Geographic Location/Coverage. The Davao Gulf is located in the southeastern part of the Philippines (Figure 1), about 984 km south of Manila. It lies approximately between 6º7’ and 7º4.5’ north latitude and 125º11.5’ east latitude. It is bounded by Davao City and the four provinces of Davao del Sur, Davao del Norte, Compostela Valley and Davao Orienta. It lies south of the wide flood plains of Davao del Norte and west of the adjacent provinces of Bukidnon and Cotabato. The gulf has an area of 6,600 km2 and a coastline of approximately 500 km. The average depth of the gulf is 17 m, volume approximately 112x109 m3. The high mountain ranges of Sarangani Province in the west and south-west, the mountain ranges of Mt. Apo (the highest Philippine peak) in the north and north-west portion of the region, and the mountain ranges of Davao del Norte and Oriental in the eastern side, surround the gulf. Within the gulf are the islands of Samal and Talikud. Soils. The surface soils of land surrounding the Davao Gulf are mostly clay and loam types that are well-suited for plantation crops (e.g. banana, pomelo, durian, and coconut), cut flowers and orchids. The Davao region, which is generally free from typhoons, has a mean rainfall of 180.9 mm/yr that is evenly distributed throughout the year (PAGASA). The mean annual temperature is 27ºC while mean humidity value is 82%. The prevailing wind direction is north during the operation of the north-east monsoon from October to May. The south- west monsoon operates from June to September. The mean speed rate during the two monsoon seasons is 16 km/hr. Extent/Size of Coastal Resources. The Davao Gulf has a water area of 10,500 km² and a total catchment area of 5,132 km² which is derived from the various watersheds of Sarangani, Davao del Norte, Davao Oriental, Compostela Valley, and Davao City. The average depth of the Gulf is 17 meters and volume of approximately 112x109 m³ (V. Dupra and S.V. Smith). Its widest point is approximately 160 km while coastline is approximately 520 km., reckoned from Calian Point in Davao del Sur to Cape San Agustin in Davao Oriental (or excluding the coastline from Calian Point to the Municipality of Sarangani). Within the Gulf are the islands of Samal and Talikud in Davao del Norte, Kopiat in Davao Oriental and Lunod in Compostela Valley (MSU- Naawan, 1995). Hydrology. The 33 major rivers and creeks that drain into the Davao Gulf make the inner part of the Gulf estuarine in character (V. Dupra and S.V. Smith). The water of the Gulf is oceanic in nature considering that the Pacific Equatorial current flows westward and northwest as it reaches the western boundary rim (eastern part of Mindanao) of the Pacific Ocean. The water mass is affected by the tidal force resulting from the earth’s rotation on its axis. Water exchange is mainly tidal with relatively good surface mixing during strong monsoon winds. The northern portion is generally estuarine in character due to the massive influx of freshwater from the flood plains especially during the rainy season. Prevailing Tidal Fluctuations. The Gulf has a unique pattern of water movement. During flood tide, water mass south of Samal Island flows southwest averaging about 0.26 to 0.42 m/sec. In the northern portion of the island, between Bassa Point and Gill Point, water mass flows northeast, then southward and swiftly veers east-northeast during the peak tide current. During a flooding event, the more saline oceanic waters move through the deeper section of the Gulf pushing the older water mass northward. Tide waves occurring ahead at the eastern section cause older water to wave towards the area of low elevation at the western side. Eddies and standing oscillations are present. Watershed. The Davao Gulf is the final catchment for all runoffs, erosion and effluents coming from several watersheds in the region whose headwaters come from the mountain ranges of Sarangani Province in the west and south-west portion of the region, the mountain ranges of Mount Apo (the Philippines’ highest peak) in the south portion, the mountain ranges of Davao del Norte in the north and north-west portion, and mountain ranges of Compostela Valley and Davao Oriental in the eastern side. Thirty-three tributaries or rivers and creeks drain into the Gulf (Figure 1). These tributaries make up 12 major watersheds and 8 micro watersheds, as defined by the River Basin Committee for the Davao Gulf Tributaries (DENR XI). Province Watershed Davao del Sur Balutakay Watershed Digos Watershed Lais Watershed Padada-Miral Watershed Sibulan Watershed Tagum-Libuganon-Saug Watershed Davao del Norte Tuganay Watershed Davao River Watershed Davao City Lipadas-Talomo Watershed Hijo Watershed Compostela Valley Kingking Watershed Davao Oriental Sumlog Watershed Figure 1. Twelve major watersheds of the Davao Gulf The Davao Gulf is endowed with major coastal habitats such as mangroves, seagrass, coral reefs and soft-bottom communities that directly and indirectly support fisheries. In recent years, man-made habitats such as artificial reefs were introduced to enhance fish stock. Mangroves .The estimated mangrove cover of the Gulf differs significantly among studies, probably because of the methods used. Some of these estimates were based on spot satellite maps that need on-ground validation while the others were based on topographic maps using different scales. Of the estimated 2,683 hectares of mangroves based on the 1950 NAMRIA maps, 1,391 hectares had been converted into fishponds and 845 hectares, for other purposes. By 1995, only 295 hectares (11%) had been accounted for (BFAR, 2000). View Table 1: Distribution and approximate mangrove area for each municipality in the Davao Gulf. An inventory of mangrove area using composable data at various periods shows the distribution and approximate mangrove area at Davao Gulf. A study by the University of the Philippines in the Visayas Foundation, Inc. (2000) listed 20 species of mangroves in the Gulf (View Table 2). Fourteen of them were classified as true mangrove species with the most common belonging to genera Rhizopora, Sonneratia and Avicennia. Brgy Cagangohan of Panabo (Davao del Norte) and Lunod Island of Mabini (Compostela Valley) have the most number of mangrove species. Trees reaching 20 meters high still exist in barangays Bato and Tuban in Sta. Cruz, Davao del Sur. Of the 65 known species of mangroves worldwide (UNDP/UNESCO, 1986), 50 species belonging to 26 families can be found in the Philippines (Calumpong, 1997). In the Gulf, 27 true mangroves and 23 mangrove associates are grown in the first on-site mangrove laboratory in Southern Philippines, the San Isidro Mangrovetum in the Island Garden City of Samal (IGaCos). With the assistance of the Coastal Environmentalist Conservation of Samal Island, Inc. (CECSI), a federation of five people’s organizations in IGaCos, the DENR in Region XI plans to propagate all 47 true mangrove species In year 2004, seaweed projects amounting to P550,000.00 were awarded to 11 registered people’s organizations (PO) in the Gulf. These projects where each PO got P50,000.00 through the Presidential Commitment and National Security Plan Fund benefited 720 people, excluding those that got funding assistance from the Fisheries Resource Management Project (FRMP) of the Department of Agriculture-Bureau of Ffisheries and Aquatic Resources in Region XI (DA-BFAR XI). Seagrasses. There were nine species of seagrasses that were observed in 12 sites around the Davao Gulf excluding Davao Oriental (UPVFI, 2000). The seagrass species are Cymodocea rotundata, C. serrudata, Halodule pinifolia, H. uninervis, Syringodium isoetifolium, Halophila minor, H. ovalis, Thalassia hemprichii and Enhalus acoroides. Species diversity varied considerably between areas. Seaweeds.Twelve species of seaweeds, the most common of which were Genus Padina and Enteropmorpha, were also counted. (View Table 3: Seaweed species observed in 12 sampling stations in the Davao Gulf ) Corals. Manta tow surveys covering 33.8 kilometers of reefs in the Gulf showed that only one-fourth of the coral cover was live (View Table 4). Of the 19 areas surveyed, only the corals in Tubalan were in very good condition. Areas with poor values of 10% and below were found in Agdao, Malita and Valez (Toril) in Davao City. Thirty-four genera of hard corals and three genera of soft corals were identified, suggesting high species diversity (View Table 5). As shown in Table 6, the total length of reef formation was estimated to be around 412.1 km. (UPVFI, 2000). These were mostly reefs surrounding the islands and shoals of Samal in Davao del Norte (127.4 km.) and the fringing reefs of the mainland of Davao Oriental (114 km.) and Davao del Sur (102.7 km.). Live coral cover was noted to be decreasing over a period of five years (MSU, 1995 and UPVFI, 2000). Fisheries. The Davao Gulf is an important spawning and nursery for tuna, according to a study commissioned by the Fishery Resources Management Bureau of the Bureau of Fisheries and Aquatic Resources (BFAR). (See Economic Indicators for details.) Marine Turtles. The turtle population worldwide is declining and listed as endangered by the CITES. Of the seven species of marine turtles still existing, five are found in the Philippines. All of these are present in the Davao Gulf. Since 1998, the DENR XI has tagged and released at least 59 turtles. Despite local stories of nesting grounds around the Gulf, only the local government of Davao City has created a Pawikan Task Force to spearhead the management and conservation of marine turtles in the area in response to the recent discovery of turtle nests in Punta Dumalag. The municipal government of Pantukan in Compostela Valley also passed a resolution providing incentives to fisherfolks who can capture and release sea turtles. Dugongs. Dugongs (Dugong dugon) or sea cows, which feed on seagrass, have been sighted near the shores of Davao Gulf particularly in the coasts of Malalag, Malita and Don Marcelino in Davao del Sur; IGACOS in Davao del Norte, and Gov. Generoso in Davao Oriental. These timid creatures are likewise endangered under CITES. Dwindling seagrass habitats and other anthropogenic causes contribute to the continued decline of the dugong population. Dolphins and Whales. The Davao Gulf serves as a feeding ground for various species of highly migratory cetaceans such as dolphins and whales. The survey in March 2004 by a composite team from the DA-BFAR, the Save Davao Gulf Foundation, Inc. (SDGFI), and the WWF- Philippines, confirmed the presence of 11 cetaceans in the Gulf making it the second top cetacean diversity sight in the Philippines, next to Babuyan Islands that has 13. Of the 11 cetaceans discovered, seven species are whales while four species are dolphins. Sightings, which have been frequent based on persistent reports by fishermen to include cases of unfortunate beaching, are estimated at 77 (DA-BFAR, 2004). These were around the southern portion of Ligid Island, Samal Island and south of Barangay Matina in Davao City. It should be noted, however, that eight of the 11 species are listed in Convention on the International Trade of Endangered Species (CITES) as threatened by extinction unless protected and conserved. The pygmy6 sperm whale, which was the last to be discovered in the Gulf, is classified under CITES as species that is “not necessarily threatened with extinction, but in which trade must be controlled in order to avoid utilization that is incompatible with their survival”. Birds. The Davao Gulf is an important feeding area for egrets and ducks, and an important staging for migratory shorebirds. In May 1987, Howes (1987) visited four sites in the Gulf and observed small numbers of Egretta eulophates, E. garzetta, E. intermedia, 445 Dendrocygna arcuata, 26 Anas luzonica and 675 shorebirds of 17 species including Numenius madagascariensis. Migratory of Malalag in Davao del Sur and Carmen in Davao del Norte.
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