Spatial properties of sessile benthic organisms and the design of repeat visual survey transects

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The Alliance for Freshwater Life: A global call to unite efforts for freshwater biodiversity science and conservation

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Identifying a suite of surrogate freshwaterscape fish species: a case study of conservation prioritization in Ontario's Far North,Canada

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Spatial and temporal patterns in fish community structure and abundance in the largest U.S. river swamp,the Atchafalaya River floodplain,Louisiana

Long‐term monitoring is critical for documenting population and community trends and for management, especially in large river‐floodplain ecosystems that provide important services. Levees have reduced active floodplains in most large rivers, but connectivity in some reaches could promote community resilience. Using multivariate tools and regression, we examined spatial and temporal structure in fish community samples from two decades (>1000 samples, >100 sites) in one of the largest relatively intact river‐floodplain ecosystems in North America – the Atchafalaya River (ARB), Louisiana. Assemblages exhibited significant structure temporally and spatially, with most substantial effects of year and hydrologic subdivisions; however, season and water level also influenced community structure. Temporal trends in communities were limited to few areas, while declines in species richness were more widespread; however, rarefied richness trends suggested that declines were slight. Recent and long‐term declines in abundance of economically important species (e.g., Black Crappie, Largemouth Bass, Bigmouth Buffalo) and increases in others (e.g., Smallmouth Buffalo, Blue Catfish, Freshwater Drum) drove differences among time periods. Our results suggest that the hydrologic subdivisions of the ARB may be an appropriate scale at which to manage fish populations, hydrology and water quality. Although we could not account for several important factors affecting fish communities in the ARB (e.g., hurricanes, major floods), and were limited by sampling variability, our findings highlight the utility of long‐term datasets from large river‐floodplain ecosystems for identifying important scales for management, determining species contributions to community change and forming hypotheses about anthropogenic and environmental drivers of variation in fish communities.     

Biogeographic freshwater fish pattern legacy revealed despite rapid socio‐economic changes in China

Understanding drivers of freshwater fish assemblages is critically important for biodiversity conservation strategies, especially in rapidly developing countries, which often have environmental protections lagging behind economic development. The influences of natural and human factors in structuring fish assemblages and their relative contributions are likely to change given the increasing magnitude of human activities. To discriminate natural and human drivers of fish diversity and assemblage patterns in developing countries with rapid socio‐economic development, a dataset of 908 freshwater fish species and 13 metrics including three categories of both natural (i.e., biogeographic) and human drivers (i.e., economic growth, inland fisheries) in China were analysed with machine learning algorithms (i.e., self‐organizing map, random forest). Here, we found that biogeographic drivers explained 21.8% of the observed fish assemblage patterns in China and remained stronger predictors when compared to human drivers (i.e., 15.6%, respectively). Freshwater fish species richness was positively correlated to rainfall, air temperature, surface water area and inland fisheries production but negatively correlated with urbanization. In addition, the strong structuring effects of climatic variables on Chinese fish richness patterns suggested that the fish assemblages could be particularly vulnerable to climate change. Our results showed that natural biogeographic factors still dominate in driving freshwater fish assemblage patterns despite increased human disturbances on aquatic ecosystems in a rapidly developing country. These findings consequently suggested that we should consider both natural (e.g., climate) and human (e.g., urbanization, inland fisheries) factors when establishing aquatic conservation strategies and priorities for developing countries that are experiencing rapid socio‐economic changes.     

Connectivity,habitat, and flow regime influence fish assemblage structure: Implications for environmental water management in a perennial river of the wet–dry tropics of northern Australia

1. Environmental water management seeks to balance competing demands between the water needed to sustain human populations and their economic activities and that required to sustain functioning freshwater ecosystems and the species they support. It must be predicated on an understanding of the environmental, hydrological, and biological factors that determine the distribution and abundance of aquatic species.
2. The Daly River of the wet–dry tropics of northern Australia consists of a perennially flowing main stem and large tributaries, as well as many small to large naturally intermittent tributaries, and associated off‐channel wetlands. Increased groundwater abstraction to support irrigated agriculture during the dry season threatens to reduce dry‐season flows that maintain perenniality and persistence of freshwater fishes.
3. Fish assemblages were surveyed at 55 locations during the dry season over a 2‐year period with the goal of establishing the key landscape‐scale and local‐scale (i.e. habitat) drivers of fish species distribution.
4. Longitudinal (upstream/downstream) and lateral (river/floodplain) gradients in assemblage structure were observed with the latter dependent on the position in the river landscape. Underlying these gradients, stream flow intermittency influenced assemblage composition, species richness, and body size distributions. Natural constraints to dispersal were identified and their influence on assemblage structure was also dependent on position within the catchment.
5. Eight distinct assemblage types were identified, defined by differences in the abundance of species within five groups differing in functional traits describing body size, spawning requirements, and dispersal capacity. These functional groups largely comprised species widely distributed in northern Australia.
6. The results of the study are discussed with reference to the environmental flow needs of the Daly River and other rivers of northern Australia. The findings may also be applied to environmental flow management in savannah rivers elsewhere.

     

Freshwater fish community structured more by dispersal limitation than by environmental heterogeneity

Abstract –  We examined the relative contribution of environmental heterogeneity and dispersal limitation on freshwater fish community composition in 18 Greek protected lakes and reservoirs. Environmental heterogeneity was measured by spatial pattern metrics (calculated by digital map processing, e.g., patch richness density, area-weighted mean patch area), altitude, maximum lake depth and trophic status. Dispersal limitation was measured by straight-line distances among lake centres. Ecosystems were clustered according to species composition. We examined the correlation of similarity in species composition among ecosystems with that of environmental heterogeneity and with straight-line distances, for the entire dataset, as well as for the occurring clusters. Fish species richness increased with ecosystem area and decreased with altitude. The clusters identified (aquatic ecosystems of Northern vs. ecosystems of Western Greece), implied an underlying biogeographical pattern as defined, with Pindus range acting as a natural barrier. Between ecosystems similarity, based on fish species composition, showed a weak to insignificant correlation with environmental heterogeneity, but was significantly correlated to dispersal limitation for the entire dataset as well as within each occurring cluster. Thus, natural barriers, species biogeography and dispersal limitation played a more significant role in shaping freshwater fish communities than environmental heterogeneity.     

Advances in remote sensing of freshwater fish habitat: A systematic review to identify current approaches,strengths and challenges

Remote sensing technology offers the ability to derive information on freshwater fish habitats across broad geographic areas and has the potential to transform approaches to monitoring. However, the numerous platforms, sensors and analytical software that are available may overwhelm those interested in utilizing this important technology and thus limit its broad application and uptake. Our review is intended to shed light on the capacity of this technology to transform freshwater fish habitat monitoring by examining the fundamental characteristics of the major remote sensing technologies that have been used for characterizing freshwater habitats, conducting a systematic literature review of studies that have used remote sensing technologies to characterize freshwater fish habitats and, highlighting some of the key habitat features, fish species and regions, that have been examined. Lastly, we identify the relative strengths and weaknesses of the various remote sensing technologies that can be used, recommend future research that could help improve the use of these technologies, and, provide a series of important considerations for those who are interested in utilizing these technologies for freshwater fish habitat characterization.     

Captive breeding and sanctuaries for the endangered African anabantid Sandelia bainsii, the Eastern Cape rocky

The African anabantid Sandelia bainsii Castelnau is in danger of extinction in the near future if urgent steps are not taken to prevent further degradation of its habitat. A combination of environmental education programmes, environmental journalism, captive breeding programmes, provision of sanctuaries, survey work and new research are being used to prevent the extinction of S. bainsii. A recent study using video recordings has for the first time clarified the reproductive behaviour of this anabantid. This new information will aid in the planning of the captive breeding strategy. Several small trial sanctuary areas have been established within the Kowie River catchment area, South Africa. Environmental education is an important component involving school groups, youth groups, concerned adults and National Science and Technology Festival audiences. The severe pressures put on the freshwater ecosystems within this relatively arid country have been highlighted. A clear management plan is required if this large anabantid and other local freshwater species are to survive. This paper summarizes existing knowledge of S. bainsii and suggests positive conservation steps which should be implemented within the natural range of this species     

Science for conserving Amazon freshwater ecosystems

1. The Amazon Basin is being degraded at unprecedented rates, yet conservation efforts have implemented protected areas to curb deforestation, leaving freshwater ecosystems vulnerable to degradation. Amazon freshwater ecosystems are largely unprotected because a terrestrial bias has limited the ability of science to affect policy.
2. Overcoming this bias requires increasing exchange of information among stakeholders across the basin to raise awareness of threats to Amazon freshwater ecosystems and promote discussions and access to conservation solutions. To help address this need, this Special Issue collates 15 synthetic articles that advance knowledge and identify conservation solutions.
3. Three articles highlight the importance of considering the hydrological and limnological processes that control the integrity of these freshwater ecosystems and offer new insights on how to extrapolate them across the basin.
4. Three articles on crocodilians, aquatic mammals, and migratory fishes document threats and knowledge gaps, and identify the missing role of governments as an impediment to conservation of their populations.
5. Three articles evaluate the multi-faceted effects of hydropower dams on fish, birds, and floodplain trees. They reinforce perceptions that dams are key environmental threats and offer guidance for improving protocols for dam site selection and impact assessment.
6. Three articles assessing the effectiveness of protected areas to safeguard fish and aquatic invertebrates show there is an urgent need to redesign the Amazon protected area network to adequately protect freshwater biota.
7. Three forward-looking articles show that: (i) conservation initiatives by local communities are ‘bright spots’ for freshwater conservation; (ii) microchemistry analyses of the ear bones of fishes could boost the knowledge base needed to conserve them; and (iii) strengthening the Amazon conservation framework requires a reversal of Brazil's current governmental priorities, remobilization of stakeholders, investments in capacity building, and expanding protections to terrestrial and freshwater ecosystems.

     

Moving beyond fitting fish into equations: Progressing the fish passage debate in the Anthropocene

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The randomised response technique: A valuable approach to monitor pathways of aquatic biological invasions

Anglers can be significant vectors for non‐native species (NNS) in freshwater ecosystems, and monitoring their behaviour can be a useful way to counteract biological invasions. However, anglers may be unwilling to reveal their real behaviour in conventional surveys. In this study, the Randomised Response Technique (RRT) and the Bean Method (BM) survey technique were compared using direct questions to obtain frequency estimates of four angler behaviours that may affect NNS management in freshwater ecosystems: angling without a license, release of macroinvertebrates in the environment, use of fish bait and unauthorised fish restocking. Higher estimates were obtained from responses to RRT than BM questions, and BM provided contradictory results. Use of the RRT is recommended in those human dimension studies that explore angler behaviour as a vector for aquatic invasions.     

Introduction of non‐native freshwater fish: is it all bad?

Risk perceptions are important to the policy process, but there is often a well‐established pattern of small risks being over assessed. This is also true with the issue of non‐native freshwater fish introductions, where a great majority of research focuses on the few negative cases. The attitude towards ‘non‐natives’ is a continually evolving process and varies according to current societal values. Here I show that on the global scale, the majority of freshwater fish introductions are not identified as having an ecological impact while having great societal benefits. Case studies from the African lakes are discussed in order to illustrate contrasting outcomes following fish introductions. Looking into the future, the environmental changes that freshwater ecosystems may encounter will have inevitable implications on the distribution of our native freshwater fish species and the need to rely on non‐native introductions may become a growing reality. Aquaculture production is regularly increasing and our dependence on it is likely to become greater as it provides an important substitute for the declining production of capture fisheries. With it the number of freshwater fish introductions will increase and a more realistic attitude, albeit controversial, will need to be debated. This would mean protecting some introductions that present beneficial outcomes for biodiversity alongside a more systematic ban of species or families of fish presenting a higher historical ecological risk. The public perception of risk is something which cannot be ignored by any government or ruling body, but in order to gain public support in the fight for conservation of freshwater fish biodiversity, the message needs to be clear, detailed and educational.     

Neotropical freshwater fishes imperilled by unsustainable policies

Neotropical freshwater fishes are the most diverse on the planet (>5,500 species), although nations in Latin America have been negligent regarding their conservation. National policies have historically encouraged unsustainable practices, and recent decades have witnessed a sharp increase in harmful activities. Our aim with this review was to expose this situation and illustrate how national policies constitute the main threat to freshwater fish biodiversity. We explain that the most devastating, pervasive and systemic threats are rooted in official policies, particularly unsustainable activities (e.g. hydropower, water diversion, mining, aquaculture, agriculture and fishing), poor management/conservation (e.g. fish stocking and passages) and harmful legislation (e.g. poor licensing, non‐native species). We provide a broad portrait of the Neotropical scenario, where unsustainable policies have caused considerable damage to freshwater ecosystems, and focus on major examples from Brazil, where development projects have caused large‐scale losses to fish biodiversity. Such modus operandi of human development is incompatible with the persistence of biodiversity, and no simple solution is available to correct or minimize its effects. The current situation demands a profound behavioural shift towards better practices and policies, or these multiple high‐impact activities will continue eroding freshwater fish biodiversity and impairing essential ecosystem services.     

Modelling the habitat requirement of riverine fish species at the European scale: sensitivity to temperature and precipitation and associated uncertainty

Abstract – Species distribution models (SDMs) have been widely used for different purposes such as studying species niche or forecasting the effects of global change on species distribution. Nevertheless, these models are often calibrated on datasets that only cover a fraction of the species’ realised niches, which could lead to unrealistic results. The aim of this study was to model the habitat requirements of 21 freshwater fish species that are native to Europe, using a dataset that accurately reflects their realised niches. Both temperature and precipitation were used as climatic factors to model the habitat requirements of the species, and the uncertainty associated with the fitted environment–occurrence relationships was examined. The results demonstrated the importance of accounting for these two climatic components when estimating the habitat requirements of riverine fish species and whether the uncertainty associated with model expectations varies with the species and the environmental factor considered. These results are discussed with regard to the known ecology of the 21 riverine fish species and within the perspective of climate change.     

Revisiting ecological integrity 30 years later: non‐native species and the misdiagnosis of freshwater ecosystem health

Assessing the ecological integrity of freshwater ecosystems has become a priority to protect the threatened biodiversity they hold and secure future accessibility to the services they provide. Some of the most widespread applications of biological indicators are fish‐based indices. These have mostly mirrored the approach proposed by Karr 30 years ago (Index of Biotic Integrity; IBI), based on the comparison of observed and expected composition and structure of local fish assemblages in the absence of major perturbations, using the so‐called reference condition approach. Despite the notable success of the implementation of fish‐based indices, most of them overlook non‐native species as a source of ecosystem degradation, and evaluations are focused on the physico‐chemical condition of freshwater ecosystems and their effects on freshwater biodiversity. Almost 90% of 83 reviewed IBIs did not consider non‐native species when defining reference conditions. Most IBIs used non‐native species in conjunction with native ones to construct the metrics that conform to the index. The response of the IBI to the effect of non‐native species has hardly ever been tested. When developing and evaluating IBIs, attention was mostly directed to ensuring the correct response of the index to physico‐chemical parameters, which could otherwise be characterized more effectively using alternative methods. Current application of IBIs entails a misuse of biological indicators by overlooking some types of degradation that cannot be otherwise evaluated by traditional methods. This constrains the capacity to adequately respond to one of the most challenging and common threats to the conservation of freshwater fish diversity.     

Voracious invader or benign feline? A review of the environmental biology of European catfish Silurus glanis in its native and introduced ranges*

A popular species for food and sport, the European catfish (Silurus glanis) is well‐studied in its native range, but little studied in its introduced range. Silurus glanis is the largest‐bodied freshwater fish of Europe and is historically known to take a wide range of food items including human remains. As a result of its piscivorous diet, S. glanis is assumed to be an invasive fish species presenting a risk to native species and ecosystems. To assess the potential risks of S. glanis introductions, published and ‘grey’ literature on the species’ environmental biology (but not aquaculture) was extensively reviewed. Silurus glanis appears well adapted to, and sufficiently robust for, translocation and introduction outside its native range. A nest‐guarding species, S. glanis is long‐lived, rather sedentary and produces relatively fewer eggs per body mass than many fish species. It appears to establish relatively easily, although more so in warmer (i.e. Mediterranean) than in northern countries (e.g. Belgium, UK). Telemetry data suggest that dispersal is linked to flooding/spates and human translation of the species. Potential impacts in its introduced European range include disease transmission, hybridization (in Greece with native endemic Aristotle’s catfish [Silurus aristotelis]), predation on native species and possibly the modification of food web structure in some regions. However, S. glanis has also been reported (France, Spain, Turkmenistan) to prey intensively on other non‐native species and in its native Germany to be a poor biomanipulation tool for top‐down predation of zooplanktivorous fishes. As such, S. glanis is unlikely to exert trophic pressure on native fishes except in circumstances where other human impacts are already in force. In summary, virtually all aspects of the environmental biology of introduced S. glanis require further study to determine the potential risks of its introduction to novel environments.     

Trait–environment relationships in Amazon stream fish assemblages

Studies of trait–environment relationships provide important tools for the prediction of the response of biological communities to environmental alterations. The Amazon basin presents enormous potential for the development of research on this type of relationship, given the diversity of both its fish fauna and the aquatic ecosystems this fauna inhabits. The present study investigated the association between local environmental variables and the functional traits of fish in 54 streams of six major Amazonian basins. We identified the relationship between the characteristics of the streams (channel morphology, channel habitat units, riparian vegetation cover, large woody fragments and instream cover for aquatic organisms) and fish traits related to locomotion, habitat use and feeding behaviour. The fish fauna of the broader, deeper and more slowly flowing streams was dominated by nektobenthic species that exploit autochthonous resources such as fish and invertebrates. In narrow, fast‐flowing streams, by contrast, there was a predominance of benthic fishes with varying feeding habits, including periphytivorous and invertivorous species. Narrow, shady streams were inhabited by nektonic species adapted for the exploitation of resources from the marginal vegetation. The results of this study contribute to the understanding of the association between the functional structure of fish assemblages and local environmental variables in Amazonian streams. We hope that these findings will stimulate further research into the natural variation in stream fish assemblages that will ensure the development of more effective management strategies that better protect these important aquatic ecosystems.     

Freshwater conservation planning informed and validated by public participation: The Ebro catchment,Spain, as a case study

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Role of photoperiod and melatonin in the regulation of ovarian functions in Indian carp <Emphasis Type="Italic">Catla catla</Emphasis>: basic information for future application

The major carp Catla catla is a popular freshwater edible fish and an extensively cultured species in India. However, basic information on the physiology of reproduction is lacking in this species. By virtue of its surface feeding habit, it maintains close contact with environmental light, and is a species of choice for the study of temporal organization of reproduction under natural and experimental conditions for understanding environmental and/or endocrine mechanisms that control the annual reproductive cycle. The present review covers information gathered in recent years to emphasize the temporal pattern of reproductive events and the importance of photoperiod and melatonin, a hormone of the pineal gland that links the environment with the endocrine system in the regulation of reproduction. Finally, the outcome of the research is discussed in terms of its direct and indirect applications to aquaculture of this species with a view to manipulate its breeding at a desired time of the year to meet market demand.