Environmental variables and diversity index as a tool for management in tropical man‐made lakes

Fish and water samples were collected from various randomly situated sampling sites in two tropical man‐made lakes, Peechi and Pothundi reservoirs, in South India. The fish samples collected during 2014 to 2015 were taxonomically identified and the fish diversity indices of these reservoirs evaluated. The water samples collected were analysed for such environmental variables as pH, electrical conductivity, dissolved oxygen concentration, alkalinity, hardness, chlorophyll and nutrient concentrations. T‐tests indicated significant difference in both the fish diversity and environmental variables between these two reservoirs. The Pearson correlation test identified electrical conductivity as a highly correlated environmental variable to the ichthyodiversity index in Peechi and Pothundi reservoirs, with coefficients of 0.939 and 0.7012, respectively. Principal co‐ordinate analysis also was conducted on the variables to identify the best combination of variables subjective to the particular sampling site influencing the fish diversity. The analyses explained 72.8% of the total variations for Peechi reservoir, which was represented with eigenvalues of 7.53 and 3.393, respectively, for the first two dimensions. A similar analysis of Pothundi reservoir produced eigenvalues 7.05 and 3.01, respectively, for the first two dimensions, explaining 67.1% of the total inertia. The individual factor maps (IFM‐I and IFM‐II) for Peechi and Pothundi reservoirs identified a high diversity at sampling site 3 in Peechi reservoir, and a similar finding for sites 3 and 7 in Pothundi reservoir, being related to the interactions with other environmental variables, which were greatly influenced by the predominance of macrophytes. The latter is a characteristic of rainfed tropical reservoirs, with special reference to the native fish diversity and environmental variables. The findings of this study suggest management decisions for any aquatic system may be considered after prior assessment of environmental variables and the ichthyodiversity index of the indicated waterbody.