Monitoring of tropical freshwater fish resources for sustainable use

Human activities strengthen the influence of deterministic processes in the mechanisms of fish community assembly in tropical rivers of Yunnan, China

Human-induced global alterations have worsened the severe decrease in fish biodiversity in rivers. To successfully reduce the pace of reduction in fish diversity, it is crucial to prioritize the understanding of how human activities impact the processes that shape and maintain fish diversity. Traditional fish survey methods are based on catch collection and morphological identification, which is often time-consuming and ineffective. Hence, these methods are inadequate for conducting thorough and detailed large-scale surveys of fish ecology. The rapid progress in molecular biology techniques has transformed environmental DNA (eDNA) technique into a highly promising method for studying fish ecology. In this work, we conducted the first systematic study of fish diversity and its formation and maintenance mechanism in the Xishuangbanna section of the Lancang River using eDNA metabarcoding. The eDNA metabarcoding detected a total of 159 species of freshwater fishes spanning 13 orders, 34 families, and 99 genera. The fishes in the order cypriniformes were shown to be overwhelmingly dominant. At different intensities of anthropogenic activity, we found differences in fish community composition and assembly. The analysis of the Sloan's neutral community model fitting revealed that stochastic processes were the dominant factor in the shaping of fish communities in the Xishuangbanna section of the Lancang River. We have further confirmed this result by using the phylogenetic normalized stochasticity ratio. Furthermore, our findings indicate that as human activities get more intense, the influence of stochastic processes on the shaping of fish communities decreases, while the influence of deterministic processes eventually becomes more prominent. Finally, we discovered that salinity positively correlated with fish community changes in the high-intensity anthropogenic sample sites, but all environmental factors had little effect on fish community changes in the low-intensity and moderate-intensity anthropogenic sample sites. Our study not only validated the potential application of eDNA metabarcoding for monitoring fish diversity in tropical rivers, but also revealed how fish communities respond to human activities. This knowledge will serve as a solid foundation for the protection of fish resources in tropical rivers.

New insights into biologic interpretation of bioinformatic pipelines for fish eDNA metabarcoding: A case study in Pearl River estuary

Environmental DNA (eDNA) metabarcoding is an emerging tool for monitoring biological communities in aquatic ecosystems. The selection of bioinformatic pipelines significantly impacts the results of biodiversity assessments. However, there is currently no consensus on the appropriate bioinformatic pipelines for fish community analysis in eDNA metabarcoding. In this study, we compared three bioinformatic pipelines (Uparse, DADA2, and UNOISE3) using real and mock (constructed with 15/30 known fish) communities to investigate the differences in biological interpretation during the data analysis process in eDNA metabarcoding. Performance evaluation and diversity analyses revealed that the choice of bioinformatic pipeline could impact the biological results of metabarcoding experiments. Among the three pipelines, the operational taxonomic units (OTU)-based pipeline (Uparse) showed the best performance (sensitivity: 0.6250 ± 0.0166; compositional similarity: 0.4000 ± 0.0571), the highest richness (25-102) and minimal inter-group differences in alpha diversity. It suggested the OTU-based pipeline possessed superior capability in fish diversity monitoring compared to ASV/ZOTU-based pipeline. Additionally, the Bray-Curtis distance matrix achieved the highest discriminative effect in the PCoA (43.3%-53.89%) and inter-group analysis (P < 0.01), indicating it was better at distinguishing compositional differences or specific genera of fish community at different sampling sites than other distance matrices. These findings provide new insights into fish community monitoring through eDNA metabarcoding in estuarine environments.

Participatory Research with Fishers to Improve Knowledge on Small-Scale Fisheries in Tropical Rivers

Freshwater small-scale fisheries sustain millions of livelihoods worldwide, but a lack of monitoring makes it difficult to check the sustainability of these fisheries. We aim to compare and describe participatory research methods used in studies with fishers in the Tapajos River, a poorly known tropical river in the Brazilian Amazon. We address three interview approaches, two ways to do fisheries monitoring and two approaches for georeferenced mapping based on fishers’ knowledge, which can provide data about at least 16 topics related to fisheries. We highlight major advantages and shortcomings of these methods and illustrate their potential with examples of results on fisheries and fish biology of Peacock bass (Cichla spp. tucunaré in Brazil), an important commercial fish in the Brazilian Amazon. The interviews, participatory monitoring and mapping revealed which fish are more valued by local communities, how fish abundance and sizes varied over time, when fish are more often caught and show reproductive activity, and which sites or habitats fish need to reproduce. In addition to providing useful data from many sites in a cost-effective way, participatory methods can bring the additional benefit of including local stakeholders in the monitoring, management, and research activities.

Gender Concerns When Noah the Economist Ranks Biodiversity Protection Policies

Because the funds to protect biodiversity are very limited, biodiversity protection policies are prioritized using the Noah’s Ark perspective. I discuss how gender affects Noah’s assessment of key elements of his ranking: Discounting, changes in total economic value, marginal costs, changes in ecological value, and the probability of policy success. This incremental approach makes visible the breadth of the mechanisms by which gender differentiated social constructs interact to affect Noah in a richly complex manner.