Effects of Road Crossings on Habitat Connectivity for Stream‐Resident Fish

Road crossings can act as barriers to the movement of stream fishes, resulting in habitat fragmentation, reduced population resilience to environmental disturbance and higher risks of extinction. Strategic barrier removal has the potential to improve connectivity in stream networks, but managers lack a consistent framework for determining which projects will most benefit target species. The objective of this study is to develop a method for identifying and prioritizing action on road crossings in order to restore stream network connectivity. We demonstrate the method using a case study from the Pine‐Popple watershed in Wisconsin. First, we propose a new metric for quantifying stream connectivity status for stream‐resident fish. The metric quantifies the individual and cumulative effects of barriers on reach and watershed level connectivity, while accounting for natural barriers, distance‐based dispersal limitations and variation in habitat type and quality. We conducted a comprehensive field survey of road crossings in the watershed to identify barriers and estimate replacement costs. Of the 190 surveyed road crossings, 74% were determined to be barriers to the movement of at least one species or life stage of fish, primarily due to high water velocity, low water depth or outlet drops. The results of the barrier removal prioritization show that initial projects targeted for mitigation create much greater improvements in connectivity per unit cost than later projects. Benefit–cost curves from this type of analysis can be used to evaluate potential projects within and among watersheds and minimize overall expenditures for specified restoration targets. Copyright © 2014 John Wiley & Sons, Ltd.     

Changes in fish communities following recolonization of the Cedar River,WA, USA by Pacific salmon after 103 years of local extirpation

Migration barriers are a major reason for species loss and population decline of freshwater organisms. Significant efforts have been made to remove or provide passage around these barriers; however, our understanding of the ecological effects of these efforts is minimal. Installation of a fish passage facility at the Landsburg Dam, WA, USA provided migratory fish access to habitat from which they had been excluded for over 100 years. Relying on voluntary recruitment, we examined the effectiveness of this facility in restoring coho (Oncorhynchus kisutch) salmon populations above the diversion, and whether reintroduction of native anadromous species affected the distribution and abundance of resident trout (O. mykiss and O. clarki). Before the ladder, late summer total salmonid (trout only) density increased with distance from the dam. This pattern was reversed after the ladder was opened, as total salmonid density (salmon + trout) approximately doubled in the three reaches closest to the dam. These changes were primarily due to the addition of coho, but small trout density also increased in lower reaches and decreased in upper reaches. A nearby source population, dispersal by adults and juveniles, low density of resident trout and high quality habitat above the barrier likely promoted rapid colonization of targeted species. Our results suggest that barrier removal creates an opportunity for migratory species to re‐establish populations leading to range expansion and potentially to increased population size. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of a high‐head dam as a dispersal barrier to fish community structure of the Upper Mississippi River

In river systems, high‐head dams may increase the distance‐decay of fish community similarity by creating nearly impermeable dispersal barriers to certain species from upstream reaches. Substantial evidence suggests that migratory species are impacted by dams, and most previous studies in stream/river networks have focused on small streams and headwaters. Here, we assess whether a high‐head dam (Lock and Dam 19; LD 19) on a large river, the Upper Mississippi River (UMR), substantially alters fish community structure relative to variability expected to occur independent of the dam's effect as a fish dispersal barrier. Using fish catch per unit effort data, we modelled the distance‐decay function for the UMR fish community and then estimated the similarity that would be expected to occur across LD19 and compared it with measured similarity. Measured similarity in the fish community above and below LD19 was close to the expected value based on the distance‐decay function, suggesting LD19 does not create an abrupt transition in the fish community. Although some migratory fish species no longer occur above LD19 (e.g., skipjack herring, Alosa chrysochloris), these species do not occur in high abundance below the dam and so do not drive variation in fish community structure. Instead, much of the variation in species structure is driven by the loss/gain of species across the latitudinal gradient. Lock and Dam 19 does not appear to be a clear transition point in the river's fish community, although it may function as a meaningful barrier for particular species (e.g., invasive species) and warrant future attention from a management perspective.     

USING A NON‐PHYSICAL BEHAVIOURAL BARRIER TO ALTER MIGRATION ROUTING OF JUVENILE CHINOOK SALMON IN THE SACRAMENTO–SAN JOAQUIN RIVER DELTA

Anthropogenic alterations to river systems, such as irrigation and hydroelectric development, can negatively affect fish populations by reducing survival when fish are routed through potentially dangerous locations. Non‐physical barriers using behavioural stimuli are one means of guiding fish away from such locations without obstructing water flow. In the Sacramento–San Joaquin River Delta, we evaluated a bio‐acoustic fish fence (BAFF) composed of strobe lights, sound and a bubble curtain, which was intended to divert juvenile Chinook salmon (Oncorhynchus tshawytscha) away from Georgiana Slough, a low‐survival migration route that branches off the Sacramento River. To quantify fish response to the BAFF, we estimated individual entrainment probabilities from two‐dimensional movement paths of juvenile salmon implanted with acoustic transmitters. Overall, 7.7% of the fish were entrained into Georgiana Slough when the BAFF was on, and 22.3% were entrained when the BAFF was off, but a number of other factors influenced the performance of the BAFF. The effectiveness of the BAFF declined with increasing river discharge, likely because increased water velocities reduced the ability of fish to avoid being swept across the BAFF into Georgiana Slough. The BAFF reduced entrainment probability by up to 40 percentage points near the critical streakline, which defined the streamwise division of flow vectors entering each channel. However, the effect of the BAFF declined moving in either direction away from the critical streakline. Our study shows how fish behaviour and the environment interacted to influence the performance of a non‐physical behavioural barrier in an applied setting. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.     

Hydropower Development,Riverine Connectivity,and Non‐sport Fish Species: criteria for Hydraulic Design of Fishways

Hydropower barriers are among the most conspicuous anthropogenic alterations to natural riverine connectivity, resulting in species‐specific effects linked to dispersal abilities, especially swimming performance. They may present a particular problem for small‐bodied ‘non‐sport fish’, such as those that characterize the freshwater communities of temperate regions in the Southern Hemisphere. Recent studies have suggested that nature‐like fishways could ensure passage of diverse fish assemblages through hydropower barriers. Through experiments performed in a swim tunnel, we present, for the first time, fishway design criteria for two non‐sport species endemic to Chile, a country experiencing rapid hydropower development. In`cremental velocity tests showed that Cheirodon galusdae and juveniles of Basilichthys microlepidotus were capable of very similar standardized critical swimming speeds of 69.7 and 69.6 cm s^?1, respectively. When expressed in units of body lengths, C. galusdae was capable of very high critical speeds of 16.2 bl s^?1, whereas for B. microlepidotus, this was 7.6 bl s^?1. However, fixed velocity tests revealed that the swimming endurance of the latter species was slightly higher. Dimensionless analysis showed a clear relationship between fatigue time and fish Froude number, similar to that already described for subcarangiforms. Based on these results, we present fishway design curves indicating a transition from sustained to prolonged swimming at a fishway length of 15 m. Our results show that the swimming capacity of these species is well‐suited to the mean flow velocity field described for nature‐like fishways. However, more work is required to understand the effects of turbulence on the passage of non‐sport species. Copyright © 2016 John Wiley & Sons, Ltd.     

River fragmentation in the northern Sandomierz Basin (SE Poland)

River fragmentation is a process highly detrimental for fish survival by impeding their migrations. Although fragmentation by big dams has been studied, there is still a big deficiency of data related to small barriers. This study was designed as a detailed, local-scale analysis of several chosen river stretches in the Sandomierz Basin, Poland. It aimed to: (1) map all natural and artificial barriers in the study area, (2) assess the impacts of these barriers on fish migration, (3) compare findings to existing databases, and (4) make recommendations for improved barrier management. Ten lowland rivers covering a total 424 km length were surveyed by river walkovers and kayak surveys, with all the barriers mapped and all the artificial structures assessed for fish migration using the ICE protocol protocol for ecological continuity. There were 67 beaver dams and 89 artificial barriers recorded, with only 24% of the latter being included in national databases. The average artificial barrier density in all the surveyed rivers was 0.2 barriers/km and varied from 0.75 barriers/km in first order streams to 0.01 barriers/km in sixth order river. The findings revealed that 18% of the barriers were passable for all fish species, with 35% totally impassable. The analysis of specific barrier parameters indicated that water depth at the barrier had a greater influence on fish passability than the barrier height. Several barriers were proposed for removal to specifically improve the potential for fish migration.     

Habitat fragmentation has interactive effects on the population genetic diversity and individual behaviour of a freshwater salmonid fish

Sufficient genetic diversity can aid populations to persist in dynamic and fragmented environments. Understanding which mechanisms regulate genetic diversity of riverine fish can therefore advance current conservation strategies. The aim of this study was to investigate how habitat fragmentation interacted with population genetic diversity and individual behaviour of freshwater fish in large river systems. We studied a population of the long‐distance migratory, iteroparous freshwater salmonid European grayling (Thymallus thymallus) in south‐eastern Norway. Genotyping (n = 527) and radio‐tracking (n = 54) of adult fish throughout a 169‐km river section revealed three major migration barriers limiting gene flow and depleting genetic diversity upstream. Individuals from upstream areas that had dispersed downstream of barriers showed different movement behaviour than local genotypes. No natal philopatry was found in a large unfragmented river section, in contrast to strong fidelity to spawning tributaries known for individuals overwintering in lakes. We conclude that (a) upstream sub‐populations in fragmented rivers show less genetic variation, making it less likely for them to adapt to environmental changes; (b) fish with distinct genotypes in the same habitat can differ in their behaviour; (c) spawning site selection (natal philopatry) can differ between fish of the same species living in different habitats. Together this implies that habitat loss and fragmentation may differently affect individual fish of the same species if they live in different types or sections of habitat. Studying behaviour and genetic diversity of fish can unravel their complex ecology and help minimize human impact.     

Not just a migration problem: Metapopulations,habitat shifts,and gene flow are also important for fishway science and management

Worldwide, fishways are increasingly criticized for failing to meet conservation goals. We argue that this is largely due to the dominance of diadromous species of the Northern Hemisphere (e.g., Salmonidae) in the research that underpins the concepts and methods of fishway science and management. With highly diverse life histories, swimming abilities and spatial ecologies, most freshwater fish species do not conform to the stereotype imposed by this framework. This is leading to a global proliferation of fishways that are often unsuitable for native species. The vast majority of fish populations do not undertake extensive migrations between clearly separated critical habitats, yet the movement of individuals and the genetic information they carry is critically important for population viability. We briefly review some of the latest advances in spatial ecological modelling for dendritic networks to better define what it means to achieve effective fish passage at a barrier. Through a combination of critical habitat assessment and the modelling of metapopulations, climate change‐driven habitat shifts, and adaptive gene flow, we recommend a conceptual and methodological framework for fishway target‐setting and monitoring suitable for a wide range of species. In the process, we raise a number of issues that should contribute to the ongoing debate about fish passage research and the design and monitoring of fishways.     

The Effects of DAM Removal on River Colonization by Sea Lamprey Petromyzon Marinus

Habitat fragmentation is an important cause of biodiversity loss in freshwater systems, as worldwide rivers have been fragmented by dams and other hydraulic structures. To restore freshwater fish populations, some barriers have been removed, but the long‐term ecological effects of this removal have been rarely quantified. In the present study, we quantified the effects of barrier removal on river colonization by anadromous sea lamprey (Petromyzon marinus) by analyzing the spatial distribution and nest density in a small coastal river (France) from 1994 to 2011. Our results demonstrated the benefit of dam removal within few years after restoration. Indeed, the spatial distribution of nests shifted significantly upstream and was more uniform throughout the river after removal. Our results also suggest that the spatial patterns of habitat colonization were affected by the density of nests, river flow and connectivity. Finally, although the number of nests was significantly higher after removal, it was not possible to clearly identify the contribution of intrinsic versus external factors involved in this pattern. Further investigations are therefore needed to quantify the potential subsequent effects on juvenile recruitment and the overall population dynamics. Copyright © 2014 John Wiley & Sons, Ltd.     

GUIDING OUT‐MIGRATING JUVENILE SEA LAMPREY (PETROMYZON MARINUS) WITH PULSED DIRECT CURRENT

Non‐physical stimuli can deter or guide fish without affecting water flow or navigation and therefore have been investigated to improve fish passage at anthropogenic barriers and to control movement of invasive fish. Upstream fish migration can be blocked or guided without physical structure by electrifying the water, but directional downstream fish guidance with electricity has received little attention. We tested two non‐uniform pulsed direct current electric systems, each having different electrode orientations (vertical versus horizontal), to determine their ability to guide out‐migrating juvenile sea lamprey (Petromyzon marinus) and rainbow trout (Oncorhynchus mykiss). Both systems guided significantly more juvenile sea lamprey to a specific location in our experimental raceway when activated than when deactivated, but guidance efficiency decreased at the highest water velocities tested. At the electric field setting that effectively guided sea lamprey, rainbow trout were guided by the vertical electrode system, but most were blocked by the horizontal electrode system. Additional research should characterize the response of other species to non‐uniform fields of pulsed DC and develop electrode configurations that guide fish over a range of water velocity. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Impoverishment of YOY‐fish assemblages by intense commercial navigation in a large Lowland river

Navigation‐induced physical forces have been suggested to modify the structure of riverine fish assemblages by impeding especially the recruitment of littoral bound species. To investigate the effect of vessel frequency on fish, we compared the composition and seasonal succession of young‐of‐the‐year (YOY) fish assemblages in three similarly degraded river reaches differing in average vessel passages (2, 6 and 41 per day). Fish were caught by electrofishing biweekly between May and September. Multivariate tests were used to analyse differences between YOY‐fish assemblages and hurdle regression models applied to determine abiotic factors predicting fish occurrence and abundance. Roach (Rutilus rutilus) and perch (Perca fluviatilis) densities were compared. Roach larvae remain in the littoral zone while perch larvae shift to the pelagic zone immediately after hatch. YOY‐fish assemblage structure substantially changed along the traffic intensity gradient. In the high traffic intensity reach, species number and total fish density were markedly reduced compared to the other reaches. Roach densities were lowest in the high traffic intensity reach whereas perch densities did not decline along the gradient. Hurdle regressions confirmed a stronger effect of commercial navigation traffic intensity on roach than on perch. The total zooplankton biomass was highest in the high traffic intensity reach. Our results provide empirical evidence that intensive commercial navigation impoverishes fish assemblages in width‐restricted waterways. They underlined that in particular those species that have their first nursery habitats in shoreline areas were more affected by intensive commercial navigation than species whose larvae live predominantly pelagic. The results indicate that the negative effect of intensive navigation on riverine fish results primarily from the navigation‐induced hydraulic disturbances along the banks. Therefore, mitigation of navigation‐induced hydraulic forces is required to prevent degradation of fish communities in waterways. Copyright © 2010 John Wiley & Sons, Ltd.     

FISH HABITAT OPTIMIZATION TO PRIORITIZE RIVER RESTORATION DECISIONS

This paper examines and ranks restoration alternatives for improving fish habitat by evaluating tradeoffs between fish production and restoration costs. Optimization modelling is used to maximize out‐migrating coho salmon (Oncorhynchus kisutch) from a natal stream and is applied as a case study in California's Shasta River. Restoration activities that alter flow and water temperature conditions are the decision variables in the model and include relocating a major diversion, increasing riparian shading, increasing instream flow, restoring a cool‐water spring and removing a dam. A budget constraint limits total restoration expenditures. This approach combines simple fish population modelling with flow and water quality modelling to explore management strategies and aid decision making. Previous fish habitat optimization research typically uses single restoration strategies, usually by altering reservoir releases or modifying outlet structures. Our method enlarges the solution space to more accurately represent extensive and integrated solutions to fish habitat problems. Results indicate that restoration alternatives can be prioritized by fish habitat improvement and restoration cost. For the Shasta River case study, considerable habitat restoration investments were required before fish productivity increased substantially. This exercise illustrates the potential of ecological optimization for highlighting promising restoration approaches and dismissing poor alternatives. Copyright © 2011 John Wiley & Sons, Ltd.     

Guiding downstream migrating Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) of different life stages in a large river using bubbles

Salmonid repeat spawners are precious individuals for wild populations due to their high fecundity and previous spawning experience, making them important in environmental policy. However, repeat spawners rarely exist above hydropower dams in regulated rivers as the mortality of post-spawners (kelts) when passing through turbines during downstream migration is very high. To mitigate this problem, there are different technical solutions that potentially guide fish toward available fishways. Bubble barriers represent one alternative to costly physical guiding structures, but the efficiency of bubbles for guiding downstream migrating kelts has not been tested. In this study, we evaluate a 100 m long bubble barrier in guiding salmonids—both smolts and kelts—away from the main current and toward an alternative fishway in Ume River, a large regulated river in northern Sweden. We used both acoustic telemetry and sonar to measure the guiding effect of the bubble barrier for downstream migrating fish. We found that more than twice as many salmonids chose the alternative fishway when the bubble barrier was turned on. This was true both for smolts and kelts, suggesting that bubble barriers can be used to guide salmonids of different life stages in rivers with flow rates over 500 m³ s⁻¹. Indeed, our study indicates that bubble barriers are low-cost structures that could be rapidly applied in many regulated rivers to support salmonid migration.     

异齿裂腹鱼通过鱼道内流速障碍能力及行为

鱼类通过流速障碍能力是鱼道设计的主要生态指标,目前国内外主要使用封闭游泳水槽进行鱼类各种游泳速度指标及游泳行为研究,其水流流态及鱼类游泳行为与鱼类通过鱼道的实际状态有较大的差距,有必要结合鱼类游泳速度指标来探索能够更加准确量化鱼类通过鱼道流场的游泳能力测试方法。首先,在封闭游泳水槽中通过速度递增法测得异齿裂腹鱼临界游泳速度(101.01±20.86 cm/s)和突进游泳速度(196.94±21.80 cm/s);然后,以临界游泳速度和藏木水电站鱼道竖缝流速(110.00 cm/s)为参考,通过在开放游泳水槽内加不同束窄梯形体,形成类竖缝式鱼道的鱼类自主游泳能力测试水槽,开展两种底坡条件下4级短竖缝(工况1和工况2竖缝流速为101.55±14.87 cm/s、114.63±24.28 cm/s,竖缝顺水流长度均为40 cm)和单级长竖缝(工况3竖缝流速为137.45±17.63 cm/s、竖缝顺水流长度为160 cm)下试验鱼通过流速障碍能力和行为研究。试验结果表明:工况1、工况2下试验鱼通过4级竖缝成功率分别为82.05%、84.62%,通过流速大于临界游泳速度的竖缝时,持续爆发游泳时间为0.52±0.34 s;工况3下93.33%试验鱼以209.43±21.76 cm/s游泳速度成功通过单级长竖缝;3种工况下试验鱼通过流速大于临界游泳速度的竖缝时,以与突进游泳速度无显著性差异(P0.05)的恒定游泳速度(214.01±30.64 cm/s)上溯。鱼类游泳轨迹与流场耦合分析表明:鱼类上溯所需时间及路径长度与其选择的游泳路径密切相关,试验鱼通过借助回流区同向水流推动,增加上溯效率。本文研究方法及研究结论可为鱼道设计、改造、评价提供依据。     

Optimizing Green Infrastructure Implementation with a Land Parcel-Based Credit Trading Approach on Different Spatial Scales

Implementing green infrastructure (GI) to reach certain stormwater reduction goal may be a challenging task for some land parcels (LP) in urban areas due to their unfavorable landuse conditions. In this paper, we proposed a capacity/credit trading (CT) method that allows city LPs with favorable landuse conditions to build more GIs than required and trade their extra capacity as monetary credit to LPs with building difficulties; this will allow the whole city area to achieve general stormwater mitigation goal in a more cost effective way. We investigated the effects of CT on cost reduction and (re)distribution of GIs among LPs over different trading scales, and an optimization model was constructed on the basis of different zoning of CT. The model was applied to determine GI distributions among individual LPs in order to minimize the overall cost. With a case study, we demonstrated that, without CT, requiring individual LPs to meet the mitigation goal on their own can be costly, and the cost grows with implementation pressure from storm runoff reduction; engaging CT for GI implementation reduced the cost significantly even at a small trading scale. Our analysis showed that, cost increment for GI implementation can be cut in half by performing CT at a spatial scale of 500–600 m that includes 5–6 LPs; when the CT trading zone is expanded to 1200 m that include 17 LPs, the cost increment can be cut by 3/4. The benefit of CT is obtained by re-distributing GIs among different LPs; but the spatial scale of CT needs to be limited to preserve the virtue of onsite treatment of stormwater with GIs. The proposed approach can be used to take advantage of the city landuse diversities to lower the overall cost of GI implementation for stormwater management.

     

Mechanically reshaping stream banks alters fish community composition

Mechanically reshaping stream banks is a common practice to mitigate bank erosion in streams that have been extensively channelised and lowered for land drainage. A common perception regarding this activity is that fish populations will be largely unaffected, at least in the short term, because the low‐flow wetted channel remains undisturbed. However, the response of fish populations to this practice has rarely been quantitatively evaluated. Using a Before‐After‐Control‐Impact design, we assessed fish community responses to a catchment‐scale bank reshaping event in a fourth‐order low‐gradient stream that drains an intensive agricultural landscape. Quantitative electric fishing and fish habitat data were collected 2 months before and annually for 3 years after the reshaping event. After reshaping, deposited fine sediment levels increased in impact reaches, and there was a significant reduction in anguillid eel biomass (by 49%). In contrast, densities of obligate benthic gobiid bully species increased significantly in impact reaches—potentially due to reduced predation pressure from eels. Three years after bank reshaping, fish community structure had largely returned to its preimpact state in the reshaped areas. Our results suggest that, even in highly modified stream channels, further bank modification can reduce instream habitat quality and displace eels for at least 1 year. Managers should endeavour to use bank erosion control measures that conserve bank‐edge cover, especially in streams with populations of anguillid eels, because these fish are declining globally.     

Predicted impacts of proposed hydroelectric facilities on fish migration routes upstream from the Pantanal wetland (Brazil)

There are 104 hydroelectric facilities proposed to be installed in the watersheds that feed the Pantanal, a vast floodplain wetland located mostly in Brazil. The Pantanal is host to 23 long‐distance migratory fish species that ascend upland tributaries to spawn. A Geographic Information System was used to predict the impact of hydroelectric dams on potential migration routes for these species. Both anthropogenic (hydroelectric dams) and natural barriers were included in the analysis. Natural barriers were identified by river slope. Critical river slopes of 10 and 25%, above which fish were predicted to be incapable of ascending, were modeled as natural barriers. Based on this model, we show that between 2 and 14% of rivers in the Pantanal watershed are naturally blocked to fish migration. An additional 5 to 9% of rivers are currently blocked due to 35 existing hydroelectric facilities. If all proposed dams are built, the area flooded by new reservoirs will triple and the river kilometers blocked will double, blocking 25 to 32% of the river system to fish migration. The Taquari and Cuiabá River sub‐basins will be the most impacted, each having more than 70% of their rivers blocked. The impact of individual proposed facilities on the loss of migration routes is related to their proximity to existing barriers. Fourteen of the proposed dams are upstream from existing barriers and will therefore not further restrict long‐distance fish migration routes while proposed dams are predicted to close an additional 11,000 to 12,000 km of river channels.     

Assessing the recovery of fish assemblages downstream of hydrological barriers in India's Western Ghats

River flow regulation by dams and barrages threatens freshwater fish diversity globally. However, factors contributing to the recovery of fish communities downstream of barriers to river flow are not well understood. It is crucial to identify processes that might enable river restoration despite the presence of river barriers. In this study, we assess recovery of fish species, including endemics, downstream of large and small barriers in the Malaprabha basin in the Western Ghats of India. We define “fish species recovery” as the proportion of fish species occurring in river reaches downstream of barriers, of the species pool occurring in upstream unregulated segments with similar elevation, stream order, and habitat characteristics. As per the serial discontinuity concept, we predicted that recovery will reduce immediately after, but gradually increase with, increasing distance downstream of barriers, due to contributions from unregulated streams joining the river. As expected, fish recovery decreased immediately downstream of barriers and increased at greater distances and declined when the number of upstream barriers increased, indicating cumulative impacts. Dissolved oxygen and total alkalinity were positively and negatively correlated with both recovery and distance from barrier. Water temperature and rocky instream habitat influenced recovery positively, but independent of distance from barriers. Recovery of fish species, including Western Ghats endemics, was promising even under the current level of river regulation in the area, mainly due to connectivity with undammed tributaries. Strict limits on future stream regulation within already regulated basins will be critical for conservation of freshwater fish biodiversity in this region.