Effect of an intensive mechanical removal effort on a population of non‐native rainbow trout Oncorhynchus mykiss in a South African headwater stream

相似文献   

Long‐term plant community changes in managed fens in Ohio,USA

• 1. Long‐term studies are necessary to describe effects of restoration efforts on plant communities and invasive species in North American fen communities. In 1986, 1999 and 2000, wetland plant communities and abiotic factors were sampled in two fens in Ohio that were actively managed as a state nature preserve since 1986. The correlation between plant species and environmental conditions was examined in 1986 to 2000, and changes in woody plant cover were measured on aerial photographs from 1938 to 1997 to analyse long‐term effects of management practices.
• 2. 142 vascular plant species and 32 bryophyte taxa were found in these rich fens, including 13 rare (i.e. state‐listed as endangered, threatened or potentially threatened) and 14 alien species. TWINSPAN analyses identified nine plant community types, and species distributions were correlated with several abiotic factors (groundwater depth, pH, soil organic content, distance from wetland edge and depth of peat). Communities along the wetland edge in deep peat had higher richness, more woody species, more alien species and fewer rare species than communities in areas near sources of flowing groundwater with more marl and less peat.
• 3. There was little change in species richness, evenness, and Shannon's diversity from 1986 to 2000. However, plant species assemblages changed during the study, and changes were different in unmanipulated transects compared with those where habitat managers removed invasive woody plants. An aerial photograph analysis indicated that woody plant cover increased by about 1% each year during 1938 to 1997 despite current management efforts to remove invasive trees and shrubs. Additional strategies should be directed toward reducing shrub encroachment and invasive species while promoting rare species.

Copyright © 2007 John Wiley & Sons, Ltd.     

Fish use of ecohydraulic‐based mesohabitat units in a low‐gradient Illinois stream: implications for stream restoration

• 1. A classification scheme for ecohydraulic‐based mesohabitat units was developed for a summer low‐flow period. Mesohabitat unit designations were based on the integration of three‐dimensional channel hydraulics, geomorphic maintenance processes of bed morphology, and biological resource needs of fish. Ecological relevance of the units was evaluated by a study of fish mesohabitat use patterns, and species relationships to feeding guild. By portraying the stream as a mosaic of hydraulic habitat patches that provide specific biotic resource needs, this study's aim was to advance how ecological information may be incorporated into the stream restoration design process.
• 2. Nine mesohabitat units were designated, including pool‐front, ‐mid, and ‐rear units, scour pool, simple and complex riffles, glide, submerged point bar, and channel expansion marginal deadwater. Physical habitat structure differed among the nine mesohabitat units by length, water depth, and bed slope and complexity. Fish were collected in specific unit volumes by use of prepositioned areal electrofishing devices, in which distinct patterns of fish mesohabitat use were observed.
• 3. A key finding was the differences in fish assemblages among the pool units, in which fish densities were greatest in the pool‐front and scour pool units. Also, fish density in the pool‐front unit was positively correlated with pool entrance slope. Biomass was greatest in the pool‐front and ‐mid units, and it was correlated with maximum mid‐pool depth. Density and biomass were generally lowest in the pool‐rear unit. Other unique relationships were also observed among the mesohabitat units.
• 4. Based on feeding guild, patterns of fish mesohabitat use were observed for this summer low‐flow period; insectivores dominantly used pool‐front and scour pool units, herbivores dominantly used complex riffle units, and piscivores used pool‐front and ‐mid units.
• 5. Useful ecological information was derived from fish species‐habitat relationships observed in this study, linking mesohabitat units with species requirements for food resources. Such findings support advancements to ecological design strategies for stream restoration that promote hydraulic habitat diversity.

Copyright © 2008 John Wiley & Sons, Ltd.     

Ocean warming alters species abundance patterns and increases species diversity in an African sub‐tropical reef‐fish community

The impacts of ocean warming resulting from recent climate change on the abundance patterns of marine species have been well documented in temperate seas of the northern hemisphere, but the impacts of a widening tropical belt are largely unexplored. Using measurements of sea surface temperature and spear‐fishing records for 84 species spanning a 19‐yr period, we examined the effects of ocean warming on a sub‐tropical reef‐fish community on the southeastern coast of Africa. Corresponding with a 0.46°C increase in average sea surface temperature between the time periods 1989–97 and 2002–2007, the ratio of species showing an overall decrease/ no change/increase in abundance was 1 : 3 : 2 among six species at the northern limits of their distribution in the region (temperate species), 1 : 15 : 6 among 22 broadly distributed species, and 1 : 5 : 9 among 15 species at the southern limits of their distribution (tropical species). Also, the relative abundance of temperate species as a whole decreased by 10–13% whereas that of tropical species increased by 9%, and broadly distributed species showed little change. Average species richness and diversity increased 33 and 15% respectively between the two time periods. These results are broadly consistent with a predicted poleward shift in species ranges and a predicted increase in species richness and diversity with increasing sea temperature. Our findings confirm that large‐scale climate change causing a widening of the tropical belt and subsequent ocean warming is having a profound impact on marine species abundance patterns and community composition at a local scale in the sub‐tropics.     

Long‐term changes of marine subtidal benthic communities in North East Asia (Yellow and Japan seas) in a global change context: A review

1. A review of the long‐term changes and variations in benthic communities and the current status of the marine invasive species (MIS) in shallow waters of the Yellow Sea (Chinese sector) and the Sea of Japan (Russian and partly Korean sectors) is presented. This paper reflects on the progress and lessons learned, recommending actions for the future about the conservation of biodiversity.
2. In the Bohai Sea, the benthic ecosystem has been degenerating due to anthropogenic activities such as overfishing and pollution since the 1950s. The dominant position of K‐strategy species is gradually being lost and replaced by R‐strategy species. In the Yellow Sea, the macrobenthic community is different from other areas due to the Yellow Sea Cold Water Mass. Many economic species have been destroyed, and the biotic structure has changed significantly due to overfishing and climate change.
3. In the Russian sector of the Sea of Japan, the macrobenthic communities in the shallow‐water soft bottom have generally been in a stable condition for the last decades, except for some heavily polluted or disturbed areas due to dredging operations. The abundance of select large invertebrate species has changed considerably due to commercial fishing and poaching. Variations in macro? and meiobenthic communities under aquaculture conditions have occurred on a local scale during the last five decades.
4. MIS show obvious differences between China and Russia in the following aspects: introduction pathways of MIS, composition and number of non‐native species, threats and impacts of MIS to native communities and ecosystems, and economic and public health impacts.
5. Long‐term monitoring programmes should be developed to reveal future biotic changes and to separate the effects of cyclic variations of benthic communities from the impacts of pollution and eutrophication. Standardization of sampling procedures is required to compare changes/alternations in benthos across various regions worldwide.

     

Assessing long‐term fish responses and short‐term solutions to flow regulation in a dryland river basin

Water resource development and non‐native species have been cited as primary drivers associated with the decline of native fishes in dryland rivers. To explore this topic, long‐term trends in the fish community composition of the Bill Williams River basin were studied over a 30‐year period (Arizona, USA). We sampled 31 sites throughout the basin that were included in fish surveys by Arizona Game and Fish in 1994–97 and the Bureau of Land Management in 1979–80. We found that non‐native species have proliferated throughout the entire basin, with greater densities in the lower elevations. Native species have persisted throughout most of the major river segments, but have experienced significant declines in frequency of occurrence and abundance in areas also containing high abundances of non‐native species. Next, we assessed the short‐term response of the fish assemblage to an experimental flood event from the system's only dam (i.e. Alamo Dam). In response to the flood, we observed a short‐term reduction in the abundance of non‐native species in sites close to the dam, but the fish assemblage returned to its preflood composition within 8 days of the event, with the exception of small‐bodied fish, which sustained lower postflood densities. Our findings demonstrate the importance of natural flow regime on the balance of native and non‐native species at the basin scale within dryland rivers and highlight minimal effects on non‐native fishes in response to short duration flood releases below dams.     

Adapting a multi‐species tool for single‐species impact assessments: Managing fishes at risk in Canada

1. To assess the impacts of human activity on fishes and fish habitat, impact assessment tools use single‐ and multi‐species approaches depending on the ecological and socio‐economic objectives. In Canadian aquatic ecosystems, single‐ and multi‐species impact assessments are guided by the Species at Risk Act and Fisheries Act, respectively. Yet, for species protected under the Species at Risk Act, the sparse data often require alternative approaches to risk assessment.
2. The goal of this study was to evaluate whether a database‐derived multi‐species tool – the Habitat Ecosystem Assessment Tool (HEAT) – can be used for single‐species impact assessments. Using an empirical example of proposed drain maintenance in a tributary of Lake St. Clair, the net loss of suitable habitat was evaluated across six conservation targets, ranging from single species, such as the pugnose shiner (Notropis anogenus) and the yellow perch (Perca flavescens), to the entire fish assemblage. Model outcomes were compared across various habitat suitability indices, spatial resolutions, and environmental habitat layers.
3. The net loss of suitable habitat varied widely across conservation targets and was greatest for the rare specialist species (pugnose shiner). Single‐species conservation targets were more sensitive to variation in spatial resolution and uncertainty in model input parameters. The results of this study emphasize that single‐ and multi‐species conservation targets should not be considered equal, especially when species differ in abundance and niche breadth.
4. This study demonstrates the flexibility of HEAT for evaluating potential impacts of human disturbance on fishes and their habitat. Future development of this tool should expand beyond physical habitat, to include other factors relevant to species distribution and survival (e.g. biotic interactions).

     

Analysis of the plant composition of manatee (Trichechus manatus manatus) faeces in a lake in south‐eastern Mexico

相似文献   

Effects of a rock‐ramp fishway on summer fish assemblage in a Lake Huron tributary

The use of nature‐like fishways to increase ecosystem connectivity has increased in recent years, but their effectiveness has rarely been evaluated. A rock ramp was constructed in the Shiawassee River in 2009, and post‐construction effects (2011–2012) were evaluated on the summer fish assemblage by comparing fish assemblage composition to a nearby free‐flowing river and a nearby river with a dam. Patterns of fish species richness, mean catch‐per‐unit‐effort and proportional abundance in reaches upstream and downstream of the rock ramp, dam and comparable sites in the free‐flowing river were evaluated. Overall, species richness by site and proportional abundance in the rock‐ramp river were more similar to the free‐flowing river, while species richness by reach was more similar to the dammed river. These findings suggest that the rock ramp has improved connectivity for the summer fish assemblage, but has not fully restored conditions to the level observed in a free‐flowing river.     

Quantifying fish species richness and abundance in Amazonian streams: assessment of a multiple gear method suitable for Terra firme stream fish assemblages

A multigear sampling method to quantify fish richness and abundance in Amazonian Terra firme streams was assessed. This method is based on the four‐pass removal method using the combined application of different nets. The efficiency of the method was explored over 10 replicated sites along three streams over day, night and seasons. Use of four successive passes allowed both abundant and rare species to be collected and the abundance of common species to be estimated. On average, a high proportion (41%) of rare species was collected per sample (only one or two individuals) after four fishing passes. The efficiency of the sampling method to detect species richness per sample between successive passes was estimated using an autosimilarity approach. Although species richness and abundance increased with successive passes, no major differences were obtained between the third and fourth pass. A single pass considerably underestimated the richness and abundance of species in these type of streams, and night sampling also increased beta‐diversity by at least 20%. Abundance estimates demonstrated high efficiency with an overall sampling error of only 8 and 11% for samples and single species, respectively. Capture efficiency differed among fish species exhibiting different ecological traits and showed significant differences among seasons for total samples. Results supported the robustness of the method and its suitability to quantify fish richness and abundance in small, wadeable Amazonian Terra firme streams inhabited by highly diverse fish assemblages.     

Determining long‐term changes in a skate assemblage with aggregated landings and limited species data

Sustainable fisheries management requires assessment of exploited populations and communities. Traditional fisheries stock assessment methods need species‐specific input data, which for skates have only recently become available in Europe. To overcome this limitation, a Bayesian multispecies biomass production model was developed. In addition to aggregated landings, input data are short time series with species‐specific information (landings and biomass indices). Applying the approach to four main skate species and a group of two skate species, all managed together in the Bay of Biscay (Northeast Atlantic), long‐term changes in the skate assemblage composition were identified. Since the 1990s, Leucoraja naevus became increasingly dominant, while the contributions of the other three species (Raja brachyura, Raja clavata and Raja montagui) declined. The abundance of the grouped Leucoraja fullonica and L. circularis has also strongly decreased, suggesting long‐term overexploitation. All species except this species group are expected to increase over the next decade under current harvest rates. Currently, the species considered here are managed under a single fishing quota making it unlikely that the group of the two most depleted species will recover soon. The multispecies modelling approach bears promise for other harvested assemblages for which only grouped harvest information is available for certain periods.     

Fish assemblage structure and aquatic pollution in a Brazilian stream: some limitations of diversity indices and models for environmental impact studies

Abstract –  The aim of this study was to describe and quantify the effect of aquatic pollution on the fish assemblage structure of the Corumbataí River (Brazil), by comparing two sites with different water quality characteristics. The results revealed that abundance of individuals was low at the polluted site (B). However, the two sites did not differ significantly in species richness (total and average). This fact contradicts theories stating that portions where the transverse area of the channel is larger should present a higher biological richness. It was also observed that the ichthyofauna of site B had higher evenness, and, consequently, a tendency to a higher diversity than that at site A. This demonstrates that diversity estimates should be used cautiously in environmental impact studies, as they do not necessarily indicate better conditions of communities living in more preserved environments.     

Modelling stream fish species distribution in a river network: the relative effects of temperature versus physical factors

Abstract – The relative influence of temperature versus local physical factors on the spatial distribution of riverine fish species was investigated in a large watershed of south-western France. Using generalised additive models and hierarchical partitioning, we modelled the ecological responses of 28 fish species to a set of five environmental predictors, and we quantified the independent effect of each predictor. The spatial distribution of fish species was primarily determined by both mean temperature and position along the upstream–downstream gradient. However, responses to these environmental factors varied according to the species considered. Fish species with strong thermal requirements (e.g., common carp, black bullhead, Atlantic salmon) were mainly sensitive to temperature whereas longitudinal gradient was of primary importance for downstream species (e.g., common bream, largemouth bass, pike perch). Both the statistical methods used gave concordant results and appeared complementary. This dual-approach, quantifying the relative contribution of each environmental factor, appears particularly useful to understand the spatial distribution of stream fish species. Separating the effects of temperature versus habitat factors is crucial to accurately predict species distribution modifications in the current context of global change.     

Diet of the Eurasian otter (Lutra lutra) on the River Gradac,Serbia: Predation in a brown trout‐dominated stream

相似文献   

海南岛近岸海域鱼类物种组成和多样性的季节变动

根据2006年～2007年间在海南岛近岸海域进行的4个航次底拖网调查资料,分析了该海域鱼类物种组成和生物多样性特征。发现该海域鱼类种类较为丰富,调查共采集到鱼类292种,隶属于21目100科172属;其中暖水性种类数占83.32%,暖温性种类数占16.78%;与中国黄渤海共有种76种,与东海共有种220种,与南海大陆架、大陆坡和南海诸岛海域共有种分别为279种、42种和51种。鱼类优势种[相对重要性指数（IRI）〉500]依次为发光鲷（Acropoma japonicum）、斑鳍天竺鱼（Apogonichthys carinatus）、黄斑鲾（Leiognathus bindus）、皮氏叫姑鱼（Johnius belengeri）、大头白姑鱼（Argyrosomus macrocephalus）、（Therapon theraps）、棕斑腹刺鲀（Gas-trophysus spadiceus）和麦氏犀鳕（Bregmaceros macclellandi）。以生物量为基础采用5个指数研究了该海域鱼类多样性现状,并采用季节更替指数（AI）和迁移指数（MI）对各季节鱼类群落的稳定性进行了分析。结果显示,该海域鱼类多样性水平较高,相邻季节的鱼类物种相似性也较高,随着鱼类的洄游,群落的稳定性出现较大波动。     

Developing a landscape‐scale,multi‐species,and cost‐efficient conservation strategy for imperilled aquatic species in the Upper Tennessee River Basin,USA

相似文献   

Monitoring a loss: Detection of the semi‐aquatic crocodile lizard (Shinisaurus crocodilurus) in inaccessible habitats via environmental DNA

相似文献   

Longitudinal segregation of Astyanax janeiroensis in Rio Ubatiba: a Neotropical stream of south‐east Brazil

Abstract – In this study, we explored patterns of size and abundance of Astyanax janeiroensis in Rio Ubatiba (Rio de Janeiro, south‐east Brazil) in relation to reproduction. A. janeiroensis broadcast their eggs in the water column throughout the year. Samples at seven sites conducted every second month from July 1994 to August 1995 revealed a predominance of larger adult specimens upstream and immature juveniles downstream. We hypothesize that upstream movements of adult individuals is a response to drifting of eggs and larvae.     

Behaviour and physiology of mountain whitefish ( Prosopium williamsoni) relative to short‐term changes in river flow

Despite the growing recognition that river flow can have an effect on the growth, distribution and survival of fishes, little is known about the underlying mechanisms to explain this effect. Furthermore, there are few examples of integrated measures of behaviour and physiology to study the responses of fish to river hydrology. Here, axial swimming muscle electromyograms were logged as a sensitive indicator of activity from 19 mountain whitefish ( Prosopium williamsoni) across a large range of hourly discharge magnitudes (mean = 621 m³·s^?1, range = 0–1770 m³·s^?1) in a hydropeaking reach of the Columbia River, Canada. Hourly mean discharge had a significant positive effect on swimming muscle activity. However, a large amount of the variance was unexplained, possibly due to social interactions, feeding and/or flow‐refuging behaviours. Fluctuating flows were no more energetically costly than stable flows. Discharge magnitude had a significant positive effect on blood cortisol concentrations. Yet, cortisol concentrations were low overall (mean ± SD = 1.60 ± 0.09 ng·ml^?1), suggesting that the small observed response could be the result of routine physiological processes rather than a stress response per se. Based on low blood lactate concentrations, mountain whitefish were not swimming exhaustively (i.e., anaerobic burst‐type swimming) at high flows.     

The decline of endangered stone crayfish (Austropotamobius torrentium) in southern Germany is related to the spread of invasive alien species and land‐use change

相似文献