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Environmental Assessment of Fishery Resources in Magat Reservoir
Thesis Abstract:
This study analyzed the environmental problems confronting the Magat watershed in lsabela province, Philippines, with emphasis on the possible impacts of the 16 July 1990 earthquake on the reservoir's fishery productivity. The interrelationship of the physico-chemical, biological, and socioeconomic components of the reservoir was discussed in relation to both human interventions and natural calamities in the watershed.
As a result of human interventions, the watershed had been transformed into grasslands and agricultural lands at the expense of primary and secondary forests. The 16 July 1990 earthquake, representing a major perturbation, moved huge volumes of soil eroded along the mountain areas of the Cordillera and Caraballo mountains. This accelerated the sedimentation of the Magat reservoir. Deposition of eroded materials into the Magat riverine ecosystem reduced algal growth and reportedly caused the temporary disappearance of some freshwater fish. The occasional deposition of erosion materials in waterways during the rainy season had caused turbidity and sedimentation of waterways resulting in the decline offish population.
Data on the quality of the reservoir before and after the calamity showed significant differences which could account for the cumulative effects of changes in the chemical and physical conditions.
Declining fishery productivity of the reservoir affected the socioeconomic condition of Magat fisher folks because fish catch had decreased from 393,4 78 kg in 1984 to 54,823 kg in 1991 and the culture period was longer (5-6 months up to one year).