Seasonal movements and residency of small-bodied fish in a north temperate urban watershed demonstrate connectivity between a stream and stormwater drain

Despite their often physical connection, neighbouring stormwater drains and urban streams are typically managed quite differently; with drains mostly regarded as poor fish habitat. The goal of this study was to evaluate the interconnectedness of an urban stream (Watts Creek) and adjoining earthen surface stormwater drain (Kizell Drain) from the perspective of fish residency and movements over an entire year. Using a stationary passive integrated transponder (PIT) array, we quantified and compared the direction of movements among Watts Creek, Kizell Drain, and the area downstream of their confluence (herein termed Main) for four common stream fishes. We also determined the residency time (percentage of total time in days) within each of these reaches by combining data from the array and recaptured (with electrofishing and identified with hand-held PIT reader) or portably detected (with mobile PIT reader) fish. While the movements of creek chub (Semotilus atromaculatus) and central mudminnow (Umbra limi) varied across seasons, creek chub resided significantly longer in Watts, while central mudminnow spent more time in Kizell and Main. Longnose dace (Rhinichthys cataractae) moved into and resided most often within Watts. The movements and residency time for white sucker (Catostomus commersonii) did not vary among the reaches. We conclude there is a high degree of connectivity between Watts Creek and Kizell Drain and that, with the exception of longnose dace, the three other species utilize the habitat available in Kizell. This study demonstrates the biological potential of earthen stormwater drains and as a result we recommend these systems be managed as a functional component of urban watersheds.     

Turning passive detection systems into field experiments: an application using wetland fishes and enclosures to track fine-scale movement and habitat choice

Understanding habitat selection and movement remains a key question in behavioral ecology. Yet, obtaining a sufficiently high spatiotemporal resolution of the movement paths of organisms remains a major challenge, despite recent technological advances. Observing fine-scale movement and habitat choice decisions in the field can prove to be difficult and expensive, particularly in expansive habitats such as wetlands. We describe the application of passive integrated transponder (PIT) systems to field enclosures for tracking detailed fish behaviors in an experimental setting. PIT systems have been applied to habitats with clear passageways, at fixed locations or in controlled laboratory and mesocosm settings, but their use in unconfined habitats and field-based experimental setups remains limited. In an Everglades enclosure, we continuously tracked the movement and habitat use of PIT-tagged centrarchids across three habitats of varying depth and complexity using multiple flatbed antennas for 14 days. Fish used all three habitats, with marked species-specific diel movement patterns across habitats, and short-lived movements that would be likely missed by other tracking techniques. Findings suggest that the application of PIT systems to field enclosures can be an insightful approach for gaining continuous, undisturbed and detailed movement data in unconfined habitats, and for experimentally manipulating both internal and external drivers of these behaviors.     

Habitat use of redfin bullies (Gobiomorphus huttoni) in a small upland stream in Manawatu, New Zealand

This study uses Passive Integrated Transponder (PIT) technology to describe the habitat use patterns of the small, benthic redfin bully (Gobiomorphus huttoni). A 100-m reach of small upland stream in Manawatu, New Zealand was mapped to scale and inventoried for microhabitat variables. Flow velocity, depth, surface turbulence, substrate size and interstitial refuge space availability were measured in 0.25-m² quadrats throughout the reach. A total of 67 redfin bullies were PIT tagged within the reach and monitored during day and night surveys in 2008 with a portable PIT monitoring system. Of these, 72 % were detected at least once and 64 % were detected 5 times or more within the study reach. Univariate analyses showed that redfin bullies utilized microhabitats that had larger substrate particles and more interstitial refuge spaces compared with all microhabitats available in the reach. During the day, redfin bullies were found in areas with larger substrates than areas where they were found at night. No differences in microhabitat use were found regarding gender, body size or season. Multivariate analysis revealed four macrohabitat types and showed that redfin bullies used deeper, complex macrohabitats during the day, then spread out to occupy all available macrohabitats at night. These findings have implications for river managers trying to cope with increasing anthropogenic impacts such as sedimentation.     

Ecological values of Hamilton urban streams (North Island, New Zealand): constraints and opportunities for restoration

Urban streams globally are characterised by degraded habitat conditions and low aquatic biodiversity, but are increasingly becoming the focus of restoration activities. We investigated habitat quality, ecological function, and fish and macroinvertebrate community composition of gully streams in Hamilton City, New Zealand, and compared these with a selection of periurban sites surrounded by rural land. A similar complement of fish species was found at urban and periurban sites, including two threatened species, with only one introduced fish widespread (Gambusia affinis). Stream macroinvertebrate community metrics indicated low ecological condition at most urban and periurban sites, but highlighted the presence of one high value urban site with a fauna dominated by sensitive taxa. Light-trapping around seepages in city gullies revealed the presence of several caddisfly species normally associated with native forest, suggesting that seepage habitats can provide important refugia for some aquatic insects in urban environments. Qualitative measures of stream habitat were not significantly different between urban and periurban sites, but urban streams had significantly lower hydraulic function and higher biogeochemical function than periurban streams. These functional differences are thought to reflect, respectively, (1) the combined effects of channel modification and stormwater hydrology, and (2) the influence of riparian vegetation providing shade and enhancing habitat in streams. Significant relationships between some macroinvertebrate community metrics and riparian vegetation buffering and bank protection suggest that riparian enhancement may have beneficial ecological outcomes in some urban streams. Other actions that may contribute to urban stream restoration goals include an integrated catchment approach to resolving fish passage issues, active reintroduction of wood to streams to enhance cover and habitat heterogeneity, and seeding of depauperate streams with native migratory fish to help initiate natural recolonisation.     

Development of a spatially universal framework for classifying stream assemblages with application to conservation planning for Great Lakes lotic fish communities

Classifications are typically specific to particular issues or areas, leading to patchworks of subjectively defined spatial units. Stream conservation is hindered by the lack of a universal habitat classification system and would benefit from an independent hydrology‐guided spatial framework of units encompassing all aquatic habitats at multiple spatial scales within large regions. We present a system that explicitly separates the spatial framework from any particular classification developed from the framework. The framework was constructed from landscape variables that are hydrologically and biologically relevant, covered all space within the study area, and was nested hierarchically and spatially related at scales ranging from the stream reach to the entire region; classifications may be developed from any subset of the 9 basins, 107 watersheds, 459 subwatersheds, or 10,000s of valley segments or stream reaches. To illustrate the advantages of this approach, we developed a fish‐guided classification generated from a framework for the Great Lakes region that produced a mosaic of habitat units which, when aggregated, formed larger patches of more general conditions at progressively broader spatial scales. We identified greater than 1,200 distinct fish habitat types at the valley segment scale, most of which were rare. Comparisons of biodiversity and species assemblages are easily examined at any scale. This system can identify and quantify habitat types, evaluate habitat quality for conservation and/or restoration, and assist managers and policymakers with prioritization of protection and restoration efforts. Similar spatial frameworks and habitat classifications can be developed for any organism in any riverine ecosystem.     

Mapping the Relative Probability of Common Toad Occurrence in Terrestrial Lowland Farm Habitat in the United Kingdom

Introduction

The common toad (Bufo bufo) is of increasing conservation concern in the United Kingdom (UK) due to dramatic population declines occurring in the past century. Many of these population declines coincided with reductions in both terrestrial and aquatic habitat availability and quality and have been primarily attributed to the effect of agricultural land conversion (of natural and semi-natural habitats to arable and pasture fields) and pond drainage. However, there is little evidence available to link habitat availability with common toad population declines, especially when examined at a broad landscape scale. Assessing such patterns of population declines at the landscape scale, for instance, require an understanding of how this species uses terrestrial habitat.

Methods

We intensively studied the terrestrial resource selection of a large population of common toads in Oxfordshire, England, UK. Adult common toads were fitted with passive integrated transponder (PIT) tags to allow detection in the terrestrial environment using a portable PIT antenna once toads left the pond and before going into hibernation (April/May-October 2012 and 2013). We developed a population-level resource selection function (RSF) to assess the relative probability of toad occurrence in the terrestrial environment by collecting location data for 90 recaptured toads.

Results

The predicted relative probability of toad occurrence for this population was greatest in wooded habitat near to water bodies; relative probability of occurrence declined dramatically > 50 m from these habitats. Toads also tended to select habitat near to their breeding pond and toad occurrence was negatively related to urban environments.     

Simple predictions of instream habitat model outputs for fish habitat guilds in large streams

1. In the context of a generalised modification of hydraulic conditions in medium to large streams, modelling the impacts of stream regulation on fish communities in multiple streams is an important challenge for basic and applied freshwater ecology. Conventional instream habitat models such as PHABSIM link a hydraulic model with preference curves for various species to estimate habitat value changes with discharge in stream reaches. Despite world‐wide applications, they have been scarcely used in multiple sites with multiple species. 2. We assigned 21 size classes of European fish species to four habitat guilds (cluster analysis grouping size classes with comparable microhabitat preference curves). Then, we ran a conventional instream habitat model on 28 French stream reaches belonging to the `barbel zone', to estimate habitat values versus discharge curves for the 21 size classes. We summarised the outputs as mean habitat values for guilds, and tested if they were predictable from average characteristics of reaches (discharge, depth, width, particle size). 3. As was obtained elsewhere for populations, habitat values for guilds were strongly related to average, dimensionless characteristics of reaches. The Reynolds number of reaches, equivalent to a discharge per width unit, reflected most of the discharge‐dependent changes in habitat values (within reaches). In particular, habitat values of species preferring bank (respectively midstream) microhabitats decreased (respectively increased) with increasing Reynolds number. The Froude number at median discharge was the major predictor of reach‐dependent but discharge‐independent variations in habitat values. Habitat values of species preferring riffle versus pool or bank microhabitats were higher in reaches with high Froude numbers. These relationships were consistent with existing knowledge on the different species. 4. Such results suggest that the input variables required to estimate habitat values for fish communities can be greatly simplified, as illustrated by a general estimation of the sensitivity of species preferring midstream habitats to discharge changes in any reach. Cost‐efficient alternatives to conventional instream habitat models should facilitate their validation in multiple sites, a point that remains critical in instream habitat modelling of fish communities.     

Effect of emergent aquatic insects on bat foraging in a riparian forest

1. Riparian zones serve several ecological functions for bats. They provide a source of prey and likely provide favourable structural habitats and shelter from predators. Many studies have shown that bats use the space above streams, ponds or riparian vegetation as feeding habitat. These studies, however, have never distinguished between the effects of habitat structure and prey availability on the foraging activities of bats. Such effects can only be distinguished by an experimental approach. We predicted that bat activity along a stream is influenced by the number of emerged aquatic insects. 2. We evaluated the response of terrestrial consumers, insectivorous bats, to changes in the abundance of emergent aquatic insects by conducting a manipulative field experiment. In a deciduous riparian forest in Japan, aquatic insect flux from the stream to the riparian zone was controlled with an insect-proof cover over a 1.2 km stream reach. 3. We estimated the abundance of emergent aquatic and flying terrestrial arthropods near the treatment and control reaches using Malaise traps. The foraging activity of bats was evaluated in both treatment and control reaches using ultrasonic detectors. 4. The insect-proof cover effectively reduced the flux of emergent aquatic insects to the riparian zone adjacent to the treatment reach. Adjacent to the control reach, adult aquatic insect biomass was highest in spring, and then decreased gradually. Terrestrial insect biomass increased gradually during the summer at both treatment and control reaches. 5. Foraging activity of bats was correlated with insect abundance. In spring, foraging activity of bats at the control reach was significantly greater than at the treatment reach, and increased at both sites with increasing terrestrial insect abundance. 6. Our result suggests that the flux of aquatic insects emerging from streams is one of the most important factors affecting the distribution of riparian-foraging bats. As is the case with other riparian consumers, resource subsidies from streams can directly enhance the performance or population density of riparian-dependent bats. To conserve and manage bat populations, it is important to protect not only forest ecosystems, but also adjacent aquatic systems such as streams.     

Predator effects on aquatic community assembly: disentangling the roles of habitat selection and post-colonization processes

Top predators are known to play an important role in the assembly of communities via two mechanisms: (1) by altering the colonization (or emigration) patterns of prey through behavioral habitat selection, and (2) by altering vital rates (e.g. mortality, birth) of prey after colonization. While both these mechanisms act to determine assembly, research has focused on either their combined overall effects (confounding them), or examined them singly. As a result, it remains unclear how these mechanisms act to sequentially shape community structure. In this study, we experimentally disentangle habitat selection and post‐colonization effects of predaceous fish to test their independent and combined influence on the assembly of insect and larval amphibian communities in experimental freshwater habitats. Specifically, we ask, ‘do the behavioral choices of colonists continue to structure aquatic communities even after post‐colonization processes have occurred?’ Like previous studies, we found that colonization was strongly reduced by the presence of fish cues. More importantly, these effects of fish on prey colonization behavior combined independently with post‐colonization processes to determine the overall effect of predators on community assembly. Although habitat selection and predation both reduced abundance and biomass of most taxa in the post‐colonization communities, these factors had qualitatively different effects on aspects of trophic structure. Habitat selection altered the ratio of secondary to primary consumer abundance and biomass, while post‐colonization predation drove strong trophic cascades not observed in response to habitat selection. Our results suggest that behavioral choices regarding habitat selection can have lasting and unique effects on the structure of aquatic communities.     

Seasonal zooplankton dynamics in main channel and backwater habitats of the Upper Mississippi River

This study used stratified random sampling to examine the spatial and temporal distribution of zooplankton communities in a large floodplain river (Mississippi River, USA). Potential mechanisms controlling zooplankton abundance and community structure were considered. Main channel and backwater habitats included in this study differed between a turbid upper pool reach where aquatic macrophytes were sparse and a lower pool reach which was considerably less turbid and had extensive aquatic macrophyte coverage. Samples were collected monthly during the summer over a 2-year period and multivariate analysis was used to examine the spatial and temporal distribution of zooplankton. Significant differences were found in zooplankton density and community composition among habitats and reaches within the pool. Rotifers were the dominant taxa and seasonality was pronounced, with peak densities often occurring in late-spring. Community structure varied by habitat and reach, which suggests that water quality, physical habitat characteristics, presence of aquatic macrophytes, and zooplankton sources can all influence the zooplankton communities of the Upper Mississippi River. Characterization of the zooplankton communities provides a basis for understanding changes in the river ecosystem and examination of zooplankton communities among habitats provides insight into the mechanisms affecting zooplankton dynamics.     

东苕溪中下游河岸类型对鱼类多样性的影响

河流修复工程被美国《科学》杂志列入2000年最具发展潜力的六大领域之一,河流修复工程对水生生态系统的影响也成为各国科学家的研究热点。本文以东苕溪中下游河段为对象,研究4种不同河岸类型（自然河岸 水生植物（A）、自然河岸 无水生植物（B）、人工河岸 水生植物（C）、人工河岸 无水生植物（D））对鱼类生物多样性的影响。本次调查共采集鱼类标本499尾,经鉴定为32种,隶属于7目10科24属。鱼类生物多样性结果显示A、B的物种丰度和Shannon-Wiener指数与D存在显著差异（P<0.05）; A的优势度指数与D存在显著性差异（P<0.05）; A、C的均匀度与D存在显著性差异。鱼类群落NMDS排序与相似性分析（ANOSIM）显示D与A、B、C能完全分开,且D与A、C存在显著性差异（P<0.05）,其中A与C存在显著性差异。因此,河流修复工程中水生植被的恢复对于水生生物多样性的维持至关重要,且恢复水生植被的河流修复工程会减少该工程对鱼类群落结构和生物多样的负面影响。     

Aquatic Habitat Dynamics along a Braided Alpine River Ecosystem (Tagliamento River, Northeast Italy)

Aquatic habitat change caused by flooding was quantified along the Fiume Tagliamento, a morphologically intact gravel-bed river ecosystem in northeast Italy. Five different geomorphic reaches (each around 1.5 km), ranging from near the headwaters at 800 m above sea level (a.s.l.) to near the mouth at 5 m a.s.l., were studied over a 1-year period. All floodplain water bodies in each reach were delineated in August 1999 using a differential global positioning system. Each reach was remapped twice (in December 1999 and August 2000) to investigate the impact of autumn and spring flood seasons on aquatic habitat composition and configuration. A high degree (nearly 62%) of aquatic habitat turnover was documented in a braided headwater floodplain. The degree of aquatic habitat turnover decreased with decreasing elevation to approximately 20% turnover in a meandering reach at 5 m a.s.l. In contrast to turnover, braiding, sinuosity, and aquatic habitat composition changed little in response to flooding in all reaches. Location of aquatic habitats in floodplains changed considerably (turnover), whereas habitat configuration and composition remained relatively stable. These results support the applicability of the shifting mosaic steady-state model to riverine floodplain environments.     

River fish assemblages along an elevation gradient in the eastern extremity of Europe

Studies on assemblages of freshwater fishes along elevational gradients of rivers are lacking, even in Europe. In this paper we have explored the entire range of elevational gradients existing in the European part of Russia. We analyzed how fish biodiversity (species richness, abundance, diversity indices) at 435 river sites differed by elevation. The impact of elevation on the distribution of freshwater fish species was analyzed using regression and ordination methods. For the first time for a large area of Eastern Europe, optimum points and niche breadth for fish species along altitude gradients were estimated. Our analyses showed: (1) species richness and Shannon index decreased in the upper part of the gradient; fish abundance showed a unimodal response to elevation; highest numbers were found at elevations between 250 and 500 m; (2) ordination analysis demonstrated an upstream-downstream gradient of the fish assemblages; (3) regression analysis showed significant preferences for elevation by 19 species, all of which were monotonic; (4) optimum and niche breadth (tolerance) were highly variable between species; only five species (brown trout, grayling, common minnow, bullhead and stone loach) were encountered at elevations above 650 m; and (5) in our region, the habitat of grayling was higher in the mountains, and its abundance (numbers) at extreme elevations was greater, than brown trout. These results show how fish assemblages differ with elevation. Our findings identify the data that can be used for regional environmental monitoring of the state of small rivers and for aquatic conservation.     

Comparison between PIT and radio telemetry to evaluate winter habitat use and activity patterns of juvenile Atlantic salmon and brown trout

Winter habitat use and activity patterns of juvenile Atlantic salmon and brown trout were analysed in a comparative study between Passive Integrated Transponder (PIT) technology, radio telemetry and underwater observation by snorkelling. Two study periods were conducted in Stoney River, Newfoundland, Canada. During Study period I, 49 juvenile Atlantic salmon (fork length: 11.0–18.0 cm) and 7 brown trout (11.0–17.3 cm) were tagged with PIT tags and/or radio transmitters in late winter of 2004. During Study period II, 18 juvenile Atlantic salmon (fork length: 12.0–18.4 cm) and 23 brown trout (10.9–20.8 cm) were tagged and tracked twice a day at 10:00 h and 22:00 h on five consecutive days in late winter of 2005. From the 56 fish released during Study period I, on average 19.6 ± 6.0% of the PIT tagged fish and 99.3 ± 2.2% of the radio tagged fish were relocated during any given survey. Over the Study period II, 39% of fish emigrated from the study site. PIT technology had an efficiency of 39.2 ± 14.1% to detect the remaining fish. In contrast, radio telemetry relocated on average 96.9 ± 6.5% of the tagged fish whereas by snorkelling on average only 4.1 ± 5.6% of the tagged fish were observed. PIT telemetry may however be more efficient in smaller, less heterogeneous streams. The advantage of PIT technology over radio telemetry is clearly that it is relatively less costly permitting higher numbers of individuals to be tagged and there is no limit in the operational life of the transponder. In winter, juvenile salmonids preferred low flow velocity and no preferences were observed for any specific water depth over the range of available water depths. Fish selected preferentially boulder habitat over other substrates in the environment. Habitat utilisation did not differ between day and night. The use of winter preference indices may be important for future habitat modelling.     

Factors influencing the spatial ecology of Lake Sturgeon and Walleye within an impounded reach of the Winnipeg River

Impoundments of free-flowing rivers for hydropower generation often confine fish to relatively small reaches that can restrict movement, limit habitat availability, and alter life history strategies. Here, acoustic telemetry was used to describe the seasonal habitat use, locomotory activity, and depth use for Lake Sturgeon (Acipenser fulvescens) and Walleye (Sander vitreus) within an impounded reach on the Winnipeg River, Manitoba, Canada. Lake Sturgeon foraged and overwintered in the riverine-lacustrine transitionary habitat as well as immediately below the tailrace of the upstream run-of-river facility. Walleye demonstrated high site fidelity to the upstream habitat situated near the tailrace of a hydropower facility. Contrary to Lake Sturgeon, that used multiple habitat types, Walleye used the tailrace for spawning, foraging, and overwintering, given their high residency rates throughout all months at this location. Activity for both species increased with water temperature and when residing in habitat types located farther upstream, but were minimally active during the winter season throughout the impounded reach. On average, Lake Sturgeon utilized 73% of the available depth while Walleye utilized 62% of the available depth across habitat types and months. Overall, the habitat located within the tailrace and below run-of-river facilities should be a conservation priority for both Lake Sturgeon and Walleye populations. There was persistent presence of Lake Sturgeon and Walleye throughout the spawning, foraging, and overwintering periods in the SSGS tailrace and within the first rkm downstream of the tailrace. The habitat proximal to run-of-river facilities generally encompasses small areas of the total potential habitat within impoundments, yet is important to both species studied here. The results provide information on the seasonal habitat use and biological responses to environmental cues for Lake Sturgeon and Walleye that will enhance management and ecological understanding for populations that are confined to impounded reaches.     

Effects of damming on the biological integrity of fish assemblages in the middle Lancang-Mekong River basin

The Lancang-Mekong River basin contains a diverse assemblage of freshwater fish species; however, their populations are threatened by current and planned dam construction along the river. Fish assemblages are sensitive indicators of environmental degradation and can be used to assess aquatic ecosystem health. This research compared the fish fauna at the Xiaowan hydropower dam located on the middle reaches of the Lancang-Mekong River at three time periods: in 2008 (before impoundment), 2010 (water storage) and 2011 (full operation). A modified fish index of biological integrity (modified F-IBI) was developed and it synthesized information on the taxonomic composition, trophic guilds, and tolerance levels of the fish and habitat diversity to quantitatively assess the condition of fish populations before and after damming. This index also was used to assess the longitudinal diversity of the fish fauna along the river channel and could assess the barrier effect associated with the dam. Jaccard's index of similarity was used as a feasible tool to assess fish diversity loss and biotic homogenization. The analysis clearly showed a homogenization of the fish communities after damming, and the reservoir impoundment region showed much more serious homogenization than the downstream region. The Xiaowan dam had an immediate and profound effect on the fish fauna in this region of the Lancang-Mekong River. A total of eight cascading dams are planned for development in this region, and, unless conservation mitigation efforts are considered, the results could be devastating on the native fish populations of middle reaches of the Lancang-Mekong River basin.     

Characteristics of the Cross-Sectional Vorticity of the Natural Spawning Grounds of Schizothorax prenanti and a Vague-Set Similarity Model for Ecological Restoration

Schizothorax prenanti is an endemic fish in the mountain rivers of southwestern China with unique protection value. To further explore the vortex motion of hydraulic habitats, which is closely related to the fish breeding process, the cross-sectional vorticity was used to evaluate the hydraulic conditions of the natural spawning habitat of S. prenanti. A coupled level-set and volume-of-fluid (CLSVOF) three-dimensional (3D) model was applied to simulate the hydraulic habitat of the Weimen reach, a typical natural spawning ground for S. prenanti in the upper Yangtze River. The model was used in conjunction with the Wilcoxon rank sum test to distinguish the distributions of vertical vorticity in spawning and non-spawning reaches. Statistical analysis revealed that the cross-sectional vorticity in spawning reaches was significantly greater than in non-spawning reaches, with likely biological significance in the spawning process. The range of cross-sectional mean values of vorticity was 0.17 s^-1–0.35 s^-1 in areas with concentrated fish sperm and eggs; the minimum value was 0.17 s^-1, and the majority of values were greater than 0.26 s^-1. Based on this study, a vague-set similarity model was used to assess the effectiveness of ecological restoration by evaluating the similarity of the cross-sectional vorticity of the natural spawning reach and rehabilitated spawning reach after implementing ecological restoration measures. The outcome might provide a theoretical basis for the recovery of damaged S. prenanti spawning grounds and act as an important complement for the assessment of recovery effectiveness and as a useful reference for the coordination of ecological water use with the demands of hydraulic and hydropower engineering.     

Environmental DNA quantification in a spatial and temporal context: a case study examining the removal of brook trout from a high alpine basin

Analysis of aquatic environmental DNA (eDNA) is a promising tool to determine species distribution, abundance, and biomass. Understanding how the amount of eDNA collected is affected by spatial and temporal processes needs to become better understood before eDNA quantification can be used in species management. In this study, we analyzed how the amount of eDNA changed across space and time in a high mountain basin where nonnative fish were being removed. We sampled from restoration (sites with fish removal activities; n?=?6) and control sites (sites with no fish removal activities where fish were present; n?=?3) and found the number and biomass of fish removed were related to the quantities of DNA collected and not related to site position within the drainage. Our results indicate that the amount of eDNA collected in an open system can provide an index of population size despite inherent complications of analyzing a spatially connected and temporally dynamic watershed. However, there are complications when applying these methods in species management: (1) small increases in eDNA density corresponded to large increases in trout density; (2) eDNA and traditional field techniques disproportionately target certain life stages, complicating comparisons between techniques; and (3) eDNA index values may need to be calibrated when sampling different species, life stages, environments, and habitats. We call for further research before this process can be used in a management context.     

Effects of pasture development on the ecological functions of riparian forests in Hokkaido in northern Japan

In the summer, the forest canopy lowers the water temperature, which is very important for anadromous fish, and its population density is significantly lower in grassland streams. Leaf litter and terrestrial invertebrates are the critical food resources for stream organisms. In a basin where the riparian forest is preserved, but other areas have been cut, the amount of leaf litter is almost equivalent to that in an intact natural basin. The annual input of terrestrial invertebrates falling into the forested reaches was 1.7 times greater than that in the grassland reaches, and fish biomass was significantly less in the grassland reaches. In-stream large woody debris creates storage sites for organic and inorganic matter and enhances habitat diversity for aquatic biota. However, the volume and number of large wood pieces decreased significantly with pasture development, because it clears the riparian forests and covers the riverbanks with grass. Fine sediment is a prominent by-product of agricultural development and adversely impacts periphyton productivity, the density and diversity of aquatic invertebrates, fish feeding, fish spawning and egg survival. We also examine the adequate width of a riparian buffer if it is to be able to satisfy its ecological functions.     

Habitat persistence for sedentary organisms in managed rivers: the case for the federally endangered dwarf wedgemussel (Alasmidonta heterodon) in the Delaware River

1. To manage the environmental flow requirements of sedentary taxa, such as mussels and aquatic insects with fixed retreats, we need a measure of habitat availability over a variety of flows (i.e. a measure of persistent habitat). Habitat suitability measures in current environmental flow assessments are measured on a ‘flow by flow’ basis and thus are not appropriate for these taxa. Here, we present a novel measure of persistent habitat suitability for the dwarf wedgemussel (Alasmidonta heterodon), listed as federally endangered in the U.S.A., in three reaches of the Delaware River. 2. We used a two‐dimensional hydrodynamic model to quantify suitable habitat over a range of flows based on modelled depth, velocity, Froude number, shear velocity and shear stress at three scales (individual mussel, mussel bed and reach). Baseline potentially persistent habitat was quantified as the sum of pixels that met all thresholds identified for these variables for flows ≥40 m³ s^?1, and we calculated the loss of persistently suitable habitat by sequentially summing suitable habitat estimates at lower flows. We estimated the proportion of mussel beds exposed at each flow and the amount of change in the size of the mussel bed for one reach. 3. For two reaches, mussel beds occupied areas with lower velocity, shear velocity, shear stress and Froude number than the reach average at all flows. In the third reach, this was true only at higher flows. Together, these results indicate that beds were possible refuge areas from the effects of these hydrological parameters. Two reaches showed an increase in the amount of exposed mussel beds with decreasing flow. 4. Baseline potentially persistent habitat was less than half the areal extent of potentially suitable habitat, and it decreased with decreasing flow. Actually identified beds and modelled persistent habitat showed good spatial overlap, but identified beds occupied only a portion of the total modelled persistent habitat, indicating either that additional suitable habitat is available or the need to improve habitat criteria. At one site, persistent beds (beds where mussels were routinely collected) were located at sites with stable substratum, whereas marginal beds (beds where mussels were infrequently collected or that were lost following a large flood event) were located in scoured areas. 5. Taken together, these model results support a multifaceted approach, which incorporates the effects of low and high flow stressors, to quantify habitat suitability for mussels and other sedentary taxa. Models of persistent habitat can provide a more holistic environmental flow assessment of rivers.