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1.
  1. A genetically distinct population of the Maloti minnow Pseudobarbus quathlambae (Lesotho's only endemic fish) is known only from the Mohale catchment, and was formerly abundant in the Senqunyane, Bokong and Jorodane rivers which flow into Mohale Reservoir.
  2. Situated ~4 km downstream of Mohale Reservoir, the Semongkoaneng waterfall has historically prevented larger fish species from moving upstream into areas inhabited by P. quathlambae. After the filling of the Mohale Reservoir in 2003, an inter‐basin transfer (IBT) linking it to Katse Reservoir was opened and in 2006 the smallmouth yellowfish Labeobarbus aeneus, a larger more aggressive species, was recorded in the reservoir, presumably introduced via the IBT.
  3. The objectives of the present study were to: (1) establish whether any additional non‐native fish species were present in the Mohale catchment; (2) ascertain whether L. aeneus has dispersed into the rivers flowing into Mohale Reservoir; and (3) gauge whether the Mohale population of P. quathlambae is in decline. Twenty‐eight sites situated on major rivers flowing into the reservoir, and four sites in the reservoir itself, were surveyed to evaluate changes in fish populations and habitat quality.
  4. Results indicate that P. quathlambae has all but disappeared from its natural range: only five individuals were recorded in the Jorodane and Bokong rivers, and none were recorded in the Senqunyane River – a former stronghold for the species. On the other hand, L. aeneus was recorded in all three rivers and is probably responsible for the decline of the P. quathlambae population, given that there does not appear to have been major deterioration in habitat conditions. Another non‐native fish, the Orange River mudfish Labeo capensis, was recorded in the Mohale catchment for the first time. Urgent conservation action is required to prevent the Mohale lineage of P. quathlambae from becoming extinct.
Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

2.
  1. Populations of the European shads Alosa alosa (Linnaeus, 1758) and Alosa fallax Lacépède, 1800 (Alosa spp.) are protected under legislation because of their vulnerability to human disturbances. In particular, river impoundments block their upstream migration, preventing access to spawning areas. Knowledge on the spatial extent of their spawning is important for informing conservation and river management plans.
  2. Determining the spatial extent of Alosa spp. spawning is challenging. They enter rivers over a 2‐3‐month period and the species potentially migrate different distances upstream. Capture and handling can be problematic, spawning events generally occur at night, and kick‐sampling for eggs is limited to shallow water. Assessing their spatial extent of spawning could, however, incorporate non‐invasive sampling tools, such as environmental DNA (eDNA).
  3. An eDNA assay for Alosa spp. was successfully developed, based on the cytochrome c oxidase subunit I gene segment and quantitative polymerase chain reaction (qPCR). Application in spring 2017 to the River Teme (River Severn catchment, western England) revealed high sensitivity in both laboratory and field trials. Field data indicated Alosa spp. spawning between May and June, with migrants mainly restricted to areas downstream of the final impoundment.
  4. eDNA can thus be used as a non‐invasive sampling tool to determine the freshwater distribution of these fishes in Europe, enhancing their conservation at local and regional scales.
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3.
  1. This study reports the first known record of breeding of the Critically Endangered Twee River redfin ‘Pseudobarbuserubescens in an artificial impoundment. This followed an introduction of 48 individuals into a 10 ha impoundment within the species' native range more than a decade ago.
  2. Sampling the impoundment using three fyke nets set overnight yielded 2838 P. erubescens, which included both juveniles and adults capable of spawning. Fork length measurements of a subsample of 250 individuals ranged from 29 to 125 mm with length cohorts indicating multiple spawning events.
  3. This demonstrates that this species can successfully reproduce in lentic environments and suggests that artificial impoundments could be stocked to provide refugia for P. erubescens and other highly threatened small cyprinids while conservation strategies are developed to mitigate against habitat loss resulting from alien fish invasions, increased human use of water, and from climate change in rivers.
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4.
The serial discontinuity concept (SDC) proposes that hypolimnetic‐releasing impoundments cause major disruptions to the naturally occurring physical, chemical and biological gradients of rivers but that this impact diminishes with distance downstream. Such a gradient in discharge, flow velocity and temperature regime occurs below a large hypolimnetic‐releasing impoundment, the Hume Dam, on the River Murray in south‐eastern Australia. To examine the effects of this disturbance gradient on a warm‐water large‐bodied freshwater fish, the Murray cod (Maccullochella peelii), a bioenergetics model was developed and calibrated to explore energy expended under differing water velocities and temperature regimes. Model simulations predicted negative growth of juveniles directly downstream of the impoundment, due largely to the energetic costs associated with active and, to a lesser extent, standard metabolism outweighing the achievable energetic gains through food consumption. As flow velocity and temperature regimes became more favourable downstream, so did the simulated growth of the species. It was not until +239 km downstream of the impoundment that the model predicted that flow velocity and temperature regimes were suitable for greater weight gains. The modelled growth responses of juvenile Murray cod are consistent with the predictions of the SDC, emphasising that changes in the bioenergetics of individuals are likely to be reflected in reduced growth rates under the changed flow velocity and temperature regimes imposed by disturbance gradients. This research represents a valuable step in the biological understanding of Murray cod within variable riverine environments and emphasises the urgency required to mitigate impacts associated with hypolimnetic impoundments.  相似文献   

5.
Stream fish distributions are commonly linked to environmental disturbances affecting terrestrial landscapes. In Great Plains prairie streams, the independent and interactive effects of watershed impoundments and land cover changes remain poorly understood despite their prevalence and assumed contribution to declining stream fish diversity. We used structural equation models and fish community samples from third‐order streams in the Kansas River and Arkansas River basins of Kansas, USA to test the simultaneous effects of geographic location, terrestrial landscape alteration, watershed impoundments and local habitat on species richness for stream‐associated and impoundment‐associated habitat guilds. Watershed impoundment density increased from west to east in both basins, while per cent altered terrestrial landscape (urbanisation + row‐crop agriculture) averaged ~50% in the west, declined throughout the Flint Hills ecoregion and increased (Kansas River basin ~80%) or decreased (Arkansas River basin ~30%) to the east. Geographic location had the strongest effect on richness for both guilds across basins, supporting known zoogeography patterns. In addition to location, impoundment species richness was positively correlated with local habitat in both basins; whereas stream‐species richness was negatively correlated with landscape alterations (Kansas River basin) or landscape alterations and watershed impoundments (Arkansas River basin). These findings suggest that convergences in the relative proportions of impoundment and stream species (i.e., community structure) in the eastern extent of both basins are related to positive effects of increased habitat opportunities for impoundment species and negative effects caused by landscape alterations (Kansas River basin) or landscape alterations plus watershed impoundments (Arkansas River basin) for stream species.  相似文献   

6.
Understanding spatial patterns in population characteristics and the principal natal environments supporting riverine fish populations are important for fisheries management. Fin ray microchemistry was used to identify natal environment, and age estimates from sectioned fin rays were used to estimate growth and mortality rates for spotted bass, Micropterus punctulatus (Rafinesque), in a segment of the Ohio River (Smithland Pool) and three tributaries. Differences in water Sr:Ca and Ba:Ca among the Ohio River and tributaries were reflected in fin ray edge Sr:Ca and Ba:Ca. Fourteen percent of spotted bass ≥ age 2 captured in the Ohio River originated in tributaries, whereas 10% captured in tributaries originated in the Ohio River. Spotted bass in the Ohio River reached larger maximum size (L∞ = 448.7) than conspecifics in tributaries (L∞ = 324.4), although mortality rates were not different. Although 86% of spotted bass were collected in their inferred natal environment, small tributaries may be a supplemental source of recruitment for the spotted bass stock in Smithland Pool.  相似文献   

7.
Population characteristics of gizzard shad, Dorosoma cepedianum (Lesueur), an ecologically important fish species in Midwestern and southern USA impoundments, vary widely among water bodies. Impoundment productivity is known to influence population variables (e.g., recruitment, growth, mortality, size and age composition), but the role of impoundment morphometry (e.g., surface area, depth) is unknown. Differences in population characteristics of gizzard shad were compared between large and small impoundments across an impoundment–productivity gradient (indexed by total phosphorus [TP] concentration). Populations shifted from those comprised mostly of low abundances (indexed by catch per unit effort [CPUE], fish/hr of electric fishing) of long‐lived, large adults to those comprised of high abundances of short‐lived, small adults as TP increased. However, the trends in population variables across the TP gradient were less apparent in small impoundments than in large impoundments owing to considerable variation at a given TP level. Further analysis revealed that CPUE of gizzard shad was lowest in the smallest impoundments (<33 ha surface area) regardless of TP concentrations, probably because of more frequent winter kills. Overall, population characteristics were influenced by both density‐dependent effects and impoundment characteristics. Characteristics of gizzard shad were highly variable among populations, which have important consequences for ecosystem structure and function.  相似文献   

8.
  1. Large dams have been repeatedly implicated in declines of riverine species, but the impacts of small dams are largely understudied. The placement of small dams (< 5 m high) on headwater streams, their density, and lack of regulation suggests that these dams may also have significant adverse impacts on headwater biota.
  2. The objective of this study was to determine whether small impoundments affect downstream salamander abundance and water quality. Salamanders were identified and counted from 10 paired catchments draining either a small impoundment (< 0.8 ha) or a free‐flowing stream. A binomial mixture model was used to estimate abundance after accounting for incomplete detection.
  3. Estimated abundance of larval Desmognathus conanti, Eurycea wilderae, and Pseudotriton ruber was 3.9, 19.6, and 9.8 times greater downstream of small impoundments than in unaltered streams. Iron concentrations and pH had positive effects on salamander abundance while conductivity was negatively associated with salamander abundance.
  4. Increases in abundance may be due to increased hydrologic stability below dams, different geomorphology, and altered water quality. Despite their small size, small impoundments can have localized, downstream effects on water chemistry and species abundance and may create high quality habitat for some stream species in a heterogeneous landscape.
Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

9.
  • 1. The lacustrine brown trout (Salmo trutta) is endangered and of high conservation importance. In the only spawning habitat of the population in the Bavarian Lake Walchensee, the River Obernach, a substantial decrease in spawning runs has been reported. In this study, the present ecological state of the spawning stream was analysed with the objective of identifying life‐stage specific limitations to successful recruitment attributable to deficiencies in (i) spawning migration, (ii) spawning habitat quality, and (iii) habitat quality for juveniles.
  • 2. Structural stream analysis showed that discharge and several migration barriers — particularly near the river outlet into the lake — prevent successful spawning migrations at normal water levels. Migration barriers are probably the main limiting factor for reproduction of lacustrine brown trout, whereas structural variability of the Obernach meets the habitat requirements of both spawners and juveniles.
  • 3. Spawning site quality was suitable for trout, as indicated by stream substratum texture and high exchange rates between free‐flowing water and the interstitial zone in physico‐chemical parameters (redox potential, dissolved oxygen, pH, temperature and conductivity).
  • 4. Analyses of fish community structure revealed dominance of lithophilic species, in particular of riverine brown trout (Salmo trutta). Its density and intact demographic population structure suggest that spawning and juvenile habitat quality for salmonids is not limiting. Recapture of stocked lacustrine trout juveniles also indicates habitat suitability for the juvenile stage.
  • 5. In conclusion, the results show that the methodology used in this study is suitable for the identification of life‐stage specific habitat deficiencies in lacustrine brown trout and other fish species. Availability of habitat data throughout the species' distribution range is a first crucial step for the development of an effective recovery plan. Copyright © 2009 John Wiley & Sons, Ltd.
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10.
  1. Fisheries and the presence of low‐head obstacles are considered major threats for anadromous lampreys, including the sea lamprey (Petromyzon marinus). Nonetheless, research is still needed to increase our understanding of their effect and to implement effective conservation and management measures. Petromyzon marinus receives conservation protection in Europe through the Bern Convention and the European Habitats Directive and is listed as ‘Vulnerable’ in Spain.
  2. The aim of this study was to investigate the impact of low‐head obstacles and fisheries on the spawning migration of P. marinus in the highly impounded River Ulla (in north‐west Spain). Nineteen lamprey were radio‐tracked in 2012 and 2013, and historical data (2002–16) on fishing captures were analysed (n = 25 607) to provide a population‐level approach.
  3. The retention of individuals by low‐head obstacles, including pesqueiras constructed for lamprey fishing, and extraction by fisheries at those structures, caused a significant reduction of migrants upstream of each impoundment (mean: 24% individuals per obstacle). A delay in migration (mean: 6.3 days per obstacle) seems to be an important limiting factor for lamprey conservation in this river. Thus, based on the recorded delay, lamprey would need c. 5 months to pass the 23 obstacles present before reaching the first spawning areas and 9.5 months to cover the accessible river section (45 obstacles), which is far longer than the 3–5 months of spawning migration of P. marinus in this river.
  4. Consequently, obstacle removal or permeabilization should be prioritized for lamprey conservation in this river. This would reduce migration delay, the retention of individuals, and the catchability of lamprey at pesqueiras (with alternative routes to avoid traps). Basic information on fisheries management is still lacking, especially on stock exploitation rates and on lamprey population status and dynamics. Future studies should also investigate the role of lamprey exchange between basins (a lack of homing) in the resilience of lamprey populations.
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