TANAUAN CITY, BATANGAS – The Bureau of Fisheries and Aquatic Resources (BFAR) has asked fish cage operators in Taal Lake on Friday to immediately harvest their existing tilapia stocks, warning that a fish kill might occur anytime.
In a phone interview, BFAR-Inland Fisheries Research Station officer-in-charge Nenita Kawit said they recorded low levels of the lake’s dissolved oxygen (DO) in four sampling stations namely Sampaloc, Talisay; Balakilong and Buso-Buso, Laurel and Banyaga, Agoncillo.
She said that the onset of a rainy season brought about a sudden drop in water temperature, which led to the sudden drop of the lake’s DO.
Kawit added that the alternating wind directions of southeasterly wind “salatan” and the northeasterly wind “amihan,” and the southwest monsoon “habagat,” have contributed to the lake’s poor water quality in the past days.
The normal DO level is 6 parts per million (ppm) but latest findings in May 15 showed that the DO level have dropped from 6.15 to 5.10 ppm in Sampaloc; 5.83 to 4.30 ppm in Balakilong; 5.83 to 4.30 ppm in Buso-Buso 5.76 to 5.10 ppm.
Barangay Banyaga in Agoncillo town had the least amount of DO at 3.83 ppm.
Aside from this, the BFAR also found traces of hydrogen sulfide in all four stations, which are also signs of the lake’s worsening state.
“We are advising the operators to immediately harvest their harvestable tilapia stocks because the water quality is poor and the dissolved oxygen in low, which indicates that a fish kill might occur anytime,” Kawit told The Filipino Connection in an interview.
She also reminded the cage operators not to dump their dead fishes to the lake’s open waters but instead bury them in areas far from the lake as fish decomposition only worsens the lake’s water quality by further depleting its oxygen.
Agriculture officials said that it takes about 6-7 months to harvest a tilapia in Taal Lake, which supplies about 40 percent of the tilapia demand in the Calabarzon (Cavite-Laguna-Batangas-Rizal-Quezon) Region.
Agoncillo municipal agriculturist Digna Jonson said no fish kill incidents have been reported so far in their area but they continue to monitor the lake and prepare for a possible fish kill.
“Fish cage operators are already aware that the lake’s water quality is now poor and they already did an emergency harvest of stocks,” Jonson said in separate interview. “We are prepared, if not a 100 percent for natural calamities,” she added.
While fish kills are natural occurrences, the BFAR earlier admitted that irresponsible aquaculture practices such overstocking and overfeeding tilapia stocks in the cage also contribute to fish kills.
The big bulk of unconsumed feeds and fish feces that settles at the lake’s bottom waters deplete the lake oxygen as they decompose.
While the agency recommends that a fish cage operator must stock only 30,000 to 50,000 tilapia fingerlings in a cage, the operators usually exceed the limit in order to meet their quota.
In September 28, typhoon Pedring had destroyed 52.7 metric tons of bangus and tilapia fish worth P3.8 million in Agoncillo. The town currently has 1,500 of the 6,000 allotted number of fish cages in Taal Lake.
The BFAR also reported in May 30, 2011 that the fish kill damaged about 750 metric tons of tilapia in the lake worth about P57 million, affecting the cage areas of Agoncillo, Laurel, Talisay, San Nicolas and Mataas na Kahoy.
Taal, which has a surface area of 24,356 square meters, is the world’s third largest lake next to Laguna and Lanao Lakes. It was declared a protected area in 1996 through the National Integrated Protected Areas System Act, by virtue of Presidential Proclamation 906.