The Mekong River, well known for its aquatic biodiversity, is important to the social, physical, and economic health of millions living in China, Myanmar, Laos, Thailand, Cambodia, and Vietnam. This ...paper explores the social and environmental impacts of several Mekong basin hydropower dams and groupings of dams and the geographies of their impacts. Specifically, we examined the 3S (Sesan, Sekong Srepok) river system in northeastern Cambodia, the Central Highlands of Vietnam, and southern Laos; the Khone Falls area in southern Laos; the lower Mun River Basin in northeastern Thailand; and the upper Mekong River in Yunnan Province, China, northeastern Myanmar, northern Laos, and northern Thailand. Evidence shows that these dams and groupings of dams are affecting fish migrations, river hydrology, and sediment transfers. Such changes are negatively impacting riparian communities up to 1000 km away. Because many communities depend on the river and its resources for their food and livelihood, changes to the river have impacted, and will continue to negatively impact, food and economic security. While social and environmental impact assessments have been carried out for these projects, greater consideration of the scale and cumulative impacts of dams is necessary.
Over the last few decades, considerable concern has been expressed about the threat of Mekong River Basin hydropower dams to a range of important freshwater riverine fisheries, particularly for fish ...that seasonally migrate long distances. However, much less attention has been given to the threat of hydropower dams to fish biodiversity in the high-diversity Mekong River Basin, the focus of this paper. Through reviewing the existing state of knowledge regarding Mekong River Basin fish biodiversity, and threats to it, we argue that even though no species are definitively known to have been extirpated from the Mekong River Basin to date, hydropower dam development and various other developments nevertheless pose a serious threat to fish biodiversity. Indeed, dams typically significantly block fish migrations and fish larvae distribution, cause river fragmentation, fundamentally alter river hydrology, and change water quality, all factors that have the potential to intersect with each other and lead to significant species extirpation and extinction, or in some cases, functional extinction, when a small population remains but the important larger population is lost permanently. The circumstances are further exacerbated by the lag time between impact and when that impact becomes evident, cumulative impacts, a lack of consistent data collection, including the collection of base-line data, and insufficient post-project research related to biodiversity. We contend that much more could and should be done to ensure that the Mekong River basin’s exceptional fish biodiversity is not variously diminished and destroyed during the coming years.
The Mekong River is a globally important river system, known for its unique flood pulse hydrology, ecological productivity, and biodiversity. Flooded forests provide critical terrestrial nutrient ...inputs and habitat to support aquatic species. However, the Mekong River is under threat from anthropogenic stressors, including deforestation from land cultivation and urbanization, and dam construction that inundates forests and encourages road development. This study investigated spatio-temporal patterns of deforestation in Cambodia and portions of neighboring Laos and Vietnam that form the Srepok–Sesan–Sekong watershed. A random forest model predicted tree cover change over a 25-year period (1993–2017) using the Landsat satellite archive. Then, a statistical predictive deforestation model was developed using annual-resolution predictors such as land-cover change, hydropower development, forest fragmentation, and socio-economic, topo-edaphic and climatic predictors. The results show that almost 19% of primary forest (nearly 24,000 km2) was lost, with more deforestation in floodplain (31%) than upland (18%) areas. Our results corroborate studies showing extremely high rates of deforestation in Cambodia. Given the rapidly accelerating deforestation rates, even in protected areas and community forests, influenced by a growing population and economy and extreme poverty, our study highlights landscape features indicating an increased risk of future deforestation, supporting a spatial framework for future conservation and mitigation efforts.
Hydropower dams are a source of renewable energy, but dam development and hydropower generation negatively affect freshwater ecosystems, biodiversity, and food security. We assess the effects of ...hydropower dam development on spatial-temporal changes in fish biodiversity from 2007 to 2014 in the Sekong, Sesan, and Srepok Basins-major tributaries to the Mekong River. By analyzing a 7-year fish monitoring dataset, and regressing fish abundance and biodiversity trends against cumulative number of upstream dams, we found that hydropower dams reduced fish biodiversity, including migratory, IUCN threatened and indicator species in the Sesan and Srepok Basins where most dams have been constructed. Meanwhile, fish biodiversity increased in the Sekong, the basin with the fewest dams. Fish fauna in the Sesan and Srepok Basins decreased from 60 and 29 species in 2007 to 42 and 25 species in 2014, respectively; while they increased from 33 in 2007 to 56 species in 2014 in the Sekong Basin. This is one of the first empirical studies to show reduced diversity following dam construction and fragmentation, and increased diversity in less regulated rivers in the Mekong River. Our results underscore the importance of the Sekong Basin to fish biodiversity and highlight the likely significance of all remaining free-flowing sections of the Lower Mekong Basin, including the Sekong, Cambodian Mekong, and Tonle Sap Rivers to migratory and threatened fish species. To preserve biodiversity, developing alternative renewable sources of energy or re-operating existing dams to increase power generation are recommended over constructing new hydropower dams.
Tonle Sap Lake (TSL) is a highly productive system and hosts a high fish diversity and is of paramount importance for sustaining protein supply for over 15 million Cambodians. Nevertheless, the ...ecology and factors influencing the spatial distribution of many fishes within the lake remain poorly understood. Using commercial fishing lot catch data from 1994/1995 to 1999/2000, fishing seasons and environmental data (land cover and bioclimatic variables), we describe spatial distribution of the eight most commercially important fish species, and investigate the effects of environmental factors on their distributions in the TSL. We found a strong variability in fish biomass across areas and between species. Specifically, Channa micropeltes was most abundant in the southern and northern sections of the TSL. Channa striata and Trichopodus microlepis were more common in the northern part of the TSL. Cyclocheilos enoplos, Barbonymus gonionotus, Pangasianodon hypophthalmus, and Gymnostomus spp. were abundant in the southern areas of the TSL while Phalacronotus spp. were abundant in few areas in both the north and the south. Flooded forest positively explained the variation in the biomass of P. hypophthalmus, C. striata, C. enopolos, and Phalacronotus spp. Likewise, the lake’s open water positively affects the biomass of P. hypophthalmus, C. enopolos, and Phalacronotus spp., while the agricultural field negatively impacts Gymnostomus spp. biomass distribution. We also found that some areas consistently hosted high fish biomass (e.g., lot 2, Kampong Thom; lot 6, Pursat; lot 2, Battambang, etc.). We, therefore, suggest that fisheries management and conservation planning focus on those areas, considering those areas significance as core fish habitat and important for catching fish.
•Plastics function as a habitat for a community of biologically active organisms.•Polymer type does not significantly influence community composition or activity.•Biofouled plastics deplete oxygen, ...causing anoxic/hypoxic conditions.•Biofouled plastics foster net heterotrophic environments.•Plastic pollution yields greater ecosystem impacts than previously thought.
Plastics in aquatic ecosystems rapidly undergo biofouling, giving rise to a new ecosystem on their surface, the 'plastisphere.' Few studies quantify the impact of plastics and their associated community on ecosystem traits from biodiversity and functional traits to metabolic function. It has been suspected that impacts on ecosystems may depend on its state but comparative studies of ecosystem responses are rare in the published literature. We quantified algal biomass, bacterial and algal biodiversity (16S and 18S rRNA), and metabolic traits of the community growing on the surface of different plastic polymers incubated within rivers of the Lower Mekong Basin. The rivers selected have different ecological characteristics but are similar regarding their high degree of plastic pollution. We examined the effects of plastics colonized with biofilms on ecosystem production, community dark respiration, and the epiplastic community's capability to influence nitrogen, phosphorus, organic carbon, and oxygen in water. Finally, we present conceptual models to guide our understanding of plastic pollution within freshwaters. Our findings showed limited microalgal biomass and bacterial dominance, with potential pathogens present. The location significantly influenced community composition, highlighting the role of environmental conditions in shaping community development. When assessing the effects on ecosystem productivity, our experiments showed that biofouled plastics led to a significant drop in oxygen concentration within river water, leading to hypoxic/anoxic conditions with subsequent profound impacts on system metabolism and the capability of influencing biogeochemical cycles. Scaling our findings revealed that plastic pollution may exert a more substantial and ecosystem-altering impact than initially assumed, particularly in areas with poorly managed plastic waste. These results highlighted that the plastisphere functions as a habitat for biologically active organisms which play a pivotal role in essential ecosystem processes. This warrants dedicated attention and investigation, particularly in sensitive ecosystems like the Mekong River, which supports a rich biodiversity and the livelihoods of 65 million people.
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Recreational angling has been implicated in population declines of some marine and freshwater fish, but this activity is rarely considered as a threat or even halted when endangered species are ...targeted. Indeed, in some cases, anglers are drawn to fish for rare or endangered species. Conservation‐oriented behaviours such as catch‐and‐release are often practiced voluntarily due to the ethics of anglers, yet even in these cases, some fishing mortality occurs. Nonetheless, there are many indirect conservation benefits associated with recreational angling. Here, we present a series of case‐studies and consider whether catch‐and‐release angling for endangered fish is a conservation problem or a conservation action. If recreational angling activities contribute to population‐level consequences that are contrary to recovery strategies, then angling for endangered species would seem to be a poor option. However, as revealed by several case‐studies, there is much evidence that anglers are vocal and effective proponents of fish and habitat conservation, and for endangered species, they are often the only voice when other stakeholders are not engaged. Anglers may contribute directly to conservation actions via user fees (e.g. licences), philanthropic donations or by volunteering in research, education and restoration activities. However, it is important to quantify post‐release mortality as well as understand the full suite of factors influencing a given population or species to know the potential risks. A risk assessment approach outlined in the paper may be used by managers to determine when the benefits of angling for endangered species outweigh the risks.
The giant freshwater whipray is a large-bodied stingray species that is listed as endangered across its known range from India through Southeast Asia. However, little is known about the species’ ...ecology, biology, and conservation status. We reviewed all available literature, articles, and reports on the species found through database and internet searches in order to consolidate and update information on the giant freshwater whipray. We found that remarkably little research has been done, and most existing information on the species is derived from fisher catch reports. Whiprays of 300 kg or more have been reported in most countries where it occurs. The available evidence suggests that this species is endangered across its range by numerous threats, including fishing, bycatch, bottom trawls, pollution, and habitat destruction and fragmentation. Various reports indicate declines in population size, genetic diversity, and body size. Relatively stable populations may persist in the Maeklong River, Thailand, the Mekong River in Cambodia, and insular Southeast Asia. More work is needed to understand the species’ spatio-temporal distribution, reproductive behavior, migration patterns, and general ecological and biological characteristics in order to inform effective management and conservation plans. Due to difficulties in sampling this rare species and monitoring fisher catches, partnership and collaboration with all stakeholders, including local fishers, government officials, and researchers, is essential to produce conservation gains for the giant freshwater whipray.
Aim: In light of the current biodiversity crisis, there is a need to identify and protect species at greatest risk of extinction. Ecological theory and global-scale analyses of bird and mammal faunas ...suggest that small-bodied species are less vulnerable to extinction, yet this hypothesis remains untested for the largest group of vertebrates, fish. Here, we compare body-size distributions of freshwater and marine fishes under different levels of global extinction risk (i.e. listed as vulnerable, endangered or critically endangered according to the IUCN Red List of Threatened Species) from different major sources of threat (habitat loss/degradation, human harvesting, invasive species and pollution). Location: Global, freshwater and marine. Methods: We collated maximum body length data for 22,800 freshwater and marine fishes and compared body-size frequency distributions after controlling for phylogeny. Results: We found that large-bodied marine fishes are under greater threat of global extinction, whereas both small-and large-bodied freshwater species are more likely to be at risk. Our results support the notion that commercial fishing activities disproportionately threaten large-bodied marine and freshwater species, whereas habitat degradation and loss threaten smaller-bodied marine fishes. Main conclusions: Our study provides compelling evidence that global fish extinction risk does not universally scale with body size. Given the central role of body size for trophic position and the functioning of food webs, human activities may have strikingly different effects on community organization and food web structure in freshwater and marine systems.
Population genetic analyses can evaluate how evolutionary processes shape diversity and inform conservation and management of imperiled species. Taimen (Hucho taimen), the world's largest freshwater ...salmonid, is threatened, endangered, or extirpated across much of its range due to anthropogenic activity including overfishing and habitat degradation. We generated genetic data using high throughput sequencing of reduced representation libraries for taimen from multiple drainages in Mongolia and Russia. Nucleotide diversity estimates were within the range documented in other salmonids, suggesting moderate diversity despite widespread population declines. Similar to other recent studies, our analyses revealed pronounced differentiation among the Arctic (Selenge) and Pacific (Amur and Tugur) drainages, suggesting historical isolation among these systems. However, we found evidence for finer-scale structure within the Pacific drainages, including unexpected differentiation between tributaries and the mainstem of the Tugur River. Differentiation across the Amur and Tugur basins together with coalescent-based demographic modeling suggests the ancestors of Tugur tributary taimen likely diverged in the eastern Amur basin, prior to eventual colonization of the Tugur basin. Our results suggest the potential for differentiation of taimen at different geographic scales, and suggest more thorough geographic and genomic sampling may be needed to inform conservation and management of this iconic salmonid.