Mainit reflects sorry state of local lakes

Lake Mainit in northeastern Mindanao is symptomatic of Philippine lakes.

It is threatened by overexploitation, resulting in decreasing fish catches, according to a study made by Mindanao State University (MSU).

At 223 meters deep, Lake Mainit, between Agusan del Norte and Surigao del Norte, is the country’s deepest lake.

At 17,060 hectares, it is the fourth largest with a coastline of 62 kilometers, 28 river tributaries and one outlet river that flows into Butuan Bay.

This highly productive and diverse wetland ecosystem supports a thriving freshwater fishery and the livelihood of more than 3,000 fishers using highly diverse gears.

An MSU survey shows that five crustaceans, 10 mollusks, 41 species of fish and 15 species of aquatic plants are found in Lake Mainit and its outlet, the Kalinawan River.

The survey found that, in terms of fisheries and vegetation, Lake Mainit and Kalinawan river are distinct ecosystems.

Lake fishery, for example, is inhabited predominantly by white goby while the river is dominated by mullet.

Submerged plants such as eel grass and Hydrilla are common in the lake while the river is covered by floating flora like the water hyacinth.

In recent decades, human encroachment threatens the lake’s biodiversity and productivity, said Dr. Wilfredo H. Uy of the Institute of Fisheries Research and Development at the Naawan campus in Misamis Oriental.

Pollution, high fishing pressure and unsustainable practices, fisheries policies that are not followed – all have taken their toll, he said.

"It is reflective of the state of Philippine lakes, which are overexploited," Uy told Malaya Business Insight.

"Overexploitation starts as soon as local fish are harvested and sold outside the local communities," he said.

Certain species of fish are feared to have been lost, he said, adding that at least 13 of 37 species reported in 1990 are no longer found in the lake.

The population of the once abundant giant mottled eel, for example, has drastically declined because of the massive fishing of the adult eels during their seasonal spawning runs along the Kalinawan River.

The native white goby remains the most important fishery resource in Lake Mainit, but current fish catch is about 63 percent compared to that in 1997-1998, said Uy.

Spear fishing in Alegria, Surigao del Norte and modified fish trap in Santiago, Surigao del Sur have caused decline in eel and snapper catches, he pointed out.

"Many species are caught in progressively smaller sizes, resulting in lower economic value and hence, marginal income for fisheries," he said during a national congress on Philippine lakes convened by the Philippine Council for Aquatic and Marine Research and Development (PCAMRD) and the Southeast Asian Regional Center for Graduate Study and Research in Agriculture (SEARCA).

As a result, Uy said, the annual fish catch from the lake has been drastically reduced, from 15,108 tons in 1980-1981 to only about 831.50 tons in 2007-2008, which is a measly 5.5 percent of the production level 26 years ago.

Present estimates from a 14-month catch data for the six major landing areas indicate 274.15 tons; extrapolating on estimates based on this data and from 28 monitoring stations show an annual landed catch of just 620 tons.

The present catch is about 4 percent of the total annual catch of 15,108 tons reported in 1981.

The lake is now undergoing what Uy called a "fishing down" phenomenon, with many fish caught in progressively smaller sizes and lower economic value.

"Lake Mainit experiences the typical syndrome of a threatened fisheries: biodiversity loss, high fishing pressure, use of unsustainable fishing gears and methods, declining fish catch and catch-per-unit-effort, decreasing size of fish caught, and marginal or meager incomes barely enough to meet basic daily needs of food, health and children’s education," he observed in a study.

Environmental problems include siltation in Tubay; mining and quarrying in Alegria and Santiago; burning of farm waste in Santiago and Mainit; and overgrowth of aquatic plants in Jabonga, said Uy who led MSU research on lake biodiversity.

There is still hope. The Lake Mainit Development Alliance, a grouping of eight towns, is behind the Lake Mainit Development Agenda. A fisheries management program is being integrated to help restore Lake Mainit fisheries to more sustainable levels.

Among the management recommendations are measures to sustain and increase fish production, including the establishment of land-based livelihood to ease the pressure on lake fishery.

Fish stock enhancement through seeding, fish sanctuaries and rehabilitation strategies are being suggested.

Technical assistance on sustainable methods of aquafarming is needed.

Aquaculture activities should also be regulated to prevent overexploitation.

As shown by the negative impact of the janitor fish in Laguna Lake, Uy said, the practice of introducing exotic and potentially invasive alien species for aquaculture must be halted. (PAUL ICAMINA/Malaya)

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