Tanauan, Batangas – “With this kind of weather, a fish kill could happen anytime.”
Thus warned Lea Villanueva, aquaculture center chief of the Bureau of Fisheries and Aquatic Resources (BFAR)-Inland Fisheries Research Station here, who, together with aquaculturist Maurita Rosana, fears that a fish kill could occur in at least three Batangas towns – Laurel, Talisay and Agoncillo.
“Hindi na kami makatulog, tumingin ka lang sa labas, pag-ganyang cloudy ay nade-deplete na ang oxygen dahil walang photosynthesis at susundan pa ng heavy rain for three to four days, asahan nyo na ang fish kill (We can’t sleep anymore. Look outside, when it’s cloudy oxygen is depleted because there’s no photosynthesis, and with three to four days of heavy rain, expect a fish kill),” Rosana told The STAR.
Fish kills usually take place during the rainy months when the level of hydrogen sulfide in the waters of Agoncillo, Laurel and Talisay is high, resulting in toxic gas emissions that, in turn, deplete Taal Lake’s oxygen supply.
A yearlong study showed that 25 major fish kills occurred between March and August.
According to researchers, the presence of heavy loads of organic sediment and increased levels of ammonia, hydrogen sulfide and nitrite in the lake contribute to a fish kill.
Improper aquaculture practices are also blamed for the deaths of fish.
BFAR advised fish cage operators to harvest their fish before the rainy season when fish kills are likely to happen.
“We already gave warnings to fish cage owners through text and fax messages,” Rosana said, adding that when the reading of the dissolved oxygen level reaches 4, “we advise them to do an emergency harvest.”
Rosana said there are several reasons for a fish kill such as parasites, bacteria, algal bloom or die-off, oxygen depletion and sulfur.
“At this stage, we could predict an oxygen depletion that would be the most probable cause of the fish kill,” Rosana said.
Rosana also said the large organic load in Taal Lake due to excessive feed and fish wastes from tilapia cages could also trigger a fish kill.
“Off-flavor or muddy taste is a clear sign of an impending fish kill,” she said, although off-flavor happens regularly in fish cages and rarely in open water.
However, off-flavor has affected open water fish such as tawilis and maliputo since last February, she said.
Tawilis, according to Rosana, used to fetch P80 to P120 per kilo but is now being sold at P20 per kilo, as it has a muddy taste.
High levels of nitrogen and phosphorous in fish cage areas in Barangays Sampaloc in Talisay, Leviste in Laurel, and Manalao in Agoncillo cause the off-flavor, she said.
Likewise, fish caught from open water areas in Cuenca and Tanauan towns also has had off-flavor since March, Rosana said.
Over-construction of fish cages
She said the over-construction of fish cages in the Pansipit River in San Nicolas town hampers the water in Taal Lake from flowing into Balayan Bay, thus causing the rapid growth of algae and planktons in the lake.
As of July 2000, there had been 10,000 fish cages in the lake, according to a survey of the tilapia cage industry conducted by Simeona Aypa for the European Union-funded FISHTRAT Project and coordinated by the Philippine Council for Aquatic and Marine Research and Development.
Each cage, measuring 10 x 10 x 5 meters on the average, is stocked with tilapia fingerlings at 50-100 per cubic meter. The fingerlings are heavily fed with six different types of commercial feeds.
In order for fish cage operators to observe proper culture management and environmental protection, Rosana recommended the strict implementation of fishery laws by the towns concerned as well as training.
Villanueva, for her part, said the BFAR and local governments saw the urgency in enforcing the lake’s unified rules and regulations as a solution to the annual fish kills.
An ordinance, approved by the Protected Areas Management Board (PAMB) on March 21, 2007, provides designated fish cage zones and sanctuary areas; limits the number of cages from 10,000 to 6,000; and enforces other rules on proper aquaculture management.
Villanueva said the ordinance has been pending for over a year now and the PAMB is still waiting for the approval of Environment and Natural Resources Secretary Lito Atienza so it could be enacted into law. “Once we have regulated the number of cages, fish kills would be prevented and water can move freely in the lake,” she said.
Taal Lake, which has a surface area of 24,356 square meters, is the country’s third largest, next to Laguna de Bay and Lake Lanao. It was declared a protected area in 1996.