Fish Populations In Rivers Research Articles

Habitat use of barbel (Barbus barbus) in a restored urban Danube tributary

Tributaries play a vital role in fish spawning and recruitment, significantly influencing mainstem river fish populations. However, in the Anthropocene era, tributaries within river networks suffered ecological degradation due to fragmentation and channelization. This has led to reduced distribution ranges and declining populations of various riverine species, underscoring the urgency of conservation and rehabilitation efforts. Our study explores the potential for reintroducing fish from the mainstem Danube River into the Wien River, an urban tributary that has undergone partial rehabilitation. We assessed habitat use and movement patterns of 20 adult barbel (Barbus barbus), a species classified as ‘near threatened’ in Austria, collected from the Danube River during the spawning season. These barbel were tagged with radio telemetry tags and relocated into the upper reaches of the Wien River, surmounting several artificial barriers in the lower sections. Although spawning activity was not observed among the barbel, possibly due to prevailing water temperatures, our data suggest that the Wien River could function as a viable temporary habitat. Barbel were notably inclined to inhabit deeper pool and run habitats. Their daily movements and home ranges were relatively limited, ranging from 0.0 to 1.1 km and 100 m to 2.9 km, respectively. One contributing factor to restricted movement was the presence of beaver and knotweed dams, which created temporary migration obstacles. On average, the barbel remained within the system for more than a month. Most of these fish migrated downstream at the onset of a significant high-flow event. Our assessment suggests that while the Wien River may not serve as a permanent habitat, it could function as a temporary habitat for migratory fish. However, to ensure accurate assessments of the restored Wien River as a spawning habitat, it is imperative to reevaluate the findings under stable spawning conditions and gather comprehensive data on relevant abiotic factors. This study advocates for the restoration of longitudinal connectivity between tributaries and mainstem rivers as a means to counteract biodiversity loss in Anthropocene river ecosystems.

Effects of Rapid Thermal Cycling (Cold Shock) on Fish Health: Evidence from Controlled Laboratory Experiments, Behavior, and Telemetry

Powerplants frequently use river water for cooling, subsequently discharging warm effluent. Some of these plants can cycle on and off rapidly based on electricity demand, resulting in dramatic temperature fluctuations in the receiving waters. To understand the impacts on resident fish populations in the Upper Mississippi River, we (i) assessed the effects of rapid water cooling on three native fish species; (ii) investigated whether smallmouth bass (Micropterus dolomieu) behavior favored movement into thermal plumes when given a choice of cooler or ambient water; and (iii) tracked native M. dolomieu with acoustic tags and recorded core body temperature during the thermal cycling process of a steam electric powerplant. In cold shock experiments, mortality was associated with rapid temperature declines and dependent on the final (cold) holding temperature. The species or developmental stage of the tested organism did not affect survival. When given a choice between warm and ambient waters, M. dolomieu exhibited little inclination to acclimate to the warmer water and instead “self-regulated” by moving in and out of the warm water plume. This finding was supported by telemetry data on M. dolomieu. The core temperature of the fish never increased more than 2 °C above the ambient (upstream) Mississippi River temperature, even during warm effluent discharge.

Optimizing data quantity and quality for side-looking echosounder surveys in large rivers

The increased use of side-looking echosounder surveys in large rivers necessitates the creation and evaluation of standardized sampling protocols to effectively sample these habitats. Using data from five Ohio River pools, we evaluated the effects of habitat and transect direction on the quality and quantity of mobile, side-looking, split-beam echosounder data to determine how these factors may affect survey design in large rivers. Split beam echosounder data were collected using two multiplexing 200 kHz transducers offset in angle to maximize water column coverage. Using mixed-effects models, we evaluated the effects of habitat (main channel vs. tributary) and transect direction (upstream vs. downstream movement of the vessel) on fish density and the number of targets per fish track (series of acoustic targets from an individual fish). We also used a skewness test in conjunction with a Kolmogorov-Smirnov test to determine the distribution of fish orientations relative to the transducer and examine differences in the distribution of fish orientations among habitats, transect directions, and years. Mean fish densities were greater in tributary habitat relative to main channel habitat, whereas main channel habitat had a higher mean number of targets per fish track when compared to tributaries. Upstream-facing transects had greater mean fish density estimates and mean number of targets per fish track than downstream-facing transects. Although most fish were oriented perpendicular to the transducer, we identified habitat, transect direction, and annual differences in the distribution of fish orientations. These results suggest that researchers and managers that plan to use side-looking echosounders to assess fish populations in large rivers should ensure that standardized protocols include main channel and tributaries, and are expanded to encompass other relevant habitats (e.g., backwaters and side channels). Further, managers should use fish orientation data to select or develop TS-L equations that best matches the fish orientation distribution of each survey to ensure accurate density and size estimates.

Diverse portfolios: Investing in tributaries for restoration of large river fishes in the Anthropocene

Rehabilitation of large Anthropocene rivers requires engagement of diverse stakeholders across a broad range of sociopolitical boundaries. Competing objectives often constrain options for ecological restoration of large rivers whereas fewer competing objectives may exist in a subset of tributaries. Further, tributaries contribute toward building a “portfolio” of river ecosystem assets through physical and biological processes that may present opportunities to enhance the resilience of large river fishes. Our goal is to review roles of tributaries in enhancing mainstem large river fish populations. We present case histories from two greatly altered and distinct large-river tributary systems that highlight how tributaries contribute four portfolio assets to support large-river fish populations: 1) habitat diversity, 2) connectivity, 3) ecological asynchrony, and 4) density-dependent processes. Finally, we identify future research directions to advance our understanding of tributary roles and inform conservation actions. In the Missouri River United States, we focus on conservation efforts for the state endangered lake sturgeon, which inhabits large rivers and tributaries in the Midwest and Eastern United States. In the Colorado River, Grand Canyon United States, we focus on conservation efforts for recovery of the federally threatened humpback chub. In the Missouri River, habitat diversity focused on physical habitats such as substrate for reproduction, and deep-water habitats for refuge, whereas augmenting habitat diversity for Colorado River fishes focused on managing populations in tributaries with minimally impaired thermal and flow regimes. Connectivity enhancements in the Missouri River focused on increasing habitat accessibility that may require removal of physical structures like low-head dams; whereas in the Colorado River, the lack of connectivity may benefit native fishes as the disconnection provides refuge from non-native fish predation. Hydrologic variability among tributaries was present in both systems, likely underscoring ecological asynchrony. These case studies also described density dependent processes that could influence success of restoration actions. Although actions to restore populations varied by river system, these examples show that these four portfolio assets can help guide restoration activities across a diverse range of mainstem rivers and their tributaries. Using these assets as a guide, we suggest these can be transferable to other large river-tributary systems.

Land-use and land-cover affect inland fish catch in two rivers of Central Africa

Land-cover change can affect inland fisheries, which underpin food security of millions of people worldwide. Removal of forests from very large floodplains has been found to decrease fish catch via loss of feeding and nursery habitat for fish. However, it is unknown if similar effects occur in smaller rivers with limited floodplain areas. Little is also known about the mechanisms by which land-cover changes affect inland fish catch. Here, we assessed land-use and land-cover (LULC) effects on fish catch, diet, and condition at sites in two medium-sized rivers of Cameroon, in Central Africa. We found that LULC explained 30% of the variation in fish catch, with the catch of five species being positively, and of two species being negatively, related to floodplain forests. The niche breadth of fish diets was higher in the river surrounded by forests than in the river surrounded by agricultural land. However, contrary to expectations, condition of the fish, as indicated by occurrence of diseases or deformities, eroded fins, lesions or tumors, was not related to LULC. Our results support the notions that floodplain forests support fish populations in rivers with limited floodplain areas in ways similar to that of rivers with large floodplains, and that LULC affects fish populations via changes in fish diets and instream habitat features (i.e., riparian canopy closure, water clarity, substrate heterogeneity, and habitat volume). These effects imply that prevailing changes in LULC threaten the food and livelihood security services provided by inland fisheries, highlighting the importance of policies that maintain native vegetation along riverbanks and in floodplain areas.

Dysfunctional information feedbacks cause the emergence of management panaceas in social-ecological systems: The case of fish stocking in inland recreational fisheries

Social-ecological systems are characterized by interconnections between social (e.g., angler communities) and ecological systems (e.g., fish populations in lakes and rivers). One means by which human actions feedback on ecosystems is through management actions, some of which are controversial due to the possible downsides for biodiversity and ecosystem functioning. In complex systems, sub-optimal management strategies may become entrenched. In such cases, leverage points must be identified to escape undesirable stable states. Based on a review of published and grey literature about the management practice of fish stocking in German inland recreational fisheries, we describe key pathways characterizing social-ecological interactions and resulting outcomes. The pathways we review suggest that missing or dysfunctional information feedbacks predispose privately governed fisheries-management systems typical of Germany to develop stocking as a panacea in operational management. Similar outcomes are likely in open access recreational fisheries. Three key feedback cycles reinforce each other to maintain stocking in the manager's toolbox. The first is that the lack of dedicated monitoring in many fisheries and ignorance of research results breaks a feedback signal from the management measure of stocking to the evaluation of outcomes. The lack of ability of those involved in stocking to conclusively learn when stocking works and when it fails to deliver additive effects reinforces personal norms by managers and anglers that stocking may be necessary to sustain fisheries. A related second feedback is that stocking may increase catch rates in the short-term, which increases angler expectations for catch and stocking as a safeguard of the catch, in turn fostering linear cause-and-effect mental models and the emergence of a pro-stocking social norm among anglers. A third key feedback is among hatchery operators and fisheries managers in fishing clubs, where hatchery operators are often key informants about stocking practices while concurrently having commercial interests to sell fish for stocking. This creates economic incentives that perpetuate stocking. The amount of resource investments by angler communities through stocking is additionally fostered and maintained by monetary resource availability, size and type of ecosystem that is managed and governance processes as well as political inertia. Thus, the maintenance of stocking as a panacea is intimately linked to a range of psychological, social, economic and governance drivers. We use our case study to illustrate how information-related feedback loops can trap natural resource management strategies into a suboptimal basin of attraction, and provide recommendations on leverage points to possibly break these loops. Collaborative active adaptive management of natural resources and reducing the temptation to rely on economic incentives by hatcheries may be needed to introduce possibilities for learning and thereby avoid the entrenchment of stocking and related activities as a panacea. The lessons learned around stocking are applicable to a range of social-ecological issues in recreation and planning whenever feedback flows of information are critical to direct management and when these flows are either distorted by disinformation, wrong incentives or not present at all. The study has several implications for fisheries and natural resource management:-Establishment of regular monitoring systems that are trusted by stakeholder can be recommended and is key to break dysfunctional information feedbacks and move social-ecological systems, such as recreational fisheries, on more sustainable trajectories.-Changing fish stocking under private fishing right systems can happen either through bottom-up approaches based on co-production of knowledge and using principles of adaptive management or from the top-down by implementing hard constraints on the possibility for self-organized stocking policies.-The former strategy will be more time-consuming and may fail in some situations, but is likely to create less conflicts and more durable outcomes from a social perspective.-Alternative to fish stocking, such as improvement of habitats or harvest constraints, should be considered whenever feasible. Establishment of regular monitoring systems that are trusted by stakeholder can be recommended and is key to break dysfunctional information feedbacks and move social-ecological systems, such as recreational fisheries, on more sustainable trajectories. Changing fish stocking under private fishing right systems can happen either through bottom-up approaches based on co-production of knowledge and using principles of adaptive management or from the top-down by implementing hard constraints on the possibility for self-organized stocking policies. The former strategy will be more time-consuming and may fail in some situations, but is likely to create less conflicts and more durable outcomes from a social perspective. Alternative to fish stocking, such as improvement of habitats or harvest constraints, should be considered whenever feasible.

Length Weight Relationships and Condition Factor of Sicydium sp. (Gobiidae) from the Yallahs River and Swift River, Jamaica

Sicydium sp., commonly known as gobies, are migratory freshwater fish that spend most of their life cycle in rivers, but when the larvae emerge they drift downstream to the sea where further development of juveniles occurs. Although Sicydium sp. are abundant in Jamaican rivers, little is known about the ecology of these species on the island and throughout the Caribbean. This study examines aspects of the ecology and biology of Sicydium populations in Jamaica. Fish sampling was carried out using dip nets and bottom kick nets at sites along the south coast in the Yallahs River, and along the north coast in the Swift River. A total of 850 gobies were captured, measured, and weighed. The values of the allometry coefficient or growth pattern (b) in the length weight relationships (LWR) were significantly different among males, females, and juveniles (p < 0.05). The growth pattern derived from LWR's was positive for females, males, and juveniles in the Yallahs River, and positive for females and juveniles but negative for males in the Swift River. The mean Fulton's condition factor (K) indicates that fish populations in both rivers are healthy and in good condition. These results augment the body of knowledge on Sicydium gobies in Jamaica.

Barrier removal and dynamics of intermittent stream habitat regulate persistence and structure of fish community

Barrier effects observed in the presence of weirs are exacerbated by low water levels. We conducted a 10-year study to assess the ecological effects of stream restoration while analysing the possibility of a seasonal lack of hydrological continuity, with multiple measurements before and after restoring stream structural continuity. The research hypothesis assumes that in intermittent streams, there would be little or no change in the fish community downstream the barrier before vs. after barrier removal, and a significant change upstream the barrier before vs. after. Our results indicate, that by removing small barriers, their detrimental effects on the longitudinal passage of riverine fishes and fish assemblages can be rehabilitated. In the wet season, fish migrants from the mainstem river appeared in the downstream section of the stream. Stream intermittency, however, placed a habitat filter over the assemblage. Thus, after barrier removal, only two small-bodied fish species that tolerate periodic oxygen deficiencies and rising water temperatures gradually shifted upstream and formed stable populations. We emphasize, that we should not refrain from restoring the longitudinal continuity of intermittent streams, because they periodically provide fish valuable refugia and can also be a source of new generations and strengthen fish populations in mainstem river.

Differential impacts of a wildfire and post-fire sedimentation event on platypus and fish populations in a Victorian upland river

Context Wildfire can affect freshwater ecosystems in many ways, notably when post-fire rainfall washes ash and sediment into waterways. Aims We investigated species-specific effects of bushfire and subsequent channel sedimentation on the abundance of platypus and fish populations in the upper Buffalo River, Australia. Methods Pre- and post-fire population surveys were conducted using fyke nets. Key results There was no evidence that fish numbers declined because of direct fire effects. However, native two-spined blackfish and Macquarie perch numbers dropped dramatically following post-fire sedimentation, whereas non-native redfin perch increased, most likely as a result of migration from a nearby lake. Platypus captures were consistently recorded at all survey sites both before and after the fire and sediment inflows occurred, with many juveniles being recorded in the first post-fire breeding season. Conclusions The platypus’s greater resilience to post-fire sediment inflows than that of native fish presumably reflects its reliance on lungs rather than gills and its ability to take refuge in burrows. It also has a broad diet, flexible foraging behaviour, is highly vagile and typically stores enough fat to support fasting for up to 2–3 weeks. Implications Management of fire-affected aquatic ecosystems must consider species-specific responses of freshwater vertebrates to fire.

Environmental requirements and heterogeneity of rheophilic fish nursery habitats in European lowland rivers: Current insights and future challenges

AbstractThe large‐scale degradation of riparian ecotones and of the connectivity between rivers and their floodplains has resulted in a drastic decline of rheophilic fish populations in European temperate lowland rivers. Recent river restoration projects have had variable success in effectively restoring these fish populations. Knowledge on nursery habitat requirements is considered essential for effective population restoration. However, a detailed understanding of the role of habitat heterogeneity in young‐of‐the‐year (YOY) fish population development is limited. Therefore, we carried out a synthesis of the available knowledge on nursery habitat requirements of rheophilic fish species found in European temperate lowland rivers (&lt;200 m elevation). From a total of 603 papers, 77 studies with primary information were selected, containing 390 associations between habitat features and YOY fish. As expected, most studies focused on static components of physical riparian habitat. Generally, YOY fish require habitats of shallow depth (&lt;0.5 m), with slow‐flowing water (&lt;0.2 m/s), gentle bank slope (&lt;20°), variety in substratum types (fine sand to gravel), relatively warm water and high food availability. Surprisingly, no clear ontogenetic habitat shifts between larvae and juveniles were found, which may be explained by the limited spatial–temporal resolution of most studies. Since 2011, studies on habitat heterogeneity have increased, but few have explicitly assessed its role in relation to movement patterns of YOY fish for nursery success. Therefore, we recommend that future research focuses on fish movement patterns between habitat patches in heterogeneous (river‐floodplain) environments, to increase the knowledge base for effective recovery of rheophilic fish populations.

Improving hydroacoustic sampling in large rivers: Evaluating factors influencing target detectability

AbstractMobile hydroacoustic sampling is increasingly being used to monitor fish populations in large rivers; however, several factors may influence the ability to sample fishes with this gear in these environments. This study sought to address the effects of vessel speed, wind speed, the coefficient of variation (CV) of transducer pitch angle, and beam compensation (BC) on hydroacoustic detectability to advance and inform mobile, horizontally oriented hydroacoustic sampling in large rivers. A series of four replicate surveys was conducted past 23 artificial targets at three vessel speeds in a large river. Wind speed data during surveys were obtained, and post‐processing of hydroacoustic data was conducted separately under maximum BC values of 6 and 12 dB. Results revealed significant negative effects of wind speed and transducer pitch CV on buoy detectability, as well as negative interactions between vessel speed and wind speed, with detectability decreasing as wind speed increased, particularly at slower vessel speeds. We suggest this may be due to increased vessel and transducer motion during periods of increased wind speed. Detectability also significantly increased under an expanded BC due to a greater proportion of the water volume being analyzed; however, further work is necessary before implementing greater BC settings in large rivers. These results ultimately display the interactive and negative effects of wind speed and vessel speed on horizontal hydroacoustic detectability in large rivers, revealing important considerations for hydroacoustic monitoring and sampling efforts in these systems.

Lateral and longitudinal fish environmental DNA distribution in dynamic riverine habitats

AbstractAssessing the status and distribution of fish populations in rivers is essential for management and conservation efforts in these dynamic habitats. Currently, methods detecting environmental DNA (eDNA) are being established as an alternative and/or complementary approach to the traditional monitoring of fish species. In lotic systems, a sound understanding of hydrological conditions and their influence on the local target detection probability and DNA quantity is key for the interpretation of eDNA‐based results. However, the effect of seasonal and diurnal changes in discharge and the comparability of semi‐quantitative results between species remain hardly addressed. We conducted a cage experiment with four fish species (three salmonid and one cyprinid species) in a glacier‐fed, fish‐free river in Tyrol (Austria) during summer, fall, and winter discharge situations (i.e., 25‐fold increase from winter to summer). Each season, water samples were obtained on three consecutive days at 13 locations downstream of the cages including lateral sampling every 1–2 m across the wetted width. Fish eDNA was quantified by species‐specific endpoint PCR followed by capillary electrophoresis. Close to the cages, lateral eDNA distribution was heterogenous and mirrored cage placement within the stream. In addition to the diluting effect of increased discharge, longitudinal signal changes within the first 20 m were weakest at high discharge. For downstream locations with laterally homogenous eDNA distribution, the signals decreased significantly with increasing distance and discharge. Generally, the eDNA of the larger‐bodied salmonid species was less frequently detected, and signal strengths were lower compared to the cyprinid species. This study exemplifies the importance of hydrological conditions for the interpretation of eDNA‐based data across seasons. To control for heterogenous eDNA distribution and enable comparisons over time, sampling schemes in lotic habitats need to incorporate hydrological conditions and species traits.

Rapid change in Yangtze fisheries and its implications for global freshwater ecosystem management

AbstractFreshwater capture fisheries are globally essential for food security and aquatic biodiversity conservation. The Yangtze River Basin is the third longest and one of the most human‐influenced drainage basins worldwide. Since the founding of P. R. China in 1949, this large river system has suffered increasing human perturbation and its sustainable development is now severely challenged. Meta‐analysis showed that Yangtze River fisheries have experienced an extraordinary process of utilization–over‐exploitation–protection during the past 70 years, to an extent that other globally important rivers may never have encountered. Its fisheries appear to have collapsed over the past four decades, with yield decreasing to only 25% of an historical peak of 400,000 metric tonnes in the late 1950s. Endemic, migratory and rare fishes have been highly threatened with obvious changes in fish community structure and aquatic biodiversity. Anthropogenic activities, including impoundment of water in dams, discharge of pollutants and riverine modification for vessel navigation, have caused large decreases in fisheries yields. Projections from surplus production modelling showed potential for improvement under fishing ban scenarios, but without any prospect for full recovery to historical stock status. This study revealed that the change in fisheries resources was dominated by the social–ecological watershed system, and an integrated approach to river basin management is warranted. Better management of freshwater ecosystems to integrate food security with biodiversity conservation is urgently needed throughout the world, and the changes evident in the Yangtze River fish populations can serve as an informative global reference.

Microbiota associated with the skin, gills, and gut of the fish Parachondrostoma toxostoma from the Rhône basin

Abstract The close relationships between hosts and their microbiota underlie the current concept of holobionts. This biological entity enlarges our perception of the genomic diversity supported by individuals/species and the potential abilities of hosts to respond to the environment. We investigated a total of 54 specimens of the sofie fish Parachrondrostoma toxostoma (Pt) for the taxonomic and functional composition of microbiota associated with the skin, gills, and gut tissues. Five wild populations from the Ardèche and Durance river basins in the Mediterranean part of the large catchment of the Rhône (southern France) were compared. We found that the skin microbiota was more diverse and variable in bacterial community composition than the gut microbiota. These differences suggest that different deterministic factors underlie the composition of these bacterial communities, resulting in tissue‐specific variation of the microbiota composition between wild fish populations inhabiting two rivers. Microbiota diversity and composition differed between wild Pt populations at both regional and local spatial scales. Using the Picrust tool, the taxonomic variation of the microbiota composition in the river fish populations could be associated with the enrichment of predicted metabolic pathways. In particular, carbohydrate metabolism was more represented and xenobiotic biodegradation pathways less represented in the gut microbiota of Pt populations from the Ardèche than of those from the Durance. This result suggests variability in the ability to acclimate to environmental features through the assimilation of food resources from plants and the detoxification of xenobiotic components. This study opens perspectives in the detection of subtle shifts in environmental features through the description of the microbiota composition, and in the potential prediction of the functional capacities of species to acclimate.

Upper Caraş River (Danube watershed) fish populations fragmentation – technical rehabilitation proposal

Abstract We propose a technical solution for fish movement based on the flow of water over a spill threshold. Such barriers are common in the Danube system. The proposed system has a range of operating components which are easily detachable from the spill threshold, are resistant to corrosion and will not harm the fish. In fact, if designed to complement swimming abilities of target fish, it should provide adequate passage for both adults and juveniles. If implemented correctly, the design may offer a solution to help displaced fish recolonize upstream habitats.

Impact of acid precipitation on historical monuments and statues

Abstract A host of deleterious factors can impact the aging and integrity of historical monuments and statues. These may include natural causes such as water, wind, and temperature variation as well as the even more detrimental human causes of industrial pollution, urban warming, and fossil fuel emissions from vehicles all of which contribute to the development of acid precipitation. In addition, where the use of fossil fuels is wide-spread the occurrence of acid precipitation tends to be more prevalent and as a result serious damage can occur to the natural environment. Acid precipitation causes irreparable damage to vegetation, wildlife, and fish populations in lakes, streams, and rivers. Also, damage caused by acid precipitation can be quite recognizable on historical monuments and statues constructed from carbonate-based stone. The stone derived from carbonate sources such as limestone, dolomite, and marble have been widely used for thousands of years in the construction of monuments and statues. Carbonate-based stone was often chosen because of its abundance, suitability for shaping, and robust quality. Many historic works of art which not only characterize a period of art but also create powerful images of the artist and artwork have survived for thousands of years. The emergence of acid precipitation though has caused irreparable damage and destruction to many of these irreplaceable works of art, monuments, and statues. In this study, the research focuses on better understanding of acid precipitation and its impact on items of cultural heritage such as historical monuments and statues. Sample cases were chosen to emphasize and evaluate deleterious impact which may have occurred to these items of cultural heritage. According to research evaluation results from this study the researcher has provided recommendations for resolving the impacts of acid precipitation on these historical monuments and statues. Keywords: fossil fuels, acid precipitation, historical artefacts, marble statues.&#x0D; Keywords: fossil fuels, acid precipitation, historical artefacts, marble statues.

River fragmentation and fish population structure: a comparison of three Swiss midland rivers

AbstractAnthropogenic river fragmentation has the potential to alter fish population structure and diversity, but it can be difficult to infer whether observed effects reflect the obstruction of fish movement or population responses to altered flow regimes or habitat structure concomitant with fragmentation. We addressed the influence of habitat fragmentation on the European Chub (Squalius cephalus), a large-bodied fish with strong swimming ability that is a ubiquitous habitat generalist that occurs at high densities in lentic and lotic habitats. European Chub populations have never been stocked and are little affected by habitat alterations. Thus, they are good sentinels for the effects of fragmentation per se. We used microsatellite genotyping of 1726 fish from 38 sites to compare the genetic structure and diversity of European Chub populations from 3 Swiss midland rivers that are unequally affected by man-made fragmentation. The Thur is unfragmented, the adjacent Glatt is strongly fragmented by tall ba...

Ichthyofauna of the Aksu River of Balkhash Basin

The Aksu River is one of the main rivers of Zhetysu (Seven Rivers) and flows into Lake Balkhash. The current ichthyofauna of the Aksu River is represented by seven indigenous and eleven alien species. The largest number of alien fish species are noted on a large part of the piedmont and estuary river sections. The structure and species composition of river fish populations have changed over the last 20 years. The Chinese false gudgeon Abbottina rivularis and the Siberian dace Leuciscus baicalensis have appeared in it, and the former has reached a substantial abundance. The species structure of fish populations in the piedmont part is extremely unstable and depends on its hydrological regime.

Does the non‐native European catfish Silurus glanis threaten French river fish populations?

Summary The European catfish, Silurus glanis, was widely introduced in western Europe, and it has now established self‐sustaining populations in numerous large rivers of western France. Using data collected from surveys conducted by the French National Agency for Water and Aquatic Environment (Onema) from 1989 to 2010 in more than 500 sites throughout the country (10636 electrofishing surveys), we investigated the potential impact of the European catfish on fish communities in French rivers. In the first part of the analysis, we compared trends observed before and after the European catfish was established at given sites (before–after analysis). Species richness, evenness and diversity decreased significantly after the European catfish was established at 1.4%, 1.4% and 5.8% of the sites, respectively. Total fish biomass and density decreased significantly at 6.6% and 2.9% of the sites, respectively. In the second part of the analysis, we compared sites with European catfish against sites lacking European catfish during the same period (with–without analysis). Fish species richness was significantly higher in sites with European catfish. No significant differences in fish diversity, evenness, total fish biomass or density were found between sites with or without European catfish. While our results indicate that the European catfish may in a few cases impact fish communities or populations, it does not appear to be responsible for a countrywide collapse in fish assemblages.

Eff icacy of angler catch data as a population and conservation monitoring tool for the f lagship Mahseer f ishes (Tor spp.) of Southern India

Abstract Mahseer (Tor spp.) are flagship fishes in South Asian rivers. Their populations are threatened through poaching and habitat disturbance, yet they are highly prized game fishes due to their large size, appearance and sporting qualities. The international recreational angling community has frequently been cited as playing a vital role in conserving these fishes while also providing economic benefit to poor rural communities. Owing to a lack of scientific data and the considerable challenges associated with monitoring fish populations in large monsoonal rivers, efforts to determine the long‐term trends in their populations has focused on sport‐fishing catch records. Here, catch data collected between 1998 and 2012 from Galibore, a former fishing camp on the River Cauvery, Karnataka, India, were analysed to determine the catch per unit effort (CPUE – by number and weight) as an indicator of relative fish abundance, along with the size structure of catches. This fishery operated a mandatory catch‐and‐release (C&amp;R) policy, and provided the fish community with protection from illegal fishing. Between 1998 and 2012, 23 620 hours fishing effort were applied to catch and release 6161 mahseer, ranging in size from 1 to 104 lbs (0.45–46.8 kg) in weight. Across the period, CPUE in number increased significantly over time with a concomitant decrease in CPUE by weight, revealing strong recruitment in the population and a shift in population size structure. This suggests a strong response to the C&amp;R policy and the reduction in illegal fishing, indicating that conservation strategies focusing on the beneficial and negative aspects of exploitation can be successful in achieving positive outcomes. These outputs from angler catch data provide insights into the mahseer population that were impossible to collect by any alternative method. They provide the most comprehensive analysis of a long‐term dataset specific to any of the mahseer species across their entire geographical range and demonstrate the value of organised angling as a conservation monitoring tool to enhance biological data, and inform conservation and fishery management actions. Copyright © 2014 John Wiley &amp; Sons, Ltd.