By Laguna de Bay is our country’s largest lake and was once a part of Manila Bay.
By Dr. Rafael Guerrero III
The lake has an area of 90,000 hectares (ha), a shoreline of 228 kilometers, and an average depth of 2.5 meters. It is bounded by the provinces of Rizal and Laguna and some portions of Metro Manila. Water in the lake is supplied by 21 tributaries, with the Pagsanjan River and Santa Cruz River as major contributors. The lake is highly eutrophic (senriched with nutrients) with heavy loads of nitrates and phosphates washed into it from domestic and agricultural sources.
The fisheries of Laguna de Bay are the primary use of the lake, according to the Laguna Lake Development Authority (LLDA), the government agency tasked with the management and development of the freshwater resource that is also used as a source of water for domestic supply, irrigation, transportation, energy generation, recreation, and eco-tourism. The fisheries of the lake consist of the open water fisheries exploited by over 13,000 small fishers, and aquaculture with the growing of milkfish (Chanos chanos) and bighead carp (Aristichthys nobilis) in pens operated by “big companies and moneyed individuals” and Nile tilapia (Oreochromis niloticus) in cages of small operators.
The fisheries production of Laguna de Bay from open water fishing was 86,282 metric tons (mt) in 1963, made up largely of indigenous snails, shrimp, and non-omnivorous fishes feeding on shrimp and snails like the silver perch or “ayuňgin,” white goby or “biya,” and the Manila catfish or “kanduli”.
However, fisheries production in the lake declined to only 20,700 mt in 1973 due to over-fishing and the use of illegal fishing gear such as the motorized push net.
To utilize the abundant growth of floating microorganisms (phytoplankton and zooplankton) in the lake, the milkfish, an omnivorous fish, was introduced in 1970 by the LLDA to enhance the fisheries of Laguna de Bay. With the success of the experimental culture of milkfish in pens demonstrated by the LLDA, the private sector followed suit with the construction of 4,800 ha of fishpens (accounting for 5% of the lake’s total area) in 1973, which boosted the fisheries production of the lake with 19,000 mt of milkfish without affecting the catch of open water fishers. The culture of Nile tilapia in cages was also introduced by the LLDA in the lake in 1977.
Fishpens are structures built of bamboo and/or anahaw (Livistonia rotondifolia) posts that are driven into the lake’s mud bottom to support the enclosing net for containing the cultured fish. Ranging in size from 5 to 50 ha, the pens are stocked with milkfish fingerlings at the rate of 30,000-60,000 ha. After 4-6 months of culture without artificial feeding, 4-10 tons per ha of market-size fish (250-400 grams each) are harvested.
With the commercial success of milkfish pen culture in Laguna de Bay, the area for fishpens in the lake increased to 30,000 ha (accounting for 33% of the lake’s total area) in 1983. This markedly reduced the open water fishing area in the lake for small fishers, resulting in social conflict and the poor growth of the cultured fish because the lake’s carrying capacity had been exceeded.
To provide the small fishers and other stakeholders access to fishing and navigation in the lake, the LLDA formulated and implemented the Laguna Lake Fishery Zoning and Management Plan (ZOMAP) in 1985 “to rationalize the distribution of fishpens in accordance with navigational requirements and to reduce the total fishpen area within the lake’s carrying capacity.” In the ZOMAP, the regulations for a fishpen belt with a total area of 10,000 ha and total area of 5,000 ha for cages were enforced.
In 2015, the lake’s fisheries production was 156,831 mt with 61% (95,667 mt) coming from open water fishing and 39% (61,164 mt) from aquaculture providing 15% of the fish requirement of the Laguna de Bay Basin, which has 20 million people. The milkfish and tilapia cultured in the lake supply as much as 36% of the same required by the Metro Manila populace.
This story appeared in Agriculture Monthly’s October 2017 issue.
