Riverine Habitats Research Articles

Gradients in Catostomid Assemblages along a Reservoir Cascade

AbstractSerial impoundment of major rivers leads to alterations of natural flow dynamics and disrupts longitudinal connectivity. Catostomid fishes (suckers, family Catostomidae) are typically found in riverine or backwater habitats yet are able to persist in impounded river systems. To the detriment of conservation, there is limited information about distribution of catostomid fishes in impounded rivers. We examined the longitudinal distribution of catostomid fishes over 23 reservoirs of the Tennessee River reservoir cascade, encompassing approximately 1600 km. Our goal was to develop a basin‐scale perspective to guide conservation efforts. Catostomid species composition and assemblage structure changed longitudinally along the reservoir cascade. Catostomid species biodiversity was greatest in reservoirs lower in the cascade. Assemblage composition shifted from dominance by spotted sucker Minytrema melanops and buffalos Ictiobus spp. in the lower reservoirs to carpsuckers Carpiodes spp. midway through the cascade and redhorses Moxostoma spp. in the upper reservoirs. Most species did not extend the length of the cascade, and some species were rare, found in low numbers and in few reservoirs. The observed gradients in catostomid assemblages suggest the need for basin‐scale conservation measures focusing on three broad areas: (1) conservation and management of the up‐lake riverine reaches of the lower reservoirs, (2) maintenance of the access to quality habitat in tributaries to the upper reservoirs and (3) reintroductions into currently unoccupied habitat within species' historic distributions. Copyright © 2017 John Wiley & Sons, Ltd.

Neogene paleogeography provides context for understanding the origin and spatial distribution of cryptic diversity in a widespread Balkan freshwater amphipod.

BackgroundThe Balkans are a major worldwide biodiversity and endemism hotspot. Among the freshwater biota, amphipods are known for their high cryptic diversity. However, little is known about the temporal and paleogeographic aspects of their evolutionary history. We used paleogeography as a framework for understanding the onset of diversification in Gammarus roeselii: (1) we hypothesised that, given the high number of isolated waterbodies in the Balkans, the species is characterised by high level of cryptic diversity, even on a local scale; (2) the long geological history of the region might promote pre-Pleistocene divergence between lineages; (3) given that G. roeselii thrives both in lakes and rivers, its evolutionary history could be linked to the Balkan Neogene paleolake system; (4) we inspected whether the Pleistocene decline of hydrological networks could have any impact on the diversification of G. roeselii.Material and MethodsDNA was extracted from 177 individuals collected from 26 sites all over Balkans. All individuals were amplified for ca. 650 bp long fragment of the mtDNA cytochrome oxidase subunit I (COI). After defining molecular operational taxonomic units (MOTU) based on COI, 50 individuals were amplified for ca. 900 bp long fragment of the nuclear 28S rDNA. Molecular diversity, divergence, differentiation and historical demography based on COI sequences were estimated for each MOTU. The relative frequency, geographic distribution and molecular divergence between COI haplotypes were presented as a median-joining network. COI was used also to reconstruct time-calibrated phylogeny with Bayesian inference. Probabilities of ancestors’ occurrence in riverine or lacustrine habitats, as well their possible geographic locations, were estimated with the Bayesian method. A Neighbour Joining tree was constructed to illustrate the phylogenetic relationships between 28S rDNA haplotypes.ResultsWe revealed that G. roeselii includes at least 13 cryptic species or molecular operational taxonomic units (MOTUs), mostly of Miocene origin. A substantial Pleistocene diversification within-MOTUs was observed in several cases. We evidenced secondary contacts between very divergent MOTUs and introgression of nDNA. The Miocene ancestors could live in either lacustrine or riverine habitats yet their presumed geographic localisations overlapped with those of the Neogene lakes. Several extant riverine populations had Pleistocene lacustrine ancestors.DiscussionNeogene divergence of lineages resulting in substantial cryptic diversity may be a common phenomenon in extant freshwater benthic crustaceans occupying areas that were not glaciated during the Pleistocene. Evolution of G. roeselii could be associated with gradual deterioration of the paleolakes. The within-MOTU diversification might be driven by fragmentation of river systems during the Pleistocene. Extant ancient lakes could serve as local microrefugia during that time.

Annual Changes in Seasonal River Water Temperatures in the Eastern and Western United States

Changes in river water temperatures are anticipated to have direct effects on thermal habitat and fish population vital rates, and therefore, understanding temporal trends in water temperatures may be necessary for predicting changes in thermal habitat and how species might respond to such changes. However, many investigations into trends in water temperatures use regression methods that assume long-term monotonic changes in temperature, when in fact changes are likely to be nonmonotonic. Therefore, our objective was to highlight the need and provide an example of an analytical method to better quantify the short-term, nonmonotonic temporal changes in thermal habitat that are likely necessary to determine the effects of changing thermal conditions on fish populations and communities. To achieve this objective, this study uses Bayesian dynamic linear models (DLMs) to examine seasonal trends in river water temperatures from sites located in the eastern and western United States, regions that have dramatically different riverine habitats and fish communities. We estimated the annual rate of change in water temperature and found little evidence of seasonal changes in water temperatures in the eastern U.S. We found more evidence of warming for river sites located in the western U.S., particularly during the fall and winter seasons. Use of DLMs provided a more detailed view of temporal dynamics in river thermal habitat compared to more traditional methods by quantifying year-to-year changes and associated uncertainty, providing managers with the information needed to adapt decision making to short-term changes in habitat conditions that may be necessary for conserving aquatic resources in the face of a changing climate.

Abiotic factors drive the structure of aquatic plant assemblages in riverine habitats of the Brazilian “Pantanal”

The “Pantanal” wetland is one of the largest centers of diversity of aquatic macrophytes of Brazil. The objective of this work was to present a checklist of aquatic macrophytes, and to investigate structure and patterns of occurrence regarding physico-chemical parameters, at Amolar, in the Paraguay River sub-region, in the mid-western “Pantanal” wetland, Corumba (MS). No previous aquatic plant study has been carried out there so far. The study was conducted in June 2009 in 391 plots (0.5 × 0.5 m). We recorded 65 species of aquatic macrophytes, from 49 genera and 27 families. The richest families were Fabaceae, Poaceae, Convolvulaceae, Onagraceae, and Lentibulariaceae. The most representative life forms were emergent and free floating, comprising the most frequent species: Hymenachne amplexicaulis (Rudge) Nees, Salvinia auriculata Aubl., Ricciocarpos natans (L.) Corda, Lemna aequinoctialis Welw. and Azolla filiculoides Lam. presented the highest relative cover, as well as the highest importance value, followed by S. auriculata. The structure of the community of aquatic macrophytes presents relation with physico-chemical variables, chiefly depth: many species occurred exclusively in shallow areas and others in deep zones. The life forms partially explain the species zonation of macrophytes in relation to depth.

The value of abandoned olive groves for blackcaps (Sylvia atricapilla) in a Mediterranean agroecosystem: a year-round telemetry study

The European Common Agricultural Policy has promoted the intensification of productive olive orchards and the abandonment of the unproductive ones. This strategy has resulted in a significant loss of biodiversity and ecosystem functionality of this type of agroecosystem. Here, we studied the blackcap Sylvia atricapilla, a common frugivorous bird species, in an olive-dominated agroecosystem of southern Spain to assess the effects of the abandonment of olive groves and undergrowth structure on habitat selection in this species. By means of radiotelemetry, we determined habitat selection of blackcaps during both the breeding (N = 30) and the non-breeding (N = 27) seasons of 2011 and 2012. We found that outside the breeding season, olive groves were widely used by blackcaps, which invariably preferred abandoned olive groves over intensively managed ones. Additionally, deciduous woods and poplar plantation were positively selected, whereas open habitats and Pinus forests were avoided. Generally, woody habitats without undergrowth or with herbaceous undergrowth were avoided. During the breeding season, the species selected mainly riverine habitats and poplar plantations, favoring habitats with well-developed undergrowth. Our results suggest that the blackcap could benefit from maintaining patches of abandoned olive groves freely left to natural succession within intensive olive groves. In such a landscape, ecological services (i.e., seed dispersal provided by frugivorous birds) and functioning could also improve as a consequence of these measures.

Application of large wood in regulated riverine habitats facilitates native fishes but not invasive alien round goby (Neogobius melanostomus)

Application of large wood in regulated riverine habitats facilitates native fishes but not invasive alien round goby (Neogobius melanostomus)

Population trends and current status of the endangered Pyrenean sculpin Cottus hispaniolensis in the Spanish part of the Garonne drainage

The status of Pyrenean sculpin Cottus hispaniolensis was assessed in the Spanish part of the Garonne drainage on the basis of its distribution and abundance from 2001 to 2016. Population trends showed a progressive reduction in range extension and density, exacerbated by a severe spate occurred in 2013. However, C. hispaniolensis was resilient to this natural disturbance by compensating for mortality with increasing recruitment. Both occurrence and density of Pyrenean sculpin showed a positive correlation with coarse substrates. Riverine habitat deterioration, mainly channelization, presence of dams and flow regulation are the main factors threatening sculpin populations. Several management measures are proposed.

Ontogenetic shifts in habitat use during the dry season by an amphidromous shrimp in a tropical lowland river

Caridean shrimp have considerable effects on ecosystem processes and, thus, understanding their use of key habitats is important for determining their potential ecological effect. The present study examined the meso-habitat use of Macrobrachium spinipes, a large-bodied and important amphidromous species, in the Daly River, northern Australia. We examined shrimp abundance at four common meso-habitat types; sand bank, rock bars, undercut and structurally complex banks and mid-channel areas at five sites on three occasions during the dry season (May to October). We found that habitat use changed considerably first, with ontogeny, and, second, with the colonisation of habitats with algae and macrophytes as the dry season progressed. As juveniles, their habitat use was strongly associated with well structured bank environments early in the dry season. By the mid-dry season, juveniles were more abundant within sand habitats recently colonised with macrophytes and filamentous algae. Females showed little change in habitat use, whereas large-bodied dominant males generally favoured rock bars and heavily structured bank environments. The present study has provided significant insights into the changes in use of key riverine habitats throughout the dry season by an ecologically important species. This information will be of considerable value to the determination of environmental flow requirements and food-web investigations.

Analysis of Vortex Pool-and-Chute Fishway

Fishways are constructed in riverine habitats where structures such as culverts, dams, and flood channels have negatively impacted flow conditions suitable for the movement of native and migratory fish species. These auxiliary channels are engineered to resist gravitational force with frictional force, resulting in sustained depth and reduced velocity over a range of design flow rates. The Chézy hydraulic resistance coefficient accounts for such forces and provides a metric useful for determining the effectiveness of a fishway to alter flow conditions prohibitive to the passage of fish. The objective of this analysis was to use a scale model of an innovative vortex pool-and-chute fishway, that operates with both plunging and streaming flow simultaneously, designed by Michael Love and Associates, to determine the Chézy resistance coefficients over a range of flow rates under controlled hydraulic conditions. Using dimensional analysis to ensure proper scaling allowed laboratory measurements of the model to be translated into a real-world prototype design. The conceptual prototype fishway is a 144-foot-long by 30-foot-wide channel with an 8% slope. A 1:15 scale model was constructed to evaluate the design at prototype equivalent flow rates between 58 and 283 cubic feet per second (cfs). Chézy coefficients were estimated by two different calculation methods; the streaming flow method and the streaming and plunging flow method. Coefficients ranging between 22.3 and 39.2 ft1/2/s were determined by the streaming flow calculation method, whereas the streaming and plunging flow calculation method yielded estimates from 18.9 to 25.0 ft1/2/s at corresponding flow rates. For flows that were exclusively plunging, values of 32.2 to 41.9 ft1/2/s were found. In general, Chézy coefficient estimates were observed to decrease with increasing discharge and values were found to be comparable to those calculated for fishways implemented at similar slopes. The preliminary model fishway results indicated that implementation of a prototype fishway could effectively alter flows for adequate fish passage under the given conditions. KEYWORDS: Hydraulics; Fish Passage; Fishway; Chézy Coefficient; Geometric Scaling; Froude Scaling; Streaming Flow; Plunging Flow; Dimensional Analysis; Similitude

The Hydra regeneration assay reveals ecological risks in running waters: a new proposal to detect environmental teratogenic threats.

The regenerative ability of Hydra vulgaris was tested as potential biomarker for the development of a new eco-toxicological index. The test is based on the regeneration rate and the aberration frequency of the columna (body and adhesive foot) after separation from head and tentacles by a bistoury. Particularly, 45 columnae were submerged in the rearing solution (that is Hydra medium) to have control, and 285 in potential contaminated waters to have treatments, collected from 19 sites along 10 rivers in central Italy. ANCOVA and chi-square tests were used to compare values from each site to a laboratory control. Subsequently the values on regeneration rate and aberration frequency were inserted in a double entry matrix, where the match of the two entries in the matrix provides the score of the proposed Teratogenic Risk Index (TRI). Each score corresponded to one of the 5 teratogenic risk classes, to which a risk level was associated: from 1 (no risk) to 5 (very high risk). On the whole, 32% of the studied sites were classified as no teratogenic risk while the remaining showed a variable risk level from low to very high. This study proposed for the first time an early warning system to detect the presence of teratogens in running waters, providing a rapid and cost-effective evaluation method. Therefore, TRI may contribute to initiate adequate measures to manage riverine habitats, and to monitor the running water teratogenic status. Specifically, this index may provide the opportunity to identify the disturbance sources and then to drive the decisions, together with competent authorities, on the catchment and landscape management and on the possible use of waters for urban, agricultural, and industrial activities, since they may show significant effects on the human health.

Status of the imperiled Alabama Sturgeon (Scaphirhynchus suttkusiWilliams and Clemmer, 1991)

Summary The Alabama Sturgeon (ALS) Scaphirhynchus suttkusi has the smallest maximum size (78 cm FL), most restricted native range (the Mobile Basin, restricted to large coastal plain rivers), and the lowest abundance of any North American sturgeon. This riverine species is currently restricted to 524 RKM in the lower Cahaba and Alabama rivers in south Alabama. A commercial fishery existed in the 1890s, and it was still ‘not uncommon’ in Alabama in the 1930s. However, by the 1980s there was a sharp decrease in reports and confirmed collections of ALS. The recent collapse is due to loss and fragmentation of free-flowing riverine habitat and blockage of migratory routes due to construction of dams. Since 1997, state and federal agencies have collected only six individuals while expending over 3000 personnel-da in effort. Propagation efforts have proven unsuccessful to date. The last sighting of an ALS (not captured) was by Alabama Department of Conservation and Natural Resources (ADCNR) fisheries biologists in the Alabama River in April 2009. The last confirmed collection of an ALS occurred in April 2007. This specimen was implanted with a sonic tag, providing valuable habitat and movement data. Very little is known about life history or population structure of this species. Controversy surrounded designation of the ALS as federally endangered in the U.S. under the Endangered Species Act, with a business-oriented coalition challenging the listing through the federal circuit court of appeals. Recovery efforts are focused on obtaining individuals for propagation and providing fish passage through navigation locks on the Alabama River, although this option may not be viable for the ALS. The outlook for the ALS is bleak unless adequate number of individuals can be collected for propagation, access can be provided to historical spawning grounds in the lower Cahaba River, and flow and habitat can be restored to meet life history requirements. However, preliminary results from environmental DNA (eDNA) analysis in 2015 detected the presence of ALS in the Alabama River and may guide future collection efforts.

English

A study on the population size, habitat association and dietary composition of Boutourlini’s blue monkeys (Cercopithecus mitis boutourlinii) was carried out from January, 2015 to September, 2016 in Komto Protected Forest. Data was collected for a total of 58 days encompassing both the wet and dry seasons. Scan sampling method was used to collect data on the diet and foraging behaviour of Boutourlini’s blue monkeys. Population size was determined by total counting method. A total of two groups (natural and riverine forest) and 29 individuals of Boutourlini’s blue monkeys were recorded in the study area. Natural forest group was selected to study about the diet and foraging behaviour of Boutourlini’s blue monkeys. The overall dietary composition of Boutourlini’s blue monkeys was dominated by young leaves which accounted for 27.40% of the total diet. In addition, they fed on mature leaves (20.3%), fruits (15.38%), flowers (11.24%), shoots (8.99%), bark (6.91%), seeds (4.93%) and animal matter (3.37%). They consumed a total of 21 plant species belonging to 18 families. Syzygium guineense was the most consumed plant species and constituted 16.68% of Boutourlini’s blue monkey diet followed by Ficus sur (13.13%) and Prunus africana (12.01%). The most often utilized foraging method was capturing and manipulating food using both hands. This accounted for 47.97% of total foraging observations followed by grabbing (31.46%) and pulling (11.93%). Boutourlini’s blue monkeys were restricted to natural and riverine forest habitats in Komto Protected Forest. Preference of such taper ecological niche resulted from selective deforestation for timber and charcoal production, trampling of habitats by livestock and agricultural land expansion. To ensure future conservation of Boutourlini’s blue monkeys, habitat rehabilitation, enforcement of laws against deforestation for timber and charcoal production, and other appropriate management and conservation strategies should be designed.    Key words: Boutourlini’s blue monkeys, diet, foraging behavior, habitat association, Komto Protected Forest.

The Neocortex of Indian River Dolphins (Genus Platanista): Comparative, Qualitative and Quantitative Analysis

We investigated the morphology of four primary neocortical projection areas (somatomotor, somatosensory, auditory, visual) qualitatively and quantitatively in the Indian river dolphins (Platanista gangetica gangetica, P. gangetica minor) with histological and stereological methods. For comparison, we included brains of other toothed whale species. Design-based stereology was applied to the primary neocortical areas (M1, S1, A1, V1) of the Indian river dolphins and compared to those of the bottlenose dolphin with respect to layers III and V. These neocortical fields were identified using existing electrophysiological and morphological data from marine dolphins as to their topography and histological structure, including the characteristics of the neuron populations concerned. In contrast to other toothed whales, the visual area (V1) of the ‘blind' river dolphins seems to be rather small. M1 is displaced laterally and the auditory area (A1) is larger than in marine species with respect to total brain size. The layering is similar in the cortices of all the toothed whale brains investigated; a layer IV could not be identified. Cell density in layer III is always higher than in layer V. The maximal neuron density in P. gangetica gangetica is found in layer III of A1, followed by layers III in V1, S1, and M1. The cell density in layer V is at a similar level in all primary areas. There are, however, some differences in neuron density between the two subspecies of Indian river dolphins. Taken as a whole, it appears that the neocortex of platanistids exhibits a considerable expansion of the auditory field. Even more than other toothed whales, they seem to depend on their biosonar abilities for navigation, hunting, and communication in their riverine habitat.

Nest Sites of Middle Spotted WoodpeckersLeiopicus mediusin a Primeval Forest

Forest management usually reduces the diversity and amount of substrates in which woodpeckers can excavate holes. In such conditions the recorded patterns of nest site selection could reflect a more reduced array of substrates than the species' nest site preferences. We analysed new data on nest sites of Middle Spotted Woodpeckers Leiopicus medius collected during 27 breeding seasons (1987–2013) in the strictly protected fragments of the Bialowieza National Park in Poland. The birds could use diverse excavation substrates, of various statures, that varied in condition from living and healthy to dead and completely rotten. Middle Spotted Woodpeckers used a wide array of tree species, with little overlap in the species used in the riverine habitat (mostly Alnus glutinosa, and Fraxinus excelsior) and oak—hornbeam habitats (Carpinus betulus and Quercus robur). The birds preferred to excavate in Q. robur but avoided Tilia cordata and Picea abies. They placed holes in large trees (median girth at breast height:...

Studies on the Wetland Biodiversity and Conservation with reference to Habitat, Prey Abundance and Foraging by Two species of Herons

Kerala is the one of the green states of India and is well known for its wetlands. The present study is based on abundance of food and foraging by two species of herons (median egret and large egret) in different type of wetland habitats of Malappuram, Palakkad and Kozhikode districts, Kerala, India. Both the large egret and median egret are piscivorous. During non-breeding season the most preferred habitat of large egret (Egretta alba-37.44%) and median egret (Egretta intermedia-62.56%) are the coastal area and riverine habitats. During breeding season they prefer human habitation with close proximity of riverine habitats and lakes where they build their nests. Utilisation of different habitats, various foraging strategies employed by the species, threats to the wetland in the study area and need for their conservation are also highlighted.

Adventures of an expeditionary biologist: Neuroethology of ultrasonic communication in amphibians

Animal communication occurs when a signal generated by one individual is transmitted through an appropriate channel and results in a behavioral change in a second individual. We have explored specific morphological, physiological, and behavioral adaptations in a wide variety of taxa that appear to have evolved specifically to tailor and sculpt intraspecific communication systems. In this lecture, I will review one of these adaptational studies that involves two distantly related organisms: the concave-eared torrent frog (Odorrana tormota), calling near fast-flowing mountain streams of Anhui Province, Central China, and the endemic Bornean frog, Huia cavitympanum, living in a very similar riverine habitat in Sarawak, Malaysia. In addition to the high-pitched audible components, these species’ calls contain previously unreported ultrasonic harmonics. Our studies of these two Asian frogs revealed that they communicate acoustically using ultrasound and that their auditory systems are sensitive up to 34-38 kHz. This extraordinary upward extension into the ultrasonic range of both the harmonic content of the advertisement calls and the frogs’ hearing sensitivity is likely to have coevolved in response to the intense, predominately low-frequency ambient noise from local streams.

Assessing the natural and anthropogenic influences on basin-wide fish species richness

Theory predicts that the number of fish species increases with river size in natural free-flowing rivers, but the relationship is lost under intensive exploitation of water resources associated with dams and/or landscape developments. In this paper, we aim to identify orthomorphic issues that disrupt theoretical species patterns based on a multi-year, basin-wide assessment in the Danshuei River Watershed of Taiwan. We hypothesize that multiple human-induced modifications fragment habitat areas leading to decreases of local fish species richness. We integrally relate natural and anthropogenic influences on fish species richness by a multiple linear regression model that is driven by a combination of factors including river network structure controls, water quality alterations of habitat, and disruption of channel connectivity with major discontinuities in habitat caused by dams.We found that stream order is a major forcing factor representing natural influence on fish species richness. In addition to stream order, we identified dams, dissolved oxygen deficiency (DO), and excessive total phosphorus (TP) as major anthropogenic influences on the richness of fish species. Our results showed that anthropogenic influences were operating at various spatial scales that inherently regulate the physical, chemical, and biological condition of fish habitats. Moreover, our probability-based risk assessment revealed causes of species richness reduction and opportunities for mitigation. Risks of species richness reduction caused by dams were determined by the position of dams and the contribution of tributaries in the drainage network. Risks associated with TP and DO were higher in human-activity-intensified downstream reaches. Our methodology provides a structural framework for assessing changes in basin-wide fish species richness under the mixed natural and human-modified river network and habitat conditions. Based on our analysis results, we recommend that a focus on landscape and riverine habitats and maintaining long-term monitoring programs are crucial for effective watershed management and river conservation plans.

Monitoring and distribution modelling of invasive species along riverine habitats at very high resolution

Monitoring and species distribution models (SDMs) are increasingly used to support conservation planning but are rarely projected at a very high resolution for conservation management. In this study, we compared the population distribution and size of five invasive plant species along an 18 km alluvial system in Switzerland, over a period of 11 years. Exhaustive inventories of past (2001) to current (2012) populations showed a massive increase in invaded areas over the eleven years. Impatiens glandulifera and Reynoutria japonica were the species with the largest increases in population number and size. The ecological preferences of each species were then modelled at 1 m resolution, using environmental variables expressing topography, disturbances, dispersal, soil texture and light availability. SDMs successfully depicted the niches at very high resolution. Some of the important predictors (e.g., canopy density, distance to river) would have been unhelpful at a coarser resolution. From these very-high-resolution models, we predicted the potential distribution and abundance of species and derived two indices indicating the amount of habitat still available for future species colonisation, crucial information for management. Large, empty areas were predicted to be suitable for each species, suggesting that the observed increase in population size may continue in the future. The two proposed range-filling indices and abundance models may be used efficiently in future studies at very fine resolution to prioritise eradication efforts in previously invaded areas and controls in areas at high risk of invasion. To our knowledge, this is the first study investigating the efficiency of SDMs to predict invasions at such a fine resolution.

Impacts of Dams and Global Warming on Fish Biodiversity in the Indo-Burma Hotspot.

Both hydropower dams and global warming pose threats to freshwater fish diversity. While the extent of global warming may be reduced by a shift towards energy generation by large dams in order to reduce fossil-fuel use, such dams profoundly modify riverine habitats. Furthermore, the threats posed by dams and global warming will interact: for example, dams constrain range adjustments by fishes that might compensate for warming temperatures. Evaluation of their combined or synergistic effects is thus essential for adequate assessment of the consequences of planned water-resource developments. We made projections of the responses of 363 fish species within the Indo-Burma global biodiversity hotspot to the separate and joint impacts of dams and global warming. The hotspot encompasses the Lower Mekong Basin, which is the world’s largest freshwater capture fishery. Projections for 81 dam-building scenarios revealed progressive impacts upon projected species richness, habitable area, and the proportion of threatened species as generating capacity increased. Projections from 126 global-warming scenarios included a rise in species richness, a reduction in habitable area, and an increase in the proportion of threatened species; however, there was substantial variation in the extent of these changes among warming projections. Projections from scenarios that combined the effects of dams and global warming were derived either by simply adding the two threats, or by combining them in a synergistic manner that took account of the likelihood that habitat shifts under global warming would be constrained by river fragmentation. Impacts on fish diversity under the synergistic projections were 10–20% higher than those attributable to additive scenarios, and were exacerbated as generating capacity increased—particularly if CO2 emissions remained high. The impacts of dams, especially those on river mainstreams, are likely to be greater, more predictable and more immediately pressing for fishes than the consequences of global warming. Limits upon dam construction should therefore be a priority action for conserving fish biodiversity in the Indo-Burma hotspot. This would minimize synergistic impacts attributable to dams plus global warming, and help ensure the continued provision of ecosystem services represented by the Lower Mekong fishery.

Towards using thermal stress thresholds to predict salmonid invasion potential

The salmonids rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta are amongst the world’s worst invaders with devastating impacts where introduced. Information on their invasive potential is key to predicting range expansion in recipient environments. Salmonids were introduced into the Keiskamma River system, South Africa in the late 1890s, established and spread throughout its headwaters. This provided an opportunity to document their distribution in relation to stream thermal regimes. Salmonids conformed to documented thermal tolerances predominantly occupying cool-water sites (13.7 ± 3.5 °C). Salmonid probability of occurrence was assessed using seven-day moving average of daily mean water temperatures (MWAT) and exceedances of 100 and 59 days reduce the probability of occurrence for S. trutta and O. mykiss to 0.5 respectively, with probability of occurrence falling to zero at 150 days for both species. Greater tolerance of MWAT exceedance was observed in impoundment (233 days) rather than riverine (146 days) habitats. Epilimnetic releases from impoundments increased temporal heat loads and average temperatures were 3 °C higher below than immediately above impoundments. Salmonids did not occupy all sites within their thermal preferendum, indicating invasion debt and further potential to spread. These models highlight subtle ecological niche differences between both salmonids with O. mykiss more likely to survive warmer water temperatures than S. trutta, but at the expense of a lower altitudinal range and with a greater susceptibility to extinction with an increase in water temperatures. Aquaculture and fisheries enhancements using salmonids are increasing, and these results may contribute to risk assessments for salmonid invasions globally.