Fish recruitment in a large,temperate floodplain: the importance of annual flooding,temperature and habitat complexity

1. Large river floodplains are considered key nursery habitats for many species of riverine fish. The lower Volga River floodplains (Russian Federation) are still relatively undisturbed, serving as a suitable model for studying the influence of flooding and temperature on fish recruitment in floodplain rivers. 2. We examined the interannual variability in recruitment success of young‐of‐the‐year (YOY) fish in the lower Volga floodplain in relation to flood pulse characteristics and rising water temperatures in the spring. We sampled four areas with different flooding regimes, in three consecutive years (2006–2008). 3. Extensive areas with a long duration of flooding accommodated high densities of young fish. This suggests that extended inundation improves the recruitment success of river fish. In areas with extensive flooding, the biomass of YOY of most fish species was about three times higher in 2006 and 2007 than in 2008. We hypothesise that low spring temperatures in 2008 may have caused this reduced recruitment and that a flood synchronised with rising temperature enhances recruitment success. 4. Extensive flooding was particularly favourable for species characterised by large body size, delayed maturation, high fecundity and low parental investment, such as pike Esox lucius, roach Rutilus rutilus and ide Leuciscus idus. Gibel carp Carassius gibelio, a species tolerant of high temperature and hypoxia, did particularly well in small waterbodies in the driest parts of the floodplain. 5. Structural characteristics of floodplain waterbodies explained much of YOY fish density. These species–environment associations varied from year to year, but some species such as common bream Abramis brama, roach and gibel carp showed consistent relationships with structural habitat characteristics in all years, despite large interannual fluctuations in flood pulse and spring temperature.     

Investigations on the Ecology and Fish Fauna of the Mahakam River in East Kalimantan (Borneo), Indonesia

Water quality was determined on the Mahakam River floodplain from 1980 to 1987. Five water-body types were distinguished, i.e. slow-flowing and faster-flowing rivers, lakes, small waterbodies and swamps. Water quality in large rivers was stable in the short but not the long term. In all other ecotypes variability was higher, with marked fluctuations being recorded in small waterbodies. A total of 147 indigenous freshwater fish species have so far been identified from the Mahakam. The zoogeographical consequences are discussed. Migratory patterns were inferred for four fish species, Helostoma temmincki, Leptobarbus hoe-venii, Puntius schwanenfeldii and Thynnichthys vaillanti. Juvenile H. temmincki (< 3 cm SL) migrate at the surface in schools of 40-80 individuals at speeds of 0.48-1.08 km · h⁻¹, travelling 3.8-8.6 km · h⁻¹. Fecundities for P. schwanenfeldii (7,900–16,000 eggs), T. vaillanti (2,900–24,000 eggs) and H. temmincki (6,200–9,100 eggs) were determined.     

Comparative use of side and main channels by small‐bodied fish in a large,unimpounded river

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Ichthyofaunal survey of rivers within Ewekoro cement manufacturing operational areas

A total of 298 fish specimens belonging to seven families were caught during ichthyoplanktonic survey of three rivers within the Ewekoro cement facility catchment area located in southwestern Nigeria. The highest numbers of specimens were caught from Alaguntan (37.0%) and Elebute (36.6%) rivers while 28.9% of the fish samples were collected from Itori River. The fish population and species diversity recorded in the catchment rivers were significantly lower (p < 0.05) than comparative catches from Ewekoro River located about 30 km downstream of the factory operational area. The food items ingested by the specimens across the seasons in the catchment rivers revealed obvious differences in diet with some degree of overlap in the fish trophic preferences. However, the omnivorous species dominated the catches in each of the rivers, irrespective of season. Categorization of the fish specimens based on habitat-related adaptive physiology showed that a significant number of the fish from Alaguntan and Itori Rivers have accessory respiratory organs. The four species with accessory respiratory organs were Polypterus senegalus Curv., Clarias gariepinus C. & V., Ctenopoma kingslayae Gun. and Channa obscura Smith. Of the 12 fish species recorded in the Ewekoro cement facility catchment rivers, only P. senegalus, C. gariepinus, C. obscura and Oreochromis niloticus (Trew.) are valuable food fishes in southwestern Nigeria.     

The distributions of larval and juvenile fishes in Amazonian rivers of different nutrient status

1. Previous work has indicated, at least in two river systems, that some Characiformes species migrate from nutrient‐poor rivers to spawn in nutrient‐rich rivers. In the present work, larval and juvenile fish were surveyed to index spawning activity in order to determine whether this spawning pattern is repeated in nine major tributaries of the Amazon basin. 2. Adult Mylossoma aureum, M. duriventre, Colossoma macropomum, Anodus elongatus, Triportheus elongatus, Brycon cephalus, Semaprochilodus insignis, S. taeniurus and Prochilodus nigricans were recorded in nutrient‐poor and nutrient‐rich rivers. However, larval and juvenile individuals of these species were found in nutrient‐rich rivers only, indicating that spawning activity was restricted to that river type. 3. Concentration of suspended solids in the river was correlated with total ichthyoplankton density and related to species composition of juvenile characiform assemblages. 4. Our findings reinforce the hypothesis that nutrient‐rich rivers and associated floodplains function as spawning and nursery grounds, and suggest that they function as source habitats for these species in the Amazon Basin.     

The influence of Eurasian beaver Castor fiber activity on fish assemblages in small steppe rivers in Russia

In recent decades, the Eurasian beaver (Castor fiber) has once again become the keystone species in small river ecosystems in Russia. In many places, beaver activity has resulted in a significant change in lotic habitats, affecting the diversity, density, and biomass of aquatic organisms, including fish. While many studies have considered the ecosystem impacts of beavers, relatively few have focused on understanding the influence of beaver activity on steppe rivers. We conducted the first quantitative study of beaver impacts on fish assemblages in beaver-influenced and beaver-free sites on two small steppe rivers in the Don River basin in Russia. The presence of beavers altered the habitats in small steppe rivers and affected the diversity, density, and biomass of fish. A comparison of the number of species, density, and biomass of fish in six types of river habitats showed that these parameters were lower in beaver ponds than at riverine sites without beaver activity. Three fish species primarily preferred a single habitat type. Barbatula barbatula was found in riffles, Misgurnus fossilis in old beaver ponds, and Eudontomyzon mariae in abandoned beaver ponds. Beavers impacted fish distribution and density by changing dissolved oxygen, pH, and water current velocity. Overall, our results showed that the presence of beavers led to a temporary homogenization of fish habitats at a local scale in the valleys of small steppe rivers because beavers occupied these rivers only for a short period. However, habitat heterogeneity may increase if the beaver population stays stable or expands in the future.

     

Stream–floodplain connectivity and fish assemblage diversity in the Champlain Valley, Vermont, U.S.A.

To evaluate the influence of main channel–floodplain connectivity on fish assemblage diversity in floodplains associated with streams and small rivers, fish assemblages and habitat characteristics were surveyed at 24 stream reaches in the Champlain Valley of Vermont, U.S.A. Fish assemblages differed markedly between the main channel and the floodplain. Fish assemblage diversity was greatest at reaches that exhibited high floodplain connectivity. Whereas certain species inhabited only main channels or floodplains, others utilized both main channel and floodplain habitats. Both floodplain fish α-diversity and γ-diversity of the entire stream corridor were positively correlated with connectivity between the main channel and its floodplain. Consistent with these results, species turnover (as measured by β-diversity) was negatively correlated with floodplain connectivity. Floodplains with waterbodies characterized by a wide range of water depths and turbidity levels exhibited high fish diversity. The results suggest that by separating rivers from their floodplains, incision and subsequent channel widening will have detrimental effects on multiple aspects of fish assemblage diversity across the stream–floodplain ecosystem.     

GENETIC STRUCTURE OF THE FROGS GEOCRINIA LUTEA AND GEOCRINIA ROSEA REFLECTS EXTREME POPULATION DIVERGENCE AND RANGE CHANGES,NOT DISPERSAL BARRIERS

I describe the genetic structure of two frog species, Geocrinia rosea and Geocrinia lutea, using allozyme electrophoresis to understand population structure and thereby possible mechanisms of divergence and speciation. The sampling regimes represented the entire range of both species and provided replicated tests of the impact of ridges, rivers, and dry forest on gene flow. Geocrinia rosea and G. lutea were highly genetically subdivided (F_ST = 0.69, 0.64, respectively). In the extreme, there were fixed allelic differences between populations that were only 4 km (G. rosea) or 1.25 km (G. lutea) apart. In addition to localized divergence, two-dimensional scaling of genetic distance allowed the recognition of broad-scale genetic groups, each consisting of several sample sites. Patterns of divergence were unrelated to the presence of ridges, rivers, or dry forest. I argue that range contraction and expansion, combined with extreme genetic divergence in single, isolated populations, best accounts for the genetic structure of these species.     

崇明岛内河夏季鱼类群落组成及分布特征

崇明岛为世界最大的河口冲积沙岛,岛内河网水系发达。2018年6月,选择崇明岛内主要代表性河道包括北横引河、南横引河和竖河（庙港、堡镇港、八滧港）,设置16个固定站点,对内河鱼类开展了拖网调查,分析了崇明岛内河夏季鱼类群落组成及分布特征。调查期间共采集到鱼类4417尾,分属6目9科30种,主要为鲤形目鲤科鱼类;其中,淡水鱼类27种,洄游鱼类2种,近海鱼类1种。从空间分布来看,北横引河记录鱼类20种,南横引河记录鱼类17种,竖河记录鱼类18种,不同河道鱼类种类组成及优势种特征存在明显差异,其共有优势种为鲫Carassius auratus、似鳊Pseudobrama simoni和翘嘴红鲌Erythroculter ilishaeformis,部分种类只在特定的河段有记录。北横引河各站点平均物种数、丰度和生物量均高于南横引河和竖河,但3类河道间不存在显著差异（P>0.05）;主要优势种鲫、翘嘴红鲌和似鳊平均体长均以北横引河为最大,且在南横引河与北横引河中的个体体长均存在极显著差异（P<0.01）。聚类和排序分析结果表明,北横引河和南横引河鱼类组成差异较大,而竖河介于两者之间。相似性分析的结果也表明,南、北横引河鱼类群落结构差异极显著（R=0.524,P=0.008）,且这两组间鱼类种类组成的平均相异性最高,为43.92%,造成两组间差异的主要物种有10种（贡献率均大于5%）。综合来看,崇明岛内河鱼类群落组成与分布特征不同于一般的内陆河流,而具有河口型岛屿的特点。未来需要在长期监测基础上,综合多种因素,对崇明岛内河鱼类组成、分布、变化趋势及内在机理开展系统研究。     

Sources of fish in the ephemeral western iishana region of the Cuvelai–Etosha Basin in Angola and Namibia

The triangle between the Kavango and Kunene rivers is drained by the Cuvelai, an ephemeral and deltaic drainage system covering more than 100 000 km². In good rainfall years, the area becomes populated by fish communities dominated by five species migrating southward towards the endorheic Etosha Pan, the basin’s terminal sump. When water dries up, fish subsequently die-off and their sudden appearance in rainy years has captivated scientists for decades. The current study was prompted by hitherto untapped indigenous knowledge through narratives of opportunistic fish harvesting of migrating fish at temporary connections between the Kunene River and the Cuvelai- Etosha Basin. A reconnaissance fish survey in 2017 was complemented by digital satellite images and elevation data analyses. Results support the presence of at least three major ephemeral fish migration routes. The dominant fish genera migrating upstream in Kunene tributaries comprise Enteromius, Oreochromis and Clarias, all eurytopic and known to undertake upstream, lateral and downstream migrations on floodplains. Although other notable fish refugia in the Cuvelai–Etosha Basin are yet to be identified, there is a necessity for the protection and management of these migration routes in tandem with studies on the nature and extent of this inter-basin fish migration under climate change and variability.     

Reproduction, Growth, and Migration of Fishes in a Regulated Lowland Tributary: Potential Recruitment to the River Meuse

Many European rivers are characterized by a canalized main channel, steep stony embankments, the absence of aquatic vegetation, regulated flow dynamics, reduced hydrological connectivity to the floodplains and a lack of spawning and nursery areas for many fish species. In such regulated rivers, tributaries may be particularly important for recruitment of fish populations in the main channel. This paper describes the reproduction, growth and migration of fishes in the Everlose Beek, a regulated lowland tributary stream of the river Meuse (The Netherlands), using bi-weekly sampling from January to December 2002. A total of 8615 fishes were caught, belonging to 13 different species. The fish species were classified into three groups, viz., residents, migrants and transients, based on the presence of various life-stages in the tributary. Size-frequency data suggest that each group uses the Everlose Beek differently: (i) Stone loach (Barbatula barbatula), Gudgeon (Gobio gobio) and Three-spined stickleback (Gasterosteus aculeatus) were resident species using the tributary as a spawning, nursery and adult habitat; (ii) Bream (Abramis brama), Roach (Rutilus rutilus), Rudd (R. erythrophthalmus), Tench (Tinca tinca), and Pike (Esox lucius) were migratory species, using the tributary as a spawning area, as well as a nursery habitat during their first year of growth, but migrating towards the river Meuse typically at a length of 5–15 cm; and (iii) Bleak (Alburnus alburnus), Sunbleak (Leucaspius delineatus), Carp (Cyprinus carpio), Crucian carp (Carassius carassius), and Perch (Perca _,fluviatilis) were transient species, characterized by an absence of reproduction, ^.and the occurrence in very low densities of >age-1 juveniles and adults only. Lowland tributaries, such as the Everlose Beek, can contribute to the recruitment of particularly migrant species, hence contributing to fish populations of the regulated river Meuse.     

Habitat and relative abundance of fishes in small rivers in eastern Thailand

Total relative abundance of fish and species richness at 95 sites in small rivers varied significantly with physicochemical factors. Species richness was negatively and positively related with pH and dissolved oxygen, respectively. Relative abundance varied inversely with discharge and ambient ammonia and, directly with depth, substratum, ambient oxygen and alkalinity. Fish were represented by 62 species, the most common being Rasbora paviei, Puntius binotatus and Channa gachua. Canonical correspondence analysis related species and their relative abundances with eight environmental variables into four groups. The most species-rich group was associated with approximately average values for the significant variables. The group with the fewest species was associated with high oxygen and low ammonia and alkalinity. The other two groups had similar numbers of species, one being associated with high ammonia and alkalinity and low oxygen. Species in the other group were found at locations where rivers were relatively wide with comparatively high oxygen and low ammonia concentrations.     

Feeding habits of three sympatric mammals in NE Spain: the American mink, the spotted genet, and the Eurasian otter

Diet composition, niche measures, and prey consumption of three sympatric species of carnivores, one non-native and introduced, the American minkNeovison vison Schreber, 1777, and two native, the spotted genetGenetta genetta Linnaeus, 1758 and the Eurasian otterLutra lutra Linnaeus, 1758, were studied in a Spanish Mediterranean area. The study was based on the analysis of prey remains in the faeces of the predators. Faeces of mink (n = 444), genet (n = 310), and otter (n = 108) were collected all year round for four years along the Llobregat (21 km) and Gavarresa rivers (12 km). Simultaneously, and in the same area, prey species density and weight were estimated by means of trapping. The diet of mink and genet was dominated by the American crayfishProcambarus clarkii, while the otter fed almost exclusively on fish. Compared to the mink, the genet seemed to specialise more on small mammals while the mink specialised more on aquatic birds, especially in autumn-winter. Niche overlap was higher between mink and genet than between either of them and the otter.     

Vegetation,invertebrate, and fish community response to past and current flow regulation in floodplains of the Savannah River,Southeastern USA

In 2005 and 2006, the United States Army Corps of Engineers released experimental flows to mimic natural spring flooding on the highly regulated lower Savannah River in the Southeastern US. We used vegetation, invertebrate, and fish communities to assess how past regulation and current experimental releases were affecting the ecological conditions on floodplains. The nearby Altamaha River, of similar size but retaining near-natural spring pulses, served as a reference. We did not find that past flow regulation of the Savannah River had significantly altered floodplain forest structure. However, numbers of tree seedlings in bottomland hardwood forests were higher during a year with an artificial pulse than one without. Analyses of invertebrate and fish communities suggested some limited differences in floodplain community structure between rivers, with differences being most pronounced for predaceous Dytiscidae beetles and Esox spp. fishes. Artificial re-creation of small spring flood pulses down the Savannah River in 2005 and 2006 elicited some responses from fish and invertebrates, but did not shift species assemblages towards those occurring on Altamaha River floodplains.     

The role of the predatory trahira (Pisces: Erythrinidae) in structuring fish assemblages in lakes of a Neotropical floodplain

We performed an experimental manipulation of trahira Hoplias aff. malabaricus in a series of isolated lakes of the upper Paraná River floodplain to evaluate its short-term impact on the structure of fish assemblages. The effects of trahira density (treatment groups: addition, removal, and reference) in two habitat categories (open and macrophyte-covered areas) on attributes of the fish assemblage structure were evaluated (using rm-ANOVA) over 120 days. Reductions in species richness were recorded in all assemblages and were more pronounced at the end of the experiment within macrophyte-covered areas of the lakes where H. aff. malabaricus was removed. In these lakes, the number of fish was also significantly smaller and evenness was significantly higher than in those in which trahira were added or maintained at natural densities. The increase of the relative abundance of all size classes over the first 60 days on the assemblages where trahira was present, and the decrease of the small-sized fish where trahira was absent contributed to the lack of pronounced alterations in total biomass. The absence of the predator from its preferred habitat was found to negatively affect the less abundant species, which seemed to be highly sensitive to the effects of interspecific competition among prey species. In addition to the well-known effects of hydrological seasonality, the role played by native predators might be important in determining the persistence of local species in the fish assemblages of Neotropical floodplains.     

The Significance of Meander Restoration for the Hydrogeomorphology and Recovery of Wetland Organisms in the Kushiro River,a Lowland River in Japan

The meanders and floodplains of the Kushiro River were restored in March 2011. A 1.6‐km stretch of the straightened main channel was remeandered by reconnecting the cutoff former channel and backfilling the straightened reach, and a 2.4‐km meander channel was restored. Additionally, flood levees were removed to promote river–floodplain interactions. There were four objectives of this restoration project: to restore the in‐stream habitat for native fish and invertebrates; to restore floodplain vegetation by increasing flooding frequency and raising the groundwater table; to reduce sediment and nutrient loads in the core wetland areas; to restore a river–floodplain landscape typical to naturally meandering rivers. In this project, not only the natural landscape of a meandering river but also its function was successfully restored. The monitoring results indicated that these goals were likely achieved in the short term after the restoration. The abundance and species richness of fish and invertebrate species increased, most likely because the lentic species that formerly inhabited the cutoff channel remained in the backwater and deep pools created in the restored reach. In addition, lotic species immigrated from neighboring reaches. The removal of flood levees and backfilling of the formerly straightened reach were very effective in increasing the frequency of flooding over the floodplains and raising the water table. The wetland vegetation recovered rapidly 1 year after the completion of the meander restoration. Sediment‐laden floodwater spread over the floodplain, and approximately 80–90% of the fine sediment carried by the water was filtered out by the wetland vegetation.     

Abundance of young‐of‐the‐year migratory Characiforms in floodplain areas of the middle Solimões‐Amazon River at flooding 2007/2008

To test the influence of the largest Central Amazon fish consumption centre on the potential fish population recruitment, young‐of‐the‐year (YOY) abundances of matrinxã Brycon amazonicus (Spix and Agassiz, 1829), jaraquis Semaprochilodus insignis (Jardine and Schomburgk, 1841), S. taeniurus (Valenciennes, 1821) and tambaqui Colossoma macropomum (Cuvier, 1818) were estimated in two floodplain areas of the middle Solimões‐Amazon River – one near the city of Manaus and the other 500 km from Manaus – in the 2007–2008 flooding. Matrinxã presented the highest abundance among the four species, with 87.8% of captured individuals. The difference was significant in the representation of YOY matrinxãs between the two studied areas, with the input more significant in the last months of flooding in the area 500 km from Manaus. Jaraquis represented 12.1% of captures and showed no difference between areas. Tambaqui abundance was shown to be critical in both areas, with the capture of only 28 YOY (0.1%), and with no differences between the two floodplains. Matrinxã and jaraquis are more likely to present stabile stocks in the middle Solimões‐Amazon River; on the other hand, matrinxã requires attention due to differences in the YOY input between the two areas and in their low input in the Upper Amazon River, near Manaus. Based on the present work and on the landing history in Manaus, tambaqui is still considered as under strong overexploitation, showing some of the characteristics of overfishing recruitment in the middle Solimões‐Amazon.     

Mechanisms behind changes in fish biodiversity in the floodplains of Bangladesh

Fish species composition in two permanent floodplains (Beels) was monitored during 1992–1999. In one, small prawns (Macrobrachium spp.) replaced `beel-resident' species such as Puntius sophore, Colisa fasciatus, and Mastacembelus pancalus, while in the other beel no significant changes were observed. The reduction of the water area of the affected beel during the dry season and a resulting increase of the fishing effort was the main cause. The results are discussed in the context of overall developments in floodplain fisheries related to water and fisheries management and led to the formulation of a rapid fish biodiversity method.     

Seasonal dynamics of riverine fish communities using eDNA

As fish communities are a major concern in rivers ecosystems, we investigated if their environmental (e)DNA signals vary according to the sampling period or hydromorphological conditions. Three rivers were studied over a year using eDNA metabarcoding approach. The majority of the species (c. 80%) were detected all year round in two rivers having similar hydromorphological conditions, whereas in the river affected by an upstream lake waterflow, more species were detected sporadically (42%). For all the rivers, in more than 98% of the occasional detections, the reads abundance represented <0.4% of the total reads per site and per sampling session. Even if the majority of the fish communities remained similar over the year for each of the three rivers, specific seasonal patterns were observed. We studied if the waterflow or the reproduction period had an effect on the observed dynamics. Waterflow, which influences eDNA downstream transportation, had a global influence in taxonomic richness, while the fishes' reproductive period had only an influence on certain species. Our results may help selecting the best sampling strategy according to research objectives. To study fish communities at local scale, seasons of low waterflow periods are recommended. This particularly helps to restraint effects of external eDNA coming from connections with other aquatic environment (tributaries, lakes, wetlands, sewage effluents, etc.). To obtain a more integrative overview of the fish community living in a river basin, high waterflow or breeding seasons are preferable for enhancing species detection probability, especially for rare species.