UNDER WATCH | Policemen in Talisay, Batangas, monitor the Taal Lake shoreline in Barangay Poblacion 6 in this photo taken on Monday. At least 300 tons of freshwater fish in this town have been lost to fish kill since last week due to low levels of dissolved oxygen. (Photo from the Facebook page of the Talisay Police Station)
LUCENA CITY, Quezon, Philippines — At least 343 tons of tilapia (black carp) and “bangus” (milkfish), including fingerlings, died in another fish kill phenomenon in Taal Lake in Batangas province, authorities said on Monday.
The fish kill that started last week already destroyed 300 tons of freshwater fish in the town of Talisay, 32 tons in Agoncillo and 11 tons in Laurel, according to Sammy Malvas, Bureau of Fisheries and Aquatic Resources director in Calabarzon (Cavite, Laguna, Batangas, Rizal, Quezon).
The three towns are among the localities in Batangas that surround the lake, along with the municipalities of Sta. Teresita, San Nicolas, Alitagtag, Cuenca, Balete and Mataasnakahoy, and the cities of Tanauan and Lipa.
Malvas placed the estimated value of dead fish to around P45 million, affecting 156 fish case operators.
“Based on our water samplings, the dissolved oxygen level is low in the affected area,” Malvas said.
He explained that the dissolved oxygen level drops every time there is a sudden change in the water temperature, usually from hot to cold and vice versa.
Fish kill is a natural phenomenon in Taal Lake that occurs when the weather triggers a drop in dissolved oxygen in the water.
Tilapia and bangus cage farming is a multimillion-peso industry in Taal Lake, the country’s third-largest freshwater body.
Low oxygen level
Fish cage owners were advised to monitor their cages and take measures by installing oxygen tanks and pumps to augment the declining oxygen level.
The water’s dissolved oxygen level serves as a parameter used to check whether the water remains favorable to aquaculture. The oxygen level is considered normal at 6 parts per million at the lake’s surface level.
In August last year, at least 31 tons of cultured tilapia also died in fish cages in Taal Lake in Agoncillo town due to low levels of dissolved oxygen in the water.
Malvas said they had advised the affected cage operators to immediately harvest the remaining marketable fish to recover part of their investments.
Since last week, fish cage operators have begun harvesting in areas that remained unaffected.
Taal Lake has more than 7,000 cage structures for milkfish and tilapia production.
“We also advised fish cage operators to lessen their fish feed during this time,” Malvas added.
Last February, the Department of Environment and Natural Resources (DENR) had ordered fish cage operators to stop scattering sinking fish feed in Taal Lake.
According to the DENR, the commercial fish in the lake do not consume all the sinking feed, and the excess settles at the bottom of the lake and rots. The rotten feed affects the water quality of the lake, the DENR noted.
Cheaper sinking feed is made up of sticky pellets, which break up into fine powder when they hit the water.
No volcano link
But Malvas maintained that the fish kill was not connected to the restiveness of Taal Volcano, which sits in the middle of the lake.
The Philippine Institute of Volcanology and Seismology (Phivolcs) which has been recording continuous activity at Taal Volcano, warned in an advisory on July 13 that “should current low-level activity worsen or pronounced changes in monitored parameters forewarn of increasing unrest, the alert level may be raised to alert level 2.”
In its 5 a.m. bulletin on Monday, the Phivolcs reported that the volcano emitted 5,887 tons of sulfur dioxide over the past 24 hours that rose to 900 meters above Taal Volcano Island. It also reported that four tremors were recorded by the seismic stations of the Taal Volcano Network.
The Phivolcs reminded the public that alert level 1 prevails over Taal Volcano, “which means that it is still in an abnormal condition and should not be interpreted to have ceased unrest or ceased the threat of eruptive activity.”
Taal Volcano has been on alert level 1 since July 11, 2022.