No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Assessing the Biological Relevance of Aquatic Connectivity to Stream Fish Communities
Abstract
Recent advances in the ability to quantify longitudinal connectivity of riverine systems is enabling a better understanding of how connectivity affects fish assemblages. However, the role of connectivity relative to other factors, such as land use, in structuring biological assemblages is just emerging. We assessed the relevance of a structural connectivity index to stream fish communities at a relatively large scale (across five watersheds of Lake Ontario), while controlling for confounding habitat variables such as land use, elevation and stream topology. The results were assessed to determine whether species’ sensitivities to connectivity are in accordance with expectations of life history. Our results indicated that at large scales, structural connectivity explains significant amounts of variation in community structure (1 to 5.4% as measured by Bray-Curtis similarity), but remains secondary to other habitat components. Connectivity also was significantly related to abundance in 3 of the 7 species assessed. The lower explanatory power of our models compared to studies done at smaller scales suggests that the relevance of connectivity to fish communities is scale dependent and diminishes relative to other environmental factors at larger spatial extents.
... Landscape metrics, such as patch connectedness and fragment size, need not be exclusively terrestrial; in fact, aquatic connectivity is increasingly recognized as an important factor shaping lotic fish communities (Ward et al. 2002, Mahlum et al. 2014). It has long been accepted that dams have negative consequences for anadromous fish, such as Chinook Salmon (Oncorhynchus tshawytscha; Raymond 1979), but the extent of the impact of impassable culverts and other features that create impasses for fish communities as a whole is a relatively new area of study (Benton et al. 2008, Alexandre and Almeida 2010, Perkin and Gido 2012, Mahlum et al. 2014, Jackson 2016. ...
... Landscape metrics, such as patch connectedness and fragment size, need not be exclusively terrestrial; in fact, aquatic connectivity is increasingly recognized as an important factor shaping lotic fish communities (Ward et al. 2002, Mahlum et al. 2014). It has long been accepted that dams have negative consequences for anadromous fish, such as Chinook Salmon (Oncorhynchus tshawytscha; Raymond 1979), but the extent of the impact of impassable culverts and other features that create impasses for fish communities as a whole is a relatively new area of study (Benton et al. 2008, Alexandre and Almeida 2010, Perkin and Gido 2012, Mahlum et al. 2014, Jackson 2016. For example, Perkin and Gido (2012), in their study of 12 stream networks in the Great Plains, found that road crossings were inversely correlated with fish species richness and high levels of homogeneity between fish communities at different sites. ...
... However, dams and culverts do not exist in isolation from other environmental factors. Mahlum et al. (2014) addressed this issue in their study of stream connectivity at five watersheds in southern Ontario by accounting for such confounding variables as elevation and land cover. ...
Lewis Creek has the highest known fish diversity of any watershed in Vermont. In 2016, I used a backpack electrofisher to sample the fish community at 28 sites throughout the watershed to determine the distribution of individual species and to understand some of the relationships between the terrestrial environment and the fish communities. I collected 30 samples, with an average effort of 1188 seconds and captured a total of 3707 individual fish, representing 28 species, 2 of which were new for the watershed. The site-specific species richness was best explained by elevation (r2 = 0.5), flow accumulation (r2 = 0.4), and stream power (r2 = 0.35), all of which can be considered proxies of the River Continuum Concept. Sites where the richness deviated the most from the value predicted by elevation alone can be explained in part by additional environmental information – stream gradient, dendritic connectivity, and proximity to source populations – or by sampling inconsistencies. In addition, efforts by the Vermont Fish and Wildlife Service to improve angling in the Champlain Valley are likely responsible for the decline and/or distributional changes of several native species, although these projects have been successful in accomplishing their stated goals, at least within Lewis Creek. Also several stream reaches can be identified where anthropogenic modifications to the terrestrial environment likely play an outsized role in shaping the fish community. A random forest regression model offered few novel insights into the patterns of fish assemblages in Vermont—perhaps due to the relatively small sample size, strong environmental correlations, and lack of replicate watersheds.
... Indeed, connectivity indices have been developed to address this issue by including additional information on, for example, passability of barriers, (upstream) migration ability, patch size, habitat quality, population structure, and life history traits (Branco, Segurado, Santos, Pinheiro, & Ferreira, 2012;Cote, Kehler, Bourne, & Wiersma, 2009;McKay, Schramski, Conyngham, & Fischenich, 2013;Schick & Lindley, 2007). This has led to successful application of graph theory and connectivity indices in understanding channel networks and guiding the restoration and management of riverine systems (e.g., Branco, Segurado, Santos, & Ferreira, 2014;Mahlum, Kehler, Cote, Wiersma, & Stanfield, 2014;Segurado, Branco, & Ferreira, 2013). ...
... The value of such an approach is illustrated using the case study of the River Lyon, an intensively studied tributary of the River Tay in Scotland with a substantial hydropower influence where previous studies provide valuable background data (Geris, Tetzlaff, Seibert, Vis, & Soulsby, 2015;Jackson et al., 2007;Mulet, 2004). The objectives of this study are (a) to assess the impacts of river regulation on longitudinal connectivity, that is, the likely ability of Atlantic salmon individuals to pass barriers located along the longitudinal profile of a river network (Cote et al., 2009;Mahlum et al., 2014), where we apply a weighting for habitat quality using two approaches based on (1) information on reach type morphology (sensu Montgomery & Buffington, 1997) and (2) predicted salmon fry density from the Scottish national fry density model (Millar, Millidine, Middlemas, & Malcolm, 2015); (b) to determine the importance of such weighting approaches, we compare results with the more commonly used WA weighting to assess how the different approaches can misinform assessments of regulation impacts; and (c) to estimate the likely loss of production brought about by different impoundments. ...
... To assess the impact of regulation on connectivity in the Lyon channel network, we used the dendritic connectivity index for anadromous fish species (DCI d ; Cote et al., 2009;Mahlum et al., 2014). The index gives a global measure of a system's connectivity, and it can inform habitat management by indicating which sections of the river network are important to maintain high levels of connectivity. ...
Habitat fragmentation in channel networks and riverine ecosystems is increasing globally due to the construction of barriers and river regulation. The resulting divergence from the natural state poses a threat to ecosystem integrity. Consequently, a trade-off is required between the conservation of biodiversity in channel networks and socioeconomic factors including power generation, potable water supplies, fisheries and tourism. Many of Scotland's rivers are regulated for hydropower generation but also support populations of Atlantic salmon (Salmo salar L.) that have high economic and conservation value. This paper investigates the use of connectivity metrics and weightings to assess the impact of river barriers (impoundments) associated with hydropower regulation on natural longitudinal channel connectivity for Atlantic salmon. We applied two different weighting approaches in the connectivity models that accounted for spatial variability in habitat quality for spawning and fry production and contrasted these models with a more traditional approach using wetted area. Assessments of habitat loss using the habitat quality weighted models contrasted with those using the less biologically relevant wetted area. This highlights the importance of including relevant ecological and hydrogeomorphic information in assessing regulation impacts on natural channel connectivity. Specifically, we highlight scenarios where losing a smaller area of productive habitat can have a larger impact on Atlantic salmon than losing a greater area of less suitable habitat. It is recommended that future channel connectivity assessments should attempt to include biologically relevant weightings, rather than relying on simpler metrics like wetted area which can produce misleading assessments of barrier impacts.
... size, passability), which might modulate the intensity of their impact on metacommunity dynamics (Perkin and Gido, 2012;Poff and Hart, 2002). Most studies on the effects of connectivity loss caused by dams on aquatic organisms (Perkin and Gido, 2012;Mahlum et al., 2014;Wang et al., 2021;Díaz et al., 2021) focus on small, highly fragmented catchments without considering the additional effect of the centrality/ isolation gradient. Furthermore, in large catchments, dispersal could be a limiting factor, but it is not represented in commonly used indices such as the Dendritic Connectivity Index (Mahlum et al., 2014). ...
... Most studies on the effects of connectivity loss caused by dams on aquatic organisms (Perkin and Gido, 2012;Mahlum et al., 2014;Wang et al., 2021;Díaz et al., 2021) focus on small, highly fragmented catchments without considering the additional effect of the centrality/ isolation gradient. Furthermore, in large catchments, dispersal could be a limiting factor, but it is not represented in commonly used indices such as the Dendritic Connectivity Index (Mahlum et al., 2014). Indices that describe the effects of fragmentation and dispersal limitation simultaneously have been recently developed (Rodeles et al., 2021), compared with other fragmentation indices (Jumani et al., 2020), and included in software packages (Baldan et al., 2022b), but never used to explain biodiversity patterns at the catchment scale. ...
The loss of longitudinal connectivity affects river systems globally, being one of the leading causes of the freshwater biodiversity crisis. Barriers alter the dispersal of aquatic organisms and limit the exchange of species between local communities, disrupting metacommunity dynamics. However, the interplay between connectivity losses due to dams and other drivers of metacommunity structure, such as the configuration of the river network, needs to be explored. In this paper, we analyzed the response of fish communities to the network position and the fragmentation induced by dams while controlling for human pressures and environmental gradients. We studied three large European catchments covering a fragmentation gradient: Upper Danube (Austrian section), Ebro (Spain), and Odra/Oder (Poland). We quantified fragmentation through reach-scaled connectivity indices that account for the position of barriers along the dendritic network and the dispersal capacity of the organisms. We used generalized linear models to explain species richness and Local Contributions to Beta Diversity (LCBD) and multilinear regressions on the distance matrix to describe Beta Diversity and its Replacement and Richness Difference components. Results show that species richness was not affected by fragmentation. Network centrality metrics were relevant drivers of beta diversity for catchments with lower fragmentation (Ebro, Odra), and fragmentation indices were strong beta diversity predictors for the catchment with higher fragmentation (Danube). We conclude that in highly fragmented catchments, the effects of network centrality/isolation on biodiversity could be masked by the effects of dam fragmentation. In such catchments, metapopulation and metacommunity dynamics can be strongly altered by barriers, and the restoration of longitudinal connectivity (i.e. the natural centrality/isolation gradient) is urgent to prevent local extinctions.
... In contrast, structural connectivity indices are not data-intensive and can be calculated with relative ease across broader spatial scales. However, they provide only a crude estimate of connectivity, which may or may not reflect actual conditions at the scale of their application (Mahlum et al 2014). Given these drawbacks, potential connectivity metrics present a more suitable choice in the absence of empirical data. ...
... Since different species perceive habitats at different spatial scales across their life-history stages, their response to fragmentation and flow alteration will likely be scale-dependent, and also influenced by their habitat and resource requirements (Rossi andvan Halder 2010, Llausàs andJoan 2012). Generally, as spatial scales of analysis increases, other confounding landscape-level variables (such as elevation, land use, discharge) begin to influence response communities (Mahlum et al 2014). The application of spatial graph and network models across hierarchical river networks presents an opportunity to better understand factors influencing ecological connectivity across spatial scales (Erős and Lowe 2019). ...
Background. Rivers continue to be harnessed to meet humanity's growing demands for electricity, water, and flood control. While the socioecological impacts of river infrastructure projects (RIPs) have been well-documented, methodological approaches to quantify river fragmentation and flow alteration vary widely in spatiotemporal scope, required data, and interpretation. Aim. In this review, we first present a framework to visualise the effects of different kinds of RIPs on river fragmentation and flow alteration. We then review available methods to quantify connectivity and flow alteration, along with their data requirements, scale of application, advantages, and disadvantages. Finally, we present decision-making trees to help stakeholders select among these methods based on their objectives, resource availability, and the characteristics of the project(s) being evaluated. Methods. Thematic searches of peer-reviewed literature using topic-relevant keywords were conducted on Google Scholar. The bibliography of selected papers was also reviewed, resulting in the selection of 79 publications. Papers that did not define or apply a specific metric were excluded. With respect to fragmentation, we selected papers focused on instream connectivity and excluded those dealing with overland hydrologic connections. For flow alteration, we selected papers that quantified the extent of alteration and excluded those aimed at prescribing environmental flows. Results. The expected hydrological consequences of various RIP types were 'mapped' on a conceptual fragmentation-flow alteration plot. We compiled 29 metrics of river fragmentation and 13 metrics to flow alteration, and used these to develop decision-making trees to facilitate method selection. Discussion. Despite recent advances in metric development, further work is needed to better understand the relationships between and among metrics, assess their ecological significance and spatiotemporal scale of application, and develop more informative methods that can be effectively applied in data-scarce regions. These objectives are especially critical given the growing use of such metrics in basin-wide conservation and development planning.
... Barrier removals provide excellent controlled experiments to directly measure the importance of dispersal limitations on fish communities (Hitt et al., 2012). In contrast to controlled restoration experiments, analyses assessing existing habitat fragmentation effects on fish assemblages may not fill a fundamental knowledge gap in dispersal limitations unless there is consideration of barrier permeability (Pépino et al., 2012) and other potential constraints, such as landscape condition (Mahlum et al., 2014b) or intrinsic population characteristics, such as small population size (Fraser et al., 2014) or vulnerability to extinction (Schrott et al., 2005). Furthermore, prioritizing barriers for removal requires many assumptions about the potential for improving ecological conditions, and many fish-related studies have not considered whether habitat availability is, in fact, the limiting factor (Kuby et al., 2005). ...
... For example, Perkin et al. (2015) documented the compounding role of dewatering and habitat fragmentation on the decline of endemic minnows in streams of the Great Plains, USA. Hence, the importance of barriers, or lack thereof, must be viewed within the context of existing landscape conditions (Mahlum et al., 2014b), in order to prioritize restoration objectives. ...
In-stream barriers may impose constraints on the ecological effectiveness of restoration strategies by limiting colonization. We assessed the importance of dispersal limitations to fish community recovery following long-term pollution abatement, water quality remediation, and species introductions within the White Oak Creek watershed near Oak Ridge, Tennessee (USA). Long-term (26 years) responses in fish species richness, biomass, and community composition to water quality remediation were evaluated in light of physical barriers (culverts and weirs). We found that barriers to dispersal were potentially limiting fish community recovery by preventing colonization by introduced species and seasonal migrants. Changes in richness were negatively related to barrier index, a measure of the degree of isolation by barriers. Following introductions, upstream passage for six fish species above non-passable barriers was not observed. Highly isolated sites were dominated by a few equilibrium species, whereas less isolated sites showed more variation in life history strategies with increasing periodic and opportunistic strategists. The importance of barriers on community dynamics decreased over time—an indication of increasing community stability, homogenization of fauna, and improved water quality. However, isolating the role of dispersal limitation was complicated by multiple interacting stressors, such as the compounding effects of barriers and pervasive water quality conditions.
... Disturbed river continuum is considered to be a major factor negatively affecting species diversity and the potential for survival of valuable species 5,8,11,[25][26][27][28][29] . Hydraulic structures indirectly and directly affect the ecological status and use the value of waters upstream and downstream of the damming. ...
Since 1990 and in particular, after the implementation of the Water Frame Directive, many positive effects of pro-ecological projects are evident; unfortunately, examples of adverse effects have also been observed. This study aims to indicate how some ill-considered actions, called “pro-ecological”, may lead to habitat degradation and the disappearance of valuable hydrobiont species. Two watercourses, representing the lowland gravel stream and sandy stream type, were selected for the study. Literature indicated that in the past, these watercourses were characterized by an excellent ecological status and the presence of valuable rheophilic fauna and flora. Environmental parameters were recorded, macroinvertebrates and ichthyofauna were sampled and analyzed, and finally, indexes were calculated. The results were compared with literature data. In the course of studies conducted in 2011–2015, drastic habitat deterioration and extensive changes in the species structure of ichthyofauna and aquatic invertebrates were observed. Changes in the Smolnica stream have been caused by the three retention basins constructed in 2000, along the lower and middle course; while in Kiszewko, however, the factor for habitat deterioration was connected with the excessive expansion of the Eurasian beaver (Castor fiber), which created a beaver pond 20 m in width, with impoundment elevations of up to 2 m.
... It builds upon and extends the geometric network framework and associated tools provided by ArcGIS Desktop to assess the longitudinal connectivity of rivers and individual and cumulative impacts of barriers. The geometric network framework has been recognized by others as a useful modelling framework for river barrier assessment [32] and FIPEX has already been used to support longitudinal connectivity studies of the Amazon River [33], the Mekong River [34], rivers in Ireland [35], rivers in Scotland [36], and rivers in Canada [6,37,38]. FIPEX also has potential to assist with uncertainty assessment and sensitivity analyses because it streamlines the process of running and rerunning analyses. For example, a previous application of an earlier ver- sion of FIPEX revealed that the method of quantifying river habitat can impact connectivity assessments using the DCI statistics [6]. ...
FIPEX v10.4 is designed to decrease the time required to assess the individual and cumulative effects of river barriers to fish passage and to assess river connectivity from headwaters to outflow (i.e., longitudinal connectivity) Loss of longitudinal connectivity due to anthropogenic barriers is a global problem contributing to unprecedented biodiversity loss in freshwater biomes. Yet, assessing longitudinal connectivity from the perspective of fish and prioritizing ecological restoration is challenging without specialized tools. The Fish Passage Extension (FIPEX) v10.4 is designed to bridge network analysis and Geographic Information System (GIS) in support of river connectivity assessments. It is developed as an open source VB.NET ‘Add-In’ for ArcGIS Desktop (v10.4+) with an option to run R statistical software scripts to calculate the Dendritic Connectivity Index (DCI).
... La franchissabilité établie sur une base théorique (obstacles et passes) peut se montrer fort différente dans les faits [Buddenderof et al., 2019], ce qui est susceptible de réduire l'efficacité des modèles. Il se peut également qu'il y ait un seuil maximum de connectivité à partir duquel il n'y a plus de réponse des organismes [Mahlum et al., 2014] comme cela s'observe pour la proportion de galets. Il n'y a pas non plus de bassin contrôle, par ailleurs inexistant sur le plan théorique, comme point de comparaison. ...
Grâce au projet européen LIFE+ Walphy (2009-2013), des travaux de restauration sur trois masses d'eau ont été réalisés, ainsi qu'un suivi scientifique de leur efficacité via des relevés avant et après travaux. Les travaux concernaient l'amélioration de la continuité longitudinale avec 23 obstacles effacés ou aménagés dans le bassin du Bocq, et l'amélioration de la continuité transversale avec 3,7 km de cours d'eau réhabilités selon différentes techniques. Depuis, cinq stations ont fait l'objet de relevés hydromorphologiques et biologiques. Grâce à une comparaison avant/après travaux, les résultats ont démontré l'efficacité à court terme des aménagements entrepris. Dix ans après, la question de la pérennité des aménagements et de leurs bénéfices écologiques se posait, à l'échelle stationnelle, et à l'échelle de la masse d'eau. L'évaluation actuelle (2021) s'est faite selon ces deux échelles, et est basée sur un suivi géomorphologique et écologique des stations aménagées et des stations de contrôle, ainsi que l'analyse des données des stations DCE. Il ressort une certaine variabilité dans la pérennité des aménagements, selon le type de travaux. Hydromorphologiquement, l'analyse des sites restaurés montre généralement une légère baisse des gains obtenus quelques années après les travaux. Cela pourrait être attribué au comblement des annexes hydrauliques ou à une dispersion des galets injectés. Biologiquement, le bilan est positif, mais des différences quant au temps et à l'intensité de réponse des indicateurs apparaissent, selon le type d'aménagement et l'échelle considérée. A l'échelle de la masse d'eau, certains paramètres piscicoles montrent des changements concomitants avec l'augmentation de la continuité longitudinale. Mots-clefs : Restauration hydromorphologique, continuité longitudinale, continuité latérale, monitoring, Walphy Thanks to the European LIFE+ Walphy project (2009-2013), restoration work has been carried out on three bodies of water, as well as scientific monitoring of their effectiveness via pre-and post-work surveys. The work concerned the improvement of longitudinal continuity with 23 obstacles cleared or arranged in the Bocq basin, and the improvement of transverse continuity with 13 km of watercourses rehabilitated using different techniques. Since then, five stations have been the subject of hydromorphological and biological surveys. Thanks to a comparison before/after the works, the results demonstrated the short-term effectiveness of the developments undertaken. Ten years later, the question of the sustainability of developments and their ecological benefits arose, at the station scale, and at the scale of the water body. The current assessment (2021) is therefore located in time and space and is based on monitoring undeveloped control stations. Station monitoring includes ecological and geomorphological monitoring. There is some variability in the sustainability of the facilities, depending on the type of work. Hydromorphologically, the analysis of the restored sites generally shows a slight drop in the gains obtained a few years after the works. This could be attributed to the filling of the hydraulic annexes or to a dispersion of the pebbles included. Biologically, the results are positive; differences in the timing and intensity of the response of the indicators displayed, depending on the type of development and the scale considered. At the scale of the water body, the results show a downward trend in hydromorphological quality.
... For this analysis, all barriers were considered impassable (i.e., passability set to zero). DCI values range from 0 to 100, with 100 representing fully passable (completely unfragmented) systems whereas low DCI values indicate a low degree of connectivity and a high degree of habitat fragmentation [55,56]. To compare habitat fragmentation conditions among barrier types, four DCI values were calculated for each species: large dams only, small dams only, waterfalls only, and all barriers combined. ...
Species conservation often faces many challenges, such as addressing threats from multiple stressor sources, representing under-studied taxa, and understanding implications of spatial extent. To overcome these challenges, we assessed contemporary anthropogenic threats from stream fragmentation and landscape disturbance as well as future habitat suitability under climate change for traditionally well-studied (fishes) and under-studied (mussels) imperiled fluvial taxa in Michigan, USA. To understand how threats to species vary spatially, predicted habitat suitability was analyzed for three hierarchically nested spatial extents: statewide, within species’ biogeographic ranges, and within river patches fragmented by barriers. Comparison of current and future habitat suitability for 27 fish and 23 mussel species indicates large potential statewide gains for many warmwater and/or large river fishes and several mussel species, however these gains are greatly diminished by biogeographic range limitations and habitat fragmentation among current and future habitats. One mussel species and several cold- and coolwater fishes are projected to have significant habitat losses under climate change irrespective of spatial extent. On average, 79% of habitats for mussels and 58% for fishes were considered moderately to severely disturbed from current human landscape activities. Habitat fragmentation was greater for fishes than mussels, with large dams playing a primary role in fragmenting habitats relative to small dams and waterfalls. Results indicate that threat assessments can vary substantially according to spatial extent and taxa, and consideration of both contemporary and future threats to habitats is needed to inform conservation of imperiled fluvial organisms.
... For example, Januchowski-Hartley et al. (2021) used a model-based approach to predict the likelihood that road-river infrastructure was either a bridge or culvert and Januchowski-Hartley et al. (2019) also used existing data on the heights of assessed instream barriers to predict height (and hence passability) at unassessed structures lacking height information. Similarly, Mahlum et al. (2014) used stream slope as a predictor of passability at unassessed culverts. ...
Fragmentation of river systems is a key driver of freshwater biodiversity loss. Instream structure inventories are an essential component of delivering a strategic approach to restoring river connectivity. We used a range of data sources to collate the best available information on fish passage barriers and instream structures across the whole of New Zealand. To support implementation of new national policy objectives to maintain and improve river connectivity, the structure inventory has been integrated with a new fish passage assessment mobile application that allows river managers and asset owners to ground-truth, update and add records to the database. The data are provided open access and are being used for environmental reporting and to support strategic prioritisation of barrier mitigation actions. We used these data to quantify river connectivity at regional and national scales and demonstrated that at least half of New Zealand's river network is upstream of fish migration barriers. Limitations to our calculation of upstream river connectivity included the unknown influence of unrecorded structures, particularly on private land, missing information within recorded data, the large number of instream structures that have been identified but not yet assessed for their risk to fish passage, and spatial errors in the automated pairing of structures to a digital river network. A critical challenge for river managers is understanding the consequences of these uncertainties in the data for prioritisation and decision-making regarding barrier removal or mitigation.
... Tout d'abord, les effets qu'on attribue à ces milieux ne sont pas pleinement démontrés, au contraire même, plusieurs études semblent en désamorcer les impacts (e.g. Touchart, 1999 ;Mahlum et al., 2014 ;Van Looy et al., 2014 ;Villeneuve et al., 2015 ;Bravard, 2018). Ensuite, les travaux de restauration écologique comportent un certain niveau d'incertitudes, en raison de la jeunesse de ces pratiques et du grand nombre de variables auxquelles elles sont confrontées (Graf, 2008). ...
... It has been suggested that fish assemblages in dendritic drainages may be especially sensitive to fragmentation, but empirical studies have yielded mixed results (Fausch 2010, Fuller et al. 2015. Some studies have found that stream fragmentation affects fish species richness and assemblage composition (Nislow et al. 2011, Miyazono andTaylor 2013), but other studies have found little effect of connectivity on local assemblage structure (Branco et al. 2012, Mahlum et al. 2014, Tonkin et al. 2014. Further, it has been noted that although highly connected systems allow populations to disperse into empty patches, connectivity also allows pathogens, predators, and competitors to move about a landscape, and the net effect of connectivity on population persistence can be uncertain (Haddad et al. 2014). ...
... The RCI can be computed for each reach where community data is available and can be used as a predictor in multivariate community analysis. The effect of fragmentation on biotic communities is expected to be mediated by the spatial scales and extents analyzed (Mahlum et al., 2014). Furthermore, the use of such metrics could complement spatial covariates based on Euclidean distance, river-based distance, and flow connected distance (Ver Hoef and Erin, 2010) in a variance-partitioning algorithm to quantify the dir_distance_type = "asymmetric", disp_type = "threshold", param_u = 0, param_d = 3 a Parameters that are not specified are assigned their default values. ...
Fragmentation affects river ecosystems worldwide by dampening the movement and dispersal of aquatic organisms and material (such as sediment, water, nutrients) across the river network. In this paper, we develop river connectivity indices to explain biodiversity patterns, prioritize reaches that need habitat restoration and barriers that need improvement. We provide a general framework for calculating connectivity indices by disentangling the contribution of the river network's physical setup (structural connectivity) from the process-driven and biota-related contribution (functional connectivity). To facilitate the calculations, the R package ‘riverconn’ is introduced. A prioritization of habitats and barriers is carried out for the Ebro river (North-West Iberian Peninsula) using indices setups accounting for different classes of organisms and dispersal traits. Resulting prioritizations are very diverse. ‘Riverconn’ can support scientists and managers working on riverscape planning and population and community ecology by providing a means to compute and compare a wide array of fragmentation indices.
... The RCI can be computed for each reach where community data is available and can be used as a predictor in multivariate community analysis. The effect of fragmentation on biotic communities is expected to be mediated by the spatial scales and extents analyzed (Mahlum et al., 2014). Furthermore, the use of such metrics could complement spatial covariates based on Euclidean distance, river-based distance, and flow connected distance (Ver Hoef and Erin, 2010) in a variance-partitioning algorithm to quantify the dir_distance_type = "asymmetric", disp_type = "threshold", param_u = 0, param_d = 3 a Parameters that are not specified are assigned their default values. ...
Fragmentation affects river ecosystems worldwide by dampening movement and dispersal of organisms across the river network. Fragmentation indices were developed to explain biodiversity patterns, prioritize reaches that need habitat restoration and barriers that need improvement. This paper provides a general framework for calculating fragmentation indices by disentangling the contribution due to the river network's physical setup (structural connectivity) from the biota-related contribution (functional connectivity). To facilitate the calculations, the R package riverconn is introduced. A prioritization of habitats and barriers is carried out for the Ebro river (North-West Iberian Peninsula) using indices setups accounting for different classes of organisms and dispersal traits. Resulting prioritizations are very diverse. A software like riverconn can support scientists and managers working on riverscape planning, population and community ecology by providing a wide array of fragmentation indices.
... Dams, reservoirs and diversions act as barriers causing river networks to fragment longitudinally and laterally [19,33,35], resulting in the loss of connectivity between different segments of a river and between the river and the sea (Figure 1). Fragmentation degrades the health of river ecosystems, often leading to the decline in migratory fish species [12,35,40,41]. The DCI has two subindices, measuring the degree of connectivity between different segments of a river (internal connectivity) and that measures the degree of connectivity between the river and the sea (external connectivity). ...
This paper illustrates an approach to measuring economic benefits and ecological and social impacts of various configurations of reservoir systems for basin-wide planning. It suggests indicators and examines their behavior under several reservoir arrangement scenarios using two river basins in Sri Lanka as examples. A river regulation index is modified to take into account the volume of flow captured by reservoirs and their placement and type. Indices of connectivity illustrate that the lowest river connectivity in a basin results from a single new reservoir placed on the main stem of a previously unregulated river between the two locations that command 50% and 75% of the basin area. The ratio of the total affected population to the total number of beneficiaries is shown to increase as the cumulative reservoir capacity in a river basin increases. An integrated index comparing the performance of different reservoir system configurations shows that while results differ from basin to basin, the cumulative effects of a large number of small reservoirs may be comparable to those with a few large reservoirs, especially at higher storage capacities.
... Because all the dams in the Yangtze River Basin were built on the tributaries before 1980, the impact on connectivity was small, and the DCI was higher than 80, which represents an almost natural state. (Katopodis, 2005;Mahlum, Kehler, Cote, Wiersma, & Stanfield, 2014), as well as the local ecology and economy. In addition, fish migration and spawning can also be realized by means of joint reservoir operation scheduling for cascade hydropower stations to improve the connectivity, but this method can only be used for short periods of time and it is not a long-term solution (Cai et al., 2020). ...
Dams are built on rivers for power generation, flood prevention and control, and water resources utilization. However, dams also reduce the connectivity of rivers, which hinders the exchange of material and organisms within rivers. The Yangtze River Basin and the Yellow River Basin are the two largest river basins in China. In this study, the connectivity of these two huge and highly impacted systems was investigated. The Dendritic Connectivity Index (DCI) was applied to evaluate the impact on river connectivity of dams with a reservoir capacity of larger than 0.1 km³. The results show that river connectivity decreased following an increase in dam construction. The connectivity of the Yangtze River Basin was close to 80 (0 is completely disconnected and 100 is connectivity under natural condition) in the 1980s, but declined significantly after the Gezhouba Dam was constructed on the mainstream of the Yangtze River. From 1980 to 2010, the connectivity of the Yellow River Basin was always lower than that of the Yangtze River Basin. The changes in the connectivity indices of potamodromous fish (DCIp) and diadromous fish (DCId) were determined for the period of 1980–2010. In the Yangtze River Basin, the DCIp decreased by 67.28% and the DCId decreased by 65.72%. In the Yellow River Basin, the DCIp decreased by 43.8% and the DCId decreased by 100%. In conclusion, the construction of dams, especially those on the main stream, has reduced the connectivity of the basin. The connectivity of the Yangtze River Basin and the Yellow River Basin has been severely affected.
... Tout d'abord, les effets qu'on attribue à ces milieux ne sont pas pleinement démontrés, au contraire même, plusieurs études semblent en désamorcer les impacts (e.g. Touchart, 1999 ;Mahlum et al., 2014 ;Van Looy et al., 2014 ;Villeneuve et al., 2015 ;Bravard, 2018). Ensuite, les travaux de restauration écologique comportent un certain niveau d'incertitudes, en raison de la jeunesse de ces pratiques et du grand nombre de variables auxquelles elles sont confrontées (Graf, 2008). ...
Au fil du temps, quasiment tous les réseaux hydrographiques de la planète ont été lourdement aménagés avec des ouvrages hydrauliques transversaux à l’écoulement des cours d’eau, qui ont enrichi le panorama des milieux aquatiques continentaux créant des retenues de seuil en rivière, des étangs et des lacs de barrage. Toutefois, aujourd’hui ceux-ci sont au centre de préoccupations de politiques environnementales qui ont comme objectif leur effacement, afin de rétablir les conditions supposées antérieures à leur création. Plusieurs membres de la communauté scientifique se montrent prudents face aux résultats que ces opérations de restauration écologique devraient atteindre et ils proposent d’intégrer ces milieux aquatiques artificiels au sein des politiques environnementales, pour protéger leurs particularités et les bénéfices qu’ils apportent aux sociétés. Toutefois, pour faire cela il est nécessaire de comprendre leur fonctionnement et de développer une vision globale qui les assimile aux milieux aquatiques considérés comme naturels. Ainsi l’objectif de cet article est de passer en revue la littérature scientifique à propos de certaines caractéristiques du biotope des retenues de seuils en rivière, des étangs et des lacs de barrages et de les comparer avec celles des cours d’eau et des lacs naturels, pour voir de combien le fonctionnement des milieux aquatiques artificiels et naturels s’écarte. Les résultats de cette synthèse ont mis en avant le caractère hybride des milieux aquatiques artificiels examinés, qui croisent en même temps des traits lentiques et des traits lotiques. Cela a permis le développement d’une vision globale qui intègre les milieux aquatiques artificiels et naturels, selon un gradient de conditions abiotiques.
... Based on the perceptions of the local fishers, the production of 15 ethnospecies declined following the impoundment (Table 1). Many studies have shown that impoundments for hydroelectric projects may provoke a reduction in fish populations due to a number of different types of impact, such as the blocking of migration routes (Perkin and Gido 2012;Mahlum et al. 2014), injuries to the fish in the turbines (McKinstry et al. 2007), shifts in the flood pulse (Santos, et al. 2018), changes in the physicalchemical properties of the water (Preece and Jones 2002;Olden and Naiman 2010), and alterations in the trophic structure of the impounded ecosystem (Agostinho et al. 2016;Oliveira et al. 2018). All these factors may have contributed to the decline in fishery production in the Madeira Basin. ...
This study aimed to investigate the environmental impacts generated by the hydroelectric complex in the Madeira River, Brazilian Amazon, based on the perceptions of local fishers and fishery database, it focus attention on three main impacts: (i) on local fishery stocks; (ii) in fish fauna and (iii) on the aquatic ecosystems. The local fishers were selected through the ‘‘snowball’’ approach for the application of semi-structured interviews. All the local fishers confirmed having perceived a decline in fishery productivity following the impounding of the Madeira River. Changes in the condition of the fish were also perceived by the local fishers, including exophthalmia (82%), a reduction in the weight or length of the fish (25%), and irregular breeding patterns (14%). In the case of impacts on the river, changes in the hydrological cycle were the process remembered most frequently (75%). The results elucidated a range of environmental impacts caused by the hydroelectric dams of the Madeira River.
... Thus, for resident or potamodromous fish, connectivity is expected to depend more on the "largest fragment", whereas for diadromous fish it depends on the position of the barrier in relation to the river mouth [15]. This index has been successfully used to assess effects of fragmentation on diversity, abundance and distribution patterns of riverine fish in some river systems [21][22][23]. Some limitations of DCI have also been recognised, most importantly the consideration of the barrier placement only as a theoretical approximation expressed as the distance to the lowest point of the network [17] included an additional metric for placement of barriers within the river network, namely the river volume related to discharge and channel dimensions. ...
Background:
Fragmentation (establishment of barriers e.g., hydropower dams, reservoirs for irrigation) is considered one of the greatest threats to conservation of river systems worldwide. In this paper we determine the fragmentation status of central Chilean river networks using two indices, namely Fragmentation Index (FI) and Longest Fragment (LF). These are based on the number of barriers and their placement as well as river length available for fish movement. FI and LF were applied to eight Andean river basins of central Chile in order to assess their natural, current (2018) and future (2050) fragmentation at the doorstep of a hydropower boom. Subsequently, we exemplify the use of these indices to evaluate different placement scenarios of new hydropower dams in order to maximize hydropower use and at the same time minimize impact on fish communities.
Results:
In the natural scenario 4 barriers (waterfalls) were present. To these 4 barriers, 80 new ones of anthropogenic origin were added in the current (2018) scenario, whereas 377 new barriers are expected in near future (2050). Therefore, compared to the ‘natural’ scenario, in 2050 we expect 115-fold increase in fragmentation in analysed river systems, which is clearly reflected by the increase of the FI values in time. At the same time, the LF diminished by 12% on average in the future scenario. The fastest increase of fragmentation will occur in small and medium rivers that correspond to 1st, 2nd and 3rd Strahler orders. Finally, case study on configuration of potential hydropower plants in the Biobio basin showed that hydropower output would be maximized and negative effects on fish communities minimised if new hydropower plants would be located in tributaries of the upper basin.
Conclusions:
Fragmentation of Chilean Andean river systems is expected to severely increase in near future, affecting their connectivity and ecological function as well as resilience to other anthropogenic stressors. Indices proposed here allowed quantification of this fragmentation and evaluation of different planning scenarios. Our results suggest that in order to minimise their environmental impact, new barriers should be placed in tributaries in the upper basin and river reaches above existing barriers.
... For example, Segurado et al. [19] introduced dams into the analysis of structural connectivity of the Tagus river network in Portugal based on a landscape connectivity metric. When assessing the effect of barriers on aquatic biological communities, the Dendritic Connectivity Index (DCI) is widely used and modified to quantify longitudinal connectivity [1,3,[20][21][22][23]. In previous studies, anthropogenic barriers include dams, culvert, and roads, and natural barriers include waterfalls and beaver dams [22,[24][25][26]. ...
A large variety of barriers can affect longitudinal connectivity, which leads to shipping blocking and even flood hazard. However, few existing methods can quantify physically the river channel connectivity from the barrier’s details perspective in a watershed. This paper establishes a new model of the River Channel Connectivity Index (RCCI) to quantify the unobstructed degree of river flow in river channels within geographic information system (GIS ) platforms based on the modified concept of time accessibility. A comprehensive classification system of barriers is setup before these barriers are identified by the remote sensing technology. The model is applied to Dashi Watershed in suburban Beijing, China. Results show that submersible bridges and sediment siltation are the main barriers in the watershed. RCCI values in the mountainous areas are generally higher than that of the plains. The assessment results verified by two historical flood events show that the RCCI can reveal where the river channel connectivity is impaired, how serious it is, and what the reason is for managers. Through scenarios’ results, the best restoration measure for each tributary is obtained from the perspective of reducing flood hazards. The new RCCI method not only has methodological significance, but also helps policymakers to enhance river flooding reduction and determine restoration priorities of the river channel.
... Longitudinal connectivity is quantified using a novel extension of the dendritic connectivity index (DCI) proposed by Cote et al. (2009). More specifically, we evaluate DCI at the local, segment-level scale (Mahlum et al., 2004) separately for each habitat type (lowland river, lowland stream, highland river, highland stream and submontane stream) and then take the minimum value as an overall measure of segment connectivity. In this way, our model adopts a "limiting factors" approach by focusing on the habitat type in shortest supply. ...
Spatial prioritization tools provide a means of finding efficient trade‐offs between biodiversity protection and the delivery of ecosystem services. Although a large number of prioritization approaches have been proposed in the literature, most are specifically designed for terrestrial systems. When applied to river ecosystems, they often fail to adequately account for the essential role that landscape connectivity plays in maintaining both biodiversity and ecosystem services. This is particularly true of longitudinal connectivity, which in many river catchments is highly altered by the presence of dams, stream‐road crossings, and other artificial structures.
We propose a novel framework for coordinating river conservation and connectivity restoration. As part of this, we formulate an optimization model for deciding which subcatchments to designate for ecosystem services and which to include in a river protected area (RPA) network, while also deciding which existing river barriers to remove in order to maximize longitudinal connectivity within the RPA network. In addition to constraints on the size and makeup of the RPA network, the model also considers the suitability of sites for conservation, based on a biological integrity index, and connectivity to multiple habitat types. We demonstrate the usefulness of our approach using a case study involving four managed river catchments located in Hungary.
Results show that large increases in connectivity‐weighted habitat can be achieved through targeted selection of barrier removals and that the benefits of barrier removal are strongly depend on RPA network size. We find that (i) highly suboptimal solutions are produced if habitat conservation planning and connectivity restoration are done separately and (ii) RPA acquisition provides substantially greater marginal benefits than barrier removal given limited resources.
Synthesis and applications . Finding a balance between conservation and ecosystem services provision should give more consideration to connectivity restoration planning, especially in multi‐use riverscapes. We present the first modelling framework to directly integrate and optimize river conservation and connectivity restoration planning. This framework can help conservation managers to account better for connectivity, resulting in more effective catchment scale maintenance of biological integrity and ecosystem services delivery.
... Dams alter the habitat for these species and create insurmountable barriers to their movement along river corridors; these impacts will be exacerbated by future climate change and predicted contraction of species ranges. Studies from other regions have confirmed the biological relevance of the DCI for freshwater fishes, linking declines in alpha (local) and beta (river network) diversity with incremental increases in river fragmentation (23,24). On the basis of the projected decreases in DCI values with ongoing hydropower development, we anticipate similar declines in alpha and beta diversity of fishes in the Andean Amazon-particularly the Marañón, Ucayali, Beni, Mamoré, and Madre de Dios basins (Table 2). ...
Andes-to-Amazon river connectivity controls numerous natural and human systems in the greater Amazon. However, it is being rapidly altered by a wave of new hydropower development, the impacts of which have been previously underestimated. We document 142 dams existing or under construction and 160 proposed dams for rivers draining the Andean headwaters of the Amazon. Existing dams have fragmented the tributary networks of six of eight major Andean Amazon river basins. Proposed dams could result in significant losses in river connectivity in river mainstems of five of eight major systems—the Napo, Marañón, Ucayali, Beni, and Mamoré. With a newly reported 671 freshwater fish species inhabiting the Andean headwaters of the Amazon (>500 m), dams threaten previously unrecognized biodiversity, particularly among endemic and migratory species. Because Andean rivers contribute most of the sediment in the mainstem Amazon, losses in river connectivity translate to drastic alteration of river channel and floodplain geomorphology and associated ecosystem services.
... First, if there are no nearby animals to recolonize the newly available habitat (Langford et al. 2009), or if the quality of habitat in the newly restored area is inadequate, improvements to fish passage alone may not restore fish communities (Pretty et al. 2003;Tummers et al. 2016). This is supported by studies that observed that fragmentation is a secondary stressor relative to land use in fish communities (Branco et al. 2011;Mahlum et al. 2014a). In our national park study area, however, water quality is considered good and it has minimal anthropogenic influences relative to the adjacent landscape. ...
The restoration of four partial stream barriers was evaluated in watersheds of Terra Nova National Park, Newfoundland, Canada from 2009 to 2011. Brook trout (n = 462) were tagged and tracked moving through our study sites using PIT telemetry and the restoration actions were assessed using three different measures: passage success rates; the range of passable flows; and the availability of passable flows. We considered the observed results within a Before-After Control-Impact (BACI) design that included reference reaches and pre-restoration observations. The conclusions of BACI analyses were also contrasted with those that would have been obtained from commonly used Before-After (B-A) or Control-Impact (C-I) study designs. While the restoration actions changed hydrological conditions in a way that should facilitate fish passage, our biological measures indicated that success was variable across culverts and within culverts depending on the measure evaluated. Furthermore, the natural temporal and spatial variability of fish movements often resulted in different conclusions between the more robust BACI design and the more commonly used B-A and C-I designs. Our results demonstrate that restoration of partial barriers may not always yield dramatic improvements. Furthermore, without suitable controls, the chances of drawing false conclusions regarding restorations in temporally and spatially dynamic systems are substantial.
... We also point out that other connectivity metrics could be used in place of the C metric. For example, the popular DCI P metric of Cote et al. (2009) computed at the individual subnetwork scale (referred to as DCI S by Mahlum et al. 2014b) could just as easily be integrated into our model by redefining parameter w jk ¼ vk V . To continue, constraint (5) determines the cumulative passability z jk between subnetworks j and k. ...
... The distribution models for the Lake Simcoe watershed did not include the presence of stream barriers and, as a result, areas predicted to have suitable habitat may not possess brook trout. Few studies have incorporated stream barriers into their distribution models because there is often a lack of knowledge on the location of barriers and the amount of connectivity they provide (see Mahlum et al. 2014). Knowledge of barrier position in the Lake Simcoe watershed can help managers identify areas with suitable brook trout habitat that may benefit from barrier remediation efforts. ...
... Anderson et al. 2012) have been developed. However, models such as FishXing have been shown to be very conservative and do not accurately predict fish passage in actual streams (Mahlum et al. 2014b), and Bayesian belief networks require extensive knowledge of the probability of passage for all fish species, which is not available for most of the species in this study. ...
ContextThe cumulative impact of broad scale environmental change includes altered land-cover and fragmentation. Both altered land-cover and fragmentation have a negative effect on species diversity, but the scale they act on may differ because land-cover alters environmental characteristics, whereas fragmentation alters movement among sites. Objectives
We evaluated the scale specific effects of land-cover, fragmentation, and habitat size on alpha and beta diversity (total, turnover, and nestedness). Methods
Stream fish communities were sampled across five urbanizing watersheds. Generalized mixed linear models were used to test how diversity (alpha and beta) is affected by land-cover, connectivity, and habitat size. Indices of land-cover were calculated from correspondence analyses on land-cover data, fragmentation was estimated with the dendritic connectivity index, and habitat size was calculated as the length of the stream segment (alpha diversity) or the length of the stream network (beta diversity). ResultsAlpha diversity was most strongly related to land-cover variables associated with urban development and agriculture (negative relationship with urbanization). Whereas, beta diversity was most strongly influenced by habitat size (positive relationship) and fragmentation (positive relationship). Turnover was positively correlated with fragmentation and habitat size, whereas species loss was negatively correlated with habitat size. Conclusions
Land-cover has a larger effect on alpha diversity because it alters the environmental conditions at a site, whereas fragmentation has a larger effect on beta diversity because it affects the movement of individuals among sites. Assessing the cumulative impact of environmental change requires a multiscale approach that simultaneously considers alpha and beta diversity.
... Movement and distribution of fish within a stream is often influenced by the presence, type and number of barriers located within the stream network(Cote et al., 2009;Bourne, Kehler, Wiersma, & Cote, 2011;Perkins & Gido, 2012;Mahulum, Kehler, Cote, Wiersma, & Stanfield, 2014). This phenomenon is more well known in upland streams; however, we found evidence barriers may have affected young fish assemblages in upper reaches of floodplain tributaries.Rankin and West Fork Mill creeks had lower DCI scores and upper and lower reaches in these tributaries tended to have dissimilar young fish assemblages respectively. ...
Small, adventitious tributaries (<3 orders of magnitude smaller than the stream it flows into) are a conspicuous feature of many river–floodplain systems, but their value as fish reproduction and nursery habitat is not well understood compared to oxbow lakes and the main river channel (MRC). Moreover, connectivity of tributaries to the MRC is often less impacted by anthropogenic modifications (e.g., dams and levees) compared to oxbow lakes. From April to July 2012, larval and juvenile fish were collected in the Fourche LaFave River (Arkansas, USA) system to better understand fish nursery habitat function of tributaries relative to oxbow lakes and the MRC. Nonmetric multidimensional scaling ordination of juvenile and larval fish genera revealed distinct fish assemblages in MRC and floodplain habitats. Ordination of juvenile fish at the species level resulted in distinct fish assemblages in tributary versus oxbow lake habitats. Tributaries had more unique species and higher abundance of shared species than oxbow lakes and MRC. Additionally, of the 46 species identified, all but six were collected in lower tributary reaches. Connectivity was strongly associated with both ordinations and was important in describing patterns of fish variation among habitats and between tributaries. Of the tributaries sampled, the least fragmented stream had the most similar fish assemblages between upper and lower sections. Findings of this study revealed tributaries are an important, yet overlooked, feature in the river–floodplain model. Especially in years of drought, channel–floodplain connectivity can be limited, but tributaries can be used by fishes for reproduction and nursery habitat.
... We also point out that other connectivity metrics could be used in place of the C metric. For example, the popular DCI P metric of Cote et al. (2009) computed at the individual subnetwork scale (referred to as DCI S by Mahlum et al., 2014b) could just as easily be integrated into our model by redening parameter w jk = v k V . ...
The presence of dams, stream–road crossings and other infrastructure often compromises the connectivity of rivers, leading to reduced fish abundance and diversity. The assessment and mitigation of river barriers is critical to the success of restoration efforts aimed at restoring river integrity.
In this study, we present a combined modelling approach involving statistical regression methods and mixed integer linear programming to maximize resident fish species richness within a catchment through targeted barrier mitigation. Compared to existing approaches, our proposed method provides enhanced biological realism while avoiding the use of complex and computationally intensive population/ecosystem models.
To estimate barrier passability quickly and at low cost, we further outline a rapid barrier assessment methodology. The methodology is used to characterize potential passage barriers for various fish species common to the UK but can be readily adapted to different planning areas and other species of interest.
We demonstrate the applicability of our barrier assessment and prioritization approach based on a case study of the River Wey, located in south‐east England. We find that significant increases in species richness can be achieved for modest investment in barrier mitigation. In particular, dams and weirs with low passability located on mid‐ to high‐order streams are identified as top priorities for mitigation.
Synthesis and applications . Our study shows the benefits of combining a coarse resolution barrier assessment methodology with state‐of‐the‐art optimization modelling to cost‐effectively plan fish passage barrier mitigation actions. The modelling approach can help inform on‐the‐ground river restoration decision‐making by providing a recommended course of action that best allocates limited resources in order to restore longitudinal connectivity and maximize ecological gains.
... 76, 90, 105, and 106), leading to general statements such as "habitat fragmentation is one of the major causes of local and regional species extinctions in fresh water ecosystems," 104 whereas other studies have been unable to detect the effects of fragmentation, or found its effects to be less severe than the effects of other drivers (e.g., Refs. [107][108][109]. ...
Increases in river fragmentation globally threaten freshwater biodiversity. Rivers are fragmented by many agents, both natural and anthropogenic. We review the distribution and frequency of these major agents, along with their effects on connectivity and habitat quality. Most fragmentation research has focused on terrestrial habitats, but theories and generalizations developed in terrestrial habitats do not always apply well to river networks. For example, terrestrial habitats are usually conceptualized as two-dimensional, whereas rivers often are conceptualized as one-dimensional or dendritic. In addition, river flow often leads to highly asymmetric effects of barriers on habitat and permeability. New approaches tailored to river networks can be applied to describe the network-wide effects of multiple barriers on both connectivity and habitat quality. The net effects of anthropogenic fragmentation on freshwater biodiversity are likely underestimated, because of time lags in effects and the difficulty of generating a single, simple signal of fragmentation that applies to all aquatic species. We conclude by presenting a decision tree for managing freshwater fragmentation, as well as some research horizons for evaluating fragmented riverscapes.
© 2015 New York Academy of Sciences.
According to Department of Fisheries and Oceans Canada, culverts and other stream crossings must be designed to ensure fish passage. The effects of ice processes on these fish passage designs have never been assessed. This study is the first to document ice processes on two different types of fish passage designs (streambed simulation and baffle). The results of a two-year field monitoring campaign showed that the culvert simulating the streambed retains a natural ice regime, i.e., both freeze-up and break-up occurred concurrently with the rest of the stream, while multiple supercooling events were recorded under a thin ice cover. As for the culvert with baffles, it was observed that the ice cover formed earlier and stayed longer in the culvert which can create a barrier for fish transiting through them.
Infrastructure-induced fragmentation of riverine ecosystems has prompted the need for more effective aquatic restoration efforts globally. Fragmentation assessments have been extensively undertaken to inform connectivity restoration efforts for fish and other aquatic biota, but they have potentially underestimated the extent of fragmentation by fixating on large dams and overlooking the contribution of other barriers like road crossings and small irrigation structures. The current study addresses this limitation in Mekong region countries (MReCs) of Southeast Asia, by assessing the fragmentation impacts of road crossings and small irrigation structures together with large dams. Our analysis indicates that the basin-scale fragmentation impact of road crossings is similar to that of large dams in MReCs, while small irrigation structures have a far greater impact. These findings raise concerns about the real global extent of aquatic fragmentation, and highlight the need for decision-makers to think beyond dams when attempting to restore connectivity for aquatic biota.
A key question in sustainable development is how much alteration in natural systems, such as river basins, is acceptable? One of the ways by which humans alter a river basin is by building water storage infrastructure. While storage reservoirs deliver numerous benefits, they can also induce social and environmental costs by displacing people, fragmenting river networks and altering downstream flow regimes. In such a context, merely capping total water withdrawal from rivers for human consumption is not sufficient. River basin plans should also identify optimal (acceptable) limits to surface storage capacities, and optimal numbers, degrees of distribution and locations of storage infrastructure. It remains largely unclear, however, whether it is possible to define a hydrologically, ecologically and socially justified ‘surface water storage boundary’ for a river basin. An associated question is what would be the ‘best’ arrangement of this bounding storage capacity in the basin's river network (in terms of numbers, sizes and locations of reservoirs) to maximize water storage benefits and minimize environmental and social costs. The main objective of this review is to examine contemporary knowledge on surface water storage development with a focus on tools and approaches that may help to answer the above questions of a ‘surface water storage boundary’ and its ‘optimum arrangement’ for a river basin. In order to achieve this objective, our review introduces two novel concepts: the ‘storage scale’ and the ‘sustainable storage development framework.’ The ‘storage scale’ has four elements – capacity, number, distribution and location – individual scales that help visualize a ‘surface water storage boundary’ and its ‘optimum arrangement’ for a typical river basin. The ‘sustainable storage development framework’ consists of three dimensions – economic benefits, ecosystems and society- and a set of indicators quantifying each dimension. This review shows that optimal levels of the elements of the ‘storage scale’ may be identified using the ‘sustainable storage development framework’.
The number of dams operating in the Brazilian Amazon region has grown at an increasingly rapid rate in recent years. Despite being considered beneficial by providing clean energy, hydroelectric dams’ plants have negative impacts on the ecological processes that are fundamental to maintaining ecosystem services and conserving biodiversity in the Amazon. In this context, this thesis aims to identify and evaluate the environmental impacts generated by the Santo Antônio and Jirau dams on the aquatic ecosystems and fisheries activity of the Madeira River basin. To fulfill this objective, this thesis was structured in two chapters. In the first chapter, the influence of the Madeira river hydroelectric complex on the local fishery stocks was evaluated. This study investigated the hypothesis that the instability of the flood pulse caused by the construction of the dams has caused a significant reduction in the fish stocks of the Madeira River. This hypothesis was tested using fishery landings data obtained in fishing colony (Z-31) “Dr. Renato Pereira Gonçalves ”, located in the municipality of Humaitá, Amazonas State, from January 2002 to September 2017. The collected data were daily recorded at the colony and include the fishing ground (point), the date of the beginning and the end of each fishing trip, type of fish caught and total catch (kg). This study indicated reductions of 39% in the mean annual catch and 34% in the mean monthly catches. The results also point out that the decline of fisheries recorded for the Humatiá colony is mainly related to the increase of the Madeira River fluviometry average after the construction of the hydroelectric dams. In the second chapter, the impacts generated by the Madeira River hydroelectric complex were evaluated through the perception of local fishers (22 Men and 6 Women) and the fishery database from the Z-31 colony. This study aimed to investigate the environmental impacts generated by the hydroelectric complex in the Madeira River based on the perceptions of local fishers and fishery database, it focuses attention on three main points: (i) local fishery stocks; (ii) the fish and (iii) the aquatic ecosystems. The local fishers were selected through the “snowball” approach for the application of semi-structured interviews. All the fishers confirmed having perceived a decline in fishery productivity following the impounding of the Madeira River. Changes in fishes' conditions were also perceived by the local fishers, including exophthalmia (82%), a reduction in the weight or length of the fish (25%), and irregular breeding season (14%). Regarding impacts on the river, changes in the hydrological cycle were the process most frequently remembered (75%). The results of this thesis elucidate several environmental impacts caused by the implantation of hydroelectric power plants in the Madeira River and highlight the high risk of these enterprises for aquatic ecosystems, fishing activities, and Amazonian riverside populations. It is hoped that this thesis may help to prevent, mitigate or even fairly compensate for similar impacts both in other parts of the concerned river basin and in other basins in the Amazon region.
Diadromous fish populations are strongly affected by in-stream barriers that cause river network fragmentation, constraining productivity or preventing completion of their lifecycle. Removal or reduction of barrier impacts is a restoration measure associated with unambiguous benefits. Management of barriers is therefore often prioritised above other restoration actions. Barrier management is prioritised at local and national scales depending on funding. However, barrier prioritisation is potentially sub-optimal because existing tools do not consider habitat quality. Furthermore, effects of partial barriers (those passable under certain conditions) are uncertain, depending on location and potential cumulative effects.
A framework is presented for assessing effects of impassable manmade barriers (IMBs) on longitudinal river network connectivity (percentage of upstream habitat accessible from the river mouth) for Atlantic salmon across spatial scales, using Scotland as an example. The framework integrates juvenile habitat quality and network connectivity models to (1) provide information necessary for local and national prioritisation of barriers, and (2) assess potential effects of passable manmade barriers (PMBs) within a sensitivity framework.
If only IMBs are considered, high levels of longitudinal connectivity are observed across most of Scotland's rivers. Barrier prioritisation is sensitive to habitat weighting: not accounting for habitat quality can lead to over- or underestimating the importance of IMBs. Prioritisation is also highly sensitive to the passability of PMBs: if passability drops to <97% (combined up- and downstream passability), the mean effect of PMBs becomes greater than IMBs at the national level. Moreover, impacts on catchment connectivity, and thus production (number of juvenile salmon produced by the river), could be severe, suggesting a better understanding of the passability of PMBs is important for future management of migration barriers. The presented framework can be transferred to other catchments, regions, or countries where necessary data are available, making it a valuable tool to the broader restoration community.
The decommissioning and planned removal of the Hogansburg Dam on the St. Regis River in New York has stimulated interest in the potential effects of that barrier removal on the St. Regis watershed. There will be immediate and systemic effects of the Hogansburg Dam removal, which may include inundation of habitats below the dam or dewatering of habitats above the dam, possibly affecting local fish assemblages and (or) local native mussel assemblages; and expansion of stream network connectivity, which has the potential to open a large area of the watershed to migratory aquatic species. Information was collected about biota, water quality, sediment distribution, riverbed dimensions in the vicinity of the dam, and habitat characteristics of headwater sample sites. Complete fish assemblages were collected, but species of special concern associated with the connectivity changes included, American Eel, Atlantic Salmon, Brook Trout, Eastern Sand Darter, and Lake Sturgeon. Freshwater mussels in the vicinity of the dam also were examined and may be at risk of exposure (without a rescue plan) after dam removal. Reservoir sediment will be transported downstream and will alter aquatic habitat as it moves through the system. The dam removal will open more than 440 kilometers of stream habitat to migratory species, allowing them to more easily complete their life cycles. Fish assemblages above the dam may be altered by migrating fishes, but resident Brook Trout are not expected to be adversely affected.
The robustness of quantitative measures of compositional dissimilarity between sites was evaluated using extensive computer simulations of species’ abundance patterns over one and two dimensional configurations of sample sites in ecological space. Robustness was equated with the strength, over a range of models, of the linear and monotonic (rank-order) relationship between the compositional dissimilarities and the corresponding Euclidean distances between sites measured in the ecological space. The range of models reflected different assumptions about species’ response curve shape, sampling pattern of sites, noise level of the data, species’ interactions, trends in total site abundance, and beta diversity of gradients.
The Kulczynski, Bray-Curtis and Relativized Manhattan measures were found to have not only a robust monotonic relationship with ecological distance, but also a robust linear (proportional) relationship until ecological distances became large. Less robust measures included Chord distance, Kendall’s coefficient, Chisquared distance, Manhattan distance, and Euclidean distance.
A new ordination method, hybrid multidimensional scaling (HMDS), is introduced that combines metric and nonmetric criteria, and so takes advantage of the particular properties of robust dissimilarity measures such as the Kulczynski measure.
Landscape pattern indicators or 'metrics' provide simple measures of landscape structure that can be easily calculated with readily available data and software. Unfortunately, the ecological relevance of many metrics (i.e. the relationship between metric values and the real-world ecological processes that they are meant to serve as proxies for) is often unproven and questionable, and concerns are regularly voiced that such metrics fail to capture important aspects of landscape function. In this paper, I provide a review of landscape measures that may better link landscape pattern and function, ranging from approaches that extend existing metrics by incorporating a more functional component (e.g. core area measures, least cost distances) to those rooted in graph, network, and electrical circuit theory. While more 'functional' approaches are becoming increasingly popular, the selection of appropriate landscape metrics in many applications involves tradeoffs regarding data requirements, ease of calculation, functional basis, and simplicity of interpretation by a range of specialist and non-specialist stakeholders. Regardless, there continues to be a need for landscape metrics because they are seen by many land managers and stakeholders as simple, intuitive tools for assessing and monitoring changes in landscape pattern and, by extension, the effects on underlying ecological processes. Future needs include: (1) the development of more user-friendly landscape analysis software that can simplify graph-based analyses and visualization; and (2) studies that clarify the strengths and weaknesses of different approaches, including the potential limitations and biases in graph and network-based measures.
Spatial graphs in landscape ecology and conservation have emerged recently as a powerful methodology to model patterns in the topology and connectivity of habitat patches (structural connectivity) and the movement of genes, individuals or populations among these patches (potential functional connectivity). Most spatial graph’s applications to date have been in the terrestrial realm, whereas the use of spatially explicit graph-based methods in the freshwater sciences has lagged far behind. Although at first patch-based spatial graphs were not considered suitable for representing the branching network of riverine landscapes, here we argue that the application of graphs can be a useful tool for quantifying habitat connectivity of freshwater ecosystems. In this review we provide an overview of the potential of patch-based spatial graphs in freshwater ecology and conservation, and present a conceptual framework for the topological analysis of stream networks (i.e., riverscape graphs) from a hierarchical patch-based context. By highlighting the potential application of graph theory in freshwater sciences we hope to illustrate the generality of spatial network analyses in landscape ecology and conservation.
Developing,spatially explicit conservation,strategies for stream,fishes requires an understanding of the spatial structure of dispersal within,stream,networks. We explored,spatial patterns,of stream,fish dispersal by evaluating how the size and proximity of connected streams (i.e., stream network topology) explained,variation in fish assemblage,structure and how,this relationship varied with local stream,size. We used,data,from,the US Environmental,Protection Agency’s Environmental,Monitoring,and,Assessment Program,in wadeable,streams,of the Mid-Atlantic Highlands,region (n¼ 308 sites). We quantified stream network,topology,with a continuous,analysis based on the rate of downstream,flow accumulation,from sites and with a discrete analysis based on the presence of mainstem river confluences (i.e., basin area .250 km,) within,20 fluvial km,(fkm) from sites. Continuous,variation in stream,network,topology,was,related to local species richness within a distance of ;10 fkm, suggesting an influence of fish dispersal within this spatial grain. This effect was explained largely by catostomid species, cyprinid species, and riverine species, but was not explained by zoogeographic regions, ecoregions, sampling period, or spatial autocorrelation. Sites near mainstem river confluences supported greater species richness and abundance of catostomid, cyprinid, and,ictalurid fishes than did sites .20 fkm,from,such,confluences. Assemblages,at sites on the smallest streams were not related to stream network topology, consistent with the hypothesis that local stream size regulates,the influence,of regional,dispersal. These results demonstrate,that the size and,proximity,of connected,streams,influence,the spatial distribution,of fish and,suggest,that these influences,can,be incorporated,into the designs of stream,bioassessments,and,reserves to enhance,management,efficacy. Key words: stream network topology, fish assemblage structure, dispersal, conservation, bioassess-
Millions of dollars are spent annually on watershed restoration and stream habitat improvement in the U.S. Pacific Northwest in an effort to increase fish populations. It is generally accepted that watershed restoration should focus on restoring natural processes that create and maintain habitat rather than manipulating instream habitats. However, most process-based restoration is site-specific, that is, conducted on a short stream reach. To synthesize site-specific techniques into a process-based watershed restoration strategy, we reviewed the effectiveness of various restoration techniques at improving fish habitat and developed a hierarchical strategy for prioritizing them. The hierarchical strategy we present is based on three elements: (1) principles of watershed processes, (2) protecting existing high-quality habitats, and (3) current knowledge of the effectiveness of specific techniques. Initially, efforts should focus on protecting areas with intact processes and high-quality habitat. Following a watershed assessment, we recommend that restoration focus on reconnecting isolated high-quality fish habitats, such as instream or off-channel habitats made inaccessible by culverts or other artificial obstructions. Once the connectivity of habitats within a basin has been restored, efforts should focus on restoring hydrologic, geologic (sediment delivery and routing), and riparian processes through road decommissioning and maintenance, exclusion of livestock, and restoration of riparian areas. Instream habitat enhancement (e.g., additions of wood, boulders, or nutrients) should be employed after restoring natural processes or where short-term improvements in habitat are needed (e.g., habitat for endangered species). Finally, existing research and monitoring is inadequate for all the techniques we reviewed, and additional, comprehensive physical and biological evaluations of most watershed restoration methods are needed.
Low-head barriers used in the control of parasitic sea lamprey (Petromyzon marinus) in the basin of the Laurentian Great Lakes can alter the richness and composition of nontarget fishes in tributary streams. Identification of taxa sensitive to these barriers is an important step toward mitigating these effects. Upstream-downstream distributions of fishes in 24 pairs of barrier and reference streams from throughout the basin were estimated using electrofishing surveys. For 48 common species from 34 genera and 12 taxonomic families, 8-19 species, 5-16 genera, and 2-7 fami- lies showed evidence of being sensitive to barriers, with the variation in number depending on the statistical measure applied. Barriers did not differentially affect species from certain genera or families, nor did they affect species of cer- tain body form. Therefore, taxonomic affiliation and swimming morphology are not useful for predicting sensitivity to barriers for fishes that co-occurred with sea lampreys but were not sampled adequately by our survey. Our estimates of sensitivity will help fisheries managers make sound, defensible decisions regarding the construction, modification (for fish passage), and removal of small, in-stream barriers.
We use linear mixed models to predict winter steelhead (Oncorhynchus mykiss) redd density from geology, land use, and climate variables in the Willamette River basin, Oregon. Landscape variables included in the set of best models were alluvium, hillslope < 6%, landslide-derived geology, young (<40 years) forest, shrub vegetation, agricultural land use, and mafic volcanic geology. Our approach enables us to model the temporal correlation between annual redd counts at the same site while extracting patterns of relative redd density across sites that are consistent even among years with varying strengths of steelhead returns. We use our model to predict redd density (redds per kilometre) upstream of 111 probable migration barriers as well as the 95% confidence interval around the redd density prediction and the total number of potential redds behind each barrier. Using a metric that incorporates uncertainty, we identified high-priority barriers that might have been overlooked using only stream length or mean predicted fish benefit and we clearly differentiated between otherwise similar barriers. We show that landscape features can be used to describe and predict the distribution of winter steelhead redds and that these models can be used immediately to improve decision-making for anadromous salmonids.
Movements of brook trout (Salvelinus fontinalis) were studied in two high-elevation (>2700 m) Colorado streams by marking (n = 4005) and recapturing fish using weirs and electrofishing at locations spaced up to 4500 m apart. Movement was most common in the upstream direction during summer, and about equal upstream and downstream between summers. Highest rates of movement occurred during and just after runoff, and before spawning, but substantial numbers of fish moved throughout the summer. Fish captured moving through weirs tended to be longer but in poorer condition than fish captured during electrofishing in 500-m reaches between weirs (i.e., the general population). On the basis of capture histories for individual fish, 59 and 66% in the two streams moved at least 50 m (up to 3380 m), even though most could be tracked only for several months. Thus, significant proportions of fish in electrofishing samples spaced throughout the stream bore marks from locations up to 2000 m away, indicating that long-range movements were relatively common. This conclusion is contrary to most literature on resident stream salmonids. We show how methods commonly used to study movement may he seriously biased, and suggest that movement may be more widespread than currently recognized.
This study presents a broad analysis of freshwater fish species biodiversity in relation to environmental and stress metrics throughout Canada. Species presenceabsence data were used to calculate richness and rarity indices by tertiary watershed. Richness is higher in the southern parts of Canada, whereas rarity is concentrated in a "ring of rarity" around the periphery of the country. Environmental and stress indices were developed for each watershed using readily available mapped information. The environmental index was estimated using growing degree-days above 5°C, elevation range (m) within the watershed, mean annual sunshine hours, and mean annual vapour pressure (kPa). The number of crop farms, forestry, waste management, and petroleum refining facilities, road density (km·1000 km2), dwelling density, and discharge sites (chimneys and laundry outlets) per 1000 km2 described the human stresses in each watershed. Conservation priority rankings were developed for the watersheds using an integrative index of the three indices. Watersheds in southern Ontario and British Columbia were ranked high because they contain the greatest biodiversity and the most stress. This study indicates how regional analyses can guide fisheries and watershed management.
Physical habitat was quantified in 105 randomly selected streams across the Northern Lakes and Forests Ecoregion during 1998 and 1999 to develop a stream habitat index for the region. Physical habitat measures (106) were classified into four groups: substrate, instream cover, riparian zone–land use, and geomorphology–hydrology. Variable reduction procedures yielded seven variables: sinuosity, percent of substrate gravel or larger, percent substrate as detritus or muck, percent of bank with forested cover, amount of bank erosion, number of large logs per 100 m, and mean length of pools. Streams were separated by a gradient value of 3 m/km (low N = 70; high N = 35) and assigned to model and test data sets. For low-gradient streams in the model data set, the seven habitat variables explained 47% of the variation in index of biotic integrity (IBI) scores. To produce the habitat index, the coefficients in the regression were used to weight each of the seven variables. For low-gradient streams in the test data set, the habitat index explained 20% of the variation in IBI scores. A habitat index could not be developed for high-gradient sites, probably due to the low number of sites. Comparison of habitat to IBI scores provides resource managers with a method to evaluate the contribution of habitat quality to the IBI score.
Effects of fragmentation on the ecology of organisms occupying dendritic ecological networks (DENs) have recently been described through both conceptual and mathematical models, but few hypotheses have been tested in complex, real-world ecosystems. Stream fishes provide a model system for assessing effects of fragmentation on the structure of communities occurring within DENs, including how fragmentation alters metacommunity dynamics and biodiversity. A recently developed habitat-availability measure, the "dendritic connectivity index" (DCI), allows for assigning quantitative measures of connectivity in DENs regardless of network extent or complexity, and might be used to predict fish community response to fragmentation. We characterized stream fish community structure in 12 DENs in the Great Plains, USA, during periods of dynamic (summer) and muted (fall) discharge regimes to test the DCI as a predictive model of fish community response to fragmentation imposed by road crossings. Results indicated that fish communities in stream segments isolated by road crossings had reduced species richness (alpha diversity) relative to communities that maintained connectivity with the surrounding DEN during summer and fall. Furthermore, isolated communities had greater dissimilarity (beta diversity) to downstream sites notisolated by road crossings during summer and fall. Finally, dissimilarity among communities within DENs decreased as a function of increased habitat connectivity (measured using the DCI) for summer and fall, suggesting that communities within highly connected DENs tend to be more homogeneous. Our results indicate that the DCI is sensitive to community effects of fragmentation in riverscapes and might be used by managers to predict ecological responses to changes in habitat connectivity. Moreover, our findings illustrate that relating structural connectivity of riverscapes to functional connectivity among communities might aid in maintaining metacommunity dynamics and biodiversity in complex dendritic ecosystems.
Implicit in the question, ''How should I prioritize restoration actions?'' is often the unstated question, ''What should I restore?'' Distinguishing between these questions helps clarify the restoration planning process, which has four distinct steps: (1) identify the restoration goal, (2) select a project prioritization approach that is consistent with the goal, (3) use watershed assessments to identify restoration actions, and (4) prioritize the list of actions. A well-crafted restoration goal identifies the biological objective of restoration, addresses underlying causes of habitat change, and recognizes that social, economic, and land use objectives may constrain restoration options. Once restoration goals are identified, one of six general approaches can be selected for prioritizing restoration actions: project type, refugia, decision support systems, single-species analysis, multispecies analysis, and cost effectiveness. Prioritizing by project type, refugia, or a decision support system requires the least quantitative information, and each approach is relatively easy to use. Single-species, multispecies, and cost effectiveness approaches require more information and effort but often most directly address legal requirements. Watershed assessments provide most of the information used to identify and prioritize actions and should be explicitly and carefully designed to support the goals and prioritization scheme. Watershed assessments identify causes of habitat degradation, habitat losses with the greatest effect on biota and ecosystems, and local land and water uses that may limit restoration opportunities. Results of assessments are translated into suites of restoration options, and analysis of land use and economic constraints helps to evaluate the feasibility of various options. Finally, actions are prioritized based on assessment results and the selected prioritization scheme. In general, we recommend the use of simple decision support systems for cases in which watershed assessments provide incomplete information; the cost effectiveness approach is recommended for cases in which watershed assessments identify (1) restoration actions needed to restore riverine habitats, (2) biological benefits associated with each action, and (3) costs of restoration actions. Dramatic declines of diadromous and freshwater fish populations have prompted substantial efforts to restore or rehabilitate riverine habitats. However, many river and watershed restoration projects fail to accomplish their objectives, and restoration efforts continue to achieve less than the desired outcomes (Bond and Lake 2003; Palmer et al. 2005; Roni et al. 2008, this issue). Specific causes of project failure vary, but include a misunderstanding of the natural potential of restoration sites (Muhar et al. 1995; Frissell 1997), a lack of understanding of geomorphological controls on habitat responses (Frissell and Nawa 1992; Kondolf 2000), nonnative species invasions (Klotzli and Grootjans 2001; Bond and Lake 2003), and presence of undetected water quality impairments (Cowx and Van Zyll de Jong 2004; Roni et al. 2008, this issue). Scientists and managers also have recognized that population declines are largely a result of attempts to manage individual species or habitat characteristics rather than whole ecosystems (Nehlsen et al. 1991; Doppelt et al. 1993; Frissell et al. 1997). Thus, scientists and managers now accept that river restora-tion is more likely to be successful at restoring individual or multiple species and preventing the demise of other species if there is careful consideration of the watershed or ecosystem context in which individual restoration actions are set (Lichatowich et al. 1995; Reeves et al. 1995; Beechie and Bolton 1999; Palmer et al. 2005). Nevertheless, legal mandates (e.g., Clean Water Act or Endangered Species Act in the United States) drive the continuing focus of restoration plans on single species or water quality attributes instead of watersheds or ecosystems (Karr 1991; Beechie et al. 2003a). Moreover, the scientific literature on stream restoration typically focuses on isolated steps in the planning
We examined the importance of zonation and species additions in explaining longitudinal changes in the fish assemblage of a Rocky Mountain stream that descends onto the Great Plains of Wyoming. Community changes along an elevational gradient from 2,234 to 1,230 m above mean sea level reflected a combination of zonation and downstream addition of species. Zonation was evident on a broad spatial scale as a result of stream temperatures. A coldwater trout (Salmonidae) assemblage dominated headwater reaches but was replaced by a warmwater minnow–sucker (Cyprinidae–Catostomidae) assemblage below 2,000 m. Within the warmwater zone, fish community change was due mainly to the addition of new species downstream. Headwater sites were dominated by members of the insectivore feeding guild, and other trophic guilds were added downstream. The major gradient of habitat change downstream consisted of a decrease in pool habitat and increases in stream width, depth, current velocity, turbidity, and proportion of the channel consisting of run habitat. Minor gradients of habitat change involved streambank condition and substrate particle size. Contrary to streams in forested regions, habitat diversity did not increase downstream, suggesting that increased living space and moderating environmental conditions contributed to the downstream increase in species richness. Local habitat modification due to cattle grazing or alterations in streamflow caused minor changes in fish assemblages but did not disrupt the dominant longitudinal patterns. Broad-scale zonation based on temperature regime and additive patterns within zones should typify other streams originating in montane regions
1. In this review, we first summarize how hydrologic connectivity has been studied for riverine fish capable of moving long distances, and then identify research opportunities that have clear conservation significance. Migratory species, such as anadromous salmonids, are good model organisms for understanding ecological connectivity in rivers because the spatial scale over which movements occur among freshwater habitats is large enough to be easily observed with available techniques; they are often economically or culturally valuable with habitats that can be easily fragmented by human activities; and they integrate landscape conditions from multiple surrounding catchment(s) with in‐river conditions. Studies have focussed on three themes: (i) relatively stable connections (connections controlled by processes that act over broad spatio‐temporal scales >1000 km ² and >100 years); (ii) dynamic connections (connections controlled by processes acting over fine to moderate spatio‐temporal scales ∼1–1000 km ² and <1–100 years); and (iii) anthropogenic influences on hydrologic connectivity, including actions that disrupt or enhance natural connections experienced by fish.
2. We outline eight challenges to understanding the role of connectivity in riverine fish ecology, organized under three foci: (i) addressing the constraints of river structure; (ii) embracing temporal complexity in hydrologic connectivity; and (iii) managing connectivity for riverine fishes. Challenges include the spatial structure of stream networks, the force and direction of flow, scale‐dependence of connectivity, shifting boundaries, complexity of behaviour and life histories and quantifying anthropogenic influence on connectivity and aligning management goals. As we discuss each challenge, we summarize relevant approaches in the literature and provide additional suggestions for improving research and management of connectivity for riverine fishes.
3. Specifically, we suggest that rapid advances are possible in the following arenas: (i) incorporating network structure and river discharge into analyses; (ii) increasing explicit consideration of temporal complexity and fish behaviour in the scope of analyses; and (iii) parsing degrees of human and natural influences on connectivity and defining acceptable alterations. Multiscale analyses are most likely to identify dominant patterns of connections and disconnections, and the appropriate scale at which to focus conservation activities.
Increasingly, river managers are turning from hard engineering solutions to ecologically based restoration activities in order to improve degraded waterways. River restoration projects aim to maintain or increase ecosystem goods and services while protecting downstream and coastal ecosystems. There is growing interest in applying river restoration techniques to solve environmental problems, yet little agreement exists on what constitutes a successful river restoration effort.
We propose five criteria for measuring success, with emphasis on an ecological perspective. First, the design of an ecological river restoration project should be based on a specified guiding image of a more dynamic, healthy river that could exist at the site. Secondly, the river's ecological condition must be measurably improved. Thirdly, the river system must be more self‐sustaining and resilient to external perturbations so that only minimal follow‐up maintenance is needed. Fourthly, during the construction phase, no lasting harm should be inflicted on the ecosystem. Fifthly, both pre‐ and post‐assessment must be completed and data made publicly available.
Determining if these five criteria have been met for a particular project requires development of an assessment protocol. We suggest standards of evaluation for each of the five criteria and provide examples of suitable indicators.
Synthesis and applications . Billions of dollars are currently spent restoring streams and rivers, yet to date there are no agreed upon standards for what constitutes ecologically beneficial stream and river restoration. We propose five criteria that must be met for a river restoration project to be considered ecologically successful. It is critical that the broad restoration community, including funding agencies, practitioners and citizen restoration groups, adopt criteria for defining and assessing ecological success in restoration. Standards are needed because progress in the science and practice of river restoration has been hampered by the lack of agreed upon criteria for judging ecological success. Without well‐accepted criteria that are ultimately supported by funding and implementing agencies, there is little incentive for practitioners to assess and report restoration outcomes. Improving methods and weighing the ecological benefits of various restoration approaches require organized national‐level reporting systems.
Large-scale culvert replacement programs could benefit migratory fish populations by reconnecting reproductive and foraging habitats in fragmented watersheds. The objectives of this study were to: (1) identify stream and culvert characteristics contributing to fish passage barriers within an Appalachian watershed, U.S.A.; (2) quantify the total amount of Brook trout (Salvelinus fontinalis) reproductive habitat isolated above culverts; and (3) use an ecological currency to identify culvert replacement priorities and stream mitigation credit opportunities. We surveyed 120 state-owned culverts and used a fish passage assessment filter to determine the “passability” of each culvert. We then constructed a geographic information system stream network model to quantify the amount of trout reproductive habitat isolated by culverts. Ninety-seven percent of surveyed culverts were classified as obstacles or complete barriers to trout dispersal. Culvert impassability was higher in small streams with slopes exceeding 3–5%, suggesting a direct relationship between slope and impassability. Thirty-three percent of Brook trout reproductive habitat, representing over 200 km of stream, was isolated by culverts. This is a conservative estimate, because we did not survey privately or federally owned culverts. The top 20 prioritized culverts accounted for nearly half of the habitat loss. Our results indicate that standard culvert designs placed in streams with slopes exceeding 5% consistently produce trout dispersal barriers and should be avoided during new road construction. The process developed here provides an efficient method for identifying culvert replacement priorities and may be used to maximize watershed scale benefits of stream restoration.
Movements of brook trout (Salvelinus fontinalis) were studied in two high-elevation (>2700 m) Colorado streams by marking (n = 4005) and recapturing fish using weirs and electrofishing at locations spaced up to 4500 m apart. Movement was most common in the upstream direction during summer, and about equal upstream and downstream between summers. Highest rates of movement occurred during and just after runoff, and before spawning, but substantial numbers of fish moved throughout the summer. Fish captured moving through weirs tended to be longer but in poorer condition than fish captured during electrofishing in 500-m reaches between weirs (i.e., the general population). On the basis of capture histories for individual fish, 59 and 66% in the two streams moved at least 50 m (up to 3380 m), even though most could be tracked only for several months. Thus, significant proportions of fish in electrofishing samples spaced throughout the stream bore marks from locations up to 2000 m away, indicating that long-range movements were relatively common. This conclusion is contrary to most literature on resident stream salmonids. We show how methods commonly used to study movement may he seriously biased, and suggest that movement may be more widespread than currently recognized.
Competition between brook trout (Salvelinus fontinalis) and brown trout (Salmo truttta) was studied by measuring characteristics of daytime positions held by brook trout before and after removal of the brown trout from 1800 m of a stream. We used four criteria as indices of position quality: "water velocity difference" (the difference between velocity at the focal point and in the fastest current within 60 cm of the fish), water depth, distance to stream bed, and lighting. After brown trout removal, brook trout larger than 15 cm chose resting positions with more favorable water velocity characteristics and more often in shade. The position shift was greatest for the largest brook trout, those of 20–30 cm. Feeding positions of brook trout changed little upon brown trout removal according to our criteria. The shift in resting positions of brook trout after release from competition with brown trout indicates that brown trout excluded brook trout from preferred resting positions, a critical and scarce resource. The combined effects of such interspecific competition, differential susceptibility to angling, differential response to environmental factors, and predation of brown trout on juvenile brook trout may account for declines of brook trout populations while brown trout populations expand in many streams of the northeastern United States where the two species are sympatric.Key words: brook trout, brown trout, competition, ecological release, microhabitat use, resting positions, feeding positions, stream, Michigan
Anthropogenic barriers to fish passage, such as culverts and dams, are major factors impeding the persistence and recovery of aquatic species. Considerable work has focused on mitigating these impacts; however, activities associated with measuring and restoring connectivity of aquatic ecosystems often face challenges in determining the passability of barriers by aquatic species. Hydrological modeling software that incorporates biological aspects of a focal species is often used as a relatively inexpensive method for assessing barrier passability for restoration decisions. However, the biological relevance of these approaches remains to be rigorously tested. We assessed passage rates of PIT-tagged Brook Trout Salvelinus fontinalis through four road culverts and adjacent reference sites (unaltered areas of the streams) on the island of Newfoundland to determine whether upstream passage through road culverts was more restrictive than unaltered reference areas of the stream. Next, we examined the usefulness of barrier passability predictions derived from FishXing software by comparing them with in situ movement data for this species. Brook Trout passage for three of the four reference sites had a significantly higher range of passable stream flows compared with that for culverts, indicating the presence of velocity barriers in culverts. However, FishXing predictions of suitable fish passage discharges were conservative, and tagged fish successfully navigated partial barriers that were at least 2–3 times the upper limits of stream flow predicted to allow successful passage. The results of our study show a clear need for an improved understanding of fish movement through these structures so that barrier assessment techniques can be refined. The implications of not doing so may lead to restoration actions that result in limited biological benefit.Received February 6, 2013; accepted July 2, 2013
We evaluated the effect of backpack electrofishing effort intensity on the precision of estimates of fish density in a southern Ontario stream. Single‐pass electrofishing was conducted on 30 sites at three electrofishing effort intensities (5, 10 and 15 s/m ² ). We found that an effort of 5 s/m ² yielded an average catch that was 78% of the 15‐s/m ² effort. An asymptotic model effectively described the catch–effort relationship for most fish taxa in the stream (i.e., Rainbow Trout Oncorhynchus mykiss , Brown Trout Salmo trutta , sculpin Cottus sp., dace Rhinichthys sp., and darter Etheostoma sp.). Using the catchability parameters of this model, we evaluated the trade‐off between sampling many sites at low intensity or fewer sites at higher intensity. The survey design that maximizes precision of fish‐density estimates depends on the average time spent traveling between sites and the average area of sites. For southern Ontario streams, where sample sites were approximately 300 m ² and travel time between sites was 75 min, the optimum electrofishing effort intensity was approximately 5 s/m ² . The applicability of these results to other systems was demonstrated by showing how this optimum intensity was affected by differences in catchability rates of fish and travel distances. These findings will be used to standardize single pass electrofishing catches in nonshield areas of Ontario, and the approach may prove useful in other areas where this fishing technique is effective.
Received January 5, 2012; accepted December 7, 2012
The inland fisheries of North America (i.e. Canada and the United States of America) are diverse in terms of the sectors that harvest fish, the waters fished and the species targeted. Aboriginal fisheries have a long tradition of harvesting fish for food and ceremonial purposes using gears such as dip nets and spears, and targeting species such as suckers (Catostomidae) and upriver migrating salmon (Salmonidae). The commercial sector includes large-scale industrial operations on the Great Lakes and Mississippi River as well as smaller-scale fisheries throughout North America that harvest fish for food or the bait industry. The recreational fishery is the largest sector (millions of participants) and includes everything from specialised catch-and-release fisheries for muskellunge, Esox masquinongy Mitchill and black bass (Micropterus spp.) to put-and-take fisheries for rainbow trout, Oncorhynchus mykiss (Walbaum). All sectors provide substantial socio-economic benefit and regionally can have significant cultural value and yield an important amount of food protein. Using the best available information and a number of assumptions, total harvest for all three sectors in the inland waters of North America was estimated to be >480 000 t yr−1. Nonetheless, there are a number of internal threats that face these fisheries including over-exploitation, bycatch/release mortality as well as external threats such as inter-sectoral conflict, environmental change, water availability, invasive species and habitat alteration. Given that most inland fisheries are managed at the state/provincial level, there is a need to adopt management strategies that are holistic, coordinated and trans-jurisdictional if inland fisheries in North America are to be sustainable in the future. There is also a critical need for information management systems that enable regional data to be scaled up to the national or continental level, which would facilitate the generation of inland fisheries status reports and the monitoring of trends through time. All stakeholders must recognise that while inland fisheries tend to not receive the same attention from the media, public or politicians as marine fisheries, the potential for local and broad-scale irreversible changes exist and need to be identified and addressed if the many ecosystem services that inland fisheries provide are to be maintained.
We propose that the Concept provides a framework for integrating predictable and observable biological features of lotic systems. Implications of the concept in the areas of structure, function, and stability of riverine ecosystems are discussed. -from Authors
Habitat fragmentation in aquatic systems has led to widespread isolation of stream fishes. Metapopulation theory predicts that persistence is directly related to local patch size and its characteristics, but because these relationships tend to be taxon-specific, empirical data are important. We assembled 246 observations of occurrence of westslope cutthroat trout (WCT), a taxon of concern in the western U.S. and Canada, in stream networks isolated for up to 100 years (median 40 years) above human-made barriers, mostly culverts, at road crossings within U.S. National Forests. We used logistic regression to analyse how WCT occurrence varied with patch size, isolation time and stream-level covariates. Occurrence was positively related to stream length and habitat quality within the isolated stream network and negatively related to elevation and channel gradient. Unexpectedly, the probability of occurrence was not related to how long a habitat patch had been isolated. At the median elevation (1354 m) and channel gradient (14%), and where habitat quality was poor, WCT were likely to occur (probability >0.5) if an isolated stream network was at least 1.7 km. If habitat quality was high, about 0.2 km of habitat produced the same probability. Although there are important limitations, this analysis provides the first empirical estimate for how patch size and patch-level characteristics influence persistence of WCT in isolated stream networks.
A key challenge in aquatic restoration efforts is documenting locations where ecological connectivity is disrupted in water bodies that are dammed or crossed by roads (road crossings). To prioritize actions aimed at restoring connectivity, we argue that there is a need for systematic inventories of these potential barriers at regional and national scales. Here, we address this limitation for the North American Great Lakes basin by compiling the best available spatial data on the locations of dams and road crossings. Our spatial database documents 38 times as many road crossings as dams in the Great Lakes basin, and case studies indicate that, on average, only 36% of road crossings in the area are fully passable to fish. It is therefore essential that decision makers account for both road crossings and dams when attempting to restore aquatic ecosystem connectivity. Given that road crossing structures are commonly upgraded as part of road maintenance, many opportunities exist to restore connections within aquatic ecosystems at minimal added cost by ensuring upgrade designs permit water flow and the passage of fish and other organisms. Our findings highlight the necessity for improved dam and road crossing inventories that traverse political boundaries to facilitate the restoration of aquatic ecosystem connectivity from local to global scales.
Loss of natural river network connectivity is presumed to be one of the more generalized and important human-induced alterations in natural environments and is frequently perceived as one of the main causes of the decline of freshwater fish species.The purpose of the present study was to ascertain the impact of barriers on the distribution of freshwater fish species with distinct life histories. In this study 196 sites in three river basins in Western Iberia were sampled and analyzed for the presence of barriers. Three alternative analytical approaches based on Generalized Linear Models (GLM) were used to test the contribution of connectivity-related variables to species distribution: (1) explore whether connectivity-related variables are included in the best-fitting distribution models; (2) use models calibrated at non-disturbed sites to compute deviations from model predictions made at sites with connectivity-related disturbances; and (3) use a hierarchical partitioning approach, in which the improvement of model fit due to the inclusion of connectivity as a predictor variable is assessed using all possible variable combinations.The results indicate a general lack of influence of barriers on freshwater fish species distributions. The effects of environment and human pressures exceeded the isolated effect of connectivity losses. Further studies based on experimental designs that are more specifically directed at this specific issue are needed in order to fully understand the effects of barriers on species and communities. A more thorough assessment of the effects of connectivity on fish is crucial to the implementation of adequate restoration actions that are in turn needed to achieve the goals of the European Water Framework Directive.
Neither linear nor two-dimensional frameworks may be the most appropriate for fish and other species constrained to disperse within river-creek systems. In particular, the hierarchical, dendritic structures of riverine networks are not well captured by existing spatial models. Here I use a simple geometric model and metapopulation modeling to make three points concerning the ecological consequences of dendritic landscapes. First, connectivity patterns of river-creek networks differ from linear landscapes, and these differences in connectivity can either enhance or reduce metapopulation persistence compared to linear systems, depending on the details of dispersal. Second, habitat fragmentation in dendritic landscapes has different (and arguably more severe) consequences on fragment size than in either linear or two-dimensional systems, resulting in both smaller fragments and higher variance in fragment size. Third, dendritic landscapes can induce striking mismatches between the geometry of dispersal and the geometry of disturbance, and as is the case for arid-lands fishes, such mismatches can be important for population persistence.
While it is widely acknowledged that culverted road-stream crossings may impede fish passage, effects of culverts on movement of nongame and small-bodied fishes have not been extensively studied and studies generally have not accounted for spatial variation in capture probabilities. We estimated probabilities for upstream and downstream movement of small (30-120 mm standard length) benthic and water column fishes across stream reaches with and without culverts at four road-stream crossings over a 4-6-week period. Movement and reach-specific capture probabilities were estimated using multistate capture-recapture models. Although none of the culverts were complete barriers to passage, only a bottomless-box culvert appeared to permit unrestricted upstream and downstream movements by benthic fishes based on model estimates of movement probabilities. At two box culverts that were perched above the water surface at base flow, observed movements were limited to water column fishes and to intervals when runoff from storm events raised water levels above the perched level. Only a single fish was observed to move through a partially embedded pipe culvert. Estimates for probabilities of movement over distances equal to at least the length of one culvert were low (e.g., generally ≤0.03, estimated for 1-2-week intervals) and had wide 95% confidence intervals as a consequence of few observed movements to nonadjacent reaches. Estimates of capture probabilities varied among reaches by a factor of 2 to over 10, illustrating the importance of accounting for spatially variable capture rates when estimating movement probabilities with capture-recapture data. Longer-term studies are needed to evaluate temporal variability in stream fish passage at culverts (e.g., in relation to streamflow variability) and to thereby better quantify the degree of population fragmentation caused by road-stream crossings with culverts.
This paper examines the usage and measurement of “landscape connectivity” in 33 recent studies. Connectivity is defined as the degree to which a landscape facilitates or impedes movement of organisms among resource patches. However, connectivity is actually used in a variety of ways in the literature. This has led to confusion and lack of clarity related to (1) function vs structure, (2) patch isolation vs landscape connectivity and, (3) corridors vs connectivity. We suggest the term connectivity should be reserved for its original purpose. We highlight nine studies; these include modeling studies that actually measured connectivity in accordance with the definition, and empirical studies that measured key components of connectivity. We found that measurements of connectivity provide results that can be interpreted as recommending habitat fragmentation to enhance landscape connectivity. We discuss reasons for this misleading conclusion, and suggest a new way of quantifying connectivity, which avoids this problem. We also recommend a method for reducing sampling intensity in landscape-scale empirical studies of connectivity.
The term riverine landscape implies a holistic geomorphic perspective of the extensive interconnected series of biotopes and environmental gradients that, with their biotic communities, constitute fluvial systems. Natural disturbance regimes maintain multiple interactive pathways (connectivity) across the riverine landscape. Disturbance and environmental gradients, acting in concert, result in a positive feedback between connectivity and spatio-temporal heterogeneity that leads to the broadscale patterns and processes responsible for high levels of biodiversity. Anthropogenic impacts such as flow regulation, channelization, and bank stabilization, by (1) disrupting natural disturbance regimes, (2) truncating environmental gradients, and (3) severing interactive pathways, eliminate upstream-downstream linkages and isolate river channels from riparian/floodplain systems and contiguous groundwater aquifers. These alterations interfere with successional trajectories, habitat diversification, migratory pathways and other processes, thereby reducing biodiversity. Ecosystem management is necessary to maintain or restore biodiversity at a landscape scale. To be effective, conservation efforts should be based on a solid conceptual foundation and a holistic understanding of natural river ecosystems. Such background knowledge is necessary to re-establish environmental gradients, to reconnect interactive pathways, and to reconstitute some semblance of the natural dynamics responsible for high levels of biodiversity. The challenge for the future lies in protecting the ecological integrity and biodiversity of aquatic systems in the face of increasing pressures on our freshwater resources. This will require integrating sound scientific principles with management perspectives that recognize floodplains and groundwaters as integral components of rivers and that are based on sustaining, rather than suppressing, environmental heterogeneity.
Nonparametric multivariate analysis of ecological data using permutation tests has two main challenges: (1) to partition the variability in the data according to a complex design or model, as is often required in ecological experiments, and (2) to base the analysis on a multivariate distance measure (such as the semimetric Bray-Curtis measure) that is reasonable for ecological data sets. Previous nonparametric methods have succeeded in one or other of these areas, but not in both. A recent contribution to Ecological Monographs by Legendre and Anderson, called distance-based redundancy analysis (db-RDA), does achieve both. It does this by calculating principal coordinates and subsequently correcting for negative eigenvalues, if they are present, by adding a constant to squared distances. We show here that such a correction is not necessary. Partitioning can be achieved directly from the distance matrix itself, with no corrections and no eigenanalysis, even if the distance measure used is semimetric. An ecological example is given to show the differences in these statistical methods. Empirical simulations, based on parameters estimated from real ecological species abundance data, showed that db-RDA done on multifactorial designs (using the correction) does not have type 1 error consistent with the significance level chosen for the analysis (i.e., does not provide an exact test), whereas the direct method described and advocated here does.
From headwaters to mouth, the physical variables within a river system present a continuous gradient of physical conditions. This gradient should elicit a series of responses within the constituent populations resulting in a continuum of biotic adjustments and consistent patterns of loading, transport, utilization, and storage of organic matter along the length of a river. Based on the energy equilibrium theory of fluvial geomorphologists, we hypothesize that the structural and functional characteristics of stream communities are adapted to conform to the most probable position or mean state of the physical system. We reason that producer and consumer communities characteristic of a given river reach become established in harmony with the dynamic physical conditions of the channel. In natural stream systems, biological communities can be characterized as forming a temporal continuum of synchronized species replacements. This continuous replacement functions to distribute the utilization of energy inputs over time. Thus, the biological system moves towards a balance between a tendency for efficient use of energy inputs through resource partitioning (food, substrate, etc.) and an opposing tendency for a uniform rate of energy processing throughout the year. We theorize that biological communities developed in natural streams assume processing strategies involving minimum energy loss. Downstream communities are fashioned to capitalize on upstream processing inefficiencies. Both the upstream inefficiency (leakage) and the downstream adjustments seem predictable. We propose that this River Continuum Concept provides a framework for integrating predictable and observable biological features of lotic systems. Implications of the concept in the areas of structure, function, and stability of riverine ecosystems are discussed.Key words: river continuum; stream ecosystems; ecosystem structure, function; resource partitioning; ecosystem stability; community succession; river zonation; stream geomorphology
We present a new multivariate technique for testing the significance of individual terms in a multifactorial analysis-of-variance model for multispecies response variables. The technique will allow researchers to base analyses on measures of association (distance measures) that are ecologically relevant. In addition, unlike other distance-based hypothesis-testing techniques, this method allows tests of significance of interaction terms in a linear model. The technique uses the existing method of redundancy analysis (RDA) but allows the analysis to be based on Bray-Curtis or other ecologically meaningful measures through the use of principal coordinate analysis (PCoA). Steps in the procedure include: (1) calculating a matrix of distances among replicates using a distance measure of choice (e.g., Bray-Curtis); (2) determining the principal coordinates (including a correction for negative eigenvalues, if necessary), which preserve these distances; (3) creating a matrix of dummy variables corresponding to the design of the experiment (i.e., individual terms in a linear model); (4) analyzing the relationship between the principal coordinates (species data) and the dummy variables (model) using RDA; and (5) implementing a test by permutation for particular statistics corresponding to the particular terms in the model. This method has certain advantages not shared by other multivariate testing procedures. We demonstrate the use of this technique with experimental ecological data from intertidal assemblages and show how the presence of significant multivariate interactions can be interpreted. It is our view that distance-based RDA will be extremely useful to ecologists measuring multispecies responses to structured multifactorial experimental designs.
In this paper it is shown that the classical maximum likelihood principle can be considered to be a method of asymptotic realization of an optimum estimate with respect to a very general information theoretic criterion. This observation shows an extension of the principle to provide answers to many practical problems of statistical model fitting.
We developed an automated procedure for modeling spatial distribution of fish occurrence using logistic regression models and geographic information system (GIS) tools. Predictors were measured from a digital elevation model (DEM) and stream layers. We evaluated the accuracy of GIS measures of reach slope through a comparison with field measures. Resource selection function models were used to explain presence-absence of bull trout (Salvelinus confluentus), rainbow trout, (Oncorhynchus mykiss), nonnative brook trout (Salvelinus fontinalis), and all fishes. Our models were extrapolated based on low, medium, and high levels of probability to produce reach-scale maps across 12 000 km2. We attempted to improve models by adding land-use variables; however, the terrain best suited to road building and harvest also contained the habitat selected by rainbow trout, whereas bull trout generally selected terrain too steep for land use. These confounding factors emphasize the need for process-based investigations in addition to correlative approaches to identify habitat requirements. This automated method provides a rapid evaluation of fish habitat across remote areas useful for salmonid conservation and research planning.
We used mark-recapture techniques to examine the effects of four types of road crossings on fish movement during spring base flows and summer low flows in small streams of the Ouachita Mountains, west-central Arkansas. We assessed movement for 21 fish species in seven families through culvert, slab, open-box, and ford crossings and through natural reaches. We detected no seasonal or directional bias in fish movement through any crossing type or the natural reaches. Overall fish movement was an order of magnitude lower through culverts than through other crossings or natural reaches, except no movement was detected through the slab crossing. In contrast, open-box and ford crossings showed little difference from natural reaches in overall movement of fishes. Numbers of species that traversed crossings and movement within three of four dominant fish families (Centrarchidae, Cyprinidae, and Fundulidae) also were reduced at culverts relative to ford and open-box crossings and natural reaches. In spring, retention of fishes was consistently highest in stream segments upstream of crossings and lowest in downstream segments for all crossing types, a response attributed to scouring associated with spring spates. Water velocity at crossings was inversely related to fish movement; culvert crossings consistently had the highest velocities and open-box crossings had the lowest. A key requirement for improving road crossing designs for small-stream fish passage will be determination of critical levels of water velocity through crossings.
The density, biomass and estimated production of brook trout Salvelinus fontinalis and Atlantic salmon Salmo salar were related to habitat factors in streams of Terra Nova National Park, Newfoundland, Canada. Fish communities at 29 sites (18 brooks; 15 watersheds) were sampled in the summer of 2002, 2003 and 2005. Salmonid density, biomass per unit area and production (derived from biomass and fish size using allometric P:B relationships) were compared with site habitat characteristics (wetted width, lactustrine habitat, per cent riffle habitat, canopy coverage and stream gradient), using an interactive stepwise multiple linear regression. Salmonid biomass (mean: 2·87 g m−2; range: 0·33–10·88 g m−2) and estimated production (mean: 3·05 g m−2 year−1; range: 0·32–10·98 g m−2 year−1) within the study area varied by an order of magnitude, however, habitat variables accounted for much of this variation. Specifically, wetted width and lacustrine area of the tributary played important roles in explaining density, biomass and production. Wetted width was important for all measurements of brook trout and total salmonids while lacustrine area was important for all measurements of Atlantic salmon and played a lesser role in total salmonid biomass. Other factors such as the percentage of riffle habitat, site gradient and canopy coverage provided modest improvements to the fit of some relationships. When models using the same environmental factors were compared, those using production estimates derived from allometric P:B equations in the literature provided improved predictive capability than did those from direct density and biomass estimates. It is proposed that allometric P:B relationships have utility in improving comparisons of stream fish communities, particularly in studies with insufficient resources to measure production directly.
Abstract – The blue shiner (Cyprinella caerulea) is a federally threatened cyprinid that inhabits discrete habitat patches, but whether the fish in these patches represent distinct subpopulations or a continuous population is not known. Movement patterns of adult blue shiners among habitat patches in the Conasauga River (Tennessee and Georgia, USA) were investigated to determine if movement among patches was unrestricted, or if each patch represented a relatively discrete subpopulation. Movement was restricted to a small proportion of individuals at any given time, and most fish that moved did so between adjacent habitat patches. The average distance moved by blue shiners over the two study periods (1997 and 1998) was just 130.7 m. Riffle and glide mesohabitats were not barriers to the dispersal of blue shiners, and fish moved both upstream and downstream in approximately equal numbers. It is suggested that the fish that are mobile at a given time are responsible for recolonization of habitat patches via cumulative, stepwise movements between adjacent patches, and that intervening patches must be present to maintain connectivity of the entire population. Blue shiners exist as relatively discrete subpopulations in the Conasauga River. This finding emphasizes the importance of protecting habitat integrity throughout the entire course of the river to prevent isolation of subpopulations. This species may be used as a model for the conservation of other patch-restricted aquatic species.†
Structural modifications to landscapes affect the ability of organisms to access different habitat patches. There exist, however, very few general methods by which to relate modifications to expectations of effects, and even fewer that enable understanding of how multiple modifications may interact. In the absence of any guiding principles, ecologists have assumed that interactions will result in complex landscape-scale effects. One way of understanding such effects is through rendering a landscape as a graph or network, among the simplest of which are dendritic networks typified by stream systems. Yet even for stream networks, there are no known general principles concerning the nature of interactions between multiple modifications. We developed a model to describe the ability of fish to access and use different habitat patches within dendritic networks. We used mathematical and numerical analyses of the model to investigate how the habitat value of a network is affected by changes in connectivity and habitat quality, and then to examine interactions between multiple modifications. Rather than showing complex interactions, our analytic and simulation-based results show that the combined effect of multiple modifications approximately equals the sum of individually predicted effects. Dendritic networks thus appear to respond far more simply to multiple modifications than has previously been assumed. These results have implications for stream management planning, and offer a firm foundation from which to better understand population processes within dendritic networks.
Key Words catchment, disturbance, stressor response, stream health, river ■ Abstract Local habitat and biological diversity of streams and rivers are strongly influenced by landform and land use within the surrounding valley at multiple scales. However, empirical associations between land use and stream response only varyingly succeed in implicating pathways of influence. This is the case for a number of reasons, including (a) covariation of anthropogenic and natural gradients in the landscape; (b) the existence of multiple, scale-dependent mechanisms; (c) nonlinear responses; and (d) the difficulties of separating present-day from historical influences. Further research is needed that examines responses to land use under different management strategies and that employs response variables that have greater diagnostic value than many of the aggregated measures in current use. In every respect, the valley rules the stream.