Fish Community Responses to Human-Induced Stresses in the Lower Mekong Basin

Vanna Nuon,Peng Bun Ngor,Sovan Lek,Nam So,Gaël Grenouillet

doi:10.3390/w12123522

Abstract

The Mekong River is one of the world’s largest rivers and has an annual captured fish production of about 2.3 million tonnes, equivalent to around 11 billion USD. Although the Mekong provides important ecological and socioeconomic benefits to millions of people, it is facing intensive change due to anthropogenic stressors. Therefore, it is necessary to understand the changes to the spatiotemporal fish communities to inform sustainable fisheries management. Here, we aimed to characterize patterns of the fish communities and identify the ecological status of each fish community using daily catch data from 2007 to 2018 at 25 monitoring sites in the Lower Mekong Basin (LMB). The collected data were classified by a self-organizing map into four main groups. Group 4 represented the lower Vietnam Mekong Delta (VMD), while groups 1, 2, and 3 were subdivided into subgroups 1a (upper LMB), 1b (upper and middle LMB), 2a (Mekong River below the Khone Falls and Sesan River), 2b (Mekong River below the Khone Falls and Sekong, Sesan and Srepok (3S) Rivers), 3a (Floodplain-Tonle Sap and Songkhram) and 3b (upper VMD). Among the 571 species recorded, 119 were identified as indicator species. Based on the abundance and biomass comparison curves, the fish community of 2b was in a healthier condition with a positive W-statistic value while the rest had a negative W-statistic value. The highest species richness and diversity were observed in 3a and 2b, so these subgroups deserve high management and conservation priority. Likewise, 1a should also be considered as a high priority area since it harbors several endangered and long-distant migratory fishes. It was also noticed that the fish communities of groups 3 and 4, located far from the hydropower dams, remained mostly unchanged compared to those of groups 1 and 2, close to the mainstream and tributary dams in the upper LMB and 3S Rivers.

Highlights

Freshwater ecosystems are under threat from various stressors, such as land degradation, pollution, water extraction, and dam construction [1,2,3,4,5]
The highest species richness and diversity were observed at the Tonle Sap and Songkhram floodplains and the Mekong River below the Khone Falls and the 3S
A more focused, follow-up study should be conducted in the upper and middle Lower Mekong Basin (LMB) to identify which environmental factors driving the temporal change in species composition to inform fisheries management and conservation in that area as well as the whole LMB

Summary

Introduction

Freshwater ecosystems are under threat from various stressors, such as land degradation, pollution, water extraction, and dam construction [1,2,3,4,5]. Anthropogenic hydrological changes have modified freshwater ecosystems and altered the physical characteristics of the aquatic habitat, strongly affecting. Water 2020, 12, 3522 the structure and composition of fish communities [6,7,8]. Overfishing by both legal and illegal fishers acts as a key factor that may dramatically lessen fish populations [9,10]. Fish are very sensitive to changes in the aquatic environment due to their dependence on both the physical environment and the other aquatic organisms, so a fish community with an altered composition may indicate a change in the quality of the environment. The health of each fish community can reflect the status of the entire aquatic community [13,14,15]

Objectives

Methods

Results

Discussion

Conclusion