A field comparison of different boat electrofishers with comments on standardization

Using seasonally collected data (2009-2010) from 15 sampling sites that represent first- to fifth-order streams within the Qingyi watershed, we examined the spatio-temporal patterns of fish assemblages along two longitudinal gradients to explore the effects of a large dam on fish assemblages at the watershed scale. No significant variation was observed in either species richness or assemblage structure across seasons. Species richness significantly varied according to stream order and gradient. Dam construction appeared to decrease species richness upstream substantially, while a significant decrease between gradients only occurred within fourth-order streams. Along the gradient without the large dam, fish assemblage structures presented distinct separation between two neighboring stream orders, with the exception of fourth-order versus fifth-order streams. However, the gradient disrupted by a large dam displayed the opposite pattern in the spatial variation of fish assemblages related with stream orders. Significant between-gradient differences in fish assemblage structures were only observed within fourth-order streams. Species distributions were determined by local habitat environmental factors, including elevation, substrate, water depth, current discharge, wetted width, and conductivity. Our results suggested that dam construction might alter the longitudinal pattern in fish species richness and assemblage structure in Qingyi Stream, despite the localized nature of the ecological effect of dams.

The Guadiamar River (SW Iberian Peninsula) received a major toxic spill (6 hm3) from a tailing pond in 1998 that defaunated 67 km of the main stem. Following early mud removal works, the fish assemblage was annually monitored at four affected sampling sites and one located in the upstream non-affected reach of the Guadiamar River as reference. Fish abundance and assemblage structure were analysed. Principal response curve was applied to assess the recovery trends and to identify the most influential species. A non-metric multidimensional scaling ordination and permutational multivariate analysis of variance were applied to evaluate changes in fish assemblage structure between sites and years. Overall, the affected reaches harboured fish within 2 years of the spill. Colonists arrived mainly from the upstream and downstream non-affected Guadiamar River reaches and, to a lesser extent, from three lateral tributaries. It is likely that the proximity, connectivity and environmental conditions of non-affected fish sources greatly influenced the recolonization process in each site. The structure of the fish community in the affected sites was initially similar to that in the unaffected reference stretch but changed dramatically with time, and each site followed its own trajectory. Currently, long-term threats such as mining leachates, urban sewage, agricultural pollution and exotic fish species expansion have probably exceeded the initial spill effect. This highlights the large effect of anthropogenic factors on freshwater ecosystem resilience, and the need to significantly reduce both pollution and exotic species if the affected reach of the Guadiamar River is to recover fully. Copyright © 2015 John Wiley & Sons, Ltd.

Although the Mekong River is one of the world's 35 biodiversity hot spots, the large‐scale patterns of fish diversity and assemblage structure remain poorly addressed. This study aimed to investigate the fish distribution patterns in the Lower Mekong River (LMR) and to identify their environmental determinants. Daily fish catch data (i.e. from December 2000 to November 2001) at 38 sites distributed along the LMR were related to 15 physicochemical and 19 climatic variables. As a result, four different clusters were defined according to the similarity in assemblage composition and 80 indicator species were identified. While fish species richness was highest in the Mekong delta and lowest in the upper part of the LMR, the diversity index was highest in the middle part of the LMR and lowest in the delta. We found that fish assemblages changed along the environmental gradients and that the main drivers affecting the fish assemblage structure were the seasonal variation of temperature, precipitation, dissolved oxygen, pH and total phosphorus. Specifically, upstream assemblages were characterised by cyprinids and Pangasius catfish, well suited to low temperature, high dissolved oxygen and high pH. Fish assemblages in the delta were dominated by perch‐like fish and clupeids, more tolerant to high temperatures, and high levels of nutrients (nitrates and total phosphorus) and salinity. Overall, the patterns were consistent between seasons. Our study contributes to establishing the first holistic fish community study in the LMR.

\n We assessed the effects of land use on the structure of stream fish assemblages in Northwest Patagonia, Argentina. To this end, a total of 18 sites distributed in 15 streams were sampled during the low water period. At each site, 26 regional and local scale variables were used to describe the environmental conditions. The macroinvertebrate density, and the composition and abundance of fish were then recorded. Statistical associations between local assemblage structures and environmental variables were quantified by canonical correspondence analyses. The results revealed that, at a regional scale, the fish assemblages were primarily determined by watershed features like altitude and catchment area, and by land use effects (exotic forest and pasture). Assemblage compositions were also related to some local-scale features such as water velocity, food availability (density of benthic macroinvertebrates), instream characteristic and riparian features. Also, the observed fish species richness was low. Overall, exotic salmonids largely dominated in the samples both in numbers of individuals (98.9%) and in biomass (99.9%), whereas native fish (Hatcheria macraei and Odontesthes hatcheri) were scarcely represented. Rainbow trout (Oncorhynchus mykiss) was the most abundant fish, and was present in all streams. Native species were restricted to five streams located in the ecotone between the Andes and the steppe, where salmonids were also present. Salmonids were the only fish at Andean streams which suggest the existence of a strong geographic segregation between native and exotic species. Some aspects related to the incidence of the introduced species in the structure of fish assemblages are discussed.\n

Assemblage Organization of Stream Fishes: The Effect of Rivers on Adventitious Streams

River classification is a necessary starting point for understanding river ecosystems and developing management guidelines. Using GIS to analyse an Andean river basin, we compare the application of two geomorphic classification methods at the segment scale: The Geomorphic Units Survey Classification System (GUS) and the Functional Process Zones (FPZ). Segment definition follows a manual procedure in GUS and a semi‐automated procedure in FPZ. Our objective was to assess the relationship between geomorphology and fish assemblages' structure. Fish sampling was carried out in collaboration with participants from local indigenous Mapuche‐Pewenche communities. Non‐parametric multivariate statistical analyses were conducted in order to quantify and describe geomorphic patterns and whether fish assemblages responded consistently with river classifications. Both classifications give insight into the physical characteristics of rivers, such as slope and floodplain width, that make habitat available for different fish assemblages. The two methods provide results that consistently coincide in their identification of geographic distribution and main geomorphic variables of different river types (geomorphic types) throughout the river network. The variation of different river geomorphologies was associated with variation in fish assemblage structure. Geomorphic variables that best characterize the distribution pattern of fish assemblages were elevation, confinement and valley floor width. Confined rivers accommodated highly similar fish assemblages dominated by invasive trout (Salmo trutta and Oncorhynchus mykiss). Unconfined rivers located at higher elevations had greater temporal variability and were mainly composed of trout and native catfish Trichomycterus areolatus. Semiconfined rivers presented the highest geomorphic variability and were associated with high spatial and temporal variability of fish assemblages characterized by both native and non‐native species. The association between fish assemblages and fluvial geomorphology could help in prioritizing rivers for exotic fish species control. These findings should aid in restoring highly intervened Andean rivers and improving management techniques in basins with a variety of human activities.

SUMMARY 1. Biological resilience is of heightened concern in increasingly anthropogenic landscapes. Quantification of faunal resilience across a wide range of spatial scales and geographical areas is necessary to understand factors influencing the rate and degree of recovery, especially in fragmented ecosystems. 2. We evaluated the recovery of a riverine fish assemblage from a major diesel oil pipeline spill and associated fish kill in 37 km of the Reedy River, South Carolina, U.S.A. The fish assemblage was monitored at four disturbed sites within the fish kill zone and one upstream, undisturbed reference site over a 112-month (9.3-year) period following the disturbance. We used non-metric multidimensional scaling (NMS) ordination to evaluate change in fish assemblage structure among sites and to determine the degree of recovery in assemblage structure. 3. NMS ordination of species relative abundance in two dimensions represented 93% of the total variation in fish assemblage structure among samples and illustrated recovery of the fish assemblage. Initial dissimilarity in assemblage structure was evident between the disturbed sites and the reference site, reflecting high mortality from the oil spill. The disturbed sites as a group increased in similarity to the reference assemblage with time, while the reference assemblage remained relatively stable. Strongest similarity in assemblage structure between the disturbed group and the reference group was achieved by October 2000 (52 months post-disturbance), indicating recovery from the oil spill. Remaining variation in assemblage structure was consistent with longitudinal site position and comparable to that of an undisturbed reference river, attributable to inherent longitudinal variation along the 37-kilometre river section. 4. Recovery rate among sites varied in relation to proximity and connectivity to recolonisation sources on a landscape scale. Recovery of the uppermost disturbed site was faster than the other disturbed sites because of its proximity to the undisturbed main stem fish assemblage, whereas the three most downstream sites were slower to recover largely because of isolation by anthropogenic barriers. These observations illustrate the influence of fragmentation on fish assemblage resilience at large spatial scales.

Understanding drivers of freshwater fish assemblages is critically important for biodiversity conservation strategies, especially in rapidly developing countries, which often have environmental protections lagging behind economic development. The influences of natural and human factors in structuring fish assemblages and their relative contributions are likely to change given the increasing magnitude of human activities. To discriminate natural and human drivers of fish diversity and assemblage patterns in developing countries with rapid socio‐economic development, a dataset of 908 freshwater fish species and 13 metrics including three categories of both natural (i.e., biogeographic) and human drivers (i.e., economic growth, inland fisheries) in China were analysed with machine learning algorithms (i.e., self‐organizing map, random forest). Here, we found that biogeographic drivers explained 21.8% of the observed fish assemblage patterns in China and remained stronger predictors when compared to human drivers (i.e., 15.6%, respectively). Freshwater fish species richness was positively correlated to rainfall, air temperature, surface water area and inland fisheries production but negatively correlated with urbanization. In addition, the strong structuring effects of climatic variables on Chinese fish richness patterns suggested that the fish assemblages could be particularly vulnerable to climate change. Our results showed that natural biogeographic factors still dominate in driving freshwater fish assemblage patterns despite increased human disturbances on aquatic ecosystems in a rapidly developing country. These findings consequently suggested that we should consider both natural (e.g., climate) and human (e.g., urbanization, inland fisheries) factors when establishing aquatic conservation strategies and priorities for developing countries that are experiencing rapid socio‐economic changes.

River regulation and development are the foremost problems threatening lotic fishes and other aquatic biota in the United States. The operation of hydroelectric facilities can influence both habitat availability and environmental stability in downstream reaches. We evaluated the relative influence of habitat complexity and environmental stability on fish assemblage structure at unregulated and hydropower‐regulated reaches of the Flint River in southwestern Georgia. The availability of different habitat types was highly variable at the regulated reach owing to large, daily fluctuations in discharge. Habitat‐specific fish assemblages also differed between reaches, as a greater number of species occupied identical habitat types at the unregulated reach, most notably in shallow, slow‐flowing habitats. Differences in fish assemblage structure between study reaches in comparable habitat types were explained equally well by patterns of habitat structure and variability. Within‐reach patterns of fish assemblage structure were best explained by patterns of habitat structure at both study reaches. However, the relative influence of habitat complexity and habitat stability differed within each study reach, habitat variability influencing fish assemblage structure to a greater extent at the regulated reach than at the unregulated reach. These differences suggest that both habitat structure and variability influence Flint River fish assemblages and that flow regulation associated with hydropower operation primarily affects riverine fish communities by increasing environmental variability. Thus, flow management plans for regulated rivers based on minimum flows may be most effective when implemented in conjunction with plans that reduce the spatial and temporal variability of habitat availability, particularly in shallow, slow‐flowing habitats.

Channelization and urbanization are anthropogenic alterations that act on the reach- and catchment-scale, respectively, to degrade stream habitats. As urban areas continue to expand in the tropics the number of channelized streams will likely increase as well. We examined in-stream habitat and fish assemblage structure in stream reaches with a range of channel alterations and sub-catchment urban land use in the Rio Piedras watershed, Puerto Rico. Nine reaches were surveyed and classified into three categories: unaltered channels (natural), channels that had been straightened and may have reinforced banks (intermediate), or channels where the bank and bottom was replaced with concrete (concrete-channelized). Fishes were sampled using triple-pass electrofishing and relevant reach- and catchment-scale abiotic environmental variables were measured for each site. Fish assemblage structure in the Rio Piedras appears to be influenced by both reach- and catchment-scale abiotic environmental factors. Natural and intermediate reaches with moderately high levels of sub-catchment urbanization had relatively high biomass, species-rich, and native-dominated fish assemblages whereas concrete-channelized reaches with very highly urbanized sub-catchments had fish assemblages with few to no native species and highly abundant, tolerant, and exotic species.

A description of the patterns in spatial variability of fish assemblages is particularly relevant to guarantee an adequate management of these marine resources. Thirty six trawls were considered on six seagrass meadows (10 km apart) in three islands (100 km apart) of the Canary Islands to (i) analyze the spatial variability in the structure (richness, abundance and diversity) of fish assemblages associated with Cymodocea nodosa seagrass meadows, and to (ii) assess how the structural complexity of this habitat affects fish assemblage structure. A total of 3,616 fishes were captured, belonging to 30 species and 15 families. The total length of ca. 95% of individuals was < 10 cm, and ca. 90% of individuals were juveniles. Spatial variability in fish assemblage structure was larger when considering the scale of meadows than the scale of islands (27.28% vs. 6.64% respectively, in the amount of explained total variability); the smallest spatial scale (i.e., the variability among replicated trawls within each seagrass meadow) accumulated the largest amount of variability (66.07%). Differences in fish assemblage structure were largely driven by changes in the abundance of a few species, including Diplodus annularis, Spondyliosoma cantharus, Mullus surmuletus and Symphodus trutta. These species recruited into seagrass meadows, and confirmed the nursery role of this habitat in the canarian coastal waters. Mean shoot density and variation of the seagrass canopy height were the descriptors that accounted for the most variability when explaining patterns in fish assemblage structure.

Conservation of lotic fishes requires consideration of complex patterns among a changing mosaic of fish assemblage structure at multiple spatial scales. Studies have demonstrated the influence of localized competition and predation among stream fishes, but researchers have been largely unable to determine to what extent interspecific interactions act to control fish assemblage structure. Recent declines to geographic range and abundance of Plains Topminnow (Fundulus sciadicus (Cope)) have been anecdotally attributed to altered fish assemblages and potential competitive or predatory associations; however, important species interactions have yet to be identified. Variation among fish assemblage structure at 473 locations known to historically support Plains Topminnow was described in Nebraska to demonstrate the role of assemblage dynamics in regulating species occurrence. Nonrandom patterns of fish assemblage composition in terms of Plains Topminnow persistence were apparent statewide, and multiple...

BackgroundSince the late 1990s, bigheaded carps (largely silver carp [Hypophthalmichthys molitrix] but also bighead carp [H. nobilis]) have established throughout the lower Mississippi River basin. Using previously studied oxbow lakes in the lower White River basin, Arkansas, we compared current (2017, “post-carp” establishment) fish assemblages to historical (2002, “pre-carp” establishment) fish assemblages. Fish assemblages were comprehensively assessed using multiple gears, including boat electrofishing, mini-fyke nets, and experimental small-mesh gill nets.ResultsT-tests suggested that fish assemblage indices of richness, diversity, evenness, and dominance were often greater (P < 0.05) during the post-carp period as reflected by boat electrofishing and experimental gill nets. However, all indices were generally similar (P > 0.05) between the pre-carp and post-carp period with fish assemblages depicted using mini-fyke nets. Nonmetric multidimensional scaling analyses indicated that fish assemblages differed structurally between pre-carp and post-carp periods. Assemblage differences were linked to both small and large abundance changes for more than 20 species. Abundances of gizzard shad (Dorosoma cepedianum), emerald shiner (Notropis atherinoides), pugnose minnow (Opsopoeodus emiliae), crappies (Pomoxis spp.), bluegill (Lepomis macrochirus), orangespotted sunfish (L. humilis), and yellow bass (Morone mississippiensis) declined between the pre-carp and post-carp periods. Conversely, abundances of weed shiner (N. texanus), pallid shiner (Hybopsis amnis), longear sunfish (L. megalotis), buffalofishes (Ictiobus spp.), and gars (Lepisosteus spp.) generally increased during the same period.ConclusionsAlthough not possible to conclude assemblage shifts were entirely related to bigheaded carps due to the absence of an appropriate reference system where carps did not establish, the wide establishment of these carps is one of the most pervasive changes to have occurred in the lower White River ecosystem during the past two decades. Thus, it is probable to conclude that post-carp establishment observations from this study were at least, in part, attributable to bigheaded carp establishment. Impacts of further range expansions by bigheaded carps in the White River and other lower Mississippi River sub-basins are unclear, though this study suggests probable effects on native fish assemblages, underscoring the need for further research and monitoring.

news and update ISSN 1948-6596 thesis abstract Potential impacts of climate change on the distribution of fresh- water fishes in French streams and uncertainty of projections Laetitia Buisson PhD, Laboratoire Evolution et Diversite Biologique, Universite Paul Sabatier, Toulouse, and La- boratoire d’Ecologie Fonctionnelle, ENSAT, Castanet-Tolosan, France Current address: Laboratoire Evolution et Diversite Biologique, Universite Paul Sabatier, Tou- louse, France; E-mail: buisson@cict.fr; http://www.edb.ups-tlse.fr/ Climate change and its impact on biodiversity are receiving increasing attention from scientists and people managing natural ecosystems. Recent modifications of climate have induced diverse functional (e.g. phenology, physiology) and struc- tural (e.g. species distribution shifts, range con- traction, local extinctions) responses among or- ganisms (Walther et al. 2002). Given the projec- tions of future climate change, these responses are expected to continue throughout the 21st century and climate change could thus have major consequences on species and assemblages. A common approach to project the potential im- pacts of environmental changes on the distribu- tion of biodiversity is the use of species distribu- tion models (SDM) (e.g. Thuiller 2003). These cor- relative models first relate the present-day spe- cies distribution to a set of climate and other envi- ronmental descriptors. Then, the application of scenarios of future climate changes provides pre- dictions of the habitats potentially suitable in the future for the species. In spite of their widespread use, a growing concern has emerged for the vari- ability in the predicted impacts by such models due to the methodological decisions taken during the modeling process (Thuiller 2004). Improve- ments in the accuracy of predictions combined with an estimation of the uncertainty inherent to those predictions are thus urgently needed. Among freshwater ecosystems, stream fish have no physiological ability to regulate their body temperature and could therefore be very sensitive to climate warming, especially cold-stenotherm fish such as salmonid species. Stream fish also have to cope with hydrological variability of streams and strong anthropogenic pressures (e.g. habitat loss, stream fragmentation). In addition, they have limited dispersal ability within hydro- graphic networks in which they currently live. Yet their response to current and future climate change has been poorly documented and few studies have used SDM to assess the potential consequences of the on-going climate change on freshwater fish species distribution, especially in European streams. In that context, the aim of my PhD thesis was to assess the potential impacts of climate change on fish in French streams, mainly on spe- cies distribution and assemblages’ structure. I used fish data provided by the Office National de l’Eau et des Milieux Aquatiques (ONEMA), the in- stitution in charge of the protection and conserva- tion of freshwater ecosystems in France. These data were combined with climate and environ- mental descriptors through the use of correlative statistical modeling. As my goal was to provide reliable estimates of the future impacts of climate change on stream fish, I have considered recent criticisms (e.g. choice of statistical method, pure bioclimatic models) of species distribution models by justifying each step and optimizing the use of such models. In all, five papers are derived from my PhD work. The first three papers set the bases for the building of the models by considering the uncertainty in predictions, while the latest two assess the impacts of climate change on stream fish species and assemblages. In stream fish ecology, many studies have been conducted to identify the environmental drivers structuring fish assemblages (reviewed in Matthews 1998). It appears that fish species distri- bution and structure of fish assemblages are de- termined by a complex interplay of biotic, abiotic and spatial factors (Jackson et al. 2001). Disentan- © 2009 the authors; journal compilation © 2009 The International Biogeography Society — frontiers of biogeography 1.2, 2009

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