Article

Re-building brown trout populations in dredged boreal forest streams: In-stream restoration combined with stocking of young trout

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Abstract

1. Rivers in boreal forested areas were often dredged to facilitate the transport of timber resulting in channels with simplified bed structure and flow fields and reduced habitat suitability for stream organisms, especially lotic fishes. Currently, many streams are being restored to improve their physical habitat, by replacing boulders and gravel and removing constraining embankments. The most compelling justification behind stream restoration of former floatways has been the enhancement of native fish populations, specifically salmonids. 2. We examined the success of a stream management programme aimed at re-building diminished brown trout (Salmo trutta) populations by monitoring densities of young-of-year and older trout in 18 managed and three reference streams during 2000–2005. Rehabilitation included in-stream restoration combined with a 5-year post-restoration period of stocking young brown trout. Our space-for-time substitution design comprised four pre-management, four under-management, 10 post-management and three reference streams. 3. Densities of young-of-year brown trout, indicating population establishment, were significantly higher in post- compared with pre-management streams. However, density of young-of-year brown trout in post-management streams was significantly lower compared with near-pristine reference streams. Furthermore, success of managed brown trout population re-building varied, indicating stream-specific responses to management measures. Density of burbot (Lota lota), a native generalist predator, was associated with low recruitment of brown trout. 4. Stream-specific responses imply that rehabilitation of brown trout populations cannot be precisely predicted thereby limiting application. Our findings support the importance of adaptive stream restoration and management, with focus on identifying factor(s) limiting the establishment of target fish populations.

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... Since the 1970s, timber floating in Fennoscandia was gradually replaced by road transportation (Muotka & Syrjänen 2007, Palm et al. 2007. Immediately thereafter, attempts to recreate habitat diversity were initiated with the primary aim of enhancing living conditions for salmonid populations (Muotka & Laasonen 2002, Luhta et al. 2012. In practice, different habitats (shelter, riffles, pools and spawning grounds) have been established by adding in-stream structures (e.g. ...
... In practice, different habitats (shelter, riffles, pools and spawning grounds) have been established by adding in-stream structures (e.g. current deflectors, boulder dams and gravel beds) and reopening side channels (Stewart et al. 2009, Luhta et al. 2012, Nilsson et al. 2015. ...
... Another important finding was that stockings of alevins/YOY were negatively related to restoration outcomes. Previous studies have also suggested that the benefits of current stockings are moderate at best (Luhta et al. 2012, Syrjänen et al. 2015. Therefore, it would be better to shift the focus of salmonid management from a strong reliance on stocking towards measures addressing factors that continue to limit natural recruitment and population establishment. ...
Thesis
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The degradation of rivers and streams has led to world-wide efforts to restore freshwater habitats. A good understanding of the social-ecological context is considered key to successful restoration. In this thesis, a multidisciplinary framework was applied to study ecological and social dimensions of restoration success. First, the long-term performance of in-stream restoration measures was examined by conducting repeated cross-sectional surveys in restored streams up to 20 years post-restoration. Next, nationwide electrofishing data were used to assess the density responses of juvenile salmonids to habitat restoration and factors influencing restoration success were examined. Finally, changes in the provision of ecosystem services were evaluated by comparing the perceptions of restoration outcomes between two user groups and three study rivers. The results indicated that the restoration-induced increase in habitat heterogeneity persisted over time, initiating an overall positive development also in biological metrics (i.e. juvenile salmonids and aquatic mosses). However, overall substrate variability in restored streams remained lower than in near-pristine streams, with a shortage of gravel beds. Fish responses varied strongly between rivers, which was explained mainly by watershed scale (e.g. river basin size, dominant geology) and local (potential interspecific competition) factors. Site-specific differences were also observed in the delivery of ecosystem services, mainly reflecting stakeholder perceptions of landscape value and fish provisioning. Overall, the results show that setting indicators and target levels for restoration success is grounded on perspective. Socially conscious ecological restoration that acknowledges local specialities and needs in priority setting, planning and implementation has the potential to provide multiple benefits for river ecosystems and society.
... In a review from northern Europe, Nilsson et al. (2015) showed that only one of the five papers that studied fish populations demonstrated a positive response to in-stream restoration. Similarly, Luhta et al. (2012) found slightly positive, but streamspecific effects on the density of young-of-the-year (YOY) brown trout. In contrast, Whiteway et al. (2010) and Roni et al. (2008) concluded that in-stream habitat improvement generally benefits juvenile salmonids, although the responses vary widely among species and life stages. ...
... Recovering salmonid populations may be vulnerable to predators and competitors (Ward et al. 2008) and increased densities of predators may be associated with low recruitment of salmonids (Ward et al. 2008;Luhta et al. 2012). It remains unclear, however, if and how habitat restoration influences potential predators and competitors of juvenile salmonids (Nilsson et al. 2005). ...
... In-stream restoration is often supported by stocking, also referred to as assisted colonization . Although this is a controversial measure, its use may be justified for species with scattered distributions, particularly if the target species has disappeared completely from a river (Luhta et al. 2012;Stoll et al. 2013). In Finland, stockings of Atlantic salmon and migratory brown trout have been conducted for more than a century (Luhta et al. 2012;Syrjänen et al. 2015). ...
Article
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River restoration offers the potential to enhance biological integrity, often measured as fish population changes. We used a meta-analytical approach to synthesize density responses to in-stream habitat restoration by young-of-the year (YOY) brown trout and Atlantic salmon in 28 rivers (overall 32 restoration projects) in Finland. We also examined which local and watershed-scale factors most influenced restoration success. Finally, we conducted an expert survey to obtain an independent estimate of a sufficient density enhancement for restoration to be considered successful. Despite strong context-dependency , habitat restoration had an overall positive effect on YOY salmonid density. When compared to target levels derived from the expert survey, density responses mainly reached the minimum expected success rate, but remained short of the level considered to reflect distinct success. Variability in restoration responses of trout was linked mainly to river size, predominant geology, water quality and potential interspecific competition (trout vs. European bull-head). Fishing mortality tended to obscure positive effects of restoration and stocking by YOY fish affected negatively trout's response to restoration,().,-volV) (0123456789().,-volV) supporting a shift towards self-sustainable schemes in fisheries management. These results imply that habitat restoration is a useful approach for improving the ecological and conservational status of salmonid populations in boreal rivers. To further improve the success rate, and thereby public acceptance, of restorations they need to be complemented by other management measures that enhance the potential for the recovery of threatened salmonid populations.
... Many rivers that have been severely impacted by habitat degradation are also stocked with hatchery-reared fish to restore lost or low-density salmonid populations (e.g. Luhta, Huusko, & Louhi, 2012). ...
... River restoration by addition of wood has in several previous studies been shown to increase densities of juvenile salmonids (e.g. Johnson, Rodgers, Solazzi, & Nickelson, 2005;Louhi, Vehanen, Huusko, Mäki-Petäys, & Muotka, 2016;Luhta et al., 2012;Thompson et al., 2018), and wood loading of up to 0.16 large wood pieces/m 2 has been shown to increase trout abundance based on electrofishing data (Degerman, Sers, Törnblom, & Angelstam, 2004). The wood densities of the treated sections in our study were near this limit, but still not as high as those found in pristine forest streams in North America (Fausch & Northcote, 1992). ...
Article
• Habitat structural complexity affects the behaviour and physiology of individuals, and responses to the environment can be immediate or influence performance later in life through delayed effects. • Here, we investigated how structural enrichment, both pre‐release in the hatchery rearing environment and post‐release in the wild, influenced winter growth and site fidelity of brown trout stocked into side channels of a regulated river. • Experiencing structural enrichment in the rearing environment during 3 months in autumn had no pre‐release effect on growth, but a delayed positive effect after release during the subsequent winter. Moreover, trout recaptured in wood‐treated sections of the side channels had grown more than trout recaptured in control sections. Wood enrichment in the side channels also increased overwinter site fidelity. • These results show that adding structure during a relatively short period may alter growth trajectories, and adding wood to side channels is a cost‐effective method to enhance winter habitat carrying capacity for juvenile salmonids in regulated rivers.
... Growing awareness of the value of healthy ecosystems and the need to adapt to future changes in climate has put a focus on restoration of ecosystems, especially rivers (Bernhardt et al. 2005, Palmer et al. 2008, Arthington et al. 2010. Recent river restoration approaches include renaturalization of flows; that is, environmental flows (Tharme 2003) and flood protection (Nardini and Pavan 2012); reconfiguration of channels (Nilsson et al. 2005a); defragmentation, that is, dam removal (Bednarek 2001, Lejon et al. 2009), and rebuilding of populations (Luhta et al. 2012). There is a dearth of detailed, scientifically based guidelines for stream restoration. ...
... One reason for stream restoration in northern Europe is the rehabilitation of brown trout populations, which are popular game fish. Reconstruction of lost spawning beds and retention of added spawning bed substrate is key for success in this matter (Rosenfeld et al. 2011, Luhta et al. 2012) and these goals are more likely to be reached in slow-flowing, boulder-rich stream reaches like the demonstration sites. Another reason for stream restoration is increasing water retention during heavy rains and flood-erosion events, predicted to become more frequent as a result of climate change (Nilsson et al. 2013). ...
Article
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Some ecological restoration projects include elements of trial and error where new measures are repeatedly tried, evaluated, and modified until satisfactory results are achieved. Thereafter, the resulting methods may be applied on larger scales. A difficult step is judging whether developed "best-practice" methods have become reasonably ecologically functional or whether further experimentation "demonstration" methods can lead to yet better results. Here, we use a stream restoration project as a case study for evaluating methods and abiotic effects and outlining stakeholder support for demonstration restoration measures, rather than only using best-practice methods. Our work was located in the Vindel River system, a free-flowing river that is part of the Natura 2000 network. The river was exploited for timber floating from 1850-1976, and rapids in the main channel and tributaries below timberline were channelized to increase timber transport capacity. Several side channels in multi-channeled rapids were blocked and the flow was concentrated to a single channel from which boulders and large wood were removed. Hence, previously heterogeneous environments were replaced by more homogeneous systems with limited habitat for riverine species. The restoration project strives to alleviate the effects of fragmentation and channelization in affected rapids by returning coarse sediment from channel margins to the main channel. However, only smaller, angular sediment is available given blasting of large boulders, and large (old-growth) wood is largely absent; therefore, original levels of large boulders and large wood in channels cannot be achieved with standard restoration practices. In 10 demonstration sites, we compensated for this by adding large boulders and large wood (i.e., entire trees) from adjacent upland areas to previously best-practice restored reaches and compared their hydraulic characteristics with 10 other best-practice sites. The demonstration sites exhibited significantly reduced and more variable current velocities, and wider channels, but with less variation than pre-restoration. The ecological response to this restoration has not yet been studied, but potential outcomes are discussed.
... Despite research suggesting that at least 4-8 years are needed postrestoration to determine the full fish population responses (Hunt 1976;Binns and Remmick 1994), monitoring time for projects in our analysis has not significantly increased over time (Table 4), and over three-quarters of all projects monitored for less than 5 years. In some catchments, years to decades may be needed to rebuild fish populations to sustainable levels (Luhta et al. 2012). More than a year or two is needed for populations to expand into existing and new habitats O'Neal et al. 2016), and multiple generations may be required to detect adult responses (Roni et al. 2002). ...
Article
Due to declines in salmonid populations, in-stream restoration structures have been used for over 80 years to increase abundance of fish. However, the relative effectiveness of these structures remains unclear for some species or regions, partly due to contrasting conclusions from two previous meta-analyses. To update and reconcile these previous analyses, we conducted a meta-analysis using data available from 1969 to 2019 to estimate the effect of in-stream structures on salmonid abundance (number and density) and biomass. Data from 100 stream restoration projects showed a significant increase in salmonid abundance (effect size 0.636) and biomass (0.621), consistent with previous reviews and studies, and a stronger effect was found in adults than juvenile fish. Despite a shift towards using more natural structures (wood and boulders) since the 1990s, structures have not become more effective. However, most projects monitor for less than 5 years, which may be insufficient time in some systems for channel morphology to adjust and population changes to be apparent. Process-based techniques, which give more space for the river, allow more long-term self-sustaining restoration.
... designs and successfully detected a restoration response (e.g., Lennox et al. 2011;Luhta et al. 2012;Louhi et al. 2016). Thus, the EPT design has been successfully used to evaluate regional restoration programs and is a viable alternative to mBACI or other designs, assuming that one is not also interested in detailed information on the effectiveness of individual projects. ...
Article
Large regional programs to restore riverine habitat for fish and aquatic organisms have become common throughout North America, Europe, and elsewhere. Evaluating the effectiveness of projects implemented under these programs – sometimes called programmatic monitoring and evaluation – has proven challenging and little guidance exists on programmatic monitoring and evaluation approaches and their effectiveness. In this paper, we review different approaches for evaluating the effectiveness of river restoration projects implemented across a region. These programmatic monitoring and evaluation approaches include case studies, meta‐analyses, multiple before‐after control‐impact (mBACI), extensive post‐treatment (EPT), intensively monitored watersheds (IMW), and hybrid programmatic approaches that use a combination of different experimental designs. For each approach, we discuss the pros and cons as well as provide examples. The most appropriate approach depends in part on the questions that the programmatic monitoring and evaluation strives to address, the spatial and temporal scale at which detection of a response is expected, and the scale of inference. Case studies and the mBACI approaches can answer questions about individual projects, but have several limitations in terms of cost, timely results, and feasibility. A meta‐analysis, which can provide broadly applicable results, is dependent upon a large number of case studies being completed. The EPT approach can provide relatively quick and easy to interpret results, though it requires a large population of completed projects and careful selection of controls. The IMW approach has been broadly applied in western North America, but has had limited success and appears to be tractable only in small catchments where restoration and monitoring can be well controlled. Based on results from recent efforts in the U.S. and Europe, the most feasible programmatic monitoring and evaluation approach in terms of cost, implementability, and producing timely results, appears to be a hybrid approach that uses a combination of EPT and mBACI approaches. This article is protected by copyright. All rights reserved.
... These represent a subset of populations that were previously studied by Lemopoulos et al. (2017). In short, three resident populations (KR1-KR3) in headwater streams were sampled by electrofishing in 2015 (Reid et al. 2009;Luhta et al. 2012). The length of the sampled sections varied between streams from 300 to 800 m. ...
Article
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Candidate genes associated with migration have been identified in multiple taxa: including salmonids, many of whom perform migrations requiring a series of physiological changes associated with the freshwater-saltwater transition. We screened over 5500 SNPs for signatures of selection related to migratory behaviour of brown trout Salmo trutta by focusing on ten differentially migrating freshwater populations from two watersheds (the Koutajoki and the Oulujoki). We found eight outlier SNPs potentially associated with migratory vs. resident life history using multiple (≥3) outlier detection approaches. Comparison of three migratory vs. resident population pairs in the Koutajoki watershed revealed seven outlier SNPs, of which three mapped close to genes ZNF665-like, GRM4-like and PCDH8-like that have been previously associated with migration and smoltification in salmonids. Two outlier SNPs mapped to genes involved in mucus secretion (ST3GAL1-like) and osmoregulation (C14orf37-like). The last two strongly supported outlier SNPs mapped to thermally-induced genes (FNTA1-like, FAM134C-like). Within the Oulujoki, the only consistent outlier SNP mapped close to a gene (EZH2) that is associated with compensatory growth in fasted trout. Our results suggest that a relatively small yet common set of genes responsible for physiological functions associated with resident and migratory life histories are evolutionarily conserved.
... The biological responses to stream restoration have been largely variable (Luhta et al. 2012, Nilsson et al. 2015 or have shown little evidence of ecological success (Louhi et al. 2011). For example, the short-term evaluation of restoration success on the river Kiiminkijoki showed no response of one-year-old salmon to restoration. ...
Article
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Stream restoration often aims to enhance fisheries by improving stream conditions for target fish species. However, river restoration has a potential impact on a variety of ecosystem services. Among stakeholders, the emerging expectations about restoration attain different priorities. How well these expectations are met influences social perceptions of success or failure. Although public support for restoration is known to have a significant impact on the sustainability and overall success of restoration, social aspects are rarely considered in this context. To address these issues, we conducted a questionnaire study among the residents and fishermen of three recently restored rivers in Finland. Results indicate that both user groups highly supported the restoration goals, but they were not always satisfied with the restoration outcomes. The changes in landscape value and amenity and fish provisioning had the highest influence on the user groups’ attitudes. Restoration-induced changes in ecosystem services showed clear variation between the different locations, but the differences in the perceptions of the two user groups were less evident. Comparing perceptions between the user groups and locations and applying the ecosystem services approach are a novel contribution to the debate on restoration success. Our study highlights the importance of perspective, social-ecological context, and adequate communication for success.
... Although SFTS has limitations (Pickett 1989, Fukami and Wardle 2005, Walker et al. 2010, this method has been used in terrestrial ecology for over a century (e.g., Cowles 1899, Bazzaz 1975, Chapin et al. 1994, Myster and Malahy 2008, Walker and Shiels 2008. In recent years, it has also become more prevalent in freshwater studies (e.g., Nilsson et al. 1997, Holl and Crone 2004, Louhi et al. 2011, Hansen and Hayes 2012, Lorenz et al. 2012, Luhta et al. 2012). Thus, the use of SFTS to study stream restoration and its surrounding riparian habitats should provide insight into the recovery of communities after restoration that would otherwise take decades to understand. ...
Article
A lack of ecological responses in stream restoration projects has been prevalent throughout recent literature with many studies reporting insufficient time for recovery. We assessed the relative importance of time, site variables, and landscape setting for understanding how plant species richness and understory productivity recover over time in riparian zones of northern Swedish streams. We used a space-for-time substitution consisting of 13 stream reaches restored 5-25 years ago, as well as five unrestored channelized reference reaches. We inventoried the riparian zone for all vascular plant species along 60-m study reaches and quantified cover and biomass in plots. We found that while species richness increased with time, understory biomass decreased. Forbs made up the majority of the species added, while the biomass of graminoids decreased the most over time, suggesting that the reduced dominance of graminoids favored less productive forbs. Species richness and density patterns could be attributed to dispersal limitation, with anemochorous species being more associated with time after restoration than hydrochorous, zoochorous, or vegetatively reproducing species. Using multiple linear regression, we found that time along with riparian slope and riparian buffer width (e.g., distance to logging activities) explained the most variability in species richness, but that variability in total understory biomass was explained primarily by time. The plant community composition of restored reaches differed from that of channelized references, but the difference did not increase over time. Rather, different time categories had different successional trajectories that seemed to converge on a unique climax community for that time period. Given our results, timelines for achieving species richness objectives should be extended to 25 years or longer if recovery is defined as a saturation of the accumulation of species over time. Other recommendations include making riparian slopes as gentle as possible given the landscape context and expanding riparian buffer width for restoration to have as much impact as possible.
... In fact, the presence of yearling, but not of smaller, trout forced ABs to shift to microhabitats with higher current velocities. Some field studies have indicated that the numbers of brown trout are reduced in areas preferred by bullheads (Gaudin & Caillere 1990;Hesthagen et al. 2004;Luhta et al. 2012), yet other studies have concluded that bullheads have no significant effects on densities of juvenile trout or Atlantic salmon (Pihlaja et al. 1998;Jørgensen et al. 1999), and even opposite results, a salmonid being superior to bullheads, have been reported. For example, in a manipulative experiment, Ruetz et al. (2003) found reduced growth of slimy sculpin (Cottus cognatus) in the presence of brown trout. ...
Article
Stream-dwelling salmonids and bullheads occupy similar resource niches in northern rivers. It is therefore tempting to assume that they might be involved in a competitive interaction, with potential implications for the habitat use and growth of brown trout (Salmo trutta). We conducted artificial-stream experiments to test whether a putative competitor, Alpine bullhead (Cottus poecilopus), had an effect on the habitat use of under-yearling (0+) and yearling (1+) trout. We hypothesised that (i) 1+ trout would be competitively superior to 0+ trout, forcing the younger fish to suboptimal habitats, and that (ii) bullhead might affect the habitat use and prey selection of 0+ trout but less so that of 1+ trout. Against our predictions, no effect of bullhead was found on the habitat use of either age class of brown trout. Instead, yearling trout seemed to force bullheads to suboptimal microhabitats with high current velocities. Presence of yearlings also decreased the growth of under-yearling fish and caused a shift in their diet composition. These findings suggest that competitive interactions may not limit the coexistence of brown trout and bullheads in boreal rivers. Intraspecific interactions between trout age classes may be more important, with potentially detrimental effects on the growth and overwintering success of 0+ trout.
... We only excluded studies (e.g. Luhta et al., 2012) if they included other measures, such as fish stocking, that enhanced natural recovery after physical restoration. The streams in which restoration projects have been evaluated are all situated in the boreal region of northern Fennoscandia. ...
Article
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We reviewed follow-up studies from Finnish and Swedish streams that have been restored after timber-floating to assess the abiotic and biotic responses to restoration. More specifically, from a review of 18 case studies (16 published and 2 unpublished) we determined whether different taxonomic groups react differently or require different periods of time to respond to the same type of restoration. Restoration entailed returning coarse sediment (cobbles and boulders) and sometimes large wood to previously channelized turbulent reaches, primarily with the objective of meeting habitat requirements of naturally reproducing salmonid fish. The restored streams showed a consistent increase in channel complexity and retention capacity, but the biotic responses were weak or absent in most species groups. Aquatic mosses growing on boulders were drastically reduced shortly after restoration but in most studies they recovered after a few years. Riparian plants, macroinvertebrates, and fish did not show any consistent trends in response. We discuss seven alternative explanations to these inconsistent results and conclude that two decades is probably too short a time for most organisms to recover. We recommend long-term monitoring using standardized methods, a landscape-scale perspective, and a wider range of organisms to improve the basis for judging to what extent restoration in boreal streams has achieved its goal of reducing the impacts from timber-floating. This article is protected by copyright. All rights reserved.
Technical Report
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Vaelluskalakantojen palauttaminen rakennettuihin vesistöihin edellyttää monialaista tutkimustietoa kalojen elinkierron eri vaiheisiin liittyvistä haasteista ja niiden korjaustoimista. Myös vesistöjen eri käyttäjien ja intressiryhmien on löydettävä yhteinen tahtotila jokiympäristön ja sen kalaston kestävälle käytölle. Tämä puolestaan edellyttää viranomaisten, eri toiminnanharjoittajien ja sidosryhmien välillä avointa vuoropuhelua, yhteisten sovitteluratkaisujen hakemista ja omista eduista joustamista. Vaelluskalojen palauttamiseen liittyviin tietotarpeisiin on vastattu Luonnonvarakeskuksen (Luke) monialaisilla tutkimushankkeilla, joita on toteutettu rakennetuissa vesistöissä eri puolilla maatamme sekä Luken Kainuun kalantutkimusaseman kokeellisissa olosuhteissa. Tähän raporttiin on koottu vuosina 2011–2018 toiminnassa olleiden Luonnonvarakeskuksen (vuoteen 2015 asti Riista- ja kalatalouden tutkimuslaitos) hankkeiden tärkeimmät tulokset sekä julkaisuluettelo. Tässä esiteltäviä hankkeita ja raportin koostamista ohjasi erikoistutkija Aki Mäki-Petäys kevääseen 2019 asti. Useat näistä hankkeista on tehty yhteistyössä Helsingin, Itä-Suomen, Jyväskylän ja Oulun yliopistojen, Suomen ympäristökeskuksen (SYKE), Elintarviketurvallisuusviraston (Evira), Metsähallituksen, ELY-keskusten ja Pohjois-Pohjanmaan liiton kanssa, ja joissakin tapauksissa nämä tahot ovat olleet myös hankkeiden päävastuullisia toteuttajia. Tutkimushankkeita on rahoitettu myös osana laajempia ja useampivuotisia Public-Private-Partnership (PPP) – hankekokonaisuuksia, missä vesivoimayhtiöiden rahoitus on ollut merkittävässä osassa. Vaelluskalojen palauttaminen on monin paikoin mahdollista, jos eri käyttäjät ja intressiryhmät ovat sitoutuneet pitkäjänteiseen yhteistyöhön. Vesistökohteet ovat erilaisia, joten kaikkiin kohteisiin sopivaa ratkaisua ei yleensä ole, vaan toimenpiteissä on aina huomioitava vesistöjen erityispiirteet sekä mahdolliset muut reunaehdot. Kohteesta riippuen, toimenpiteinä tarvitaan: x Toimivat kalojen vaellusväylät patojen ohitse sekä ylä- että alavirtaan, x Elinympäristökunnostuksia sekä joki- ja purouomissa että niiden valuma-alueilla, x Istutuskalojen sekä – toiminnan laadullista kehittämistä, x Riittävää kalastuksen säätelyä, x Myös muiden eliöryhmien kuin vaelluskalojen elinolosuhteiden parantamista, x Realistisesti asetettuja vesistökohtaisia tavoitteita, x Toimenpiteiden vaikuttavuuden seurantaa, x Tehokasta ja yleistajuista viestintää sekä kaikkien sidosryhmien sitouttamista yhteistyöhön, x Ajallisia ja taloudellisia resursseja. Aihepiirin tutkimustoimintaa viedään Lukessa eteenpäin vuodesta 2019 alkaen mm. Sateenvarjo III-, Kalatalouden ympäristöohjelma-, RiverGo- sekä monissa muissa yhteistyöhankkeissa. Toivomme, että tämä työ toimii tietopakettina monille muillekin hankkeille!
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Adfluvial brown trout, Salmo trutta m. lacustris (L.), was common in all Finnish watercourses with large lakes at the beginning of the 20th century. Nowadays, the stocks are severely declined in central and southern Finland due to damming and dredging of riverine reproduction areas, organic pollution from the paper and pulp industry, and increasing river fishing. However, adfluvial brown trout is an iconic species in recreational fisheries, and is captured mainly by rod and line in rivers, and by gillnets and trolling in all large lakes. The importance of the species to commercial fishing in Finland is generally negligible. Unregulated lake fishing, mainly with gillnets, however, led to a severe collapse of the southern stocks from the 1960s to the 1990s. To compensate for the decline of wild stocks, stocking streams with eggs and fry was started at the beginning of the 20th century. From the 1970s onwards, this largely changed to extensive direct stocking into lakes of parr and smolts. Yet, the southern adfluvial brown trout stocks have not recovered, and catches of adfluvial brown trout in lakes are almost entirely based on stocking directly into lakes of 2–3 -year-old smolts derived from hatchery brood stocks. Lake Inari is now the only large lake with a significant (12–38 %) contribution of wild fish to the catch. Today, water quality in most large watercourses is suitable for brown trout, reproduction areas are being restored, and prey fish stocks in lakes are adequate. Mainly voluntary protection of wild individuals in river fishing began to spread from 2005, and wild adfluvial brown trout were finally protected by law in 2016 in southern Finland. However, along with the protection of the wild fish, the minimum size limit of 600 mm, imposed in 2014, was again decreased to 500 mm effectively preventing the recovery of wild stocks subject to intensive gillnet fishing. Based on a population model built for two important Finnish adfluvial brown trout stocks, the current fishing mortality rates need to be decreased substantially in order to rebuild the severely depleted stocks. The bycatch mortality of juvenile fish should be minimized and the minimum size limit kept at 600 mm or more. Bag limits and obligatory catch-and-release provide management measures to further decrease fishing mortality.
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The growing concern on declining salmonid populations has resulted in numerous restoration projects with variable responses worldwide. In this spatially replicated multiyear study, we assessed the long-term (12 years postrestoration) effects of in-stream habitat restoration (i.e., addition of boulders or large woody debris (LWD) together with boulders) on densities of three age-classes of juvenile brown trout (Salmo trutta) in six forest streams in northern Finland. LWD combined with boulders was more beneficial, particularly for the larger trout (age-2 and older), than were boulder structures alone, indicating that the more diverse habitat created by LWD may have provided a safeguard against drought for the larger fish. Density of age-0+ trout showed a significant long-term increase in boulder-restored sections, providing evidence that log structures may need to be complemented by stony enhancement structures to guarantee the availability of suitable stream habitat for all trout age-classes. As trout densities are known to exhibit inherently wide interannual variability that tracks climatically induced hydrological variation, long-term postrestoration monitoring that encompasses extreme hydrological events is critical for evaluating the success of restoration projects.
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Ecological restoration has grown rapidly and now encompasses not only classic ecological theory but also utilitarian concerns, such as preparedness for climate change and provisioning of ecosystem services. Three dominant perspectives compete to influence the science and practice of river restoration. A strong focus on channel morphology has led to approaches that involve major Earth-moving activities, such as channel reconfiguration with the unmet assumption that ecological recovery will follow. Functional perspectives of river restoration aim to regain the full suite of biogeochemical, ecological, and hydrogeomorphic processes that make up a healthy river, and though there is well-accepted theory to support this, research on methods to implement and assess functional restoration projects is in its infancy. A plethora of new studies worldwide provide data on why and how rivers are being restored as well as the project outcomes. Measurable improvements postrestoration vary by restoration method and measure of outcome.
Article
Artificial drainage of forested wetlands to increase timber production has profoundly altered the hydrology of North-European landscapes during the 20th century. Nowadays, drainage ditches and small dredged streams can comprise most fluvial water bodies there, but the resulting ecological effects are poorly documented. In the current study, we explored, using fish as an indicator group, consequences of the transformation of natural stream networks to a mixture of natural and artificial watercourses. We asked whether the transformation results in impoverishment, enrichment or re-assembling of the communities both at watercourse and the landscape scales. We sampled fish in 98 sites in five well-forested regions in Estonia where ditches formed 83–92%, dredged streams 4–7%, and natural streams 3–10% of the total length of small watercourses. Based on a total of 6370 individual fish of 20 species, we found that, compared to natural streams, ditches had an impoverished fauna at both scales and both in terms of species richness and assemblage composition. Only natural streams hosted characteristic species (with Barbatula barbatula, Lampetra planeri and Lota lota emerging as significant indicators), while dredged streams had intermediate assemblages. The habitat factors explaining those drainage-related differences included a reduced flow velocity, loss of stream channel variability, less transparent water, and abundant aquatic vegetation. Hence, for stream-dwelling fish, drained forest landscapes represent degraded habitats rather than novel ecosystems, which contrasts with the transformation of terrestrial assemblages. Future studies should address whether that reflects the situation for whole aquatic assemblages, and how is the functioning of the hydrological systems affected. We suggest that the critical management issues for environmental mitigation of ditching effects on fish include basin scale spatial planning, protecting of the remaining natural streams, and rehabilitation of ditch channels in flat landscapes lacking beavers.
Conference Paper
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Traditionally, when assessing stream habitats the focus has been placed on structural endpoints, such as flow and depth fields, or species diversity and other community attributes. The evaluation of ecosystem processes, i.e. functional endpoints, has got less attention. Here we forwarded a hypothesis whether the leaf retention could be used as a simple, stream-function-oriented method for assessing mesohabitat quality and restoration success. The biotic communities of streams in temperate zone forested areas are highly dependent on organic material, such as the leaf fall from the riparian trees in autumn. Consequently, a high retentive capacity of a stream could indicate beneficial conditions for benthic organisms, which in turn would propagate up in stream food webs. Our experimental results verified the view that complex stream bed structure indicates high leaf retention, and vice versa. Considering the elemental importance of leaf litter to forest streams the retention rate seems to be a good candidate for a simple stream-function-oriented tool for assessing the success of rehabilitation of streams with reduced bed heterogeneity.
Article
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Evaluating the effectiveness of instream structures for increasing trout populations is complicated by a paucity of long-term studies. We report on a study spanning 23 years to assess the effect of installing log weirs on stream habitat and trout abundance. Structures were installed in a randomly selected half of a 500 m study reach in six small Colorado, USA, mountain streams in 1988, and habitat and trout abundance and biomass were measured annually from 1987 to 1994. When five of the streams were resampled in 2009, none of the 53 logs had moved, and all but one were functioning properly. Pool volume remained more than three times higher in treatment sections than in adjacent controls, and mean depth was also greater. Adult trout abundance increased rapidly after structures were installed and remained 53% higher in treatment sections than in controls 21 years later. Effects on juvenile trout abundance were not detected, probably because fry recruitment is strongly influenced by effects of snowmelt runoff, which vary annually among basins. This evaluation shows that instream structures placed in small, stable channels can function for more than two decades when properly installed and can cause long-lasting increases in trout abundance when habitat is limiting.
Article
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Stream restoration has received much attention in recent years, yet there has been little effort to evaluate its impacts on physical habitat, stability, and biota. A popular but controversial stream restoration approach is natural channel design (NCD), which cannot be adequately evaluated without a long-term, independent assessment of its effects on stream habitat. Six reaches of five Catskill Mountain streams in southeastern New York were restored during 2000–2003 following NCD techniques to decrease bed and bank degradation, decrease sediment loads, and improve water quality. Habitat surveys were conducted during summer low flows from 2001 to 2007. The effects of the NCD projects on stream condition were assessed via a before–after–control–impact study design to quantify the net changes in stream and bank habitat variables relative to those in unaltered control reaches. Analysis of variance tests of three different measures of bank stability show that on average stream stability increased at treatment sites for 2–5 years after restoration. Mean channel depth, thalweg depth, and the pool–riffle ratio generally increased, whereas mean channel width, percent streambank coverage by trees, and shade decreased. Habitat suitability indices for local salmonid species increased at four of six reaches after restoration. The changes in channel dimensions rendered them generally more characteristic of stabler stream forms in the given valley settings. Although these studies were done relatively soon after project completion, our findings demonstrate that habitat conditions can be improved in degraded Catskill Mountain streams through NCD restoration.
Article
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Community ecological theory may play an important role in the development of a science of restoration ecology. Not only will the practice of restoration bene- fit from an increased focus on theory, but basic re- search in community ecology will also benefit. We pose several major thematic questions that are rele- vant to restoration from the perspective of community ecological theory and, for each, identify specific areas that are in critical need of further research to advance the science of restoration ecology. We ask, what are appropriate restoration endpoints from a community ecology perspective? The problem of measuring resto- ration at the community level, particularly given the high amount of variability inherent in most natural communities, is not easy, and may require a focus on restoration of community function (e.g., trophic struc- ture) rather than a focus on the restoration of particu- lar species. We ask, what are the benefits and limita- tions of using species composition or biodiversity measures as endpoints in restoration ecology? Since reestablishing all native species may rarely be possi- ble, research is needed on the relationship between species richness and community stability of restored sites and on functional redundancy among species in regional colonist "pools." Efforts targeted at restoring system function must take into account the role of in- dividual species, particularly if some species play a disproportionate role in processing material or are strong interactors. We ask, is restoration of habitat a sufficient approach to reestablish species and func- tion? Many untested assumptions concerning the rela- tionship between physical habitat structure and resto- ration ecology are being made in practical restoration efforts. We need rigorous testing of these assump- tions, particularly to determine how generally they apply to different taxa and habitats. We ask, to what extent can empirical and theoretical work on commu- nity succession and dispersal contribute to restoration ecology? We distinguish systems in which succession theory may be broadly applicable from those in which it is probably not. If community development is highly predictable, it may be feasible to manipulate natural succession processes to accelerate restoration. We close by stressing that the science of restoration ecology is so intertwined with basic ecological theory that practical restoration efforts should rely heavily on what is known from theoretical and empirical re- search on how communities develop and are struc- tured over time.
Article
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Natural-channel-design (NCD) restorations were recently implemented within large segments of five first- and second-order streams in the Catskill Mountains of New York in an attempt to increase channel stability, reduce bed and bank erosion, and sustain water quality. In conjunction with these efforts, 54 fish and habitat surveys were done from 1999 to 2007 at six restored reaches and five stable control reaches to evaluate the effects of NCD restoration on fish assemblages, habitat, and bank stability. A before–after–control–impact study design and two-factor analysis of variance were used to quantify the net changes in habitat and fish population and community indices at treatment reaches relative to those at unaltered control reaches. The density and biomass of fish communities were often dominated by one or two small prey species and no or few predator species before restoration and by one or more trout (Salmonidae) species after restoration. Significant increases in community richness (30%), diversity (40%), species or biomass equitability (32%), and total biomass (up to 52%) in at least four of the six restored reaches demonstrate that NCD restorations can improve the health and sustainability of fish communities in geomorphically unstable Catskill Mountain streams over the short to marginally long term. Bank stability, stream habitat, and trout habitat suitability indices (HSIs) generally improved significantly at the restored reaches, but key habitat features and trout HSIs did not change or decreased at two of them. Fish communities and trout populations at these two reaches were not positively affected by NCD restorations. Though NCD restorations often had a positive effect on habitat and fish communities, our results show that the initial habitat conditions limit the relative improvements than can be achieved, habitat quality and stability do not necessarily respond in unison, and biotic and abiotic responses cannot always be generalized.
Article
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Between 1992 and 2003, we assessed the density of age-0+ brown trout (Salmo trutta) in a channelized stream in northern Sweden, which was restored using two different schemes. One section of the stream was restored by the addition of boulders and reconstruction of gravel beds (boulder + gravel section), whereas another section was restored through addition of boulders only (boulder-only section). In addition, we compared the substrate size composition of gravel beds and the egg-to-fry survival between the two stream sections, and we related the density of age-0+ brown trout to the area of reconstructed gravel beds. After the restoration, the density of age-0+ brown trout increased significantly in the boulder + gravel section and was positively correlated with the area of reconstructed gravel beds. By contrast, the density of age-0+ brown trout did not change in the boulder-only treatment. Egg-to-fry survival was significantly higher in the boulder + gravel section compared with the boulder-only section, probably because of the higher content of sand and fines in the gravel beds of the latter treatment. This study shows that the density of age-0+ brown trout was limited by the availability and quality of spawning substrate rather than by the structural habitat complexity.
Article
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Despite the widespread use of stream restoration structures to improve fish habitat, few quantitative studies have evaluated their effectiveness. This study uses a meta-analysis approach to test the effectiveness of five types of in-stream restoration structures (weirs, deflectors, cover structures, boulder placement, and large woody debris) on both salmonid abundance and physical habitat characteristics. Compilation of data from 211 stream restoration projects showed a significant increase in pool area, average depth, large woody debris, and percent cover, as well as a decrease in riffle area, following the installation of in-stream structures. There was also a significant increase in salmonid density (mean effect size of 0.51, or 167%) and biomass (mean effect size of 0.48, or 162%) following the installation of structures. Large differences were observed between species, with rainbow trout (Oncorhynchus mykiss) showing the largest increases in density and biomass. This compilation highlights the potential of in-stream structures to create better habitat for and increase the abundance of salmonids, but the scarcity of long-term monitoring of the effectiveness of in-stream structures is problematic.
Article
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Population enumeration is a key component of fisheries investigations for riverine salmonines. We examined the reliability of a rapid population assessment technique for stream salmonines that depends on a single episode of electrofishing rather than traditional multiple fishing, removal, or mark–recapture methods. We show that for 12 sites sampled in 1992 on Wilmot Creek, a small, coldwater tributary to Lake Ontario, the catch of salmonines from a single electrofishing episode predicted the population estimate obtained with a more time-consuming multiple-pass removal method. When we collected similar data from eight additional Lake Ontario tributary sites in 1994, the relationship was not significantly different from that obtained in 1992. We also conducted nonparametric analyses of covariance on subsets of these data and found no significant differences in the above relationship for rainbow trout Oncorhynchus mykiss versus brown trout Salmo trutta or for age-0 versus older fish, although the statistical power of the species comparison was low because of the small number of samples containing brown trout. The regression model developed from the pooled 1992 and 1994 data predicts population sizes that only slightly exceed estimates obtained with the removal method at 12 other sites throughout southern Ontario. We use the rapid assessment technique to obtain rainbow and brown trout population estimates with measurable precision for an entire catchment and show that the error in our site-specific estimator of population size is small relative to among-site sampling error, even though our sampling fraction is relatively large compared to that of typical surveys. Finally, we provide suggestions to potential users of the proposed methodology regarding data collection and analytical techniques.
Article
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Stream restoration projects often aim to benefit aquatic biota and frequently use the reappearance of sensitive nongame fish species as a measure of restoration success. However, mitigation of human influence will only benefit a given species where static habitat characteristics are suitable for that species and where potential source populations are within the range of their dispersal capability. We used spatial autoregressive habitat models to simulate the effect of watershed-scale stream restoration on the distributions of six sediment-sensitive fish species in Wisconsin, USA, streams. These models consider the probability of occurrence of a species in a given stream segment as a function of characteristics of that segment as well as the characteristics of neighboring segments. Populations of individual species are predicted to be restorable in 0.2%-2.8% of Wisconsin streams. Streams with high restoration potential for one or more species generally have high watershed human land use but are also closely connected through the stream network to relatively undisturbed streams. These results indicate that habitat restoration for nongame stream fishes will be most effective when it builds onto existing suitable habitat because of both dispersal limitation and spatial autocorrelation of habitat characteristics.
Article
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The degradation of inland aquatic habitats caused by decades of human activities has led to worldwide efforts to rehabilitate freshwater habitats for fisheries and aquatic resources. We reviewed published evaluations of stream rehabilitation techniques from throughout the world, including studies on road improvement, riparian rehabilitation, floodplain connectivity and rehabilitation, instream habitat improvement, nutrient addition, and other, less-common techniques. We summarize current knowledge about the effectiveness of these techniques for improving physical habitat and water quality and increasing fish and biotic production. Despite locating 345 studies on effectiveness of stream rehabilitation, firm conclusions about many specific techniques were difficult to make because of the limited information provided on physical habitat, water quality, and biota and because of the short duration and limited scope of most published evaluations. Reconnection of isolated habitats, floodplain rehabilitation, and instream habitat improvement have, however, proven effective for improving habitat and increasing local fish abundance under many circumstances. Techniques such as riparian rehabilitation, road improvements (sediment reduction), dam removal, and restoration of natural flood regimes have shown promise for restoring natural processes that create and maintain habitats, but no long-term studies documenting their success have yet been published. Our review demonstrates that the failure of many rehabilitation projects to achieve objectives is attributable to inadequate assessment of historic conditions and factors limiting biotic production; poor understanding of watershed-scale processes that influence localized projects; and monitoring at inappropriate spatial and temporal scales. We suggest an interim approach to sequencing rehabilitation projects that partially addresses these needs through protecting high-quality habitats and restoring connectivity and watershed processes before implementing instream habitat improvement projects.
Article
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The River2D two‐dimensional hydraulic and habitat model was used to simulate fall‐run chinook salmon (Oncorhynchus tschawytscha) spawning and fry and juvenile rearing habitat before and after restoration of stream channel sites for a range of streamflows on the Merced River and Clear Creek, California. For the Merced River, hydraulic and structural data were collected for four sites before and after restoration, representing all habitat types within the restoration reach. Habitat simulated for these sites was extrapolated to the entire restoration reach based on habitat mapping. For Clear Creek, hydraulic and structural data were collected for four sites before restoration and pre‐restoration habitat was simulated. The topographic plan for the restoration was used to simulate habitat after restoration. While the restoration generally increased spawning habitat, it was less successful for rearing habitat. The results of this modeling show how they can be used in a cost‐effective adaptive management framework to evaluate restoration project design prior to construction.
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Summary 1. Increasingly, river managers are turning from hard engineering solutions to ecologi- cally based restoration activities in order to improve degraded waterways. River resto- ration projects aim to maintain or increase ecosystem goods and services while protecting downstream and coastal ecosystems. There is growing interest in applying river restoration techniques to solve environmental problems, yet little agreement exists on what constitutes a successful river restoration effort. 2. We propose five criteria for measuring success, with emphasis on an ecological perspective. First, the design of an ecological river restoration project should be based on a specified guiding image of a more dynamic, healthy river that could exist at the site. Secondly, the river's ecological condition must be measurably improved. Thirdly, the river system must be more self-sustaining and resilient to external perturbations so that only minimal follow-up maintenance is needed. Fourthly, during the construction phase, no lasting harm should be inflicted on the ecosystem. Fifthly, both pre- and post- assessment must be completed and data made publicly available. 3. Determining if these five criteria have been met for a particular project requires development of an assessment protocol. We suggest standards of evaluation for each of the five criteria and provide examples of suitable indicators. 4. Synthesis and applications. Billions of dollars are currently spent restoring streams and rivers, yet to date there are no agreed upon standards for what constitutes ecolog- ically beneficial stream and river restoration. We propose five criteria that must be met for a river restoration project to be considered ecologically successful. It is critical that the broad restoration community, including funding agencies, practitioners and citizen restoration groups, adopt criteria for defining and assessing ecological success in restoration. Standards are needed because progress in the science and practice of river restoration has been hampered by the lack of agreed upon criteria for judging ecological success. Without well-accepted criteria that are ultimately supported by funding and implementing agencies, there is little incentive for practitioners to assess and report restoration outcomes. Improving methods and weighing the ecological benefits of various restoration approaches require organized national-level reporting systems.
Article
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Effects of four types of habitat improvement structures have been evaluated in Låktabäcken Creek, a steep and infertile brown trout, Salmo trutta L., stream in Northern Sweden. Boulder dams proved to be the most efficient structure, increasing brown trout densities by up to three times and standing crop by up to five times their original values. Log deflectors gave similar effects on standing crop while boulder groupings and boulder deflectors seemed to be inefficient. Older/larger fish were primarily favoured. No increase in growth or enhanced condition has been registered. Obviously, profitable stream positions for older fish were lacking in Läktabäcken Creek. An increase in the amount of cover and an increase in the winter survival might be secondary effects of alterations.
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Restoration projects are often developed with little consideration for understanding their effects on wildlife. We contend, however, that monitoring treatment effects on wildlife should be an integral component of the design and execution of any management activity, including restoration. Thus, we provide a conceptual framework for the design and implementation of monitoring studies to understand the effects of restoration on wildlife. Our underlying premise is that effective monitoring hinges on an appropriate study design for unbiased and precise estimates of the response variables. We advocate using measures of population dynamics for response variables given that they provide the most direct measures of wildlife status and trends. The species to be monitored should be those constituting an assemblage of umbrella species that represent the range of spatial and functional requirements of wildlife in a restored ecological system. Selection of umbrella species should be based on strong empirical evidence that justifies their usage. We also advocate that monitoring be designed as true experiments or quasi-experiments rather than as observational studies to allow for stronger inferences regarding the effects of restoration on wildlife. Our primary message is that if monitoring is to be done, it must be scientifically based.
Article
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Establishment success of invasive species depends largely on the size of the initial source populati on because small populations are more likely to fail due to stochastic or inverse density-dependent Allee effects. However, there are difficulties involved in using propagule pressure as an explanatory variable to account for establishment success because records concerning the size of initial source populations are typically (i) non-existent, (ii) only rough estimates and/or (iii) based on indirect measurements. The focus of this study was the establishment success of a deliberately introduced non-native salmonid, Salvelinus fontinalis as a function of actual site-specific propagule pressure. Additionally, we investigated whether newly released fish located suita ble habitat patches, potentially facilitating the spread of the invader across Finnish stream systems. We found that the propagule pressure leading to highly successful establishment amounted to approximately 8000 released individuals. Additionally we also noted that one fourth of the newly introduced fish rapidly located suitable habitat patches (small tributaries) during initial dispersal, thus potentially increasing establishment success and the spread of the invader. The results suggest that by considering both propagule pressure and initial dispersal it will be possible to understand the latter stages of the invasion process, eventually leading to an improved capability in predicting successful invaders and sites that will be invaded.
Article
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Summary Drought is a natural disturbance of aquatic ecosystems and can be a major factor in structuring aquatic communities. For individuals, populations and communities to persist in disturbed environments, they must have refuge from disturbance or disturbance must be minimal. Refugia convey spatial and temporal resistance or resilience in the face of disturbance, but the role of refugia in aquatic systems remains poorly understood. We review available literature on aquatic refugia for fishes in order to synthesise current knowledge and provide suggestions for needed research. Our objectives were to clarify definitions of disturbance and refugia in the context of drought in aquatic systems, review how refuge habitats influence fish community structure, and consider the potential impact of refugia on fish population and community dynamics during drought. Droughts cause a decrease in surface area/volume and an increase in extremes of physical and chemical water quality parameters. These conditions are linked with biotic interactions that structure the community of fishes residing in low-flow or dry season refugia by increasing mortality rates, decreasing birth rates and/or increasing migration rates. Many aquatic organisms seek refuge from disturbance and/or have adaptations (e.g. physiological tolerance) that provide refuge. Drought in aquatic systems leads to shifts in refugia spacing and connectance at multiple spatial and temporal scales. Refuge size, disturbance intensity, and mobility of organisms is predicted to play a large role in population persistence. We expect that refuge habitats will experience net immigration during drying and net emigration after rewetting, with the opposite occurring in surrounding habitat patches. Population dynamics of fishes using refugia during drought are best modelled by modified source-sink dynamics, but dynamics are likely to change with spatial scale.
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1. Most Finnish streams were channelised during the 19th and 20th century to facilitate timber floating. By the late 1970s, extensive programmes were initiated to restore these degraded streams. The responses of fish populations to restoration have been little studied, however, and monitoring of other stream biota has been negligible. In this paper, we review results from a set of studies on the effects of stream restoration on habitat structure, brown trout populations, benthic macroinvertebrates and leaf retention.
Article
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Restoration ecology is a young academic field, but one with enough history to judge it against past and current expectations of the science's potential. The practice of ecological restoration has been identified as providing ideal experimental settings for tests of ecological theory; restoration was to be the ‘acid test’ of our ecological understanding. Over the past decade, restoration science has gained a strong academic foothold, addressing problems faced by restoration practitioners, bringing new focus to existing ecological theory and fostering a handful of novel ecological ideas. In particular, recent advances in plant community ecology have been strongly linked with issues in ecological restoration. Evolving models of succession, assembly and state-transition are at the heart of both community ecology and ecological restoration. Recent research on seed and recruitment limitation, soil processes, and diversity–function relationships also share strong links to restoration. Further opportunities may lie ahead in the ecology of plant ontogeny, and on the effects of contingency, such as year effects and priority effects. Ecology may inform current restoration practice, but there is considerable room for greater integration between academic scientists and restoration practitioners.
Article
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1. Degradation of stream habitat because of anthropogenic activities (e.g. channelisation) has had a dramatic impact on fluvial environments and their biota, and as a consequence, increasing effort has been directed towards the restoration of degraded rivers. However, a major problem is that the success (or failure) of restoration has been rarely tested using a well-designed monitoring programme to allow reliable detection of an impact, if any exists. We used a spatially and temporally replicated, balanced Before-After-Control-Impact design to assess the impact of stream habitat rehabilitation on the densities and growth of brown trout of three age-classes in North Finnish forest streams. 2. Three separate sections in each of six streams were selected for the study. After 3 years of pre-rehabilitation monitoring, two randomly selected sections in each stream were restored; one using large woody debris and boulders and the other using only boulders. A third section remained as an unmodified control. Monitoring of fish densities continued for 3 years after rehabilitation. 3. Rehabilitation clearly increased streambed complexity, but did not have detectable effects on brown trout stocks in either of the rehabilitation schemes (LWD or stones), except for age-2+ and older fish which decreased in abundance compared to control reaches. A severe drought after rehabilitation in late summer 2002 reduced densities of trout to a low level in all streams, overriding any local effects of rehabilitation. Rehabilitation structures seemed to provide some safeguard against drought for age-2 and older, but not for the younger age-classes. 4. Our results add to the growing body of literature suggesting that large-scale regional factors may overwhelm local management efforts. To be successful in the future, stream rehabilitation schemes must include drought refuge areas for fish and other stream biota.
Article
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Log floating in the 19th to mid 20th centuries has profoundly changed the environmental conditions in many northern river systems of the world. Regulation of flow by dams, straightening and narrowing of channels by various piers and wing dams, and homogenization of bed structure are some of the major impacts. As a result, the conditions for many riverine organisms have been altered. Removing physical constructions and returning boulders to the channels can potentially restore conditions for these organisms. Here we describe the history of log driving, review its impact on physical and biological conditions and processes, and predict the responses to restoration. Reviewing the literature on comparable restoration efforts and building upon this knowledge, using boreal Swedish rivers as an example, we address the last point. We hypothesize that restoration measures will make rivers wider and more sinuous, and provide rougher bottoms, thus improving land-water interactions and increasing the retention capacity of water, sediment, organic matter and nutrients. The geomorphic and hydraulic/hydrologic alterations are supposed to favor production, diversity, migration and reproduction of riparian and aquatic organisms. The response rates are likely to vary according to the types of processes and organisms. Some habitat components, such as beds of very large boulders and bedrock outcrops, and availability of sediment and large woody debris are believed to be extremely difficult to restore. Monitoring and evaluation at several scales are needed to test our predictions.
Article
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In the northern coast of Spain there are rivers with Atlantic salmon populations. In the upper reaches of one of these streams, river Pas, the effectiveness of habitat enhancement measures was evaluated, under different instream flow conditions. By means of the Instream Flow Incremental Methodology and using a two dimensional hydraulic model (River2D, Steffler P (2000) Software River2D. Two Dimensional Depth Averaged Finite Element Hydrodynamic Model. University of Alberta, Canada), the potential value of stream habitat for different salmon development stages requirements was measured by Weighted Useable Area (WUA). This habitat evaluation was carried out for the unmodified stream reach, which represent the control or natural conditions. Habitat improvement measures (alternate deflectors and low dams) were simulated in the original riverbed topography. Over this modified base, habitat was estimated running River2D again. By comparing the salmon habitat evaluations in the control conditions with those obtained under those improvement conditions we have been able to assess the effectiveness of each one, and the instream flow environment at which maximum improvement is reached. The maximum habitat improvement was obtained around 10m3/s for the adult salmon, and for the fry and parr it was around 6m3/s. However, the habitat simulation results show that with both improvement measures, under a natural flow regime the mean annual habitat increases around 1% of the WUA in relation to the control conditions, which is not a significant improvement. A similar small WUA increase was obtained when changing the bed topography, considering geomorphological adjustments due to the new erosion and sedimentation areas caused by the presence of these structures. Therefore, these types of habitat improvement measures are not recommended in these stream reaches.
Book
Monitoring Ecological Impacts provides the tools needed by professional ecologists, scientists, engineers, planners and managers to design assessment programs that can reliably monitor, detect and allow management of human impacts on the natural environment. The procedures described are well grounded in inferential logic, and the statistical models needed to analyse complex data are given. Step-by-step guidelines and flow diagrams provide the reader with clear and useable protocols, which can be applied in any region of the world and to a wide range of human impacts. In addition, real examples are used to show how the theory can be put into practice. Although the context of this book is flowing water environments, especially rivers and streams, the advice for designing assessment programs can be applied to any ecosystem.
Article
Environmental changes caused by human activities, and especially the damming of many rivers flowing into the Baltic Sea for hydroelectric power, have had serious consequences for stocks of migratory fish in the last 50 yr. The chapter is concerned with two methods for enhancing salmon and trout stocks: restoration of dredged rapids for spawning and nursery areas, and stocking of the rapids with parr. The results of restoration and stocking in Finnish rivers are discussed. -J.W.Cooper
Chapter
Publisher Summary This chapter presents that in many respects, the rivers in the Fennoscandian Shield ecoregion are in better shape than the rivers in most other European ecoregions. This fact is in most parts related to its low population density and the relatively low intensity of land use in the catchment. Human population size and the intensity of pressure on nature tend to go hand in hand and the rivers in the ecoregion reflect this general picture. Moreover, due to the prevailing climate characterized by relativatively high wetness, running waters are regionally abundant and the pollution situation is in most cases not serious. However, there are numerous environmental problems creating challenges for future developments in the ecoregion. Despite pressure from a multitude of human impacts that the chapter outlines, the situation in the Fennoscandian Shield ecoregion is even improving, in some respects, as negative effects of environmental impacts become better understood, legislation is made more efficient, and ruthless exploitation exceptional.
Article
The theory leading to the maximum likelihood (ML) estimation of population size from removal data is reviewed. The assumptions of the removal method are that changes in population size occur only through capture, and the probability of capture is equal for all individuals in a population during the removal sequence. A modification of the multinomial model is proposed and a new estimator developed. In the new model the likelihood density of the probability of capture is weighted with a beta prior. The case where α = β = 1 (uniform prior) is compared with ML estimation and found to have lower bias and variance. The new method, unlike previous methods, does not fail for any catch vector thus avoiding the substitution of the total catch for the estimate of N when infinite estimates occur. The assumptions that result from applying large sample theory while estimating the variance of ML estimates are reviewed, and a condition presented for the inadequacy of asymptotic variance formulae when using the weighted estimator (α = β = 1). Examples illustrating the use of the new method are given; one example illustrates the use of the new method when previous methods fail. Various assumption violations are investigated and the new method is found to be more robust against the violation of assumptions than previous methods.
Article
Restoration schemes often rely on the assumption that enhancing habitat complexity through addition of in-stream structures such as boulders and woody debris leads to increased biodiversity, but evidence for this assumption is scarce. We compared structural heterogeneity and fish and invertebrate diversity at restored, unrestored, and reference sites on tributaries of the Ume River, northern Sweden, where several kilometers of streams have been restored from channelization through placement of boulders into the channel. Structural heterogeneity at the study sites was assessed using a contour tracer at two spatial resolutions likely to be affected by restoration. These are the patch scale (0.7 m), reflecting substratum characteristics, and the reach scale (50 m), reflecting general channel topography. Fish and invertebrate samples collected via electroshocking were used to assess taxonomic richness, taxonomic density, evenness, and assemblage composition at the study sites. Measures of structural heterogeneity were substantially higher at restored relative to channelized sites; however, components of fish and invertebrate diversity were similar between these treatments. At restored sites, measures of structural heterogeneity and fish and invertebrate diversity were consistent with, or slightly exceeded reference levels. This implies that local (patch to reach) heterogeneity did not structure fish and invertebrate assemblages in the study streams. Our results suggest that restoration might have little beneficial effect on biodiversity if the restoration schemes (and the original impact under amelioration) do not affect structural heterogeneity relevant to the target
Article
The number and identity of fish species occurring at a site at a particular time provide basic information for assessing biological integrity, inferring fish assemblage - environment relationships, and determining biodiversity patterns. Conclusions are often dependent on how sufficiently species richness and composition of fish assemblages are characterized by sampling. The proportion of total species richness obtained in a sample is an explicit measure of sampling sufficiency. However, because total species richness (TSRtru) at a site is often unknown, sampling sufficiency cannot be determined directly. To overcome this difficulty, we developed a new approach, which is based on a relationship between the proportion of TSRtru or %TSRtru and the similarity among replicate samples (autosimilarity). With autosimilarity measured with the Jaccard coefficient (JC), a simple relationship was established: %TSRtru = 100JC. Fourteen sites where TSRtru was reached or approached during sampling were selected from four surveys to validate this relationship. We used the approach to estimate the sample sizes required for 90, 95, and 100% TSRtru, indicating that widely differing sampling efforts among sites are needed to obtain the same proportion of the local species pool. The results strongly support the use of the new approach in evaluating sampling sufficiency in stream and river fish surveys.
Article
We provide a quantitative examination of the utility of escapement data for monitoring changes in salmonid populations caused by habitat alterations. We used Monte Carlo simulations to determine the precision, duration of monitoring, and the effect size required to achieve acceptable statistical inferences based on before-after (BA) and before-after-control-impact (BACI) comparisons. There was generally less than a 50% chance of detecting a population response unless the population change was large (more than a twofold increase) or the post-treatment monitoring period long (>10 years). Statistical power was improved by increasing the precision of escapement estimates, but the extent of improvement was dependent on the magnitude of population response to treatment, the duration of monitoring, and the extent of natural variability in abundance. BACI comparisons generally had a 10-15% lower probability of detecting a population change than BA comparisons unless the degree of covariation in survival rates between control and treatment stocks was very strong. Autocorrelation in error, simulating patterns of high and low survival rates over time, generally reduced power by 5-15%. Our results identify the conditions where escapement information can be used to make reliable inferences on salmonid population changes and provides a means for evaluating alternative monitoring designs.
Article
We applied a randomized factorial design with three sedimentation treatments (high, low, and zero sediment addition) and two predation-risk levels (predator present or absent) to assess whether the survival and emergence of brown trout (Salmo trutta) alevins were affected by sedimentation and (or) chemical cues from a predatory fish (burbot, Lota lota). In this laboratory experiment, survival was only related to the finest organic sediment fraction (<0.074 mm), which decreased embryo survival, although only constituting less than 1.5% of all sediments. Control fish tended to postpone emergence when exposed to predator odour, whereas fish in the high-sedimentation treatment showed no response to predators. Alevins that received high sedimentation had larger yolk sacs at emergence compared with control fish. Sedimentation may thus have serious fitness consequences on salmonids, as fry with larger yolk sacs are poor swimmers and therefore more vulnerable to predation or downstream displacement. Fine-sediment deposition from the catchment or stream banks may cause a serious threat to salmonid populations, and more effective erosion control is needed to reduce inputs of fine sediments to river habitats.
Article
We examined the effect of an increase in large wood on the summer population size, smolt abundance, and freshwater survival of steelhead (Oncorhynchus mykiss), coastal cutthroat trout (Oncorhynchus clarki clarki), and coho salmon (Oncorhynchus kisutch). We examined these parameters for five brood years prior to the addition of wood and five brood years after in Tenmile Creek, a direct ocean tributary on the Oregon coast. Over the same time frame, a nearby reference stream, Cummins Creek, was also sampled for the same parameters. The input of large wood into Tenmile Creek resulted from a planned habitat restoration project in 1996 and an unplanned addition of wood from a winter storm the same year. Steelhead smolt abundance, steelhead freshwater survival, and coho salmon freshwater survival increased in Tenmile Creek after the input of large wood. Steelhead age-0+ summer populations and steelhead smolt populations increased in the reference stream, although steelhead freshwater survival did not. Coho salmon populations remained unchanged in the reference stream. Our results illustrate the potential shortcomings of the before-after-control-impact study design under field conditions and the potential for misinterpreting results had we employed a more modest sampling plan.
Article
Aim We investigated watershed-scale abiotic environmental factors associated with population establishment of one of the ‘world’s 100 worst alien invaders’ on a temperate Atlantic island. Within the context of the conservation implications, we aimed to quantify (1) the early history and demographics (numbers and origins) of human-mediated brown trout (Salmo trutta) introductions, (2) the current distribution of established populations, and (3) the watershed-scale environmental factors that may resist or facilitate trout establishment.
Article
Methods used to estimate fish abundance in streams should be chosen based on the precision required by the study, the available time, and the number and kinds of species targeted. When entire assemblages of predominantly small, nongame fishes are to be sampled, most existing procedures have limitations. We compared estimates of species richness, abundance, and assemblage structure based on catch per effort (CPE) during a single tow-barge electrofishing sample versus intensive tow-bare electrofishing removal sampling procedures with block nets in paired, contiguous stations on nine streams in southern Wisconsin. Use of block nets had little effect on CPE during single upstream electrofishing passes; for stations approximately 35 times the mean stream width in length, the overall influence of fish entering and leaving the station appeared to be negligible. Estimates of abundance, based on total catch and based on the removal model, were higher in removal stations than in CPE stations. However, estimates of abundance between stations were correlated, and estimates of species richness and assemblage structure were similar. Relative to removal sampling, a single upstream CPE pass adequately assessed fish species richness, abundance, and assemblage structure in small streams.
Article
The occurrence and density of ≥ 1+ brown trout, Salmo trutta L., and their relationship with prevailing instream and catchment characteristics were studied in 50 small forest streams, partially dredged for forest ditching. The occurrence of trout at a stream site was largely determined by the abundance of pools, size of upper catchment and water pH. Moreover, at sites where trout occurred, the abundance of pools was lower at dredged locations than at those in a natural state. In riffles in a natural state, there was a positive relationship between trout density and three instream variables: the abundance of stream pools, cascades and instream vegetation, while an inverse relationship was found with the abundance of substratum of 2–10 cm in diameter. Of the catchment variables, correspondingly, the proportion of forest in the upper catchment was positively related and the proportion of peatland negatively related to trout density. No significant regression model could be fitted for dredged riffles. The possibility of enhancing trout populations in dredged riffles is discussed.
Article
A semi-quantitative technique of assessing trout, Salmo trutta L., and juvenile Atlantic salmon, Salmo salar L., stocks in small rivers is described and evaluated against a commonly used quantitative method. The results indicate that for 0+ and >0+ juvenile salmon and trout a log10 n+1 transformed linear regression accounted for between 68.6% and 90.2% of the total variance in the relationship between the semi-quantitative and the quantitative result. The use of a categorization system is recommended and the applicability of the technique to an extensive juvenile salmonid monitoring programme is described.
Article
Stream channel morphology and hydraulic conditions were measured before and after channel modification and boulder structure placements in a channelized boreal river to determine whether more favourable rearing habitat for brown trout, Salmo trutta L., was created. The assessment was performed using physical habitat simulation (PHABSIM) procedures based on summer and winter habitat preferences of brown trout for depth, velocity and substrate. The results showed that the availability of potential physical trout habitat can be increased in the study river at simulated low and moderate flow conditions by reconstruction of the river bed and placing instream boulder structures. The resulting diversity of depth and velocity conditions created a spatially more complex microhabitat structure. Improved habitat conditions were able to sustain a larger trout population. Hydraulic habitat models, like the PHABSIM framework, seem to be a suitable procedure to evaluate the benefits of physical habitat enhancement.
Article
Many successful invasions have taken place in systems where harmful disturbance has changed habitat conditions. However, less attention has been paid to the role of habitat restoration, which modifies habitats and thus also has the potential to facilitate invasions. We examined whether in-stream habitat restorations have the potential to either facilitate or resist invasion by two widely introduced non-native stream salmonids, Salvelinus fontinalis Mitchill and Oncorhynchus mykiss Walbaum, in Finland. A physical habitat simulation system was used to calculate whether the habitat area for the target species increased or decreased following the restorations. For comparison, we also reported results for four native stream fish species. The simulations showed that the restored streams provided the highest amount of usable habitat area for the native species, particularly for Salmo salar L. and Gottus gobio L. However, it was interesting to note that the restorations significantly increased habitat quality for the two non-native species, especially at low flows. Nevertheless, the non-native species had the lowest amount of usable habitat area overall. The modeling results indicated that not only habitat destruction but also habitat restoration could contribute to the spread of non-native species. Fisheries and wildlife managers should be aware of the possibility, when restoring habitats in order to preserve native ecosystems, that non-native species could manage to gain a foothold in restored habitats and use them as population sources for further spread. Knowing the widespread negative effect of non-native species, this risk should not be underestimated.
Article
Abstract Stream fish assemblages were sampled by multiple-pass electrofishing and supplementary seine netting in 31 sites in the Johnstone River, north Queensland and 28 sites in the Mary River, southeastern Queensland to determine the sampling effort required to adequately describe the assemblages in terms of fish abundances, species composition and assemblage structure. A significantly greater proportion of the total number of fishes present at each site was collected by the first electrofishing pass in the Mary River (46%) than in the Johnstone River (37%) and this difference was suggested to be due to higher water conductivity in the former river. The mean proportion of the total species richness detected by the first pass was also significantly higher in the Mary River than in the Johnstone River (89% and 82%, respectively). Multivariate comparisons offish assemblage structure revealed that data collected by the first electrofishing pass poorly estimated the actual assemblage structure within a site and that up to three passes were required for estimates of assemblage structure to stabilize. This effect was evident for comparisons based on both absolute abundance and relative abundance data and was particularly marked for comparisons based on presence/absence data. This latter result suggests that, even though most species were detected on the first pass, the addition of rare species by subsequent passes had an important effect on the resultant description of assemblage structure. Supplementary seine netting had a greater effect on the determination of assemblage structure in the Mary River than in the Johnstone River. The results are discussed with reference to sampling design in studies of stream fish assemblages and a sampling protocol is recommended that enables the accurate determination of abundance, richness and assemblage structure in small- to medium-sized streams.
Article
Generalized habitat criteria for spawning sites of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) using depth, water velocity and substrate size were created based on published information. In addition, information on critical intragravel conditions for egg development was summarized. Salmon spawned mostly in relatively deep, swift-velocity habitats (20–50 cm, 35–65 cm s−1), whereas trout selected slightly shallower and slower flowing spawning sites (15–45 cm, 20–55 cm s−1). Salmon and trout preferred pebbles (16–64 mm) for spawning. The minimum oxygen concentration for successful incubation of eggs varies with the developmental stage of eggs, and supply of it may be reduced by deposited fine sediment. Habitat criteria for spawning sites are narrower than those for small juveniles; therefore the use of separate criteria is recommended. In addition to the traditional habitat criteria variables (depth, water velocity, substrate), the critical intragravel factors affecting egg survival should be incorporated in biologically meaningful criteria for spawning habitat modelling. Copyright © 2008 John Wiley & Sons, Ltd.
Article
Abstract Data from Lake Ontario tributaries were used to evaluate the efficacy of single-pass backpack electric fishing for stream fish monitoring by: testing the relationship between single-pass catch-per-unit-effort (CPUE) and multiple-pass-based population estimates; comparing species richness estimates derived from single-pass and multiple-pass data and assessing the concordance of fish assemblage patterns described using single-pass and multiple-pass data. Significant correlations were calculated between single-pass CPUE and removal-based population estimates for total catch, 15 species, six taxonomic families, five feeding and four reproductive guilds and tolerant/intolerant species. Strong correlations were more commonly associated with the abundance of individual species than other metrics. Capture probability was not affected by stream size or habitat complexity for most measures. Species accumulation curves and significant correlations (r2 = 0.9) between single-pass and multiple-pass electric fishing indicate that single-pass surveys provide a representative index of species diversity. In addition, within and among-site variation in fish community composition based on single-pass and multiple-pass data were similar.
Article
We used strong inference with Akaike's Information Criterion (AIC) to assess the processes capable of explaining long-term (1984–1995) variation in the per capita rate of change of mottled sculpin (Cottus bairdi) populations in the Coweeta Creek drainage (USA). We sampled two fourth-and one fifth-order sites (BCA [uppermost], BCB, and CC [lowermost]) along a downstream gradient, and the study encompassed extensive flow variation. Physical habitat availability varied significantly both within and among the sites. Sculpin densities in all sites were highly stable (coefficients of variation 0.23–0.41) and sampling variability was low (coefficients of variation 0.11–0.15). Population sta-bility was positively associated with habitat stability, and the only significant correlations of population parameters among sites involved juveniles. Sculpin densities were signifi-cantly higher in BCB than in CC. The data suggest that, despite their proximity, the dynamics of populations within the sites are being determined by small-scale (i.e., 30–50 m) rather than broad-scale spatial processes. Both AIC and Dennis and Taper analyses indicated that simple density dependence had the greatest ability to explain variation in r for all life-history classes in all sites (AIC, seven of nine cases; Dennis and Taper, nine of nine cases). Multiprocess models had little explanatory power. When adults were removed from two sites, juvenile sculpin shifted into microhabitats formerly occupied by adults. No shifts occurred in control sites. Consequently, it is likely that the patterns of density dependence observed in all three sites were a consequence of intraspecific competition for space. Our findings argue for a multitiered approach to the study of population variation, one that encompasses long-term monitoring, spatial variation, and experimental testing of potential mechanisms.
Article
1There is controversy over how the success of ecological restoration should be measured. Traditionally, emphasis has been placed on species diversity and other community attributes, whereas the restoration of ecosystem processes has received less attention. Here, we combine replicated field experiments and a field survey to provide an ecosystem-level measure of stream restoration success.2Numerous headwater streams in Finland, and in many other parts of the world, have been channelized for timber transport, resulting in channels with simplified structure and flow. Recently, programmes have been launched to restore these streams to their pre-channelization condition. While the efficacy of restoration in improving fish habitat has been tested, little is known about effects on other stream biota or on the retention of leaf litter, despite its importance in trophic dynamics of forested headwater streams. Using a before-after-control-intervention (BACI) designed experiment with multiple reference and experimental streams, we examined restoration-induced changes in retention efficiency by conducting leaf-release experiments before (1993) and after (1996) restoration.3Substrate heterogeneity increased, but moss cover decreased dramatically following restoration. Retention efficiency in restored streams was higher than in channelized, but lower than in natural, streams. Algae-feeding scrapers were the only macroinvertebrate group whose density increased significantly after restoration.4Aquatic mosses were a key retentive feature in both channelized and natural streams, but their importance to retention was strikingly reduced by restoration. During restoration work, mosses are detached from large areas of the stream bed, exposing bare stone surfaces for colonization by periphytic algae.5A more effective restoration technique would involve the use of moss transplants, or the addition of large woody debris, to increase retentiveness and thus enhance the availability of organic material to benthic consumers. This case study on rivers illustrates how restoration projects benefit from an ecosystem perspective and from measures of ecosystem processes in assessing restoration success.
Article
1.Five side-channels and small tributaries of the River Avon (Hampshire, UK) were examined between spring 1999 and spring 2000 using point abundance sampling by electrofishing to determine the status of fish listed in Annex II of the EC Habitats Directive prior to habitat management works to enhance spring feeding habitat of wading birds.2.Seasonal patterns of abundance and microhabitat use of bullhead Cottus gobio and accompanying fish species were examined. Parr of Atlantic salmon Salmo salar were sufficiently abundant for microhabitat analysis at one site only. Only two specimens of brook lamprey Lampetra fluviatilis were observed, one at each of two sites. Bullhead was amongst the most abundant fish species at all five sites, 0+ bullhead predominating.3.Bullhead microhabitat preferences were generally similar at all five sites, but seasonal variations were observed, as was the case for the accompanying fish species, which included dace Leuciscus leuciscus, chub Leuciscus cephalus, stone loach Barbatula barbatula, roach Rutilus rutilus, and threespine stickleback Gasterosteus aculeatus.4.Bullhead conservation status is discussed, in particular the possible exemption of British bullhead populations, such as already granted for those of Finland, from Annex II of the Habitats Directive. © Crown Copyright 2004 Reproduced with the permission of Her Majesty's Stationary Office. Published by John Wiley & Sons, Ltd.
Article
The influence of water quality, physical habitat and species richness on the occurrence, density and size of brown trout at 216 stream sites in southern Sweden was studied. Discriminant analysis showed that the occurrence of trout at a locality was largely determined by oxygen conditions and medium-sized substrata. At localities where trout occurred, the density of + trout was highest in narrow streams with high oxygen concentrations. For older trout, >0+ in age, stream size and temperature were negatively related to density. Biotic factors also appeared to affect trout density, as trout density was inversely related to abundance of predators and coexisting species. Even intraspecific competition appeared to be important as length of 0+ trout was inversely related to trout density. It is suggested that improvements of water quality may be an effective way to restore sea trout populations in southern Sweden, especially in narrow streams where smolt production has the highest potential.
Article
Inappropriate land use practices, pollutants, exploitation, and overpopulation have simplified stream habitats and degraded water quality worldwide. Management agencies are now being tasked to ameliorate impacts and restore stream “health,” yet there is a dearth of rigorous scientific methods and theory on which to base sound restoration design and monitoring. Despite this, many localized restoration projects are being constructed to stabilize erosion and enhance habitat heterogeneity in streams. Many restoration attempts adopt the paradigm that increasing habitat heterogeneity will lead to restoration of biotic diversity, yet there have been few studies that have manipulated variation of a physical parameter independent of the mean to isolate the effects of heterogeneity per se. We conducted a field experiment to mimic restoration of habitat heterogeneity in a shallow. stony stream. By using an experimental approach rather than a detailed assessment of existing restoration work, we were able to control the starting conditions of replicate riffles so that organism responses could be unambiguously attributed to the heterogeneity treatments. We successfully manipulated the variability of streambed particle sizes and consequently near-bed flow characteristics of entire riffles. These factors define axes of habitat heterogeneity at scales relevant to the resident macroinvertebrate fauna. Despite this, we were unable to distinguish differences in community structure between high and low habitat heterogeneity treatments. Power analysis indicated that macroinvertebrate populations were more sensitive to individual site conditions at each riffle than to the heterogeneity treatments, suggesting that increasing habitat heterogeneity may be an ineffective technique if the restoration goals are to promote macroinvertebrate recovery in denuded streams. With extremely high variability between replicate riffles, monitoring programs for localized restoration projects or point source impacts are unlikely to detect gradual shifts in community structure until the differences between the reference and treatment sites are extreme. Innovative measurement of other parameters, such as ecosystem function variables (e.g., production, respiration, decomposition), may be more appropriate indicators of change at local scales.
Article
1. This paper introduces key messages from a number of papers emanating from the Second International Symposium on Riverine Landscapes held in August 2004 in Sweden, focusing on river restoration. Together these papers provide an overview of the science of river restoration, and point out future research needs. 2. Restoration tests the feasibility of recreating complex ecosystems from more simple and degraded states, thereby presenting a major challenge to ecological science. Therefore, close cooperation between practitioners and scientists would be beneficial, but most river restoration projects are currently performed with little or no scientific involvement. 3. Key messages emanating from this series of papers are: The scope, i.e. the maximum and minimum spatial extent and temporal duration of habitat use, of species targeted for restoration should be acknowledged, so that all relevant stages in their life cycles are considered. Species that have been lost from a stream cannot be assumed to recolonise spontaneously, calling for strategies to ensure the return of target species to be integrated into projects. Possible effects of invasive exotic species also need to be incorporated into project plans, either to minimise the impact of exotics, or to modify the expected outcome of restoration in cases where extirpation of exotics is impractical. 4. Restoration of important ecological processes often implies improving connectivity of the stream. For example, longitudinal and lateral connectivity can be enhanced by restoring fluvial dynamics on flood-suppressed rivers and by increasing water availability in rivers subject to water diversion or withdrawal, thereby increasing habitat and species diversity. Restoring links between surface and ground water flow enhances vertical connectivity and communities associated with the hyporheic zone. 5. Future restoration schemes should consider where in the catchment to locate projects to make restoration most effective, consider the cumulative effects of many small projects, and evaluate the potential to restore ecosystem processes under highly constrained conditions such as in urban areas. Moreover, restoration projects should be properly monitored to assess whether restoration has been successful, thus enabling adaptive management and learning for the future from both successful and unsuccessful restorations.
Article
Summary1. Faced with widespread degradation of riverine ecosystems, stream restoration has greatly increased. Such restoration is rarely planned and executed with inputs from ecological theory. In this paper, we seek to identify principles from ecological theory that have been, or could be, used to guide stream restoration.2. In attempts to re-establish populations, knowledge of the species’ life history, habitat template and spatio-temporal scope is critical. In many cases dispersal will be a critical process in maintaining viable populations at the landscape scale, and special attention should be given to the unique geometry of stream systems3. One way by which organisms survive natural disturbances is by the use of refugia, many forms of which may have been lost with degradation. Restoring refugia may therefore be critical to survival of target populations, particularly in facilitating resilience to ongoing anthropogenic disturbance regimes.4. Restoring connectivity, especially longitudinal connectivity, has been a major restoration goal. In restoring lateral connectivity there has been an increasing awareness of the riparian zone as a critical transition zone between streams and their catchments.5. Increased knowledge of food web structure – bottom-up versus top-down control, trophic cascades and subsidies – are yet to be applied to stream restoration efforts.6. In restoration, species are drawn from the regional species pool. Having overcome dispersal and environmental constraints (filters), species persistence may be governed by local internal dynamics, which are referred to as assembly rules.7. While restoration projects often define goals and endpoints, the succession pathways and mechanisms (e.g. facilitation) by which these may be achieved are rarely considered. This occurs in spite of a large of body of general theory on which to draw.8. Stream restoration has neglected ecosystem processes. The concept that increasing biodiversity increases ecosystem functioning is very relevant to stream restoration. Whether biodiversity affects ecosystem processes, such as decomposition, in streams is equivocal.9. Considering the spatial scale of restoration projects is critical to success. Success is more likely with large-scale projects, but they will often be infeasible in terms of the available resources and conflicts of interest. Small-scale restoration may remedy specific problems. In general, restoration should occur at the appropriate spatial scale such that restoration is not reversed by the prevailing disturbance regime.10. The effectiveness and predictability of stream ecosystem restoration will improve with an increased understanding of the processes by which ecosystems develop and are maintained. Ideas from general ecological theory can clearly be better incorporated into stream restoration projects. This will provide a twofold benefit in providing an opportunity both to improve restoration outcomes and to test ecological theory.