Spawning behaviour and early development of the Clanwilliam yellowfish (Barbus capensis; Cyprinidae), linked to experimental dam releases in the Olifants River,South Africa

This paper describes an investigation of how experimental releases of pulses of high flow from Clanwilliam Dam (Olifants River, South Africa) affect spawning of the Clanwilliam yellowfish, Barbus capensis. This species is endemic to the Olifants River system and is listed as rare in the Red Data Book of fishes for South Africa. Spawning sites are described, as is the spawning behaviour of B. capensis after specific experimental pulses released during the suspected spawning season of the species. Spawning and the developmental stages of embryos, free embryos, and larval B. capensis were studied using direct observations, video recordings, and microscopic examination of live embryos. B. capensis was found to be a repeat-spawner over several days as well as a multiple-spawner throughout the 4 month reproductive season. At present, spawning of B. capensis occurs down-stream of the dam sporadically (and possibly with limited recruitment), concurrent with releases of water for irrigation purposes. Experimental pulses appeared to trigger an increase in spawning activity, as an abundance of larvae was found down-stream 2 months later. It is suggested that a water-release strategy from Clanwilliam Dam could be designed to increase the number of B. capensis in the Olifants River. © 1997 John Wiley & Sons, Ltd.     

The Importance of Shallow‐Low Velocity Habitats to Juvenile Fish in the Middle Mississippi River

Habitat management is a crucial aspect of fisheries management. Without knowledge of habitat associations, fisheries scientists are unable to effectively make habitat conservation or restoration recommendations. This becomes especially prominent when trying to manage commercially harvested populations and protect threatened or endangered species. To determine juvenile fishes habitat associations in the Middle Mississippi River, we analysed mini‐trawl catch data of six common juvenile fish species: blue catfish (Ictalurus furcatus), channel catfish (Ictalurus punctatus), channel shiner (Notropis wickliffi), freshwater drum (Aplodinotus grunniens), paddlefish (Polyodon spathula), and shovelnose sturgeon (Scaphirhynchus platorynchus). Overall, we conducted 2251 mini‐trawl sampling efforts between 2002 and 2013, resulting in the capture of 23,742 target specimens. Catch per unit effort was evaluated by structural habitat (i.e. velocity, depth, and substrate). Overall, these data suggest that juvenile fish species are more prevalent in shallow water and slower velocities. Ultimately the information garnered during this evaluation should be incorporated when considering habitat modifications, especially those modifications that impact the availability of shallow‐low velocity habitats. Copyright © 2016 John Wiley & Sons, Ltd.     

Migratory patterns and return to the catch site of adult brown trout (Salmo trutta L.) in a regulated river

The spawning migration and local homing of adult brown trout was analysed using radio telemetry in a regulated river in central Norway. Twenty‐eight large (37–64 cm) brown trout (Salmo trutta L.) were tracked before, during and after spawning in the River Nea, a watercourse with several obstructions, including an outlet tunnel from a power station and a regulated stretch (26 km) with 45 weirs. Two major patterns of spawning migration were found: (1) about half (n = 16; 57%) of the trout moved very little and remained in the deeper pools of the river from June until November; (2) about half (n = 12; 43%) of the trout migrated relatively long distances (12.5–28 km) up the river prior to the spawning period where they stayed in the outlets of small tributaries, or in rapids on the main river during the spawning period. We assume that these trout belong to a population of lake‐run migratory trout using the River Nea for spawning. There was no significant difference in body length of migratory and stationary brown trout and no significant difference in total distance moved by migratory males (30.5 km, n = 6) and females (20.5 km, n = 6, p > 0.05). Among migratory trout, we found no correlation between body length and migrated distance. Of the 12 migratory trout, nine undertook fast upward migration in periods of high water flow (> 100 m³/s). They passed the outlet tunnel from the power station and negotiated two to 35 weirs before reaching their main reproduction areas. Three trout crossed several weirs when the discharge was low (10–40 m³/s). When there was low discharge, fish remained at the outlet tunnel for up to four weeks and showed a high level of activity. Postspawning downstream migration started between 25 September and 25 October. Most migratory trout (n = 9) wintered in pools on the lower part of the river or in weir basins; only two trout descended to the lake (Selbusjøen) in late autumn. Copyright © 2004 John Wiley & Sons, Ltd.     

Spawning and recruitment patterns of major fish species in Bontanga Reservoir, Ghana, West Africa

The spawning and recruitment patterns of the major Cichlid fish species, including Hemichromis fasciatus, Oreochromis niloticus, Sarotherodon galilaeus, Tilapia zillii and other species, Auchenoglanis occidentalis, Brycinus nurse, Clarias gariepinus and Marcusenius senegalensis were studied for 24 months in Bontanga Reservoir, Ghana, using length‐based fish stock assessment approaches. The species spawned throughout the year, with two spawning pulses described as major and minor spawning seasons. The major spawning season occurred from March to September for the Cichlids, and from May to September for the other species. The minor spawning season, indicative of extended spawning, occurred from October to March for all the fish stocks. Fish spawning began with the onset of the rains in April/May, peaking by June/July, before the rainfall peak in August for all the fish stocks studied. Recruitment was found to occur throughout the year, with major and minor pulses coinciding with the major and minor spawning seasons. Accordingly, the most appropriate time for a possible closed fishing period appears to be from June to August, 1 month after the start of, and before the end of, the rains. The estimated mean standard length (L_m) for first time spawners of A. occidentalis, B. nurse, C. gariepinus and H. faciatus were 11.7, 12.7, 2.7 and 7.5 cm respectively. The estimated maturity–length ratio of 0.4 and 0.2 for O. niloticus, S. galilaeus and T. zillii were lower than the known 0.7 for normal growth, suggesting the tilapias matured faster, and at a smaller size, in the reservoir. Apparent sexual precocity associated with early maturity, year‐round spawning and recruitment were some important adaptations found to have sustained the reservoir fisheries, even during high fishing pressures. For conservation and sustainable exploitation of the fisheries, instituting a closed fishing season, mesh size regulations, withdrawal rights and a community‐based fishery management system are recommended.     

半日河川水库法在确定排涝规模中的应用

沿海地区挡潮闸排水能力设计既受闸上河道来、蓄水及排涝标准的影响,又与潮汐变化等因素有关,水流情况属于变量变速流,各处的水位、流量及流速均不断变化,其计算相当复杂。以连云港徐圩新区为例,推演了半日河川水库蓄泄能力计算法在确定闸孔净宽时计算结果较准确,对沿海地区排涝规模的确定具有一定的推广作用。     

Spatial Distribution and Habitat Use of Spawning American Shad in the St. Johns River,Florida

American shad Alosa sapidissima populations along the Atlantic Coast of North America are near historic lows despite management actions designed to rebuild stocks. Florida's St. Johns River supports the southernmost population of this anadromous species, and as water use in the St. Johns basin increases, there is concern that their spawning may be affected. We assessed American Shad movement and habitat use in the St. Johns River during three spawning migrations (2009–2011) using acoustic telemetry. Spatial distribution patterns of telemetered shad during each year were largely similar; most shad were located within reaches from Lake Monroe (rkm 276) to just downstream of Lake Harney (rkm 308); some individuals made excursions as far upstream as Lake Poinsett (rkm 386+). Water levels varied among years (low‐water level: 2009 and 2011; higher water level: 2010), and lower water levels may have contributed to an apparent constriction of spawning grounds in 2009 and 2011. Telemetered shad selected deeper sections of river with faster currents. Our results verified that the primary spawning grounds for American shad in the St. Johns have not changed substantially in the past 50 years; thus, these areas should rank high for habitat protection. We also demonstrated linkages between American Shad distribution and habitat use and river flow that should be further developed and considered in future water withdrawal, regulation, or conservation efforts. Copyright © 2015 John Wiley & Sons, Ltd.     

Riverine characteristics dictate composition of fish assemblages and limit fisheries in reservoirs of the upper Paraná River basin

A qualitative comparative approach has been used to review whether fish assemblage characteristics, such as paucity of lacustrine‐adapted fish species, long food chains, and disproportionate number of piscivorous species, limit fishery yields in reservoirs of the Upper Paraná River basin. The paucity of lacustrine‐adapted species appears to limit fishery yields, but attempts to introduce lacustrine species have been generally unsuccessful. The food chains of species targeted by the fisheries are relatively long, but short food chains seem to be an adaptation of lacustrine species. Because reservoirs with many piscivorous species sustain high fishery yields elsewhere in the world, the hypothesis that an excessive number of piscivores limits yields is not supported. Instead, inadequacies of fish assemblages in reservoirs of the Upper Paraná River basin appear to be symptomatic of an unsuitable environment for lacustrine fish species. The physical characteristics of reservoirs in the Upper Paraná River basin, exacerbated by climatic patterns, may preclude the emergence of successful reservoir species from within the extant pool of riverine species. The resulting assemblages have characteristics that are neither riverine nor lacustrine, and are maladapted to support fisheries in the reservoirs. The introduction of lacustrine species is destined to failure because environmental characteristics are not lacustrine, except in reservoirs positioned high in the watershed, where increased retention times allow lacustrine conditions. Published in 2001 by John Wiley & Sons, Ltd.     

Diversity and Community Structure of Fishes in the Regulated Versus Unregulated Tributaries of the Mekong River

Diversity and community structure of fishes were studied in three neighbouring tributaries of the Mekong River in Thailand, namely the Mun, Songkhram and Gam Rivers. The rivers are located in the same ecoregion but have contrasting levels of both hydrological regulations and mitigation measures; the Mun River has a hydropower dam with a fish ladder and sluice gates that are opened during the wet season each year, the Gam River has several irrigation dams with a fish ladder at each dam site, and the Songkhram River has no dams along its river course. A total of 124 freshwater fish species were sampled in these rivers from August 2009 to June 2010. Overall species richness was highest in the Songkhram River (112), followed by the Mun (97) and Gam (54) Rivers. Average per site species richness was also significantly different among rivers but not among sampling months. Abundance–biomass comparison plots revealed considerably overlapping distributions of these two metrics from the dry to early rainy seasons in the Songkhram River and, to a lesser extent, in the Mun River. Fish assemblage data were classified into six clusters with similar community structure. Fish assemblages in the Gam River constituted a single cluster, while those in the other two rivers formed multiple clusters depending on the sampling season. The results of the cluster analysis are discussed in relation to the dominance of the three migration guilds (white, black, and grey fishes) of the Mekong River fishes. The effectiveness of the mitigation measures was determined to be limited in alleviating adverse impacts of dams in these tributaries of the Mekong River. Copyright © 2014 John Wiley & Sons, Ltd.     

Community Structure of Age‐0 Fishes in Paired Mainstem and Created Shallow‐water Habitats in the Lower Missouri River

Anthropogenic alterations to aquatic ecosystems have greatly reduced and homogenized riverine habitat, especially those used by larval and juvenile fishes. Creation of shallow‐water habitats is used as a restoration technique in response to altered conditions in several studies globally, but only recently in the USA. In the summer of 2012, the U.S. Army Corps of Engineers sampled larval and juvenile fishes at six paired sites (mainstem and constructed chute shallow‐water habitats) along a section of the Missouri River between Rulo, NE and St. Louis, MO, USA. From those samples, we enumerated and identified a total of 7622 fishes representing 12 families. Community responses of fishes to created shallow‐water habitats were assessed by comparisons of species richness and diversity measures between paired sites and among sampling events. Shannon entropy measures were transformed, and gamma diversity (total diversity) was partitioned into two components, alpha (within community) and beta (between community) diversity using a multiplicative decomposition method. Mantel test results suggest site location, time of sampling event and habitat type were drivers of larval and juvenile community structure. Paired t‐test results indicated little to no differences in beta diversity between habitat types; however, chute habitats had significantly higher alpha and gamma diversity as well as increased abundances of Asian carp larvae when compared with mainstem shallow‐water habitat. Our results not only show the importance of created shallow‐water habitat in promoting stream fish diversity but also highlight the role space and time may play in future restoration and management efforts. Copyright © 2015 John Wiley & Sons, Ltd.     

Immediate downstream effects of the Petit-Saut dam on young neotropical fish in a large tributary of the Sinnamary River (French Guiana,South America)

The effects of artificially low runoffs in the Sinnamary River, French Guiana, South America, on flow patterns and on richness and abundance of young fish in Venus Creek, one of its main downstream tributaries were examined. After Petit-Saut dam's gates were closed, the areas adjacent to this tributary were never once flooded for the entire duration of the rainy season. The daily maximal averages of water speed at the tributary's mouth were found to be significantly increased. Young fish sampled using light-traps were less abundant and less diverse after dam closure. Young Characiformes appeared to be the most affected by these flow disturbances. These findings enabled us to develop a conceptual model of the consequences of impoundment on young fish assemblages through the modifications of tributaries and associated floodplains hydrology. Because of flow reduction in the river during the first year of impoundment, young fish that previously had a tendency of being trapped in tributaries and flooded areas were then at risk of being flushed away. The pattern of flow release by dam operations is known to be very different from natural flow variations. The consequences for downstream tributaries will be similar to those of channelization: lack of adjacent flooding areas and higher rates of downstream water transfer. How the recovery of downstream fish assemblages will occur is discussed. © 1998 John Wiley & Sons, Ltd.     

Effects of stream hydraulics and other environmental variables on density of Narapa bonettoi (Oligochaeta) in the Paraná River system

Hydraulic and substratum conditions have been identified as two stream features which affect the benthic community composition, abundance and distribution. However, little attention has been given to the influence of hydraulic variables in large river beds. The aim of this study was to analyse the incidence of the near‐bottom hydraulic conditions and other environmental variables on the density of Narapa bonettoi (Oligochaeta, Narapidae), a typical and dominant species found in sandy bed rivers of diverse hierarchy of the Paraná River basin. A large amount of existing and available benthic data were used. The highest correlations among N. bonettoi densities and environmental variables were obtained with the hydraulic variables of friction Reynolds number (R_*) and shear stress (τ₀); the substratum type (sand, silt and clay) and organic matter content. The results show that N. bonettoi density would be related with the hydraulic variables following a ‘bell‐shaped’ tendency, e.g. with the friction Reynolds number, N. bonettoi would have a preference for transition values of turbulence (～40 < R_* < ～50), which is equivalent to τ₀ between ～0.6 and ～0.8 kg ^?2. Densities show a slight decreasing tendency toward the maximum R_* values, suggesting that the species does not support a completely developed turbulence (R_* > ～70). Significant but negative correlations were reported in the literature between benthic macroinvertebrates typical of smaller and steeper streams and R_* values far beyond the threshold 70 value. N. bonettoi shows a clear preference for a completely sandy substratum and for sand particles sizes around 300 µm. Finally, considering the important role played by the hydraulic variables on the benthic community studied herein, the contagious distribution pattern of N. bonettoi, reported by other authors, would be principally linked with the interactions between current and sediment near the bottom rather than with the mobility of these organisms. Copyright © 2008 John Wiley & Sons, Ltd.     

二维水流数学模型在多分汊河道鱼类栖息地设计中的应用

多分汊河道汇合或分流口水流流态复杂,常常存在河口滩及深槽,复杂多样的水文水力条件为鱼类提供了良好的进食及休憩场所。针对多分汊河道边界复杂的特点,建立了基于一般曲线坐标系下的平面二维水流数学模型。将所建立的数学模型应用于大渡河乐山段安谷水电站左岸生态河网建设和鱼类栖息地设计,对工程投运前后河段的水深、流速、流场、分流比进行模拟和对比分析,设置生态工程措施,使得鱼类产卵场河段水流特性仍满足鱼类栖息地要求。从安谷水电站运行效果看,设计的生态措施对河道鱼类栖息改善取得了较好的实践效果。     

Meta‐analyses,Metrics and Motivation: Mixed Messages in the Fish Passage Debate

Over recent years, there has been increasing challenge to the accepted wisdom that the environmental impacts of river engineering can be adequately mitigated through the installation of infrastructure, such as fish passes. This has led to a debate on the value of fish passage with some arguing that increased research and development will advance solutions for a variety of structures that are suitable for multiple species and transferable to different regions. Others suggest that policies and management strategies should reflect the realization that current mitigation technology frequently fails and can itself have negative impacts. Meta‐analyses of the results of studies on fish passage effectiveness have led to the challenge of conventional views by highlighting lower than expected efficiencies, wide variation between and within fish pass designs, and bias towards consideration of a limited number of commercially important species mainly from northern temperate regions. Results of meta‐analyses can also be controversial, and difficulties can arise when nuances associated with individual studies are lost and when metrics used are not standardized. Intrinsic variation in fish passage efficiency between and within species due to differences in patterns of movement and motivation may not be considered, and in many situations, current metrics are not appropriate. Quantification of variation in trends in fish passage efficiency over time and with spatial scale is lacking and should be the focus of future reviews. It is time to accept that fish passage does not provide a universally effective mitigation solution, particularly when designs and strategies are transferred to other regions and species for which they were not originally designed. Admitting to cases of failure is an essential first step to advancing water resources planning and regulation based on well‐informed decision‐making processes. Copyright © 2016 John Wiley & Sons, Ltd.     

Typology of a Great River Using Fish Assemblages: Implications for the Bioassessment of the Danube River

Matching habitat typology and ecological assemblages can be useful in environmental management. We examined whether a priori defined riverine sections correspond with distinct fish assemblage types along the >2000 km long course of the Danube River, Europe. We also tested whether different sampling methods (i.e. day and night inshore electric fishing and offshore benthic trawling) provide consistent typological results. Analysis of assemblage similarities, indicator species analysis, non‐metric multidimensional scaling (NMDS) and k‐means analyses indicated that fish assemblages of the a priori defined Upper‐, Middle and Lower‐Danubian sections differed slightly, but within class variability was high. Although indicator species analysis showed that the Upper‐Danube belongs to the barbel (Barbus barbus) zone and the Middle‐ and Lower Danube belong to the bream (Abramis spp) zone, indicator values of the character species were generally low. The NMDS analyses suggested a weak gradient in assemblage structure along the course of the river with relatively high variability between neighbouring sites. K‐means analyses revealed that many sampling sites were in a different class than the a priori defined sections, and classifications at other group numbers did not lead to better classification outcome. Overall, the results do not suggest clearly distinguishable assemblage types with distinct boundaries in the potamal section of a great river. Nevertheless, the division of the potamon to smaller sections may explain some variability in fish assemblage structure, and could be used for bioassessment purposes. The study also shows the importance of multihabitat and multigear surveys in the typological assessment of great rivers. Copyright © 2016 John Wiley & Sons, Ltd.     

Evidence of Lake Whitefish Spawning in the Detroit River: Implications for Habitat and Population Recovery

Historic reports imply that the lower Detroit River was once a prolific spawning area for lake whitefish (Coregonus clupeaformis) prior to the construction of the Livingstone shipping channel in 1911. Large numbers of lake whitefish migrated into the river in fall where they spawned on expansive limestone bedrock and gravel bars. Lake whitefish were harvested in the river during this time by commercial fisheries and for fish culture operations. The last reported landing of lake whitefish from the Detroit River was in 1925. Loss of suitable spawning habitat during the construction of the shipping channels as well as the effects of over-fishing, sea lamprey (Petromyzon marinus) predation, loss of riparian wetlands, and other perturbations to riverine habitat are associated with the disappearance of lake whitefish spawning runs. Because lake whitefish are recovering in Lake Erie with substantial spawning occurring in the western basin, we suspected they may once again be using the Detroit River to spawn. We sampled in the Detroit River for lake whitefish adults and eggs in late fall of 2005 and for lake whitefish eggs and fish larvae in 2006 to assess the extent of reproduction in the river. A spawning-ready male lake whitefish was collected in gillnets and several dozen viable lake whitefish eggs were collected with a pump in the Detroit River in November and December 2005. No lake whitefish eggs were found at lower river sites in March of 2006, but viable lake whitefish eggs were found at Belle Isle in the upper river in early April. Several hundred lake whitefish larvae were collected in the river during March through early May 2006. Peak larval densities (30 fish/1,000 m³ of water) were observed during the week of 3 April. Because high numbers of lake whitefish larvae were collected from mid-and downstream sample sites in the river, we believe that production of lake whitefish in the Detroit River may be a substantial contribution to the lake whitefish population in Lake Erie.     

Fish assemblage response to rehabilitation of a sand‐slugged lowland river

The impact of excessive sediment supply on river channels has been described in many areas of the world. Sediment deposition disturbance alters habitat structure by decreasing channel depth, changing substrate composition and burying woody debris. River rehabilitation is occurring worldwide, but information is scant on fish assemblage responses to rehabilitation in sediment‐disturbed lowland rivers. Sediment removal and large woody debris (LWD) replacement were used to experimentally rehabilitate habitat along a 1500 m stretch of the Glenelg River in western Victoria, Australia. Using an asymmetrical before‐after control‐impact (BACI) design, fish were captured before and after the reach was rehabilitated, from two control reaches and from a ‘higher quality’ reference reach. After two years post‐rehabilitation monitoring, the fish assemblage at the rehabilitated reach did not differ from control reaches. Temporal changes in taxa richness and the abundance of Philypnodon grandiceps, Nannoperca spp. and three angling taxa occurred after rehabilitation (winter 2003) compared with the before period (winter 2002), but these effects did not differ between rehabilitated and control locations. Highest taxa richness and abundances occurred at the reference location. High salinity coincided with the timing of rehabilitation works, associated with low river discharges due to drought. The negative effects of other large‐scale disturbances may have impaired the effectiveness of reach‐scale rehabilitation or the effects of rehabilitation may take longer than two years to develop in a lowland river subjected to multiple environmental disturbances. Copyright © 2009 John Wiley & Sons, Ltd.     

浊漳河三典型支流的水质对比研究

基于对浊漳河水系三典型支流2008年逐月进行水质监测分析,通过时空变异两个角度对这3条支流的水质进行了对比研究.结果表明:①以农业非点源污染为主的河谷平川河流水质最好;以农业非点源污染为主的高山峡谷河流,由于受到农业活动的影响,水质相对较差;受工业废水和城市生活污水污染的支流河流水质最差,有机物和氮磷指标严重超标.②3条支流中4个化学指标(NH4+-N、TN、TP、CODMn)在不同水域、不同季节具有明显差异.以农业非点源污染为主的河流氮营养盐浓度在丰水期较高,在枯水期较低,TP浓度和CODMn浓度在各个雨期之间变化不大,且相对稳定;以点源污染严重的河流氮营养盐浓度在枯水期最高,在丰水期最低,个别断面TP和CODMn污染表现突出.     

Seasonal movements of shortnose sturgeon (Acipenser brevirostrum) in the Altamaha River,Georgia

Shortnose sturgeon (Acipenser brevirostrum) populations were decimated by a variety of anthropogenic activities throughout much of the 20th century. Understanding the spatial and temporal dynamics of spawning migrations within natal rivers is a critical information gap with regard to habitat protection and ultimately, species recovery. The objectives of this study were to document and describe seasonal movements of shortnose sturgeon in the Altamaha River system, Georgia. Passive acoustic telemetry was used to monitor the movements of 40 adult individuals from April 2011 through February 2014. Telemetry data revealed that during much of the year, the adults resided within the tidally influenced portion of the river, with most detections occurring near the freshwater–saltwater interface. Upstream movements to potential spawning habitat occurred during winter and early spring, and most fish returned to the lower estuary by April. Upstream migrations appeared to be triggered by environmental cues and were initiated when mean weekly temperatures in the lower Altamaha River were 11.6–16.9 °C. Unlike spawning migrations documented in northern rivers, the pattern of movement observed in this study was a single‐step migration without an apparent resting or staging period. Upstream migrations during nonspawning months were also observed and appeared to correspond with increasing discharge, which potentially resulted in increased channel navigability and habitat availability in nondrought years. This study further illustrates the clinal variations in life history typical of the species and may have important implications on river‐specific strategies for species recovery.     

Fish Assemblage and Ecosystem Metabolism Responses to Reconnection of the Bird's Point‐New Madrid Floodway during the 2011 Mississippi River Flood

Understanding the ecological function of developed large rivers remains elusive because these systems have long been altered for multiple uses. In particular, floodplains of large rivers, such as the Mississippi River, have been contained behind extensive levees. A historic flood occurred in the lower Mississippi River system during spring of 2011, prompting the US Army Corps of Engineers to activate the Bird's Point‐New Madrid floodway, a 55 000‐ha, agriculturally dominated, leveed area. Water entered the floodway at flows >1 m s^?1 through two crevasses created in the upper portion of the levee and exited through a crevasse at the lower end. During the month, the floodway was inundated; we quantified discharge, water chemistry, primary production and fish production in the floodway and the adjacent river. Water entering the floodway was retained <1.3 d, and nutrient concentrations were not elevated in the floodway beyond those in the river, despite expected contributions from a legacy of fertilization. Primary production equaled respiration in the floodway, while the adjacent river was heterotrophic. Gizzard shad and freshwater drum were more abundant in the floodway than the river, while channel catfish were more abundant in the river. Growth rates of young native fishes, normalized for temperature, were the same in the floodway and the river, with the exception of gizzard shad, which grew faster in the floodway. Fish community structure, especially in the lower floodway, was temporally and spatially dynamic. Even though it has been heavily modified for agriculture, the floodway provided benefits, albeit limited, to the Mississippi River. With multifunctional management and strategic planning, systems such as these may provide substantial services such as flood abatement, nutrient transformation and fish production in the Mississippi River basin and potentially reduce nutrient loading downstream in areas such as the Gulf of Mexico. Copyright © 2015 John Wiley & Sons, Ltd.     

Spatial and temporal distribution of ichthyoplankton during an unusual period of low flow in a tributary of the São Francisco River,Brazil

Flow‐dependent fish specialists require specific conditions for reproduction, so the success and reproductive intensity of these animals are determined by the flood regime. Thus, this study investigated the spatial and temporal reproductive patterns of fish, especially migratory Prochilodus species (flow‐dependent specialists) in an unusual period of low flow in the Pará River sub‐basin, one of the main tributaries of the upper São Francisco River. For this, ichthyoplankton collections were carried out between November 2013 and February 2014. Data were analysed considering the spatial and temporal variations in density of eggs and larvae for the upper, middle, and lower portions of the Pará River sub‐basin, and correlating this to some environmental variables. The results showed that the small headwater stretch of the Pará River is one relevant spawning area for migratory fish species. However, this area is isolated by the Cajuru reservoir, which makes it uncertain the recruitment of these embryos, due to interruption of natural drift between spawning/nursery areas caused for reservoirs. Larvae of newly hatched migratory species found in tributaries of the lower Pará River sub‐basin also indicate these species use these tributaries as spawning grounds and migratory routes. The period in which the research was conducted represented the most atypical low flow, one in the last 75 years, resulting in the low variability in the environmental parameters. Although few parameters increased briefly in this low flow period influenced by greater rainfall in December, this precipitation was possibly responsible for the final gonadal maturation and spawning of migratory species.