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Tonle Sap Ecosystem Fish Species Biological Groups and Hydroecological Index

Nguyen T. Hai Yen, Kengo Sunada, Satoru Oishi, Kou Ikejima


The Tonle Sap ecosystem in the lower part of the Mekong River basin is influenced by hydrological regimes of the river. It is considered that the drastic seasonal changes of lake water level from 1 to 14 m strongly influenced the hatching and feeding grounds of Tonle Sap fish communities. The aim of this study was to determine the relationship between the fish communities and the hydrological parameters in the Tonle Sap ecosystem in order to develop a hydroecological index by using these parameters. This index is then used to assess the relationship between the Tonle Sap ecosystem hydrological condition and fish production. Four fish biological groups in the rank of k and r-strategists were classified by clustering analysis based on nine biological attributes. Five of eight potential hydrological parameters were identified by the multi-parameter analysis; those parameters are average drought inundated area, drought duration, maximum flood inundated area, receding duration, and flood timing. The values of each selected parameter was categorized into three groups and assigned a set of scores of 1, 3 and 5 based on two thresholds values (lower ai and upper bi) and narrated as poor, fair and good conditions respectively. The annual hydroecological score was calculated be averaging the yearly scores of these parameters. The hydroecological index showed that the highest score (5) was year 2000 and the lowest score (1) was year 1998 during period 1995-2002. The inundated area and flood timing were the most factors that influence fish production. Importantly, the constituted hydroecological index was significantly correlated (P is less than 0.05) with total Dai (bagnet) fish catch in year y and k fish species in year y+1 indicating that the index can be used as the monitoring tool to assess the relationship between hydrological regimes and fish production and to support for hydropolicy decisions.


Tonle Sap ecosystem, hydroecological index, Dai fish catch, fish biological attribute, multi-parameters analysis.

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