Water quality and weather trends preceding fish kill occurrences in Lake Taal (Luzon Is., Philippines) and recommendations on its long-term monitoring

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Lake Taal is one of the most unique lake ecosystems in the world. The decline in the lake’s water quality together with other environmental and human-mediated factors has helped intensify the occurrences of massive fish kills in recent years. Available water quality data collected from areas devoted to aquaculture, were analyzed together with available weather data to determine long-term changes as well as monitor probable water quality and weather trends preceding known fish kill occurrences. There was no observed spatial variability among data from different monitoring sites which means that fewer but more evenlyspaced monitoring stations are recommended for the lake. The lack of important parameters (i.e. primary production, nutrients, plankton and fish) as well as the limited measurement of physicochemical parameters in surface water have hampered a more in-depth analysis of the lake’s long-term limnological characteristics. Detected temporal variations in the water quality parameters are attributed to climate and human-induced factors. As to the dataset’s usefulness for fish kill monitoring, our analysis revealed trends preceding documented fish kill occurrences - such as increased wind speed and high temperatures one to three days preceding fish kill incidences - may be used as indicators of an impending fish kill. Links between strong wind speed and varying air temperatures to tropical lakes’ thermal and oxycline regime was discovered and recommended for further studies. Moreover, continuing lake monitoring is needed to strongly ascertain the cause of fish kill incidences and to ultimately increase the chances of anticipating massive fish kill events.