Upland Tributaries Research Articles

Late Glacial and Holocene evolution of the estuarine section of the Nida River

Based on the results of detailed geological-geomorphological studies, old maps from the past 200 years, and historical data, the paper is the first to present the structure of the valley floor in the estuary of the Nida River, an upland tributary of the Vistula, and discuss changes in the development and course of their channels. The aim of the study was to grasp the importance of local factors, both natural (palaeogeographical, lithological and tectonic) and anthropogenic, in the morphogenesis of this section, where a relatively small upland stream crossed in the medieval and modern periods by important overland and water routes of the Polish-Lithuanian Commonwealth flows into the Vistula River, which is ten times larger. The discussed section is not deltaic in character. The branching of the Nida into several simultaneously functioning outlet arms may have been caused by the blocking of outflow from the valley during floods and the drainage of the flood waters at the valley mouth in several directions, via channels both permanent and periodic. Changes in the numbers and locations of the Nida estuaries in recent centuries have both natural and anthropogenic causes. The interaction between the main stream and its many-times smaller tributary in the studied section has resulted in a complex mosaic of forms and cut-and-fills of both streams, but with the Vistula playing the dominant role. The cut-and-fills of the Vistula “enclose” the Nida alluvium inside its valley on the Winiary-Nowy Korczyn line, while the cut-and-fills of the Nida only occur in a very narrow strip under the edge of the terrace. The Nida followed abandoned channels of the Vistula on Holocene cut-and-fill IIA, flowing parallel to the Vistula for 9 km. The floor of the Nida Valley lacks Holocene mineral-organic and mineral sediments, characteristic of other upland tributaries from loess areas. The regulation of the Vistula in the mid-19th century and the Nida in the first half of the 20th century fixed the courses of the rivers, completely changing the sedi­mentation regime in the estuarine section of the Nida, where backflow and associated sedimentation of fine-grained deposits occurred.

Phylogenetic Evidence for the Cyphocharax saladensis Clade with Description of a New Species of Cyphocharax Endemic to the Upper Rio Paraguai Basin (Teleostei: Curimatidae)

New genetic and morphological data support the recognition of a distinct monophyletic group, the Cyphocharax saladensis clade, which includes C. vanderi, C. saladensis, C. boiadeiro, and a new species. This four-species group can be recognized by modifications in the laterosensory system with instances of incomplete or interrupted poring, by the ontogenetic development of the lateral line with larger specimens having a more developed laterosensory system, and by the presence of a patch of dark pigmentation over the caudal peduncle. The new species is described from the upper Rio Correntes, an upland tributary of the upper Rio Paraguai in central Brazil and is diagnosed by the presence of a thin longitudinal black stripe, by the variable shapes of the dark blotches on the caudal peduncle, and by morphometric and meristic data. New mitochondrial data from paratypes provide clear evidence of genetic distinction between the new species and congeners, and additionally place it as the sister species to C. boiadeiro from the upper Rio Araguaia. Based on the updated molecular phylogeny and biogeographic information, we propose an evolutionary hypothesis with four events of river captures with subsequent allopatric speciation of the new species and C. boiadeiro in the Correntes and Araguaia systems. The new species is suggested to be categorized as Near Threatened, living in a strongly impacted region of the Brazilian Cerrado.

Heavy metal pollution in selected upland tributaries of Sri Lanka: comprehension towards the localization of sources of pollution.

This study aimed to assess the heavy metal (HM) profile of the main upland tributaries of three major rivers, the Mahaweli, the Deduru and the Gin Rivers, which are commonly used for urban water supply in Sri Lanka. The HM profiles of arsenic (As), cadmium (Cd), lead (Pb) and mercury (Hg) were investigated by ICP-MS. Land-use classification was performed to locate the main sources of pollution. Mean pH, TDS and conductivity showed significant inter-site mean differences (p < 0.001). The mean contents of the HMs, considering all rivers, were observed in the order [Hg] > [As] > [Pb] > [Cd] at the sources and [As] > [Hg] > [Pb] > [Cd] at the river mouths. Particularly, in the Mahaweli River, the mean As content was 0.08 ± 0.05 μg·L-1 and showed an increasing trend from the source to the river mouth. In the Deduru River, the mean Hg content was 0.14 ± 0.15 μg·L-1, and of all rivers studied, the highest content of 0.50 ± 0.17 μg·L-1 was recorded. The Gin River showed significant inter-site mean differences (p < 0.05) in [Pb], [As] and [Hg]. In all rivers studied, [As] was significantly higher in water samples collected near agricultural lands and urban areas as compared with the other land-use/cover types, which was further proved by a significant positive correlation (coefficient = 0.479, p = 0.0325). We, therefore, emphasized that HM pollution is more likely due to anthropogenic activities in the upper catchment with less lithogenic contamination. However, national water quality management should be further strengthened and new policy enforcement is emphasized.

Fauna de peixes de um rio fragmentado na Mata Atlântica

Abstract: This study sought to identify the ichthyofauna composition of the Muzambinho River, an upland tributary of the Paraná River. We also investigate whether waterfalls in the region can serve as barriers to the dispersal of fish species. For this purpose, collections were carried out at 34 points on the Muzambinho River using different techniques. In all, 37 species were recorded, some of which were endemic, and the majority were native. Among these species, some are predominant in degraded places and can be used as bioindicators. The results also demonstrate zonation in the ichthyofauna composition in Muzambinho that segregates the fauna into three sessions separated by waterfalls: Lower Muzambinho, Upper Muzambinho, and Sao Domingos. We conclude that, for the ideal preservation of the ichthyofauna of the Muzambinho River, it is necessary to preserve its sections independently, which would guarantee the maintenance of naturally isolated strains.

Mapping floodplain bathymetry in the middle-lower Amazon River using inundation frequency and field control

This paper presents the geomorphic classification and bathymetry (at 100 m) of 12 major floodplains along a 900 km reach of the middle-lower Amazon River (Manaus – Monte Alegre; total floodplain area of 5164 km2), based on the inundation frequency (IF) derived from 36 yr of Landsat data. Using a mathematical relationship between IF and surveyed depth at the Curuai floodplain in June 2004, this IF-depth model is applied across floodplains of the middle-lower Amazon to estimate bathymetry. The applicability of the model is justified by similar grain size distribution (dominantly silt and clay) of sediment in the surface water of floodplain lakes (the main materials constructing the floodplains), as well as a hydrogeomorphic classification of this reach: seven floodplains lying on the alluvial plain dominated by the Amazon-flood pulse (Type I), three floodplains incised in valleys dominated by sediment-poor upland tributaries (Type II) and two floodplains of mixed types. This classification is used to distinguish the sensitivity of floodplains to the IF-depth model, where Type I floodplains of higher sensitivity provide a more accurate depth estimation. The bathymetry for both types is validated with field survey data across eight floodplains (covering over 200 km survey distance) collected in June – July 2016 and adjusted by the difference between mean June 2004 and June/July 2016 water level. Correlation coefficients of 0.87 (Type I) and 0.94 (Type II) indicate a strong relationship between estimated and measured depth for both floodplain types, while the root mean square error of 1.03 m (Type I) and 1.02 m (Type II) suggest that bathymetry is estimated to around 1 m error, equivalent to 10.9% and 10.8% of maximum water level variability, respectively. We offer the first field-validated and complete bathymetry map for the middle-lower Amazon River with accuracy that can be used to evaluate the role of floodplains in influencing biodiversity, sedimentation, flood control and biogeochemical cycling.

Further Development of Small Hydropower Facilities May Alter Nutrient Transport to the Pantanal Wetland of Brazil

Small hydropower (SHP) facilities, defined variably but usually by installed capacities of &amp;lt;10–50 MW, are proliferating around the world, particularly in tropical and subtropical regions. Compared to larger dams, SHPs are generally viewed as having less environmental impact, although there has been little research to support that assertion. Numerous SHPs have been built, and many more are in development or proposed, in rivers that drain into the Pantanal, a world-renowned floodplain wetland system located mostly in Brazil. The upland tributaries are important sources of nutrients to the Pantanal, affecting the biological productivity of downstream floodplains. This study presents measurements from upstream and downstream of 25 current hydropower facilities, most of which are SHPs, throughout the upland watersheds of the Upper Paraguay River basin to reveal how these facilities may affect the concentrations and transport of nutrients in rivers flowing to the Pantanal. Artificial neural network models estimated the impact of building 80 future SHPs on nutrient transport into the Pantanal, based on observations at current facilities as well as the spatial distribution of future facilities. Overall impacts of current hydropower facilities were not large, and in most cases were indistinguishable based on comparisons between upstream and downstream. The short water residence times of reservoirs associated with SHPs likely explain their tendency to have little or no effect on nutrient transport. However, model predictions for hydropower facilities that may be built in the future, many on rivers with higher discharge and sediment loads, point to significant reductions in overall TN (8%) and TP (29%) transport, with potential negative consequences for river and floodplain productivity. Negative impacts may be either because the rivers carry low nutrient concentrations and are thereby sensitive to oligotrophication, or they are particularly important overall nutrient sources supporting ecosystem productivity in downstream rivers and floodplains. Together with a parallel study of sediment transport, these results support recommendations that several river systems presently lacking dams in their lower reaches should be excluded from future hydropower development to maintain the nutrient and sediment supply to the Pantanal.

Further Development of Small Hydropower Facilities Will Significantly Reduce Sediment Transport to the Pantanal Wetland of Brazil

Small hydropower (SHP) facilities, are commonly being built around the world. SHPs are viewed as less environmentally harmful than larger dams, although there has been little research to support that assertion. Numerous SHPs have been built, and many more are in development or proposed, in rivers that drain into the Pantanal, a world-renowned floodplain wetland. Three river systems with the largest contributions of sediments to the Pantanal—the Cuiaba, upper Taquari, and Coxim rivers—remain largely undammed. The upland tributaries transport sediments and nutrients into the Pantanal, thereby affecting geomorphological dynamics and biological productivity of downstream floodplains. This study presents measurements from upstream and downstream of current hydropower facilities, most of which are SHPs, throughout the upland watersheds of the Upper Paraguay River basin to reveal how these facilities may affect the transport of suspended sediments and of bedload sediments. In addition, a predictive model using artificial neural networks estimates the impact of building 80 future SHPs on sediment transport based on observations at current facilities as well as the spatial distribution of future facilities. More than half of current facilities retained suspended sediments: 14 of the 29 facilities showed >20% net retention of suspended sediments, two others retained between 10-20%, seven were within 10%, and six showed >10% net release. Bedload sediment transport was a small component of total sediment transport in rivers with high total sediment loads. Multiyear series of satellite images confirm sediment accumulation in several cases. Model predictions of the impacts of future hydropower facilities on suspended sediment concentrations and transport show retention of a large fraction (often much >20%) of sediment inputs. Summing riverine transport rates for inflows into the Pantanal indicates that currently envisioned future hydropower development would reduce the suspended sediment transport by ~62% from the current rate. This study shows that if SHPs are built on sediment-rich rivers, this may prove problematic for the facilities as well as for downstream ecosystems. These results support recommendations that several river systems presently lacking dams in their lower reaches should be excluded from future hydropower development to maintain the sediment supply to the Pantanal.

Nitrogen biogeochemistry in a boreal headwater stream network in interior Alaska

High latitude, boreal watersheds are nitrogen (N)-limited ecosystems that export large amounts of organic carbon (C). Key controls on C cycling in these environments are the biogeochemical processes affecting the N cycle. A study was conducted in Nome Creek, an upland tributary of the Yukon River, and two headwater tributaries to Nome Creek, to examine the relation between seasonal and transport-associated changes in C and N pools and N-cycling processes using laboratory bioassays of water and sediment samples and in-stream tracer tests. Dissolved organic nitrogen (DON) exceeded dissolved inorganic nitrogen (DIN) in Nome Creek except late in the summer season, with little variation in organic C:N ratios with time or transport distance. DIN was dominant in the headwater tributaries. Rates of organic N mineralization and denitrification in laboratory incubations were positively correlated with sediment organic C content, while nitrification rates differed greatly between two headwater tributaries with similar drainages. Additions of DIN or urea did not stimulate microbial activity. In-stream tracer tests with nitrate and urea indicated that uptake rates were slow relative to transport rates; simulated rates of uptake in stream storage zones were higher than rates assessed in the laboratory bioassays. In general, N-cycle processes were more active and had a greater overall impact in the headwater tributaries and were minimized in Nome Creek, the larger, higher velocity, transport-dominated stream. Given expectations of permafrost thaw and increased hydrologic cycling that will flush more inorganic N from headwater streams, our results suggest higher N loads from these systems in the future.

Predicted impacts of proposed hydroelectric facilities on fish migration routes upstream from the Pantanal wetland (Brazil)

AbstractThere are 104 hydroelectric facilities proposed to be installed in the watersheds that feed the Pantanal, a vast floodplain wetland located mostly in Brazil. The Pantanal is host to 23 long‐distance migratory fish species that ascend upland tributaries to spawn. A Geographic Information System was used to predict the impact of hydroelectric dams on potential migration routes for these species. Both anthropogenic (hydroelectric dams) and natural barriers were included in the analysis. Natural barriers were identified by river slope. Critical river slopes of 10 and 25%, above which fish were predicted to be incapable of ascending, were modeled as natural barriers. Based on this model, we show that between 2 and 14% of rivers in the Pantanal watershed are naturally blocked to fish migration. An additional 5 to 9% of rivers are currently blocked due to 35 existing hydroelectric facilities. If all proposed dams are built, the area flooded by new reservoirs will triple and the river kilometers blocked will double, blocking 25 to 32% of the river system to fish migration. The Taquari and Cuiabá River sub‐basins will be the most impacted, each having more than 70% of their rivers blocked. The impact of individual proposed facilities on the loss of migration routes is related to their proximity to existing barriers. Fourteen of the proposed dams are upstream from existing barriers and will therefore not further restrict long‐distance fish migration routes while proposed dams are predicted to close an additional 11,000 to 12,000 km of river channels.

First record of horned carp Schismatorynchos nukta (Sykes, 1839) (Cypriniformes: Cyprinidae) from Bangladesh and its present status

The horned carp, Schismatorynchos nukta (Sykes, 1839) has been recorded for the first time from Bangladesh geographical area under the investigated genus of Schismatorynchos (Bleeker 1855). This fish was collected from seine net catch while exploring the hilly upstream of Sangu river at Tindu and Remakri (Thanchi, Bandarban, Bangadesh) during the winter in 2015. The species S. nukta is mostly distributed in the upland tributaries of Krishna river systems at northern Western Ghats, Maharashtra and Karnataka in India. It is reported as endemic species of Western Ghats biodiversity hotspot. Its distribution (IUCN status) and habitat conditions are dealt in the present paper. The findings add some information on its global distribution form and Indian endemic status.J. Biodivers. Conserv. Bioresour. Manag. 2017, 3(1): 85-92

Coal grunters shift benthic objects to access macroinvertebrates in a headwater stream

Few fishes have been documented shifting objects to access prey. Coal grunters were observed using the mouth, snout or nape to lift, flip or roll benthic objects and expose benthic macroinvertebrates during a series of daytime snorkelling sessions in a clear, sandy upland tributary of the Mitchell River, northern Queensland, Australia.

Weathering of Zinc-(Zn)-bearing Mine Wastes in a Neutral Mine Drainage Setting, Gunnerside Gill, Yorkshire

Numerous areas throughout the world are affected by circum-neutral pH, low iron (Fe) drainage with high concentrations of zinc (Zn) arising from discharges from, and weathering of, mine wastes. Gunnerside Gill, a small upland tributary in the headwaters of the River Swale in Yorkshire, is such a site affected by historic lead and zinc mining. The aim of the study is to assess the controls on Zn mobilisation from the mine tailings and floodplain sediments to the river water through a column leaching experiment. Sphalerite has been identified as the primary Zn mineral in the bedrock within Gunnerside Gill. However, there is more evidence of secondary phases of Zn were including Fe oxides and phosphates present within the samples and the BCR data suggests it is these phases that appear to be undergoing the majority of the Zn dissolution.

Hydrological characteristics and water resources management in the Nile Basin

The longest of the World's Large Rivers, the Nile, is also one of the most ancient in terms of the impact of human civilisations. The basin's potential in terms of irrigated agricultural development and hydropower is immense, at the same time, large-scale vulnerable ecosystems such as biodiverse upland tributaries, floodplain swamps and a once fertile and healthy delta depend on its free flow. Sharp cultural boundaries between the Upper and the Lower Basin match profound environmental differences and changes in population pressure in relation to discharge. At present, large-scale engineering and highly debated technical and political solutions have tamed the large river, reduced to a trickle when it finally reaches the Mediterranean. Despite this, the challenge of consolidating a stable agreement between the Basin's nations is yet far from being met; a situation that creates political tension in one of the most troubled regions of the globe. The present review revisits the intertwining of Nile hydropolitics, linked to economic and political powers that go far beyond the Basin's boundaries, with the basin's hydrology to highlight critical environmental and social impacts undermining ecosystem services. Engineering operations aiming at controlling river discharge and harnessing its hydropower are exacerbating transboundary conflicts and converting the river into a large man-made channel. It is suggested that a change of focus from water quantities (i.e. river discharge in m3) to encompass a broader perception including water quality and economic and environmental benefits that can be derived from water use, could promote more agreeable environmentally acceptable solutions.

Diurnal fluctuation of zinc concentration in metal polluted rivers and its potential impact on water quality and flux estimates

Diurnal fluctuations of metals have been observed in the South Tyne river catchment, UK, in both upland tributaries and major river reaches. Zinc exhibits the most pronounced cyclicity, with concentrations increasing during the night to a maximum near 05:00 before decreasing during the day. This trend is the inverse of pH and temperature observations, which are thought to be the predominant drivers behind the cyclicity. Photosynthetic reactions of biomass and algae alter the pH within the river systems, therefore promoting hydrous metal oxide precipitation during the daylight which consequently allows divalent cations including zinc to sorb onto them. This mechanism may be supported by direct uptake of zinc by algae and other biogeochemical reactions which combine to create large differences in zinc concentrations; during base flow zinc concentrations increased by 326% from the minima over 48 hours. Maximum concentrations are not being captured during routine water quality analysis resulting in inaccurate and misleading EQS results and total flux estimations, for example the annual total zinc flux in a small tributary increases from 17 to 76 tonnes/year when routine grab sample data are supplemented with 24-hour sampling results.

Linking metrics of hydrological function and transit times to landscape controls in a heterogeneous mesoscale catchment

AbstractLong‐term river flow data and one year of isotopic tracer data in a nested 749 km2 catchment were analysed conjunctively to evaluate the relationships between hydrometric statistics, transit times, and catchment characteristics. The catchment comprised two distinct geomorphic provinces; upland headwaters draining glaciated landscapes underlain by crystalline geology and lowland headwaters draining a major regional sandstone aquifer. In the uplands, flow regimes were ‘flashy’ with high runoff coefficients for storm hydrographs, steep recession curves and strong nonlinearity in event responses. In the lowlands, runoff coefficients were low, recessions less steep, and event responses more linear. Flow data from the catchment outfall showing damping of these extremes, but was most strongly influenced by the upland headwaters where precipitation was highest. The damping of variability in stable water isotopes between precipitation inputs and streamflow outputs reflected this; with upland tributaries least damped and lowland tributaries most damped. Attempts to quantify the mean transit times of the sampling points met with mixed success; partly reflecting the short run (1 year) of data, but mainly as a result of the marked damping in lowland sites. As a consequence, MTT estimates can only be said to be in the order of a few years in upland sites, but are probably decadal or greater in lowland tributaries. Again, the catchment outfall averages these extremes, but is more similar to the upland headwaters. Despite the difficulties in quantifying MTTs, it is clear that they, like the hydrological response, primarily reflect the dominant control of catchment soil cover, which in turn is determined by geology and glacial history. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Assessment of the conservation status of endemic sculpinCottus haemusi(Cottidae) in the river Vit (Danube Tributary), northwest Bulgaria

Cottus haemusi (Marinov and Dikov, 1986. Acta Zool. Bulg. 3, 18–23) is an endemic fish species that is restricted to the upper tributaries of the river Vit, Northwest Bulgaria. After its discovery in 1986, no further investigation of the C. haemusi population has been conducted. The aims of the present study were to determine its current population status based on the distribution, abundance and size structure of the C. haemusi population and to analyse the main environmental parameters of its habitat. Five upland tributaries and the main river were examined in low-water periods in 2009 and 2010. Two-pass electrofishing surveys were performed at 14 sites to estimate species presence, abundance and size distribution. C. haemusi was only detected in two tributaries of the river Vit: Kostina and Toplja. The current investigation failed to find the species at previously recorded sites. The total distribution area of this species is estimated to be 16 200 m 2 . The observed abundance of the Vit sculpin ranged from 5.6 to 8.4 individuals·100 m –2 , with a mean of 7.0 individuals·100 m –2 . Investigation of the size structure revealed the relatively low contribution of one-summer-old individuals. Microhabitat preferences did not differ significantly from other European cottidae species. Only a higher percentage of cobbles distinguished sites with sculpins from those without. The restricted distribution andlossofthebullheadpopulationfromsomelocalitiesintheriverVitcould beexplainedbyhumandisturbanceandthedeteriorationofnaturalhabitat. Several protection measures are discussed.

A Multi-Taxa Biological Survey of Passage Creek, Virginia

Identifying and conserving functioning headwater ecosystems is essential for ensuring the structure and function of natural ecosystem processes. The Passage Creek watershed (PCW) in Virginia is an upland tributary system of the North Fork Shenandoah River, which is found within the Potomac River basin. The PCW appears to maintain an array of terrestrial and fluvial habitats now uncommon in many adjacent watersheds because of human disturbance. We assessed the biotic condition of the PCW by sampling the fish, mollusk, and salamander assemblages throughout the watershed. We observed 29 fish, 9 salamander, and 4 aquatic mollusk species representing a variety of life histories and functional groups. Furthermore, we found that due to spatial differences in abundance and species richness, each assemblage offered unique insight into the condition of the PCW. The fish assemblage was indicative of those found in least disturbed areas within the Potomac basin, while salamander abundance and richness indicated areas of habitat degradation. Though we observed only one mussel species, the presence of native mussels suggested the PCW has maintained sufficient ecological condition to support long-lived animals potentially sensitive to low-level, additive, and compounding long-term disturbances, while neighboring watershed assemblages have collapsed. Given the relatively high species richness found within PCW, this watershed may be pivotal to the overall persistence of aquatic species in the Potomac basin and should receive high priority for future conservation efforts.

Appraising riparian management effects on benthic macroinvertebrates in the Wye River system

1. Agriculture, urbanization or forestry in river catchments can influence river organisms through diffuse effects on hydrology and hydrochemistry, or local effects on habitat character, bank erosion and sediment delivery. Riparian buffer zones are sometimes established to mitigate undesirable effects on salmonids, but consequences for organisms such as macroinvertebrates are less well known. 2. Riparian fencing and tree coppicing were carried out on upland tributaries of the Welsh River Wye (UK) from 1997 onwards with the aim of enhancing conditions for salmonid fish. The present study used routine, agency monitoring data to compare assemblages in three recently managed streams and five adjacent control streams. Data between 1995 and 2004 were used to assess treatment effects through time. 3. Post-treatment (2000–2004) assemblages were richer in recently managed streams than in controls, mostly due to apparent gains of taxa typical of channel margins and lowland, warmer conditions. However, results were equivocal because invertebrate families typical of lowland, more eutrophic conditions increased in occurrence in all reaches irrespective of treatment, while overall richness declined. 4. This study illustrates how routine monitoring data can reveal some effects of riparian land-use and management on stream biota. However, improved experimental design, ideally using a before–after control–intervention approach, would have allowed more effective assessment in this case study where confounding trends were so marked. We advocate using such approaches in future restoration studies to allow stronger inference and greater statistical power. The recent general decline in the richness of typical headwater organisms in the Wye system requires investigation. Copyright © 2010 John Wiley & Sons, Ltd.

Description of Neblinichthys brevibracchium and N. echinasus from the upper Mazaruni River, Guyana (Siluriformes: Loricariidae), and recognition of N. roraima and N. yaravi as distinct species

Neblinichthys brevibracchium and N. echinasus are new sympatric species from upland tributaries of the Mazaruni River (Essequibo River basin) of Guyana. These two new species are the first Neblinichthys reported from Guyana. Adult males of both new species have short pectoral-fin spines and several series of hypertrophied odontodes covering the entire dorsal surface and along the entire edge of the snout. They are distinguished from each other by dorsal-fin base length/standard length (18.1-22.8% in N. brevibracchium vs. 24.3-27.0% in N. echinasus), dorsal-anal distance/SL (13.7-18.3% in N. brevibracchium vs. 11.9-12.5% in N. echinasus), by having the snout decreasing in steep arc just anterior to eyes and then flattening in area anterior of nares in N. brevibracchium vs. the snout tapering shallowly and continuously from eyes to snout tip in N. echinasus); and by having the adpressed dorsal fin reaching the anterior preadipose plate in N. brevibracchium (vs. not reaching anterior preadipose plate in N. echinasus). They are distinguished from all congeners by lacking odontodes on the opercle (vs. odontodes present); and by completely lacking an iris operculum (vs. congeners with small iris operculum present or at least dorsal portion of iris flat instead of rounded). Neblinichthys echinasus and N. brevibracchium differ from all congeners by having a spotted or vermiculated pigment pattern on the abdomen (vs. abdomen plain); in N. echinasus the abdomen is darkly pigmented with bold white spots and in Neblinichthys brevibracchium the abdomen is light-colored with gray spots and vermiculations. Neblinichthys brevibracchium and N. echinasus differ from N. roraima by having one to two preadipose plates (vs. four or more). New observations revealed Neblinichthys roraima and N. yaravi to be distinct, with N. roraima having four or more preadipose plates and N. yaravi having one or two. Both are present in the upper río Caroní, an Orinoco tributary that drains the slopes of Mount Roraima and other mountains of the Pacaraima Range in Venezuela and interdigitates with headwaters of the Mazaruni River.

Observations of American Eels Using an Upland Passage Facility and Effects of Passage on the Population Structure

AbstractOver two seasons, we observed passage of American eels Anguilla rostrata at an eel passage facility (eel ladder) placed adjacent to an upland mill dam on a small tributary to the Hudson River, New York. American eel use of the ladder was significantly correlated with freshets and moon phase, similar to other studies of eel migration. Most of the migrants were young (&lt;20 cm total length). Several large American eels (&gt;35 cm) exhibited local movements, including use of the ladder, as shown by recaptures of individuals marked with coded wire tags. Operation of the eel ladder greatly reduced the density of small American eels below the mill dam. Placing eel ladders on upland obstructions has the potential to enhance the productivity of silver (sexually mature) eels, an important consideration in the Hudson Valley, where hundreds of barriers have been constructed on upland tributaries.