Trophic flexibility of the otter (Lutra lutra) in southern Italy

Diet composition of otters (Lutra lutra) was investigated in 2001 by spraints analysis (N=1323) on five rivers of southern Italy, with the aim of assessing the influence of fish availability, elevation and discharge on the consumption of food resources alternative to fish. Data were expressed as per cent frequency of occurrence (%FO) and per cent volume (%V). The study confirmed the great feeding adaptability of the otter that, in rivers partially interconnected and flowing on a small area, showed a strong fish eating habit in some rivers (Sinni and Mercure-Lao) and a diet mainly constituted by alternative resources in other ones (amphibians in the rivers Cogliandrino and Frido, crustaceans in the River Battendiero). Fish consumption for the five rivers was significantly correlated with fish biomass and with mean summer discharge, while it was inversely correlated with the mean altitude of the five rivers. The lack of a clear seasonality in the consumption of food sources alternative to fish together with the correlation between fish use and fish biomass for each river indicated fish availability as the main factor affecting otter relying to non-fish preys. Otter diet seemed influenced by the characteristics of river habitats (altitude, discharge and consequently fish biomass) more than by summer drought, typical of Mediterranean regions. The %FO and the %V allowed to drawn a similar picture of otter diet. Nonetheless the %V was useful for better illustrating diet variation among the different rivers and we argue that it could be useful in habitats where the otter feeds on preys with different proportions of indigestible remains.     

Fighting the flow: downstream–upstream linkages in the ecology of diadromous fish faunas in West Coast New Zealand rivers

1. Diadromy is a dominating behavioural characteristic of fish faunas in New Zealand rivers, with amphidromy and catadromy being the most common strategies.
2. Juvenile life stages of amphidromous and catadromous species migrate from the sea, through river systems, to find habitats for feeding, growth, maturation and reproduction.
3. Studies of fish distributions in rivers of the West Coast of the South Island of New Zealand show that, in most species, these migrations result in more or less continuous distributions from the lower reaches to the upstream limits of each species' range.
4. Upstream penetration of rivers varies widely between species and this generates downstream–upstream trajectories of declining species richness.
5. Parallel trajectories of declining downstream–upstream abundance are likely in each species.
6. These patterns demonstrate the presence of downstream–upstream linkages in the community ecology of freshwater fishes in New Zealand rivers.     

Lakes and rivers as islands: species-area relationships in the fish faunas of Ontario

Synopsis Fish species richness in 82 lakes in Ontario, Canada was significantly correlated with surface area. In this region, latitude explained only a small amount of the variation in fish species richness. Thus, our study provides a clear demonstration of the relation between fish species richness and lake area without the confounding effects of latitude and physiography inherent in analyses from broader geographic regions. By comparison with the species-area relationship obtained, we show that acidification clearly depressed the number of fish species in 66 acid-stressed lakes in Ontario. Fish species richness was also significantly correlated with both drainage and surface areas of 21 Ontario rivers. Slopes of species-area regressions of lakes and rivers did not differ significantly, suggesting that species are added to these habitats at similar rates. However, our regression analyses show that rivers support more species of fish per unit surface area of water. Although these results are consistent with some predictions of island biogeography theory, we suggest that fish species richness is more likely to be a simple function of habitat diversity, rather than an equilibrial balance between immigration and extinction.     

Patterns of fish species richness in the Seine River basin,France

Variation in fish assemblage structure was examined in different rivers of the Seine Basin. Factor analysis was used to identify similarities among samples and species, and to show ichtyological changes along an upstream-downstream gradient. Fish species richness was correlated with catchment area, distance from the source and number of individuals. Relationships between species richness and number of individuals in a sample were largely an artifact of sampling.Species richness increased with river size, reached a maximum in midsize rivers, then decreased in large rivers. This species richness pattern was consistent with the model of the River Continuum Concept. However, possible causes could include greater pollution effects in large rivers. Distribution of feeding guilds was related to river size. Species richness and proportion of omnivores and piscivores increased with river size, whereas species richness and proportion of invertivores declined downstream. These patterns suggest that trophic diversity of fish assemblages may be related to food availability.     

Reservoirs promote the taxonomic homogenization of fish communities within river basins

Most studies analyzing patterns in biotic homogenization of fish communities have used large-scale approaches, while the community-level effects of species introductions and local extinctions within river basins have been sparsely analyzed. In this article, we examine patterns in freshwater fish α- and β-diversity in relation to the presence of reservoirs in a Mediterranean river (Guadiana river; Iberian Peninsula). We used fish samples from 182 river localities and 59 reservoir ones to address two main questions: (i) do reservoirs favor the establishment of invasive fish species?; and (ii) do reservoirs bear taxonomically homogenized fish communities? Although total species richness was not different between rivers and reservoirs, the latter had more invasive species and less native ones. Fish species found in reservoirs tended to be larger ones, but invasive species of any size showed higher preferences for reservoirs. Native species that were rare or absent in reservoirs were those that showed higher sensitivity to invasive species in rivers. Reservoir fish communities were taxonomically homogenized in relation to river ones, both when considering all fish species and using only natives or only invasive ones. Our results suggest that invasive species occupying reservoirs constitute an ecological filter excluding most native species from such systems. Invasive species in the study area are often widely introduced elsewhere, while native species found in reservoirs are congeneric and ecologically similar to those found in other Iberian studies. Thus, we conclude that reservoirs promote taxonomic homogenization at multiple spatial scales, while could also be promoting the functional homogenization of Iberian fish communities.     

Species richness and spatial variation in fish assemblage structure in two rivers of the Wet Tropics of northern Queensland,Australia

Synopsis Fish assemblages were sampled at 22 sites within the Mulgrave and South Johnstone Rivers of the Wet Tropics World Heritage Area, north Queensland. Flow regimes of these rivers are highly predictable, by Australian standards, due to low annual and seasonal variability. A gradual downstream change in fish assemblage structure, correlated with gradual change in habitat, substrate and type of in-stream cover, was observed in the Mulgrave River but not the South Johnstone. A reduced species richness was observed in the South Johnstone relative to the Mulgrave probably due to the effect of two high gradient sections located in the former river and a more diverse array of habitat types present in the latter. Both rivers contained more species than other tropical Australian rivers of greater size. Possible reasons for this included the constant and predictable flow regime and the greater diversity of habitats found in rivers of the Wet Tropics compared to other tropical Australian rivers.To whom correspondence should be addressed     

Increasing southern invasion enhances congruence between endemic and exotic Mediterranean fish fauna

Species movements in relation with global warming may increase the spatial overlap between exotic and endemic species, which is a critical issue for the conservation of biodiversity. The Mediterranean Sea, which is a receptacle for exotic species while being a hotspot for endemism, provides exceptional material for a case study. The aim of our study was to quantify (i) the increasing invasion from southern fish exotic species (Red Sea and Atlantic Ocean) that the Mediterranean biota is experiencing and (ii) the spatial overlap between exotic and endemic Mediterranean fish fauna following the northward movement of exotic species within the Mediterranean Sea in the context of global warming. The historical invasion dynamic of exotic fish species and the sea surface temperature series were reconstructed from 1810 to 2006 in order to estimate the correlation between invasion rate and climate. The geographical distributions of exotic and endemic fish richness before and after the period of global warming were used to assess the dynamic of spatial congruence. The results revealed (i) an acceleration of successful introductions from the Red Sea and (ii) the introduction of Atlantic species from lower latitudes in correlation with the increasing temperature of the Mediterranean Sea. We also showed an increasing overlap between the spatial distributions of endemic and exotic species richness. Taken together, our results suggest that endemic fish species are facing a growing number of exotic species because the Mediterranean Sea is acting as a catchment basin for southern species.     

海河流域河流生境功能识别及区域差异

城市群快速发展严重影响着区域水生态系统的完整性,大尺度流域的河流生境功能辨识和分析尚缺乏系统研究。以海河流域为例,根据河段蜿蜒度、河段比降、断流风险、盐度等4个指标,构建了河流生境功能的分类指标体系。通过多源空间数据和人工判读,划分了6254条河段,在此基础上将河流生境类型划分为15类。通过52个监测样点的鱼类调查数据,分析了不同河流生境的水生生物特征差异,揭示了鱼类多样性高的区域多位于河流比降大、断流风险低的区域,而河流蜿蜒度对于鱼类多样性影响较小。根据京津冀13个地级市的河流生境差异,提出京津冀城市群的生态安全构建需要充分考虑河流生境的空间异质性,并制定融合城市发展目标、水资源利用需求和河流生境功能的综合指标体系。     

Seasonal changes in fish community structure of intermittent streams in the middle reaches of the Guadiana basin, Portugal

Seven sites on three tributaries with intermittent flow regimes in the middle reaches of the Guadiana, i.e. Xévora, Caia and Degebe, were sampled approximately every 3 months from April 1995 to April 1997. The density and biomass of fish were greater in downstream rivers and sites. Along the Xévora River, a series of point abundance samples showed evidence of fish zonation along the river. Canonical correspondence analysis (CCA) suggested a simple relationship between the different species and their preferred habitat. The small-sized Rutilus alburnoides and Leuciscus pyrenaicus used most or all of the habitats with some cover and flowing water. Greater concentrations of larger fish were found in downstream reaches which generally had greater depths as stream width increased: large Barbus microcephalus , B. steindachneri and B. comiza preferred such sites on the Degebe River. Droughts in seasonal Mediterranean streams such as the Guadiana River are a predictable natural disturbance. In the summer, flow ceases and some stretches of river consist of isolated pools. This results in intense aggregations of fish and possible competition for food and/or space. Although some species are well adapted to natural droughts, habitat degradation and possibly the introduction of exotic species contribute to marked variability in species composition.     

Flood regime,dam regulation and fish in the Upper Paraná River: effects on assemblage attributes,reproduction and recruitment

The flood regime is the most important force determining seasonality in neotropical rivers. In the Upper Paran River floodplain, it is the primary factor influencing biological processes. The aim of this paper is to summarize information on the influence of dam-controlled floods on some fish assemblage attributes, reproduction and recruitment in the Upper Paran River floodplain, providing preliminary guidelines for dam operation upstream. Fish were collected in different habitats of the Upper Paran River floodplain (river, channels and lagoons) in the period from 1986 to 2001. The high water period in the Paran River usually occurs from November/December to April/May. Annual variation in the hydrograph affects species with distinct life history strategies differently, and influences the composition and structure of fish assemblages. Large floods were associated with higher species richness. Frequencies of individuals with ripe and partially spent gonads, which indicate spawning, were higher during the period of increasing water level. Dependence on floods seems to be lowest in sedentary species that develop parental care, and highest in large migratory species that spawn in the upper stretches of the basin and use flooded areas as nurseries. Migratory fishes were favored by annual floods that lasted more than 75 days, with longer floods yielding larger populations. The occurrence of high water levels at the beginning of summer is fundamental to the spawning success of migratory species. However, the flood may be less important for recruitment of juveniles if it is of short duration. Dam operation upstream (releasing more water during the raining season) has potential to promote greater floods with appropriate duration improving recruitment, particularly for migratory species.     

Using fish guilds to assess community responses to temperature and flow regimes in unregulated and regulated Canadian rivers

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Vulnerability of riparian zones to invasion by exotic vascular plants

We compared the invasibility of riparian plant communities high on river banks with those on floodplain floors for four South African rivers. Analyses of abundant and significant riparian species showed that the floors have 3.1 times more exotic plants than the banks. The percent exotics ranges from 5% to 11% of total species richness for the banks, and from 20% to 30% for the floors. Species richness and percent exotics are negatively correlated for the banks, but not correlated for the floors.Despite great differences in climate, species richness, and landuse history, the percentages of exotic plants in three rivers in the Pacific Northwest of the USA and one river in southwestern France are similar to those in South Africa (24-30% vs. 20-30%, respectively). Furthermore, the high proportions of exotic species in these riparian plant communities are comparable to those reported for vascular plant communities on islands. We conclude that the macro-channel floor regions of the riparian zones of South African rivers are highly vulnerable to invasion by exotic vascular plants.     

The presence of anadromous twaite shad (Alosa fallax) in the Ebro River (western Mediterranean,Spain): an indicator of the population's recovery?

Although the Ebro River is one of the largest Mediterranean rivers, the presence of anadromous fish species was near to complete extirpation since the second half of the 20th century. However, many mature twaite shads (Alosa fallax) were captured at the lower reaches of this river (Xerta's weir site, 63 river km) in spring 2005, suggesting a natural recovery of this population. In this study, the first biological data on twaite shad from the Ebro River are presented, and their significance for the species conservation and recovery are discussed. The historical reasons for the decline of this species are reviewed, and data supports the proposal for urgent construction of a proper fish passage for anadromous species at the Xerta's weir. This action would allow fish access to a further 60 km of river upstream of the weir, representing a 200% increase in the amount of freshwater habitat and potential spawning areas. Improved access together with restrictive fishery regulations will assist with renewed interest in the fishery and conservation of the species.     

Ephemeral floodplain habitats provide best growth conditions for juvenile Chinook salmon in a California river

We reared juvenile Chinook salmon for two consecutive flood seasons within various habitats of the Cosumnes River and its floodplain to compare fish growth in river and floodplain habitats. Fish were placed in enclosures during times when wild salmon would naturally be rearing in floodplain habitats. We found significant differences in growth rates between salmon reared in floodplain and river enclosures. Salmon reared in seasonally inundated habitats with annual terrestrial vegetation experienced higher growth rates than those reared in a perennial pond on the floodplain. Growth of fish in the non-tidal river upstream of the floodplain varied with flow in the river. When flows were high, there was little growth and high mortality, but when the flows were low and clear, the fish grew rapidly. Fish displayed very poor growth in tidally influenced river habitat below the floodplain, a habitat type to which juveniles are commonly displaced during high flow events due to a lack of channel complexity in the main-stem river. Overall, ephemeral floodplain habitats supported higher growth rates for juvenile Chinook salmon than more permanent habitats in either the floodplain or river. Variable responses in both growth and mortality, however, indicate the importance of providing habitat complexity for juvenile salmon in floodplain reaches of streams, so fish can find optimal places for rearing under different flow conditions.     

A comparison between aquatic birds of lakes and coastal rivers in Florida

Aquatic birds were counted on five Gulf coast Florida rivers to determine if these river systems supported densities, biomass and species richness similar to those found on Florida lakes. Forty-two species were identified and for the species that were found on both Florida streams and lakes similar densities and biomass were encountered. As with Florida lakes, stream bird abundance and species richness were higher in winter months than in summer months, a consequence of migratory bird populations. Total bird abundance, biomass per unit of phosphorus, and species richness per unit of area were similar to data collected on Florida lakes. Thus, Florida rivers are capable of supplying sufficient resources to maintain bird densities, biomass and species richness values similar to lakes of equal size and nutrient concentrations and are therefore important habitats for aquatic bird populations. An examination of individual habitat characteristics indicates that water depth was inversely correlated and submersed aquatic vegetation was positively correlated with bird density, biomass and species richness within the river systems. While both habitat characteristics are important they are also inversely related making it difficult to separate the individual significance of each characteristic.     

Functional heterogeneity of dry-season fish refugia across a Mediterranean catchment: the role of habitat and predation

SUMMARY 1. Fish in Mediterranean streams survive through the summer in residual surface waters, encompassing a broad range of abiotic and biotic conditions. Yet, the extent to which fish assemblages may be shaped by functional heterogeneity in dry-season refugia is largely unknown. This study addresses this issue, by examining fish assemblage and population attributes, and predation patterns in residual summer habitats (12 pools and six runs) across a Mediterranean catchment in south-west Portugal.
2. Species richness was fairly constant among runs but increased with pool size, with the addition of exotics and rare natives to large pools resulting in nested subsets. The four most common species (chub, nase, loach and eel) were considered generalists in terms of their use of dry-season refugia. Conversely, rare species presented more specialised habitats, with barbel and exotics favouring pools and stickleback favouring runs.
3. Age and size of the two most common species varied among dry-season habitats. Age 0 chub were restricted to runs, where spawning stages (age 2 and older fish) were also more represented. Age 0 nase also concentrated in runs, but the individuals collected in pools exhibited greater growth. Conversely, age 2 and older nase were proportionally more abundant in pools, but with greater growth and better condition in runs.
4. The otter was the main fish predator, consuming fish of all species and size classes, irrespective of habitat. Otter activity concentrated in pools, where predation risk for cyprinids seemed to be much higher than in runs.
5. Dry-season refugia apparently vary in functional importance for different fish species and life stages, acting as complementary units in the landscape. Therefore, the presence of both pool and run refugia trough the summer dry season may play a critical role in promoting the persistence of native species in Mediterranean streams.     

Spatial patterns of the biological traits of freshwater fish communities in south‐west France

Spatial patterns in the combinations of biological traits of fish communities were studied in the Garonne River system (57 000 km², south‐west France). Fish species assemblages were recorded at 554 sampling sites, and the biological traits of species were described using a fuzzy‐coding method. A co‐inertia analysis of species distributions and biological traits identified some spatial patterns of species trait combinations. Fish species richness progressively increased from up‐ to downstream sections, and the longitudinal patterns of fish assemblages partitioned the river into clear biogeographic areas, such as the brown trout Salmo trutta (headwater streams), the grayling Thymallus thymallus , the barbel Barbus barbus and the bream Abramis brama zones (most downstream sections), which fitted with Huet's well‐known zonation for western European rivers. Only a few biological traits, chiefly related to life‐history attributes, significantly influenced the observed fish distributions. Fecundity, potential size, maximum age and reproductive factor increased from headwater to plain reaches. As a theoretical framework for assessing and predicting the functional organization of stream fish communities, spatial variations in species traits can be related to habitat conditions, thus providing explicit spatial schemes that may be useful to the design of both scientific studies and river management.     

Longitudinal patterns of fish assemblages in small unregulated subbasins: evaluating reach- and watershed-scale parameters

Fish assemblage relationships with environmental parameters were studied in four small unregulated subbasins in the speciose Upper Green River Basin of central Kentucky, USA. One subbasin drains into a tributary of the Green River and produced the lowest species (28) richness. The three other subbasins drain directly into the Green River and supported 41−59 species. Parameters were partitioned into watershed- and reach-scale spatial categories. Watershed area per stream segment and stream-size related environmental parameters at the reach scale produced the highest loadings of a principle components analysis (PCA), and both PCA Axes 1 and 2 for all subbasins were reflective either of watershed area or stream-size parameters. Small loadings were produced by all watershed-scale land-use parameters and all reach-scale water chemistry parameters. Fish richness and diversity were positively correlated with watershed area for the two largest subbasins and for the three Upper Green River subbasins combined. The lack of a linear relationship, however, between the residuals of multiple linear regression models between richness and diversity versus stream width, percent bedrock, percent pool and percent fine substrates indicated that a simple species area relationship was not operating. A detrended correspondence analysis (DCA) performed for each subbasin showed that several fish species were associated mainly either with small, upland segments or conversely the largest, deeper segments, and each subbasin yielded significant correlations between the environmental PCA loadings and fish assemblage DCA site scores. These results indicated that within the regional scale, and in absence of steep disturbance gradients, stream fish assemblages can reflect natural hydrologic and geomorphic gradients.     

Distribution of fishes in the Río Guayalejo-Río Tamesí system and relationships with environmental factors in northeastern Mexico

A priority issue in ecology and biogeography is understanding the patterns in species diversity and the causal factors of their distribution, which allows the generation of information for conservation strategies. The longitudinal distribution of fishes and their relationships with environmental variables were studied in the Guayalejo-Río Tamesí system (northeastern Mexico) from February 2000 to July 2001. A total of 5918 fish were caught in 27 collections along an altitudinal gradient in the main river course, from high mountain (1500 masl) to coastal plain near Tampico. Forty-three native and five exotic species, belonging to 35 genera in 23 families, were identified. Cluster analyses identified four major fish habitats in the river system. A distinctive euryhaline marine fish habitat (1) occurs near the mouth with native and two exotic species. Two other habitats consist essentially of freshwater fish species that are distributed along the longitudinal gradient. One of these habitats (habitat 4) shows greater diversity, as per the Shannon index value, and also includes amphidromous fish, in addition to two exotic freshwater fish; the other (habitat 2) includes freshwater, euryhaline and three exotic species. The changes in the frequency of occurrence and the abundance of Gambusia vittata, Astyanax mexicanus, and Xiphophorus variatus contribute to explaining differences between these habitats. Another habitat (3) is represented by two sampling sites located near the mouth and consist of freshwater and euryhaline fish and three exotic cyprinids with broad salinity tolerance. The low abundance and richness of exotic species suggest little impact on native fish fauna in this river. The fish assemblage of the Guayalejo-Tamesí river system species changes along a longitudinal gradient with the addition, replacement and presence of indicator species. Upstream fish fauna is mostly composed of freshwater species, some of them generalists that inhabit the entire longitudinal gradient, others that are restricted to certain sites, and the remainder of species is an assemblage composed of a mixture of euryhaline freshwater and marine species near the mouth.     

Turnover patterns in fish versus macroinvertebrates — implications for conservation planning

Spatial patterns in taxonomic richness and turnover for fish and aquatic macroinvertebrates are compared to assess the relative usefulness of each taxonomic group in mapping biodiversity patterns. Fish and aquatic macroinvertebrate species data for sites down the longitudinal axes of nine rivers in four provinces along the eastern side of South Africa were analysed. Fish and aquatic macroinvertebrate data from previous studies and recent river surveys were used in analyses of species richness and turnover. Fish proved to be not useful for mapping biodiversity patterns, as measured by turnover, whereas aquatic macroinvertebrate species patterns exhibited predictable patterns of turnover with downstream distance. Average turnover rates could be decomposed into turnover of common (‘core’) species, which were accelerated by presence of rare and narrow-range species. Disruptions to the river continuum impacted on the rate of turnover. Consistent with other research on South African rivers, aquatic macroinvertebrate communities could be grouped into upland versus lowland assemblages, and also be defined by longitudinal zones. Fish biodiversity patterns should be viewed at a riverscape scale, whereas macroinvertebrate patterns are more easily discerned at a segment-reach scale, and applied to reflect connectivity and environmental gradients respectively.