Ecology of fish spawning and nursery zones in the flood plain,using a new sampling approach

Horizontal zonation of fish reproduction, a lotic-to-lentic succession similar to that seen with increasing stream order, was evident from the relative abundance of larval and 0 + juvenile fishes in three floodplain spawning and nursery areas (lotic, semi-lotic, lentic) of the Upper Rhône River, France. Although the lotic and lentic ecosystems provided similar estimates of standing crop (0 + juveniles), differences were apparent in the reproductive and trophic guild structure of the YOY taxocoenoses at the three sites. A new sampling approach (Random Point-Abundance Sampling and modified electrofishing) is described for early-life fish ecology. The electrofishing method employed is mobile, effective for all sizes of larvae and 0 + juveniles of most species, quantitative, and applicable to a number of freshwater situations; and the punctual data resulting from this sampling approach are comparable both spatially and temporally.     

Evaluation of a sweep net electrofishing method for the collection of small fish and shrimp in lotic freshwater environments

A major limitation of methods for collecting small fish and shrimp is that no single method is equally effective for all species or all life history stages. We compared the efficacy of the sweep net electrofishing (SNE) method with two other commonly used sampling methods for the collection of small fish and shrimp, the standard sweep net (SW) and the point abundance electrofishing (PAE) method developed by Copp & Penaz (1988). The effectiveness of the three methods was compared under three different current speeds in an Australian lowland river. The SNE method collected an order of magnitude more shrimp and a greater size range than the other two methods, irrespective of the current speed. The SNE method captured a similar number of fish to the SW method, but significantly more individuals than the PAE method. However, the two electrofishing methods caught a greater size range of both fish and shrimp than did the SW method. The effectiveness of the SNE method appears to be due to its ability to immediately capture shocked individuals, thereby lessening the likelihood of escape. Whilst the SNE method is not quantitative, its high level of effectiveness is likely to be particularly useful in systems with low densities of fish and shrimp.     

Method-integrated fish assemblage structure at two spatial scales along a free-flowing stretch of the Austrian Danube

Fish assemblages in large rivers are highly diverse communities. However, a single method to describe these complex systems adequately is not available as of yet. In this paper we propose a combination of normalized catch-per-unit-effort data of three fish sampling methods, thus providing a more inclusive representation of the overall assemblage. We investigate fish species occurrence and abundance in a survey at three consecutive sites in the free-flowing main channel of the Austrian Danube east of Vienna. Using boat and wading electrofishing, as well as longline fishing we collected data in four mesohabitats at each site. We analysed richness, assemblage structure and abundance of single species and tested site and mesohabitat as differentiating forces on the fish assemblage structure, applying PERMANOVA and NMDS. The investigated sites are populated by a species-rich fish assemblage, of which we collected a total of 36 species. The composition of the assemblage was rather consistent except for the occasional occurrence of rare species. At the smaller mesohabitat scale, however, the assemblages differed considerably and hydromorphological conditions were apparently the major structuring force. Overall, the combination of methods considerably improves the assessment across sites and mesohabitats and contributes to our understanding of large river fish assemblages.     

二滩水电站水库形成后鱼类种类组成的演变

本文对二滩水库建成前后,雅砻江下游长约380km河段的鱼类种类结构、生态类群及相对资源量的变化进行了研究。结果表明水库建成后不同区段的鱼类种类结构发生了变化,喜栖静水和缓流环境的种类逐渐在库区占主导地位,适应急流环境的种类主要分布于库尾和支流等局部水域中,一些外来种已经定居并在某些水域形成了优势种群。在水库建成后的头几年,由于鱼类种群密度增加还导致了渔业捕捞量大幅度上升。针对上述变化,结合雅砻江梯级电站建设可能带来的进一步环境改变,作者提出了建立自然保护江段、开展人工繁殖放流、进行水库生态调度以及防止外来种入侵等措施和建议。     

Inter and intraspecific variation in fish body size constrains microhabitat use in a subtropical drainage

Microhabitat characteristics are expected to influence the distribution of stream fish species at fine spatial scales (e.g., within riffle segments). Body size is probably the most important trait that constrains microhabitat occupation by fish, but the effect of intraspecific variation has been understudied. We investigated how physical microhabitat characteristics affect species and body size distribution of fish within a stream riffle segment in a coastal subtropical drainage of Brazil. Fishes were sampled by electrofishing 56 riffle plots along a 730-m long stream segment. Species composition was significantly related to four microhabitat characteristics: substrate size, flow velocity, distance to margin and depth. In addition, mean body size increased with increasing substrate size and depth of microhabitat sampling plots. However, when including species identity in linear mixed-effects models (LMM), we observed a different relationship between body size and microhabitat characteristics, but most of the variation was explained by species identity. Thus, we fitted LMMs separately for each species and found species-specific relations between intraspecific variation in body size and microhabitat characteristics. The low variation explained in the models suggests that other fine scale factors, such as biotic interactions and dispersal from adjacent habitat patches, should be incorporated in modeling microhabitat use by stream fish. Our findings suggest that body size is important by itself, but intraspecific variation in body size also constrains microhabitat use differently for each species, which may depend on other species-specific traits, such as morphology, behavior and life history.     

Mortality induced by electrofishing and handling in five young‐of‐the‐year cyprinids: effect of the fish size,species and anode size

Immediate mortality induced by electrofishing and handling of young‐of the‐year (YOY) fish of five cyprinid species (bitterling Rhodeus amarus, chub Leuciscus cephalus, bleak Alburnus alburnus, barbel Barbus barbus, roach Rutilus rutilus) was quantified during routine YOY fish monitoring (point abundance sampling with backpack electrofisher, in situ identification and measurement). Sampled, identified and measured fish were held in screened containers immersed in the river for 5 h after electrofishing. Bleak exhibited significantly higher mortality (17%) than all other species (1–3%). Mortality decreased significantly with fish length; fish <35 mm exhibited the highest mortality. Anode size (10, 20, and 30 cm diameter) had no direct effect on mortality. Point abundance electrofishing with in situ identification and measurement is a safe method for sampling riverine YOY cyprinids.     

Environmental DNA metabarcoding as an effective and rapid tool for fish monitoring in canals

We focus on a case study along an English canal comparing environmental DNA (eDNA) metabarcoding with two types of electrofishing techniques (wade-and-reach and boom-boat). In addition to corroborating data obtained by electrofishing, eDNA provided a wider snapshot of fish assemblages. Given the semi-lotic nature of canals, we encourage the use of eDNA as a fast and cost-effective tool to detect and monitor whole fish communities.     

Allopatric speciation in the desert: diversification of cichlids at their geographical and ecological range limit in Iran

Collated electrofishing data from wadeable riffles of boreal rivers in Finland revealed a substantial shift in the fish assemblage composition, accompanied by a decline in total fish density and a reduction in species richness from early summer to late autumn. As the major changes in fish assemblages, the density of cyprinids decreased sharply from June towards autumn, whereas salmonids peaked in September. These shifts were considered to originate mainly from spawning migrations, fish movements to winter refuge habitat and other temperature-related responses of rheophilic versus eurytopic fish species. Temporal change in fish assemblages induced a prominent variation in the monthly fish-based index values used for bioassessment. The proportion of sampled sites classified as high or good in ecological status within the Water Framework Directive (WFD) based on fish increased from 25.9% in July to 68.3% in October. These results, combined with the observed timing of young of the year (0+) fish recruitment to electrofishing catch, suggest that sampling of fish in boreal rivers for WFD monitoring should be restricted to a considerably shorter period than the prevailing practice in order to avoid temporal bias.     

Using new electrofishing technology to amp‐up fish sampling in estuarine habitats

A prototype, boat‐mounted electrofisher capable of operation in estuarine waters (where electrical conductivities often exceed 20 000 µS cm^?1) was assessed. Electrofishing was compared to fyke and mesh netting in four riverine estuaries and to seining in a lagoonal estuary (consisting of a series of brackish coastal lakes separated from the sea by a barrier system of sand dunes). Fish assemblage composition, length distributions and the probability of detecting ecological fish guilds (relating to estuary use, position in the water column and body size) were compared among gears. The assemblage composition of electrofishing samples differed from those of fyke nets in all riverine estuaries and from mesh netting in two. The assemblage composition of electrofishing samples differed from those of seining in structured seagrass habitats of the lagoonal estuary. When all species were pooled, the electrofisher sampled a broader range of lengths than either fyke or mesh netting in riverine estuaries or seining in lagoonal estuaries. The bias of electrofishing and netting towards particular species and size classes affected the probability of detecting some ecological guilds, highlighting the potential implications of gear choice on understanding estuarine ecological function. The detection of guilds varied with gear type and environmental conditions, including stratification, water depth and surface electrical conductivity. Assessments with the aim to characterize the structure of fish assemblages will benefit from the use of multiple gears. Electrofishing shows immense promise for discretely sampling highly structured habitats to test hypotheses about their use.     

Immediate impacts of the second impoundment on fish communities in the Three Gorges Reservoir

Long and short term investigations have revealed dramatic changes in fish communities after impoundments by reservoirs. However, the process of these changes during impoundment remains poorly studied. In 2005 and 2006, before and during the second stage of impoundment of the Three Gorges Reservoir (TGR), in the upper reaches of the Yangtze, China, we investigated fish catches to assess the impacts of reservoir filling on fish community structure. We conducted sampling at 2 sites, Wanzhou reach, which had been inundated by the first water filling in 2003, and Fuling reach, which still remained a riverine site before this water filling. The results revealed an evident and immediate shift of fish communities from lotic to lentic components. In the Wanzhou reach, during the filling, the abundance percentage of lentic fish increased to 94% compared to 69% before the filling. In the Fuling reach, after the filling, lotic fish declined in abundance from 99% to 85%, while lentic fish increased from less than 1% to 12% in abundance. Based on our investigation and the regulation scheme of the TGR, we predicted that after the completion of the Three Gorges Dam (TGD), there would be typical lacustrine, transitional and riverine zones in TGR, with their corresponding fish assemblages. We suggest that long term monitoring should be conducted to evaluate the future ecological effects, and different strategies implemented in these three zones for conservation purposes.     

The coexistence of fish species in streams: relationships between assemblage attributes and trophic and environmental variables

Diet overlap and niche breadth are well-known species traits from trophic ecology that can assist in explaining how species interact and coexist as well as the ecological mechanisms that influence biodiversity. In the present study, we analyzed the relationships between these trophic variables and indicators of resource availability with some attributes of fish assemblages (species richness, Shannon diversity index, evenness, density and individual body size). The physical and chemical characteristics of the biotopes (topography, water quality and conservation of slopes) were examined to identify possible patterns. Monthly sampling using electrofishing was conducted in 2003 along five streams located in the Cuiabá River watershed. The relationships between environmental variables and attributes of fish assemblages were evaluated using Spearman correlation. Species richness and abundance varied among streams, with higher values (54 and 82 species) found in low-gradient streams that drained small swampy areas discharging in Cuiabá River. Diet overlap showed significant and negative correlations with species richness, the diversity index, abundance, variation in body size and food availability and positive correlations with evenness and niche breadth. Environments that had greater food availability had a reduced variety of food items (smaller amplitude) and distinct values in terms of dietary overlap. Nevertheless, to explain resource partitioning in a fish assemblage (overlap), it is necessary to consider food availability and niche breadth (degree of trophic specialization) beyond the interaction of these variables with species richness and density. In conclusion, high diversity and abundance values were strongly associated with a high degree of trophic specialization (low amplitude of trophic niche) and a small degree of overlap in the diet.     

Temporal changes in fish diversity in lotic and lentic environments along a reservoir cascade

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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.     

Interacting effects of spatial gradients and fishing gears on characterization of fish assemblages in large reservoirs

Understanding the variation of fish assemblages in reservoirs is crucial for precise interpretations of ecological processes. However, representative samples in such environments are subjected both to spatial zonation (longitudinal and transversal gradients) and limitations of fishing gears. We used a large zoned reservoir (Itaipu, Brazil) to perform a quasi-experiment that assessed the relative role of spatial gradients and fishing methods on fish diversity and composition. Active (cast nets, electrofishing and seines) and passive (gillnets and longlines) fishing gears were employed in lotic, transitional and lentic habitats of the reservoir and three large tributaries. In total 6281 individuals of 101 species were captured. Sampling methods and spatial gradients had an influence on species composition, with significant interactions between these factors. In addition, results produced by a variation partitioning analysis suggested that 21 % of the species richness was explained by the sampling methods and 7 % by the longitudinal gradient; whereas for species composition, 12 and 3 % corresponded to sampling methods and transversal gradients, respectively. Overall, our results suggest that variations among fishing gears is greater than across strong spatial gradients, emphasizing the importance of using multiple and complementary fishing methods in reservoirs for characterization of fish assemblages. The interactions between spatial gradients and sampling methods were higher with transversal than with longitudinal gradients, suggesting that substantial differences in species richness and composition among sampling gears depend to some extent on habitat. The approach used here would be applicable to any large zoned inland waterscape.     

Fish Assemblages and Habitat in a Malaysian Blackwater Peat Swamp

Fish captured by electrofishing from lotic reaches within and immediately outside the North Selangor blackwater peat swamp forest were placed into six assemblages. Species richness varied among assemblages from 7 to 32 but most species were not regular members of an assemblage. Swamp water was low in dissolved oxygen and buffering capacity and high in color and acidity. Assemblages were associated with four discrete aggregations of abiotic conditions including oxygen, pH, color, conductivity and organic content of the substrate. Assemblages relatively rich in species and numerical abundance were associated with habitats comparatively high in oxygen and color and low in acidity. Species-poor assemblages were associated with habitats particularly low in oxygen and high in acidity.     

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.     

Effects of sampling techniques on population assessment of invasive round goby Neogobius melanostomus

In this study, a comparison of point abundance sampling (PAS) electrofishing, angling with two different hook sizes and trap‐based fishing was performed in a non‐wadeable river to analyse their effects on catch per unit effort (CPUE) and population characteristics of invasive round goby Neogobius melanostomus. PAS electrofishing was identified as the most effective (mean ± s.e . CPUE = 57 ± 4 N. melanostomus min^?1) and least selective method in terms of size, feeding status and species composition. Angling had the second highest CPUE, but was more size selective and resulted in a higher proportion of males compared to electrofishing [overall sex ratio angling (female:male) = 1:0·92, electrofishing 1:0·65]. Owing to low CPUE (0·012 ± 0·004) and low frequency of occurrence, minnow traps were least suitable for N. melanostomus population assessment. The results of this study suggest that a higher degree of standardization and inter‐calibration is useful to achieve better comparability of population data of invasive N. melanostomus and other benthic fish species.     

Observations of Size-related Asymmetries in Diet and Energy Intake of Rainbow Trout in a Regulated River

We examined diet and diel energy intake of rainbow trout, Oncorhynchus mykiss, of different lengths captured by electrofishing between 1991 and 1997 in the Lee's Ferry tailwater, Colorado River, below Glen Canyon Dam, Arizona. Trout diets reflected a depauperate food base and indicated limited potential of different fish size-groups to partition food resources. As evidenced by relative stomach volumes of ingested matter, mid-sized and large trout tended to consume more algae than did small fish, suggesting that they consumed diets of lower nutritional quality. An energy intake model indicated that median consumers among mid-sized and large fish generally failed annually to surpass estimated maintenance energy requirements and that median consumers among mid-sized trout failed to meet or exceed maintenance requirements during all seasons. In contrast, median consumers among small trout met or surpassed maintenance energy requirements during most years and in summer. Results support a hypothesis that larger rainbow trout in lotic systems are food-limited more often than smaller fish.