictions to support freshwater and marine management of diadromous fish species

Diadromous fish species have a complex life cycle during which they migrate between marine and freshwater habitats. They experience multiple human-induced pressures in both environments, likely exacerbated by climate change, leading to dramatic population declines across their distribution ranges. Currently Species Distribution Models (SDMs) have been applied separately in both their continental and marine habitats to improve our understanding of their lifecycles and help with species management. Integrating the freshwater-sea continuum into the decisions would now be a step further in improving their management. With this objective, we developed a decision tree that links marine and freshwater SDM outputs with current observations of population functionality and suggested management guidance options for the viability of these species. Potential effects of climate change were included through future SDM projections to guide integrative and long-term management. Several criteria were proposed to assess the SDM validity considering the main sources of SDM uncertainties and local expert knowledge on habitat and population status. The framework was applied to approximately one hundred catchments from southern Portugal to southern Scandinavia for four diadromous species. At the European level, management guidance options differed between the two anadromous and two catadromous species. Platichthys flesus and Chelon ramada European populations seemed in better state than those of Alosa alosa and A. fallax. Finally, with the help of national diadromous species experts, we focused on four catchments distributed along the European latitudinal gradient to test the proposed methodology and demonstrate local management challenges in terms of freshwater-sea continuity.

From the modeling of diadromous species’ marine distributions to the characterization of their current and future marine habitats

IntroductionMany diadromous fish species are currently facing the threat of generalized population extirpations across their range, and conservation efforts implemented primarily within the continental domain may not be sufficient to ensure their viability. In consequence, better understanding the use of the marine environment by these species turned out to be critical.Material and methodWe developed marine species distribution models for two species, Allis shad (Alosa alosa) and the European flounder (Platichthys flesus), and proposed a way to interpret the habitat suitability from a more functional perspective. Our approach defined marine habitats as highly suitable environments that remained with a high potential through the species life stage duration at sea. First, a species-specific probabilistic threshold was applied to select for highly suitable environments each year of the simulations. Then, annual maps of high suitability were combined into recurrence maps showing areas were the environmental conditions remained the most suitable across the life at sea of the given species, these areas being called ‘marine habitats’. We applied this approach to study the current and future marine habitats of Allis shad and European flounder under climate change scenarios.ResultsThe main current marine habitats of these species were coastal, primarily in the Bay of Biscay for Allis shad and in the English Channel-North Sea for European flounder. These habitats are expected to experience minimal changes by mid-century, and the species may even benefit from new habitats at higher latitudes. However, the European flounder is likely to face greater challenges in the central part of its range by the end of the century, as potential spawning grounds may be threatened.DiscussionThis study provided a way to rethink ‘traditional’ suitability maps by integrating basic knowledge on the diadromous species life at sea. Our findings were part of a larger effort to link continental and marine habitats in improving management of diadromous species.

Extinction risks and threats facing the freshwater fishes of Britain

Abstract Extinctions occur naturally in all environments, but rates have accelerated rapidly during the Anthropocene, especially in fresh water. Despite supporting many fish species of conservation importance, there has never been a formal assessment of their extinction risks in Britain, which has impeded their inclusion in relevant legislation and policy. This study therefore used the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species™ Categories and Criteria to conduct the first systematic assessment of the extinction risks and threats facing the native freshwater and diadromous fishes of Britain. In addition, national assessments were produced for England, Scotland and Wales, reflecting the level at which environmental policy decisions are taken in Britain. Seven species were categorized as being threatened with extinction at the regional level, with European eel Anguilla anguilla and allis shad Alosa alosa classified as Critically Endangered, Atlantic salmon Salmo salar, vendace Coregonus albula and European whitefish Coregonus lavaretus classified as Endangered, and Arctic charr Salvelinus alpinus and twaite shad Alosa fallax classified as Vulnerable. In addition, burbot Lota lota was classified as Regionally Extinct, ferox trout Salmo ferox was categorized as Data Deficient, and 25 species were categorized as Least Concern. European sturgeon Acipenser sturio and houting Coregonus oxyrinchus, although probably native, qualified as only vagrants in fresh water, so were categorized as Not Applicable. The assessments provide objective baselines against which future changes can be determined, and a key evidence base to support policy and management decisions for the conservation of freshwater and diadromous fish species and their habitats in Britain. It is recommended that the assessments are repeated every 10 years, which would enable changes in conservation status, the effectiveness of policies and where targeted interventions may be required to be examined using the Red List Index.

Trends in a European coastal fishery with a special focus on small-scale fishers – Implications for fisheries policies and management

Worldwide, commercial small-scale fisheries are under increasing pressure. The study examines trends in a commercial Baltic Sea fishery with a special focus on the German small-scale fishery (both part-time and full-time fishery) over a period of 21 years (2000–2021) against the background of the declines in the two main target species of the fishery, namely western Baltic spring-spawning herring (Clupea harengus) and western Baltic cod (Gadus morhua). Landings, revenues, and the number of fishing businesses and vessels of the commercial fishery decreased over the past 21 years although the decline of the number of vessels was less pronounced for the small-scale fishery. The proportion of part-time fishers slightly increased locally. Fishers less dependent on cod and herring responded to declining revenues by diversifying their catches, and the proportion of revenues from flatfish, freshwater and diadromous fish species increased. The study was supplemented by a questionnaire sent to part-time fishers and excerpts from in-depth interviews with full-time fishers to add context to the study. The interviews indicated that family tradition, self-actualization, and nature experience but also a lack of alternatives due to the old age of fishers caused them to continue fishing despite poor economic prospects. A realistic assessment of the challenges and opportunities facing small-scale fisheries and the inclusion of social dimensions in fisheries policies are necessary, not least to develop incentives for small-scale fishers at the regional and local level to promote sustainable fisheries and facilitate fisher’s diversification.

Characterizing state‐managed and unmanaged fisheries in coastal marine states and territories of the United States

AbstractThe status of federally managed fisheries in the United States is well monitored, but the condition of other marine fisheries, whether state‐managed, territory‐managed or unmanaged, is less understood and often unknown. We used expert surveys to characterize the management systems of non‐federally managed fisheries in US coastal marine states and overseas territories. For 311 fisheries, we estimated an overall Fisheries Management Index (FMI) and a qualitative stock status score. These measures were positively correlated, and while a wide range of research, management, enforcement and socioeconomic criteria were partially met (FMI ≥ 0.5) for 66% of fisheries, stock status was considered as partially acceptable (score ≥ 0.5) for only 45% of fisheries and acceptable (score = 1) for only 16% of fisheries. Higher FMI was typically observed in fisheries with greater commercial landed weight, value, or greater recreational catches. Fisheries from continental states had higher FMI than those from overseas territories. Invertebrates and diadromous fish species had higher FMI on average compared to those of marine fishes. Extrapolating results for surveyed fisheries to nearly 2000 non‐federally managed US fisheries while stratifying by state and importance designation (based on commercial, recreational, cultural or ecological importance), we estimate a mean overall FMI of 0.48, and estimate that only 19% of fisheries have a reliable estimate of stock status available; both measures are lower than similar estimates for federally managed fisheries. Funding or capacity constraints and information or data limitations were identified as common challenges faced by state agencies in managing fisheries under their jurisdiction.

Optimization of Artemia Feed Regimes for Larval Giant Kōkopu (Galaxias argenteus)

Optimizing the initial live feed is critical to success in fish larviculture in terms of both larval health and productivity. It is also vitally important due to the significant cost of provisioning live feeds. Glaxiids are high-value diadromous fish species found in parts of the Southern Hemisphere, which are wild-harvested and sold for human consumption in their larval form. In the emerging aquaculture of galaxiids, the live feed makes up a great proportion of the production cycle and is therefore a significant factor in achieving the economic viability of their production. In New Zealand, the endemic galaxiid species giant kōkopu (Galaxias argenteus) is considered suitable for aquaculture; however, little is known of their larval-feeding requirements. This study compares the growth performance and survival of giant kōkopu larvae over a four-week period when fed different proportions of first-molt Artemia nauplii (instar-I) and enriched, second-molt-onward Artemia (instar-II+) for different durations. The larvae in the treatment group which received the greatest proportion of Instar-I Artemia for the longest duration had the lowest mean wet weight and survival, leading to the production of the lowest total biomass of fish larvae when compared to the other feed treatments. The feed treatment that received only instar-II+ Artemia achieved an equally best total productivity. While the treatment fed a partial initial duration of mixed instar-I and instar-II+ Artemia achieved the same total productivity, the individual larvae were heavier and their body length was longer. The latter feed treatment appears to offer the best balance between the availability of feed particles in the optimum size range and a higher level of digestibility given that instar-I Artemia had higher levels of highly unsaturated fatty acids and polyunsaturated fatty acids.

First records of four tropical diadromous fish species, including the northernmost record, from Shikoku, Japan

First records of four tropical diadromous fish species, including the northernmost record, from Shikoku, Japan

Catchment-scale stream network spatio-temporal models, applied to the freshwater stages of a diadromous fish species, longfin eel (Anguilla dieffenbachii)

Spatio-temporal modelling frameworks are important tools for evaluating changes in the population structure of freshwater species, to inform population assessments. However, in the stream networks occupied by freshwater species, two data points in space are more related by physical connectivity than by straight-line, Euclidian distance. Therefore, there is a need for spatio-temporal modelling frameworks that represent the relatedness of points based on physical connectivity. We developed such a modelling framework, known as the “VAST stream network modelling framework", using the widely-employed vector autoregressive spatio-temporal modelling platform VAST and the Ornstein-Uhlenbeck process for spatial variance. Here, we demonstrate the VAST stream network spatio-temporal modelling platform with two applications to the freshwater stages of a diadromous fish species, the endemic New Zealand longfin eel (Anguilla dieffenbachii), and a simulation experiment. The first real-world application considers a single category (longfin eel) and models its probability of encounter in the Waitaki catchment, while the second distinguishes between two categories (smaller and larger longfin eels) and models their numerical densities in the greater Waikato region. These two applications demonstrate how stream network spatio-temporal models can usefully inform freshwater resource managers, providing insights into changes in fish encounter probability and density for different fish length classes and estimates of effective river length occupied. The simulation experiment uses the Waikato model as an operating model to evaluate alternative sampling scenarios for accuracy, precision and coverage, to advise on data requirements. A yearly sample size of 30 sites over a 20-year time series had the greatest precision and accuracy in trend estimates among all scenarios investigated. We also found that, for the scenario with declining female spawning biomass, increasing the yearly sample size from 15 sites to 30 sites in a 9-year time series increased the precision and resulted in unbiased estimates. There is a need to optimise sampling schemes for the freshwater stages of diadromous species, including longfin eel, and we, therefore, recommend further simulation experiments to explore scenarios of population trends, habitat features and sampling approaches.

IPODfish – A new method to infer the historical occurrence of diadromous fish species along river networks

Available information on diadromous fish species historical occurrences is generally biased and incomplete across species distribution range and spatial scales. This work aims to establish a new methodological framework (iPODfish – Inferring Past Occurrences of Diadromous Fish) to obtain a more complete representation of the historical occurrences of diadromous fish species over their full distribution range. The iPODfish is based on assumptions, rules and thresholds derived from the interplay between freshwater network features, diadromous fish species ecology and known historical occurrence. These are used to establish historical pseudo-occurrences at the segment scale, i.e., locations where the species was most likely to be present or absent. The methodology is expressed by a tree-like representation of a stepwise, information supported, decision process. It has five steps (separating main river segments from tributary segments; accounting for segments specificities; imposing the relative distance threshold; imposing the Strahler value threshold, and; establishing the sub-basin Strahler threshold), divides into two moments of application (main river followed by the tributaries) and establishes presences, pseudo-presences and pseudo-absences. The iPODfish can deal with multiple information sources, cope with data bias and provide a reliable consistent historical occurrence output at the segment scale for the known historical geographical range of the species. Despite its inference nature, iPODfish is still a conservative procedure leading to ecologically coherent outputs that may be applied to any diadromous fish species (with a relevant amount of historical data available) in any river network throughout the globe because the concepts and definitions used are general ecological features of diadromous and freshwater networks. The method outputs are applicable in biogeographical and/or macroecological studies using historical data and may prove useful to the management and conservation of diadromous fish species.

Toward a roadmap for diadromous fish conservation: the Big Five considerations

Increasing habitat fragmentation is a major contributing factor to dramatic reductions in populations of migratory species worldwide. Diadromous fish species in particular are affected by this anthropogenic disturbance, resulting in historically low population abundances. Despite a plethora of management measures and considerable investment, desired results are often lacking. Here, we highlight five important considerations – the “Big Five” – for diadromous species management: removal of barriers to migration, installation of fish passages, habitat restoration, restocking, and fisheries management. We review current management measures and their effectiveness, and propose a way forward. Current management of diadromous fish populations largely focuses on mitigation of migration barriers, but management will likely fail if other fundamental aspects of diadromous species’ life cycles are overlooked or disregarded. We therefore propose an integrated management strategy that takes into account the five major factors influencing diadromous fish species, with the ultimate goal of restoring their populations.

Recovery of Diadromous Fishes: A Kennebec River Case Study

AbstractThe lack of safe, timely, and effective fish passage at dams remains a major impediment to the restoration of diadromous fish species to their historic range and abundance. Because fish passage facilities are often ineffective, dam removal has increasingly been used to restore diadromous species. However, few quantitative studies have assessed the response of fishes to dam removal. This paper documents the long‐term response of multiple fish species in the Kennebec River, Maine, to the removal of two hydropower dams and the installation of upstream fish passage facilities that restored access to historic habitat. Edwards Dam was removed in 1999, and Fort Halifax Dam was removed in 2008. Counts of river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis), American Shad A. sapidissima, and Striped Bass Morone saxatilis at upstream dams confirmed that these species quickly recolonized the 27‐km, free‐flowing segment of the Kennebec River that became accessible after Edwards Dam was removed. Average counts of river herring increased by 228% after the removal of Edwards Dam and by 1,425% after the removal of Fort Halifax Dam. However, access to a substantial amount of habitat in the Kennebec River is blocked by ineffective passage at the lowermost dam.

An investigation of genetic connectivity shines a light on the relative roles of isolation by distance and oceanic currents in three diadromous fish species

Understanding connectivity is crucial for the effective conservation and management of biota. However, measuring connectivity directly is challenging and it is often inferred based on assumptions surrounding dispersal potential, such as environmental history and species life history traits. Genetic tools are often underutilised, yet can infer connectivity reliably. Here, we characterise and compare the genetic connectivity and genetic diversity of three diadromous Australian fish species: common galaxias (Galaxias maculatus), tupong (Pseudaphritis urvillii) and Australian grayling (Prototroctes maraena). For each species, we investigate the extent of genetic connectivity across a study region in south-eastern Australia (~700 km). We further determine the potential roles of contemporary ocean currents in shaping the patterns of genetic connectivity observed. Individuals across multiple rivers were sampled and >3000 single nucleotide polymorphisms were genotyped for each species. We found differences in genetic connectivity for the three species: common galaxias were highly connected, and Australian grayling and tupong exhibited patterns of isolation by distance. The degree of genetic connectivity for tupong and Australian grayling appeared unrelated to oceanic currents. This study indicates that the degree of connectivity for different diadromous species can vary greatly despite broadly similar life history strategies, highlighting the potential value of genetic tools for informing species-specific management plans.

Glass eel (Anguilla anguilla L.) behaviour after artificial intake by adjusted tidal barrage management

Tidal barrages on water ways constitute a major threat for diadromous fish species such as the critically endangered European eel (Anguilla anguilla L.). An unobstructed migration route between the spawning area in the Sargasso Sea and the freshwater growth habitats in Europe is crucial for the European eels’ long-term survival. Every spring however, millions of glass eels arrive at the European coast to find their inland migration route blocked. Adjusted tidal barrage management (ATBM), i.e. setting the tidal sluice doors ajar during tidal rise, is one of the mitigation measures to enhance glass eel colonisation. Although this management substantially improves the number of incoming glass eels, the fate of these migrants, confronted with abruptly shifting conditions upon sluice passage, remains un-investigated. Glass eel upstream dispersion after sluice passage by means of ATBM was investigated in a drainage canal connecting a small estuary with an adjacent polder area in Belgium. Large numbers of glass eel caught with eel ladders installed at a pumping station about 800 m upstream the tidal barrage indicate that glass eels were well able to switch to an active counter current swimming behaviour to continue upstream dispersion. On the other hand, some glass eels did not initiate active migration but settled in artificial substrates placed in the canal instead. These residents however appeared very successful in using the canal as feeding ground and in time substantially increased their overall fitness. The appearance of both migration strategies (switch to active migration or successful settlement) in this canal shows the potential of ATBM as a valuable tool for the management and restoration of the European eel population and calls for a wide application of this cost-efficient mitigation measure.

Diadromous fish modified timing of upstream migration over the last 30 years in France

Abstract Numerous studies have documented a change in the phenology of migration of diadromous fish in response to climate change. Only few studies have, however, been conducted simultaneously for multiple species and at a large spatial scale. We investigated the change in the timing of upstream migration of diadromous fish species in France. We used an original dataset collected from 40 fish‐counting devices in 28 French rivers over 10–30 years for five diadromous taxa: Alosa spp., Anguilla anguilla (with a distinction between glass eel and yellow eel), Petromyzon marinus, Salmo salar, and Salmo trutta. Except for glass eel, we found that taxa shifted their migration for earlier arrival dates. This result is consistent with numerous studies reporting advancement of the phenology of species life‐events. On average, we highlighted a phenological change of −2.3 days per decade (min = −0.2, max = −3.7). Moreover, the North Atlantic Oscillation Index, sea surface temperature, air temperature, and river discharge were found to explain the timing of upstream migration of diadromous fish taxa, highlighting the importance of factors acting at different spatial scales. Given the important phenological changes observed in our study and more widely in the scientific literature, we recommend that managers incorporate these changes into the management rules; in particular, in the case of dams whose migratory transparency (i.e. the possibility for the fishes to cross the dam) is ensured by adaptive water management and gate operations. This study benefited from large‐scale monitoring of migratory phenology of multiple species and environmental variables. These monitoring data are valuable and could allow better predictive modelling of the response of species to climate change.

Damn those damn dams: Fluvial longitudinal connectivity impairment for European diadromous fish throughout the 20th century

River longitudinal connectivity is crucial for diadromous fish species to reproduce and grow, its fragmentation by large dams may prevent these species to complete their life cycle. This work aims to evaluate the impact of large dams on the structural longitudinal connectivity at the European scale, from a Diadromous fish species perspective, since the beginning of the 20th century until the early 21st century. Based on large dam locations and completion year, a multitude of river impairment metrics were calculated at three spatial scales for six European oceanic regions and 12 time periods. The number of basins affected by large dams is overall low (0.4%), but for large river basins, that cover 78% of Europe's area, 69.5% of all basins, 55.4% of the sub-basins and 68.4% of river length are impaired. River network connectivity impairment became increasingly significant during the second half of the 20th century and is nowadays spatially widespread across Europe. Except for the North Atlantic, all oceanic regions have over 50% of impacted river length. Considering large river basins, the Mediterranean (95.2%) and West Atlantic (84.6%) regions are the most affected, while the Black (92.1%) and Caspian (96.0%) regions stand out as those with most compromised river length. In 60 years, Europe has gone from reduced impairment to over two-thirds of its large rivers with structural connectivity problems due to large dams. The number of such barriers increased significantly in the second half of the 20th century, especially main stem dams with decreasing distance to the river mouth. Currently, the structural longitudinal connectivity of European river networks is severely impacted. This concerns all regions considered, and those in southern Europe will face even higher challenges, given that this will be a future hot spot for hydropower development and predictably more affected by climate change.

Current status of economically important diadromous fish species of Turkey; European eel, Black Sea trout and sturgeon species

Turkey has a rich variety of fish species in the rivers with a total length of 177,714 km in Turkey. Freshwater fish live in rivers, streams, creeks, dam lakes, natural lakes, wetland areas, etc. The life of migratory fish is threatened by the anthropogenic impact on aquatic habitats. Human activities that disrupt river integrity can be listed as; dam and hydro power plant constructions, high levees, sluices, weirs and bridges, sand-gravel quarries, recreational works, wetland depletion, water pollutions, overfishing, habitat losses, climate changes, water pumping from a river to other river basins, drinking water, dried river beds etc. The most important diadromous fish species in Turkey are sturgeon species (Acipenseridae), European eel (Anguilla anguilla) and Black Sea trout (Salmo trutta labrax). In this study, the past and present status of these species are reviewed.

Ecological state of aquatic biocenoses in the streams of the Kola basin, Barents Sea

The ecological state of freshwater ecosystems is essential because they are actively used in human economic activities. As the habitats of valuable commercial fish species deteriorate, their population decreases rapidly. Therefore, environmental monitoring of water bodies, markedly affected by human activities, contributes to efficient natural resources management. Thus, analysis of recent data on the state of river ecosystems in the Kola Bay basin is of great interest. It shows the current state of biocenoses in some of the streams flowing into Kola Bay of the Barents Sea, an environmentally unsafe area on the Kola Peninsula. Studies have shown that in spite of ongoing human activities in the Kola Bay watershed, the state of the ecosystems in local streams generally remains satisfactory. The distribution density of Atlantic salmon juveniles in the tributaries of the Nizhnetulomsky Reservoir varies from 20 to 70 juv./100 m2. The distribution indices of trout in the River Bolshaya Lavna vary from 5 to 65 fish/100 m2 and those in streams from 10 fish/100 m2 (Goryachev Brook) to 18 fish/100 m2 (Tretiy Brook). The main factor which negatively affects the reproduction of diadromous fish species is hydrolic construction which results in the decrease of the Atlantic salmon, sea trout and whitefish stock. To efficiently maintain the ecosystems of the streams, the construction of fish-screening structures, the river channels should be recultivated and the artificial reproduction of valuable fish species should be launched.