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A Practitioner's Perspective on the Continuing Technical Merits of PHABSIM
... Based on studies and ideas conceived in the 1960s and 1970s (Stalnaker et al., 2017), the very first popular implementation of these approaches was the Physical Habitat Simulation System (PHABSIM, Milhous, 1979;, which become a fundamental element of the following Instream Flow Incremental Methodology (IFIM) developed by the U.S. Fish and Wildlife Service . PHABSIM and subsequent physical habitat simulation approaches have been stated to be the most defendable approaches, even from a legal perspective, because they render the numeric outputs necessary to overcome inaccuracies and biases linked to other more subjective methods (Reiser & Hilgert, 2018;. Nonetheless, this group of approaches represents the core component in several decision support systems (e.g., System for Environmental Flow Analysis-SEFA; Payne & Jowett, 2012) or is used extensively in some of the most sophisticated holistic approaches for the multiobjective optimization of water allocation schemes (Alexander et al., 2018). ...
... Other authors criticized particular choices within each model component, such as the use of one-dimensional (1D) hydraulic models to simulate the distribution patterns of depth and velocity under different running flows, the use of univariate HSC, or focusing exclusively on a single species, to name a few (Railsback, 2016(Railsback, , 2017. Although these concerns and criticisms are still valid for a number of studies, over the years scientists and practitioners have improved the original practices to address most of these limitations (Reiser & Hilgert, 2018). Therefore there can be found multiple studies employing two-dimensional (2D) and three-dimensional (3D) hydraulic models (e.g., Muñoz-Mas, Marcos-Garcia, et al., 2018), multivariate nonlinear habitat suitability models (e.g., Vezza, Parasiewicz, Calles, et al., 2014;, or focusing on multiple species (e.g., Alexander et al., 2018;Vezza et al., 2012), although comparatively the multispecies approach is less habitual . ...
... Rainfall-runoff models are usually implemented to determine the natural flow regime and water yield and, since historical time series are no longer valid (King & Brown, 2018;Poff, 2018;, climate change scenarios are routinely used to feed the resulting hydrological model (e.g., Muñoz-Mas, Marcos-Garcia, et al., 2018). Other relevant environmental variables that experience temporal changes (e.g., water quality or sediment transport) can likewise be modeled and included within this component (see Reiser & Hilgert, 2018, and references therein). Nevertheless, it has been stressed that e-flow assessment should at least account for water temperature, since water abstractions and climate change have combined effects on the water thermal regime (Muñoz-Mas, Marcos-Garcia, et al., 2018;. ...
... Based on studies and ideas conceived in the 1960s and 1970s (Stalnaker et al., 2017), the very first popular implementation of these approaches was the Physical Habitat Simulation System (PHABSIM, Milhous, 1979;, which become a fundamental element of the following Instream Flow Incremental Methodology (IFIM) developed by the U.S. Fish and Wildlife Service . PHABSIM and subsequent physical habitat simulation approaches have been stated to be the most defendable approaches, even from a legal perspective, because they render the numeric outputs necessary to overcome inaccuracies and biases linked to other more subjective methods (Reiser & Hilgert, 2018;. Nonetheless, this group of approaches represents the core component in several decision support systems (e.g., System for Environmental Flow Analysis-SEFA; Payne & Jowett, 2012) or is used extensively in some of the most sophisticated holistic approaches for the multiobjective optimization of water allocation schemes (Alexander et al., 2018). ...
... Other authors criticized particular choices within each model component, such as the use of one-dimensional (1D) hydraulic models to simulate the distribution patterns of depth and velocity under different running flows, the use of univariate HSC, or focusing exclusively on a single species, to name a few (Railsback, 2016(Railsback, , 2017. Although these concerns and criticisms are still valid for a number of studies, over the years scientists and practitioners have improved the original practices to address most of these limitations (Reiser & Hilgert, 2018). Therefore there can be found multiple studies employing two-dimensional (2D) and three-dimensional (3D) hydraulic models (e.g., Muñoz-Mas, Marcos-Garcia, et al., 2018), multivariate nonlinear habitat suitability models (e.g., Vezza, Parasiewicz, Calles, et al., 2014;, or focusing on multiple species (e.g., Alexander et al., 2018;Vezza et al., 2012), although comparatively the multispecies approach is less habitual . ...
... Rainfall-runoff models are usually implemented to determine the natural flow regime and water yield and, since historical time series are no longer valid (King & Brown, 2018;Poff, 2018;, climate change scenarios are routinely used to feed the resulting hydrological model (e.g., Muñoz-Mas, Marcos-Garcia, et al., 2018). Other relevant environmental variables that experience temporal changes (e.g., water quality or sediment transport) can likewise be modeled and included within this component (see Reiser & Hilgert, 2018, and references therein). Nevertheless, it has been stressed that e-flow assessment should at least account for water temperature, since water abstractions and climate change have combined effects on the water thermal regime (Muñoz-Mas, Marcos-Garcia, et al., 2018;. ...
Mountains and mountain rivers provide a multitude of invaluable goods and services to a profound portion of the planet’s population. As “water towers” of the Earth mountains are sources of the mightiest world rivers and play a pivotal role for global biodiversity, freshwater, and sediment supply. Distinct morphological, climatic, hydrological, hydrochemical, and biological features of mountainous river ecosystems, compared to lowland ones, make them particularly fragile and vulnerable to human interference. Despite a number of remote mountain areas and rivers still remaining intact from direct human pressures, the majority of mountain ecosystems, are being increasingly threatened by adverse local and global changes driven by market economy. To efficiently conserve and sustainably use mountain ecosystems and contribute to the survival of the planet, it is critical to change our standards and life attitudes by realizing and appreciating our immediate connection to the global ecosystem, change attitudes and current consumption patterns, and stimulate the ways our global society functions and interacts with the natural environment.
... Based on studies and ideas conceived in the 1960s and 1970s (Stalnaker et al., 2017), the very first popular implementation of these approaches was the Physical Habitat Simulation System (PHABSIM, Milhous, 1979;, which become a fundamental element of the following Instream Flow Incremental Methodology (IFIM) developed by the U.S. Fish and Wildlife Service . PHABSIM and subsequent physical habitat simulation approaches have been stated to be the most defendable approaches, even from a legal perspective, because they render the numeric outputs necessary to overcome inaccuracies and biases linked to other more subjective methods (Reiser & Hilgert, 2018;. Nonetheless, this group of approaches represents the core component in several decision support systems (e.g., System for Environmental Flow Analysis-SEFA; Payne & Jowett, 2012) or is used extensively in some of the most sophisticated holistic approaches for the multiobjective optimization of water allocation schemes (Alexander et al., 2018). ...
... Other authors criticized particular choices within each model component, such as the use of one-dimensional (1D) hydraulic models to simulate the distribution patterns of depth and velocity under different running flows, the use of univariate HSC, or focusing exclusively on a single species, to name a few (Railsback, 2016(Railsback, , 2017. Although these concerns and criticisms are still valid for a number of studies, over the years scientists and practitioners have improved the original practices to address most of these limitations (Reiser & Hilgert, 2018). Therefore there can be found multiple studies employing two-dimensional (2D) and three-dimensional (3D) hydraulic models (e.g., Muñoz-Mas, Marcos-Garcia, et al., 2018), multivariate nonlinear habitat suitability models (e.g., Vezza, Parasiewicz, Calles, et al., 2014;, or focusing on multiple species (e.g., Alexander et al., 2018;Vezza et al., 2012), although comparatively the multispecies approach is less habitual . ...
... Rainfall-runoff models are usually implemented to determine the natural flow regime and water yield and, since historical time series are no longer valid (King & Brown, 2018;Poff, 2018;, climate change scenarios are routinely used to feed the resulting hydrological model (e.g., Muñoz-Mas, Marcos-Garcia, et al., 2018). Other relevant environmental variables that experience temporal changes (e.g., water quality or sediment transport) can likewise be modeled and included within this component (see Reiser & Hilgert, 2018, and references therein). Nevertheless, it has been stressed that e-flow assessment should at least account for water temperature, since water abstractions and climate change have combined effects on the water thermal regime (Muñoz-Mas, Marcos-Garcia, et al., 2018;. ...
The modification of sediment and flow regimes caused by damming and river regulation has deleterious effects on the ecological and morphological river processes. This alteration of river systems triggered the implementation of safeguarding environmental flows (e-flows) defined as “the quantity, timing, and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and wellbeing that depend on these ecosystems”. In the last decades, physical habitat simulation approaches emerged as fundamental stand-alone or supplementary methods for e-flow assessment. These approaches combine three main components: (1) hydraulic simulation, (2) habitat suitability modeling, to determine the quality of the available habitat, and (3) hydrological analyses (under current and climate change scenarios). E-flow regimes are finally defined, by assessing the spatial and temporal habitat variability for the target taxa or community, after combining these three components. During the process of physical habitat simulation some river processes, such as sediment transport and morphological changes, are often neglected while uncertainties arise from every component. We reviewed the elements that should be considered in every component of the physical habitat simulation to reduce uncertainties with emphasis on the actual trends on the topic and how sediment transport and river morphodynamics can be included within this methodological framework.
... Based on studies and ideas conceived in the 1960s and 1970s (Stalnaker et al., 2017), the very first popular implementation of these approaches was the Physical Habitat Simulation System (PHABSIM, Milhous, 1979;, which become a fundamental element of the following Instream Flow Incremental Methodology (IFIM) developed by the U.S. Fish and Wildlife Service . PHABSIM and subsequent physical habitat simulation approaches have been stated to be the most defendable approaches, even from a legal perspective, because they render the numeric outputs necessary to overcome inaccuracies and biases linked to other more subjective methods (Reiser & Hilgert, 2018;. Nonetheless, this group of approaches represents the core component in several decision support systems (e.g., System for Environmental Flow Analysis-SEFA; Payne & Jowett, 2012) or is used extensively in some of the most sophisticated holistic approaches for the multiobjective optimization of water allocation schemes (Alexander et al., 2018). ...
... Other authors criticized particular choices within each model component, such as the use of one-dimensional (1D) hydraulic models to simulate the distribution patterns of depth and velocity under different running flows, the use of univariate HSC, or focusing exclusively on a single species, to name a few (Railsback, 2016(Railsback, , 2017. Although these concerns and criticisms are still valid for a number of studies, over the years scientists and practitioners have improved the original practices to address most of these limitations (Reiser & Hilgert, 2018). Therefore there can be found multiple studies employing two-dimensional (2D) and three-dimensional (3D) hydraulic models (e.g., Muñoz-Mas, Marcos-Garcia, et al., 2018), multivariate nonlinear habitat suitability models (e.g., Vezza, Parasiewicz, Calles, et al., 2014;, or focusing on multiple species (e.g., Alexander et al., 2018;Vezza et al., 2012), although comparatively the multispecies approach is less habitual . ...
... Rainfall-runoff models are usually implemented to determine the natural flow regime and water yield and, since historical time series are no longer valid (King & Brown, 2018;Poff, 2018;, climate change scenarios are routinely used to feed the resulting hydrological model (e.g., Muñoz-Mas, Marcos-Garcia, et al., 2018). Other relevant environmental variables that experience temporal changes (e.g., water quality or sediment transport) can likewise be modeled and included within this component (see Reiser & Hilgert, 2018, and references therein). Nevertheless, it has been stressed that e-flow assessment should at least account for water temperature, since water abstractions and climate change have combined effects on the water thermal regime (Muñoz-Mas, Marcos-Garcia, et al., 2018;. ...
In all available methodologies for the assessment of the environmental flow requirements, a sufficient knowledge of the natural hydrological regime is essential. In this chapter the hydrological data that are required in environmental flow assessment studies, their main characteristics, and their importance as well as the specific challenges in the case of mountainous areas are analyzed. The various available data sources, the measurement and processing of hydrological data, and the utilization of modeling techniques for the estimation of streamflow data in the case of ungauged or poorly gauged watersheds and for the naturalization of streamflow data are also presented. A short description of hydrological data series analysis for the determination of environmental water requirements is provided as well. Finally, sources for further reading are provided in each section.
... Vezza et al., 2012). Conversely, the TSK fuzzy models may be particularly indicated to detailed-scale studies where shorter river segments are of special interest as it is typically done in EFA studies involving physical habitat simulation approaches (Reiser & Hilgert, 2018). Thus, this study exemplified how different analysis techniques could be useful to resource managers for making specific decisions in line with the habitat preferences of fish species and assemblages. ...
... This conclusion is supported by the absolute values of the performance criteria, which were similar or higher than those obtained in previous studies on this research topic (Fukuda et al., 2013;Muñoz-Mas, Papadaki et al., 2016. Microhabitat studies almost systematically assumed the relevance of at least the triad velocity-depth-substratum (Fukuda et al., 2013;Garbe, Beevers, & Pender, 2016;Reiser & Hilgert, 2018), although the relevance of cover has occasionally been assumed too (Allouche, 2002;Johnson & Douglass, 2009;Muñoz-Mas, Papadaki et al., 2016). These variables are acknowledged as the most important at the microhabitat scale (Gibson, 1993), ...
... EFAs. Previous approaches based on the physical habitat simulation that evaluate representative river segments with microhabitat preference models-such as the fuzzy rule-based models present in this study-have been stated to be the most defendable approach from a legal perspective (Reiser & Hilgert, 2018;Tharme, 2003), rendering the numeric outputs necessary to overcome inaccuracy and biases linked to personal opinions. In accordance, results based on fuzzy rule-based models should be more credible to support more ecologically friendly alternatives in conflicting EFA, for instance, in regions where environmental flows lead to significant monetary losses (e.g. ...
Environmental flow assessment (EFA) involving microhabitat preference models is a common approach to set ecologically friendly flow regimes in territories with ongoing or planned projects to develop river basins, such as many rivers of Eastern Africa. However, habitat requirements of many African fish species are poorly studied, which may impair EFAs. This study investigated habitat preferences of fish assemblages, based on species presence–absence data from 300 microhabitats collected in two tributaries of the Kilombero River (Tanzania), aiming to disentangle differences in habitat preferences of African species at two levels: assemblage (i.e. between tributaries) and species (i.e. species‐specific habitat preferences). Overall, flow velocity, which implies coarser substrates and shallower microhabitats, emerged as the most important driver responsible of the changes in stream‐dwelling assemblages at the microhabitat scale. At the assemblage level, we identified two important groups of species according to habitat preferences: (a) cover‐orientated and limnophilic species, including Barbus spp., Mormyridae and Chiloglanis deckenii, and (b) rheophilic species, including Labeo cylindricus, Amphilius uranoscopus and Parakneria spekii. Rheophilic species preferred boulders, fast flow velocity and deeper microhabitats. At the species level, we identified species‐specific habitat preferences. For instance, Barbus spp. preferred low flow velocity shallow depth and fine‐to‐medium substratum, whereas L. cylindricus and P. spekii mainly selected shallow microhabitats with coarse substrata. Knowledge of habitat preferences of these assemblages and species should enhance the implementation of ongoing and future EFA studies of the region.
... In the present article, we make an important distinction: Some of these models relate fish quantity to habitat variables, whereas others model habitat on the basis of what the fish used (Fausch et al. 1988 ). This means that the first approach attempts to predict fish abundance given habitat conditions, whereas the second is a translation of habitat variables to predict what fish find suitable (Reiser and Hilgert 2018 ). In either case, low sample sizes, errors in measuring habitat variables, and the lack of a model selection procedure in the case of multiple competing models hampered these models in ways that could not be empirically validated (Fausch et al. 1988 ). ...
... Incorporating many mechanisms, however, becomes data intensive to inform parameters, challenging to code, and is more feasible for single species at relatively small scales, as opposed to entire communities (Beecher 2017, Kerr et al. 2023, Mawer et al. 2023. Practitioners often criticize agent-based models as being too theoretical (Reiser and Hilgert 2018 ), but new approaches now allow for analytical approaches using approximate Bayesian computation (van der Vaart et al. 2015 ) to extract parametric relationships between agents. In other words, the rule-based world of agent-based models can be analyzed to produce parameters that directly link to the riverscape and habitat being studied. ...
Multiple anthropogenic forces have pushed river ecosystems into undesirable states with no clear understanding of how they should be best managed. The advancement of riverine fish habitat models intended to provide management insights has slowed. Investigations into theoretical and empirical gaps to define habitat more comprehensively across different scales and ecological organizations are crucial in managing the freshwater biodiversity crisis. We introduce the concept of novel riverscapes to reconcile anthropogenic forcing, fish habitat, limitations of current fish habitat models, and opportunities for new models. We outline three priority data-driven opportunities that incorporate the novel riverscape concept: fish movement, river behavior, and drivers of novelty that all are integrated into a scale-based framework to guide the development of new models. Last, we present a case study showing how researchers, model developers, and practitioners can work collaboratively to implement the novel riverscape concept.
... This technique was developed in the frame of the Instream Flow Incremental Methodology (IFIM), which was originally defined as "a decision-support system designed to help natural resource managers and the constituencies determine the benefits or consequences of different water management alternatives" (Bovee, 1982;Bovee et al., 1998). Although some limitations have been regarded about the IFIM and the physical habitat simulation, there have been relevant advances in the models, and the majority of their purported shortcomings have either been or are in the process of being addressed (Reiser and Hilgert, 2018). The physical habitat simulation remains one of the most widely applied, and jurisdictionally recognized analytical tools for assessing instream-flow-related issues (Tharme, 2003;Martínez-Capel et al., 2017;Reiser and Hilgert, 2018). ...
... Although some limitations have been regarded about the IFIM and the physical habitat simulation, there have been relevant advances in the models, and the majority of their purported shortcomings have either been or are in the process of being addressed (Reiser and Hilgert, 2018). The physical habitat simulation remains one of the most widely applied, and jurisdictionally recognized analytical tools for assessing instream-flow-related issues (Tharme, 2003;Martínez-Capel et al., 2017;Reiser and Hilgert, 2018). ...
Highly regulated basins have traditionally required management practices to mitigate the negative environmental impacts and ensure human well-being. This paper proposes and assesses environmental and water supply deficit indicators to assist in the management of environmental flows (e-flows). For that, a water allocation model is applied, and hydrological alteration, habitat alteration and water supply indicators are quantified, normalized and integrated into a general basin management indicator. This basin management indicator is analyzed for four management approaches and seven e-flow scenarios in the Júcar River Basin (eastern Spain). Hydrological alteration indicators show a less pronounced alteration in the river sections located upstream of the basin while a higher alteration in the downstream sections. As for the habitat indicators, they experience an improvement compared to the natural regime. Based on the values of the basin management indicator, the best e-flow scenario to adopt in the Júcar River Basin is selected. The indicators proposed in this work are useful for supporting decision-making regarding the planning and management of e-flows in regulated river basins worldwide.
... Although PHABSIM-style models have been considered to be a rigorous, scientifically defensible means to evaluate changes in fish habitat (Tharme, 2003), they have been criticized on the basis of issues with their statistical methods, the lack of studies that validate model output, and the challenges associated with evaluating the biological significance of WUA (Mathur, Bason, Purdy, & Silver, 1985;Lancaster & Downes, 2010;Railsback, 2016). However, considerable efforts have been made to improve some of these shortcomings, and eco-hydraulic models continue to be a common and important component of water management decision processes (Reiser & Hilgert, 2018). ...
... To fully understand how fish populations are being affected in these watersheds, the eco-hydraulic modelling results presented herein should be interpreted along with additional work that evaluates the effects of stream temperature and prey availability on fish populations. This is consistent with contemporary instream flow assessments, which should use eco-hydraulic modelling results as one of a suite of tools the effects of changes in streamflow on fish populations (Reiser & Hilgert, 2018). ...
Periods of summertime low flows are often critical for fish. This study quantified the impacts of forest clearcutting on summertime low flows and fish habitat and how they evolved through time in two snowmelt‐dominant headwater catchments in the southern interior of British Columbia, Canada. A paired‐catchment analysis was applied to July‐September water yield, the number of days each year with flow less than 10% of mean annual discharge, and daily streamflow for each calendar day. The post‐harvest time series were divided into treatment periods of approximately 6‐10 years, which were analyzed independently to evaluate how the effects of forestry changed through time. An instream flow assessment using a physical habitat simulation (PHABSIM)‐style approach was used to relate streamflow to the availability of physical habitat for resident rainbow trout. About two decades after the onset of logging and as the extent of logging increased to approximately 50% of the catchments, reductions in daily summertime low flows became more significant for the July‐September yield (43%) and for the analysis by calendar day (11‐68%). Reductions in summertime low flows were most pronounced in the catchment with the longest post‐harvest time series. Based on the temporal patterns of response, we hypothesize that the delayed reductions in late‐summer flow represent the combined effects of a persistent advance in snowmelt timing in combination with at least a partial recovery of transpiration and interception loss from the regenerating forests. These results indicate that asymptotic hydrological recovery as time progresses follow logging is not suitable for understanding the impacts of forest harvesting on summertime low‐flows. Additionally, these reductions in streamflow corresponded to persistent decreases in modelled fish habitat availability that typically ranged from 20‐50% during the summer low‐flow period in one of the catchments, suggesting that forest harvest may have substantial delayed effects on rearing salmonids in headwater streams.
... These models have their utility (Beecher, 2017;Campbell et al., 2021;Jowett & Biggs, 2006;Reiser & Hilgert, 2018), but have also been criticized for a lack of correspondence with individual fitness (Anderson et al., 2006;Hayes et al., 2016;Mathur et al., 1985;Naman et al., 2019;Railsback, 2016) and high site specificity (Anderson et al., 2006). Furthermore, these models do not describe how food resources change with streamflows (Piccolo et al., 2014;Rosenfeld & Ptolemy, 2012), which is a critical piece of the puzzle in salmonid fitness (Chapman, 1966). ...
Bioenergetics models produce quantitative flow‐ecology relationships that summarize changes in habitat and food resources from altered flows. We used a drift‐foraging bioenergetics model to quantify the net rate of energetic intake (NREI) for trout above and below a water diversion. NREI is reduced by >95% below the water diversion in July–September, when up to 98% of unimpaired flows are diverted. We then used a risk‐based approach to estimate the maximum diversion rate, expressed as a percentage of unimpaired flow, that would produce NREI values that are not significantly lower than values under unimpaired flows throughout a 62‐year period. NREI decreased with increased precent‐of‐flow diversion rates in low‐flow months (July–September). Diversion rates of 16% in July and 9% in August and September would maintain NREI within the range of unimpaired flow conditions. In higher flow months, May–June, increasing diversions brought estimated instream flows closer to the peak NREI flow, leading to the assessment that increased diversions would increase NREI. Bioenergetic models can be used to develop protective flow rates at times of the year when fish growth and production would be high under unimpaired flows, which often coincides with when water is diverted. Our study is the first to develop protective percent‐of‐flow diversion rates for holistic flow management using a quantitative process‐based and fish‐centric ecological metric.
... Historically, practitioners have modelled fish habitat in streams and rivers using a suite of physical habitat modelling software, but their use has come under more scrutiny in recent years (Kemp & Katopodis, 2017;Railsback, 2016;Reiser & Hilgert, 2018). For physical habitat models, habitat is usually described by water depth, flow velocity, substrate and cover based on results of hydrodynamic modelling for different discharges and surveyed spatial information on morphology, in most cases, subreach scale (i.e. ...
Fish physical habitat models are a tool for guiding restoration efforts in lotic ecosystems, but often they overestimate restoration outcomes because currently they do not incorporate habitat connectivity. This persistent issue can, in extreme cases, result in little or no improvement to fish populations after the restoration, wasting valuable conservation resources.
We present a case study where practitioners applied a fish habitat model for multiple life stages of gravel spawning fishes to a 52‐km stretch of the Iller River but did so at a microscale implementation by setting up a model based on cross sections with a maximum of 200 m distance from each other. This approach provided an opportunity to assess the connectivity of habitats for gravel spawning fishes, that is, European Grayling ( Thymallus thymallus ) and Common Nase ( Chondrostoma nasus ), integrating probabilities to find suitable habitats for all life‐history stages and seasonal movements.
We used the assessed habitat estimates (availability of distinct habitat types within reaches defined by the 200 m cross sections) to calculate the minimum distance a fish would need to overcome to change from one habitat type into the other as it hypothetically ‘grew up’ from egg to full spawning adult. This approach can be interpreted as a life cycle habitat check as it considers all habitat types that are necessary to fulfil the life cycle of gravel spawning fishes including their size, distance and flow direction‐related orientation (e.g. larvae habitats only used when downstream of spawning areas).
Our results show that the assumption of complete connectivity would require long movement distances for vulnerable life stages to find suitable habitat. This puts the high priority on the creation of migration corridors and passability of migration barriers in question. Without consideration of habitat types for all life stages of a species and their spatial context, restoration will not be successful. Shortly said: A perfect migration corridor does not necessarily provide habitat connectivity.
We recommend the application of the habitat connectivity approach when predicting the effect of restoration measures and particularly setting the priority of measures for mitigation of fish migration.
... Förmågan hos korrelativa vs. mekanistiska individ-baserade modeller att simulera effekten av habitatet på strömlevande fiskar har diskuterats livligt. Speciellt har användbarheten hos den korrelativa modellen PHABSIM ("Physical Habitat Simulation System") och den individbaserade modellen inSTREAM ("individual-based Stream TRout Environmental Assessment Model") debatterats på senare år (Railsback, 2016;Beecher, 2017;Kemp, 2017;Stalnaker m.fl., 2017;Reiser & Hilgert, 2018). Trots denna debatt är jämförelser av båda typerna av modeller på samma fiskpopulation sällsynta. ...
Modeller för att simulera effekter av flöde på strömlevande fiskpopulationer är kraftfulla verktyg för att avväga miljönytta och kostnad i samband med åtgärder för att minimera vattenkraftens miljöpåverkan. Vi jämförde en korrelativ och en individbaserad fiskhabitatmodell med avseende på vilka flöden respektive modell bedömde var gynnsammast för en potentiell havsöringspopulation i naturfåran vid Blankaströms kraftverk i Emån. Den korrelativa modellen förutspådde att ett optimalt flöde för att maximera arean med högkvalitativt öringhabitat låg mellan 2 och 3 m3/s. Den individbaserade modellen fann att flöde spelade mindre roll för överlevnad hos den yngsta årsklassen (0+), samt att tillväxten hos dessa var som högst vid 3 m3/s. Högre flöden krävdes dock för lyckad reproduktion och att överlevnaden och tillväxten hos äldre juveniler (1+) gynnades av flöden mellan 5 och 8 m3/s. Korrelativa modeller kan vara användbara, då de är enkla att använda, men det är möjligt att de framförallt förutsäger habitatförekomst för 0+-öringar och sämre speglar de miljöförhållanden som krävs för 1+-öringars uppväxt samt lekfiskars reproduktionsframgång. Individbaserade modeller, å andra sidan, är något mer komplicerade, men genererar mångfacetterad data för olika livsstadier, ger mekanistiska förklaringar till observerade fenomen och kan anpassas till dynamiska flöden.
... Despite these criticisms and the time commitment required to conduct traditional hydraulic-habitat modelling approaches, they remain a widely used and important component of environmental flow needs studies and water allocation decision-making (Reiser & Hilgert, 2018). However, there have been repeated calls for simple and cost-effective tools to conduct instream-flow assessments (Ahmadi-Nedushan et al., 2006;Railsback, 2016;Saraeva & Hardy, 2009). ...
Conventional hydraulic‐habitat modelling methods are time‐consuming to implement. In response to repeated calls for more efficient and practical approaches, researchers have developed a geomorphic instream‐flow tool (GIFT) that combines a method to simulate reach‐averaged hydraulics at flows less than bankfull and depth and velocity frequency distributions to develop streamflow‐fish habitat relationships. This approach requires fewer resources to implement than conventional methods, but it has not been widely adopted because it has been subject to minimal testing and validation. This study evaluates the performance of GIFT by comparing its outputs to empirical measurements and conventional model outputs from eight rivers in western North America. The results of this comparison indicate that the root mean square errors for average depth and velocity were 0.078 m and 0.047 m/s, respectively, and the fit of modelled depth and velocity frequency distributions was satisfactory (index of agreement >0.9) for 11 of 15 surveys for depth and 12 of 15 surveys for velocity. GIFT‐derived fish habitat‐streamflow relationships peaked at lower flows than benchmark relationships in smaller streams (mean annual discharge [MAD] < 0.15 m3/s) and are markedly differed from the benchmark in the largest river (MAD of 87 m3/s). GIFT was also paired with a geomorphic regime model to predict the direction of changes in channel morphology and fish habitat following forest harvesting in one watershed. GIFT provides an alternative to conventional modelling approaches for single‐thread, gravel‐bed rivers with a MAD of around 15 m3/s or less. Application of this technique outside of these bounds, or in other regions should proceed with caution, as these scenarios have not been tested.
... The Youngs Creek hydroelectric project offers a case study where PHABSIM was used to determine instream flows to protect resident Rainbow Trout and population monitoring followed a protocol agreed to by all parties in the FERC licensing process. Monitoring indicated that the instream flow based on PHABSIM results was protective of the trout, suggesting that PHABSIM provided useful information to identify a non-harmful flow modification, consistent with comments by Reiser and Hilgert (2018), Beecher (2017), and Stalnaker et al. (2017), but other means of identifying protective instream flows might also have been successful. ...
Run‐of‐river hydropower reduces streamflow between diversion and powerhouse, potentially impacting fish. Hydropower license conditions include instream flows to protect fish, but monitoring instream flow effectiveness to protect fish is rarely reported. Monitoring a trout population before construction (baseline) and during operation of a small hydropower project with instream flows for spawning and incubation, summer rearing, and winter rearing based on a Physical Habitat Simulation System in the state of Washington indicated the instream flow protected the trout. The monitoring plan included decision points based on monitoring results. Increasing or stable population trends would trigger locking in an instream flow for the remainder of the license, while declines would trigger incremental increases in the instream flow, followed by additional monitoring and decision points. Three years of monitoring following beginning of the project indicated an apparent increase in the trout population over baseline, suggesting that the instream flow was protective, triggering finalization of instream flows. An additional year of monitoring conducted after several more years of project operation was consistent with the finding of the first 3 years of operation.
... As hypothesized, the number of large out-migrants gradually declined for both species under increased proportions of a more natural varying flow regime. A recent critique of inSTREAM pointed out that the model has not been applied in pragmatic management settings "for determining ecological flow releases for a water resource project where there are competing interests or by defining instream flow requirements in a water rights context" (Reiser and Hilgert, 2018). Here, we have shown that this relatively complex individual-based model can be useful for management problems such as deciding among alternative flow regimes. ...
Describing and understanding the relationship between streamflow and ecological processes is a classic problem in stream ecology and river management. We applied the individual-based model inSTREAM to describe the relationship between the dynamic river habitat and emergent population responses in sympatric landlocked Atlantic salmon (Salmo salar) and lake-migrating brown trout (Salmo trutta). This application explicitly describes the environmental conditions in the Gullspång Rapids, a residual flow stretch in the hydropower-regulated Gullspång River, Sweden (Svenskt elfiskeregister – SERS, 2019) etween September 2008 and September 2018. We simulated three static minimum flow scenarios and three variable natural flow regimes, contrasting highly artificial conditions with more natural dynamics. Our main response variable was the number of large (≥ 12 cm) out-migrants of salmon and trout, a proxy for successful population recruitment. The baseline model predicted an average production of 455 salmon and 532 trout out-migrants per year during 2008–2018 in this 11,700 m² spawning and rearing area. The only alternative scenario producing more out-migrants was when the minimum flow was raised by a factor of three, as this led to a modest increase in trout out-migrants. Interestingly, none of the flow alternatives produced more salmon out-migrants than the baseline model, suggesting a competitive disadvantage originating from spawning later than trout. Density-dependent population regulation, a well-known phenomenon in salmonids, was reproduced by the model. Both intra- and interspecific competition was evident. While the number of out-migrants varied with flow regime, sensitivity analyses showed that other model input, specifically velocity shelter availability and stream temperature, were just as important. Increased availability of velocity shelters (in-stream structures that reduces the swimming speed of drift-feeding fish) was the only environmental factor that increased production of both salmon and trout in silico. We conclude that in this system, flow restoration based on simplistic flow scenarios will have limited effect, unless complemented by an increase of instream structural complexity.
... The Instream Flow Incremental Methodology (IFIM; Bovee et al., 1998) and Physical Habitat Simulation (PHABSIM; Bovee, 1982) are ecohydraulic models based on habitat suitability curves (HSCs) that are frequently used for making water quantity management recommendations and decisions to protect and restore fish habitat (Annear et al., 2004;Tharme, 2003). Although the continued use of PHABSIM has recently been questioned (Railsback, 2016), PHABSIM (and more recent adaptations, such as the System for Environmental Flow Analysis, SEFA; Payne & Jowett, 2012) have continued value, including adaptability to new information (Beecher, 2017;Stalnaker, Chisholm, & Paul, 2017;Reiser & Hilgert, 2018). These HSC-based methods also remain in consistent use by instream flow programmes around the world (Tharme, 2003;Annear et al., 2009), in part because of their ability to answer specific questions about water quantity management, gain social and institutional acceptance, and function within existing legal structures (Nestler et al., 2019). ...
• The conservation of aquatic species with complex life histories requires the protection of habitat for each life stage. Coastal cutthroat trout (Oncorhynchus clarkii clarkii) exhibit both mobile and sessile stages and are of conservation concern in north‐western North America. Models that predict how habitat changes with flow can inform water management for the species but rely on habitat descriptors that change with flow and are not suited to sessile life stages.
• Spawning and incubation habitat availability and use for coastal cutthroat trout were assessed in mesohabitats and microhabitats. Primary channel units were tallied, dimensions were measured, redds were counted, and redd locations within channel units were measured.
• Primary channel units were subdivided based on relative residual depth (RRD, bed elevation in relation to maximum pool depth) and hydraulic control (HC, the lowest point on the highest ridge across the riffle that controls the water surface elevation in the upstream pool). Habitat suitability was calculated for depth (D), velocity (V), Froude number (Fr), substrate (S), RRD, and channel units.
• Redds in riffles and pools were close to hydraulic controls; suitability decreased upstream in pools and downstream in riffles. Maximum suitability values were: 21–24 cm for D, 0.05–0.10 for RRD, 61–64 cm s⁻¹ for V, >0.80 for Fr, and 1.3 to <3.8 cm for S. Channel units, RRDs, and microhabitat better identified spawning habitat than microhabitat alone.
• The results suggest that RRD and stage of zero flow are good indicators of habitat suitability for spawning through fry emergence and could be adapted for use with other species. This work generates criteria for delineating flow‐independent channel units that can be used to set more protective instream flows, prioritize the acquisition of instream water or conservation easements to protect critical habitat, and inform restoration projects to optimize habitat availability.
... Mechanistic models that link habitat conditions to individual-level fitness can address this issue (e.g. Railsback, Harvey, Jackson, & Lamberson, 2009;Van Winkle et al., 1998), but the complexity of these approaches has limited their use by practitioners (Reiser & Hilgert, 2018). ...
Quantitative habitat suitability models (HSMs) are frequently used to inform the conservation and management of lotic organisms, often in the context of instream flow management. Correlative statistical models relating hydraulic variables to habitat preferences (habitat suitability curves based on use:availability ratios) are the most common form of HSM, but face significant criticism on the grounds that habitat preference may not reflect the fitness consequences of habitat use. Consequently, there has been a drive to develop mechanistic approaches that link habitat to direct correlates of fitness.
Bioenergetic foraging models relating hydraulic conditions to energy balance are particularly well‐developed for drift‐feeding fishes (e.g. salmonids) and show promise as a more mechanistic approach to modelling suitability. However, these models are rarely validated empirically or quantitatively compared with correlative HSMs. We addressed these gaps by comparing the ability of a bioenergetics‐based HSM and two correlative HSMs (a traditional suitability index and a resource selection function) to predict density and growth of stream salmonids (juvenile steelhead, Oncorhynchus mykiss , and coastal cutthroat trout, Oncorhynchus clarki ).
Suitability estimates differed between the approaches, with both correlative models predicting higher suitability relative to the bioenergetic model at shallow depths and low to intermediate velocities, but lower suitability as depth increased. The bioenergetic model explained over 90% of variation in trout growth, compared to c . 50% for the correlative model. The bioenergetic model was also better at predicting fish density; however, the improvement was less striking and a high proportion of variation remained unexplained by either method.
Differences in suitability estimates between approaches probably reflect biotic interactions (e.g. territorial displacement or predation risk) that decouple realised habitat use from energetics‐based estimates of habitat quality. Results highlight fundamental differences between correlative HSMs, based on observed habitat use, and mechanistic HSMs, based on the physiology and behaviour of the focal taxa. They also suggest that mechanistic bioenergetics‐based models provide more rigorous estimates of habitat suitability for drift‐feeding stream fishes. The bioenergetics approach is readily accessible to instream flow practitioners because model predictions are expressed in terms of traditional habitat suitability curves.
... This raises the question, how can the requirements of invertebrates on a micro scale translate into an overall compensation flow and its interannual variation? Habitat quality models are an increasingly utilised approach in restorative studies (Reiser and Hilgert, 2018;Schneider et al., 2016;Conallin et al., 2010), yet may not account for life history requirements and temporal flow characteristics experienced by taxa, such as the frequency and duration of flow events. A broader suite ecological indices are required to achieve robust environmental flow designs (Chinnayakanahalli et al., 2011;Arthington et al., 2018), and methodological progress is required in order to determine their implementation; how are conflicting flow needs to be resolved, and how does one judge whether or not a flow regime is "good"? ...
Many rivers have undergone flow modification by impoundments to provide services such as water supply and hydropower. There is an established consensus that typical modified flow regimes do not sufficiently cater to the needs of downstream ecosystems, and more must be done to understand and mitigate their associated impacts.
This study presents a novel, transferable framework by which a small-scale impoundment in North West England is assessed through the use of linked hydro-ecological modelling in SRH-2D and CASiMiR, utilising flow velocity measurements and macroinvertebrate sampling data. Model predictions of habitat quality were supplemented by established ecological principles such as the importance of flow heterogeneity. Results are used to design environmental flow regimes, with the aim of improving ecological metrics whilst considering conflicting water demands. Based on an analysis of historical flow records, the implementation of designer flows over a 12 month period demonstrated increased peak species habitat qualities of 23–26%, characteristics such as flow heterogeneity were more naturalised, and 22% less water was released from the impoundment. Should outcomes be validated by in-stream flow experiment, there is great potential for further development and application of this method, including regional transferability for the rapid designation of environmental flows across a number of sites of similar magnitude and geography.
... Traditional PHABSIM does not take into account biotic interactions, flow effects over time or other physical variables than velocity, depth and substrate. This simplicity seems however to have been an advantage as PHABSIM is still widely used, refined and defended against criticism (Reiser and Hilgert, 2018;Stalnaker et al., 2017). PHABSIM has also spurred the development of a range of related habitat evaluation models such as RHYHABSIM (Jowett, 1989), HABSCORE (Milner et al., 1998), MesoHABSIM (Parasiewicz, 2001), among others. ...
Introduction paper (7.5 credit course) - a part of my licentiate degree at Karlstad University.
... Despite the debate, the physical habitat simulation approach (Bovee et al. 1998) is still considered the most defendable approach, from a legal perspective, to evaluate the impact of different flow regimes on the habitat suitable for the target freshwater taxa (Reiser and Hilgert 2018). It combines habitat suitability models with hydraulic simulation and hydrological data to determine the most appropriate environmental flow regime. ...
Spring-fed streams in Tokyo are important habitats for various aquatic species, whereas urbanization as well as introduction of invasive species is threatening the sustainability of such aquatic ecosystems. This study applies the System for Environmental Flow Analysis (SEFA) in a small urban river in Tokyo to assess the dynamics of the suitable habitats for the endangered freshwater fish Lefua echigonia (Jordan and Richardson 1907). A set of Habitat Suitability Curves (HSCs) for water depth, velocity and substrate was developed to evaluate the suitable habitats. The habitat assessment indicated that the Area Weighted Suitability (AWS) reached the maximum at 0.02 m³/s, which is close to the base flow of the target river; a gradual decrease in AWS was observed for higher flows. The temporal distribution of AWS, during forty-one consecutive months, showed that, on average, the best habitat conditions for adult L. echigonia occur during the period between January and July, whereas the worst situation occurs during the period between August and December. This work presents information and tools for instream habitat analysis that should help managers to conserve this aquatic species and prioritize actions to further rehabilitate urban rivers, using L. echigonia as a case study.
... Inundated floodplains can provide important habitat for all life stages of fish when discharge is high (King, Humphries, & Lake, 2003). Although the core strength of WUA is an index of potential habitat changes with flow (Reiser & Hilgert, 2018), ...
Stream restoration was implemented on the Upper Arkansas River near Leadville, Colorado, to improve brown trout (Salmo trutta) populations. Metals pollution and channel disturbance associated with historic mining, land use, and water development degraded aquatic and riparian habitat. Changes in instream habitat quality following restoration were investigated with a before–after–control–impact study design. Baseline, as‐built, and effectiveness surveys were conducted in 2013, 2014, and 2016, respectively. Two‐dimensional hydrodynamic modelling with River2D was used to estimate weighted usable area (WUA) for adult, juvenile, fry, and spawning brown trout across a range of flows. WUA was calculated from habitat suitability curves for velocity, depth, and channel substrate. Foraging positions (FP) and habitat heterogeneity were also evaluated as indices of habitat quality. All results were analysed with analysis of variance. At impact sites, WUA increased by 12.2% from 2013 to 2014 but decreased by 10.2% from 2014 to 2016, whereas FP increased by 24.8% from 2013 to 2014 but decreased by 26.1% from 2014 to 2016. Spawning habitat increased 53.3% from 2014 to 2016 at impact sites. The 15.4% increase in depth variability from 2013 to 2016 indicates that habitat heterogeneity was enhanced at impact sites. No changes in WUA, FP, or habitat heterogeneity were observed at control sites. Although changes in WUA and FP suggest that initial habitat improvements were not sustained, increased spawning habitat and depth heterogeneity suggest otherwise. Our results highlight the value of monitoring strategies that utilize multiple lines of evidence to evaluate restoration effectiveness, inform adaptive management, and improve restoration practices.
This study seeks better understanding of linkages between channel morphology, streamflow, and aquatic habitat for the effective rehabilitation of imperiled species in rivers subjected to intensive water resource management. We focused on the variability of shallow, low‐velocity (SLV) habitat over 50 years for a 56 km reach of the Rio Grande of central New Mexico (Middle Rio Grande). Hydraulic models used topographic data obtained through long‐term systematic monitoring between 1962 and 2012 to derive relationships between discharge and SLV habitat availability. We developed a temporally integrated habitat metric (TIHM) to facilitate quantitative comparisons of SLV habitat availability over seasonal hydrologic periods (base flow, spring runoff, and summer low flow) for selected years representative of contemporary discharge variations. Results showed that SLV habitat availability, as captured by TIHM values, decreased on average by 83% over the study period (1962–2012), corresponding to completion of the Cochiti Dam (1973), which profoundly altered flow and sediment regimes. Resulting channel incision and floodplain disconnection, caused shifts in discharge‐habitat relationships whereby increases in SLV habitat availability in the modern channel were strictly maximized at the upper range of modeled discharges (200 m ³ s ⁻¹ )—discharges greater than 100 m ³ s ⁻¹ are infrequent today. Ecological implications of losses to SLV habitat availability include recovery of the federally endangered Rio Grande Silvery Minnow Hybognathus amarus .
Hydraulic habitat connectivity, including the longitudinal continuum respect and lateral flood pulse, is critical for fish survival and organism dispersal. Inappropriate and excessive dredging for prevent flooding may harm river ecosystems. The main objective of this study is to evaluate whether eco-friendly dredging presented by changing local river landforms incorporating the concept of nature-based solutions could grow fish habitat quality for improving river continuity and achieving flood control effects. By combining various mathematical models and empirical formulas and verifying them with the data obtained through field surveys, we explore the interconnections of hydrology, river morphology, and the habitat dynamics of four endemic fishes in an alluvial river. The relationship between habitat structure, flood risk, and river topography, flow discharge was presented as the reference for developing the proper river dredging approaches. The results reveal that the primary habitat defects were lack of high-quality habitat, unsatisfied habitat diversity, deficiency in refugia, and disconnectivity. Longitudinal disconnectivity was induced due to shallow water depth, while lateral disconnectivity is primarily caused by fast flow velocity, suggesting different and specific dredging methods were instructed. We recommend that the corresponding eco-friendly dredging schemes for longitudinal and lateral suitable habitat linkages increase fish habitat quality and river corridor continuity. The win-win strategy for enhancing the connection between suitable habitats sustains a more beneficial aquatic corridor and simultaneously achieves alluvial flood disaster risk reduction.
Habitat Suitability Curves (HSCs) are the biological component of habitat simulation tools used to evaluate instream flow management trade‐offs (e.g., the Physical Habitat Simulation Model). However, traditional HSCs based on empirical observations of habitat use relative to availability have been criticized for generating biased estimates of flow requirements and for being poorly transferable across locations. For fish like salmonids that feed on drifting invertebrates, bioenergetics‐based foraging models that relate habitat conditions to net energy gain offer an alternative approach that addresses some of these shortcomings. To make this technique more accessible for practitioners, we present free and user‐friendly software for generating bioenergetics‐based HSCs. The software also allows sensitivity analyses of HSCs to factors like fish size or prey abundance as well as direct integration of hydraulic data. While some caveats remain, bioenergetic HSCs should offer a more rigorous and credible means for quantifying habitat suitability for instream flow modelling.
Stream habitat restoration projects are popular, but can be expensive and difficult to evaluate. We describe inSALMO, an individual-based model designed to predict habitat effects on freshwater life stages (spawning through juvenile out-migration) of salmon. We applied inSALMO to Clear Creek, California, simulating the production of total and large (>5 cm FL) Chinook Salmon Oncorhynchus tshawytscha out-migrants at a degraded and a restored site. The calibrated model reproduced observed redd locations and out-migrant timing and size. In simulations, the restored site had a much higher production of fry that established and grew before out-migration; it provided higher survival and positive growth due to moderate velocities, shallow depths, and cover for feeding and hiding. The restored site did not produce more total out-migrants because at both sites spawning gravel was sufficient and the vast majority of fry moved downstream soon after emergence. Simulations indicated that at both sites increasing food and cover availability could further increase production of large, but not total, out-migrants; spawning gravel, temperature, and flow appear nearly optimal already. Further gravel addition was predicted to increase total fry production but have little or even a negative effect on production of large out-migrants, illustrating that actions benefitting one life stage can negatively affect others. The model predicted that further enhancements (e.g., in cover availability) would be more beneficial at the restored site than at the degraded site. Restoration efforts may be most effective when concentrated in “hot spots” with good habitat for growth and predator avoidance as well as for spawning. Contradicting the traditional notion of “limiting factors,” the model indicated that several factors each have strong effects. The model provided more understanding of restoration effects than would field studies alone and could be useful for designing projects to meet specific restoration objectives.Received June 23, 2012; accepted January 2, 2013
The need to sustain the ecological values of rivers is widely recognised and embraced in policy and legislation. Here we examine a widely used approach for evaluating effects of changing flow regimes, the Instream Flow Incremental Methodology (IFIM), in particular physical habitat simulation using PHABSIM/RHYHABSIM. We review IFIM procedures and discuss limitations of habitat simulation with specific reference to New Zealand. Our objectives are to encourage a critical re-evaluation of IFIM and improve its application so that it takes into account known but frequently unaddressed problems. These generic problems are compounded by a limited knowledge of many species, the lack of rigorous description of habitat requirements, the fact that habitat suitability curves have been developed for a very limited range of conditions and a narrow view of flow requirements. The New Zealand IFIM experience has usually been limited to an evaluation of the effects of minimum streamflows on various life stages of a few species of fish and on food production for a small reach of stream. Rarely has consideration been given to transferability of results, or changes in water temperature or water quality with changing flow regimes. River mouth openings, flushing flow requirements, maintenance of lateral and longitudinal stream processes and maintenance of river channel processes are essential components of an environmental flow assessment, but have often not been considered. We also found that the IFIM process is often confused with one of its basic steps-using models to simulate a relationship between streamflow and in-channel physical habitat.
We evaluated the ability of numerical habitat models (NHM) to predict the distribution of juveniles of Atlantic salmon (Salmo salar) in a river. NHMs comprise a hydrodynamic model (to predict water depth and current speed for any given flow) and a biological model (to predict habitat quality for fish using water depth, current speed, and substrate composition). We implemented NHMs with a biological model based on (i) preference curves defined by the ratio of the use to the availability of physical conditions and (ii) a multivariate logistic regression that distinguished between the physical conditions used and avoided by fish. Preference curves provided a habitat suitability index (HSI) ranging from 0 to 1, and the logistic regression produced a habitat probabilistic index (HPI) representing the probability of observing a parr under given physical conditions. Pearson's correlation coefficients between HSI and local densities of parr ranged from 0.39 to 0.63 depending on flow. Corresponding values for HPI ranged from 0.81 to 0.98. We concluded that HPI may be a more powerful biological model than HSI for predicting local variations in fish density, forecasting fish distribution patterns, and performing summer habitat modelling for Atlantic salmon juveniles.
Instream flow needs (IFN) assessment studies are performed to provide guidelines for stream water management and to assess the impacts of different water projects such as weirs, dams and stream diversions on the available fish habitat. Many of the IFN assessment techniques require hydraulic parameters such as water depth, flow velocity, wetted perimeter or top width as input variables. The Physical Habitat Simulation System (PHABSIM), one of the most widely IFN assessment models used in North America, requires precise values of depth and velocity at numerous points within the study reach to produce relationships between streamflow and usable habitat area for different life stages of varying fish species. Numerical flow simulation is applied to obtain results for unmeasured flows. At present, the flow simulation techniques applied in most IFN assessment methods are rather simplistic. In PHABSIM, a one-dimensional approach, such as the application of HEC-2, is used to determine water surface elevations along the study reach. Then a technique based on a combination of Manning's equation and regression analysis is used to obtain the velocity distribution across the channel. As a typical length scale of physical habitat study sites is of the order of a few stream widths, the accuracy of the above approach is questionable, and a two-dimensional model may be more appropriate. The results of flow modelling of fish habitat based on one-dimensional and two-dimensional assumptions are compared. Firstly, the models are tested and compared for a hypothetical flow situation of flow over a side-bar, which shows a clear difference between the results of the one- and two-dimensional approaches. Then the two models are used to simulate the flow of water in a real fish habitat reach and the computed velocity results are compared with field velocity measurements. The results of the two-dimensional approach appear to be significantly better than the one-dimensional approach.
Generalized additive models (GAMs) offer an alternative approach to developing habitat suitability functions; these models may resolve some of the criticisms that have been made of conventional habitat suitability criteria and the associated composite suitability index (CSI). The potential advantages of GAMs include the ability to (1) account for correlation among habitat variables, (2) include interactions among variables, (3) make quantitative predictions of abundance or probability of occurrence at given flows, and (4) identify sharp thresholds in habitat selection. We developed CSIs and GAMs for two data sets—abundance of benthic invertebrates (mayflies Deleatidium spp. and caddisflies Aoteapsyche spp.) and habitat selection of large brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss—and applied them in an instream habitat analysis. The GAMs performed only slightly better than CSIs. The GAMs for two of the four taxa examined (Deleatidium and brown trout) had strong negative velocity–depth interaction terms, although their inclusion improved the model fit only marginally. The main effect of negative velocity–depth interaction terms was to constrain model predictions in deep, fast-flowing water, and these GAMs gave more realistic results when applied to conditions beyond those from which they were developed (i.e., larger rivers or higher flows). The GAMs hold a number of potential advantages over conventional CSIs and offer an opportunity to develop more defensible habitat suitability models; ultimately, however, the performance of any model will be limited by the quality of the calibration data.
A review and reanalysis of the published literature show that several assumptions are violated in the application of the Instream Flow Incremental Methodology (IFIM) without consideration of the implications of so doing. The fundamental assumption of a positive linear relationship between "potential available habitat" (WUA) and biomass of fish has neither been documented nor validated, particularly in warmwater streams. Absence of correlation precludes prediction of changes in fish populations. In some studies the test of this assumption appears to be equivalent to a calibration operation. The other assumption violated includes independent selection of habitat variables by fish. The presence of significant interaction among habitat variables can affect the stream flow recommendations. Another problem exists in application of Physical Habitat Simulation (PHABSIM): one WUA unit should not be interpreted as being equal to another in biological production or habitat value unless shown to be an exact replica. Several combinations of physical variables could give rise to the same amount of WUA, none of which may be correlated to the biomass of fish. The utilization, suitability, or preference curves should not be treated as probability functions; a rating of 1.0 is not equivalent to probability of 1.0. Care should be taken to distinguish between real behavioral preferences of fishes based on distributional occurrence from abundance (relative or absolute size) in a stream.
This document is intended to update the concepts and ideas first presented in Information Paper 12, the first attempt to describe the Instream Flow Incremental Methodology in its entirety in 1982. This also is to serve as a comprehensive introductory textbook on IFIM for training courses as it contains the most complete and comprehensive description of IFIM in existence today. This should also serve as an official guide to IFIM in publication to counteract the misconceptions about the methodology that have pervaded the professional literature since the mid-1980's as this describes IFIM as it is envisioned by its developers The document is aimed at the decisionmakers of management and allocation of natural resources in providing them an overview; and to those who design and implement studies to inform the decisionmakers. There should be enough background on model concepts, data requirements, calibration techniques, and quality assurance to help the technical user design and implement a cost-effective application of IFIM that will provide policy-relevant information. Some of the chapters deal with basic organization of IFIM, procedural sequence of applying IFIM starting with problem identification, study planning and implementation, and problem resolution.
Instream flow methods have been developed predominantly by biologists and hydrologists working for agencies having regulatory responsibility related to water development and management (Stalnaker and Arnette 1976). Such efforts over the last 30 years have provided the impetus for detailed ecological studies leading to a significant growth in the understanding of the relations between stream flow and aquatic habitats. Most of the empirical evidence gathered to date has focused on fish and benthic macro-invertebrate habitat requirements, with recent emphasis on the relation between stream flow and woody riparian vegetation and river-based recreation (Gore 1987; Orth 1987; Brown 1992; Shelby et al. 1992; Scott et al. 1993). Water management problem solving has matured from setting fixed minimum flows with no specific aquatic habitat benefit to incremental methods in which aquatic habitats are quantified as a function of stream discharge. Within this historical progression we also saw the application of a water budget which set the stage for having the fisheries manager be an integral part of an interdisciplinary decision-making system. This chapter will review the progression of circumstances and techniques leading to the development of IFIM and point toward what the future might hold.
An acoustic Doppler current profiler, underwater video system, hand-held laser range finder and global positioning receiver were used to collect data for instream flow studies on the Sacramento and lower American rivers in California. The use of the equipment decreased the time required to collect spawning criteria data for Chinook salmon Oncorhynchus tshawytscha in deep water in a given area by a factor of 3.4 and doubled the number of transects that could be modeled with the same budget. With the application of quality control criteria, discharges could be measured with an average accuracy of 2.7% versus gauge data with an accuracy of 5%. The total time required to collect data for two-dimensional habitat sites varied with the length and complexity of the sites, and was equivalent to the total time required for physical habitat simulation (PHABSIM) data collection for shorter sites, and less for longer sites.
Throughout the 20th century, the Truckee River that flows from Lake Tahoe into the Nevada desert was progressively dammed
and dewatered, which led to the collapse of its aquatic and riparian ecosystems. The federal designation of the endemic cui-ui
sucker (Chasmistes cujus) as endangered prompted a restoration program in the 1980s aimed at increasing spring flows to permit fish spawning. These
flows did promote cui-ui reproduction, as well as an unanticipated benefit, the extensive seedling recruitment of Fremont
cottonwood (Populus fremontii) and sandbar willow (Salix exigua). Recruitment was scattered in 1983 but extensive in 1987, when the hydrograph satisfied the riparian recruitment box model
that had been developed for other rivers. That model was subsequently applied to develop flow prescriptions that were implemented
from 1995 through 2000 and enabled further seedling establishment. The woodland recovery produced broad ecosystem benefits,
as evidenced by the return by 1998 of 10 of 19 riparian bird species whose populations had been locally extirpated or had
declined severely between 1868 and 1980. The dramatic partial recovery along this severely degraded desert river offers promise
that the use of instream flow regulation can promote ecosystem restoration along other dammed rivers worldwide.
The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of multiple use management of the Nation's forest resources for sustained yields of wood, water, forage, wildlife, and recreation. Through forestry research, cooperation with the States and private forest owners, and management of the National Forests and National Grasslands, it strives—as directed by Congress—to provide increasingly greater service to a growing Nation. The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an individual's income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, 1400 Independence Avenue, SW, Washington, DC 20250-9410 or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer.
Habitat models serve three main purposes: First, to predict species occurrences on the basis of abiotic and biotic variables, second to improve the understanding of species-habitat relationships and third, to quantify habitat requirements. The use of statistical models to predict the likely occurrence or distribution of species based on relevant variables is becoming an increasingly important tool in conservation planning and wildlife management. This article aims to provide an overview of the current status of development and application of statistical methodologies for analysing the species-environment association, with a clear emphasis on aquatic habitat. It describes the main types of univariate and multivariate techniques available for analysis of species-environment association, and specifically focuses on the assessment of the strengths and weaknesses of the available statistical methods to estimate habitat suitability. A second objective of this article is to propose new approaches using existing statistical methods. A wide array of habitat statistical models has been developed to analyse habitat-species relationship. Generally, physical habitat is dependent on more than one variable (e.g. depth, velocity, substrate, cover) and several suitability indices must be combined to define a composite index. Multivariate approaches are more appropriate for the analysis of aquatic habitat as they inherently consider the interrelation and correlation structure of the environmental variables. Ordinary multiple linear regression and logistic regression are popular methods often used for modelling of species and their relationships with environment. Ridge regression and Principal component regression are particularly useful when the independent variables are highly correlated. More recent regression modelling paradigms like generalized linear models (GLMs) present advantages in dealing with non-normal environmental variables. Generalized additive models (GAMs) and artificial neural networks are better suited for analysis of non-linear relationships between species distribution and environmental variables. The fuzzy logic approach presents advantages in dealing with uncertainties that often exist in habitat modelling. Appropriate methods for analysis of multi-species data are also presented. Finally, the few existing comparative studies for predictive modelling are reviewed, and advantages and disadvantages of different methods are discussed. Copyright © 2006 John Wiley & Sons, Ltd.
The Physical Habitat Simulation System (PHABSIM) was developed in the 1970s to fill an important void in instream flow assessment. Although considerable progress has been made in ecological modeling since the 1970s, there has been little change in instream flow assessment. PHABSIM has two general problems. First, PHABSIM is a habitat selection model (HSM)—but not a good one: it no longer conforms to standard practices in the wider fields of ecological and wildlife modeling, especially by using inappropriate spatial scales and outdated methods for modeling habitat preference and by producing output that lacks clear meaning. Second, HSMs, in general, are not well suited for many instream flow decisions. HSMs cannot consider variation in flow over time, whereas dynamic flow regimes are now considered essential, and HSMs do not make testable predictions of fish population responses. Alternatives to PHABSIM include analyses based on explicit understanding of species ecology, individual-based models, and more powerful modern habitat selection modeling methods.
El sistema de simulación de hábitat físico (SISIHF) se desarrolló en la década de los setenta para cubrir un vació importante en las evaluaciones del caudal circulante. Pese a que se ha conseguido un progreso considerable en la modelaje ecológica desde los setenta, ha habido pocos cambios en el tema de la evaluación de flujo fluvial. Existen dos problemas generales con el SISIHF. Primero, el SISIHF es un modelo de selección del hábitat (MSH)—pero no uno bueno: no se adhiere a las prácticas estándar actuales en los ámbitos de la ecología y la modelación de vida silvestre, en particular por que no utiliza las escalas apropiadas de tiempo y espacio, por utilizar métodos obsoletos de modelación de preferencia del hábitats y por producir salidas carentes de significado claro. Segundo, los MSH no suelen ser adecuados para tomar decisiones relativas al manejo del flujo fluvial. Los MSH no toman en cuenta las variaciones del caudal a lo largo del tiempo, cuando hoy en día la dinámica en los régimen de caudales es esencial, y los MSH no hacen predicciones falsables sobre la respuesta de las poblaciones ícticas. Alternativas al SISIHF incluyen aquellos análisis basados en un entendimiento explícito de la ecología de poblaciones, modelos basados en el individuo y mejores y más modernos métodos de modelación de selección de hábitat.
Le système de simulation de l'habitat physique (PHABSIM) a été développé dans les années 1970 pour combler un vide important dans l'évaluation des débits réservés. Bien que des progrès considérables aient été accomplis dans la modélisation écologique depuis les années 1970, il y a eu peu de changement dans l'évaluation du débit réservé. PHABSIM présente deux problèmes généraux. Tout d'abord, PHABSIM est un modèle de sélection de l'habitat (MSH), mais pas un bon: il ne se conforme plus aux pratiques habituelles dans les domaines plus larges de la modélisation écologique et de la faune, en particulier en utilisant des échelles spatiales inappropriées et des méthodes dépassées pour modéliser l'habitat et en produisant des résultats sans signification claire. Ensuite, les MSH, en général, ne sont pas bien adaptés pour de nombreuses décisions de débit minimal. Les MSH ne peuvent pas prendre en considération la variation de débit au fil du temps, alors que les régimes d'écoulement dynamiques sont désormais considérés comme essentiels, et les MSH ne permettent pas de faire des prédictions testables des réponses des populations de poissons. Les alternatives au PHABSIM comprennent des analyses basées sur la compréhension explicite de l'écologie des espèces, des modèles basés sur l'individu, et des méthodes modernes de modélisation de sélection de l'habitat plus puissantes.
Annear, T., I. Chisholm, H. Beecher, A. Locke, P. Aarrestad, N. Burkardt, C. Coomer, C. Estes, J. Hunt, R. Jacobson, G. Jobsis, J. Kauffman, J. Marshall, K. Mayes, C. Stalnaker, and R. Wentworth. 2004. Instream flows for riverine resource stewardship, revised edition. Instream Flow Council, Cheyenne, WY. 268 pp.
This paper discusses one approach for quantifying channel maintenance instream flow necessary to achieve the Forest Service Organic Act purpose of securing favorable conditions of water flows. The approach is appropriate for quantifying channel maintenance flows on perennial, unregulated, snowmelt-dominated, gravel-bed streams with alluvial reaches. The approach identifies the minimum essential regime of streamflows necessary for the channel and its floodplain to remain fully functioning with respect to sediment and flow conveyance. The paper discusses the role of water, sediment, and vegetation in maintaining a channel and provides methodologies for estimating the upper and lower limits of the required sediment transporting flows. Conceptually, these flows range from intermediate flows associated with initial coarse sediment movement from the coarse surface layer of gravel-bed streams (Phase 2 transport) up to the 25-year flow event. The paper also provides suggestions for analyzing and displaying results, implementing studies at the watershed scale, determining data needs, and post-project management and evaluation. Best application of the approach occurs at sites having long-term bedload data and streamflow records.
This study was conducted in the Klamath Basin of southwestern Oregon to evaluate the dependency of riparian plant communities upon infrequent flooding. Plant communities were sampled with 1 m(2) quadrats along established cross-sections. Data collected for purposes of hydraulic modeling included channel and floodplain elevations (i.e., cross-sectional profiles) and water surface elevations associated with specific discharges. The elevational distribution of hydrophytic plant communities relative to modeled return periods provided the basis for establishing relationships between these variables for nine sites. Results indicate that, on average, a peak flow frequency of 4,6 years (range of 3.1 to 7.6 years) was needed to sustain riparian plant communities at seven of nine sites. At two sites, results indicated return periods of more than 25 years were needed; these results possibly were influenced by local geomorphic conditions (a narrow steep channel in one case and an incised channel in the other). Overall, these results tend to confirm a strong dependency of riparian plant communities on overbank flows.
A terminology revision is proposed for the concept of weighted usable area, the habitat index which varies by discharge in a PHABSIM analysis under the Instream Flow Incremental Methodology. Weighted usable area has been traditionally computed as the sum of stream surface area within a study site, weighted by multiplying area by habitat suitability variables (most often velocity, depth, and substrate or cover) which range from 0.0 to 1.0 each, and normalized to square units (either feet or meters) per 1000 linear units. The argument is made that multiplication of actual surface area by dimensionless suitability variables results in a dimensionless habitat index that can no longer be properly referred to as area. Relative Suitability Index is proposed as a replacement to more accurately describe the concept, since habitat suitability variables are computed from species observations as the likelihood of occurrence. Examples of significant ongoing governmental policy and interpretation misunderstandings deriving from using weighted usable area as equivalent to habitat are provided as reason for change.
Decisions on managed flow releases in regulated rivers should be informed by the best available science. To do this, resource managers require adequate information regarding the tradeoffs between alternative methodologies. In this study, we quantitatively compare two competing multivariate habitat models for juvenile Chinook salmon (Oncorhynchus tshawytscha), a highly valued fish species under serious decline in a large extent of its range. We conducted large-scale snorkel surveys in the American River, California, to obtain a common dataset for model parameterization. We built one habitat model using Akaike Information Criterion analysis and model averaging, 'model G', and a second model by using a standard method of aggregating univariate habitat models, 'model A'. We calculated Cohen's kappa, percent correctly classified, sensitivity, specificity and the area under a receiver operator characteristic to compare the ability of each model to predict juvenile salmon presence and absence. We compared the predicted useable habitat of each model at nine simulated river discharges where usable habitat is equal to the product of a spatial area and the probability of habitat occupancy at that location. Generally, model G maintained greater predictive accuracy with a difference within 10% across the diagnostic statistics. Two key distinctions between models were that model G predicted 17.2% less useable habitat across simulated flows and had 5% fewer false positive classifications than model A. In contrast, model A had a tendency to over predict habitat occupancy and under predict model uncertainty. The largest discrepancy between model predictions occurred at the lowest flows simulated and in the habitats most likely to be occupied by juvenile salmon. This study supports the utility and quantitative framework of Akaike Information Criterion analysis and model averaging in developing habitat models.
The Demonstration Flow Assessment (DFA) method evaluates instream flow benefits using expert judgment and direct observation of habitat during several flows. Early DFA applications were low-effort, qualitative, and vulnerable to well-known biases. We describe a higher-effort, more quantitative DFA (or expert habitat mapping) approach that uses techniques from the judgment-based decision analysis literature to increase objectivity and reproducibility. Specific metrics—habitat types to be quantified visually during flow observations—are designed from appropriate conceptual models of how flow affects target resources. During field observations, patches of each habitat type are delineated by consensus and marked on maps for digital analysis. A case study illustrates these procedures applied to instream flows for salmon spawning and rearing.
One of the most popular models for simulating the effect of regulated streamflow on fish habitat is the Instream Flow Incremental Methodology (IFIM). This model was developed by the Instream Flow Group (IFG) and is composed of components which simulate water temperature, water quality, and physical habitat. The physical habitat component (PHABSIM), however, is so frequently the only part of the method used that PHABSIM and IFIM are often confused.
The instream flow incremental methodology (IFIM) needs to be improved to more reliably predict the effects of altering fish habitat. Two-dimensional (2-D) hydrodynamic modeling with moving boundaries by the finite element approach overcomes may limitations related to classical physical habitat simulation modeling (mostly 1-D). Some of its most important properties are: the spatial resolution of the model can be adapted to the scale of individual fish habitats and to the spatial variability of field data; the areas frequently uncovered because of flow regime are correctly taken into account through the drying–wetting capability; and the flow resistance variables are more accurate in 2-D because they can be specified as functions of the local substrate conditions or lateral shear stresses. This approach is illustrated by a study of the habitat of juvenile Atlantic salmon Salmo salar of the Moisie River (Quebec) where a water diversion has been planned. The results of simulations carried out at two sites (a braided reach and a deep, narrow channel) over a wide range of discharges are presented. Average model error was about 10% for velocity and 2% for discharges. A finite element integration procedure allowed habitat suitability indexes (HSI) to be combined with the results of the hydrodynamic model. In this manner, detailed maps of the spatial distribution of the HSI as well as a “weighted usable area” were obtained for each discharge simulated. Atlantic salmon habitat did not appear to be very sensitive to projected flow alterations. The improved accuracy and resolution in predicting the effects of altering physical habitat variables by 2-D models would permit a better understanding of the shortcomings related to biological aspects of IFIM applications.
Instream flow needs (IFN) assessment studies are performed to provide guidelines for stream water management and to assess the impacts of different water projects such as weirs, dams and stream diversions on the available fish habitat. Many of the IFN assessment techniques require hydraulic parameters such as water depth, flow velocity, wetted perimeter or top width as input variables. The Physical Habitat Simulation System (PHABSIM), one of the most widely IFN assessment models used in North America, requires precise values of depth and velocity at numerous points within the study reach to produce relationships between streamflow and usable habitat area for different life stages of varying fish species. Numerical flow simulation is applied to obtain results for unmeasured flows. At present, the flow simulation techniques applied in most IFN assessment methods are rather simplistic. In PHABSIM, a one-dimensional approach, such as the application of HEC-2, is used to determine water surface elevations along the study reach. Then a technique based on a combination of Manning's equation and regression analysis is used to obtain the velocity distribution across the channel. As a typical length scale of physical habitat study sites is of the order of a few stream widths, the accuracy of the above approach is questionable, and a two-dimensional model may be more appropriate. The results of flow modelling of fish habitat based on one-dimensional and two-dimensional assumptions are compared. Firstly, the models are tested and compared for a hypothetical flow situation of flow over a side-bar, which shows a clear difference between the results of the one- and two-dimensional approaches. Then the two models are used to simulate the flow of water in a real fish habitat reach and the computed velocity results are compared with field velocity measurements. The results of the two-dimensional approach appear to be significantly better than the one-dimensional approach.
One of the most widely applied methodologies for developing instream flow recommendations is the instream flow incremental methodology (IFIM) and its component microhabitat model, physical habitat simulation (PHABSIM). In this paper we reviewed over 1,500 habitat–flow curves obtained from 127 PHABSIM studies from western North America to develop predictions for flow needs for salmonids in this region and to test whether habitat–flow relationships for salmonids were related to watershed characteristics and geographic location. We present regressions that predict PHABSIM optima for four life history stages of four salmonid species and for all salmonid species in the database as a group, and we quantify the uncertainty in these estimates. Mean annual discharge (MAD) was the best predictor of optimum flow. The general form of the regressions was log e(optimum flow) = A × log e(MAD), where A < 1. Minor improvement in predictive power was sometimes possible with addition of latitude and longitude coordinates to the regression. This relationship is asymptotic and differs considerably from the fixed flow percentages recommended by Tennant. Our results are presented as a planning tool to (1) allow managers and project proponents to conduct a preliminary assessment of proposed water-use development projects, (2) optimize research efforts for instream flow studies and experiments, and (3) set experimental boundaries for adaptive management of stream flow.
This paper presents the results of two nonstatistical surveys (completed in 1981 and 1986) that solicited information from state and federal agencies concerning instream flow issues and practices in North America. Forty-six states and 12 Canadian provinces responded to the survey. Fifteen of the 46 states reported legislative recognition of instream flows for fisheries protection. In Canada, individual provinces generally lacked instream flow legislation, although federal legislation existed that could be used. The most commonly applied method (in use in 38 states or provinces) for assessing instream flow requirements, as reported in the survey, was the Fish and Wildlife Service Instream Flow Incremental Methodology (IFIM). Major research needs cited by survey respondents included (1) more species habitat information and preference curves, (2) techniques for determining instream flows for atypical conditions, and (3) testing of fish habitat:flow: production relationships.
The research team prepared summaries of 75 models or methods used to recommend instream flows or to characterize the quality of the aquatic habitat as it relates to flow. On the basis of these summaries, which are included in the report, and external literature, they analyzed the methods for various features - input and output variables, biologically transformed input variables, model structure, parameters estimation, procedures used to evaluate model sensitivity and to test model validity, and instream flow recommendations. Techniques for developing and validating models and for determining model sensitivity were described using instream flow methods as examples.
For many animals, selecting whether to forage during day or night is a critical fitness problem: at night, predation risks are lower but feeding is less efficient. Habitat selection is a closely related problem: the best location for nocturnal foraging could be too risky during daytime, and habitat that is safe and profitable in daytime may be unprofitable at night. We pose a theory that assumes animals select the combination of daytime and night activity (feeding vs. hiding), and habitat, that maximizes expected future fitness. Expected fitness is approximated as the predicted probability of surviving starvation and predation over a future time horizon, multiplied by a function representing the fitness benefits of growth. The theory's usefulness and generality were tested using pattern-oriented analysis of an individual-based model (IBM) of stream salmonids and the extensive literature on observed diel behavior patterns of these animals. Simulation experiments showed that the IBM reproduces eight diverse patterns observed in real populations. (1) Diel activity (whether foraging occurs during day and/or night) varies among a population's individuals, and from day to day for each individual. (2) Salmonids feed in shallower and slower water at night. (3) Individuals pack more tightly into the best habitat when feeding at night. (4) Salmonids feed relatively more at night if temperatures (and, therefore, metabolic demands) are low. (5) Daytime feeding is more common for life stages in which potential fitness increases more rapidly with growth. (6) Competition for feeding or hiding sites can shift foraging between day and night. (7) Daytime feeding is more common when food avail- ability is low. (8) Diel activity patterns are affected by the availability of good habitat for feeding or hiding. We can explain many patterns of variation in diel foraging behavior without assuming that populations or individuals vary in how inherently nocturnal or diurnal they are. Instead, these patterns can emerge from the search by individuals for good trade- offs between growth and survival under different habitat and competitive conditions.
Abstract There is an increasing demand for tools to assist in the management of environmental flows in rivers. Changes in river discharge act on biota through a hydraulic template, which is mediated by channel morphology. Hence, environmental flow assessments also need to consider channel morphology, especially if morphology has been altered by human activities. Computer models describing the preferences of fish for hydraulic microhabitats have been applied to environmental flow problems since the mid-1970s. Salmonids have been a particular focus for these methods. Other reviews have provided comprehensive coverage of the basic features and principles of such models. These are briefly discussed focusing on the developments that have occurred in the last 15 years and whose application has so far been infrequent. These include improvements to the representation of hydraulics at reach-scale and of longer river sections, and improved representation of interacting physical variables that describe habitat. The central theme is the spatial coverage and fundamental granularity of such models. Despite a broad literature, there is a lack of documented examples of the application of hydraulic-habitat models through all stages in the environmental flow decision-making process. The review concludes with four short examples that illustrate the use of model output.
Over the past two decades of refinement and application of instream flow evaluations, we have examined the hydraulic habitat of aquatic macroinvertebrates in a variety of conditions, along with the role of these macroinvertebrates in sustaining ecosystem integrity. Instream flow analyses assume that predictable changes in channel flow characteristics can, in turn, be used to predict the change in the density or distribution of lotic species or, more appropriately, the availability of useable habitat for those species. Five major hydraulic conditions most affect the distribution and ecological success of lotic biota: suspended load, bedload movement, and water column effects, such as turbulence, velocity profile, and substratum interactions (near-bed hydraulics). The interactions of these hydraulic conditions upon the morphology and behavior of the individual organisms govern the distribution of aquatic biota. Historically, management decisions employing the Physical Habitat Simulation (PHABSIM) have focused upon prediction of available habitat for life stages of target fish species. Regulatory agencies have rarely included evaluation of benthos for flow reservations. Although ‘taxonomic discomfort’ may be cited for the reluctant use or creation of benthic criteria, we suggest that a basic misunderstanding of the links between benthic macroinvertebrate and the fish communities is still a problem. This is derived from the lack of a perceived ‘value’ that can be assigned to macroinvertebrate species. With the exception of endangered mussel species (for which PHABSIM analysis is probably inappropriate), this is understandable. However, it appears that there is a greater ability to predict macroinvertebrate distribution (that is, a response to the change in habitat quality or location) and diversity without complex population models. Also, habitat suitability criteria for water quality indicator taxa (Ephemeroptera, Plecoptera, and Trichoptera; the so-called ‘EPTs’) may also provide additional management options to stream regulators. The greatest application for macroinvertebrate criteria will be in low-order streams where a more immediate link to fish communities can be established. We present an example from Queens Creek, in North Carolina, USA, in which monthly allocations required to preserve the integrity of the benthic macroinvertebrate community were significantly higher than for the target benthic fish species, Cottus bairdi. In the months when both Cottus and community diversity of macroinvertebrates were the ‘bottleneck’ life stages, preservation of only fish species could result in an additional 5–25% loss in macroinvertebrate habitat. We suggest that, as there becomes an increased emphasis on maintaining macroinvertebrates as monitors of stream health, there will be a concurrent emphasis on incorporating hydraulic habitat conditions as a part of bioassessment. Copyright © 2001 John Wiley & Sons, Ltd.
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