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Comment 1: Why It Is Time to Put PHABSIM Out to Pasture
... Current fish habitat models support evidence-based decision-making as the freshwater biodiversity crisis continues (Tickner et al. 2020 ), but they exhibit numerous shortcomings that limit their full usefulness especially under the novel riverscape concept. The persistent debate about fish habitat model design among ecologists and engineers has unfortunately polarized each view instead of unifying their fields' respective talents to address these shortcomings (Railsback 2016, Beecher 2017, Stalnaker et al. 2017, Rinaldo and Rodriguez-Iturbe 2022. The novel riverscape concept helps us mutually identify critical strengths and weaknesses of existing models, so they are used appropriately and inform the design of new models to enhance our capabilities. ...
... If we examine the legacy of fish habitat models ( type 1; see supplement S1) and the concepts that support them, we find that little has changed (Railsback 2016, Beecher 2017, Nestler et al. 2019. The difficulty of modeling fish habitat from a practical perspective, where time and resources are severely limited, ushered in the practices of prioritizing individual species instead of broader biodiversity goals, and assessing impacts separately instead of jointly. ...
... Agent-based models serve as a potential basis for examining how ecological processes at the level of individual organisms link to population-level processes (Breckling et al. 2005 , Grimm andBerger 2016 ). 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. ...
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.
... Shirvell (1989) and Gallagher and Gard (1999) considered incorporation of bedform and mesohabitat in their discussions. Railsback (2016) argued that PHABSIM was inadequate to address fish habitat, but others (Beecher, 2017;Reiser & Hilgert, 2018;Stalnaker et al., 2017) argued that PHABSIM can serve as a foundation for improving fish habitat modeling, and this study supports that contention. Hanrahan (2007) CU definition included RRD (Boessow et al., 2021); RRD is D at a location relative to maximum pool residual D (Lisle, 1987), which is maximum pool D at SZF. RRD is independent of stream channel size. ...
In the face of a changing climate and increasing human demand for water, an understanding of habitat preference has become critical for managing wild fish populations and projecting potential changes in habitat and populations. Two approaches to Physical Habitat Simulation (PHABSIM) modeling of coastal cutthroat trout Oncorhynchus clarkii clarkii spawning habitat were compared by modeling a reach, consisting of eight transects covering a pool and upstream and downstream riffles, of a small Puget Sound stream with two sets of habitat variables. The reach contained a cluster of redds 2 years in a row, assumed to be an indication of preferred spawning habitat and was located in the area of maximum spawning in the watershed, based on multiple years of redd surveys. Two PHABSIM instream flow models of the study site, one based on standard microhabitat (depth [D], velocity [V], and substrate [S]) suitabilities and the other based on D, V, and channel unit (CU) suitabilities, were developed and compared for their relative ability to correctly predict coastal cutthroat trout spawning habitat selection at the redd cluster within the PHABSIM study site. One approach was the standard use of habitat suitability criteria (HSC) for D, V, and S to indicate spawning habitat quality. The alternate approach was to replace substrate HSC with CU index HSC that incorporated dominant substrate particle diameter, CU (riffle, deep and shallow pool tail, pool body, deep and shallow pool edge, cascade, waterfall, and terrestrial), where deep and shallow units were based on relative residual depth (RRD), size of CU relative to channel width, and position within CU. Spawning habitat quality was calculated for each transect as weighted usable width with the standard HSC metrics (WUW s ) as well as the modified CU index (WUW m ). WUW m at the transects bracketing the redd cluster exceeded WUW m at the remaining six transects and was outside the 95% confidence interval for WUW m at the remaining transects. In contrast, WUW s varied less between the redd cluster and the remainder of the transects, suggesting the CU index better reflected spawning habitat quality than substrate. Incorporation of elevation relative to SZF addressed vulnerability to declining flow during incubation. Both models resulted in maximum WUA within the range of discharges that coincided with the majority of fresh cutthroat trout redds in Skookum Creek.
... 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.
... 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.
... While physical instream habitat models have been used for decades, they have occasionally been criticized for simplifying biotic-abiotic relationships (Railsback, 2016; see also comments by Beecher (2017) and Stalnaker et al. (2017)). One criticism focuses on the spatial and temporal scales used in habitat assessments (Heggenes et al., 1999). ...
While many studies provide microscale relationships between fish and habitat characteristics, studies covering longer river reaches are scarce. Modern remote sensing techniques may enable new and effective ways of mapping and assessing mesoscale habitat characteristics. Using green LIDAR-derived bathymetry and hydraulic modelling, we tested how mesoscale depth and velocity were related to fish counts of adult European grayling ( Thymallus thymallus L.) and brown trout ( Salmo trutta L.) in 500 m river sections in three separate periods during the year. Using riverbank sinuosity from aerial images and a Froude number-based index from the hydraulic model as proxies for mesoscale spatial and hydraulic heterogeneity, we tested for temporal correlations with river section fish counts of adult European grayling and brown trout. Results showed that mesoscale mean depth and velocity were correlated to period fish counts of adult European grayling. Using mixed model analysis we found that riverbank sinuosity and the Froude number-based index were significantly correlated with river section occurrence of adult European grayling during spawning. The results can be used to assess how flow-induced changes and channel adjustments at the mesoscale level can influence access to and use of relevant habitats in rivers occupied by European grayling and brown trout.
... 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.
... 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.
... Despite the established status of habitat modelling in river management, users should be aware of limitations, uncertainties and reality checks associated with mesohabitat and any instream habitat modelling approaches (Beecher, 2017;Railsback, 2016Railsback, , 2017Stalnaker, Chisholm, & Paul, 2017). Limitations in habitat classification regarding partially subjective decision-making in the field have already been discussed in previous sections, and the interested reader may refer to Poole and Frissell (1998) (Vadas & Orth, 2000). ...
Modelling the linkage between physical habitat and aquatic organisms on multiple spatial scales has become an important tool in the management of rivers. The mesoscale (100–102 m) represents an intermediate resolution in modelling that bridges the gap between available resources and conservation efforts for riverine species. However, existing mesohabitat classification schemes for lotic systems vary significantly in the definition of habitat types as well as in their application in the field. This article aims to provide an overview of current attempts to model the mesoscale pattern of physical habitats with a focus on fish. First, we outline descriptive, qualitative as well as objective, quantitative classification methods that are available in the literature. Next, the ecological relevance of the mesohabitat concept is being discussed, using single‐species and community‐level approaches as examples. Different modelling approaches that describe and quantify riverine mesohabitats are presented, and finally, limitations and uncertainties in the modelling process are discussed, followed by an outline of future perspectives in mesohabitat modelling.
... Nevertheless, there are a series of recommended steps to improve its performance (Beecher, 2017). ...
Aquatic organisms with different adaptations are used as indicators in physical habitat simulation system models. Those adaptations are critical for determining the shape of the weighted usable area/width curve and for recommending values of environmental flows. The main objective of this study is to compare the use of benthic native species (Astroblepus taczanowskii and Astroblepus vanceae) versus the introduced Oncorhynchus mykiss (rainbow trout) as target indicators for PHABSIM modelling in the Andean–Amazon piedmont rivers. We used adjusted probability distribution functions with L‐moments analyses for developing curves of use and preference to evaluate the efficiency of each indicator. Two hydraulic modelling sections were established in the Ulcumayo River with 21 and 27 cross sections, respectively. Native benthic species are usually dominant but scarcely used as focus organisms for environmental flows modelling. These species are associated with fast running and shallow waters, which makes them potentially more sensitive to the effects of flow reduction. Our results indicated that the native species were more restricted to velocity and depth than O. mykiss. Using selection curves in PHABSIM modelling, it is required between 10% to 94% of the mean monthly flow to preserve 90% of the available habitat for Astroblepus during the dry season (May to November). In contrast, rainbow trout requires 5% to 88% of the mean monthly flow. We conclude that a multispecies approach is useful for determining the required environmental instream flows contributing to a better sustainable condition for the Neotropical mountain rivers.
... As long as development and human demand for freshwater conflicts with stream fish populations, HSMs will continue to be a necessary tool. Correlative HSMs remain the standard approach but continue to be controversial (Beecher, 2017;Railsback, 2016;Stalnaker, Chisholm, & Paul, 2017), while mechanistic population models have struggled to gain a foothold with practitioners, partly due to their complexity and lack of validation. The bioenergetics-based approach may occupy a useful intermediate niche as it is grounded in the intrinsic energetics underlying habitat use but is still expressed as a simple standardised habitat suitability index that is compatible with existing modelling platforms and the broader hydraulic habitat modelling paradigm currently used by instream flow practitioners. ...
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.
... Its most recent critic, Railsback (2016), went so far as to title his paper "Why It Is Time to Put PHABSIM Out to Pasture." This prompted comments from Beecher (2017) and Stalnaker et al. (2017) and a corresponding response from Railsback (2017). Kemp and Katopodis (2017) also provided comments noting the timeliness of the Railsback (2017) paper and promoting further dialogue on the subject. ...
Relationships between fluvial aquatic habitat availability and discharge are often assumed to remain static when used with hydrologic datasets to analyze changes in habitat availability over time. Despite this assumption, studies have observed significant changes in aquatic habitat availability before and after restoration projects, dam removals, and extreme flood events. However, research is lacking on how aquatic habitat changes as a result of morphodynamic processes during more commonly occurring hydrologic conditions. This study compared Chinook salmon (Oncorhynchus tshawytscha) rearing habitat availability at 19 discharges before and after a relatively mild 8-year hydrologic period punctuated with modest floods on the lower Yuba River in California, USA. During this time, the total area of rearing habitat remained relatively consistent at discharges <2× bankfull but decreased by up to 25% at discharges >2× bankfull. Significant decreases in rearing habitat area appeared to be the result of widespread erosion on floodplains, terraces, and lateral bars, even after only modest floods. As a result, spatially delineated areas of lost habitat tended to increase in water depth and velocity at baseflow, bankfull, and floodplain-filling discharges, while areas of gained habitat decreased in depth and velocity. Although these specific results may not apply to all rivers around the world, the finding that habitat–discharge relationships change as a result of morphodynamic processes likely does transfer globally and should be considered when making long-term regulatory and management decisions, such as instream flow requirements and habitat restoration plans.
Instream flow models link a physical habitat model that predicts flow-related changes in hydraulics to a biological model that predicts the response of fish to altered velocity and depth. Habitat suitability curves (HSCs) based on frequency of habitat use (fish occurrence relative to available habitat) remain the most widely used biological models in habitat simulations. However, in some contexts fish density may be a poor indicator of habitat quality, leading to biased predictions of optimal flow. We explore the use of bioenergetics to derive mechanistic HSCs based on the fundamental energetics of habitat use. Using flow-related changes in production of Coho Salmon Oncorhynchus kisutch smolt as reference data to evaluate model predictions, we found that bioenergetic-based HSCs matched the validation data better than frequency-based HSCs, which systematically underestimated optimal flows. However, biases remained using bioenergetic HSCs, suggesting that habitat suitability may not be independent of discharge as is often assumed. Declining invertebrate drift concentration, increasing temperature, and density dependence of growth at low flows are potential mechanisms of flow-related declines in habitat suitability; measuring these effects and incorporating them into flow models is an important step in further improving model predictions, particularly at low flows.
Received December 3, 2015; accepted May 11, 2016
This paper describes the methodological concept for application of physical habitat models to restoration planning at a whole river scale. The design proposed here builds upon the Instream Flow Incremental Methodology but is focused at the need for managing large-scale habitats and river systems. It modifies the data acquisition technique and analytical resolution of standard approaches, changing the scale of physical parameters and biological response assessment from micro- to meso-scale. In terms of technological process, a highly detailed microhabitat survey of a few, short sampling sites would be replaced by mesohabitat mapping of whole-river sections. As with more traditional stream habitat models, the variation in the spatial distribution and amount of mesohabitats can provide key information on habitat quality changes corresponding to alterations in flow, channel changes, and stream improvement measures. However, the scale of simulations more closely matches restoration and system analyses, because it provides a solid base for quantitative assessment and simulation of habitat conditions for the whole stream.
Common applications of models to predict the response of fish habitat to altered stream flow (such as the Physical Habitat Simulation Model; PHABSIM) assume that fish abundance is directly related to the area of suitable habitat for limiting life stages and usually ignore flow effects on prey abundance. However, if prey availability is flow sensitive, then fish production may be more closely related to the total flux of available prey than to habitat area. We compared instream flow predictions from PHABSIM to predictions of optimal energy flux to drift-feeding juvenile coho salmon (Oncorhynchus kisutch) estimated using a drift-foraging bioenergetics model. Flux of available energy to juvenile coho salmon declined much more rapidly with decreasing flow than suitable habitat area estimated using PHABSIM, so that, relative to the bioenergetic model, predictions from PHABSIM systematically overestimated productive capacity at very low flows (i.e., underestimated the negative consequences of simulated water withdrawal). Applications of habitat suitability based models like PHABSIM may systematically overestimate low-flow productive capacity for species that prefer low velocities (e.g., pools) but are dependent on energy fluxes generated in higher velocity habitats (e.g., riffles).
umans have long been fasci- nated by the dynamism of free-flowing waters. Yet we have expended great effort to tame i rivers for transportation, water sup- ply, flood control, agriculture, and ; f
Six study sites were selected to represent the range of channel morphologies, extending from dynamic pool-riffle to transitional step-pool/plane bed reach types, used by spawning Atlantic salmon (Salmo salar) in a small upland Scottish stream. The hydraulic functioning of reaches over the range of discharges used by spawning fish was characterized, and the influence of hydraulic heterogeneity and rates of change in discharge on the frequency of spawning was assessed. Relationships between discharge and depths and velocities differed significantly between sites; thus, hydraulic responses to changes in discharge were different. The range of discharges used for spawning differed between sites, although optimum discharges were similar. Integration of hydraulic information with microhabitat suitability predicted that spawning conditions should occur at discharges higher than those utilized by fish. There was no evidence that hydraulically heterogeneous sites were used more frequently than homogeneous ones. Rather, data suggest that the frequency of utilization of sites was governed principally by the availability of suitable sediment. Flow stability was important for spawning, with periods of rapidly varying discharge avoided. It is suggested that the rate of change in discharge should be considered more explicitly when assessing environmental flow needs.
Three oxbow lakes with different connection frequencies and an adjacent reach of the middle Brazos River, Texas, were surveyed quarterly from summer 1993 to summer 1996 to examine the effects of hydrology and physicochemical attributes on fish assemblage structure. During flood events, oxbows usually were colonized by about 20 fish species from the river channel, and several fluvial specialists were rarely or never sampled from oxbows. Multivariate analyses of seine samples revealed divergent patterns of assemblage structure during periods of isolation that also were associated with a gradient of maximum water depth, temperature, and conductivity. In contrast, analysis of gill-net samples that targeted large fishes revealed low between-site and temporal variation in assemblage structure among oxbow lakes but significant differences in the structure of oxbow versus channel assemblages. The shallowest oxbow (which dried out with greatest frequency) had the most variable fish assemblage across seasons and was dominated by small colonizing species, whereas deeper oxbows and the river channel tended to have higher species richness and more stable assemblages. Despite large differences in connection frequency and distance from the river channel, the deepest oxbows had the most similar fish assemblage structure across all seasons. Multiple regression analysis suggested that the timing and frequency of flood events (yielding colonization) in the most frequently connected oxbow interact with predator abundance (yielding mortality) to influence the abundance of common lotic-adapted min-nows (red shiner Cyprinella lutrensis and bullhead minnow Pimephales vigilax) that periodically dominated the species assemblage of that oxbow after floods. Our results suggest that current hydrologic and geomorphologic dynamics in the middle Brazos River produce oxbow lakes with a range of physical characteristics yielding different disturbance and colonization regimes that strongly influence fish species assemblages. Floodplain rivers are dynamic ecosystems char-acterized by high biological diversity, productiv-ity, spatial complexity, and flow variability (Sparks 1995). Ecological processes in these sys-tems are dominated by hydrology (Poff and Allan 1995), and conceptual models emphasize flood dy-namics as a primary factor influencing fish pro-ductivity and recruitment (Junk et al. 1989; Hum-phries et al. 1999). Periodic inundation provides opportunities for aquatic organisms to access pro-ductive off-channel floodplain habitats, such as ox-bow lakes that function as spawning and nursery areas for many fish species, provide aquatic or-ganisms with refuge from disturbances in the river channel, and contribute to the biodiversity of the river–floodplain system as a whole (Halyk and Balon 1983; Sabo and Kelso 1991; Sabo et al. 1991; Hoover and Killgore 1998; Swales et al.
As demand for fresh water increases in tandem with human population growth and a changing climate, the need to understand the ecological tradeoffs of flow regulation gains greater importance. Environmental classification is a first step towards quantifying these tradeoffs by creating the framework necessary for analysing the effects of flow variability on riverine biota. Our study presents a spatially explicit hydrogeomorphic classification of streams and rivers in Washington State, USA and investigates how projected climate change is likely to affect flow regimes in the future. We calculated 99 hydrologic metrics from 15 years of continuous daily discharge data for 64 gauges with negligible upstream impact, which were entered into a Bayesian mixture model to classify flow regimes into seven major classes described by their dominant flow source as follows: groundwater (GW), rainfall (RF), rain-with-snow (RS), snow-and-rain (SandR), snow-with-rain (SR), snowmelt (SM) and ultra-snowmelt (US). The largest class sizes were represented by the transitional RS and SandR classes (14 and 12 gauges, respectively), which are ubiquitous in temperate, mountainous landscapes found in Washington. We used a recursive partitioning algorithm and random forests to predict flow class based on a suite of environmental and climate variables. Overall classification success was 75%, and the model was used to predict normative flow classes at the reach scale for the entire state. Application of future climate change scenarios to the model inputs indicated shifts of varying magnitude from snow-dominated to rain-dominated flow classes. Lastly, a geomorphic classification was developed using a digital elevation model (DEM) and climatic data to assign stream segments as either dominantly able or unable to migrate, which was cross-tabulated with the flow types to produce a 14-tier hydrogeomorphic classification. The hydrogeomorphic classification provides a framework upon which empirical flow alteration–ecological response relationships can subsequently be developed using ecological information collected throughout the region. Copyright © 2011 John Wiley & Sons, Ltd.
1. In an effort to develop quantitative relationships between various kinds of flow alteration and ecological responses, we reviewed 165 papers published over the last four decades, with a focus on more recent papers. Our aim was to determine if general relationships could be drawn from disparate case studies in the literature that might inform environmental flows science and management.
2. For all 165 papers we characterised flow alteration in terms of magnitude, frequency, duration, timing and rate of change as reported by the individual studies. Ecological responses were characterised according to taxonomic identity (macroinvertebrates, fish, riparian vegetation) and type of response (abundance, diversity, demographic parameters). A ‘qualitative’ or narrative summary of the reported results strongly corroborated previous, less comprehensive, reviews by documenting strong and variable ecological responses to all types of flow alteration. Of the 165 papers, 152 (92%) reported decreased values for recorded ecological metrics in response to a variety of types of flow alteration, whereas 21 papers (13%) reported increased values.
3. Fifty-five papers had information suitable for quantitative analysis of ecological response to flow alteration. Seventy per cent of these papers reported on alteration in flow magnitude, yielding a total of 65 data points suitable for analysis. The quantitative analysis provided some insight into the relative sensitivities of different ecological groups to alteration in flow magnitudes, but robust statistical relationships were not supported. Macroinvertebrates showed mixed responses to changes in flow magnitude, with abundance and diversity both increasing and decreasing in response to elevated flows and to reduced flows. Fish abundance, diversity and demographic rates consistently declined in response to both elevated and reduced flow magnitude. Riparian vegetation metrics both increased and decreased in response to reduced peak flows, with increases reflecting mostly enhanced non-woody vegetative cover or encroachment into the stream channel.
4. Our analyses do not support the use of the existing global literature to develop general, transferable quantitative relationships between flow alteration and ecological response; however, they do support the inference that flow alteration is associated with ecological change and that the risk of ecological change increases with increasing magnitude of flow alteration.
5. New sampling programs and analyses that target sites across well-defined gradients of flow alteration are needed to quantify ecological response and develop robust and general flow alteration–ecological response relationships. Similarly, the collection of pre- and post-alteration data for new water development programs would significantly add to our basic understanding of ecological responses to flow alteration.
1. The flow regime is a primary determinant of the structure and function of aquatic and riparian ecosystems for streams and rivers. Hydrologic alteration has impaired riverine ecosystems on a global scale, and the pace and intensity of human development greatly exceeds the ability of scientists to assess the effects on a river‐by‐river basis. Current scientific understanding of hydrologic controls on riverine ecosystems and experience gained from individual river studies support development of environmental flow standards at the regional scale.
2. This paper presents a consensus view from a group of international scientists on a new framework for assessing environmental flow needs for many streams and rivers simultaneously to foster development and implementation of environmental flow standards at the regional scale. This framework, the ecological limits of hydrologic alteration (ELOHA), is a synthesis of a number of existing hydrologic techniques and environmental flow methods that are currently being used to various degrees and that can support comprehensive regional flow management. The flexible approach allows scientists, water‐resource managers and stakeholders to analyse and synthesise available scientific information into ecologically based and socially acceptable goals and standards for management of environmental flows.
3. The ELOHA framework includes the synthesis of existing hydrologic and ecological databases from many rivers within a user‐defined region to develop scientifically defensible and empirically testable relationships between flow alteration and ecological responses. These relationships serve as the basis for the societally driven process of developing regional flow standards. This is to be achieved by first using hydrologic modelling to build a ‘hydrologic foundation’ of baseline and current hydrographs for stream and river segments throughout the region. Second, using a set of ecologically relevant flow variables, river segments within the region are classified into a few distinctive flow regime types that are expected to have different ecological characteristics. These river types can be further subclassified according to important geomorphic features that define hydraulic habitat features. Third, the deviation of current‐condition flows from baseline‐condition flow is determined. Fourth, flow alteration–ecological response relationships are developed for each river type, based on a combination of existing hydroecological literature, expert knowledge and field studies across gradients of hydrologic alteration.
4. Scientific uncertainty will exist in the flow alteration–ecological response relationships, in part because of the confounding of hydrologic alteration with other important environmental determinants of river ecosystem condition (e.g. temperature). Application of the ELOHA framework should therefore occur in a consensus context where stakeholders and decision‐makers explicitly evaluate acceptable risk as a balance between the perceived value of the ecological goals, the economic costs involved and the scientific uncertainties in functional relationships between ecological responses and flow alteration.
5. The ELOHA framework also should proceed in an adaptive management context, where collection of monitoring data or targeted field sampling data allows for testing of the proposed flow alteration–ecological response relationships. This empirical validation process allows for a fine‐tuning of environmental flow management targets. The ELOHA framework can be used both to guide basic research in hydroecology and to further implementation of more comprehensive environmental flow management of freshwater sustainability on a global scale.
We tested an assumption of the instream flow incremental methodology that depth and velocity preferences are independent of strcamflows. We had previously developed depth and velocity preferences (P[d] and P[v]) for juvenile (parr) sleelhcad Oncorhynchus mykiss at 0.86 m³/s in Morse Creek. Washington, and found parr distributed in microhabitats with higher combined depth-velocity preference (P[dv]) = P[d] × P[v]) at a similar flow (0.69 m³/s). In the present study, we evaluated the relationship between fish distribution and combined dcpth-velocity preference using an independent data set from a higher flow (2.41 m³/s) in the adjacent stream segment. Most steelhead parr were distributed in microhabitats with high P[dv]. consistent with distribution at 0.69 m³/s and significantly different than expected if fish distribution were independent of habitat preference (chi-square, P < 0.02). These results suggest that depth and velocity preferences are independent of flow.
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.
We used PIT tags implanted in juvenile Oncorhynchus mykiss to monitor movement into and out of two coastal Washington State rivers, East Twin River and West Twin River. Movement patterns revealed at least 18 life histories of steelhead O. mykiss with variations in age and seasonal migration of juveniles, juvenile use of the ocean prior to migration, years spent in the ocean, season of adult return, and iteroparity. While most migrants left the river in their first fall or winter, we did not detect any returning adults from these age-0 migrants. Adults were only produced from age-1 and older migrants, of which most were age-2 spring migrants that returned after two summers in the ocean. Our results indicated a positive relationship between fish length at tagging and the probability of being detected as a migrant, while the probability of a migrant leaving at age 1 and older decreased with increasing length at tagging among fish that were detected as migrants. We hypothesize that fish attaining a large enough size early in life to survive over the winter but not big enough to trigger migration at age 0 were more likely to remain in the river to become age-1 migrants, which were more likely to produce a returning adult steelhead. We also found evidence that density-dependent growth may influence juvenile steelhead migration patterns and production of migrants as evidenced by increasing contributing-adult steelhead escapement being negatively related to average cohort body size, probabilities of fish being detected as migrants, and production of age-1 and older migrants. We anticipate that the findings of this study can be used to inform the development of steelhead recovery strategies for East Twin and West Twin rivers, which have experienced recent declines in adult returns much like other North Pacific Ocean stocks.
Received January 20, 2016; accepted May 18, 2016
This paper relates spatial patterns of spawning by Atlantic salmon (Salmo salar L.) to channel geomorphic and hydrologic characteristics in two upland Scottish streams. The full length of each stream was surveyed and classified using a process-based typology. The precise locations of 845 spawning events were mapped over 3 successive years. These locations were classified by reach type, and a location-specific discharge was calculated for each spawning event. Fish used ‘response’ reach types (pool-riffle and transitional pool-riffle/plane bed) preferentially, avoiding ‘transport’ reach types (plane bed and step pool). The spatial distribution of reach types contrasted markedly between the streams, and as a consequence, the distribution of spawning activity differed. In each stream, fish utilised relatively high flows for spawning with almost all spawning occurring at discharges greater than location-specific median annual flows, while optimum discharges (defined as those where values of use most exceeded values of availability) were as high as two to three times greater than reach median flows. In each stream, spawning occurred over a greater flow range in response than transport reach types, primarily as a result of higher maximum utilised flows in the former. Because the channel classification procedure is process based (and therefore transferable to other geographic areas), the present study suggests that reach type may be used to predict the spatial distribution of Atlantic salmon spawning activity within a catchment. Since the data indicate that discharge use by spawning fish is reach-type specific, the results also suggest that channel morphology should be considered when identifying environmental flow requirements.
Conserving biological resources native to large river systems increasingly depends on how flow-regulated segments of these rivers are managed. Improving management will require a better understanding of linkages between river biota and temporal variability of flow and instream habitat. However, few studies have quantified responses of native fish populations to multiyear (>2 yr) patterns of hydrologic or habitat variability in flow-regulated systems. To provide these data, we quantified young-of-year (YOY) fish abundance during four years in relation to hydrologic and habitat variability in two segments of the Tallapoosa River in the southeastern United States. One segment had an unregulated flow regime, whereas the other was flow-regulated by a peak-load generating hydropower dam. We sampled fishes annually and explored how continuously recorded flow data and physical habitat simulation models (PHABSIM) for spring (April-June) and summer (July-August) preceding each sample explained fish abundances. Patterns of YOY abundance in relation to habitat availability (median area) and habitat persistence (longest period with habitat area continuously above the long-term median area) differed between unregulated and flow-regulated sites. At the unregulated site, YOY abundances were most frequently correlated with availability of shallow-slow habitat in summer (10 species) and persistence of shallow-slow and shallow-fast habitat in spring (nine species). Additionally, abundances were negatively correlated with 1-h maximum flow in summer (five species). At the flow-regulated site, YOY abundances were more frequently correlated with persistence of shallow-water habitats (four species in spring; six species in summer) than with habitat availability or magnitude of flow extremes. The associations of YOY with habitat persistence at the flow-regulated site corresponded to the effects of flow regulation on habitat patterns. Flow regulation reduced median flows during spring and summer, which resulted in median availability of shallow-water habitats comparable to the unregulated site. However, habitat persistence was severely reduced by flow fluctuations resulting from pulsed water releases for peak-load power generation. Habitat persistence, comparable to levels in the unregulated site, only occurred during summer when low rainfall or other factors occasionally curtailed power generation. As a consequence, summer-spawning species numerically dominated the fish assemblage at the flow-regulated site; five of six spring-spawning species occurring at both study sites were significantly less abundant at the flow-regulated site. Persistence of native fishes in flow-regulated systems depends, in part, on the seasonal occurrence of stable habitat conditions that facilitate reproduction and YOY survival.
We improved our predictions of fall chinook salmon (Oncorhynchus tshawytscha) habitat use by analyzing spawning habitat at the spatial scale of redd clusters. Spatial point pattern analyses indicated that redd clusters in the Hanford Reach, Columbia River, were consistent in their location from 1994 to 1995. Redd densities were 16.1 and 8.9 redds?ha-1 in 1994 and 1995, respectively, and individual redds within clusters were usually less than 30 m apart. Pattern analysis also showed strong evidence that redds were uniformly distributed within the clusters where inter-redd distances ranged from 2 to 5 m. Redd clusters were found to occur predominantly where water velocity was between 1.4 to 2 m?s-1, water depth was 2 to 4 m, and lateral slope of the riverbed was less than 4%. This habitat use represented a narrower range of use than previously reported for adult fall chinook salmon. Logistic regression analysis determined that water velocity and lateral slope were the most significant predictors of redd cluster location over a range of river discharges. Over-estimates of available spawning habitat lead to non-achievable goals for protecting and restoring critical salmonid habitat. Better predictions of spawning habitat may be possible if cluster-specific characteristics are used.
We tested an assumption of the Physical Habitat Simulation of the Instream Flow Incremental Methodology (IFIM) that fish select microhabitats based on the quality of one or several hydraulic conditions. We developed preference curves for juvenile steelhead (Oncorhynchus mykiss) in Morse Creek, Washington, USA, that accounted for availability of depths and velocities and their utilization by steelhead parr. To allow comparison of intervals among preference curves from different studies, we developed preference indices. We then evaluated the relationship between steelhead parr density and preference or preference indices for depth, velocity, and depth and velocity combined using an independent data set from a different year and an adjacent location in Morse Creek; these indices reflected observed densities of steelhead parr. There was a significant rank correlation between steelhead parr density and preferences or preference indices of steelhead parr for velocity alone and for depth and velocity combined, but not for depth alone. Steelhead parr strongly avoided habitat in which depth preference was 0.0, but velocity preference appeared to influence use of habitat where depth preference was not 0.0. Steelhead parr avoided cells with low preference indices and preferred cells with high preference indices. These relationships support an assumption of the IFIM.
Our study examined the effects of flow regulation on the spatiotemporal availability of shallow habitat patches with slow current velocity (SSCV patches) and floodplain inundation in the unregulated Yellowstone River and the regulated Missouri River in Montana and North Dakota. We mapped representative sites and used hydraulic models and hydrograph data to describe the frequency and extent of floodplain inundation and the availability of SSCV habitat over time during different water years. In the Yellowstone River the distribution, location, and size of SSCV patches varied but followed an annual pattern that was tied to the snowmelt runoff hydrograph. There was less variation in patch distribution in the Missouri River, and the pattern of habitat availability was influenced by flow regulation. Regulated flows and their effects on channel morphology and patterns of vegetation establishment resulted in 3.0–3.5 times less area of inundated woody vegetation during normal and dry years in the Missouri River compared with the Yellowstone River. The differences we observed in SSCV patch dynamics between rivers may have implications for fish populations and community structure through affecting the survival of early life stages. At a larger scale, the smaller area of vegetation inundated in the Missouri River suggests that nutrient cycling and the ecological benefits associated with a moving littoral zone are reduced by the altered flow and sediment regime in that river. Accurate assessments of the effects of flow alteration and successful efforts to restore riverine ecosystems will require consideration of physical and biotic processes that operate at multiple spatial and temporal scales.
We conducted a PHABSIM study on Bingham Creek, Washington, by using validated habitat suitability criteria for the rearing of coho salmon Oncorhynchus kisutch. We compared the relationship between weighted usable area (WUA) and flow with a previously determined empirical relationship that showed increasing coho salmon smolt production with increasing summer low flow (). The relationship between juvenile coho salmon WUA and flow indicated that the greatest amount of habitat occurred at a flow that was lower than our low-flow measurement, and the amount of habitat decreased with increasing flow. Thus, PHABSIM results were contrary to empirical measurement of coho salmon smolt production. Based on the relationship between summer flow and smolt production, production of smolts would decline if flow was reduced to the flow that maximizes WUA. The failure of PHABSIM to be consistent with empirical results may have be related to habitat suitability being influenced more by the numerous subdominant, schooling juvenile coho salmon and less by the dominant, territorial individuals, which have higher survival and prefer higher velocities.
We tested an assumption of the instream flow incremental methodology that depth and velocity preferences are independent of streamflows. We had previously developed depth and velocity preferences (P[d] and P[v]) for juvenile (parr) steelhead Oncorhynchus mykiss at 0.86 m/s in Morse Creek, Washington, and found parr distributed in microhabitats with higher combined depth–velocity preference (P[dv] = P[d] × P[v]) at a similar flow (0.69 m/s). In the present study, we evaluated the relationship between fish distribution and combined depth–velocity preference using an independent data set from a higher flow (2.41 m/s) in the adjacent stream segment. Most steelhead parr were distributed in microhabitats with high P[dv], consistent with distribution at 0.69 m/s and significantly different than expected if fish distribution were independent of habitat preference (chi-square, P < 0.02). These results suggest that depth and velocity preferences are independent of flow.
PHABSIM, part of the Instream Flow Incremental Methodology, was used to predict the spawning habitat used by chinook salmon in a 600 m long section of the Nechako River, British Columbia, Canada. Predictions of the model were compared to the location and amount of habitat actually used by adult chinook salmon in 1974, 1980, and 1986. About 3800 m2 (70 per cent) of the spawning area actually used by the population were predicted as unusable by the ‘best’ prediction, while 87 per cent of the area predicted as usable has never had recorded use. The ‘best’ prediction resulted from using close transect spacing, frequent measurements along the transect, river-specific habitat suitability criteria, and modelling habitat at the fish's position near the stream bottom. Depending upon the spacing of the transects and the habitat suitability criteria used, PHABSIM predicted 210 per cent to 660 per cent more spawning habitat was available than historically had ever been used. Chinook salmon in the Nechako River spawn mainly on the upstream face of dunes, therefore, the assumption in PHABSIM that conditions predicted at the transects remain unchanged upstream and downstream part way to the adjacent transects was false. This assumption resulted in about two-thirds of the correct predictions being made for the wrong reason. The accuracy of PHABSIM's predictions for spawning might be improved by incorporating an index of river bottom topography or velocity gradient into the model.
This paper reports the findings of research designed to assess the ability of PHABSIM to predict Atlantic salmon Salmo salar spawning habitat in the Girnock Burn, a tributary of the River Dee in northeast Scotland. It used an 18-year spawning data record to assess: (a) the ability of PHABSIM to predict between-year differences in the availability of habitat at the study site; (b) the ability of PHABSIM to predict patterns of relative suitability across the site; and (c) the influence of different Habitat Suitability Indices (HSIs) on the model's predictions with respect to (a) and (b).
Predictions of between-year and within-site habitat availability based on ‘utilization’ and ‘preference’ HSIs developed in the Dee catchment corresponded significantly (chi-squared and regression tests, P < 0.05) with the use of the site by spawning fish. However, predictions based on utilization HSIs developed in streams in southern England did not correspond significantly with patterns of site use. Results of the study indicate that PHABSIM is capable of predicting Atlantic salmon spawning habitat in upland streams such as the Girnock, but that the use of appropriate HSIs is critical. Copyright
) spawning habitat. Information exists on the microhabitat characteristics that define suitable salmon spawning habitat. However,
traditional spawning habitat models that use these characteristics to predict available spawning habitat are restricted because
they can not account for the heterogeneous nature of rivers. We present a conceptual spawning habitat model for fall chinook
salmon that describes how geomorphic features of river channels create hydraulic processes, including hyporheic flows, that
influence where salmon spawn in unconstrained reaches of large mainstem alluvial rivers. Two case studies based on empirical
data from fall chinook salmon spawning areas in the Hanford Reach of the Columbia River are presented to illustrate important
aspects of our conceptual model. We suggest that traditional habitat models and our conceptual model be combined to predict
the limits of suitable fall chinook salmon spawning habitat. This approach can incorporate quantitative measures of river
channel morphology, including general descriptors of geomorphic features at different spatial scales, in order to understand
the processes influencing redd site selection and spawning habitat use. This information is needed in order to protect existing
salmon spawning habitat in large rivers, as well as to recover habitat already lost.
While the importance of river channel morphology to salmon spawning habitat is increasingly recognized, quantitative measures of the relationships between channel morphology and habitat use are lacking. Such quantitative measures are necessary as management and regulatory agencies within the Pacific Northwest region of the USA, and elsewhere, seek to quantify potential spawning habitat and develop recovery goals for declining salmon populations. The objective of this study was to determine if fall Chinook salmon (Oncorhynchus tshawytscha) spawning areas in the Snake River, Idaho, USA, were correlated with specific bedform types at the pool–riffle scale. A bedform differencing technique was used to objectively quantify the longitudinal riverbed profile into four distinct pool–riffle units that were independent of discharge. The vertical location of thalweg points within these units was quantified with a riffle proximity index. Chinook salmon spawning areas were mapped and correlated with the pool–riffle units through the use of cross-tabulation tables. The results indicate that 84% of fall Chinook salmon spawning areas were correlated with riffles (χ2 = 57.5, df = 3, p < 0.001), with 53% of those areas located on the upstream side of riffle crests. The majority of Snake River fall Chinook salmon spawning occurred at elevations greater than 80% of the difference in elevation between the nearest riffle crest and pool bottom. The analyses of bedform morphology will assist regional fish managers in quantifying existing and potential fall Chinook salmon spawning habitat, and will provide a quantitative framework for evaluating general ecological implications of channel morphology in large gravel-bed rivers.
An expert-based approach was used to identify 10 morphological unit types within a reach of the gravel bed, regulated Yuba River, California, that is heavily utilized by spawning Chinook salmon (Oncorhynchus tshawytscha). Analysis of these units was carried out using two-dimensional hydrodynamic modeling, field-based geomorphic assessment, and detailed spawning surveying. Differently classified morphological units tended to exhibit discrete hydraulic signatures. In most cases, the Froude number adequately differentiated morphological units, but joint depth–velocity distributions proved the most effective hydraulic classification approach. Spawning activity was statistically differentiated at the mesoscale of the morphological unit. Salmon preferred lateral bar, riffle, and riffle entrance units. These units had moderately high velocity (unit median > 0.45 m s− 1) and low depth (unit median < 0.6 m), but each exhibited a unique joint depth–velocity distribution. A large proportion of redds (79%) were associated with conditions of convective flow acceleration at riffle and riffle entrance locations. In addition to reflecting microhabitat requirements of fish, it was proposed that the hydraulic segregation of preferred from avoided or tolerated morphological units was linked to the mutual association of specific hydraulic conditions with suitable caliber sediment that promotes the provision and maintenance of spawning habitat.
Effects of springtime flow alteration on side channel habitat in the Green River
- H A Coccoli
Coccoli, H. A. 1996. Effects of springtime flow alteration on side channel
habitat in the Green River. Master's thesis. Department of Civil Engineering, University of Washington, Seattle.
- N L Poff
- B D Richter
- A H Arthington
- S E Bunn
- R J Naiman
- E Kendy
- M Acreman
- C Apse
- B P Bledsoe
- M C Freeman
- J Henriksen
- R B Jacobson
- J G Kennen
- D M Merritt
- J H O'keefe
- J D Olden
- K Rogers
- R E Tharme
- A Warner
Poff, N. L., B. D. Richter, A. H. Arthington, S. E. Bunn, R. J. Naiman, E.
Kendy, M. Acreman, C. Apse, B. P. Bledsoe, M. C. Freeman, J. Henriksen, R. B. Jacobson, J. G. Kennen, D. M. Merritt, J. H. O'Keefe, J. D.
Olden, K. Rogers, R. E. Tharme, and A. Warner. 2010. The ecological
limits of hydrologic alteration (ELOHA): a new framework for developing regional environmental flow standards. Freshwater Biology
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Geological Survey, Retired, 5415 East County Road 58, Fort Collins
- Clair B Stalnaker
Clair B. Stalnaker, U.S. Geological Survey, Retired, 5415 East County Road 58, Fort Collins, CO 80524.
E-mail: clair_stalnaker@cowisp.net
Minnesota Department of Natural Resources, Ecological and Water Resources Division, River Science Unit Supervisor
- Ian Chisholm
Ian Chisholm, Minnesota Department of Natural Resources, Ecological and Water Resources Division, River Science Unit
Supervisor, Saint Paul, MN