Physico-chemical characteristics of water visited by whale sharks in Bicol Region, [Philippines] [Terminal Report]

The occurrence of whale shark aggregation in Donsol, Sorsogon has been the main attraction for local and international tourism in the Bicol. The ecotourism industry had not only brought visitors, increased LGU's revenue and developed local industry but had further resource management in the area. The seasonality of the tourism is dictated by the frequency of the visitation of these 'gentle giants'. Whale sharks are known to aggregate in areas with food pulses. Being filter feeders, zooplankton primarily composes its diet. Zooplanktons fluxes as grazers are expected to follow phytoplankton blooms. Phytoplankton blooms in areas of high nutrient and favorable physical conditions. Thus, this study was conducted to determine the physico-chemical characteristics of areas frequented by whale sharks. Particularly, the study aims to determine the physical oceanographic characteristics of the waters of Ticao Pass specifically of Donsol, Sorsogon; San Jacinto, Masbate and Pio Duran, Albay; determine some chemical characteristics of these areas ; and create a GIS-based database of these characteristics. The water of Tica Pass was generally characterized as deep with steep slopes. The coast was generally steeper from Catundulan Point to the coast before the embayment in Pio Duran. The 5 meter isobaths were farthest to the coast in waters fronting river mouths and embayment. Its water current in the northern station of Ticao Pass was generally influenced by the outflow of current from the rivers in the area. In the 1st quarter, water was generally moving towards 177+ - 103 degrees at 0.53 + - 0.33 m/s. In the 2nd quarter, current was generally moving towards 169+ - 98degrees at 0.53+ - 0.23 m/s but water current was flowing more synchronized in the 3rd quarter at the direction of 236+ - 42 at 0.76+ - 0.24 m/s. The waters of Donsol was bordered by Catundulan Point from northwest current flowing from Pilar Bay in the southeast thus resulting to formation of eddies and weak water currents between. Water temperature in Ticao Pass was conclusively coolest in January and warmest in July in all stations observed. Salinity in Donsol's coastal waters was greatly influenced by fresh water discards of Donsol River affecting 3-4 stations eastward. Despite the fresh water flows from the 5 rivers in Donsol and other freshwater sources, Ticao Pass remains strongly saline. Nitrate concentration was continuously available in the northern part of Ticao Pass whole year round. The decrease in nitrate with a corresponding increase in nitrite in October is attributed to the increase of photosynthetic activities of the primary producers. It may also be limitng primary productivity in San Jacinto. Nitrate concentration in Ticao Pass was higher than other bays facing the Pacific and in average its concentration in the study area was higher than the average nitrate concentration in the Pacific Ocean. There were upwelling areas identified in Pio Duran and Donsol based on the nitrite content of these waters. No station in the study area may be categorized as polluted in terms of nitrite. Ticao Pass was relatively more pristine than the other bays facing the Pacific. Donsol River and Pilar Bay and other river systems in the study sites play a big role in the supply of nutrients in the northern station as source of nutrients. Phosphorus was mainly coming from these river runoffs during the rainy season. It was identified to be a limiting factor to primary productivity in Ticao Pass. In Donsol River, which was believed to be connected to rivers flowing from Mayon Volcano, was the major source of silica in the northern part of Ticao Pass. Like nitrate silica may be limiting in San Jacinto but not in Pio Duran, Donsol and Pilar. Nutrients were consistently high in the waters of Donsol and nearby municipalities. Coastal waters of Donsol was distinct since nutrients was pooled between Catundulan Point and Pilar Bay thus concentrating nutrient from the fresh water sources during the rainy seasons before and during the month of October. In these months phytoplankton population may start to bloom. In January, the onset of whale shark season, nitrite and phosphorus concentration decrease. This may indicate continuous consumption of nutrients for photosynthesis. Despite this decrease there was a moderate increase in nitrate concentration. This may indicate a decrease in photosynthetic activity or decrease in primary productivity. This may be explained by the relationship of trophic levels in the aquatic food web. In the 2nd quarter, in October, physical parameters seem favorable and nutrients-nitrate, phosphorus and silica, were in abundance phytoplankton, the primary producers, finds it favorable to bloom. In the peak of primary productivity, first level consumers such as zooplanktons has abundant food supply thus population of the later increases between October and January before the onset of the whale shark visit. In the continuous grazing of zooplanktons and other herbivores and the apparent increase of their population there was a point when primary productivity population would be limited thus slightly decreasing its population and consequently decreases the consumption of nutrients. This had then implied less nitrate consumption in Ticao Pass reflected in January. The increase in zooplanktons invites the increase in 2nd level consumers such as the whale sharks. Whale sharks were known to migrate to Ticao Pass to feed on zooplanktons starting the month of December or January. The nutrients in Ticao Pass would continuously sustain the food web until it becomes limiting. This decline in primary productivity would eventually result to the die off of 1st level consumers and consequently the search of new feeding ground for the whale sharks.