Warmwater Streams Research Articles

Morphodynamics of melting ice over turbulent warm water streams

We investigate the morphodynamics of an ice layer over a turbulent stream of warm water using numerical simulations. At low water speeds, characteristic streamwise undulations appear, which can be explained by the Reynolds analogy between heat and momentum transfer. As the water speed increases, these undulations combine with spanwise ripples of a much greater length scale. These ripples are generated by a melting mechanism controlled by the instability originating from the ice–water interactions, and, through a melting/freezing process, they evolve downstream with a migration velocity much slower than the turbulence characteristic velocity.

Фауна и сообщества донных беспозвоночных ручьёв и родников Айтуарской степи (Оренбургский государственный степной заповедник)

The benthic (invertebrate) community of streams and springs in the Aytuar steppe includes 49 taxon. Chironomids are the most diverse (11). Mayflies (10), caddisflies (7) and stoneflies (5) are rich in species. Among other invertebrates, non-chironomid dipterans (8), mollusks (3), oligochaetes (1), amphipods (1), alder flies (1), bugs (1) and beetles (1) were recorded. The specificity of the fauna is determined by the presence of the genetically Siberian species M. borealis. Its negative feature is the absence of such wide-spread European taxa as the caddisflies of the genera Beraea, Crunoecia, and Parachiona, as well as genetically Siberian elements, the mollusks Parasphaerium rectidens (Starobogatov et Streletzkaja, 1967), stoneflies Arcynopteryx compacta (McLachlan, 1872), and Nemoura arctica Esben-Petersen, 1910, may-flies Cinygma lyriformis (McDunnough, 1924) and Ephemerella aurivillii Bengtsson, 1908, caddisflies Asynarchus lapponicus Zetterstedt, 1840 and Apatania stigmatella (Zetterstedt, 1840), common in the northern regions of the Urals and Cis-Urals. Were identified groups of invertebrates that are characteristic of both spring-fed water bodies and elements of the benthic fauna of warm-water streams. Five types of zoobenthocenoses were identified in streams. The zoobenthocenosis of cobbled (boulder-pebble) substra-tum is the most typical. Its abundance is 7.19 thousand ind./m2 with a biomass of 17.75 g/m2. The second type is the sand-gravel and pebble zoobenthocenoses (20.28 thousand ind./m2 with a biomass of 27.48 g/m2). Zoobentocenoses of boulder substratum with moss fouling, sandy substratum and silts are less widespread. Two types of zoobenthocenoses are found in springs. A community with the abundance and biomass of 6.8 thousand ind./m2 and 10.88 g/m2 respectively develops on boulder-pebble substratum, and on sandy substratum with coarse CPOM a community with a moderate level of development (number 3.80 thousand ind./m2 with a biomass of 6.44 g/m2) is observed.

Seasonal changes in abundance and feeding ecology of an endemic, keystone predator following the introduction of large rainbow trout Oncorhynchus mykiss

Despite documented negative effects on aquatic ecosystems, management agencies commonly receive requests to stock non-native rainbow trout Oncorhynchus mykiss (Walbaum). We used a multinomial N-mixture model and a suite of diet analyses to evaluate effects of large (265–530 mm) rainbow trout on reach-scale abundance and feeding ecology of an important endemic, keystone species, Neosho bass Micropterus velox (Hubbs and Bailey). We evaluated potential changes by seasonally sampling multiple reaches of an Ozark Highlands stream before and after the introduction of 10,800 rainbow trout. Results suggest that rainbow trout altered the distribution of Neosho bass, as indicated by a negative relationship between rainbow trout density and Neosho bass abundance. Trophically, rainbow trout and Neosho bass <101 mm were equivalent, but rainbow trout diets significantly overlapped with larger Neosho bass. High rainbow trout abundance in the spring post-stocking period changed Neosho bass diets by altering predator–prey dynamics with crayfish. Controlling for fish size revealed Neosho bass consumed larger crayfish than rainbow trout, although rainbow trout and Neosho bass between 200 and 299 mm consumed equal-sized crayfish. Outcomes of rainbow trout stockings are likely density- and size-dependent, but caution is warranted for introductions in warmwater streams.

Seasonal Diet and Habitat Use of Large, Introduced Rainbow Trout in an Ozark Highland Stream

AbstractStocking of Rainbow TroutOncorhynchus mykisscommonly provides seasonal or mitigation fisheries; however, these fish are usually small and ecosystem effects are spatially or temporally limited. Yet agencies receive requests to stock Rainbow Trout in relatively natural settings (i.e., not tailwater or mitigation fisheries), where introductions may have greater ecosystem consequences. The size of introduced fish is an important factor in determining biotic interactions with native species; therefore, our objectives were to assess the seasonal feeding ecology and microhabitat use of large (265–530 mm TL) nonnative Emmerson strain Rainbow Trout in a relatively unaltered, groundwater‐influenced, warmwater stream of the Ozark Highlands. Rainbow Trout consumed a variety of prey; however, diets differed between cool (winter and spring) and warm (summer) seasons. Cool‐season Rainbow Trout exhibited a mixed feeding strategy, with individual specialization on crayfishes and fishes and generalist feeding on Ephemeroptera and Diptera, but Gastropoda were the dominant prey. Feeding strategy in the warm season switched to individual specialization on numerous prey types. Overall, larger prey resources were important components of Rainbow Trout diets. Piscivory was relatively high in both seasons, and crayfishes were one of the most important prey types across seasons. Selection of coarse substrates and deeper‐water microhabitats (&gt;0.95 m) was similar between seasons. Rainbow Trout selected the lowest‐velocity microhabitats available during the warm season and moderate velocities in the cool season. Rainbow Trout were five times more likely to be associated with cover in the warm season. Due to their higher temperature tolerance, Emmerson strain Rainbow Trout may persist in Ozark Highland streams, where they disrupt local food webs and occupy habitat otherwise selected by native fish, such as Neosho Smallmouth BassMicropterus dolomieu velox. If native species conservation is a priority for agencies, then caution regarding Rainbow Trout stockings may be warranted.

Successful Restoration of a Native Fish Assemblage in the Blue River, Arizona

AbstractTranslocation is one of the most commonly proposed management actions for securing and recovering native fish species. However, the success of native fish translocations has varied widely due to several limiting factors, including the presence of nonnative fishes. The Blue River Native Fish Restoration Project involved construction of a fish passage barrier, removal of nonnative fish, translocation of three native fish species (Spikedace Meda fulgida, Loach Minnow Rhinichthys cobitis, and Roundtail Chub Gila robusta), and monitoring to determine the success of these actions. After construction of a physical fish passage barrier, the three focal species were stocked several times upstream of the barrier. Nonnative fish were removed annually using multiple gear types, including spearfishing, backpack electrofishing, and trapping. Monitoring data demonstrated a significant shift in the fish assemblage from one with a substantial component of nonnative fishes to one that was exclusively native fishes. Persistence, reproduction, increased abundance, and dispersal were documented for all three focal species within the study area, meeting criteria for establishment success. All nonnative fishes, including the primary targets of removal efforts—Channel Catfish Ictalurus punctatus and Green Sunfish Lepomis cyanellus—were successfully suppressed, if not eradicated entirely, during the study period. Our results illustrate the importance of long‐term monitoring to track and successfully achieve native fish recovery goals. In addition, our results demonstrate that nonnative fish can be mechanically removed from warmwater streams if initial abundance is low, distribution is restricted, and fish passage barriers are in place. Results from this study may be informative for managers hoping to improve the conservation status of warmwater stream fishes through creation of a fish passage barrier, nonnative species removal, and native fish translocation efforts.

Survival and Movement Patterns of Rainbow Trout Stocked in a Groundwater‐Influenced Warmwater Stream

AbstractStocking Rainbow Trout Oncorhynchus mykiss to create additional angling opportunities is common; however, the spatial and temporal dynamics of such stocking practices are unclear in groundwater‐influenced, warmwater streams. Our objectives were to determine Rainbow Trout dispersal from a stocking location on Spavinaw Creek, Oklahoma and to quantify apparent survival of two cohorts of Rainbow Trout stocked in November 2018 and February 2019. Rainbow Trout were PIT‐tagged prior to autumn (N = 495) and winter (N = 605) stocking and located poststocking using both an active floating array and two passive fixed arrays. We actively tracked a 6‐km extent every 2–3 weeks poststocking and found that PIT‐tagged Rainbow Trout dispersal ranged from 0 to 4 km with ~90% of detected tagged fish remaining within 1 km of the stocking location. Directional movement by stocked Rainbow Trout was evident with upstream movements related to increases in daily water discharge and downstream movements related to decreases in daily discharge. Estimated apparent weekly survival of Rainbow Trout was lowest during the first 2 weeks poststocking (91% and 75% for autumn and spring cohorts, respectively). Apparent weekly survival rates for both autumn and spring stocked fish increased through winter and spring when maximum water temperatures were below 25℃, reaching survival rates of 99% by the end of spring. Rainbow Trout persisted in Spavinaw Creek throughout the summer; however, the weekly apparent survival rate declined for both cohorts (93%) when maximum daily water temperatures exceeded 25°C. Our results can be used to guide stocking decisions in similar warmwater streams and suggest that Rainbow Trout persist through spring and summer poststocking under the conditions encountered during our study.

Fish communities and associated habitat variables in the upper Subansiri River of Arunachal Pradesh, eastern Himalaya, India

Ecological information on the rivers of eastern Himalaya, specifically the state of Arunachal Pradesh is not studied well. The present study describes fish assemblage patterns and deriving relationships between local habitat variables in the upper reaches of Subansiri River, Arunachal Pradesh. This study was carried out during October to November 2014 and February to March 2015. A total of 26 fish species belonging to eight families were recorded, in which eight species are endemic to the eastern Himalayan region. Fish species richness varied from two to 18 species in the upper reaches of Subansiri River and high species diversity was recorded in Sigin Stream (H’=2.76). Based on the seven habitat variables (water velocity, depth, channel width, percentage of substrate composition, percentage of riparian vegetation, altitude, and water temperature) then streams were categorized into lower-order and higher-order streams using principal component analysis (PCA). The site-wise fish abundance data along with habitat variable information was then subjected to the canonical correspondence analysis (CCA) for testing the association of habitat variables on fish abundance. The CCA results revealed that the abundance of large-size barbs, Neolissochilus hexagonolepis, N. nigrovittatus, Schizothorax progastus, and S. richardsonii were strongly associated with high altitude, water velocity, rich dissolved oxygen, and good riparian vegetation. On the other hand, Channa gachua, Botia rostrata, Danio rerio, Devario aequipinnatus, and Garra nasuta showed strong association with warm water streams with more conductivity.

The Influence of Groundwater on the Population Size and Total Length of Warmwater Stream Fishes

Groundwater influences stream environments in numerous ways including structuring biotic assemblages. However, associations between groundwater influence and warmwater fish assemblages are under-studied. We examined relationships between groundwater contribution, population size, and total length (TL) for 5 warmwater fishes at 32 stream reaches in the Ozark Highlands ecoregion. When we controlled for distance from an impoundment, population size and TL were significantly related to groundwater influence for all 5 species. Sunfishes were significantly less abundant in reaches with high levels of groundwater contribution (HGC reaches), whereas Ambloplites rupestris (Rock Bass) and Nocomis asper (Redspot Chub) TLs were significantly greater at HGC reaches. Reach-scale groundwater contribution explained nearly 4 times more unexplained variation among fish densities than did TL. Our study provides insight into the structuring role of groundwater on warmwater fish populations.

Large-Eddy Simulation of turbulent thermal flow mixing in a vertical T-Junction configuration

Turbulent mixing of warm and cold water streams within a vertical T-junction configuration of a nuclear power plant piping system causes near-wall temperature fluctuations which may lead to High-Cycle Thermal Fatigue (HCTF) failure of the wall material. To predict frequency and amplitude of such temperature fluctuations accurately the method of Large-Eddy Simulation (LES) in the numerical simulation code OpenFOAM is used. As an experimental test case, the turbulent mixing experiment of Kamide et al. [1], where a vertical branch pipe with a cold water stream is connected from below to a horizontal main pipe with a warm water stream to form a vertical T-junction configuration. From the various observed flow patterns, the temperature and velocity data of the ‘wall jet’ are chosen as a reference because it is known to have the highest potential for thermal fatigue. Incomplete mixing and an instability associated with large turbulent structures near the junction region lead to significant temperature fluctuations close to the wall before a vertical thermal stratification further downstream stabilizes the flow. The highest near-wall fluctuation amplitudes are 26% of the temperature difference between the streams. A spectral peak occurs at a Strouhal number of 0.2. The results of the simulations demonstrate, that the mean velocity and temperature profiles of the experiments are well captured, whereas the root-mean-square (RMS) temperature fluctuations deviate from the measurements in some cases, in particular when coarse grids are used. In order to find a lower limit for the required spatial resolution three different numerical meshes with a variable number of cells up to 28 × 106 are investigated. The results demonstrate that with a sufficient mesh resolution the velocity and temperature distributions as well as the spectral peak can be simulated with good agreement to the experimental data.

Coldwater Periods in Warmwater Streams: Microhabitat Shifts from Autumn to Winter by Smallmouth Bass

AbstractSeasonal and life stage variation in microhabitat use is an important driver of fish survival and bioenergetics, but knowledge of microhabitat selection during colder periods is generally lacking in warmwater streams. Our objective was to examine changes in microhabitat selection by age‐0 (TL ≤ 85 mm) and age‐1+ (TL &gt; 85 mm) Smallmouth Bass Micropterus dolomieu from autumn to winter in streams of the southwest Ozark Highlands ecoregion. We examined microhabitat selection (depth, velocity, substrate, cover, and temperature) during autumn 2017 (Spavinaw Creek) and winter 2018 (Spavinaw and Spring creeks). During autumn and winter, age‐0 fish selected intermediate depths of approximately 1 m, whereas age‐1+ fish selected the deepest available habitat. Water depth selection was similar across seasons for both life stages. Both age‐0 and age‐1+ bass selected areas of zero velocity, increasing substrate size, instream cover, and warmwater patches in autumn. Velocity selection differed between autumn and winter with both life stages showing stronger selection of low velocity patches (0.1–0.3 m/s) during winter. Both life stages shifted to having no substrate selection during winter. Age‐1+ bass were more likely than age‐0 bass to use cover during autumn, but this relationship shifted in winter to the age‐0 cohort increasing their selection of cover and the age‐1+ cohort decreasing their selection. Both age‐0 and age‐1+ bass selected relatively warmer habitats during autumn, but not winter. Collectively, our results highlight both seasonal and life stage variation in Smallmouth Bass microhabitat selection. As our understanding of habitat selection across seasons develops, the management of Smallmouth Bass will undoubtedly improve. Changing environmental conditions over time may influence available habitat as well as the timing of seasonal shifts across a range of spatial and temporal scales, including microhabitat patches.

Efficiency of Sampling Sunfishes Using Snorkeling in Clear, Warm-Water Streams of the South-Central United States

AbstractThe continued evaluation of fish-sampling gears and methods is essential to identify their applicability across environmental conditions and among species. Although limited by visibility, snorkeling has potential advantages relative to other fish-sampling gears in wadeable streams (e.g., minimally intrusive, cost effective, and appropriate in deeper areas). Clear water is common to warm-water streams; however, the use of snorkeling for monitoring stream-fish populations has largely focused on cold-water systems. To assess relative snorkeling efficiency in warm-water streams, we compared standardized single-pass snorkel counts to tow-barge electrofishing abundance estimates for six sunfishes (Centrarchidae) in the Ozark Highlands ecoregion of northwest Oklahoma and southwest Missouri under relatively similar environmental conditions (i.e., clear water, cobble substrates, low-flow conditions). Snorkeling efficiency was variable among sunfishes and consistently low for species with cryptic traits and habitat use. We also did not detect cryptic sunfishes (i.e., a single individual was not encountered) using snorkeling at multiple stream reaches where estimated abundance was &amp;gt; 50 within a 0.5- to 1.0-km stream reach. Our findings indicate that snorkeling has applications for monitoring sunfish populations and assemblages when using an abundance estimator or accounting for imperfect detection; however, it is inappropriate for estimating population size of cryptic sunfishes. We encourage continued research into the applicability of snorkeling to estimate warm-water stream fish abundance.

Round goby and zebra mussel interactions with darters in a warm-water stream community in southern Michigan, USA

The non-indigenous round goby (Neogobius melanostomus) entered the Flint River, Michigan, USA around 1996 while zebra mussels (Dreissena polymorpha) invaded in late 1998. We wanted to identify if there were round goby or darter (Etheostoma/Percina spp.) diet or density alterations by comparing 1998 data with our 2002 data after mussel colonization. Chironomids dominated the round goby’s pre-zebra mussel diet in August 1998 (89% by number), followed by hydropsychids (10%). After zebra mussels arrived, diets diversified; chironomids declined to 52%, hydropsychids stayed the same, gastropods were more prominent (22%) and 4% were zebra mussels. Data from a site upriver (with no round gobies or zebra mussels) showed darters consumed mostly chironomids (49%), mayflies (11%) and hydropsychids (9%), suggesting reliance on chironomid prey and other interactions compromised the ability of darters to coexist with round gobies downstream, since only one of three species present during 1998 was collected in 2002. Benthic assemblages on rocks changed dramatically (R-values =0.95) from 1998 to 2002. Blackside darter (Percina maculata) density in the presence of round gobies increased eightfold compared with 1998. We hypothesized zebra mussels fostered the growth of macrophytes, resulting in odonates composing 42% by volume of blackside darter diets in 2002 compared with 10% in 1998. Diet overlaps between small and large round gobies and blackside darters were high (Schoener Index =0.55–0.59, R-values =0.11–0.24), suggesting potential negative competitive interactions. Zebra mussel-mediated ecosystem changes may have decreased interspecific competition for food with blackside darters, allowing coexistence with round gobies. Native darters with varied diets feeding in mid-water, are most likely to coexist with round gobies, especially where dreissenids potentially mediate competitive interactions.

Calibration of the biological condition gradient in Minnesota streams: a quantitative expert-based decision system

AbstractThe Biological Condition Gradient (BCG) is a conceptual model that describes changes in aquatic communities with increasing levels of anthropogenic stress. The gradient represented by the BCG has been divided into 6 levels of condition that biologists consider readily discernible in most areas of North America. We developed quantitative BCG models for 7 warm-water stream types in Minnesota for both fish and macroinvertebrates. Panels of aquatic biologists calibrated the general BCG model to Minnesota streams by assigning test samples (271 macroinvertebrate and 288 fish samples) to BCG Levels 1 to 6. From the panelists’ descriptions of their criteria for assigning sites to levels, a set of quantitative operational rules was developed for performing the same task. We developed a decision model based on fuzzy-set theory to account for discontinuities and to identify when BCG assignments might be intermediate between adjacent levels. This model captures the consensus professional judgment of the panel...

Fish assemblage production estimates in Appalachian streams across a latitudinal and temperature gradient

AbstractProduction of biomass is central to the ecology and sustainability of fish assemblages. The goal of this study was to empirically estimate and compare fish assemblage production, production‐to‐biomass (P/B) ratios and species composition for 25 second‐ to third‐order streams spanning the Appalachian Mountains (from Vermont to North Carolina) that vary in their temperature regimes. Fish assemblage production estimates ranged from 0.15 to 6.79 g m−2 year−1, and P/B ratios ranged from 0.20 to 1.07. There were no significant differences in mean assemblage production across northern cold‐water, southern cold‐water and southern cool‐water streams (p = .35). Two warm‐water streams, not included in these comparisons, had the highest mean production and biomass values. Mean assemblage P/B was significantly higher in northern cold‐water streams relative to southern cold‐water and cool‐water streams (p = .01). Species evenness in production declined with stream temperature and differed significantly across the lower latitude cold‐water, cool‐water and warm‐water streams and the higher latitude (i.e. more northern) cold‐water streams. Our fish assemblage production estimates and P/B ratios were both lower and higher compared to previously published estimates for similar stream habitats. This study provides empirical fish assemblage production estimates to inform future research on southern Appalachian streams and on the potential impacts of varying temperature regimes on cold‐water, cool‐water and warm‐water fish production in the coming decades as climate change continues to threaten fish assemblages.

First Reproduction by Stocked Bonytail in the Upper Colorado River Basin

AbstractBonytail Gila elegans, a large‐bodied cyprinid that is endemic to the Colorado River basin of the American Southwest, was historically widespread and abundant in large warmwater streams but is now critically endangered. To increase recovery prospects, over 500,000 Bonytails have been stocked in the upper Colorado River basin since 2000, but adult survival has been low and reproduction has not been detected. We provide the first documented evidence of successful reproduction by stocked Bonytails in the upper Colorado River basin. Adult Bonytails were stocked in the Green River and accessed Stewart Lake and Johnson Bottom (managed floodplain wetlands in the middle Green River, Utah) during high flows in May 2015 (Stewart Lake only) and 2016. Draining of Stewart Lake in September 2015 revealed 19 age‐0 individuals of Gila sp. (37–64 mm TL) among over 405,000 fish. Four preserved specimens (41–48 mm TL) were verified as Bonytails by using morphological and molecular techniques. Otolith daily increment analysis confirmed reproduction by Bonytails in Stewart Lake. Bonytail reproduction was also noted during 2016 in Stewart Lake (probable) and Johnson Bottom. Young Bonytails survived despite the presence of abundant nonnative fish predators. Use of floodplain wetlands for reproduction may enhance the recovery of critically endangered Bonytail in the upper Colorado River basin.Received September 1, 2016; accepted January 2, 2017 Published online March 15, 2017

Local disruption or global condition? El Niño as weather and as climate phenomenon

El Niño denotes a periodical warm water stream in the Pacific Ocean. But who knew about this phenomenon, where and how? El Niño ‘the boy’ emerged as a fabric of local experiences and stories of extreme weather events: tropical winter storms, floods, droughts and famines in the coastal states of South America, Indonesia and Southeast Asia. In the Northern Hemisphere this rich cultural history went largely unnoticed. Only in the 1980s and 1990s did El Niño acquire global recognition as an effect of the oceanic and atmospheric currents in the tropical Pacific region. As the oceans moved from a marginal to a central position in the discourse on the Earth's climate cycles, ENSO – the ‘El Niño Southern Oscillation’ – became part of a global climate pattern. This paper explores El Niño ‘the boy’ and ENSO El Niño Southern Oscillation as juxtaposed and superposed environmental perceptions. While El Niño the boy conveyed horrific weather experiences on the human scale, ENSO became known through terrific scientific views of Earth from space. Earth observation by remote sensing satellites collected vast arrays of local measurements into new data fabrics. Studying the case of the US–French orbital satellite mission of TOPEX/Poseidon, this paper examines both the imagery from satellite data and the forecasting efforts preceding the strong El Niño winter of 1997–8. From the data and image sets of remote sensing satellites, recurring local disruptions emerged as a periodic global climate condition. Local experiences of El Niño and scientific perceptions of ENSO as a global climate cycle did not translate easily into each other. The paper discusses some of the epistemological tensions across spatial scales. While El Niño's shift from exception to regularity fed into the framing of ‘climate change’ as a global disaster, the emerging ENSO regime obscured disaster locally.

Temperature-dependent performance as a driver of warm-water fish species replacement along the river continuum

Replacement of fish species by their congeners along gradients of stream size is common in warm-water streams, but the causative environmental factors driving this turnover are not fully understood. We used laboratory experiments to test for differences in temperature-dependent egg hatch success and age-0 food ration size for three congeneric cyprinids that differ in abundance along temperature–stream size gradients. Headwater species (Pimephales promelas and Pimephales notatus) had lower thermal optima and narrower thermal breadths for hatch success compared with a river mainstem species (Pimephales vigilax). Temperature sensitivity of ration size was lowest for P. promelas, intermediate for P. notatus, and highest for P. vigilax. Using an empirical stream temperature model, we predicted water temperatures and projected hatch success and ration size for 7974 stream segments in Kansas, USA. Projected hatch success from May to July and ration size from July to September generally matched abundance–stream size patterns, suggesting that increasing temperature along the river continuum may drive replacements among Pimephales species. Our findings combined with evaluations of timing and duration of spawning seasons will improve mechanistic understanding of species replacements along the river continuum.

Effects of forest management on physical habitats and fish assemblages in Iberian eucalypt streams

In Portugal, more than 150,000ha of eucalypt plantations are managed under best management practices (BMP), in compliance with international certification systems. Some of these forestry areas extend to streams, and the riparian areas are thus protected from productive land uses. However, many other eucalypt plantations present riparian zones that are not managed under BMP and are often occupied by agricultural uses. To test the effects of forest management on physical habitats and fish assemblages in Iberian eucalypt streams, we selected three different stream reach types: (1) reaches in catchments dominated by native vegetation associations, and presenting semi-natural riparian zones (reference-REF); (2) reaches surrounded by certified eucalypt plantations (i.e., managed under BMP), and consequently, presenting protected riparian buffer zones (PRZ); and (3) reaches surrounded by eucalypt plantations (dominant) and some oak forests, and presenting disturbed riparian zones with agricultural land use (DRZ). All sites represented small, low-gradient, warmwater streams in Central Portugal (Tagus basin), and their upstream land cover was dominated by natural/semi-natural uses. PRZ sites were abiotically similar to REF sites, although PRZ sites generally presented lower potential cover for fish and tended to support a riparian vegetation that was a little more fragmented. PRZ sites supported fish assemblages that were similar to those in reference reaches, although at the functional level we found a higher abundance of native invertivores in REF sites. DRZ reaches, on the other hand, differed substantially from the other two groups. DRZ sites presented disturbed riparian vegetation (removal or substitution of native trees by exotic and/or non-woody species), eroded and modified channels, and a degradation of stream habitats (lack of riffle–poll complexes, higher silt contents, and lower potential cover for fish). The fish assemblages were also quite different, with a higher abundance of alien specimens (mainly Gobio lozanoi) and generalist spawners, and a lower proportion of native invertivores and lithophils. Riffles and morphological alteration explained the greatest proportion of variance in species composition. Our study showed that protecting stream riparian zones by implementing BMP may mitigate the effects of eucalypt forestry on Iberian fish assemblages. However, given that there are a few differences in physical condition and biological integrity between streams associated with certified plantations and reference streams we suggest additional riparian management measures in the certified areas, such as restoration of the native vegetation, removal of alien plants, and improvement of the stream habitat.

Effectiveness of Backpack Electrofishing for Removal of Non-Native Fishes from a Small Warm-Water Stream

Abstract Electrofishing is commonly used when renovating small streams to remove nuisance fishes but the likelihood of complete eradication of unwanted species, particularly warm-water fishes, is unknown. In October of 2008, we electrofished Bonita Creek, a small stream with base flows (<0.56 m3/s) in southern Arizona, and then treated the stream with rotenone to kill all of the remaining fish and quantify the effectiveness of single and multiple-pass electro fishing. Six, 100-m transects were electro fished on three consecutive days followed by a single treatment with rotenone. Fish caught using electrofishing were identified, counted and removed from each transect daily and then compared to numbers of dead fish collected during the subsequent rotenone application. Electrofishing effectiveness was highly variable among transects. Single-pass electrofishing caught an average of 23% (95% CI=5 to 40%) of the fish present, and three-pass electrofishing on consecutive days caught on average 55% (95% CI=28 to ...

Land use and surface water withdrawal effects on fish and macroinvertebrate assemblages in the Susquehanna River basin, USA

Water withdrawals in the Susquehanna River basin, USA, are increasing due to burgeoning shale gas extraction activities. In order to determine if flow alteration resulting from shale gas industry surface water withdrawals impacts fish and macroinvertebrate assemblages in lotic habitats, data were collected upstream and downstream of 12 withdrawal and three reference sites in headwater, cold water, and large warm water streams. Watershed size ranged from 4 to 517 km2 and average daily withdrawals ranged from 0.05 to 1.4 million liters. Analysis of withdrawal data indicated that approved withdrawals far exceeded actual withdrawals across all stream types. The largest withdrawals relative to stream size were from headwater streams, where on average 6.8% of average daily flow was withdrawn daily. Fish and macroinvertebrate assemblage similarity at study sites depended largely on stream sampled, rather than position upstream or downstream of withdrawals. Regression techniques were employed to determine if catchment-level variables or withdrawal metrics best described variation in fish and macroinvertebrate metrics shown to be sensitive to flow alteration. The catchment-level variables were responsible for the majority of observed variation in fish metrics. Macroinvertebrate models performed poorly, indicating that the stream sampled or variables not included in the analyses were responsible for the majority of variation. Overall, evidence suggests impacts of shale gas withdrawals within the Susquehanna basin are limited at the present state of flow alteration. Potential reasons include protective measures such as pass-by flow restrictions, which require withdrawals to cease when flows drop below a predetermined low flow threshold, maximum instantaneous and daily withdrawal limits, and recent initiation of withdrawals (1–3 years of operation).