Dip Nets Research Articles

Spatio-temporal Dynamics of Anuran Populations in the Wetlands of Korhogo, Côte d'Ivoire

Aims: The Korhogo commune contains several natural habitats that are home to a large community of frogs. But today, these habitats are facing strong anthropic pressures. This study aims to show the effect of anthropogenic activities on wetlands and the organisms that live there. Methodology: Sampling took place from June 2023 to May 2024, and samples came from experimental fishing using deep-net dip nets with 2 mm mesh or rod and line, and from commercial fishing using various gears. Results: A total of 791 individuals were caught, for a total biomass of 48.872 Kg. These individuals were divided into 5 species, 4 genera and 4 families. Spatially, diversity was highest in the lakes (80) and lowest in the rice fields (20%). Temporally, diversity was highest in the rainy season (100%) and lowest in the dry season (40%). The species Hoplobatrachus occipitalis dominated the population with 94.66% of captures. It accounted for 25.46%, 24.27%, 22.81%, 13.93% and 13.53% respectively in lakes, rice fields, rivers, wells and shallows. The strong presence of this species in the wetlands of this commune shows that these areas are highly threatened. Conclusion: This study contributes to the knowledge of the frog population and helps to combat the degradation of wetlands in the city of Korhogo.

Finfish fishery of Ashtamudi Estuary, India- A Ramsar site of International significance

The finfish catch structure of Ashtamudi Estuary, a Ramsar site of international importance was assessed from May 2019 to April 2020 covering ten major landing centers (Sakthikulangara, Sambranikodi, Mammottil kadavu, Ashtamudi, Perumon, Kurismmood, Cherikadavu, Arinalloor, Vellimon and Muttom). The annual finfish landings was estimated as 195.4 tonnes, contributed by 148 species of finfishes and a single species of Elasmobranch. Gill nets (51%) were the dominant gear in the finfish landings followed by scoop nets and hook and lines (20%), seine nets (15%), stake nets and Chinese dip nets (8%) and cast nets with (6%). The highest landing was recorded in the month of August (20.71 tonnes). The major finfish groups that contributed to the fishery of Ashtamudi Estuary were Cichlids (24.08%), catfishes (13.72%) and Mullets (10.22%). The study revealed the decline in the finfish landings from its estimated quantity of 3462 tonnes (2000–2001) might be attributed to the (1) decrease in number of active fishers, (2) declining mangrove cover, (3) loss of wetland area, (4) unsustainable fishing practices and (5) increasing anthropogenic pressures from urbanization of Kollam Corporation . In this context, the paper also discusses various management measures to improve the fish catch from the estuary in a sustainable way.

Influence of RNA-Seq library construction, sampling methods, and tissue harvesting time on gene expression estimation.

RNA sequencing (RNA-Seq) is popular for measuring gene expression in non-model organisms, including wild populations. While RNA-Seq can detect gene expression variation among wild-caught individuals and yield important insights into biological function, sampling methods can also affect gene expression estimates. We examined the influence of multiple technical variables on estimated gene expression in a non-model fish, the westslope cutthroat trout (Oncorhynchus clarkii lewisi), using two RNA-Seq library types: 3' RNA-Seq (QuantSeq) and whole mRNA-Seq (NEB). We evaluated effects of dip netting versus electrofishing, and of harvesting tissue immediately versus 5 min after euthanasia on estimated gene expression in blood, gill, and muscle. We found no significant differences in gene expression between sampling methods or tissue collection times with either library type. When library types were compared using the same blood samples, 58% of genes detected by both NEB and QuantSeq showed significantly different expression between library types, and NEB detected 31% more genes than QuantSeq. Although the two library types recovered different numbers of genes and expression levels, results with NEB and QuantSeq were consistent in that neither library type showed differences in gene expression between sampling methods and tissue harvesting times. Our study suggests that researchers can safely rely on different fish sampling strategies in the field. In addition, while QuantSeq is more cost effective, NEB detects more expressed genes. Therefore, when it is crucial to detect as many genes as possible (especially low expressed genes), when alternative splicing is of interest, or when working with an organism lacking good genomic resources, whole mRNA-Seq is more powerful.

Implementing community-engaged ecological research in Proctor Creek, an urban watershed in Atlanta, Georgia, USA.

The Southeast Region of the United States Fish and Wildlife Service (USFWS) implemented community-engaged research in Proctor Creek, an urban watershed in Northwest Atlanta, Georgia, to sample for aquatic species of concern in Atlanta, Georgia's Proctor Creek Watershed as a part of the Urban Waters Federal Partnership program. This research shifted the focus of the agency from the endangered and pristine natural spaces to a major city watershed negatively impacted by urbanization and other human influences for more than a century. Team members from USFWS, Proctor Creek Watershed residents, local students, and other stakeholders in the Urban Waters Federal Partnership (UWFP) spent three months conducting stream surveys and participating in community-led events to build relationships and learn community priorities. The team collected data at 11 sites throughout the Proctor Creek Watershed, visually assessed each site, and collected aquatic species using dip nets, seines, and traps. We observed approximately 28 aquatic species, including 13 unique fish species, and eight macroinvertebrate species, including two unique crayfish species. We also observed varying degrees of ecological health throughout the watershed. Native aquatic animal species were found at all stream sites, no matter the condition of the stream. Through creating training resources and disseminating data among team members for future sampling, the team established pathways to keep natural resource stewardship sustainable without direct federal involvement. Through engaging in community-engaged research to achieve the mission of the agency, the USFWS Proctor Creek Watershed survey helped shift the paradigm of how government agencies can connect their mission statements to the ever-changing complex needs of the American public.

Length-weight relationship, sex ratio, and diet of three fish species (Actinopterygii: Teleostei) in streams of the Pomba River basin, Paraíba do Sul river drainage, Southeastern Brazil

This study aimed to estimate the parameters of length-weight relationship, sex ratio, and diet of three freshwater fish species that inhabit streams in the Pomba River basin (Rio de Janeiro, Brazil). Fishes were sampled with seine nets (2.0 × 1.20 m, 2 mm mesh size) and dip nets (0.46 × 0.33 m, 2 mm mesh size) from October to December 2018. Measurements were taken for total length (TL - 0.1 cm precision) and total weight (TW - 0.01 g precision). Growth model parameters were estimated. This study provides new length-weight relationship data for Deuterodon intermedius (Eigenmann, 1908), Australoheros paraibae Ottoni & Costa, 2008, and Hypostomus punctatus Valenciennes, 1840. All of them ingested a wide variety of food items, including plant material like algae, animal material such as terrestrial and aquatic insects, and undefined matter such as detritus or mud. The three species showed a higher number of females. Our study provides basic information for functional diversity studies, as well as for future investigations associated with the evaluation of anthropic impacts, either occasional or chronic, on the fish assemblage structure of the Pomba River basin.

Increasing Dip Net Mesh Size Results in More Fin Splits in Post-Smolt Atlantic Salmon (Salmo salar)

ABSTRACT Dip nets are widely used to retrieve fish from the water but can cause injuries to the fish. The objective of this study was to document the potential effects of dip net mesh size with respect to external injuries, more specifically fin splits and scale losses, in Atlantic salmon (Salmo salar). The study included 273 post-smolt Atlantic salmon from two fish batches referred to as the Tank group ( w ˉ = 178 ± 36 g, n = 198) and the Cage group ( w ˉ = 1319 ± 334 g, n = 75). Four identical dip nets with mesh sizes of 5, 10, 15, and 20 mm, respectively, were used to net fish out of their enclosures before the external injuries were assessed by visual inspection. The results showed that the number and severity of fin splits increased with dip net mesh size, but no effect of mesh size on the percentage of scale losses was found. Dip-netting of five fish at a time instead of one with the 20 mm dip net, had no statistically significant effect on the examined injuries. It is concluded that the use of dip nets with smaller mesh sizes can be positive for fish welfare by reducing fin splitting.

Evidence of Spatial Stability in Core Fauna Community Structure of Holopelagic Sargassum

As Sargassum biomass continues to increase globally, it is critical to develop a better understanding of how it functions as habitat, therefore, community structure of Sargassum-associated organisms was examined from 11 sampling locations spanning the tropical Florida Straits to the more temperate Gulf Stream off the coast of Savannah, Georgia from May to September 2018 using a combination of modified shrimp trawls and dip nets. A total of 5413 organisms were collected from Sargassum habitat representing 14 species from 10 families. A core group of organisms (Platynereis dumerilii, Litiopa melanostoma, Portunus sayi, Portunus spinimanus, Leander tenuicornis, and Latreutes fucorum) were found throughout the entirety of the geographic range surveyed. This core community did not vary significantly with increasing distance to shore or latitude, nor did it correlate with environmental variables such as salinity and temperature. However, community structure did vary with clump size, with larger clumps harboring more speciose communities. The Sargassum community in the Florida Straits and Gulf Stream appear to provide habitat for a consistent group of epifaunal organisms. In turn, this stable group offers a consistent prey source for a variety of important, higher trophic level organisms.

Population Characteristics of the Etheostoma pallididorsum Distler and Metcalf (Paleback Darter), a Narrowly Distributed Endemic in the Ouachita Highlands, Arkansas

Etheostoma pallididorsum (Paleback Darter) is endemic to the headwater reaches of 2 river systems in the Ouachita Highlands of Arkansas. Records of low abundance and habitat alterations have resulted in the species' imperiled conservation status and being petitioned for federal listing under the Endangered Species Act. The objective of this study was to conduct seasonal surveys across the Paleback Darter's distribution to better characterize growth, spawning patterns, and mortality using the seasonal von Bertalanffy statistic with an optimized electronic length frequency analysis (ELEFAN), as well as assess sex ratios throughout a calendar year to better inform future conservation management decisions for the species. We established seasonal survey collection sites at 4 localities and sampled with a backpack electrofishing unit and dip nets from January 2016 to October 2017. The study indicated relatively high abundance, based on catch per unit effort (CPUE), across all sampled localities throughout the duration of the study, with representation of the entire population from 3 age classes: 0, 1, and 2. Growth and coarse spawning patterns, based on the seasonal von Bertalanffy statistic, were comparable between the populations, suggesting similar and stable environmental factors throughout the distribution. Lastly, there was evidence of multiple spawn events occurring during winter and late spring or early summer that has not been documented for this species, warranting additional research. Collectively, this study, though narrow in scope and with limited data, suggest that the Paleback Darter populations assessed are not impaired. The endemic status and narrowly fragmented distribution of the Paleback Darter, however, still renders this species vulnerable to extirpation or extinction by stochastic events.

Contribution to the Knowledge of Freshwater Shrimps (Crustacea, Decapoda) and Their Spatial Distribution in the Malebo Pool (Congo River), R.D Congo

Background and Objective: Crustaceans play a considerable role in the ecological process of aquatic ecosystems, acting at different trophic levels as herbivores, detritivores, predators and prey and constitute an important source of animal protein for humans and livestock. This study investigated the diversity of shrimp from the left bank of the Malebo Pool in the Congo River.
 Study Area: Five sampling campaigns were organized from July 2020 to August 2021 in six sites (Ngamanzo 1, Ngamanzo 2, Kinkole 1, Kinkole 2, Kinsuka 1 and Kinsuka 2) in the Malebo Pool, the terminal part of the middle Congo River.
 Methods: Shrimp samples were collected using dip nets and creels during the experimental fisheries. Physical parameters were measured monthly in situ at six sites. Chemical parameters were assessed using an ultraviolet atomic spectrophotometer. Systematic identification of shrimp was done using appropriate systematic identification keys. The structure of the shrimp populations was studied using several ecological indices.
 Results: A total of 1422 shrimp specimens were sampled. These individuals belonged to three different species (Caridina africana Macrobrachium dux and Macrobrachium sollaudii), two genera (Caridina and Macrobrachium) and two families (Atyidae and Palaemonidae). Shanon and Weaver's diversity index values ranged from 0 to 1.3 indicating that the shrimp fauna is not diverse in Malebo Pool. These species are better represented at Ngamanzo 1, Ngamanzo 2 and Kinkole 2. Redundancy analysis (RDA) showed that environmental variables such as dissolved oxygen level, conductivity, water temperature, transparency, water flow velocity, plant debris, aquatic plants and canopy strongly influence taxonomic diversity across sites.
 Conclusion: The results obtained showed that the shrimp fauna is rich and diversified in the studied part of the Malebo Pool in the Congo River and, these organisms are essential in maintaining the ecological balance in this aquatic ecosystem.

Length Weight Relationships and Condition Factor of Sicydium sp. (Gobiidae) from the Yallahs River and Swift River, Jamaica

Sicydium sp., commonly known as gobies, are migratory freshwater fish that spend most of their life cycle in rivers, but when the larvae emerge they drift downstream to the sea where further development of juveniles occurs. Although Sicydium sp. are abundant in Jamaican rivers, little is known about the ecology of these species on the island and throughout the Caribbean. This study examines aspects of the ecology and biology of Sicydium populations in Jamaica. Fish sampling was carried out using dip nets and bottom kick nets at sites along the south coast in the Yallahs River, and along the north coast in the Swift River. A total of 850 gobies were captured, measured, and weighed. The values of the allometry coefficient or growth pattern (b) in the length weight relationships (LWR) were significantly different among males, females, and juveniles (p < 0.05). The growth pattern derived from LWR's was positive for females, males, and juveniles in the Yallahs River, and positive for females and juveniles but negative for males in the Swift River. The mean Fulton's condition factor (K) indicates that fish populations in both rivers are healthy and in good condition. These results augment the body of knowledge on Sicydium gobies in Jamaica.

A survey on the traditional and indigenous fishing methods in the Kali River, Uttarakhand, India

The rain-fed river Kali (29°24’09 “N, 80°15’17 “E) of Uttarakhand was the study area. To know the fishing techniques capture fisheries status were the objectives of the study. This study will be helpful for farmers, researchers and sustainable capture fishery development practice. One year of sampling and data collection methods were; interaction- based data collection, direct interactive field survey, field own observation-measurement of different nets and communication with the local community. Fishing net classification and identification was done by literature. Three types of fishing methods were used in the area; ‘commonly used methods’ included fishing with cast nets, gill nets, dip nets, hand nets, dragged nets, hooks, and traps, whereas ‘rarely used’ (only 2%) methods included only some nets and techniques, and ‘cost-effective method’ included the use of explosives and 06 ichthyo-toxic plants. Fishing tools were designed according to fish for size specific capture of fish. The use of fishing methods depend upon the topography, geography and climatic conditions of that area.

Relative Effectiveness of D‐Frame Dip Nets, Quatrefoil Light Traps, and Towed Ichthyoplankton Nets for Larval Muskellunge

AbstractMuskellunge Esox masquinongy are large, predatory game fish whose association with shallow, complex habitats is well documented, particularly during early life stages. Despite this association, relatively little guidance exists regarding effective sampling of Muskellunge larvae and previous efforts to sample larval Muskellunge have been met with limited success. Therefore, our objective was to determine the relative effectiveness of three sampling gears for capturing naturally produced Muskellunge larvae. Larvae were sampled during 2019 and 2020 at known Muskellunge spawning locations in Snipe Lake, Wisconsin, with D‐frame dip nets (1,000‐µm mesh), quatrefoil light traps, and towed ichthyoplankton nets (1,000‐µm mesh). Sixty larval Muskellunge were captured across all gears, and catches in D‐frame dip nets comprised nearly 87% (52 of 60) of the total catch. Furthermore, D‐frame dip nets captured the broadest size range of larval Muskellunge (TL range = 14–33 mm). Greater effectiveness of D‐frame dip nets in comparison with other gears is likely related to their ability to be used in and around structurally complex habitats without fouling or clogging. Our results suggest that D‐frame dip nets should be considered as a cost‐ and time‐effective tool for targeting larval Muskellunge in complex habitats.

Reproduction of Sefidrud stone loach, Oxynoemacheilus bergianus (Cypriniformes: Nemacheilidae) in Kordan River of Namak basin, Iran

The Sefidrud stone loach/Berg loach Oxynoemacheilus bergianus is native to the Eurasia and little is known about this species. Some biological characteristics of the spices were examined in 358 specimens collected monthly from the Kordan River in Alborz Province, by dip and seine nets during September 2013 to August 2014. The total length range was 32.36-74.36mm (50.95±10.3SD), and the total weight range was 0.31-4.06g (1/12±0.68SD). The maximum age of the specimens, based on otoliths, was 5 + years for females and 4 + years for males. Based on macroscopic gonad observation, the age of maturity was 2 + for females and 1 + for males. Sex ratio was 1M:0.9F, maturation cycle consisted of five stages. The gonadosomatic index indicated that reproduction of the fish in the river system occurred between March and June, with the highest average value of 9.47 for males in April and 13.42 for females in May. Oocyte diameter ranged from 0.15 to 1.33mm, with a mean value of 0.44mm. Absolute fecundity ranged between 360 and 2560 eggs, with a mean of 1130±670 eggs. Absolute fecundity and total length (r 2 = 0.58) and total weight (r 2 = 0.66) were moderately correlated. The mean relative fecundity was 580±190 eggs per gram of body weight. Therefore, O. bergianus is a species with a premature sexual maturity, high fecundity than other loaches and reproduction happen gradually in March to June.

Evaluation of the Degradation Level of a Fluvial Basin in the Western Area of Côte d&amp;apos;Ivoire: Case of the Cavally River

The present study is a diagnosis of the level of degradation of Cavally River in Cote d'Ivoire. Several abiotic indicators such as physico-chemical parameters were appreciated. These abiotic indicators were supported by biotic indicators sensitive to some variations in quality of water. That is the use of benthic macro-invertebrates as some species of freshwater shrimps of the genus Macrobrachium. Sampling was made between September 2015 and August 2016 on the upper course of Cavally River and the area on either side of the mining zone Ity. Measures of physico-chemical parameters such as dissolved oxygen, temperature of water, hydrogen potential, electrical conductivity, mercury rate and water transparency were made by season using multi parameters. Shrimps were caught monthly using dip nets and keep nets. The extreme value of physicochemical parameters is for dissolved oxygen value were 4.90 mg/l, temperature of water (25.55°C), hydrogen potential (8.48), electrical conductivity (53.14 μS/cm), mercury rate (5.75.10-3 mg/kg) and water transparency (27.06 cm). In general, the results showed that the extreme values of physico-chemical parameters were recorded in areas with high concentrations of anthropogenic activities. In the mining areas, high levels of mercury have been recorded above those of the WHO guideline for surface water. In total, M. vollenhovenii was the most abundant species with 383 individuals out of 879 specimens caught (43.57%). It is followed by M. dux with 321 individuals (36.51%) and M. macrobrachion with an abundance of 175 individuals (19.90%). Spatially, these species have been more abundant in the upstream and downstream areas which are more or less conserved environments. However, they were less abundant in mining areas. These results show that the upper course of the Cavally River is deteriorating. That constitutes a real threat to aquatic organisms and biodiversity.

Estimation of glass eel (Anguilla anguilla) exploitation in the Severn Estuary, England

AbstractMark‐release‐recapture trials were conducted to determine the exploitation rate of glass eel Anguilla anguilla (L.) by handheld dip nets in the Severn Estuary in the spring of 2020. The glass eel were marked with Rhodamine B at a concentration of 0.1 g/L, 200 glass eel/L for 4.5 hr and then placed in fresh water for 36–48 hr to monitor mortality. In trial 1, 891 ± 100 of the 20,455 glass eel were recaptured while in trial 2,373 ± 172 of the 27,923 glass eel released were recaptured. The exploitation rate was estimated to be 4.36% (±0.49) in trial 1 and 1.33% (±0.62) in trial 2. The size of the glass eel population from trial 1 was estimated to be 24.69 t (22.46 – 28.81), and the overall exploitation rate of the fishery for the season was 7.8% (6.7% – 8.6%). Comparisons are made with studies in other estuaries and with conservation targets set by the EU Eel Regulation and the Eel Management Plan for the River Severn. The study suggests the fishery is not the main cause of the Severn RBD failing to meet escapement targets.

Aspectos reprodutivos de Serrapinnus notomelas (Characiformes: Cheirodontinae) em igarapés da bacia do rio Machado, sudoeste Amazônico

O objetivo deste estudo foi avaliar a estratégia reprodutiva de Serrapinnus notomelas em igarapés da bacia do rio Machado, sudoeste da Amazônia. As coletas foram realizadas no período de abril de 2015 a março de 2016 em dois igarapés, utilizando rede de cerco e redes de mão ao longo de um trecho de 50 m do igarapé. Foram coletados 122 indivíduos, sendo 38 machos e 84 fêmeas (proporção-sexual; 2 fêmeas: 1 macho). O tamanho dos indivíduos variou de 1,7 a 4,0 cm, não havendo diferenças entre o comprimento médio de machos e fêmeas (U = 1406,5; df = 121; p = 0,29). O tamanho da primeira reprodução para fêmeas foi de 2,6 cm e dos machos, 3,6 cm. A desova foi caracterizada como sendo do tipo total e a estação reprodutiva da espécie ocorreu no período chuvoso. Esses resultados preenchem lacunas científicas referentes à biologia de espécies de pequeno porte de igarapés amazônicos.

Age and growth of iridescent toothcarp Aphanius mento (Heckel, 1843) (Cyprinodontidae) in Seyhan Reservoir (Southeastern Mediterranean, Turkey)

The population structure of Aphanius mento in the Seyhan Reservoir was studied on the basis of 834 fish specimens (516 males and 318 females) caught on a monthly basisbetween September 2013 and August 2014. Fish were collected using dip nets of tulle with a 1mm mesh size. The maximum age of fish was found to be 4 years for both sexes combined, the 1 year old age group comprised 62.20% of male samples. The overall sex ratio of females to males was 1:1.62. Von Bertalanffy growth parameters were L∞=54.33 mm, K=0.399 year-1, t0 =-1.168 years for females, L∞ =52.72 mm, K=0.397 year-1, t0=-1.137 years for males, and L∞=56.50 mm, K=0.386 year-1, t0=-1.257 years for both sexes.The length (TL) - weight (W) relationship was W= 0.00051xTL2.635, (r= 0.965) for males, W=0.00088xTL2.464, (r= 0.987) for females and W=0.00066xTL2.554, (r = 0.974) for both sexes. Condition factor ranged from 1.696 for males and 1.613 for females to 1.664 for both sexes. The mean condition factor (CF) was not significantly different between the sexes among all fish during different months (p>0.05). The present study represents the first comprehensive information on the population structure of A. mento in the Seyhan Reservoir. The results of this study will contribute to the population management and conservation of this species and be useful in increasing knowledge on its ecology and biology.

Herpetofaunal diversity and community structure in the Murchison Falls - Albert Delta Ramsar site, Uganda

1. The area of the Murchison Falls-Albert Delta is among the most important for conservation in East Africa dueto the high species richness, and the presence of several endemic species of conservation concern.2. Here, we report a study on the diversity patterns and community structure of the herpetofauna of this area.3. Field studies were conducted in the Albert Nile Delta Ramsar site between 1st October 2017 and 9th September2018. The data collection relied on Visual Encounter Surveys (VES), pitfall trapping, and dip netting. Descriptive statistics, i.e. species numbers in each transect were used as a measure of the present biodiversity, whereasChao1 and Chao species estimator algorithms were used to predict the potential number of species found ineach site/habitat.4. A total of 898 individuals representing 25 reptile species belonging to four orders, 15 families, and 20 generawere recorded during the 12 months of surveys.5. The data shows some non-random spatial and temporal patterns whereby there is a cyclic reptilian diversitypeaking during the December-March and again towards June-August-September which are peaks of the dryseason.6. The most frequently encountered species were Varanus niloticus, Crocodylus niloticus, Agama agama, Trachylepis maculilabris, and Lygodactylus guttularis, which accounted for almost 90% of all recorded individuals.7. A total of 27 amphibian species, belonging to nine families and 10 genera were recorded during the periodof the survey. The diversity and abundance graphs would indicate amphibians having bimodal peaks (September-December, and March-May). The diversity seemed to dip during the dry season months – which is theopposite case for reptiles.

Accounting for false positive detections in occupancy studies based on environmental DNA: A case study of a threatened freshwater fish (Galaxiella pusilla)

AbstractEnvironmental DNA (eDNA) sampling is a promising method for surveying aquatic fauna. Recent eDNA studies have investigated the likelihood of false negative errors in the laboratory and in the field, but the likelihood of false positives remains poorly studied. We investigated the likelihood of both types of errors in eDNA surveys of an Australian threatened freshwater fish (Galaxiella pusilla) using laboratory experiments, field surveys, and recent advances in hierarchical site occupancy‐detection modeling. Laboratory experiments revealed high primer/probe specificity; absence of sample contamination in extraction and qPCR blanks; and rapid accumulation and deterioration of eDNA in aquaria. Hierarchical site occupancy‐detection models fitted to pilot data collected at 13 wetlands revealed that two water samples, each with two qPCRs, would be required to achieve a cumulative detection probability &gt;.95. A more comprehensive survey, in which we simultaneously used dip netting and eDNA sampling at 29 wetlands, revealed similar mean detection probabilities of the two sampling methods (trapping: 0.74 vs. eDNA: 0.68), and low probabilities of false positive errors at the water sample level (0.0080) and at the qPCR level (0.0039) for eDNA sampling. Collectively, our results illustrate that eDNA sampling can be a sensitive and specific method for monitoring the occurrence of freshwater fauna. Detection probabilities of eDNA sampling were comparable to those of a traditional sampling method, and probabilities of laboratory‐induced false positives were low. Future studies employing eDNA sampling should estimate, and properly account for, false positive errors in addition to false negatives.

Fish assemblages respond to forest cover in small Amazonian basins

The removal of native forest affects stream characteristics, processes, and organisms at the local scale. We compared the structure of fish assemblages between microbasins impacted by deforestation and those in pristine condition in the Amazonian Machado River basin, Brazil. Fish were collected with seine and dip nets along an 80-m stretch of 28 streams. At each site, we recorded physical, chemical, and land-water ecotone variables. We collected 6,586 specimens of 109 species, being 39 and 18 of them exclusively of forested and deforested streams, respectively. Non-significant differences were found for abundance and species richness between forested and deforested streams. A total of four main trophic groups were identified. Carnivores were more abundant in forested streams, whereas herbivores, omnivores and detritivores species were the most abundant in deforested streams. The deforested streams showed higher abundance and richness of algae and periphyton consumers, while forested streams presented higher abundance and richness of invertebrate consumers. Forested streams presented longer foodchains, higher occurrence and abundance of species that have more specialized habits and are intolerant to degraded environments, whereas generalist and tolerant species predominated in deforested streams. We conclude that species composition in Amazonian streams predictably responds to the degree of forest cover.