Commercial fisheries in a mega unregulated floodplain river: Assessment of the most favourable hydrological conditions for its preservation.

This paper deals with the hydrological variability effects on the primary commercial fish species inhabiting the main channel and the floodplain of the large Paraná River in its middle reaches in Argentina. Analysing more than eight decades (1935-2016) of information on the most frequent and abundant commercial species in conjunction with hydrological levels and temperature, our results show that spring-summer floods of a certain magnitude (c. 6 m) and durations (> 80 days) are crucial for sustaining commercial fisheries. Moreover, the frequency of these floods was modulated by the decadal climatic fluctuations that have occurred over the past 100 years in the Paraná Basin. An insight into the probable incidence of some anthropogenic influences is also provided.

The challenge of reducing macroplastic pollution: Testing the effectiveness of a river boom under real environmental conditions.

Improving collection technologies is crucial to develop effective and economically feasible solutions for catching plastic from riverine environments. However, floating booms are being constructed and deployed in river around the world without rigorously testing its effectiveness. In this study, we tested the effectiveness of a boom under realistic conditions for several configurations and treatments (including "C-shape" and "Slash-shape" configurations). For this, we used the same macroplastics that leak out of waste management channels in order to be as realistic as possible. In total we used 52 plastic articles of 13 different polymers. The global effectiveness of the tested C-shape boom was lower than expected under such conditions (around 37 % of retention). The effectiveness of the Slash-shape boom was considerably worst (<10 %). However, the effectiveness varies greatly according to the particular characteristics of the plastic articles (i.e., shape and polymer composition), ranged from 0 to 100 %. For example, the boom could be 100 % effective retaining plastics such as Stylofoam trays and cups, 40-20 % for food-wrappers but 0 % for disposable plates and spoons, straws, monofilament fishing lines, packaging straps, hoses, pipes, elastic bands, etc. It seems that to have a reasonable catch-effectiveness and be cost-efficient, boom designs need to be improved and tested under different environmental conditions before to reach the market. In addition, it is unrealistic to select only high buoyancy plastics for testing them.

Fishers' knowledge on a large floodplain river in South America. Contributions for sustainable management of inland fisheries.

This study presents a comparison between fishers' knowledge and fiscal records about the structure of inland fisheries in the Paraná River (Argentina). First of all, we characterized the fishing population according to the main demographic and economic indicators, identifying two different fishing areas: the northern and southern sections in the lower La Plata basin. Secondly, we carried out a comparative analysis of fiscal fishery records (from two commercial sets: 1930-1984 and 2011-2019) and local fishers' knowledge on inland commercial fisheries (frequency of occurrence and abundance). Finally, we contrasted current fishing regulations (allowed meshes and boats, fishing prohibitions, exports) to fishers' effective practices. The study area included 52 sites located along the floodplain of the middle and lower sections of the Paraná River, in the province of Santa Fe. Socioeconomic analyses identified two different groups of fishers throughout the river corridor. Results showed that fishers have detailed knowledge on nomenclature, ecology, reproductive strategy, habitat distribution, and usefulness of commercial fish species. By contrasting fishers' knowledge with fiscal records, we found similar and complementary information about the changes in abundance and frequency of occurrence in fisheries. These results highlight the need of including local knowledge as an outstanding source of information for well-planned management of fishing programs and sustainable policies. Supplementary Information: The online version contains supplementary material available at 10.1007/s11160-022-09722-x.

The use of anthropogenic debris as nesting material by the greater thornbird, an inland-wetland-associated bird of South America.

Plastic pollution has become a globally pressing environmental issue. In birds, plastic may cause harm by entangling or ingestion when used for nesting. The use of anthropogenic nesting material has so far been mostly studied in birds of terrestrial or marine habitats, but there are yet very few reports for inland water-associated birds. The aim of this study is to better understand the extension and magnitude of the use of anthropogenic debris as nesting material by the greater thornbird (Phacellodomus ruber), a bird species preferably nesting in river floodplain wetlands in South America. We found that P. ruber uses disproportionally large quantities of plastic debris as nesting material (more than 90% of some nest chambers is plastic). This occurred even if ample vegetation (commonly used as soft material) was available. Most of the artificial nesting material was derived from wrapping material released into the environment. We suggest that this species has the potential to indicate vulnerable areas to plastic pollution associated with urban waste mismanagement.

Massive plastic pollution in a mega-river of a developing country: Sediment deposition and ingestion by fish (Prochilodus lineatus).

The aim of this study was to determine the amount, composition and origin of plastic debris in one of the world largest river, the Paraná River in Argentina (South America), focusing on the impact of urban rivers, relationships among macro, meso and microplastic, socio-political issues and microplastic ingestion by fish. We recorded a huge concentration of macroplastic debris of domestic origin (up to 5.05 macroplastic items per m2) dominated largely by bags (mainly high- and low-density polyethylene), foodwrapper (polypropylene and polystyrene), foam plastics (expanded polystyrene) and beverage bottles (polyethylene terephthalate), particularly downstream from the confluence with an urban stream. This suggests inadequate waste collection, processing and final disposal in the region, which is regrettably recurrent in many cities of the Global South and Argentina in particular. We found an average of 4654 microplastic fragments m-2 in shoreline sediments of the river, ranging from 131 to 12687 microplastics m-2. In contrast to other studies from industrialized countries from Europe and North America, secondary microplastics (resulting from comminution of larger particles) were more abundant than primary ones (microbeads to cosmetics or pellets to the industry). This could be explained by differences in consumer habits and industrialization level between societies and economies. Microplastic particles (mostly fibres) were recorded in the digestive tract of 100% of the studied Prochilodus lineatus (commercial species). Contrary to recently published statements by other researchers, our results suggest neither macroplastic nor mesoplastics would serve as surrogate for microplastic items in pollution surveys, suggesting the need to consider all three size categories. The massive plastic pollution found in the Paraná River is caused by an inadequate waste management. New actions are required to properly manage waste from its inception to its final disposal.

Freshwater plastic pollution: Recognizing research biases and identifying knowledge gaps.

The overwhelming majority of research conducted to date on plastic pollution (all size fractions) has focused on marine ecosystems. In comparison, only a few studies provide evidence for the presence of plastic debris in freshwater environments. However, owing to the numerous differences between freshwater studies (including studied species and habitats, geographical locations, social and economic contexts, the type of data obtained and also the broad range of purposes), they show only fragments of the overall picture of freshwater plastic pollution. This highlights the lack of a holistic vision and evidences several knowledge gaps and data biases. Through a bibliometric analysis we identified such knowledge gaps, inconsistencies and survey trends of plastic pollution research within freshwater ecosystems. We conclude that there is a continued need to increase the field-data bases about plastics (all size fractions) in freshwater environments. This is particularly important to estimate river plastic emissions to the world's oceans. Accordingly, data about macroplastics from most polluted and larger rivers are very scarce, although macroplastics represent a huge input in terms of plastics weight. In addition, submerged macroplastics may play an important role in transporting mismanaged plastic waste, however almost no studies exist. Although many of the most plastic polluted rivers are in Asia, only 14% of the reviewed studies were carried out in this continent (even though the major inland fisheries of the world are located in Asia's rivers). The potential damage caused by macroplastics on a wide range of freshwater fauna is as yet undetermined, even though negative impacts have been well documented in similar marine species. We also noted a clear supremacy of microplastic studies over macroplastic ones, even though there is no reason to assume that freshwater ecosystems remain unaffected by macro-debris. Finally, we recommend focusing monitoring efforts in most polluted rivers worldwide, but particularly in countries with rapid economic development and poor waste management.

Influence of hydrology on the fish body condition in a large subtropical floodplain

With the objective of finding fluctuations on fish body condition in the Middle Paraná River floodplain in different hydrological scenarios, this attribute was analyzed in several trophic groups of a secondary floodplain channel and its associated lakes between 2010 and 2012. Standardized residuals generated by length-weight regressions were calculated for each species and the relative weight (Wr) of the most abundant species per group was examined. A two-way factorial ANOVA was carried out (factors: hydrology and habitats) to evaluate the existence of significant spatial-temporal differences by groups and species. Results showed that body condition in detritivorous, herbivorous and omnivorous species fluctuated significantly depending on hydrology and the environment. Optimal body condition was recorded after the largest flood pulse in most species. Body condition decreased during the low-water period and after two disconnection periods, whereas during the second flood pulse it increased in detritivores, herbivores and omnivores. No floods occurred thereafter, but two flow pulses were registered, and body condition increased under these hydrologic scenarios, with similar or higher values to those recorded after the largest pulse. These results indicate that flow pulses, which are supplementary to flood pulses, may have a positive effect on fish body condition.(AU)

Con el objetivo de conocer la fluctuación de la condición corporal de peces en la planicie de inundación del tramo medio del río Paraná ante diferentes escenarios hidrológicos, se analizó este atributo de diferentes grupos tróficos en un cauce secundario de la planicie y sus lagunas asociadas durante 2010 a 2012. Se calcularon los residuos estandarizados generados por las regresiones longitud-peso para cada especie y se examinó el peso relativo (Wr, por sus siglas en ingles) de las especies más abundantes de cada grupo. Se llevó a cabo un ANOVA factorial de dos vías (factores: hidrología y ambientes) para evaluar la existencia de diferencias significativas espacio-temporales por grupos y por especies. Los resultados mostraron que la condición corporal de las especies detritívoras, herbívoras y omnívoras fluctuó significativamente en función de la hidrología y los ambientes. Óptimas condiciones corporales se registraron en la mayoría de las especies después del mayor pulso de inundación. La condición corporal disminuyó durante el período de aguas bajas y luego de dos períodos de desconexión, mientras que, durante el segundo pulso, aumentó en detritívoros, herbívoros y omnívoros. No hubieron inundaciones luego, pero ocurrieron dos pulsos de flujo y las condiciones corporales se incrementaron bajo estos escenarios hidrológicos, presentando valores similares o incluso mayores a los registrados luego del gran pulso. Esto destaca que los pulsos de flujo complementarios a los pulsos de inundación pueden tener un efecto positivo sobre la condición corporal de peces.(AU)