Middle Uruguay River Research Articles

Fluvial terrace mapping from ALOS-PALSAR data for archaeological prospection in the middle Uruguay River basin, Argentina

Archaeological research carried out in the terminal section of the middle Uruguay River basin (Entre Ríos) since the end of the 19th century has made it possible to identify a complex network of human occupations that show differences in the settlement pattern and use of space. In the area between the Mocoretá River mouth and the Del Molino stream, located to the north of the city of Concepción del Uruguay, more than 68 archaeological sites are known. All of them are chronologically located within the Holocene and distributed in the adjacent plains, tributary courses and islands of the Argentine territory. As a result of the Pleistocene-Holocene fluvial dynamics and geological evolution, the geomorphological landscape of these banks displays three terraces in the middle course, between the cities of Federación and Concordia. The sedimentary deposits of the lower terrace, corresponding to the Holocene, are known as Concordia Formation. Previous research recorded sites distributed in different landscape units closely linked to river courses, in sectors with wide visibility (terraces, floodplains, sedimentary banks, erosion banks, dune fields and islands). Many of these sites were flooded by the Salto Grande dam, built in the 1970s. Since then, and despite the systematic archaeological research carried out in the region, the number of archaeological sites recorded is very low. This difficulty in locating the sites was the reason for the design of a prospecting model adjusted to this need. Based on known information, we designed a terrain prospection model using Geographic Information Systems. This model allowed us to identify the Holocene geoforms where it is most likely to find archaeological sites in the middle Uruguay River basin. This will enable the recording of archaeological sites to be expanded and their locations in the landscape to be characterised. This paper presents the results of geomorphometric analyses developed with a computer tool called Geomorphon, which recognises landform associations. A positive correlation was recorded between the location of the archaeological sites known to date and geomorphometric features interpreted as edges and top surfaces of the low terrace (ridges and shoulders associated with flat surfaces, from geomorph routine). This makes it possible to guide archaeological surveys towards the lower terrace (Concordia Formation) and test the model a priori.

Recruitment of migratory fish in free‐flowing rivers with limited floodplain development

Abstract Hydrological connectivity is a basic feature of river ecosystems, responsible for important ecological processes. Human activities, however, have progressively modified natural connectivity, threatening the maintenance of aquatic biodiversity. Neotropical potamodromous fish depend heavily on fluvial connectivity to complete their life cycles. However, important ecological aspects remain poorly understood, especially in river systems with limited floodplain development (i.e. channelized rivers and drylands), where the environment poses constraints to fish recruitment. The Uruguay River Basin is such a system, with several migratory fish, small floodplain areas, and limited information about recruitment dynamics and nursery grounds. The lack of information on critical habitats limits conservation and management actions, especially in scenarios of increasing environmental degradation and river regulation. This study investigated recruitment dynamics of migratory fishes in the Middle Uruguay River, a long fluvial segment targeted for hydropower development. The study investigated spatial variations in the abundance, composition and size structure of juvenile fish among different sites along an extensive fluvial gradient (ca. 650 km), comparing the main channel with tributaries. Juveniles of migratory fish were widely distributed in the region, totalling nine species, with a predominance of Characiformes. Spatial distribution was variable among species and size classes, with a differential use of tributaries, wetlands and the main channel. Juvenile composition differed between sampling sites and environments, and was correlated with different limnological and spatial variables. Greater abundances occurred in the mouth of a tributary where a small floodplain develops during the wet season. The results emphasize the importance of fluvial connectivity for fish migration, dispersal and recruitment, providing valuable information about migratory fishes in river systems with limited wetland development. These findings have significance for the management and conservation of migratory fish under scenarios of hydropower expansion, as comprehensive studies on recruitment are rare in free‐flowing rivers.

New data for palaeoclimatic reconstructions in the upper/middle Uruguay River Basin: caesalpinioid Fabaceae woods in the Late Pleistocene

AbstractThe El Palmar Formation is the principal unit deposited during the Late Pleistocene by the Uruguay River in eastern Entre Ríos province, Argentina and north-western Uruguay. The Arroyo Yuquerí fossiliferous locality (c. 31°36′ S, 58°06′ W), part of the El Palmar Formation, is one of the richest sites in fossil woods. This article describes and determines 11 fossil woods, including seven new species closely related to modern Parapiptadenia, Microlobius, Anadenanthera, Pseudopiptadenia (Mimoseae, Fabaceae) and Chloroleucon, Enterolobium and Cedrelinga (Ingeae, Fabaceae). Coexistence approach, nearest living relatives (NLR) methods and mesomorphic and vulnerability indices were used to determine palaeoclimatic conditions. Comparisons of NLR of fossil woods, coupled with other previously identified taxa, suggest that a mature and evergreen woodland was present in the middle Uruguay River Basin during some Pleistocene events (MIS 5a and MIS7, according to absolute datings of the fossiliferous sedimentary unit). This caesalpinoid legume woodland was shaped by an environment with abundant humidity, and the structure of the water conduction system in the studied species was efficient. Finally, the results indicate a more humid and warmer climate than at present in the study area.

The main channel and river confluences as spawning sites for migratory fishes in the middle Uruguay River

Abstract Evidence indicates that migratory fish reproduce in the middle Uruguay River, but the location of spawning sites remains unknown. To identify spawning sites in the basin, fish eggs and larvae were sampled monthly between October 2016 and January 2017. The sampling was carried out in three sections along the middle Uruguay River, covering two environments: the main channel and the mouth of tributaries (Comandaí, Ijuí, and Piratinim rivers). A total of 11,519 eggs and 3,211 larvae were captured, belonged to ten migratory species. Eggs and larvae of migratory fishes, were widely distributed, with predominance of segmented eggs, and larvae in yolk-sac and pre-flexion stages, with higher densities near the confluence with the Piratinim River. Larvae assemblages showed spatial variation, indicating that spawning sites differ among migratory species. This study provides new information about fish reproduction in the middle Uruguay River, revealing that migratory species spawn in different localities along the main channel and tributaries. This region may function as a critical site for fish reproduction, although it is currently threatened by the risk of hydropower expansion, emphasizing the need for measures that preserve their environmental conditions, hydrological connectivity and ecological functions.

Daily variation feeding of Astyanax lacustris (Lütken 1875) in a subtropical river

This study aimed to know the daily variation of Astyanax lacustris (Lütken 1875) feeding in a lotic environment. Fish were caught with a net for three days every three hours in the summer to capture ten individuals per hour in a stretch of the Ijuí River, Middle Uruguay River, Brazil. The captured specimens had their stomachs removed and the content analyzed and separated into seven food categories with the aid of stereomicroscope. For the analysis of food items were used the frequency of occurrence methods, volumetric method and applied the Alimentary Index (IAi). Two hundred stomachs were analyzed, of which 95% had food content. The most abundant items were algae and autochthonous insects. Astyanax lacustris feeds throughout the day especially early in the morning (9 hours) and reduces its feeding at night (24 hours and 3 hours). It was also verified variation of AI of different food items throughout the day. It is concluded that A. lacustris feeds throughout the day, especially in the daytime and that throughout the 24 hours it varies its diet due to photoperiod and food availability.

Iterative taxonomic study of Pareiorhaphis hystrix (Siluriformes, Loricariidae) suggests a single, yet phenotypically variable, species in south Brazil.

Pareiorhaphis hystrix is a widely distributed species, occurring in the upper and middle Uruguay River and in the Taquari River basin, Patos Lagoon system, southern Brazil. Morphological variation has been detected throughout the distribution of P. hystrix, and this work seeks to test the conspecific nature of populations in several occurrence areas. Specimens from six areas in the Uruguay River basin and three in the Taquari River basin were compared. Variance analysis (ANOVA) was performed for the meristic data, and Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA) were conducted for morphometric data. Molecular analyses used coI, cytb, 12S and 16S mitochondrial genes, examining nucleotide diversity, haplotype diversity, genetic distance, and delimitation of possible multiple species through the Generalized Mixed Yule Coalescent (GMYC) method. Phylogenetic relationships of studied populations were also investigated through Bayesian inference. While PCA indicated a tendency of overlap between areas, ANOVA and LDA detected a subtle differentiation between populations from the two hydrographic basins. Yet, both latter analyses recovered the population from Pelotas River, a tributary to Uruguay River, as more similar to populations from Taquari River, which is congruent to morphological observations of anterior abdominal plates. The molecular data indicated a nucleotide diversity lower than the haplotypic diversity, suggestive of recent expansion. The concatenated haplotype network points to slight differentiation between areas, with each locality presenting unique and non-shared haplotypes, although with few mutational steps in general. The species delimitation by coalescence analysis suggested the presence of a variable number of OTUs depending on the inclusion or exclusion of an outgroup. In general, the morphological data suggest a subtle variation by river basin, while the genetic data indicates a weak population structuration by hydrographic areas, especially the Chapecó and Passo Fundo rivers. However, there is still not enough differentiation between the specimens to suggest multiple species. The iterative analyses indicate that Pareiorhaphis hystrix is composed of a single, although variable, species.

First record of the mating behaviour of the spotted surubim Pseudoplatystoma corruscans in the Uruguay River.

The spotted surubim Pseudoplatystoma corruscans is a large migratory catfish native to the La Plata and San Francisco basins. Nonetheless, its reproductive dynamics and behaviour remain poorly understood. This brief note provides the first record of the mating behaviour of P. corruscans in natural conditions. This behaviour was observed in the main channel of the Middle Uruguay River (Brazil). A school of approximately 25 fish, 5 females (with protruding abdomen and larger body size) and 20 males, were followed and videotaped. The largest female led the school, followed by other fish. Some males disputed repeatedly the posterior region of the females, whereas other males continuously repelled them. Eventually, some males, apparently exhausted, floated belly up. During this event, males were in a state of pronounced agitation, and some had abrasions in the head. Polygamy characterized the mating behaviour of P. corruscans.

Length‐weight relationship of 13 middle Uruguay River basin species, Southern Brazil

Length-weight relationship (LWRs) were determined for 13 fish species from the Uruguay River. The fish were caught in six locations and sampled at each location during each season, totaling 72 samplings, starting in May 2016 and ending in February 2018. Various materials were used such as gillnets (15; 20; 25 30; 40 and 80 mm, triple mesh 150.30.150 150.40.150 and 150.50.150 mm, 8 mm trawl). We also used two longlines, 100 m long, 30 hooks each (hooks 5/0 and 12/0), baited with small fish, corn and snail. Length-weight relationship were adjusted appropriately for all species (r2 > .95). The b values of the LRW equations ranged from 2.38 in Steindachnerina brevipinna to 3.62 in Pimelodus atrobrunneus.

First evidence of a spawning site of the endangered fish Brycon orbignyanus (Valenciennes, 1850) (Characiformes, Bryconidae) in the Middle Uruguay River, Brazil

Abstract: Aim This study provides the first direct evidence about the location of a spawning site of Brycon orbignyanus (Valenciennes, 1850) in the Middle Uruguay River. Methods Sampling was carried out with a plankton net (500 µm) in November 2017 in the Uruguay River near the confluence with the Piratinim River, southern Brazil. Eggs were sorted in the field, and to confirm species identity we used the live ichthyoplankton technique. Results We captured 47 eggs of B. orbignyanus in the channel of the Uruguay River, characterized by fast flow, shallow depth (approximately 3 m) and rocky bottom, located a few kilometers upstream from its confluence with the Piratinim River. Eggs are spherical, well hydrated, semi-dense, transparent and non-adhesive, with a single membrane and large perivitelline space. Total diameter varied between 3,500 and 4,000 µm. Eggs were in early stages of embryonic development, and cells showed 8, 16 or 32 blastomeres. A total of 16 eggs hatched into larvae in the plastic bags. Larvae hatched approximately 18 hours after incubation, and took 14 days to become juvenile. Conclusion This seems to be the first record of a spawning site of B. orbignyanus in the La Plata River Basin, and points to the relevance of the Middle Uruguay River as a recruitment area for this endangered species.

First record of microplastics in two freshwater fish species (Iheringhthys labrosus and Astyanax lacustris) from the middle section of the Uruguay River, Brazil

Abstract Aim The aim was to analyze the incidence of microplastics in the diet of fish in the middle Uruguay River. Methods The present work analyzed the gastrointestinal content of two species: Astyanax lacustris and Iheringichthys labrosus. Results This study provides the first evidence of synthetic materials, such as fibres and plastics in the gastrointestinal tract of fish species in the Middle Uruguay River basin. A sample of sixty-one A. lacustris and twenty-nine I. labrosus were examined to highlight the ingestion of microplastics in the middle section of the Uruguay River in Brazil. In the A. lacustris, eleven fibres and two fragments were found in their gastrointestinal contents, corresponding to 18.1% of the specimens, while in the I. labrosus, twelve fibres and one fragment were found, corresponding to 34.5% of the specimens analyzed. Blue staining was also prevalent in the occurrence of microplastics. Conclusions These data are the first record of microplastics in this zone and represent a baseline for this contamination for future studies.

Genetic evidence supports polygamous mating system in a wild population of Prochilodus lineatus (Characiformes: Prochilodontidae), a Neotropical shoal spawner fish

ABSTRACT Behavioral observations made on fish have revealed remarkably diverse reproductive strategies, including polygamy by both sexes. Still, to date, most Neotropical species remain unstudied as to whether the observed reproductive behavior in natural populations correlates with their genetic mating systems. Here, we investigated the genetic mating system of a wild population of Prochilodus lineatus settled in the Middle Uruguay River basin. By using sibship reconstruction and parental inference methods based on microsatellites’ genotypes, we inferred 45 females and 47 males as potential parents of the 87 larvae analyzed. We found evidence supporting polygamous mating in both sexes: while a high percentage of males (44.7%) fertilized the eggs of one female, 55.3% of the inferred males fertilized eggs of up to four females. Likewise, while 44.5% of the inferred females had their eggs fertilized by one only male, 55.5% of females were fertilized by multiple males. The estimated proxy of the effective population size (Nb) was 126, exhibiting moderate to high levels of genetic diversity. The genetic evidence contributed in this study complements earlier behavioral observations of formation of spawning nuclei of aggregating breeders, which may be promoting a polygamous mating strategy in this long-distance migratory fish.

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

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

Living on the river edge: The Tigre site (K-87) new data and implications for the initial colonization of the Uruguay River basin

This paper presents new data on the initial settlement of the southeastern region of South America, based on recent research conducted at the Tigre archaeological site (K87), located in the middle Uruguay River basin, near the Uruguayan border with Brazil and Argentina. The current archaeological excavations carried out in this open-air site confirmed that it is a multicomponent site. A new series of 20 radiocarbon dates refined the chronology of recurrent human occupations at this site during the late Pleistocene (13,260 cal BP), the Pleistocene-Holocene transition (12,920–11,750 cal BP), the early Holocene (11,300–9300 cal BP), and the late Holocene (1180 cal BP), demonstrating the strategic importance of this site during the prehistory of the region. In this paper, we describe the archaeological and stratigraphic contexts of the site, and analyze the artifact assemblage of the early components. Tigre points recovered from the archaeological excavations confirm that this is a Paleoamerican point design that circulated in the region between 12,000–11,100 cal BP. In addition, associated with these points, bifaces, fractured preforms and a type of asymmetric biface with a crescent/half moon shape were recovered. These “crescent artifacts” show a high standardization in form, size and knapping technique, which is described in this paper. Finally, we discuss the geographic distribution of the Tigre points, the blade technology present in the Uruguay River basin, the presence of prestige artifacts during the settlement, and the chronology of the “Umbu tradition” of southern Brazil in relation to the previous and recent data obtained in the Tigre site.

Malvaceous wood from the Late Pleistocene El Palmar Formation of northeastern Argentina

We describe a new species of Bastardiopsis, Bastardiopsis palaeodensiflora sp. nov., which is the first fossil Malvaceae wood reported in Argentina. It was collected from the Arroyo Yuquerí of El Palmar Formation, a late Quaternary fluvial unit, located in the middle Uruguay River Basin, NE Argentina. The diagnostic features of this fossil wood are growth ring boundaries demarcated by marginal parenchyma; diffuse porous wood; vessels solitary and in radial multiples of 2–3 elements; alternate and minute-to-small sized intervessel pits; tyloses abundant; vessel-ray parenchyma pits similar in size and shape to intervessel pits; vasicentric, and diffuse axial parenchyma; rays of two distinct sizes, mostly 4–5 cells wide; prismatic crystals in upright and/or square marginal cells, sheath cells, non-septate fibres, rays and vessel elements irregularly storied. These features suggest an assignation to Bastardiopsis (K. Schumann) Hassler, a genus with five extant species, extending from the north of South America to northern Argentina, mainly distributed in tropical to temperate areas. The eco-anatomical features, the Nearest Living Relatives (NLRs), the Vulnerability Index, the Mesomorphy ratios and the Taxon Independent Approach (TIA) indicate that this fossil grew under temperate-warm and humid conditions. This is consistent with other proxies (geological, sedimentological and microfossil data) suggesting a similar environment for this region during some periods of the Late Pleistocene.

Agricultura Familiar y Agroindustrias: subordinación productiva. Los casos de la citricultura y la fruticultura de Argentina (2003-2016)

This article proposes to investigate the link between family farming (AF) and agro-industries. The research is based on a qualitative methodology and uses quantitative information. In particular, two cases (citric belt of Middle Uruguay River and fruit growing of Patagonic Valleys) based on: i) the characteristics, evolution and transformation of the actors and agents in the primary phase and marketing; ii) the configuration of the world market and its relations with the identified production restructuring at local level. In both cases, the proliferation of various commitments and proactive strategies that align agribusiness agents linked to export under heterogeneously structured circuits is recorded. Family production becomes, tending in some cases to specialize in a commercial crop and reducing its productive diversity, making it possible stabilization of subsumption because the AF becomes mere supplier of commodities to agro-industry, relegating other crops and / or activities.

The human colonization of the Southeast Plains of South America: Climatic conditions, technological innovations and the peopling of Uruguay and south of Brazil

Abstract During the late Pleistocene and early Holocene, climatic, faunistic, and ecological changes could produce social readjustments and technological innovations in human populations that were exploring and colonizing the low southeastern plains of South America. In this paper, paleoecological and archaeological data are integrated to systematize and discuss different aspects of early human settlement in Uruguay and the south of Brazil. It is possible to recognize evidence of initial human dispersion by the region between ∼14,000 and 13,100 cal BP (12,000 to 11,320 14C BP) during the late Pleistocene, when dry and cold climatic conditions prevailed in the region. Later, between 12,800 and 10,065 cal BP, a low plains Paleoamerican stemmed bifacial tradition emerged with three different techno-complexes, represented by Fishtail, Tigre, and Pay Paso projectile points. These groups were adapted to the grassland plains and characterized by the presence of wide-stemmed projectile points. The Fishtail point had been supplanted by the Tigre point, showing diversification in design of projectile points during the Pleistocene–Holocene transition. Approximately 12,000 to 11,200 cal BP in the middle Uruguay River, a social and technological reorganization occurred, along with the emergence of the Tigre techno-complex during post-Fishtail times. The advent of Tigre groups coincided with warmer and wetter climatic conditions, indicating the beginning of the Holocene. By 11,080–10,928 cal BP, new weaponry changes occurred in the region, including the production of the Pay Paso points, a regionally distinctive projectile-point style for the early Holocene. These aspects allow start discussions of cultural transmission, technological innovations and morphological variation in projectile point styles over the time and space. The field research developed over the past 15 years, in conjunction with the previous research conducted in southern Brazil, the relative high density of early sites with radiocarbon ages (n = 22), and the chronological base (67 radiocarbon ages), allow to formulate an archaeological and behavioral model about the initial peopling of the Uruguayan and southern Brazil plains.

Índice Ambiental de Perda por Fragmentação (IAPF)

River fragmentation is one of the greatest challenges on environmental planning at the light of water resources management. The need for dams for hydropower generation, irrigation and public water supply, results in increasing pressure on the ecological integrity of water bodies. This paper proposes a methodology to measure the environmental losses caused by river fragmentation by accounting the change in the value of the so called environmental fragility. The Index of Environmental Losses by River Fragmentation (a non-monetary index) was applied in the Upper and Middle Uruguay River basin, located partially in the states of Santa Catarina and Rio Grande do Sul, in the FRAG-RIO Project study area. The results show that the index could account the portions of rivers more susceptible to fragmentation, enriching the discussion and providing guidelines for the environmental planning of the Uruguay River basin

First record of the hypoptopomatine genus Eurycheilichthys Reis & Schaefer, 1993 (Siluriformes, Loricariidae) from Argentina

The hypoptopomatine genus Eurycheilichthys was so far considered to be endemic to the South of Brazil. One of its species, E. pantherinus, was described from the upper Uruguay river basin. We inform about the finding of this species within the Garibaldi creek, headwater of the arroyo Yabotí Guazú. This is the first record for Argentina which is found in a tributary of the middle Uruguay river.

First record of the hypoptopomatine genus Eurycheilichthys Reis & Schaefer, 1993 (Siluriformes, Loricariidae) from Argentina

The hypoptopomatine genus Eurycheilichthys was so far considered to be endemic to the South of Brazil. One of its species, E. pantherinus, was described from the upper Uruguay river basin. We inform about the finding of this species within the Garibaldi creek, headwater of the arroyo Yabotí Guazú. This is the first record for Argentina which is found in a tributary of the middle Uruguay river.

Perciformes, Cichlidae, Crenicichla tendybaguassu Lucena and Kullander, 1992: first record for Uruguay

The present note is the first record of the pike cichlid Crenicichla tendybaguassu for Uruguay, extending its distribution about 400 km to the South. The presence of C. tendybaguassu and their co-occurrence with other priority species for conservation in Uruguay adds greater value to conservation of the Cuareim River (Middle Uruguay River). Coloration of live breeding females is described for first time.