Article

Sensitivity of river fishes to climate change: The role of hydrological stressors on habitat range shifts

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Abstract

Abstract Climate change will predictably change hydrological patterns and processes at the catchment scale, with impacts on habitat conditions for fish. The main goal of this study is to assess how shifts in fish habitat favourability under climate change scenarios are affected by hydrological stressors. The interplay between climate and hydrological stressors has important implications in river management under climate change because management actions to control hydrological parameters are more feasible than controlling climate. This study was carried out in the Tamega catchment of the Douro basin. A set of hydrological stressor variables were generated through a process-based modelling based on current climate data (2008–2014) and also considering a high-end future climate change scenario. The resulting parameters, along with climatic and site-descriptor variables were used as explanatory variables in empirical habitat models for nine fish species using boosted regression trees. Models were calibrated for the whole Douro basin using 254 fish sampling sites and predictions under future climate change scenarios were made for the Tamega catchment. Results show that models using climatic variables but not hydrological stressors produce more stringent predictions of future favourability, predicting more distribution contractions or stronger range shifts. The use of hydrological stressors strongly influences projections of habitat favourability shifts; the integration of these stressors in the models thinned shifts in range due to climate change. Hydrological stressors were retained in the models for most species and had a high importance, demonstrating that it is important to integrate hydrology in studies of impacts of climate change on freshwater fishes. This is a relevant result because it means that management actions to control hydrological parameters in rivers will have an impact on the effects of climate change and may potentially be helpful to mitigate its negative effects on fish populations and assemblages.

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... Freshwater environments are subject to multiple stressors derived from the use that the human society makes of rivers (e.g. irrigation, power generation, flow control or industrial and domestic supply), which can alter ecological patterns and processes Segurado et al., 2016). Among these stressors, river fragmentation and alterations on natural river flow and thermal regimens are the most important affecting freshwater ecosystems (Feng et al., 2018;Jones and Petreman, 2015;Nilsson et al., 2005). ...
... Among these stressors, river fragmentation and alterations on natural river flow and thermal regimens are the most important affecting freshwater ecosystems (Feng et al., 2018;Jones and Petreman, 2015;Nilsson et al., 2005). Near future scenarios suggest an aggravation of this situation, with an increase of the magnitude and number of stressors acting upon river ecosystems and an increase of the possible interactions (Segurado et al., 2016). In one hand, climatic change shows potential alterations in water temperature and in the magnitude, intensity and frequency of rainfall and consequently in river flow (Solomon et al., 2007). ...
... In one hand, climatic change shows potential alterations in water temperature and in the magnitude, intensity and frequency of rainfall and consequently in river flow (Solomon et al., 2007). In the other hand, human population growth can cause water scarcity due to the increase in water demand and water pollution as result of industrial, domestic and agricultural waste water (Almodóvar et al., 2012;Branco et al., 2016;Segurado et al., 2016;Vörösmarty et al., 2000). Understanding the isolated and combined impact of all these alterations is necessary for the prediction of responses to changing environments and for the establishment of impact mitigation and compensation measures (Segurado et al., 2016). ...
Article
Brown trout uses river flow and thermal regimens as main stimuli for initiating and maintaining behavioral reactions such as migration and spawning. Therefore, anthropogenic alterations on these factors may have strong impacts on its populations. The aim of this work is to understand these consequences by assessing potamodromous brown trout movements in the past and present, and to model future responses. For this, brown trout movements in a fishway in the Marin River (Bidasoa basin, Northern Iberian Peninsula) have been monitored from 2008 to 2017. Random forest regression has been used to assess the influence of environmental variables on brown trout movements and to model the response under hypothetical climatic and hydrological scenarios. Results show that brown trout uses the fishway during the whole year, with more upstream movements during the spawning season. The model is able to predict accurately the timing and number of migrants. Its use under hypothetical climate change and flow regulation scenarios shows a delay in the migration time. Therefore, modelling using large time series can be a powerful tool to define management and conservation strategies and prepare compensation measures for future scenarios.
... As such, freshwater environments are subject to multiple stressors derived from the use that human society makes of rivers (e.g. irrigation, power generation, flood control or industrial and domestic supply), which can alter ecological patterns and processes Segurado et al., 2016). Dudgeon et al. (2006) identified five major threat categories that affect freshwater biodiversity: overexploitation, water pollution, flow modification, habitat degradation and species invasion. ...
... Furthermore, future scenarios of climate change show potential alterations, not only in water temperature but also in the magnitude, intensity and frequency of rainfall and consequently in river discharge (Solomon et al., 2007). This, together with the expected water scarcity as a result of the increasing water demand and pollution for industrial, domestic and agricultural supply and their waste water (Pittock and Lankford, 2010;Seckler et al., 1999), as well as river fragmentation (Nilsson et al., 2005), may negatively affect freshwater populations (Almodóvar et al., 2012;Branco et al., 2016;Sánchez-Hernández and Nunn, 2016;Segurado et al., 2016;Van Vliet et al., 2013;Vörösmarty et al., 2000). ...
... In addition, the alterations in the morphological, hydrological and climatic processes are expected to provoke a reduction of suitable physical and thermal habitat availability (Almodóvar et al., 2012;Boavida et al., 2015), with the acting associated co-stressors (e.g. oxygen depletion) Segurado et al., 2016). ...
Thesis
Full-text available
Many fish species need to move between different habitats in order to complete their life cycles. As a result, migration responds to internal and external factors, with environmental variables, such as river flow and thermal regimes, acting as the main stimuli for the onset and maintenance of migratory behavior in freshwater fish. Moreover, river fragmentation and anthropogenic alterations on these variables (e.g. river regulation) may have strong impacts on fish populations, which could be aggravated by future projections of climate change and increasing water demand. Thus, to assess these impacts and define mitigation measures, it is vital to understand fish movement patterns and the environmental variables affecting them. Native Iberian fish fauna presents the greatest European percentage of endemism, characterized by a low number of families, with most species belonging to the Cyprinidae family. The most representative species from this family are barbels and nases, for example, the Iberian barbel and the Northern straight-mouth nase. However, scarce information exists regarding the ecological requirements of these endemic species during their upstream migration. Another important family in the Iberian Peninsula, in terms of recreational fishing and ecological traits, is the Salmonidae, the brown trout being one of the most representative salmonids worldwide. Although this species has been deeply studied, most available research has been focused on anadromous populations, and studies in the south of its natural distribution are still scarce. The present thesis aims to cover some of these research gaps regarding upstream migration patterns of Iberian barbel, Northern straight-mouth nase and brown trout (both potamodromous and anadromous ecotypes), as well as to determine the environmental conditions which trigger these movements. In addition, this information is used to evaluate the effect of human impacts and assess the effect of mitigation measures on these species. In order to achieve this, the long-term movement data of these three species in four different locations of the Iberian Peninsula (Porma River (León), Tormes River (Salamanca), Marín River (Navarra) and Bidasoa River (Navarra)) were gathered, analyzed and discussed. In all the studied cases, data were collected in fishways, since they are mandatory points of passage during upstream migration. Survival analysis techniques were used to study median migration dates and patterns. Subsequently, random forest regression was used to evaluate the influence of environmental variables on the number of captures, develop models that can predict when upstream movements were more likely to occur, evaluate different scenarios of river discharge and water temperature and assess the possible effects of management and restoration actions. The long-term monitoring is an essential tool, not only for identify population changes, migration patterns and cues, but also for the evaluation of the overall effect of changes in the parameters involved in the migration and assessing the effects of mitigation measures. Therefore, continuous monitoring studies are necessary to define adaptive strategies and reliable management plans to ensure the conservation of Iberian freshwater fish.
... Large scale alterations to flow regimes based on changing precipitation could potentially impact many of these processes, leading to changes in fish community composition and species distributions (Chessman, 2013). Climate induced flow alterations have been linked to species range shifts due to the influence of hydrologic stressors (Segurado et al., 2016) and recruitment declines due to increased flow variability (Ward et al., 2015) and lower flows (Bassar et al., 2016). Biotic interactions are often mediated by stream flow, and shifts in flow regime can result in changes in the dynamics of predation and competition which may result in changes to community structure (Layher, 1993;Mammoliti, 2002). ...
Article
Climate change is expected to alter stream fish habitat potentially leading to changes in the composition and distribution of fish communities. In the Northeastern and Midwestern United States we identified the distribution and characteristics of those fish communities most and least at risk of experiencing changes in climate which deviate from the climate they are associated with. We classified stream fish communities based on a suite of climate and environmental variables with multivariate regression trees under both recent and future conditions based on eight climate models. Our findings showed that some areas, such as the majority of the Illinois, Wisconsin, and Iowa), have high levels of risk of change in stream class, while much of Kentucky, West Virginia, Virginia, Pennsylvania, Eastern Ohio, Southern Michigan, and the Atlantic Coast are at relatively low risk. Stream class shifts ranged from over 75% of segments lost (associated with cooler temperatures) to gains of over 40% (associated with warmer temperatures). Common warmwater species such as green sunfish (Lepomis cyanellus), bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides) are expected to have the largest net gains in associated stream classes, while species associated with cooler streams such as Southern redbelly dace (Chrosomus erythrogaster), slimy sculpin (Cottus cognatus), and Eastern blacknose dace (Rhinichthys atratulus) were expected to experience the largest proportional losses. By pairing our climate risk predictions with other stressors such anthropogenic land use, habitat fragmentation, and water quality impairment, we identified opportunities for preservation (low risk due to all threats), restoration (low risk due to climate, high risk due to other stressors), and adaptation (high climate risk with low risk from other stressors). Understanding which communities are at risk due to climate change will aid in developing adaptation strategies to help sustain them in the future.
... Major advantages of BRTs are their ability to handle collinearity, nonlinearity, outliers and to automatically identify interactions between explanatory variables (Elith et al., 2008). BRTs therefore constitute a powerful tool to investigate relationships between the environment and ecological responses (Dahm and Hering, 2016;Pilière et al., 2014;Segurado et al., 2016) and hence to identify the impact of multiple pressures in aquatic environments (Feld et al., 2016;. To model the continuous response variables (the FPM), a BRT model with a Gaussian distribution was selected as loss function for minimizing squared errors. ...
Thesis
Full-text available
English Abstract here, German below / Deutsche Zusammenfassung weiter unten European large rivers have been tremendously modified over centuries and transformed into waterways for inland navigation. Extensive river modifications such as river regulation, channel straightening and flood protection have resulted in multiple pressures. However, inland navigation has not been considered as a potential pressure yet. This thesis aimed to assess the role of inland navigation among the most prevailing pressures in large rivers under field conditions. A worldwide unique and complementary dataset, the Large River Fish Database (LRDB) was compiled. The LRDB consists of 2693 fish samples assessed at 358 sampling sites in 16 European large rivers. Sites were characterized by various pressure variables and frequencies of ship traffic. To derive representative samples of large rivers fish assemblages, performance of various fishing gears applied was assessed. Electrofishing samples represented highest densities of fish and highest overall biodiversity. Therefore, electrofishing is suitable for fish-based assessments of large rivers and only electrofishing samples were selected to assess multiple pressures and inland navigation. Commercial cargo navigation appeared as the most influential pressures on large rivers fish assemblages among increased velocities and the loss of floodplains. Starting at already eight passing vessels per day, densities of particularly habitat-sensitive spawners significantly declined. Moreover, recreational navigation such as river cruises and motorized sport boats had distinct ecological consequences to those of cargo vessels. Inland navigation is as detrimental as the hydromorphological degradation of the river channel and requires specific attention in river management and rehabilitation. Pleasure boating (river cruises and sport boats) will counteract river rehabilitation also in smaller waterways and delimit ecological success of the Blue Band initiative in Germany. German / Deutsch: Europäische große Flüsse wurden über Jahrhunderte entscheidend verändert und zu Wasserstraßen für die Schifffahrt ausgebaut. Flussregulierung, Begradigung und Hochwasserschutz tragen zu multiplen Stressoren bei, wobei die Schifffahrt bislang keine Beachtung als potentieller zusätzlicher Einflussfaktor (Stressor) fand. Die zentrale Fragestellung dieser Arbeit befasste sich mit der Rolle der Schifffahrt zwischen multiplen Stressoren und deren Auswirkungen auf die Fischgemeinschaften großer Flüsse. Hierzu wurde die „Large River Fish Database“ (LRDB), ein weltweit einzigartiger Datensatz zusammengestellt, der 2693 Befischungen an 358 Probestellen in 16 europäischen großen Flüssen enthält. Die Probestellen sind durch verschiedene Einflussfaktoren (Stressoren) und Schiffsverkehr beschrieben. Um ein für große Flüsse repräsentatives Abbild der Fischgemeinschaften zu erhalten, wurden zunächst die angewendeten Fischfangmethoden analysiert. Mit der Elektrofischerei wurden die höchsten Fischdichten und die höchste Biodiversität erfasst. Die Elektrofischerei ist daher für eine repräsentative Erfassung der Fischgemeinschaften großer Flüsse geeignet und wurde für weitere Analysen ausgewählt. Die kommerzielle Frachtschifffahrt trat als einer der einflussreichsten Stressoren hervor, zusammen mit erhöhter Fließgeschwindigkeit und dem Verlust von Überschwemmungsflächen. Dichten von insbesondere Habitat-sensitiven Fischen sanken bereits ab acht Frachtschiffen pro Tag signifikant ab. Darüberhinaus hatte auch die Freizeitschifffahrt (Flusskreuzfahrten und motorisierte Sportboote) deutliche und zu Frachtschiffen unterscheidbare ökologische Konsequenzen. Die Wirkungen der Schifffahrt sind ebenso verheerend wie die der hydromorphologischen Degradierung und benötigen eine gesonderte Beachtung im Flussmanagement und der Flussrevitalisierung. Freizeitboote und Flussdampfer wirken der Flussrenaturierung kleinerer Wasserstraßen entgegen und gefährden den ökologischen Erfolg des Blauen Bandes.
... Further, known stressors may operate slowly and in the long term, thus remaining rarely addressed (and addressable) in short-term monitoring surveys or with low monitoring frequencies. For example, climate change is deemed to exhibit strong interactions with hydrological stress in the Mediterranean area (Segurado et al., 2016). Measuring the effects would probably require decades of monitoring, which is why predictive modelling of future climate scenarios has become popular to generate the data required to model the combined effects of climate change and other environmental stressors. ...
... BRTs have been extensively applied as an exploratory tool to compare the nature and relative importance of functional relationships between variables across different sets of ecological observations (Buston and Elith, 2011;Descy et al., 2016;Segurado et al., 2016;Tisseuil et al., 2012;Walsh and Webb, 2016). We fit BRT models to each set of CHAB observations separately to explore relationships between environmental drivers and bloom size and to assess the degree of coherence in modeling results across monitoring products. ...
Article
Cyanobacteria blooms are a major environmental issue worldwide. Our understanding of the biophysical processes driving cyanobacterial proliferation and the ability to develop predictive models that inform resource managers and policy makers rely upon the accurate characterization of bloom dynamics. Models quantifying relationships between bloom severity and environmental drivers are often calibrated to an individual set of bloom observations, and few studies have assessed whether differences among observing platforms could lead to contrasting results in terms of relevant bloom predictors and their estimated influence on bloom severity. The aim of this study was to assess the degree of coherence of different monitoring methods in (1) capturing short- and long-term cyanobacteria bloom dynamics and (2) identifying environmental drivers associated with bloom variability. Using western Lake Erie as a case study, we applied boosted regression tree (BRT) models to long-term time series of cyanobacteria bloom estimates from multiple in-situ and remote sensing approaches to quantify the relative influence of physico-chemical and meteorological drivers on bloom variability. Results of BRT models showed remarkable consistency with known ecological requirements of cyanobacteria (e.g., nutrient loading, water temperature, and tributary discharge). However, discrepancies in inter-annual and intra-seasonal bloom dynamics across monitoring approaches led to some inconsistencies in the relative importance, shape, and sign of the modeled relationships between select environmental drivers and bloom severity. This was especially true for variables characterized by high short-term variability, such as wind forcing. These discrepancies might have implications for our understanding of the role of different environmental drivers in regulating bloom dynamics, and subsequently for the development of models capable of informing management and decision making. Our results highlight the need to develop methods to integrate multiple data sources to better characterize bloom spatio-temporal variability and improve our ability to understand and predict cyanobacteria blooms.
... Many studies linked the changes of fish communities with different environmental problems (Chang et al., 2011Piperac et al., 2016;Segurado et al., 2016;Xu et al., 2016), such as excessive wastes due to expanding industrial as well as agricultural development and increasing population, which threatened inhabitant fish communities (Cronin et al., 2002;Hubert and Renno, 2006;Liu et al., 2012). Global warming as well as human activities have caused severe water deficiency and polluted watersheds, making management of water resources towards sustainability even more challenging nowadays. ...
Article
The steep slopes of rivers can easily lead to large variations in river water quality during typhoon seasons in Taiwan, which may poses significant impacts on riverine eco-hydrological environments. This study aims to investigate the relationship between fish communities and water quality by using artificial neural networks (ANNs) for comprehending the upstream eco-hydrological system in northern Taiwan. We collected a total of 276 heterogeneous datasets with 8 water quality parameters and 25 fish species from 10 sampling sites. The self-organizing feature map (SOM) was used to cluster, analyze and visualize the heterogeneous datasets. Furthermore, the structuring index (SI) was adopted to determine the relative importance of each input variable of the SOM and identify the indicator factors. The clustering results showed that the SOM could suitably reflect the spatial characteristics of fishery sampling sites. Besides, the patterns of water quality parameters and fish species could be distinguishably (visually) classified into three eco-water quality groups: 1) typical upstream freshwater fishes that depended the most on dissolved oxygen (DO); 2) typical middle-lower reach riverine freshwater fishes that depended the most on total phosphorus (TP) and ammonia nitrogen; and 3) low lands or pond (reservoirs) freshwater fishes that depended the most on water temperature, suspended solids and chemical oxygen demand. According to the results of the SI, the representative indicators of water quality parameters and fish species consisted of DO, TP and Onychostoma barbatulum. This grouping result suggested that the methodology can be used as a guiding reference to comprehensively relate ecology to water quality. Our methods offer a cost-effective alternative to more traditional methods for identifying key water quality factors relating to fish species. In addition, visualizing the constructed topological maps of the SOM could produce detailed inter-relation between water quality and the fish species of stream habitat units.
... Such risk maps are a valuable tool for water managers and users to highlight the most vulnerable riparian regions. (Segurado et al., 2016) studied climate change effects on fish habitat conditions using hydrological stressors. The results show the effect of site descriptors, climate and hydrology for different fish species. ...
Article
Semi-arid regions are facing the challenge of managing water resources under conditions of increasing scarcity and drought. These are recently pressured by the impact of climate change favoring the shifting from using surface water to groundwater without taking sustainability issues into account. Likewise, water scarcity raises the competition for water among users, increasing the risk of social conflicts, as the availability of fresh water in sufficient quality and quantity is already one of the major factors limiting socio-economic development. In terms of hydrology, semi-arid regions are characterized by very complex hydro- and hydrogeological systems. The complexity of the water cycle contrasts strongly with the poor data availability, (1) which limits the number of analysis techniques and methods available to researchers, (2) limits the accuracy of models and predictions, and (3) consequently challenges the capabilities to develop appropriate management measures to mitigate or adapt the environment to scarcity and drought conditions. Integrated water resources management is a holistic approach to focus on both environmental as well as on socio-economic factors influencing water availability and supply. The management approaches and solutions adopted, e.g. in form of decision support for specific water resources systems, are often highly specific for individual case studies.
... Although there are several examples of such attempts (e.g. Fernandes et al., 2016;Segurado et al., 2016), these are still major challenges that river ecologists and managers are currently facing. ...
Article
River basins are extremely complex hierarchical and directional systems that are affected by a multitude of interacting stressors. This complexity hampers effective management and conservation planning to be effectively implemented, especially under climate change. The objective of this work is to provide a wide scale approach to basin management by interpreting the effect of isolated and interacting factors in several biotic elements (fish, macroinvertebrates, phytobenthos and macrophytes). For that, a case study in the Sorraia basin (Central Portugal), a Mediterranean system mainly facing water scarcity and diffuse pollution problems, was chosen. To develop the proposed framework, a combination of process-based modelling to simulate hydrological and nutrient enrichment stressors and empirical modelling to relate these stressors - along with land use and natural background - with biotic indicators, was applied. Biotic indicators based on ecological quality ratios from WFD biomonitoring data were used as response variables. Temperature, river slope, % of agriculture in the upstream catchment and total N were the variables more frequently ranked as the most relevant. Both the two significant interactions found between single hydrological and nutrient enrichment stressors indicated antagonistic effects. This study demonstrates the potentialities of coupling process-based modelling with empirical modelling within a single framework, allowing relationships among different ecosystem states to be hierarchized, interpreted and predicted at multiple spatial and temporal scales. It also demonstrates how isolated and interacting stressors can have a different impact on biotic quality. When performing conservation or management plans, the stressor hierarchy should be considered as a way of prioritizing actions in a cost-effective perspective.
... Major advantages of BRTs are their ability to handle collinearity, nonlinearity, outliers and to automatically identify interactions between explanatory variables (Elith et al., 2008). BRTs therefore constitute a powerful tool to investigate relationships between the environment and ecological responses (Dahm and Hering, 2016;Pilière et al., 2014;Segurado et al., 2016) and hence to identify the impact of multiple pressures in aquatic environments (Feld et al., 2016;Lewin et al., 2014). To model the continuous response variables (the FPM), a BRT model with a Gaussian distribution was selected as loss function for minimizing squared errors. ...
Article
Full-text available
European large rivers are exposed to multiple human pressures and maintained as waterways for inland navigation. However, little is known on the dominance and interactions of multiple pressures in large rivers and in particular inland navigation has been ignored in multi-pressure analyzes so far. We determined the response of ten fish population metrics (FPM, related to densities of diagnostic guilds and biodiversity) to 11 prevailing pressures including navigation intensity at 76 sites in eight European large rivers. Thereby, we aimed to derive indicative FPM for the most influential pressures that can serve for fish-based assessments. Pressures' influences, impacts and interactions were determined for each FPM using bootstrapped regression tree models. Increased flow velocity, navigation intensity and the loss of floodplains had the highest influences on guild densities and biodiversity. Interactions between navigation intensity and loss of floodplains and between navigation intensity and increased flow velocity were most frequent, each affecting 80% of the FPM. Further, increased sedimentation, channelization, organic siltation, the presence of artificial embankments and the presence of barriers had strong influences on at least one FPM. Thereby, each FPM was influenced by up to five pressures. However, some diagnostic FPM could be derived: Species richness, Shannon and Simpson Indices, the Fish Region Index and lithophilic and psammophilic guilds specifically indicate rhithralisation of the potamal region of large rivers. Lithophilic, phytophilic and psammophilic guilds indicate disturbance of shoreline habitats through both (i) wave action induced by passing vessels and (ii) hydromorphological degradation of the river channel that comes along with inland navigation. In European large rivers, inland navigation constitutes a highly influential pressure that adds on top of the prevailing hydromorphological degradation. Therefore, river management has to consider river hydromorphology and inland navigation to efficiently rehabilitate the potamal region of large rives.
... Estas ferramentas poderão projectar vários efeitos dos stresses em vários componentes biológicos dos ecossistemas sob cenários de mudanças climáticas e societais. Embora existam vários exemplos de tais tentativas (por exemplo, Fernandes et al. 2016;Segurado et al., 2016), estes são ainda grandes desafios que os cientistas e gestores enfrentam atualmente. ...
Conference Paper
Full-text available
RESUMO Os sistemas fluviais são essenciais para a vida e têm sido explorados desde sempre. No entanto, com o aumento da população, aumenta a necessidade de água para vários fins e as pressões exercidas sobre os sistemas aquáticos aumentam de forma continua. As alterações climáticas futuras podem fazer com que o ritmo de aumento destas pressões se torne ainda mais intenso e podem mesmo levar ao incremento do número de stresses a agir em determinado sistema. Estes stresses não agem de forma isolada, agem em combinação com outros stresses. Esta combinação pode ser simplesmente aditiva, ou pode mesmo haver uma interação entre dois ou mais stresses em que um stress afeta o modo com o outro stress se expressa no meio e podem ser de três tipos: antagonísticas, sinergísticas ou opostas. A nível de gestão, a unidade natural é a bacia, uma vez que a estrutura hierárquica e direcional das redes hidrográficas faz com que haja uma dependência do que ocorre na bacia de drenagem primária, mas também do que ocorrer na bacia de drenagem a montante. Sendo assim, o que afeta um segmento tem implicações em todos os segmentos a jusante. De modo a conseguir perceber qual a importância de stresses isolados e em interação, este estudo foca-se na bacia do Sorraia e integra modelos de processos e modelos empíricos de modo a conseguir produzir informação com detalhe suficiente para testar o efeito da interação de stresses em vários indicadores bióticos (Macrófitos, Macroinvertebrados, Fitobentos e Peixes). Escolhemos o SWAT (Soil and Water Assessment Tool) como modelo de processos e modelos baseados em árvores de regressão (Boosted Regression Trees e Random Forests) e em modelos lineares mistos (Linear Mixed Models) como modelos empíricos. Os resultados apontam para uma impossibilidade de aplicar medidas estáticas que tenham um efeito fixo em todo o gradiente do stress, uma vez que o próprio stress pode
... Most of the studies aimed at determining climate change impacts on freshwater fish habitat have focused on cold-water fish species (Rahel et al., 1996;Null et al., 2012), on thermal suitability under climate change (Mohseni et al., 2003;Sharma et al., 2007;Ficklin et al., 2013;Brown et al., 2016), or on flow discharge suitability (Hauer et al., 2013;Papadaki et al., 2016;Segurado et al., 2016). Few studies have considered the combined influences of the two factors on habitat of warm-water fish species (Mantua et al., 2010;Wenger et al., 2011a). ...
... Promote thermal-tolerance diversity when prioritizing metapopulations for conservation (Anderson et al.) 15 Manage flows Work with dam managers to optimize reservoir release schedules (Segurado et al.) 16 Restore connectivity Maintain connectivity to inlet streams to promote cooling (Griffiths and Springer Nature journal content, brought to you courtesy of Springer Nature Customer Service Center GmbH ("Springer Nature"). Springer Nature supports a reasonable amount of sharing of research papers by authors, subscribers and authorised users ("Users"), for smallscale personal, non-commercial use provided that all copyright, trade and service marks and other proprietary notices are maintained. ...
Article
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Inland fishes provide important ecosystem services to communities worldwide and are especially vulnerable to the impacts of climate change. Fish respond to climate change in diverse and nuanced ways, which creates challenges for practitioners of fish conservation, climate change adaptation, and management. Although climate change is known to affect fish globally, a comprehensive online, public database of how climate change has impacted inland fishes worldwide and adaptation or management practices that may address these impacts does not exist. We conducted an extensive, systematic primary literature review to identify peer-reviewed journal publications describing projected and documented examples of climate change impacts on inland fishes. From this standardized Fish and Climate Change database, FiCli (pronounced fick-lee), researchers and managers can query fish families, species, response types, or geographic locations to obtain summary information on inland fish responses to climate change and recommended management actions. The FiCli database is updatable and provides access to comprehensive published information to inform inland fish conservation and adaptation planning in a changing climate.
... In recent decades, the number of returning sea trout has declined in many regions of Europe (Ferguson et al., 2019;Harris & Milner, 2006). This population decline was caused by multiple human-related factors and co-stressors during upstream and downstream migrations as well as in the destination habitats (Branco et al., 2012;Dudgeon et al., 2006;Segurado et al., 2016). The cumulative effects of habitat fragmentation and destruction together with discharge regime alterations (Nilsson et al., 2005) have resulted in both a reduction in survival and an increase in the hazards of migration. ...
Article
Effective protection of migratory fish requires long‐term conservation encompassing active restoration and management measures with follow‐up studies. The main findings of long‐term (1995–2019) monitoring of anadromous and potamodromous brown trout Salmo trutta in the River Bidasoa are presented. The main aims were evaluating trout number and median migration date changes, and assessing the effects of management (closures, size limits and quotas, fish stoking) and connectivity measures (fishways and weir removals). Results showed an increasing trend in upstream migrants and decrease in migration dates (earlier migrations). Effects of overlapping measures were difficult to differentiate and were affected by environmental conditions. Statistical analysis demonstrated that fishing closures (2008–2011) and fishway construction (2008) were of great importance, whereas the effect of fish stocking (2003–2012) was variable and unclear. The unexpectedly short‐term effect of three weir removals (2014–2016) may have been due to unusually high discharges in March, affecting the recruitment during previous years.
... Although climate change is expected to decrease functional diversity and result in homogenisation of fish assemblages (Buisson et al., 2013), predicting where and when such alterations are likely to occur is critical for informing management actions aimed at maintaining freshwater ecosystem integrity (Segurado et al., 2016). Though there is still much uncertainty about how climate change will affect hydrology and how hydrology in turn will influence the ecology of stream ecosystems (Buisson & Grenouillet, 2009), there is potential for hydrologic extremes to increase in frequency and magnitude in the future (Jackson et al., 2001;Wu et al., 2014). ...
Article
Understanding the ecological dimensions of drought is critical for predicting how humans and nature will be affected by the expected increased prevalence of drought in the future. We tested life‐history‐based predictions for fish assemblage responses to drought using retrospective analysis of long‐term (1986–2003) fish surveys from two streams in the Appalachian Mountains of North America. We hypothesised that (1) fish assemblage composition would correlate with wet and dry hydrologic conditions as assemblages fluctuated within a loose equilibrium and (2) life‐history traits of fishes would correlate with dry versus wet periods such that opportunistic life‐history strategists would dominate during drought. Results showed fish assemblage changes in Little River and Cataloochee Creek correlated with drought severity measured one year prior to fish surveys. Fish assemblages at all three sampling sites in Little River and two sites in Cataloochee Creek fluctuated within a loose equilibrium, while the remaining two sites in Cataloochee Creek indicated directional change. Life‐history traits for fishes in Cataloochee Creek correlated with one‐year time lag fluctuations in drought caused by opportunistic species being dominant during drought and periodic/equilibrium species dominant during wet periods. Time series plots of fish abundances aggregated by life‐history strategy revealed dominance of opportunistic species emerged at the onset of a multi‐year drought spanning 1998–2004, particularly for the two sites undergoing directional change. Our work provides empirical evidence for theoretical linkages between life history and environmental fluctuations and can ultimately be used to predict stream fish community response to future drought regimes.
... The BRT model provides reliable estimation no matter whether the problem is collinearity and nonlinearity. To our knowledge, BRT model has been mostly used in the ecology and biology (Segurado et al., 2016). This was the one of the few times to couple the BRT and hydrology model to address hydrological cycle problem (Erdal and Karakurt, 2013;Nolan et al., 2015). ...
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Quantifying the relative effect of driving factors on polder hydrological processes and identifying the key factors are prerequisites to adopting effective measures for alleviating flooding, soil loss, and eutrophication. Based on the output results of calibrated Polder Hydrology and Nitrogen modeling System (PHNS) and Polder Hydrology and Phosphorus modeling System (PHPS), the boosted regression tree (BRT) model screened key influential factors and identified the corresponding threshold point values in a typical Chinese agricultural polder. Temporal changes in discharge and soil erosion were most sensitive to weather factors, while those of nitrogen and phosphorus exports were mainly influenced by human management actions. Precipitation was the largest contributor to the temporal variation of discharge (51.5%), soil erosion (69.4%). Vegetation cover and management factor of dryland C2 (34.5%) defined as the ratio of sediment loss from cropland to the corresponding loss from clean-tilled and continuous fallow, and phosphorus fertilization application to paddy field (30.7%) were the two determinants of phosphorus export, whilst surface water level to stop pump drainage (48.2%) had the largest contributions to nitrogen export. Precipitation from 0 to 50 mm/d contributed to a significant increase in discharge, soil erosion and nitrogen and phosphorus exports. Vegetation cover and management factor of paddy field C1 under 0.28 contributed to an elevated risk of nitrogen export, and C2 below 0.34 facilitated soil loss and phosphorus export.
... Increasingly, small and resilient species dominate fish communities, and commercial fisheries catch includes only young and small individuals [28,29]. Meanwhile, the environment of these lakes has also dramatically changed, e.g., hydrological modification due to isolation from the river [30], eutrophication [21], and climate changes [22]. However, the way life-history traits shifting is associated with environmental changes has rarely been investigated and taken into account in fisheries management and conservation in the Yangtze River basin, as is the case in other water bodies [31]. ...
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Understanding long-term changes in life-history traits is central to assessing and managing freshwater fisheries. In this study, we explored how life-history traits have shifted in association with long-term change in population status for a native fish species (freshwater sleeper, Odontobutis sinensis, a by-catch species of shrimp traps) in the middle Yangtze lakes, China. We assessed the life-history traits of the species from Honghu Lake in 2016, where abundance had been dramatically lower following about 60 years of high fishing pressure, and made comparisons to similar data from Liangzi Lake (1957), when fishing intensity was low and abundance was high, and Bao'an Lake (1993-1994), when about 10 years of intense exploitation had occurred and abundance had greatly declined. Modern Honghu Lake sleeper exhibit life-history traits that are substantially more opportunistic compared to both of the historical populations. Modern fish were larger at age-1 and had significantly faster growth rates, a higher prevalence of sexually mature individuals and increased fecundities. Fish from the historical samples were larger and had higher age class diversity and delayed sexual maturation. Combined, the data suggest that faster growth towards early sexual maturation and reduced body sizes are associated with destabilized populations and ecosystems. Similar life-history patterns are common in other fish populations under exploitation. Recovering historic fish life-history dynamics requires conservation management policies aimed at reducing harvest and improving floodplain habitats.
... We focused on an existing protected river network in south-eastern France targeting brown trout (Salmo trutta), which is acknowledged as an indicator species of cold water ecosystems due to its inherent sensitivity to warming temperatures at all stages of its life cycle (Clavero et al., 2017;Kovach et al., 2016;Muhlfeld et al., 2019;Tisseuil et al., 2012). Significant range shifts have already been observed or are forecasted for this species (Kovach et al., 2016), especially at the warm edge of its current distribution (Almodóvar et al., 2012;Filipe et al., 2013;Segurado et al., 2016), including the South of France Lassalle & Rochard, 2009). Our overall objective was to identify spatial priority areas for brown trout and determine how well an expert-designed protected area network represents those priorities. ...
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Aim Estimate the current and future distribution of brown trout and identify priority areas for conservation of the species. Location Rhône River basin and Mediterranean streams. Methods We first developed a spatially explicit species distribution model to estimate the current and future distribution of brown trout for three time horizons (2030, 2055 and 2080) and two climate change scenarios (RCP 4.5 and RCP 8.5). We then performed a prioritization analysis to identify priority areas for brown trout conservation, accounting for: (a) spatial dependencies along the riverine system, (b) several sources of uncertainty arising from climate-related forecasts and (c) different protected area scenarios by comparing hypothetical, optimal protected networks to an actual protected network designed by regional fish experts. Results Future projections of brown trout densities exhibited a general trend towards a gradual range contraction, with a significant risk of extirpation across mountainous regions of low to mid-elevation. Overall, the projected current and future distributions were well-covered by the existing protected network. In addition, up to 70% of the river reaches included in this expert-based protection network were also priorities in the optimal priority set (e.g. the best set of areas to maximize biodiversity protection). Finally, a large proportion of these reaches were invariably identified regardless of climate change scenarios and uncertainties or spatial dependencies. Main conclusions Our analytical approach highlighted priority areas for brown trout conservation which were robust to a set of climate and connectivity assumptions. This core priority network could be further refined by taking into account key fine-scale processes like thermal refugia. Therefore, we advocate for combining computational and expert-based approaches in conservation planning of riverine ecosystems to achieve a relevant consensus between regional-scale management and fine-grain ecological knowledge.
... Changes in hydrology under climate change can lead to shifts in fish habitat suitability and distribution in rivers [71]. For migratory fish species, which shift from different habitats (spawning, feeding, refuge) during their life cycle, this habitat loss is particularly worrisome, particularly in the presence of barriers to fish movement, making it essential to assess how habitat may change in the advent of future flow regimes [16]. ...
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Climate change represents a major challenge for the management of native fish communities in Mediterranean rivers, as reductions in discharge may lead to a decrease in passability through small barriers such as weirs, both in temporary and perennial rivers. Through hydraulic modelling, we investigated how discharges from a large hydropower plant in the Tagus River are expected to affect the passability of native freshwater fish species through a rock weir (Pego, Portugal), equipped with a nature-like fish ramp. We considered not only mean daily discharge values retrieved from nearby gauging stations (1991–2005) for our flow datasets, but also predicted discharge values based on climatic projections (RCP) until the end of the century (2071–2100) for the Tagus River. Results showed that a minimum flow of 3 m3 s−1 may be required to ensure the passability of all species through the ramp and that passability was significantly lower in the RCP scenarios than in the historical scenario. This study suggests that climate change may reduce the passability of native fish species in weirs, meaning that the construction of small barriers in rivers should consider the decreases in discharge predicted from global change scenarios for the suitable management of fish populations.
... A number of recent studies have indicated the impact of modified flows on various species of aquatic ecosystems: from primary producers diatoms and macrophytes [24], butterflies, grasshoppers, vascular plants [25], to birds [26]. However, much of the literature pays particular attention to the multiple impacts of altered flow characteristics on fish communities [27][28][29][30][31][32][33][34][35], because fish are the most affected by hydrological disturbances among other groups of aquatic organisms [36,37]. ...
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Aquatic ecosystems are particularly vulnerable to anthropogenic activity and climate change. The changes in flow regimes in Lithuanian lowland rivers due to the operation of hydropower plants (HPPs) and the impact of altered flow on some fish species have already been studied. The impact of climate change on future natural river runoff and the structure of fish assemblages was also investigated. However, it is still unknown how the combined effect of climate change and flow regulation related to hydropower generation may affect fish assemblages in the downstream river reaches below the Lithuanian HPPs. In this study, the physical habitat modelling system MesoHABSIM was used to simulate spatial and temporal changes in aquatic habitats availability for different fish species under the influence of HPP at different climate change scenarios. Changes in the available habitat were assessed for common fish species in four HPP-affected rivers representing different hydrological regions of Lithuania. The modelling results showed that the operation of HPP under climate change conditions in most rivers could be beneficial for small benthic fish species such as gudgeon Gobio gobio and stone loach Barbatula barbatula. Meanwhile, for larger fish species (e.g., chub Squalius cephalus and vimba Vimba vimba) the alteration in the temporal availability of suitable habitat was relatively higher.
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In the face of multiple habitat alterations originating from both natural and anthropogenic factors, the fast-changing environments pose significant challenges for maintaining ecosystem integrity. Machine learning is a powerful tool for modeling complex non-linear systems through exploratory data analysis. This study aims at exploring a machine learning-based approach to relate environmental factors with fish community for achieving sustainable riverine ecosystem management. A large number of datasets upon a wide variety of eco-environmental variables including river flow, water quality, and species composition were collected at various monitoring stations along the Xindian River of Taiwan during 2005 and 2012. Then the complicated relationship and scientific essences of these heterogonous datasets are extracted using machine learning techniques to have a more holistic consideration in searching a guiding reference useful for maintaining river-ecosystem integrity. We evaluate and select critical environmental variables by the analysis of variance (ANOVA) and the Gamma test (GT), and then we apply the adaptive network-based fuzzy inference system (ANFIS) for an estimation of fish bio-diversity using the Shannon Index (SI). The results show that the correlation between model estimation and the biodiversity index is higher than 0.75. The GT results demonstrate that biochemical oxygen demand (BOD), water temperature, total phosphorus (TP), and nitrate-nitrogen (NO3-N) are important variables for biodiversity modeling. The ANFIS results further indicate lower BOD, higher TP, and larger habitat (flow regimes) would generally provide a more suitable environment for the survival of fish species. The proposed methodology not only possesses a robust estimation capacity but also can explore the impacts of environmental variables on fish biodiversity. This study also demonstrates that machine learning is a promising avenue toward sustainable environmental management in river-ecosystem integrity.
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This study aims to describe pre-reproductive movements of Luciobarbus bocagei and Pseudochondrostoma duriense in a regulated canyon-stretch of the Tormes River (Spain), with high environmental variability, semipermeable barriers, and fishway retrofitting actions. The main objectives were to identify peak migration dates and environmental drivers, test ensemble-learning techniques to model fish migration and propose adaptive management measures. To achieve this, fish movements were 5-year monitored in a stepped fishway and Survival Analysis and Random Forest techniques were used for data analysis and modelling. Results showed that migration occurred in May–July, a wider period than the one previously reported in the literature. Movements were triggered by the increase in water temperature and photoperiod, and were strongly affected by the hydraulic river scenario (water levels and discharge) at the semipermeable barriers. Random Forest was able to include the effect of each barrier and predict accurately timing and number of migrants, classifying and ranking the importance of variables. Moreover, developed models allowed to assess fishway retrofitting actions and to predict positive effects in fish number under new, scheduled and variable environmental flow scenarios. Long-term monitoring together with ensemble-learning methods can allow the definition of cost-effective adaptive management strategies to ensure endemic fish conservation.
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Headwater stream responses to climate change will depend in part on groundwater-surface water exchanges. We used linear modeling techniques to partition likely effects of shallow groundwater seepage and air temperature on stream temperatures for 79 sites in nine focal watersheds using hourly air and water temperature measurements collected during summer months from 2012-2015 in Shenandoah National Park, Virginia, USA. Shallow groundwater effects exhibited more variation within watersheds than between them, indicating the importance of reach-scale assessments and the limited capacity to extrapolate upstream groundwater influences from downstream measurements. Boosted regression tree (BRT) models revealed intricate interactions among geomorphological landform features (stream slope, elevation, network length, contributing area, and channel confinement) and seasonal precipitation patterns (winter, spring, and summer months) that together were robust predictors of spatial and temporal variation in groundwater influence on stream temperatures. The final BRT model performed well for training data and cross-validated samples (correlation = 0.984 and 0.760, respectively). Geomorphological and precipitation predictors of groundwater influence varied in their importance between watersheds, suggesting differences in spatial and temporal controls of recharge dynamics and the depth of the groundwater source. We demonstrate an application of the final BRT model to predict groundwater effects from landform and precipitation covariates at 1075 new sites distributed at 100-m increments within focal watersheds. Our study provides a framework to estimate effects of groundwater seepage on stream temperature in unsampled locations. We discuss applications for climate change research to account for groundwater-surface water interactions when projecting future thermal thresholds for stream biota.
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River fragmentation and alterations in flow and thermal regimes are the main stressors affecting migrating fish, which could be aggravated by climate change and increasing water demand. To assess these impacts and define mitigation measures, it is vital to understand fish movement patterns and the environmental variables affecting them. This study presents a long-term (1995–2019) analysis of upstream migration patterns of anadromous and potamodromous brown trout in the lower River Bidasoa (Spain). For this, captures in a monitoring station were analyzed using Survival Analysis and Random Forest techniques. Results showed that most upstream movements of potamodromous trout occurred in October–December, whereas in June–July for anadromous trout, although with differences regarding sex and size. Both, fish numbers and dates varied over time and were related to the environmental conditions, with different influence on each ecotype. The information provided from comparative studies can be used as a basis to develop adaptive management strategies to ensure freshwater species conservation. Moreover, studies in the southern distribution range can be crucial under climate warming scenarios, where species are expected to shift coldwards.
Chapter
Rivers of the Iberian Peninsula have been influenced for a long time by intensive human use. This, together with a largely unpredictable climate and scarce water resources, resulted in a large number of hydraulic infrastructures, with more than 1000 large reservoirs spread throughout Iberian watercourses. Although climatic variation is high, most of the Iberian Peninsula is semi-arid in terms of rainfall, with a northeast to south gradient in aridity, and many streams and rivers in the Mediterranean basin are intermittent. The main Iberian rivers cross the Peninsula either east to west (Duero, Tagus, Guadiana) into the Atlantic, or west to east (Ebro) into the Mediterranean. The Iberian rivers are subject to strong hydromorphological alterations as well as widespread point-source and diffuse pollution. In addition to eutrophication in a large number of waterbodies, organic contaminants such as pesticides, and pharmaceutical and industrial products cause multiple stress and threaten a rich biodiversity. Predictions for climate change indicate that the flow regime of most Mediterranean watercourses will be affected ecologically, especially under future scenarios of increasing human land occupation.
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Freshwater fish biodiversity is experiencing an alarming decline worldwide. Understanding the main factors behind its deterioration is a key step for ecosystem restoration. In this work, large‐scale and long‐term data were used to identify the causes of the decline of native species richness in Castilla‐La Mancha. This region in central Spain covers part of six river basins belonging to four of the 11 biogeographical provinces for freshwater fish in the Iberian Peninsula. Firstly, we built a dataset that associates the presence of several fish species and a wide range of environmental variables (e.g. hydrological and hydromorphological indicators, land use classes, presence of alien fish species) at selected river sites for two different time periods (1980–2000 and 2001–2020). Secondly, we conducted an exploratory data analysis to identify possible temporal trends in the dataset. Finally, we applied the random forest algorithm to predict the response of different ecological guild‐based metrics of fish richness to the selected variables. The exploratory data analysis revealed a decrease in native fish species richness in 74% of the area studied. There was no sustained temporal trend for stressor variables, except for the number of alien species, which increased in most river sites (63%). The models of the richness of native rheophilic, native intolerant, alien rheophilic, and alien limnophilic species performed satisfactorily. Magnitude of maximum discharge, presence of alien species, land use in the catchment area and altitude were the most important predictors of richness of native intolerant and rheophilic species. Alien limnophilic species proved to be sensitive to variables related to flow regime alteration, such as the presence of dams and the number of river flow reversals, while a less degraded habitat was found to be favourable to alien rheophilic species. The results suggest that the cumulative effect of persistent altered flow regimes and water pollution, coupled with a strong increase in the number of alien species, have led to the decline of native species in the area studied. The restoration of near‐natural magnitudes of high flows when implementing environmental flows emerged as a key measure to restore ecosystem integrity. Starting from a long‐term and large‐scale dataset, this study provides new, quantitative insights into stressor–ecosystem relationships in rivers and could inform future environmental policy initiatives because it has identified the main factors leading to native fish decline and alien fish proliferation. Our findings emphasise the importance of considering metrics based on fish assemblage composition and ecological functional groups in order to disentangle the effects of stressors on fish communities.
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Climate change will induce alterations in the hydrological and landscape patterns with effects on riparian ecotones. In this study we assess the combined effect of an extreme climate and land-use change scenario on riparian woody structure and how this will translate into a future risk of riparian functionality loss. The study was conducted in the Tâmega catchment of the Douro basin. Boosted Regression Trees (BRT) were used to model two riparian landscape indicators related with the degree of connectivity (Mean Width) and complexity (Area Weighted Mean Patch Fractal Dimension). Riparian data were extracted by planimetric analysis of high spatial-resolution Word Imagery Layer (ESRI). Hydrological, climatic and land-use variables were obtained from available datasets and generated with process-based modeling using current climate data (2008-2014), while also considering the high-end RCP8.5 climate-change and “Icarus” socio-economic scenarios for the 2046-2065 time slice. Our results show that hydrological and land-use changes strongly influence future projections of riparian connectivity and complexity, albeit to diverse degrees and with differing effects. A harsh reduction in average flows may impair riparian zones while an increase in extreme rain events may benefit connectivity by promoting hydrologic dynamics with the surrounding floodplains. The expected increase in broad-leaved woodlands and mixed forests may enhance the riparian galleries by reducing the agricultural pressure on the area in the vicinity of the river. According to our results, 63% of river segments in the Tâmega basin exhibited a moderate risk of functionality loss, 16% a high risk, and 21% no risk. Weaknesses and strengths of the method are highlighted and results are discussed based on a resilience perspective with regard to riparian ecosystems.
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Thermal habitat selection and behavior by young-of-year brook trout Salvelinus fontinalis was studied in a lake in central Ontario, Canada. In May, trout foraged actively within 2 m of shore in the warmest water available (∼15°C). In early June, trout foraged near the bottom within 4 m of shore, where bottom water temperatures were near, or at, the upper thermal tolerance, for trout, of 20°C. In July, when ambient water temperatures ranged from 23°C to 27°C, trout lay on the bottom in the coldest water available (18–20°C) in discrete areas 3–8 m from shore. Flow rate of cold groundwater accounted for 87% of the variance in trout density in these areas, and the data suggest that a minimum flow rate of 125 mL·m⁻²·min⁻¹ is required for trout to take up station. When trout were displaced from holding positions, sites with greater groundwater flow were more quickly reoccupied by trout than sites with lower flow. Experimentally created trough-like depressions at these sites attracted higher densities of trout than the same sites with their natural topography and restricted trout distribution to within each depression. Preliminary behavioral observations suggest that trout lie on the bottom and defend cool microhabitats at the expense of daytime feeding. These results suggest that areas with cold groundwater may be a limiting resource for young-of-year brook trout in the littoral zone during summer, and resource managers should consider protecting such areas from lakeshore development and logging.
Technical Report
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Digital data on river networks, lakes and drainage basins (catchments) are an important pre-requisite for modelling hydrological processes, including the analysis of pressures and their impact on water resources. Datasets covering extensive areas such as the European continent are especially important for mapping and monitoring activities of European institutions. The European Water Framework Directive, for example, explicitly asks for the setup of Geographical Information Systems including detailed layers of water bodies (rivers, lakes, wetlands) and their drainage basins, while the European Environment Agency (EEA) requires adequate river and catchment data for monitoring the status and trends of water resources over the entire pan-European continent. The Catchment Characterisation and Modelling (CCM) activity of the European Commissions’ Joint Research Centre has developed advanced methodologies to derive adequate layers from digital elevation data and ancillary information. Drainage density has been modelled through a landscape typology and lakes have been considered during river mapping. Finally, the database was enriched with a set of attributes describing important characteristics of catchments and river segments. The resulting database covers the entire pan-European continent from the Atlantic to the Urals and from the Mediterranean to northern Scandinavia, including the Atlantic islands and Turkey. The use of homogeneous input data and their analysis with the same methodology ensures data with comparable and well documented characteristics (e.g., level of detail, geometric quality, attributes) over the entire area. This report details the background for developing this database, describes the methodology implemented, and discusses the strengths and limitations of the approach. It is intended to inform decision makers, scientists and technicians involved in water-related issues about the main characteristics of this product as well as on its potential for different applications.
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Assemblages of native stream fishes in California show a remarkable ability to resist invasion by introduced fishes as long as the streams are relatively undisturbed by human activity. Previous studies had indicated a high degree of spatial (microhabitat) segregation among the native fishes, which was confirmed by a principal components analysis of microhabitat use data from Deer Creek, a tributary of the Sacramento River. A null modelling study using the same data set was performed to see if competition was a major force structuring the assemblage, because theoretical studies had indicated that a competitively structured assemblage should be most able to resist invasions. The null models indicated that competition was not the major structuring force, so it is likely the assemblages are structured through a combination of morphological specialization (reflecting evolutionary history), predation, and some competition. The assemblages resist invasion through both environmental and biotic factors. Predation seems to be an especially important biotic factor.
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Climate change is expected to bring about profound rearrangement of ecological communities by affecting individual species distributions. The resulting communities arise from the idiosyncratic responses of species to future changes, which ultimately relate to both shrinking and expanding species ranges. While spatial patterns of colonisation and extirpation events have received great attention, the identification of specific drivers remains poorly explored. This study aims to investigate the relative contribution of species gain and loss to the turnover of fish assemblages in French rivers under future climate change, and to identify their principal drivers. Future projections of potential habitat suitability in 2080 derived from species distribution models for 40 fish species showed that colonisations and extirpations could play counterbalancing roles in the reshuffling of communities. Simultaneously, these two processes exhibited patchy spatial patterns, segregated along the longitudinal and altitudinal gradients, resulting in dramatic species turnover of ∼ 60% of the current composition of species assemblages. Beyond the effect of topographic location, colonisations were found to be driven by temperature seasonality while extirpations were affected by modifications in both thermal and precipitation regimes.These results generate the possibility of developing ecosystem-based management tools focused on the early identification of areas where particular species may be sensitive to climate changes. Disentangling the drivers of colonisation and extirpation processes provides ready-to-use information that may be easily integrated into conservation planning. This information could be used to identify potential hotspots of species gain and loss and to then compare these hotspots with newly favourable areas so as to consider their actual accessibility in order to facilitate future range shifts.
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Within the period 1978–2006, climate change and human interferences produced noticeable impacts on the hydrology of a small watershed, known as the Beça River basin. Climate change was characterized by a persistent raise in temperature (+0.78 °C decade−1) and a drop in the annual rainfall (−300 mm decade−1). Human interferences included the construction of a dam for electric power generation, in 1998, and since then the transference of Beça River flows from the dam lake to the adjacent Tâmega River. The impacts on catchment hydrology comprised a decline of aquifer hydraulic conductivity and effective porosity, by approximately one order of magnitude, related to a water table lowering of about 17 m within the bedrock aquifer composed of weathered and fractured Hercynian granites and Paleozoic metassediments and of saprolite layers derived therefrom. Aquifer property estimates were compared across spatial scales, namely the Beça River and the nested sub-basins scale. Sub-basin aquifers are more porous and permeable than the basin aquifer because corresponding hydraulic circuits are shallower. Comparisons were also made between aquifer properties derived from measured and simulated stream flows, which revealed effects of modeling uncertainties on the results. River flows also suffered a substantial decrease in the course of climate change and human interference, especially the overland flows (4/5 decrease) and the base flows (2/3 decrease). The inter flows were less affected (1/3 decrease) because they were partly fed with water from the aquifer storage, which in turn underwent depletion. The hydrologic changes in the Beça River basin anticipate important impacts on the local use of natural water. In this context, the aforementioned water table lowering may have caused limited access to shallow groundwater for activities such as crop irrigation from dug wells, whereas the severe decline in overland flows and base flows had certainly reduced the availability of surface water for the refilling of dam lakes and of groundwater for the supply of public and private boreholes.
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Much has been written about the influence of exotic or nonindigenous species on natural habitats and communities of organisms, but little is known of the physical or biological conditions that lead to successful invasion of native habitats and communities by exotics. We studied invasivity factors in headwater streams of the Susquehanna River West Branch, which drains portions of the northern Appalachian Plateau. A replicated (two major tributaries) 3 × 3 factorial design was used to determine landscape effects of size (stream order) and quality (land use) on abiotic (physical and chemical) and biotic (fish community structure and function) stream attributes. Seven (21%) of thirty-four fish species (brown trout, common carp, mimic shiner, bluegill, smallmouth bass, fantail darter, and banded darter) collected in the eighteen streams sampled were nonindigenous to the basin. Watershed size (stream orders 1, 3, and 5) significantly affected stream geomorphologic and habitat variables (gradient, width, depth, current velocity, diel water temperature, bank overhang, canopy cover, and woody debris density) but not water-quality variables, while land use in watersheds (conservation, mining, and agriculture) significantly affected measured water-quality variables (alkalinity and concentrations of manganese, calcium, chloride, nitrate, and total dissolved solids) but not stream physical or habitat quality. Both watershed size and land use affected fish-community variables such as presence of particular species, species density, species diversity, tolerance diversity, and mean fish size, but in both cases the effect was transparent to native-origin status of fish species. No relationships were found between occurrence of nonindigenous species in watersheds and trophic structure or functional diversity. Therefore, the hypothesis that reduced species diversity increases vulnerability to nonindigenous species was not supported. However, the spatial variation associated with both water-quality and habitat-quality factors was greater in streams with mixed (those with nonindigenous species) than with exclusively native assemblages. These findings suggest that the mechanism for successful invasion by nonindigenous or exotic species is through change in water or habitat quality associated with human or natural disturbances, such as agriculture and mining activities in watersheds. Biotic factors appear to play no or a lesser role in the invasibility of northern Appalachian lotic systems.
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Major rivers worldwide have experienced dramatic changes in flow, reducing their natural ability to adjust to and absorb disturbances. Given expected changes in global climate and water needs, this may create serious problems; including loss of native biodiversity and risks to ecosystems and humans from increased flooding or water shortages. Here, we project river discharge under different climate and water withdrawal scenarios and combine this with data on the impact of dams on large river basins to create global maps illustrating potential changes in discharge and water stress for dam-impacted and free-flowing basins. The projections indicate that every populated basin in the world will experience changes in river discharge and many will experience water stress. The magnitude of these impacts is used to identify basins likely and almost certain to require proactive or reactive management intervention. Our analysis indicates that the area in need of management action to mitigate the impacts of climate change is much greater for basins impacted by dams than for basins with free-flowing rivers. Nearly one billion people live in areas likely to require action and approximately 365 million people live in basins almost certain to require action. Proactive management efforts will minimize risks to ecosystems and people and may be less costly than reactive efforts taken only once problems have arisen.
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Stream habitat complexity is correlated with fish species diversity in selected Indiana and Panama streams. Habitat diversity was measured along 3 dimensions judged important to a wide range of fish groups and applicable to many stream conditions: stream depth, bottom type, and current.I ncreasingc ommunitya nd habitatd iversityf ollowed stream-orderg radients.N aturals treams supported fish communities of high species diversity which were seasonally more stable than the lower-diversity communities of modified streams. After disturbances such as channelization, seasonal peaks in species diversity attain levels typical of undisturbed streams. Because seasonal changes in stream quality are high, the stability of the fish community is lower in modified than in natural streams. The general correlation between habitat characteristics and presence and absence of fish species suggests that most fishes of small streams are habitat specialists.
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The effects of climate warming on the thermal habitat of 57 species of fish of the U.S. were estimated using results for a doubling of atmospheric carbon dioxide that were predicted by the Canadian Climate Center general circulation model. Baseline water temperature conditions were calculated from data collected at 1,700 U.S. Geological Survey stream monitoring stations across the U.S. Water temperatures after predicted climate change were obtained by multiplying air temperature changes by 0.9, a factor based on several field studies, and adding them to baseline water temperatures at stations in corresponding grid cells. Results indicated that habitat for cold and cool water fish would be reduced by ~50%, and that this effect would be distributed throughout the existing range of these species. Habitat losses were greater among species with smaller initial distributions and in geographic regions with the greatest warming (e.g. the central Midwest). Results for warm water fish habitat were less certain because of the poor state of knowledge regarding their high and low temperature tolerances; however, the habitat of many species of this thermal guild likely will also be substantially reduced by climate warming, whereas the habitat of other species will be increased.
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Stream fish assemblage data for 34 sites in Wisconsin and Minnesota were obtained from archived sources and were used in conjunction with long-term hydrological data to test the hypothesis that functional organization of Ash communities is related to hydrological variability. For each of the 106 species present in the data set, six categories of species traits were derived to describe habitat, trophic, morphological, and tolerance characteristics. A hierarchical clustering routine was used to identify two functionally similar groups of assemblages defined in terms of species presence/absence, Hydrological factors describing streamflow variability and predictability, as well as frequency and predictability of high flow and low flow extremes, were derived for each of the 34 sites and employed to explain differences among the functionally defined groups. Canonical discriminant analysis revealed that the hydrological data could clearly separate the two ecologically defined groups of assemblages, which were associated with either hydrologically variable streams (high coefficient of variation of daily flows, moderate frequency of spates) or hydrologically stable streams (high predictability of daily flows, stable baseflow conditions). Discriminant functions based on hydrological information classified the 34 fish assemblages into the correct ecological group with 85% accuracy. Assemblages from hydrologically variable sites had generalized feeding strategies, were associated with silt and general substrata, were characterized by slow-velocity species with headwater affinities, and were tolerant to silt. Proportions of species traits present at the 34 sites were regressed against an index of hydrological stability derived from a principal components analysis to test the hypothesis that functional organization of assemblages varied across a gradient of hydrological stability. Results were complementary with the discriminant analysis. Findings were in general agreement with theoretical predictions that variable habitats should support resource generalists while stable habitats should be characterized by a higher proportion of specialist species. Several species of fish were identified as indicative of the variable-stable hydrological gradient among stream sites, A taxonomic analysis showed strong geographic patterns in species composition of the 34 assemblages. However, zoogeographic constraints did not explain the observed relationship between stream hydrology and functional organization of fish assemblages, The strong hydrological-assemblage relations found in the 34 midwestern sites suggest that hydrological factors are significant environmental variables influencing fish assemblage structure, and that hydrological alterations induced by climate change (or other anthropogenic disturbances) could modify stream fish assemblage structure in this region.
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Freshwater fishes are highly vulnerable to human-caused climate change. Because quantitative data on status and trends are unavailable for most fish species, a systematic assessment approach that incorporates expert knowledge was developed to determine status and future vulnerability to climate change of freshwater fishes in California, USA. The method uses expert knowledge, supported by literature reviews of status and biology of the fishes, to score ten metrics for both (1) current status of each species (baseline vulnerability to extinction) and (2) likely future impacts of climate change (vulnerability to extinction). Baseline and climate change vulnerability scores were derived for 121 native and 43 alien fish species. The two scores were highly correlated and were concordant among different scorers. Native species had both greater baseline and greater climate change vulnerability than did alien species. Fifty percent of California's native fish fauna was assessed as having critical or high baseline vulnerability to extinction whereas all alien species were classified as being less or least vulnerable. For vulnerability to climate change, 82% of native species were classified as highly vulnerable, compared with only 19% for aliens. Predicted climate change effects on freshwater environments will dramatically change the fish fauna of California. Most native fishes will suffer population declines and become more restricted in their distributions; some will likely be driven to extinction. Fishes requiring cold water (
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Understanding the ability of species to shift their distribution ranges in response to climate change is crucial for conservation biologists and resources managers. Although freshwater ecosystems include some of the most imperilled fauna worldwide, such range shifts have been poorly documented in streams and rivers and have never been compared to the current velocity of climate change. Based on national monitoring data, we examined the distributional changes of 32 stream fish species in France and quantified potential time lags in species responses, providing a unique opportunity to analyze range shifts over recent decades of warming in freshwater environments. A multi-facetted approach, based on several range measures along spatial gradients, allowed us to quantify range shifts of numerous species across the whole hydrographic network between an initial period (1980–1992) and a contemporary one (2003–2009), and to contrast them to the rates of isotherm shift in elevation and stream distance. Our results highlight systematic species shifts towards higher elevation and upstream, with mean shifts in range centre of 13.7 m decade−1 and 0.6 km decade−1, respectively. Fish species displayed dispersal-driven expansions along the altitudinal gradient at their upper range limit (61.5 m decade−1), while substantial range contractions at the lower limit (6.3 km decade−1) were documented for most species along the upstream–downstream gradient. Despite being consistent with the geographic variation in climate change velocities, these patterns reveal that the majority of stream fish have not shifted at a pace sufficient to track changing climate, in particular at their range centre where range shifts lag far behind expectation. Our study provides evidence that stream fish are currently responding to recent climate warming at a greater rate than many terrestrial organisms, although not as much as needed to cope with future climate modifications.
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1. Climate change could be one of the main threats faced by aquatic ecosystems and freshwater biodiversity. Improved understanding, monitoring and forecasting of its effects are thus crucial for researchers, policy makers and biodiversity managers. 2. Here, we provide a review and some meta-analyses of the literature reporting both observed and predicted climate-induced effects on the distribution of freshwater fish. After reviewing three decades of research, we summarise how methods in assessing the effects of climate change have evolved, and whether current knowledge is geographically or taxonomically biased. We conducted multispecies qualitative and quantitative analyses to find out whether the observed responses of freshwater fish to recent changes in climate are consistent with those predicted under future climate scenarios. 3. We highlight the fact that, in recent years, freshwater fish distributions have already been affected by contemporary climate change in ways consistent with anticipated responses under future climate change scenarios: the range of most cold-water species could be reduced or shift to higher altitude or latitude, whereas that of cool-and warm-water species could expand or contract. 4. Most evidence about the effects of climate change is underpinned by the large number of studies devoted to cold-water fish species (mainly salmonids). Our knowledge is still incomplete, however, particularly due to taxonomic and geographic biases. 5. Observed and expected responses are well correlated among families, suggesting that model predictions are supported by empirical evidence. The observed effects are of greater magnitude and show higher variability than the predicted effects, however, indicating that other drivers of changes may be interacting with climate and seriously affecting freshwater fish. 6. Finally, we suggest avenues of research required to address current gaps in what we know about the climate-induced effects on freshwater fish distribution, including (i) the need for more long-term data analyses, (ii) the assessment of climate-induced effects at higher levels of organisation (e.g. assemblages), (iii) methodological improvements (e.g. accounting for uncer-tainty among projections and species' dispersal abilities, combining both distributional and empirical approaches and including multiple non-climatic stressors) and (iv) systematic confrontation of observed versus predicted effects across multi-species assemblages and at several levels of biological organisation (i.e. populations and assemblages).
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The current freshwater fish fauna crisis is such that natural resource managers urgently need to identify priorities and understand the management consequences of actions aimed at maximizing the preservation of biodiversity. Freshwater research is often poorly linked to conservation ecology; and interdisciplinary studies illustrating examples of freshwater ecosystem conservation are scarce. The Iberian Peninsula has a long history of anthropogenic disturbance that has led to the poor conservation status of its ichthyofauna, with 52 % of species now catalogued as critically endangered, endangered or vulnerable, according to UICN criteria. This paper gives an overview of the main threats (habitat degradation, hydrological alterations and exotic spe-cies) that have altered the function and connectivity of Iberian rivers. Case-study examples are provided to analyse the repercussions of these threats and the management actions planned or already performed in these systems. The interaction of many threats is responsible for native fish decline. However, fresh-water managers and researchers should not let the trees prevent them from seeing the overall wood, when seeking to achieve practical solutions with the best balanced cost benefit and the collaboration of all ecosystem researchers and stakeholders. Conservation efforts should be focused on the preservation of ecological processes, in order to achieve the goals of the Water Framework Directive and guarantee the conservation of Iberian native fish species.
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Summary Drought is a natural disturbance of aquatic ecosystems and can be a major factor in structuring aquatic communities. For individuals, populations and communities to persist in disturbed environments, they must have refuge from disturbance or disturbance must be minimal. Refugia convey spatial and temporal resistance or resilience in the face of disturbance, but the role of refugia in aquatic systems remains poorly understood. We review available literature on aquatic refugia for fishes in order to synthesise current knowledge and provide suggestions for needed research. Our objectives were to clarify definitions of disturbance and refugia in the context of drought in aquatic systems, review how refuge habitats influence fish community structure, and consider the potential impact of refugia on fish population and community dynamics during drought. Droughts cause a decrease in surface area/volume and an increase in extremes of physical and chemical water quality parameters. These conditions are linked with biotic interactions that structure the community of fishes residing in low-flow or dry season refugia by increasing mortality rates, decreasing birth rates and/or increasing migration rates. Many aquatic organisms seek refuge from disturbance and/or have adaptations (e.g. physiological tolerance) that provide refuge. Drought in aquatic systems leads to shifts in refugia spacing and connectance at multiple spatial and temporal scales. Refuge size, disturbance intensity, and mobility of organisms is predicted to play a large role in population persistence. We expect that refuge habitats will experience net immigration during drying and net emigration after rewetting, with the opposite occurring in surrounding habitat patches. Population dynamics of fishes using refugia during drought are best modelled by modified source-sink dynamics, but dynamics are likely to change with spatial scale.
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Recent observations show that human-induced climate change (CC) and land transformation (LT) are threatening wildlife globally. Thus, there is a need to assess the sensitivity of wildlife on large spatial scales and evaluate whether national parks (NPs), a key conservation tools used to protect species, will meet their mandate under future CC and LT conditions. Here, we assess the sensitivity of 277 mammals at African scale to CC at 10′ resolution, using static LT assumptions in a ‘first-cut’ estimate, in the absence of credible future LT trends. We examine the relationship between species' current distribution and macroclimatic variables using generalized additive models, and include LT indirectly as a filter. Future projections are derived using two CC scenarios (for 2050 and 2080) to estimate the spatial patterns of loss and gain in species richness that might ultimately result. We then apply the IUCN Red List criteria A3(c) of potential range loss to evaluate species sensitivity. We finally estimate the sensitivity of 141 NPs in terms of both species richness and turnover. Assuming no spread of species, 10–15% of the species are projected to fall within the critically endangered or extinct categories by 2050 and between 25% and 40% by 2080. Assuming unlimited species spread, less extreme results show proportions dropping to approximately 10–20% by 2080. Spatial patterns of richness loss and gain show contrasting latitudinal patterns with a westward range shift of species around the species-rich equatorial zone in central Africa, and an eastward shift in southern Africa, mainly because of latitudinal aridity gradients across these ecological transition zones. Xeric shrubland NPs may face significant richness losses not compensated by species influxes. Other NPs might expect substantial losses and influxes of species. On balance, the NPs might ultimately realize a substantial shift in the mammalian species composition of a magnitude unprecedented in recent geological time. To conclude, the effects of global CC and LT on wildlife communities may be most noticeable not as a loss of species from their current ranges, but instead as a fundamental change in community composition.
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In recent years an increasing number of studies have been published reporting observations of adapted behaviour and shifting species ranges of plant and animal species due to recent climate warming. Are these `fingerprints' of climate change? An international conference was organised to bring together scientists from different continents with different expertise but sharing the same issue of climate change impact studies. Ecologists, zoologists, and botanists exchanged and discussed the findings from their individual field of research. The present book is an international collection of biological signs of recent climate warming, neither based only on computer models nor on prediction for the future, but mainly on actually occurring changes in the biosphere such as adapted behaviour or shifts in the ranges of species. `Fingerprints' of Climate Change presents ecological evidence that organisms are responding to recent global warming. The observed changes may foreshadow the types of impacts likely to become more frequent and widespread with continued warming.
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Function estimation/approximation is viewed from the perspective of numerical optimization iti function space, rather than parameter space. A connection is made between stagewise additive expansions and steepest-descent minimization. A general gradient descent "boosting" paradigm is developed for additive expansions based on any fitting criterion. Specific algorithms are presented for least-squares, least absolute deviation, and Huber-M loss functions for regression, and multiclass logistic likelihood for classification. Special enhancements are derived for the particular case where the individual additive components are regression trees, and tools for interpreting such "TreeBoost" models are presented. Gradient boosting of regression trees produces competitives highly robust, interpretable procedures for both regression and classification, especially appropriate for mining less than clean data. Connections between this approach and the boosting methods of Freund and Shapire and Friedman, Hastie and Tibshirani are discussed.
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1.Freshwater systems are severely impacted by connectivity reduction due to the construction of dams and weirs. The breach of this longitudinal connectivity imperils freshwater fish species worldwide. There is thus an increasing need for numerical tools that help decision-makers correctly allocate resources to prioritize restoration actions.2.This study provides a methodology for prioritizing the removal of barriers. It is based on spatial graphs, which represent structural units as nodes and relationships between nodes as links, and uses habitat suitability modelling (Boosted Regression Trees) to weight nodes. To exemplify the application of this procedure we used the Tagus River network and evaluated the impact of the dams (29 built between 1928 and 2004) on the occurrence of each of two fish species (iberian barbel Luciobarbus bocagei – representing large potamodromous fish; and southern iberian chub Squalius pyrenaicus – representing small water-column residents) and on the combination of both.3.Results show that dam construction on the Tagus was responsible for a 48.4–54.4% reduction in river connectivity for different fish species. Actions to promote connectivity in just seven of the dams would increase connectivity by 35.0–37.2%.4.The removal of a single barrier chosen through prioritization had a greater overall connectivity increase than the random removal of seven barriers.5.Synthesis and applications. The proposed prioritisation method, using spatial graphs and habitat suitability modelling, makes it possible to model the impact of the removal or placement of an insurmountable barrier on the overall functional connectivity of a river network, facilitating resource allocation and minimising the impact of new barrier implementation.This article is protected by copyright. All rights reserved.
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With the rise of new powerful statistical techniques and GIS tools, the development of predictive habitat distribution models has rapidly increased in ecology. Such models are static and probabilistic in nature, since they statistically relate the geographical distribution of species or communities to their present environment. A wide array of models has been developed to cover aspects as diverse as biogeography, conservation biology, climate change research, and habitat or species management. In this paper, we present a review of predictive habitat distribution modeling. The variety of statistical techniques used is growing. Ordinary multiple regression and its generalized form (GLM) are very popular and are often used for modeling species distributions. Other methods include neural networks, ordination and classification methods, Bayesian models, locally weighted approaches (e.g. GAM), environmental envelopes or even combinations of these models. The selection of an appropriate method should not depend solely on statistical considerations. Some models are better suited to reflect theoretical findings on the shape and nature of the species’ response (or realized niche). Conceptual considerations include e.g. the trade-off between optimizing accuracy versus optimizing generality. In the field of static distribution modeling, the latter is mostly related to selecting appropriate predictor variables and to designing an appropriate procedure for model selection. New methods, including threshold-independent measures (e.g. receiver operating characteristic (ROC)-plots) and resampling techniques (e.g. bootstrap, cross-validation) have been introduced in ecology for testing the accuracy of predictive models. The choice of an evaluation measure should be driven primarily by the goals of the study. This may possibly lead to the attribution of different weights to the various types of prediction errors (e.g. omission, commission or confusion). Testing the model in a wider range of situations (in space and time) will permit one to define the range of applications for which the model predictions are suitable. In turn, the qualification of the model depends primarily on the goals of the study that define the qualification criteria and on the usability of the model, rather than on statistics alone.
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There is little understanding of how climate change will impact potamodromous freshwater fishes. Since the mid 1970s, a decline in annual rainfall in south-western Australia (a globally recognized biodiversity hotspot) has resulted in the rivers of the region undergoing severe reductions in surface flows (ca. 50%). There is universal agreement amongst Global Climate Models that rainfall will continue to decline in this region. Limited data are available on the movement patterns of the endemic freshwater fishes of south-western Australia or on the relationship between their life histories and hydrology. We used this region as a model to determine how dramatic hydrological change may impact potamodromous freshwater fishes. Migration patterns of fishes in the largest river in south-western Australia were quantified over a 4year period and were related to a number of key environmental variables including discharge, temperature, pH, conductivity and dissolved oxygen. Most of the endemic freshwater fishes were potamodromous, displaying lateral seasonal spawning migrations from the main channel into tributaries, and there were significant temporal differences in movement patterns between species. Using a model averaging approach, amount of discharge was clearly the best predictor of upstream and downstream movement for most species. Given past and projected reductions in surface flow and groundwater, the findings have major implications for future recruitment rates and population viabilities of potamodromous fishes. Freshwater ecosystems in drying climatic regions can only be managed effectively if such hydro-ecological relationships are considered. Proactive management and addressing existing anthropogenic stressors on aquatic ecosystems associated with the development of surface and groundwater resources and land use is required to increase the resistance and resilience of potamodromous fishes to ongoing flow reductions.
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Species inhabiting fresh waters are severely affected by climate change and other anthropogenic stressors. Effective management and conservation plans require advances in the accuracy and reliability of species distribution forecasts. Here, we forecast distribution shifts of Salmo trutta based on environmental predictors and examine the effect of using different statistical techniques and varying geographical extents on the performance and extrapolation of the models obtained. Watercourses of Ebro, Elbe and Danube river basins (c. 1,041,000 km2; Mediterranean and temperate climates, Europe). The occurrence of S. trutta and variables of climate, land cover and stream topography were assigned to stream reaches. Data obtained were used to build correlative species distribution models (SDMs) and forecasts for future decades (2020s, 2050s and 2080s) under the A1b emissions scenario, using four statistical techniques (generalised linear models, generalised additive models, random forest, and multivariate adaptive regression). The SDMs showed an excellent performance. Climate was a better predictor than stream topography, while land cover characteristics were not necessary to improve performance. Forecasts predict the distribution of S. trutta to become increasingly restricted over time. The geographical extent of data had a weak impact on model performance and gain/loss values, but better species response curves were generated using data from all three basins collectively. By 2080, 64% of the stream reaches sampled will be unsuitable habitats for S. trutta, with Elbe basin being the most affected, and virtually no new habitats will be gained in any basin. More reliable predictions are obtained when the geographical data used for modelling approximate the environmental range where the species is present. Future research incorporating both correlative and mechanistic approaches may increase robustness and accuracy of predictions.
Article
AimNortherly shifts, related to recent climate warming, have been observed in the distributions of taxa in many ecosystems and ecological roles. However, significant variation occurs among species in the magnitude of these shifts. Few studies have investigated the effects of climate warming on the distributions of freshwater species. LocationA total of 1527 lakes across Ontario, Canada. Methods We used contemporary and historical survey data to examine the relationships between species occurrences and climate and to measure the magnitude and direction of northern range-boundary shifts in 13 warm and coolwater freshwater fishes. We also tested whether range-boundary shifts differed between baitfishes and sportfishes. We then related differences in species range-boundary shifts to species traits including those related to dispersal, reproduction and ecological niche breadth. ResultsMany fishes are now more likely to occur in lakes where climate was historically limiting. Sportfish northern range boundaries shifted northward significantly over nearly 30years at a rate of approximately 12.9-17.5km per decade depending on the measure used; in contrast, baitfish northern range boundaries often shifted southward. Also, species traits explained much of the variation in species range boundaries. Main conclusionsThe northern range boundaries of warm and coolwater sportfishes in Ontario lakes appear to be shifting northward as expected based on observed climate warming. These species are shifting at rates comparable with taxa in marine and terrestrial ecosystems around the globe. In contrast to expectations, the northern range boundaries of small-bodied baitfishes appear to often contract southward. Differences in range shifts by sportfishes and baitfishes may be related to dispersal, particularly by anglers and/or their ecological roles. Understanding the range-boundary shifts underway in Ontario lake communities will help predict future shifts by freshwater fishes.
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Climate warming will adversely affect Canadian water quality and water quantity. The magnitude and timing of river flows and lake levels and water renewal times will change. In many regions, wetlands will disappear and water tables will decline. Habitats for cold stenothermic organisms will be reduced in small lakes. Warmer temperatures will affect fish migrations in some regions. Climate will interact with overexploitation, dams and diversions, habitat destruction, non-native species, and pollution to destroy native freshwater fisheries. Acute water problems in the United States and other parts of the world will threaten Canadian water security. Aquatic communities will be restructured as the result of changes to competition, changing life cycles of many organisms, and the invasions of many non-native species. Decreased water renewal will increase eutrophication and enhance many biogeochemical processes. In poorly buffered lakes and streams, climate warming will exacerbate the effects of acid precipitation. Decreases in dissolved organic carbon caused by climate warming and acidification will cause increased penetration of ultraviolet radiation in freshwaters. Increasing industrial agriculture and human populations will require more sophisticated and costly water and sewage treatment. Increased research and a national water strategy offer the only hope for preventing a freshwater crisis in Canada.
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We sketch an iterative assessment process for the effects of climate change on freshwater fisheries that uses water temperature, water quantity, and water quality variables to link the atmosphere to fishery resources. Iterative interaction among atmospheric, ecological, and fisheries scientists clarifies the information needs of each discipline and progressively improves the assessments of effects. The process incorporates information at different scales, i.e., organism/laboratory, species/habitat, and population/ecosystem. We illustrate the operation of the iterative assessment process with recent work done on the water temperature linkage, and sketch some linkages through water quantity and water quality variables. A Wild Salmonid Watch (WSW) could provide a framework for monitoring climate change and its effects on salmonid stocks on a hemispheric scale. We discuss the initial steps required to mobilize a WSW for climate change and its role as climate change develops in the decades ahead.
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With increasing computer power, the modelling tools for water resources, nowadays, not only integrate physical-based transport models with biogeochemical process models, but also couple surface water body models, groundwater models and hydrographic basin models. This paper describes how the MOHID Water Modelling System achieves the mentioned integration using object-oriented programming in FORTRAN 95. After a short historical overview of MOHID's evolution, this paper focuses on the object-oriented design of the water modelling system MOHID and the way how object-oriented features are implemented in FORTRAN 95. Attention is also given to the way how the numerical software code interacts with the graphical user interface. It follows an exemplification of how the object-oriented design is useful for implementing complex system for two cases: the operational model of the Tagus Estuary and the coupling of the Trancao Basin model to the Tagus Estuary model.
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We used three approaches to examine potential habitat loss in relation to climate warming for cold water species of fish in the North Platte River drainage in Wyoming. The projected loss of habitat varied among approaches, but all methods indicated a noticeable loss of habitat for even minor increases in temperature. An approach based on the use of summer air temperatures to define the thermal limits of cold water species estimated a loss of 9-76% of the present geographic range for temperature increases of l-5°C. A second approach, also based on air temperature limits, projected a loss of 7-64% of the stream distance currently having thermally suitable habitat for cold water fish for temperature increases of I-5°C. A third approach, based on the use of summer water temperatures to define the thermal limits of cold water species, projected a loss of 16-69% of the stream distance currently having thermally suitable habitat for temperature increases of l-5°C. In addition to habitat loss, population fragmentation would occur as remaining enclaves of cold water fish are forced to retreat to increasingly isolated headwater stream reaches.
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In the upper Colorado River basin, razorback suckers Xyrauchen texanus primarily occur as adults in low-gradient reaches of rivers or as juveniles or subadults in adjoining floodplain depressions. During the high-water years of 1995 and 1996, a number of habitat variables—zooplankton density, water temperature, quality, and depth, and vegetative cover—in a Green River floodplain depression were favorable to age-0 razorback suckers and other fishes. Conversely, main-channel habitats were not suitable as rearing sites due to lower temperatures, less food, and ineffective cover. During the spring runoff in 1995 and 1996, larval razorback suckers were found in the river after floodplains were isolated from the Green River. Although favorable nursery sites are located off-channel, the connectivity of the river and floodplain did not last long enough for all razorback sucker larvae to access these areas. Maintaining the connectivity of the floodplain to the river via levee removal and adequate flood duration will increase access to and the use of nursery habitat favorable to larval razorback suckers in the middle Green River. This study also suggests that larval razorback suckers are more likely to survive and grow in floodplain depression habitats than in main-channel habitats. Although age-0 razorback suckers grew and survived in an environment dominated by nonnative predators and competitors, the magnitude of nonnative fish impacts on razorback suckers in floodplain wetlands remains undefined.
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Walleye (Stizostedion vitreum) in Lake Erie have historically experienced large fluctuations in recruitment success, which have important implications for walleye population dynamics as well as food web interactions. Because walleye year class strength in Lake Erie likely is set during the larval life stage, we explored factors underlying larval survival during out-migration in the Maumee and Sandusky rivers, Ohio's primary walleye spawning tributaries. To evaluate our expectation that survival of larval walleye would be positively related to discharge, we estimated daily larval production and used otoliths to estimate hatch dates of larvae surviving out-migration. Comparing daily larval production and survival distributions demonstrated strong temporal patterns of larval survival that were unrelated to daily larval production patterns. Daily survival varied greatly during the larval hatch (~4 wk), with short, discrete periods (4-7 d) of high survival accounting for 75-84% of total survivors. Contrary to our original expectations, larval survival was inversely related to river discharge (P < 0.05). As river discharge increased, the amount of suspended sediments increased (r2 > 0.6, P < 0.001), likely directly increasing larval mortality. Post-out-migration densities of larval walleye in Maumee and Sandusky bays were correlated strongly (Maumee Bay: r2 = 0.99, Sandusky Bay: r2 = 0.94) with Ohio Division of Wildlife estimates of late summer juvenile abundance of Lake Erie walleye (which historically have been correlated strongly with year class strength). Because high discharge events during the larval hatch likely reduce survival, variability in river discharge underlies variability of walleye year class strength. Managers could mitigate these effects by reducing exploitation of spawning walleye and improving watershed characteristics to reduce discharge fluctuations and suspended sediments.
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The present distribution of salmonid fishes in Wyoming streams was found to be limited to regions where mean July air temperatures did not exceed 22°C. Much of the present salmonid habitat in streams is predicted to be lost if climatic warming occurs. For increases of 1, 2, 3, 4, or 5°C in mean July air temperature, the geographic area of Wyoming containing suitable salmonid habitat would be reduced by 16.2, 29.1, 38.5, 53.3, or 68.0%, respectively. This loss of geographic range would correspond to reductions of 7.5, 13.6, 21.0, 31.4, or 43.3% in the length of streams having suitable salmonid habitat. In the Rocky Mountain region, increases of 1, 2, 3, 4, or 5°C in mean July air temperature would reduce the geographic area containing suitable salmonid habitat by 16.8, 35.6, 49.8, 62.0, or 71.8%, respectively. As warming proceeds, salmonid populations would be forced into increasingly higher elevations and would become fragmented as suitable habitat for coldwater fish becomes separated from main river channels and restricted to headwater streams. A geographic information system (GIS) proved useful for combining the various databases necessary to assess the potential impact of global warming on salmonid populations. 38 refs., 9 figs., 1 tab.
Article
SYNOPSIS. Studies on the relation of temperature to tolerance, preference, metabolic rate, performance, circulation, and growth of sockeye salmon all point to a physiological optimum in the region of 15°C. Natural occurrence is limited in time and space at temperatures above 18°C despite being able to tolerate 24°C. Forms of physiological inadequacy can be demonstrated which account for such restrictions in distribution. Predictive power for locating and accounting for concentrations of young fish in thermally stratified lakes appeared to provide "proof" for the controlling influence of the physiological optimum temperature. Early literature on the ecology of sockeye supported this view. Recent studies using midwater trawls and sonar detection reveal a diurnal behavior pattern which points to a more subtle interaction of biotic andabiotic factors governing vertical distribution in which the controlling force appears to be bioenergetic efficiency. It is concluded that a mechanism of behavioral thermoregulation has evolved which favorably balances daily metabolic expenditures in order to conserve energy when food is limited.
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Worldwide aquatic ecosystems have been impacted by broad-scale environmental pressures such as agriculture, point and non-point-source pollution and land-use changes overlapping in space and time, leading to the disruption of the structure and functioning of these systems. The present paper examined the applicability of a holistic Stochastic Dynamic Methodology (StDM) in predicting the tendencies of phytoplankton communities and physicochemical conditions in reservoirs as a response to the changes in the respective watershed soil use. The case of the Douro's basin (Portugal) was used to test the StDM performance in this multi-scale approach. The StDM is a sequential modelling process developed in order to predict the ecological status of changed ecosystems, from which management strategies can be designed. The data used in the dynamic model construction included true gradients of environmental changes and was sampled from 1995 to 2004. The dynamic model developed was preceded by a conventional multivariate statistical procedure performed to discriminate the significant relationships between the selected ecological components. The model validation was based on independent data, for all the state variables considered. Overall, the simulation results are encouraging since they seem to demonstrate the StDM reliability in capturing the dynamics of the studied reservoirs. The StDM model simulations were validated for the most part of the twenty-two components selected as ecological indicators, with a performance of 50% for the physicochemical variables, 75% for the phytoplankton variables, and 100% for the Carlson trophic state indices (TSI). This approach provides a useful starting point, as a contribution for the practical implementation of the European Water Framework Directive, allowing the development of a true integrated assessment tool for water quality management, both at the scale of the reservoir body and at the scale of the respective river watershed dynamics.
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The biogeography of freshwater fish is determined in part by large-scale filters such as phylogenetic history, the spatial arrangement of catchments and environmental variability. Species are filtered from the regional pool if they possess a combination of functional traits enabling them to persist in the local environment. This article aims to quantify the relative importance of these large-scale filters in determining spatial variation in freshwater fish life-history traits and functional trait composition of Australian river basins.
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Trait analysis has potential to identify species that are vulnerable to climate change, but its predictive strength has not been adequately examined. Conditions during the recent ‘Millennium Drought’ in Australia’s Murray-Darling Basin resembled the projected future climate of the region and provided an opportunity to test the ability of traits to predict population responses to a warmer and drier environment. I used data from a large-scale monitoring program to assess how 14 dietary, life-history and physiological- tolerance traits related to changes in occurrence and abundance of 39 of the basin’s freshwater fish species. Species that fared worse under prolonged drought were significantly more likely to have an invertivorous rather than omnivorous diet, a low age at sexual maturity, a small maximum body size, a low spawning temperature, a long spawning season, low fecundity, demersal rather than planktonic eggs, and a low upper thermal limit. Rankings of drought vulnerability of fish species derived from correlations between population changes and traits showed good agreement with a previous assessment of inter-specific variation in resistance to drought, and were corroborated by independent observations of drought responses for some species. Trait analysis should have wide application to identifying species at risk from climate change, provided that sufficient traits are assessed and that adequate consideration is given to variation in trait-vulnerability relationships among different groups of organisms, geographic regions and types of ecosystems.
Article
Current climate change exacerbates the environmental restrictions on temperate species inhabiting low latitude edges of their geographical ranges. We examined how temperature variations due to current and future climate change are likely to affect populations persistence of stream-dwelling brown trout Salmo trutta at the vulnerable southern periphery of its range. Analysis of 33 years of air temperature data (19752007) by time-series models indicated a significant upward trend and a pronounced shift in air temperature around 1986-1987. This warming is associated with an ongoing population decline of brown trout, most likely caused by a loss of suitable thermal habitat in lower latitudes since the 1980s. Population decrease may not be attributed to physical habitat modification or angler pressure, as carrying capacity remained stable and populations were not overexploited. We developed regional temperature models, which predicted that unsuitable thermal habitat for brown trout increased by 93% when comparing climate conditions between 19751986 and 19932004. Predictions from climate envelope models showed that current climate change may be rendering unsuitable 12% of suitable thermal habitat each decade, resulting in an overall population decrease in the lower reaches of around 6% per year. Furthermore, brown trout catches markedly decreased 20% per year. Projections of thermal habitat loss under the ecologically friendly B2 SRES scenario showed that brown trout may lose half of their current suitable habitat within the study area by 2040 and become almost extinct by 2100. In parallel to the upstream movement of brown trout thermal habitat, warm water species are increasing their relative abundance in salmonid waters. Empirical evidence was provided of how current climate change threatens some of the most healthy native brown trout populations in Southern Europe and how forthcoming climate change is expected to further decrease the conservation status of the species.
Article
1. The upper thermal limits of the present distributions of two charr species, Dolly Varden, Salvelinus malma, and white-spotted charr, S. leucomaenis, in streams of the Japanese archipelago were examined using groundwater temperature as an index of thermal condition. The lower limits of the altitudinal distributions of Dolly Varden and white-spotted charr were delineated, respectively, by 8 and 16 °C groundwater isotherms. 2. The potential impact of future climatic warming on the geographical distribution, habitat extent and population fragmentation of each species was predicted at both the full archipelago and individual catchment levels. 3. For Dolly Varden, analysis at the full archipelago level indicated a loss of 27.6, 67.2, 79.6 and 89.6% of the current geographical range, respectively, for a 1, 2, 3 and 4 °C increase in mean annual air temperature. The present distribution area of white-spotted charr would likewise reduce by 4.1, 20.5, 33.8 and 45.6%, respectively. 4. Based on the analyses of three individual catchments, one for Dolly Varden and two for white-spotted charr, the lower habitat boundaries for the two charr species could be expected to rise increasingly to higher elevations in each catchment as warming proceeded. As a consequence, there would be large reductions in mean habitat area, with increasing habitat fragmentation followed by localized extinctions of the two species.
Article
Reductions in river discharge (water availability) like those from climate change or increased water withdrawal, reduce freshwater biodiversity. We combined two scenarios from the Intergovernmental Panel for Climate Change with a global hydrological model to build global scenarios of future losses in river discharge from climate change and increased water withdrawal. Applying these results to known relationships between fish species and discharge, we build scenarios of losses (at equilibrium) of riverine fish richness. In rivers with reduced discharge, up to 75% (quartile range 4–22%) of local fish biodiversity would be headed toward extinction by 2070 because of combined changes in climate and water consumption. Fish loss in the scenarios fell disproportionately on poor countries. Reductions in water consumption could prevent many of the extinctions in these scenarios.
Article
Predicted increases in water temperature in response to climate change will have large implications for aquatic ecosystems, such as altering thermal habitat and potential range expansion of fish species. Warmwater fish species, such as smallmouth bass, Micropterus dolomieu, may have access to additional favourable thermal habitat under increased surface-water temperatures, thereby shifting the northern limit of the distribution of the species further north in Canada and potentially negatively impacting native fish communities. We assembled a database of summer surface-water temperatures for over 13 000 lakes across Canada. The database consists of lakes with a variety of physical, chemical and biological properties. We used general linear models to develop a nation-wide maximum lake surface-water temperature model. The model was extended to predict surface-water temperatures suitable to smallmouth bass and under climate-change scenarios. Air temperature, latitude, longitude and sampling time were good predictors of present-day maximum surface-water temperature. We predicted lake surface-water temperatures for July 2100 using three climate-change scenarios. Water temperatures were predicted to increase by as much as 18 °C by 2100, with the greatest increase in northern Canada. Lakes with maximum surface-water temperatures suitable for smallmouth bass populations were spatially identified. Under several climate-change scenarios, we were able to identify lakes that will contain suitable thermal habitat and, therefore, are vulnerable to invasion by smallmouth bass in 2100. This included lakes in the Arctic that were predicted to have suitable thermal habitat by 2100.
Article
The RS-tempQ Model (reach–scale temporary flow biogeochemical model) is a conceptual model that can describe the hydrologic, sediment transport and biogeochemical processes of temporary rivers at the reach scale. The model takes into account the expansion–contraction of the inundated area of the river. It simulates the sediment transport and the nutrient fluxes that are transferred to the coastal area due to the first flash flood and during extreme rain events. The RS-tempQ Model simulates the in-stream processes during the wet and dry cycles as the river corridor expands and contracts. The model was used to assess and quantify the hydrologic and geochemical processes occurring in a temporary river reach (Krathis River) in Greece. Since the conventional gauging techniques cannot measure the flow in rivers that are split into small braided streams, discharge measurements could not be obtained in order to calibrate and verify the model. Other field measurements such as infiltration losses and sediment accumulation were used for model calibration. Copyright © 2008 John Wiley & Sons, Ltd.