Prioritising the rehabilitation of fish passage in a regulated river system based on fish movement

Environmental rehabilitation budgets are often limited, and management actions need to be prioritised to achieve the best outcomes. Prioritisation can best be done when evidence informs the decision‐making process. We acoustically tagged twenty Golden Perch (Macquaria ambigua) in the Loddon River, Australia, and tracked their movements to gain an understanding on the requirements for fish passage at a major regulating structure, the Box Creek regulator. The movements of these fish were monitored through a network of receivers located throughout the lower Loddon River and Pyramid Creek system. Five fish moved 50–120 km upstream, four of which reached the Box Creek regulator before moving back downstream to the entrance of the Kerang Lakes system. Most long distance upstream movements were associated with an increase in river discharge. The remaining 15 fish moved <20 km, with all fish being detected at least once. This pilot study indicates that Box Creek regulator is acting as a barrier for some fish within the Loddon River system. Movement data also indicate that Golden Perch migration pathways may be influenced by river discharge. The management implications of this work includes the need to reinstate fish passage at Box Creek regulator and the potential use of environmental flows to enhance colonisation of native fish species throughout the Murray Darling Basin.     

Diel distribution patterns of fishes in a temperate large lowland river

During the day, juveniles and typical inshore species in the lower Oder River, Germany, inhabited the littoral (0·05–1·50 m deep) while potamal species inhabited the mid‐channel (40–100 m from the banks). During the night, two behavioural groups were distinguished: 1) potamal species and large individuals of other species, moved from offshore to the littoral, and 2) nocturnal foraging species, became active and increased in inshore and offshore habitats. Inshore, the most significant differences at night was the increasing density of silver bream Blicca bjoerkna increasing both total biomass and total length of fishes caught. Offshore, the increasing density of whitefin gudgeon Gobio albipinnatus at night was most significant. Additional night electrofishing improved the assessment of the abundance, age and size structure of typical potamal fish species. It should be incorporated in large river fish monitoring programmes.     

Habitat utilisation by fish community in a short-term regulated river reservoir

Short-term streamflow regulation (hydropeaking) affects the ecology of regulated rivers. We examined the longitudinal and temporal changes occurring in fish assemblages in a hydropeaking single river reservoir between two power plants by using electrofishing along the shoreline, hydroacoustics and test fishing in the open water. A longitudinally changing fish community was found among bottom-dwelling fish in the fast-flowing and highly disturbed upstream part of the reservoir progressing to generalists and pelagic fish in the lentic and most stable environment at the downstream end. The fish assemblage showed temporal patterns as fish density increased during night-time darkness and also towards autumn. Our work provides evidence for gradient effects of flow regulation and contributes to awareness of the effects of disturbance (flow/habitat variability) on biological systems.     

Simple predictions of instream habitat model outputs for target fish populations

1. Bottom-up approaches based on individual behaviour can help to identify key variables influencing populations at larger scales. Instream habitat models have been developed to predict the consequences, for populations in stream reaches, of fish preferences for particular hydraulic conditions observed at the scale of individuals. Conventional instream habitat models (e.g. PHABSIM) predict habitat values for species or life stages in reaches, and their changes with discharge. Despite their worldwide use, they have been subject to continuing criticism and have been mainly limited to site-specific case studies.
2. We ran conventional instream habitat models in 58 French stream reaches dominated by brown trout. Using non-linear mixed effect models, we demonstrated that the outputs of instream habitat models (habitat values for three trout life stages and five other species) are predictable from average characteristics of reaches (discharge, depth, width and bed particle size).
3. Our models closely reflect variations in habitat values within-reaches (with discharge) and between-reaches. Within-reach changes are linked to the Reynolds number of reaches, while between-reach changes depend mainly on the Froude number at median daily discharge. These two dimensionless variables combine discharge, mean depth and mean width of reaches. Independent model validations showed robust model predictions that are consistent with studies of habitat values for brown trout made in larger streams from western North America.
4. Our results contribute to identifying the main hydraulic variables governing estimates of fish habitat values. They should facilitate habitat studies in multiple streams, at the basin or larger scales, while reducing their cost. They should enhance the biological validation of habitat model predictions, which remains critical.     

Spatio-temporal distribution patterns and conservation of fish assemblages in a Chilean coastal river

River environments are characterized by extreme spatial and temporal variation in the physical environment. The relationship of fish assemblages to environmental variation is poorly understood in many systems. In Chile zonation patterns of fish assemblages have been documented in several Andean river drainages. Coastal river drainages are comparatively small, but inordinately important because of their highly endemic flora and fauna and their proximity to major human populations. For conservation purposes it is important to understand what environmental factors affect assemblage structure of fishes especially in the comparatively high diversity coastal drainages. We studied patterns of fish distribution and abundance in three rivers of the coastal, Andalien drainage near Concepción, Chile. We used multi-dimensional scaling analyses to compare patterns among zones (rithron, transition and potamon) and high and low flow seasons. Species assemblages differed by zone, but not with season. Assemblages consisted of nested subsets of species characterized by their range of distribution among zones. One species group was composed of widespread species that occurred in all three zones, another species group consisted of species found only in transitional and potamal zones, and a final group was comprised of species found only in the potamal zone. The potamal zone contained the most diverse and abundant fish assemblage. Fish assemblages were related to both water quality and habitat structure variables. This study suggests that the key to conserving the diversity of native fish communities in coastal Chilean rivers is in the conservation of potamal regions. Unfortunately, most protected areas in Chile are in the depauperate headwaters of drainages. Protection of only headwaters is clearly inadequate and will not contribute to the conservation of this unique freshwater fish fauna.     

Regionally nested patterns of fish assemblages in floodplain lakes of the Magdalena river (Colombia)

We investigated if fish assemblages in neotropical floodplain lakes (cienagas) exhibit nestedness, and thus offer support to the managers of natural resources of the area for their decision making. The location was floodplain lakes of the middle section of the Magdalena river, Colombia. We applied the nested subset analysis for the series of 30 cienagas (27 connected to the main river and three isolated). All fish were identified taxonomically in the field and the matrix for presence-absence in all the lakes was used for the study of the pattern of nestedness. The most diverse order was Characiformes (20 species), followed by Siluriformes (19 species). Characidae and Loricaridae were the richest families. The species found in all the lakes studied were migratory species (17), and sedentary species (33). Two species (Caquetaia kraussii and Cyphocharax magdalenae) were widespread across the cienagas archipelago (100% of incidence). Nestedness analysis showed that the distribution of species over the spatial gradient studied (840 km) is significantly nested. The cienagas deemed the most hospitable were Simiti, El Llanito, and Canaletal. Roughly, 13 out of the 50 species caught show markedly idiosyncratic distributions. The resulting dataset showed a strong pattern of nestedness in the distribution of Magdalenese fishes, and differed significantly from random species assemblages. Out of all the measurements taken in the cienagas, only the size (area) and local richness are significantly related to the range of order of nested subset patterns (r=-0.59 and -0.90, respectively, at p < 0.01). Differential species extinction is suggested as the cause of a nested species assemblage, when the reorganized matrix of species occurring in habitat islands is correlated with the island area. Our results are consistent with this hypothesis.     

Determining diel variation in fish assemblages downstream of three weirs in a regulated lowland river

The diel variation in boat electrofishing catches was investigated on the lower Murray River (south-eastern Australia), downstream of three low-level weirs. Fish assemblage composition did not differ among three sites, but differed substantially between day and night. Significantly more small-bodied species ( e.g. Australian smelt Retropinna semoni , flyspecked hardyhead Craterocephalus stercusmuscarum , bony herring Nematalosa erebi and Murray rainbowfish Melanotaenia fluviatilis ) and some large-bodied predators ( e.g. golden perch Macquaria ambigua ) were caught during daytime samples. Significantly more flatheaded gudgeon Phylipnodon grandiceps , carp gudgeon Hypseleotris spp. and perch Perca fluviatilis were collected at night. The size composition of the fish assemblage also changed over the diel cycle. Significantly smaller goldfish Carassius auratus , flyspecked hardyhead, bony herring and Australian smelt were sampled during the day, while generally smaller individuals of golden perch and the common carp Cyprinus carpio were caught at night. These findings suggest that sampling during both day and night is required to adequately characterize riverine fish assemblages in the context of fish migration studies.     

Applying an index of biotic integrity based on fish assemblages in a West African river

A multivariate measure of river quality, the Index of Biotic Integrity (IBI), was adapted to a West African river, the Konkoure (Republic of Guinea). Fish assemblages were sampled using gill-nets during the dry season to provide data for the IBI. Ten metrics were subsequently defined. The capacity of the modified IBI to assess the impact of a bauxite treatment plant was tested. The IBI decreased as expected at the impacted station. Detailed examination of the data revealed that one family, the Mormyridae, was almost eliminated from the impacted station, suggesting that members of this familiy can be considered as intolerant species in future uses of the IBI in other African rivers.     

Development of a spatially universal framework for classifying stream assemblages with application to conservation planning for Great Lakes lotic fish communities

Classifications are typically specific to particular issues or areas, leading to patchworks of subjectively defined spatial units. Stream conservation is hindered by the lack of a universal habitat classification system and would benefit from an independent hydrology‐guided spatial framework of units encompassing all aquatic habitats at multiple spatial scales within large regions. We present a system that explicitly separates the spatial framework from any particular classification developed from the framework. The framework was constructed from landscape variables that are hydrologically and biologically relevant, covered all space within the study area, and was nested hierarchically and spatially related at scales ranging from the stream reach to the entire region; classifications may be developed from any subset of the 9 basins, 107 watersheds, 459 subwatersheds, or 10,000s of valley segments or stream reaches. To illustrate the advantages of this approach, we developed a fish‐guided classification generated from a framework for the Great Lakes region that produced a mosaic of habitat units which, when aggregated, formed larger patches of more general conditions at progressively broader spatial scales. We identified greater than 1,200 distinct fish habitat types at the valley segment scale, most of which were rare. Comparisons of biodiversity and species assemblages are easily examined at any scale. This system can identify and quantify habitat types, evaluate habitat quality for conservation and/or restoration, and assist managers and policymakers with prioritization of protection and restoration efforts. Similar spatial frameworks and habitat classifications can be developed for any organism in any riverine ecosystem.     

The effects of recreated instream and ecotone structures on the fish fauna of an epipotamal river

Investigations of fifteen sections of seven Austrian epipotamal (barbel region) streams between 1981 and 1984 demonstrate the impact of instream river bed structures on fish communities. Reduced spatial heterogeneity due to river straightening resulted in decreasing species number, diversity, stock density and biomass. Reincreased variability of the river bed in the frame of a subsequent restructuring project improved all community-specific values significantly within a 3-year investigation period (1988–1990). Besides the regained habitat variability in form of riffle pool sequences and other instream structures, the newly created riparian zones obviously provided important niches, e.g. as refuge areas during flooding and as nursery grounds for fish fry. The positive effects of the recreated land/water ecotone are discussed with respect to river restoration projects.     

Using macroinvertebrate species assemblages to identify river channel habitat units: an application of the functional habitats concept to a large,unpolluted Italian river (River Ticino,northern Italy)

The functional habitat concept was applied to a large Italian river for the first time. The characteristically wide range of hydraulic conditions present in this river (compared to previously-studied small, lowland, English rivers) were expected to be of central importance to biota and, therefore, to habitat definition. TWINSPAN analysis of the invertebrate assemblages sampled in the Ticino river identified five distinct habitats: two habitats in lotic areas (run-riffle and macrophytes in current), two along the river margins (with and without macrophytes) and one in backwater areas. These correspond to five of the functional habitats identified in U.K. lowland rivers. Each of these five functional habitats could be defined either in terms of hydraulics, substratum and/or presence/absence of macrophytes. Representative taxa are presented for each habitat and community structure discussed. Macrophyte and run-riffle habitats supported the most heterogeneous and abundant benthic fauna. No match was found between replicates grouped by invertebrate assemblage (the five functional habitats identified by TWINSPAN) and the grouping of the same replicates by PCA, carried out on the physical data matrix. While obvious velocity differences were found between the functional habitats, of particular note was the fact that the Froude number did not show any clear association with habitat type. In the future, improved river management will follow improved understanding of river habitats.     

Larval fish assemblage recovery: a reflection of environmental change in a large degraded river

Estuaries are globally important to fisheries but face many anthropogenic stressors that reduce water quality and degrade benthic habitat. The Maumee River estuary has been degraded by industrial contaminants, high sediment and nutrient loads, channelization and elimination of surrounding wetlands, lessening its value as spawning habitat for fishes of Lake Erie. Regulation and better management practices (BMPs) in the watershed have improved the water quality in this estuary, which should result in a response of the biotic community. We compared recent (2010/2011) larval fish assemblage data to similar data from the 1970s (1976/1977) in order to identify changes due to improved water and habitat quality. Family‐level diversity was greater in recent study years compared to the 1970s and family richness increased from 6 to 10. In addition, the abundance of lithophilic spawning fishes was significantly greater in the recent study years. Increased diversity and family richness were consistent with increased water quality in the Maumee River whereas the observed increase in abundance of lithophilic spawners was consistent with an increase in the amount or quality of benthic habitat used by species in these families for spawning. Better wastewater management and agricultural practices in coastal watersheds can benefit the early life stages of fishes, thus benefitting coastal fisheries. Furthermore, larval fish assemblages may be useful indicators of biological integrity because of their sensitivities to environmental change. Routine sampling of estuarine larval fish assemblages could provide practitioners with insight into ecosystem changes and measure the response of the biotic community to restoration.     

Spatio-temporal distribution of young fish in tributaries of natural and flow-regulated sections of a neotropical river in French Guiana

1. We investigated which environmental parameters control the variation in density, in space and time, of young stages of fish in tributaries of a natural and a flow-regulated section of the Sinnamary River, French Guiana.
2. The density of the progeny in most taxa varied in space and/or time. However, most non-Perciformes responded differently to space and/or time in the two sections.
3. Oxygen, turbidity and habitat structure (i.e. bank length, occurrence of undercut bank, richness in litter, vegetation and substratum) were important, as was the position of the sampling site relatively to the main channel in the downstream tributaries, in explaining the variation of density in space in both sections. Both habitat complexity and distance from the main channel protect young fish against unpredictable flow releases downstream from the Petit Saut dam.
4. Hydrological events played an important role in the temporal variation in densities of many fish taxa. The density of most early life and many juvenile stages (mostly Characiformes) was positively related to hydrological events.
5. Some fish taxa had reproductive habits which were relatively independent of abiotic factors, such as flow variability, and the density of their progeny did not vary with time.
6. The nursery areas of more than 45% of species in the Sinnamary River have been degraded by flow regulation.     

Simple predictions of instream habitat model outputs for fish habitat guilds in large streams

1. In the context of a generalised modification of hydraulic conditions in medium to large streams, modelling the impacts of stream regulation on fish communities in multiple streams is an important challenge for basic and applied freshwater ecology. Conventional instream habitat models such as PHABSIM link a hydraulic model with preference curves for various species to estimate habitat value changes with discharge in stream reaches. Despite world‐wide applications, they have been scarcely used in multiple sites with multiple species. 2. We assigned 21 size classes of European fish species to four habitat guilds (cluster analysis grouping size classes with comparable microhabitat preference curves). Then, we ran a conventional instream habitat model on 28 French stream reaches belonging to the `barbel zone', to estimate habitat values versus discharge curves for the 21 size classes. We summarised the outputs as mean habitat values for guilds, and tested if they were predictable from average characteristics of reaches (discharge, depth, width, particle size). 3. As was obtained elsewhere for populations, habitat values for guilds were strongly related to average, dimensionless characteristics of reaches. The Reynolds number of reaches, equivalent to a discharge per width unit, reflected most of the discharge‐dependent changes in habitat values (within reaches). In particular, habitat values of species preferring bank (respectively midstream) microhabitats decreased (respectively increased) with increasing Reynolds number. The Froude number at median discharge was the major predictor of reach‐dependent but discharge‐independent variations in habitat values. Habitat values of species preferring riffle versus pool or bank microhabitats were higher in reaches with high Froude numbers. These relationships were consistent with existing knowledge on the different species. 4. Such results suggest that the input variables required to estimate habitat values for fish communities can be greatly simplified, as illustrated by a general estimation of the sensitivity of species preferring midstream habitats to discharge changes in any reach. Cost‐efficient alternatives to conventional instream habitat models should facilitate their validation in multiple sites, a point that remains critical in instream habitat modelling of fish communities.     

Habitat diversity and fish assemblages in an African river basin (Nyagui River, Zimbabwe)

Little is known about the ecology of stream fishes in Zimbabwe and this study investigated fish communities in the Nyagui River basin and is one of the first to examine the relationship between fish assemblages and habitat diversity in Zimbabwe. Fourteen sampling stations were, for convenience, divided into three groups; upper (>1400 m above sea level), middle (1000–14000 m) and lower stations (<1000 m). A total of 24 species were collected, four of which were introduced, and the species composition differed according to the location of the stations. Species that favoured running water and/or rocks were generally absent from the upper stations, reflecting the fact that they were mostly sandy‐bottomed and still. Diversity and relative abundance increased in the mid‐ and low‐altitude stations, which were rockier and faster flowing. Both species diversity and relative abundance increased with the catchment area above each station, which was attributed to increased habitat diversity in larger streams. This view was supported by a strong correlation between habitat diversity and catchment area, and between habitat diversity and species richness and relative abundance. At present, the Nyagui system is relatively unregulated but the Kunzvi Dam, presently under construction, will change this situation and species diversity is likely to decrease owing to the loss of rheophilic species while other groups, notably cichlids and introduced species will increase.     

Reef fish assemblages in north-western Sri Lanka: distribution patterns and influences of fishing practises

The distribution and abundance of reef fishes in relation to habitat structure were studied within Bar Reef Marine Sanctuary (BRMS) and on an adjacent reef, disturbed by destructive fishing techniques, in north-western Sri Lanka, by visually censusing 135 species groups using fifty metre belt-transects. Two types of continental shelf patch-reefs are found in the study area: coral reefs and sandstone reefs, which are divided into distinct habitats, four for the coral reef (shallow reef flat, shallow patch reef, deep reef flat and Porites domes) and two for the sandstone reef (structured sandstone-reef and flat sandstone-reef). Fish assemblages varied in structure between reef types and among habitats within reef types. Functional aspects of habitat structure and composition, such as available food and shelter, seemed to be important factors influencing distribution patterns. The strongest separation in the organisation of fish assemblages in BRMS was between reef types: 19% of all species were confined to the coral-reef patches while 22% were restricted to the sandstone reef patches and 59% were represented on both reef types. In terms of distribution among habitats, 21% of all species were restricted to one habitat while only 1.5% were present in all. The highest density of fish was in the coral reef habitats while highest species diversity was found in the most structurally complex habitat: the structured sandstone-reef. This habitat also had the highest proportion of species with restricted distribution. Planktivores were the most abundant trophic group in BRMS, and the species composition of the group varied among habitats. The comparison of the disturbed reef with BRMS suggested that habitat alteration caused by destructive fishing methods has strongly influenced the fish community. Within the fished area the structure of the fish assemblages was more heterogeneous, fish abundance was lower by an order of magnitude and species numbers were lower than in BRMS.     

Relationship between flow regime and fish abundances in a gravel‐bed river, New Zealand

The key elements of the flow regime of the Waipara River on the east coast of New Zealand, that affected fish abundances were the timing of floods and the magnitude and duration of low flows. Generally, fish abundances were highest in early summer, and lowest at the beginning of winter. Spring floods opened the river mouth, allowing recruitment of diadromous fish species, and non‐diadromous fish species spawned after the floods in spring or early summer. Reductions in fish abundances over summer and autumn were consistent with the magnitude and duration of low flows, with significant reductions in the year of lowest flow and little change in abundance in the year when low flows were highest. Variations in fish abundances during periods of low flow were consistent with the amount of instream habitat available, such that abundances of species with high velocity preferences decreased during periods of low flow, whereas abundances of species with low velocity preferences increased.     

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

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Longitudinal patterns of fish assemblages in a large tropical river in southeastern Brazil: evaluating environmental influences and some concepts in river ecology

This study aimed to evaluate environmental influences on fish distribution and to assess the extent to which concepts in river ecology accommodate levels of spatio-temporal heterogeneity of fish assemblages in a 1,080-km long tropical river. A total of 25 sites were sampled between November 2002 and March 2003 in two seasons (summer/wet versus winter/dry). A thermal gradient separating the upper reaches from the lower reaches was detected. The middle-upper reaches showed higher conductivity and lower dissolved oxygen and pH levels compared with the other reaches. Although some significant associations were found between some fish abundance and environmental variables, the most abundant species (Tilapia rendalli, Geophagus brasiliensis, and Oligosarcus hepsetus) occurred in most sites and under most environmental conditions. Fish community structure varied more in space (longitudinal) than through time (seasonal). The community in the lower reach species was more diverse in comparison with the other reaches. Differences in the fish assemblage structure among the longitudinal river sections appear to have been influenced by the effects of damming, and seem to be partially consistent with the Serial Discontinuity Concept, which views dams as discontinuities within the river continuum. Only the lower river reach showed seasonal differences in the fish community structure, attributable to the influence of flooding. Management plans and biodiversity conservation will benefit by considering the effects of dam disruption and flood increased connectivity to the lotic systems. Handling editor: J. Trexler