Variation In Fish Assemblage Structure Research Articles

Spatial and Temporal Variation of Fish Assemblage Associated with Aquatic Macrophytes in Three Small Lagoons of the SOUTH-Eastern, Côte d’Ivoire

Aquatic plants play a crucial role in an aquatic ecosystem partly because these plant communities provide suitable habitats and food items to other aquatic organisms especially fish. The purpose of the present study was to examine spatial variation in fish assemblage structure associated with aquatic macrophytes in Ono, Kodjoboue and Hebe lagoons, three small lagoons of Côte d’Ivoire. Fish were monthly sampled from September 2014 to August 2016 using traps, gill nets, harpoons and hawks. The abiotic parameters namely temperature, transparency, pH, total dissolved solids, conductivity, dissolved oxygen, ammonium-nitrogen, nitrate, nitrite and phosphate were recorded for the characterization of the water mass in the lagoons. Significant variation in water parameters was observed among the sampling lagoons, except for nitrite and ammonium-nitrogen. However, no significant different was obtained between Kodjoboue and Hebe lagoons. A total of 42, 35 and 37 species were recorded respectively in Ono, Kodjoboue and Hebe lagoons, with Perciformes (22 species), Siluriformes (8 species) and Osteoglossiformes (7 species) being the most diverse Orders. Habitats with highly amounts of macrophyte cover provide the optimal environment for many fish and hence, increase the taxonomic richness, abundance, diversity and equitability. The multivariate analysis showed that temperature, dissolved oxygen, nitrate, phosphate, pH and ammonium-nitrogen and macrophyte were key environmental variables and played important roles in determining species composition of fish assemblages.

Seasonal and Spatial Variations in Fish Assemblage in the Yangtze Estuary and Adjacent Waters and Their Relationship with Environmental Factors

In this work, we identified the seasonal and spatial variations in fish assemblages and their relation to environmental variables in the Yangtze Estuary and adjacent waters. A total of 61 fish species in 32 families were identified over four seasons; of these, 12 species were dominant and Harpadon nehereus was the most dominant species. Fish varied in abundance, biomass, and species composition in different seasons; both biomass and abundance were highest in autumn and lowest in spring. Fish can be spatially divided into high-salinity assemblages and low-salinity assemblages. The spatial variation in fish assemblages was caused by the selectivity and adaptability of species for the environmental conditions of the estuary and the seasonal variation in fish assemblage structure likely resulted from migrations of dominant taxa associated with fish spawning and foraging behavior as well as the environment. The results of CCA analysis showed that temperature, depth, salinity, dissolved oxygen, and chlorophyll were the major factors affecting the fish assemblage differences throughout the seasons. Of these, temperature drove the seasonal variation in assemblage structure, while salinity significantly affected the spatial distribution of assemblages. This paper revealed the relationship between the seasonal and spatial distribution patterns of the fish assemblage and environmental factors and the results could provide a scientific basis for the management and sustainable utilization of fishery resources in the Yangtze Estuary and adjacent waters.

Complementary Sampling Methods to Improve the Monitoring of Coastal Lagoons

Monitoring the ecological status of marine coastal lagoons requires the integration of multiple indices. However, the efficacy of monitoring programs is complicated by the diverse array of habitats that conform coastal lagoons. In this study, we compared four sampling methods (25-m and 50-m beach seines, beam trawl and Riley push net) in the Ria Formosa coastal lagoon (South Portugal) for assessing fish assemblage and diversity. We compared species richness and assemblage structure with species accumulation curves and multivariate analysis, and assessed diversity patterns using taxonomic, phylogenetic and functional diversity indices. Variation in fish assemblage structure was mostly explained by gear type, and almost all diversity metrics varied not only according to sampling method but also depending on habitat characteristics and season. Based on operational costs and diversity patterns captured by each gear, we conclude that the combined use of 25-m beach seine and beam trawl is the preferred approach. The proposed methodology will provide the data necessary for assessment of ecological status of coastal lagoons.

Variation in Fish Abundance, Diversity and Assemblage Structure in Seagrass Meadows across the Atlanto-Mediterranean Province

Seagrasses worldwide provide key habitats for fish assemblages. Biogeographical disparities in ocean climate conditions and seasonal regimes are well-known drivers of the spatial and temporal variation in seagrass structure, with potential effects on associated fish assemblages. Whether taxonomically disparate fish assemblages support a similar range of ecological functions remains poorly tested in seagrass ecosystems. In this study, we examined variation in the abundance, diversity (from a taxonomic and functional perspective), and assemblage structure of fish community inhabiting nine meadows of the seagrass Cymodocea nodosa across three regions in the Mediterranean (Mallorca and Alicante) and the adjacent Atlantic (Gran Canaria), and identified which attributes typifying the structure of meadows, and large-scale variability in ocean climate, contributed most to explaining such ecological variation. Despite a similar total number of species between Mallorca and Gran Canaria, the latter region had more taxonomically and functionally diverse fish assemblages relative to the western Mediterranean regions, which translated into differences in multivariate assemblage structure. While variation in the abundance of the most conspicuous fish species was largely explained by variation in seagrass structural descriptors, most variation in diversity was accounted for by a descriptor of ocean climate (mean seasonal SST), operating at regional scales. Variation in fish assemblage structure was, to a lesser extent, also explained by local variability in seagrass structure. Beyond climatic drivers, our results suggest that lower temporal variability in the canopy structure of C. nodosa meadows in Gran Canaria provides a more consistent source of food and protection for associated fish assemblages, which likely enhances the more abundant and diverse fish assemblages there.

The Role of Aquatic Refuge Habitats for Fish, and Threats in the Context of Climate Change and Human Impact, during Seasonal Hydrological Drought in the Saxon Villages Area (Transylvania, Romania)

In spite of the obvious climate changes effects on the Carpathian Basin hydrographic nets fish fauna, studies on their potential refuge habitats in drought periods are scarce. Multiannual (2016–2021) research of fish in some streams located in the Saxon Villages area during hydrological drought periods identified, mapped, and revealed the refuge aquatic habitats presence, management needs, and importance for fish diversity and abundance for small rivers. The impact of increasing global temperature and other human activities induced hydrologic net and habitats alteration, decreased the refuge habitats needed by freshwater fish, diminished the fish abundance, and influenced the spatial and temporal variation in fish assemblage structure in the studied area. The sites more than one meter in depth in the studied lotic system were inventoried and all 500 m of these lotic systems were also checked to see what species and how many individuals were present, and if there is was difference in their abundance between refuge and non-refuge 500 m sectors. The scarce number of these refuges due to relatively high soil erosion and clogging in those basins and the cumulative effects of other human types of impact induced a high degree of pressure on the fish fauna. Overall, it reduced the role of these lotic systems as a refuge and for reproduction for the fish of downstream Târnava Mare River, into which all of them flow. Management elements were proposed to maintain and improve these refuges’ ecological support capacity.

Local Environmental Context Structures Animal-Habitat Associations Across Biogeographic Regions

The mechanisms that govern fauna-habitat associations across multiple spatial scales remain largely undefined. Can environmental factors structure fauna-habitat associations over both local and global spatial scales, alongside biogeographical processes and patterns? We compare the extent to which the use of mangroves by fishes is consistent within and between biogeographic locations, and whether any similarities and differences can be attributed to the environmental context of those forests, such as the physical environment, seascape composition and constraints on access by fishes. We focus on three important proxies of these structuring forces for fish—salinity, distance to reefs and tidal amplitude. Using directly comparable remote underwater visual census from a range of diverse environmental contexts in the Central and Eastern Indo-Pacific, we examine similarity in the family-level taxonomic composition of fish assemblages in mangrove forests. Local environmental context appears to explain similarities and differences in mangrove association by fishes at both regional and local scales across the Indo-Pacific. There were strong consistencies in taxonomic composition in similar environmental contexts despite geographic separation. Tidal amplitude was a powerful explanatory factor that interacted with both distance to reef and salinity in partitioning variation in fish assemblage structure. Substantial differences in the use of mangroves between regions appear to be independent of historical biogeography, relating instead to local context. Our findings suggest that the effects of local context on habitat suitability can play out over biogeographical scales, and global similarities in fauna-habitat associations may be partially explained by comparable environmental contexts, with important management implications.

Consistent but secondary influence of hydropeaking on stream fish assemblages in space and time

Hydropeaking corresponds to rapid artificial discharge variations, designed to address sub-daily peaks in electricity demand. It generates rapid changes in physical habitat (e.g., flow velocity and water depth) with potential impacts on stream assemblages. For assessing the generality of hydropeaking effects on fish assemblages, we present an original combination of spatial (among 45 reaches, including six groups of nearby reaches) and temporal (over 3-17 years) analyses of these effects. Our analyses involved descriptions of natural and artificial hydraulic variations in reaches, obtained after translating hourly discharge data into hydraulics. We found that the influence of hydropeaking was secondary compared to well-known spatial variations in fish assemblage structure along longitudinal gradients, and negative influences of floods on annual densities. However, the spatial and temporal analyses consistently suggested that hydropeaking may disfavour fish species typical of medium-sized streams relative to species of headwater streams (Salmo trutta, Phoxinus phoxinus, Cottus gobio). The magnitude of hydropeaking effects observed here, as well as an apparent weaker effect of ramping rates than the frequency of hydropeaks, may be due to lower ramping rates in our data set than in other studies.

Response of Fish Assemblages to Habitat Changes and Fishing Activity in a Tributary of the Jinsha River in Southwest China

AbstractReservoir impoundment affects fish habitat condition, in turn likely influencing the spatial and temporal distribution patterns of fish assemblage structure in the impounded area. Fishing activity and instream gravel and sand mining are important anthropogenic factors, and flow discharge, water temperature, and precipitation are important natural environmental variables; both anthropogenic and natural factors likely have impacted fish assemblage structure in impounded and unimpounded waterbodies. We used multivariate analysis to evaluate the combined effects of two adjacent reservoir impoundments in the main stem of a large river (Jinsha River; the upper segments of the Yangtze River), overfishing, instream gravel and sand mining, the natural flow regime, and other environmental variables (water temperature and precipitation) on fish assemblage structure in the Heishui River, a small, free‐flowing tributary upstream of the mainstream reservoirs. Fish assemblage data and abiotic data collected over 10 years (2008, 2010, and 2011–2017) were analyzed. The results showed that fish assemblages of the Heishui River temporally clustered into two groups that were strongly associated with the two downstream cascade reservoirs (Xiangjiaba and Xiluodu reservoirs) in the main‐stem Jinsha River. The relationships between fish assemblage structure and abiotic factors were tested using a distance‐based linear model and were visualized using distance‐based redundancy analysis, showing that the main factors explaining the interannual and seasonal variation in fish assemblage structure were instream gravel and sand mining, mainstream reservoir impoundment, and seasonal flow regime. Among these, instream gravel and sand mining in this tributary played the most significant role in affecting the temporal variation of fish assemblage structure and explained 34.12% of the total variability. Mainstream reservoir impoundment and seasonal flow regime exerted secondary effects on the temporal variation of fish assemblage structure and together explained 13.39% (7.00% and 6.39%, respectively) of the total variability. This study suggests that the relevant administrative agencies should focus more on free‐flowing habitat maintenance in this tributary and the control of instream gravel and sand mining.

Disentangling drivers of the abundance of coral reef fishes in the Western Indian Ocean.

AimUnderstanding the drivers of the structure of coral reef fish assemblages is vital for their future conservation. Quantifying the separate roles of natural drivers from the increasing influence of anthropogenic factors, such as fishing and climate change, is a key component of this understanding. It follows that the intrinsic role of historical biogeographical and geomorphological factors must be accounted for when trying to understand the effects of contemporary disturbances such as fishing.LocationComoros, Madagascar, Mozambique and Tanzania, Western Indian Ocean (WIO).MethodsWe modeled patterns in the density and biomass of an assemblage of reef‐associated fish species from 11 families, and their association with 16 biophysical variables.ResultsCanonical analysis of principal coordinates revealed strong country affiliations of reef fish assemblages and distance‐based linear modeling confirmed geographic location and reef geomorphology were the most significant correlates, explaining 32% of the observed variation in fish assemblage structure. Another 6%–8% of variation was explained by productivity gradients (chl_a), and reef exposure or slope. Where spatial effects were not significant between mainland continental locations, fishing effects became evident explaining 6% of the variation in data. No correlation with live coral was detected. Only 37 species, predominantly lower trophic level taxa, were significant in explaining differences in assemblages between sites.Main ConclusionsSpatial and geomorphological histories remain a major influence on the structure of reef fish assemblages in the WIO. Reef geomorphology was closely linked to standing biomass, with “ocean‐exposed” fringing reefs supporting high average biomass of ~1,000 kg/ha, while “lagoon‐exposed fringing” reefs and “inner seas patch complex” reefs yielded substantially less at ~500kg/ha. Further, the results indicate the influence of benthic communities on fish assemblages is scale dependent. Such insights will be pivotal for managers seeking to balance long‐term sustainability of artisanal reef fisheries with conservation of coral reef systems.

Fish assemblage and structure as well as hydrological parameters at Karatoya Fish Sanctuary, Panchagarh, Bangladesh

Abstract Spatiotemporal variation in fish assemblage structure was conducted from January to December 2015 in order to know the impacts of sanctuary on ichthyo-faunal diversity with its indices and major hydrological factors from six sampling stations of Karatoya fish sanctuary sectioned in the river Karatoya. A total of 69 fish species was obtained from this sanctuary including 21 threatened species where Aspidoparia jaya, Pethia ticto, Puntius sophore, Canthophrys gongota and Barilius barna was the major contributory species (> 4.17%) both in space and time. The uppermost species richness and abundance were viewed in January and lowest in May. Based on analysis of similarities (ANOSIM), fish assemblages were significantly different equally in station (P < 0.001, R = 0.15) and month (P < 0.001, R = 0.62). Through two-dimensional nonmetric multidimensional scaling (nMDS) and cluster analysis based on Bray-Curtis similarity index, assemblages were alienated into two groups at a value of 42% and 28% partition for station and month, respectively. Canonical Correspondence Analysis (CCA) recognized considerable relations between a number of fishes and hydrological parameters where dissolved oxygen (mg/l) and water temperature (oC) were the main leading factors in shaping fish assemblage structure.

Seasonal and longitudinal variation in fish assemblage structure along an unregulated stretch of the Middle Uruguay River

ABSTRACT Diversity patterns and their causes remain important questions, especially for ecosystems that preserve natural conditions. This is the case of fish diversity in large Neotropical rivers. In this context, we investigated fish diversity patterns along an extensive unregulated river section (ca. 450 km) in the Middle Uruguay River Basin. Sampling was conducted seasonally between May 2017 and March 2018, at six sites (patches) with contrasting environmental conditions. We collected 3,008 individuals belonging to 90 species. Nine were migratory, which summed relevant biomass in local assemblages (20 to 60%). We observed spatial variation in assemblage structure, but weak seasonal effects. Overall, biomass was similar among sites, but richness tended to increase downstream. Migratory fishes showed opposed trends, with higher richness and biomass upstream, particularly catfishes (Siluriformes). Ordination analyses separated sites in three groups based on variations in composition and abundance, and revealed associations between these groups and specific hydro-geomorphic conditions (i.e., flow, depth, channel width and the presence of riparian vegetation). Our study revealed that fish diversity distributes heterogeneously along the main channel, where hydro-geomorphic patches select for distinct assemblages along riverine gradients.

Do metacommunity theories explain spatial variation in fish assemblage structure in a pristine tropical river?

Abstract Understanding processes driving patterns of species distribution and diversity is one of the main objectives of community ecology. There has been a growing recognition that local environmental conditions are not the only factor structuring ecological communities, and that large‐scale spatial variation and dispersal also have major influences. The aim of our study was to evaluate spatial variation in fish assemblage structure along the longitudinal fluvial gradient of the Bita River, a nearly pristine tributary of the Orinoco River in the Llanos region of Colombia. Standardised surveys conducted at 34 sites throughout the basin during the low water period in January and March 2016 yielded 25,928 fish specimens representing 201 species. Twenty‐seven environmental variables were recorded at each site, and asymmetric eigenvector maps were used to model spatial variables. To understand spatial variation in local fish assemblages and their relationships with the environmental and spatial variables, two approaches were used. First, we applied the elements of metacommunity structure framework, followed by a variation decomposition analysis that allowed the metacommunity to be classified according to six alternative patterns of species distribution and four alternative metacommunity paradigms. We hypothesised that at a basin scale a major fraction of variation in structure is explained by a pure environmental effect and metacommunity patterns should reveal a Clementsian distribution. At a more regional scale (localities within a river section), assemblages in upstream and downstream regions may reflect different metacommunity processes. Because headwater streams are isolated within the river network, they should receive fewer migrants and may have local assemblages strongly influenced by local environmental conditions and species sorting with one of three possible distributional patterns (Clementsian, Gleasonian, or evenly spaced) would be observed. Conversely, downstream sites closer to the river mouth should be influenced by high dispersal, resulting in a greater importance of spatial factors and the mass effect, with metacommunity patterns nested along the longitudinal gradient. Our results suggest that the fish metacommunity in the Bita River exhibits a Clementsian distribution, implying that species respond to the environmental and fluvial gradient as groups along the longitudinal gradient. These replacements were associated with environmental heterogeneity, especially regarding habitat features. Similarly, the variation partitioning analysis showed that the pure environmental component was higher than the pure spatial component, which is consistent with species sorting. In this paper, we demonstrated that variation partitioning and metacommunity structure analyses provided complementary findings to infer processes structuring fish assemblages in the Bita River. Both approaches identified species sorting as the principal structuring processes in this system. Therefore, strategies to preserve fish diversity in this system must emphasise maintenance of habitat heterogeneity and connectivity.

Simultaneous assessment of two passage facilities for maintaining hydrological connectivity for subtropical coastal riverine fish

Engineering solutions that aim to restore hydrological connectivity in river systems fragmented by dams and weirs frequently include the installation of fish passage facilities (i.e. fishways). Assessment of fish passage performance is often limited to single fishway designs and with a focus on species of commercial or conservation significance, meaning that conclusions regarding fishway success may not apply to all species that require access to fragmented habitats. We simultaneously compared the population structure and fish assemblage composition at two fishways (vertical slot and fish lock designs) at weirs in a subtropical coastal river system. We used hydrological and physico-chemical water quality data to explore if fishway performance was linked to particular environmental conditions. At both fishways, fish assemblage composition differed between fishway exit and downstream river samples, yet differences between exit and river samples were not associated with hydrological variables related to the size and frequency of weir drown-out events or water quality. Population structure of the most abundant species (sea mullet, Mugil cephalus; 61% of fish samples) also differed significantly among fishway exit and river habitats. A low-level structure spanning the river channel downstream of one weir was not associated with differences in fish assemblage composition indicating that access to the fishway entrance (and therefore fishway use) was not hindered by in-stream obstructions. Eight and seven species (predominantly small-bodied species that migrate within freshwater systems) were exclusively sampled in downstream river locations at the vertical slot and fish lock fishways, respectively, indicating that neither design was fully capable of facilitating the passage of the local fish fauna. Further assessment over a broader range of hydrological conditions will be necessary to determine if use of either fishway by fish is affected by low flows. Coupled with evidence produced from landscape-scale analysis of spatial and temporal variation in fish assemblage structure and dispersal patterns of diadromous species associated with river flow regime highlight that hydrological connectivity may be maintained by natural weir drown-out events. This study highlights that factors controlling hydrological connectivity for riverine biota need to be integrated among co-occurring anthropogenic impacts to identify and overcome constraints to effective conservation management in rivers subject to water resource development.

Long-term study of reservoir cascade in south-eastern Brazil reveals spatio-temporal gradient in fish assemblages

In reservoir cascades, effects on fish assemblages are expected to strengthen over time and transfer from one reservoir to an adjacent one. To test this, fish-assemblage data from 23 years of monitoring in the Araguari reservoir cascade system, upper Paraná River basin, were analysed. The results showed a clear reduction in richness of native and migratory fish species and an increase of non-native species, following reservoir formation. Migratory species richness was higher in reservoirs that presented habitats similar to lotic stretches or tributaries upstream of the impounded area. There was a clear tendency for native species to decline and non-native fish species to increase, in a downstream direction. Fish assemblages became increasingly dissimilar as reservoirs became more distant from each other (longitudinal gradient) and were dominated by small and medium-sized species. Alongside longitudinal position, reservoir area, age and the presence of herbivorous non-native fish were found to be important predictors of variation in fish-assemblage structure. Results from the present study help clarify the potential accumulated impacts of reservoir cascades on fish diversity, which must be carefully considered in river-basin inventories for hydropower plants, and reinforce the importance of long-term monitoring, considering longitudinal and lateral dimensions of the basin.

Beta diversity of stream fish assemblages: partitioning variation between spatial and environmental factors

Abstract Studies that analyse the structure of assemblages across relevant spatial scales can ascertain generalisable patterns and be used to guide efforts that allocate resources meant to conserve regional biodiversity. Beta diversity can shed light on the underlying factors that drive variation in assemblage structure including spatial and environmental influences. The purpose of this study was to address two questions: (1) Which is more important for the structuring of fish assemblages, spatial or environmental factors? (2) What is the dominant pattern underlying species turnover between fish assemblages, species addition (i.e. nestedness) or species replacement (i.e. spatial turnover)? We examined fish beta diversity in southeastern Oklahoma by sampling 65 wadeable stream reaches and measuring 30 environmental factors at each sampling location across the Muddy Boggy River drainage. Variation in fish assemblage structure was partitioned between environmental and spatial predictors using partial redundancy analysis. Overall species turnover was calculated and separated into its two additive components of spatial turnover and nestedness to determine which of these two accounted for the most turnover across the drainage. Spatial and environmental factors combined accounted for 25.5% of fish beta diversity. Environmental factors alone accounted for 20.1%, while spatial factors alone only accounted for 3.5% of the variation among assemblages. Nine environmental factors were significantly related to fish beta diversity: (1) elevation; (2) stream order; (3) stream width; (4) % riffle habitat; (5) water temperature; (6) conductivity; (7) turbidity; (8) % gravel substrate and (9) current velocity. Overall species turnover was driven mostly by spatial turnover rather than nestedness. This pattern was found to be the same across multiple spatial scales (entire drainage, sub‐drainages, mainstems) and despite several techniques used to extract turnover coefficients. These results suggest that fish assemblages—particularly in headwater streams—are structured by environmental filtering and that these assemblages tend to be compositionally distinct, rather than being nested derivatives of one another.

Off‐reef planktivorous reef fishes respond positively to decadal‐scale no‐take marine reserve protection and negatively to benthic habitat change

AbstractThe effects of no‐take marine reserve (NTMR) protection and changes in benthic habitat on fusiliers (family Caesionidae) were investigated at four small Philippine offshore islands on time scales of 10–31 years. Fusiliers are highly mobile, schooling, medium‐sized planktivorous fish that generally feed “off‐reef.” For these reasons, and given the small size of the NTMRs (3.6–37.5 ha) in this study, it was predicted that fusilier density would be unlikely to show clear effects of NTMR protection, or to respond to changes in benthic habitat. In contrast to predictions, clear NTMR effects were observed on fusilier density at three of the four NTMRs, with durations of protection from 14 to 31 years. Furthermore, the study provided strong evidence that benthic variables, specifically cover of live hard coral and dead substratum, affect the density of fusiliers. This effect of benthic habitat on density was highlighted by several major environmental disturbances that caused shifts in the benthic habitat from live hard coral to dead substratum. For two of the three most abundant species of fusiliers individually, and for all three of them combined (Pterocaesio pisang + Caesio caerulaurea + Pterocaesio digramma/tessellata), as live hard coral cover decreased, fish density decreased. It is hypothesized that these “off‐reef” daytime feeders may have such a strong association with live hard coral cover because they use this habitat as nocturnal sleeping sites. Multivariate analyses indicated that, across all sites and times sampled, cover of live hard coral and dead substratum accounted for 38% of the variation in fish assemblage structure. These results are important as there are very few reports in the published literature of strong effects of NTMR protection or changes in benthic habitat on the density and assemblage structure of fusiliers.

Fish community dynamics in an inland floodplain system of the Okavango Delta, Botswana

Tropical floodplain fish populations fluctuate at temporal scales and understanding the variability in these systems will contribute to comprehensive management of these resources. Therefore, the aim of this study was to assess the dynamics of a floodplain fish assemblage. Data were collected using standard methods between 1999 and 2009 from the delta's panhandle. Various analytical tools (e.g. CCA, SIMPER, ANOVA, etc.) were used to assess fish assemblage dynamics at seasonal and annual scales. ANOVA and cluster analyses showed that the fish assemblage underwent significant changes along the seasonal hydrograph, while index of relative aboundance (%IRI) revealed that the fish assemblage was dominated by Clarias gariepinus, Schilbe intermedius and Hydrocynus vittatus respectively. These species, including Clarias ngamensis and Marcusenius altisambesi, contributed more than 50% to variations in fish assemblage structure along the seasonal hydrograph (based on SIMPER analysis). Furthermore, canonical correspondence analysis (CCA) revealed a significant (p=0.004) association between environmental factors and fish assemblage structure. CCA analysis also showed that spawning for different species is associated with various environmental factors. Annually, results showed that C. gariepinus dominated the fish assemblage during low flood years, while S. intermedius dominated during high flood years. Detrended correspondence analysis (DCA) showed that the hydrological gradient had a significant effect on fish assemblage structure at an annual scale, while SIMPER analysis established significant variations in fish assemblage structure among years characterized by different hydrological features. One major conclusion we made was that fish assemblages are stochastically different at an annual scale. This study contributes knowledge to floodplain fish ecology and thus enhances fisheries management.

Spatial and temporal variation of fish assemblage associated with aquatic macrophyte patches in the littoral zone of the Ayapel Swamp Complex, Colombia

Abstract: Aim The purpose of the present study was to examine spatial and temporal variation in fish assemblage structure associated with aquatic macrophytes in the littoral zone of the ASC. Methods Specimens were caught between January 2008 and February 2009, over four limnimetric moments, using both cast net and seine net. Data on the temperature, electrical conductivity, pH and dissolved oxygen was recorded for the characterization of the water mass in the sites. Results A total of 34,151 specimens from 44 species were collected. The most abundant species were Eigenmannia virescens, Astyanax caucanus, Astyanax fasciatus, Roeboides dayi and Cyphocharax magdalenae, which together accounted for more than 75% of the sample. Temporal and spatial comparisons showed variation in the environmental conditions and highlighted the existence of heterogeneous abiotic conditions (p&lt;0.05). However, the multiple comparisons test showed the existence of homogeneous spatial conditions (p&gt;0.05) regarding the fish assemblage structure. The multivariate analysis showed no significant relationship between existing environmental conditions and the fish assemblage (p=0.04). The analysis also showed the absence of a relationship between the fish assemblage and environmental variables with respect to the flood pulse and sampling sites (p&gt;0.05). Conclusion The uniformity of the fish communities that inhabit aquatic macrophyte patches in the littoral region of the ASC may be related to the availability of suitable habitat in structural terms, that probably supports a more abundant and varied wildlife.

Spatial variations in fish assemblage structure in a southeastern Brazilian reservoir.

We assessed the fish assemblage structure and composition of Nova Ponte Reservoir (Araguari River, Upper Paraná Basin, Brazil). We observed significant differences in abundance (p = 0.0003), richness (p = 0.0005) and diversity (p = 0.02) between lacustrine and riverine zones of the reservoir. Nine species were significantly more abundant in the riverine region: Astyanax altiparanae, Astyanax gr. fasciatus, Galeocharax knerii, Hoplias intermedius, Hypostomus sp., Leporinus friderici, Leporinus obtusidens, Pimelodus maculatus and Schizodon nasutus. The results indicated a longitudinal gradient in the composition and abundance of fishes in Nova Ponte Reservoir, reinforcing the importance of freely flowing riverine reaches for conserving native neotropical ichthyofauna and reflecting the strong adaptation of these species to riverine systems.

Diel variability in fish assemblages in coastal wetlands and tributaries of the St. Lawrence River: a cautionary tale for fisheries monitoring

Both coastal wetlands and tributaries of waterbodies provide important and distinct habitat for freshwater fishes. While diel migration into and out of these systems is known to occur for some species, the resulting changes in fish assemblage composition and dominance are less well understood. To evaluate diel changes in the fish assemblages of a coastal wetland and tributary, fish community surveys were completed at ten locations during the day (noon) and night (midnight) in Cooper’s Marsh, a coastal wetland in the St. Lawrence River, and the Raisin River, a nearby tributary. Catch per unit effort (CPUE) and species richness were highest in the coastal wetland during the night sampling period. Species-specific differences were also apparent with high CPUE of Mimic Shiner in the marsh at night. Differences within the river were less pronounced, suggesting less diel variability in fish assemblage structure, possibly driven by the more constrained nature of fluvial systems. These results contribute to our understanding of diel movement patterns of fishes and the natural diel variability in species assemblages that can occur. These findings also emphasize that when engaged in environmental monitoring and assessment, it is important to consider how diel variation in fish assemblage structure will influence conclusions regarding the biotic components of a given aquatic ecosystem.