Climate change didn't kill the Bangus and Tilapia in Batangas this weekend. The fishpens did.
This is according to my old UPIS classmate and U.P. Professor Dr. Benjamin Vallejo, with a PhD in Marine Biology, in his Facebook post in reaction to the Inquirer.net's report. In his status post, Dr. Vallejo said, "A drop of temperature does not cause a lowering of oxygen levels since dissolved oxygen doesn't escape as rapidly into the air if the water is cool. Also the rainy season is not due to climate change!"
Queried on his opinion on the reason for the fish kill, Dr. Vallejo gave this explanation:
They (the Bangus and Tilapia ) feed the fish in high densities ad libitum. The huge amount of fecal waste and uneaten feed end up on the lake floor. Since tropical lakes are stratified by density differences (in Greek "meromixis"), the waste on the bottom are degraded by bacteria. This is an oxygen consuming process. Thus bottom water has little oxygen while surface water (where the fish cages are) has oxygen mainly due to gas exchange with the atmosphere and photosythesis. However deep tropical lakes like Taal are what we call as "polymictic" which means the bottom layers get mixed up at least once or even twice or more times a year. In monsoonal climates the SW monsoon is strong enough to cause this turnover. Taal is a big lake and there is enough fetch to allow this natural process to happen. Taal is an abused lake and so nature can take "revenge" for all these abuses. When the lake overturns, the poorly oxygenated water ends up on the surface causing the fish kill which poor aquaculture management guaranteed this would happen. The overturning is natural. If there was no high fish density and fish waste at the bottom, there should have been no fish kill.
When asked how this can be remedied, Dr. Vallejo replied: "Take out all those fish pens and cages and let the lake recover!"
What can you say, BFAR?
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