Conservation and Ecological Management of Philippine Lakes in Relation to Fisheries and Aquaculture : Proceedings of the National Seminar-Workshop held on October 21-23, 1997, INNOTECH, Commonwealth Ave., Diliman, Quezon City, Philippines.

This volume documents the proceedings of the national seminar-workshop held October 21-23, 1997 in Quezon City which was co-organized by SEAFDEC/AQD, PCAMRD and DA-BFAR. The proceedings contains three plenary papers: (1) SEAFDEC contribution to the ecological awareness of Philippine lakes, (2) sustainable development of lake resources and the R&D agenda, and (3) aquaculture practices and their impact on lakes. Eleven technical papers discussed Lake Mahagnao in Leyte, Laguna de Bay, Lake Sebu in South Cotabato, Naujan Lake in Mindoro, Lake Danao in Cebu, Lake Buhi in Camarines Sur, Taal Lake in Taal. Abstracts of 13 other papers and posters are included in the volume. Two annexes follow: listing of lakes in the country and their common problems, recommended strategies, and action plans.

Recent Submissions

  • Conference paper

    The decline of native fishes and fisheries and the rise of aquaculture in lakes and rivers in the Philippines. 

    T Bagarinao - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    This paper reviews historical and recent data on biodiversity, fisheries, exotic fishes, and aquaculture in Philippine lakes and rivers. The country's lakes and rivers are poor in primary freshwater fishes because the Philippines' only connection with the Asian mainland had been through land bridges between Borneo, the Sulu islands, Mindanao, Palawan and Mindoro - in which islands endemic carps have evolved. Philippine lakes and rivers instead have secondary freshwater fishes such as gobies, migratory marine fishes such as mullets, and some snails, clams, and prawns. Most lakes and rivers have been severely degraded and their biodiversity reduced by siltation, pollution, overfishing, and the establishment of exotic fishes from other countries or elsewhere in the country. Many fishes first described in the Philippines in 1910-1940 by Seale, Herre, and Filipino ichthyologists have not been collected in recent years. The Laguna de Bay fishery in the early 1960s was largely dependent on the 'ayungin' Therapon plumbeus, 'biyang puti' Glossogobius giurus, and the 'kanduli' Arius manilensis that together comprised 95% of the annual 83,000 mt; another 19,000 mt came from shrimps and 245,000 mt from snails. Fishing and snail-dredging were so intense that catches declined and the whole lake fishery collapsed around 1970. After the collapse, the primary production of the lake increased and milkfish and tilapia became natural choices for aquaculture. Lake Lanao became famous for its species flock of 18 endemic carps, but these are now extinct, except perhaps two species. In 1963, these carps contributed 981 mt to the fishery, other native fishes 269 mt, shrimps and snails 257 mt, and introduced fishes 479 mt. Twenty years later, endemic carps have made up only 92 mt, native fishes 141 mt, shrimps and snails 164 mt, and introduced fishes 312 mt of the harvest from the lake. The 'kadurog' G. giurus, probably stocked in the lake with milkfish larvae in 1955, proliferated in the 1960s and apparently drove the endemic carps to extinction. The 'katolong' Hypseleotris agilis was first seen in the lake in 1977 and has since outcompeted the 'kadurog'. In Lakes Taal and Naujan, migratory marine fishes have been caught by fish corrals set across the outlets, but the catch along Pansipit River has fallen since the turn of the century and that in Butas River fell from 62 mt in 1977 to 17 mt in 1983. Catches of the endemic sardine Harengula tawilis in Lake Taal fluctuated between 4,400 mt in 1983 to 11,300 mt in 1990 and 1,400 mt in 1994. Cage culture of tilapia and milkfish has been going on in Lake Taal for 10 years. In Lakes Buhi and Bato, the endemic 'sinarapan' Mistichthys luzonensis almost disappeared due to fine-net fishing and tilapia stocking; catches have been 50-90 mt in 1983-93 but zero in 1994.
  • Conference paper

    Zooplankton diversity in Philippine Lakes. 

    AC Mamaril - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    Sustainable fisheries development partly depends on the availability of adequate zooplankton as principal food items of early life history stages of economically important fish species as well as of the adults of some species such as clupeids (e.g., Sardinella tawilis of Lake Taal in Batangas). The broad characteristics of the composition of freshwater zooplankton (Rotifera, Cladocera and Copepoda) of natural and man-made lakes in the Philippines are compared with those of the Oriental Region, in particular, and other tropical regions, in general. Two species of calanoid copepods are endemic, a somewhat remarkable occurrence considering that calanoids are represented by only five known species in the Philippines and absent in many large tropical lakes. Daphnia, which almost invariably influences food-web interactions and structures of plankton communities in temperate lakes, still has to be recorded.
  • Conference paper

    Aquaculture practices and their impact on Philippine Lakes. 

    DB Araullo - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    The rapid progress and development in the aquaculture sector during the past years has made an important contribution to the overall fish production in the Philippines. In 1996, 35.4% of the total fish production or 980,857 mt came from the aquaculture sector. Although milkfish from brackishwater ponds comprise the bulk of the produce, tilapia production from freshwater aquaculture in lakes, ponds and reservoirs is increasing annually. Fish cages and fish pens proliferate in most inland waters. The operation of such structures as livelihood for the coastal inhabitants has been recognized as a profitable venture.

    Many have gone into tilapia culture in ponds and small experimental cages in lakes and reservoirs in the 1980's. The success of tilapia culture in cages in the Bicol Region and Magat Dam in Isabela triggered the interest of other enterprising businessmen to expand the practice to other inland waters. However, problems of mass fish kill caused by deteriorating water quality have been reported.

    There is a need to strictly regulate the aquaculture practices; otherwise, more problems in the aquatic environment will be encountered. As freshwater aquaculture production is intensified, negative impact on the environment is also magnified. Under the Local Government Code, the management of inland waters is within the jurisdiction of the local government units with the assistance of the national government.

    For the proper management and sustainable use of inland water resources, this paper highlights the positive and negative impact of aquaculture practices on the aquatic environment.
  • Conference paper

    Mechanisms for lake formation in the Philippine archipelago. 

    RS Punongbayan & EL Listanco - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    Topographic depressions, which when filled with water become lakes, can originate in a number of ways as a result of volcanic processes and activities, crustal and fault movements, stream processes, dissolution of rocks, downslope or mass movements, shoreline processes, glaciation, acolian processes, organic or animal activity and meteorite impacts. Man has also made both intentionally and unintentionally artificial depressions and dams that give rise to man-made lakes. But the mechanisms of formation of most Philippine lakes remain unknown although those of some are well established. Examples are cited in this paper. Lakes with similar mechanisms of formation may possess similar geomorphological, geological, and physico-chemical characteristics.

    Directions for Philippine lacustrine research should cover issues on 1) the still unknown origin of most Philippine lakes, 2) assessment of lake-related hazards and risk mitigation in order to reduce disasters, 3) history of climate change as recorded in lacustrine sediments, and 4) policies and strategies for better utilization and development of lake resources which must recognize the truth that lakes are but ephemeral features of the landscape and do not last forever.
  • Conference paper

    Autoecology of an endemic calanoid copepod: The first step in biodiversity conservation in Lakes. 

    NE Palomar & AC Mamaril - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    Copepods, specifically calanoid copepods, play an important role in the productivity of aquatic ecosystems since they serve as a crucial link between primary producers and carnivores. In tropical reservoirs and lakes, they are not only a major source of food for many invertebrates and zooplanktivorous fish, but also good biological indicators. Calanoid/cyclopoid-cladoceran ratio is used in limnological studies as an indicator of water quality. In the past, studies in the Philippines on copepods and other freshwater zooplankton have dealt only on their taxonomy and distribution. Filipinodiaptomus insulanus is a calanoid copepod recognized as endemic to the country with its distribution restricted to the areas of Bulacan, Laguna and other parts of Rizal. Furthermore it is the only calanoid copepod found in the La Mesa Reservoir in Novaliches, Quezon City. This paper is a synthesis of three studies of F. insulanus obtained from La Mesa Reservoir. It aims to provide additional baseline information about the organism, particularly on its postembryonic development, feeding habits, and density fluctuations of its life history stage in the reservoir.
  • Conference paper

    Lake Lanao: Its past and present status 

    RP Rosagaron - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    Geographically located in Central Mindanao, Lake Lanao is the second largest lake in the Philippines. The lake is famous locally for its various uses and internationally for its endemic cyprinids. This paper intends to inform the local leaders and the national planners about Lake Lanao's dwindling fisheries resources, the extinction of some endemic cyprinids, and the current interventions as well as suggested action plans to increase fish production and to conserve the remaining species in the lake. The past and present studies on the lake are also reviewed. Early and latest statistics on the lake's fisheries production are presented to invite the interest of all sectors in coming up with the integrated approach to protect, conserve and increase its fisheries production. Local and national interventions to conserve and increase fisheries production are discussed. These include the setting up of BFAR Fisheries Station in Kialdan, Marantao; the establishment of a fish hatchery in Poona, Marantao by Southern Philippines Development Authority; the formation of Save Lake Lanao Movement by the local leaders; the creation of Lake Lanao Research and Development Council; the current concern of Philippine Council for Aquatic and Marine Research and Development-DOST; and the extension and research and development thrusts of the Mindanao State University, College of Fisheries in Marawi City.
  • Conference paper

    Impact assessment of cage culture in Lake Taal, Philippines. 

    MM Alcañices, RC Pagulayan & AC Mamaril - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    The environmental impact of cage culture on water quality of Lake Taal was assessed from March 1996 through February 1997. Three stations were considered namely: Balas, which serves as station 1 (non-cage area) and Sampaloc and Laurel, stations 2 and 3 (cage areas), respectively. Monthly water samples with two replicates were collected using a van Dorn sampler at 0, 5, 10 and 15-m depths in all stations. Below surface water from the inside of the cages was also collected. Water temperature, water transparency, pH, and conductivity were determined in situ. Dissolved oxygen, chloride, NO3, NH3, PO4, and total P were analyzed in the laboratory. Phytoplankton density and algal biomass (through cholorophyll a) and primary productivity indices were determined with the light-and-dark bottle method.

    Of the water quality parameters, conductivity and DO had significant differences between non-cage and cage areas. Conductivity gave significant difference (P<0.01) between control and cage area during the wet season. Highest conductivity value (2100 µ S/cm) was observed in station 3. Mean values of DO gave significant differences (P<0.05) in the different stations throughout the study period. A decrease of DO to 2.5 mg/1 was observed below 10-m depth around the cage areas. Analysis indicates that cage culture leads to oxygen depletion in the water column. The presence of cage structures decreased the flow rate resulting to weak circulation. The reduced water circulation in effect decreased the supply of oxygen and removal of toxic waste metabolites from the vicinity of the fish farm, and reduced the supply of plankton. These results suggest that the impact of cage culture in Lake Taal is minor but can alter the lake ecosystem if not properly managed. Zoning and continuous water quality monitoring are needed.
  • Conference paper

    Species and proximate composition of Laguna de Bay phytoplankton cultured in three different nitrogen-phosphorus ratios and their utilization by Nile tilapia. 

    ML Cuvin-Aralar, U Focken, K Becker & CB Santiago - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    Natural phytoplankton populations from Laguna de Bay were used in outdoor batch culture experiment in 1-ton capacity circular concrete tanks and 60-liter glass aquaria for a maximum duration of 72 days. The treatments consisted of the following nitrogen-phosphorus ratios: 2N: 1P, 6N: 1P, and 12N: 1P. The growth and species composition of phytoplankton were monitored in each of the three treatments. The phytoplankton were partially harvested at weekly intervals. The proximate composition of the freeze-dried harvest was also analyzed. The freeze-dried harvest was also used to feed Nile tilapia Oreochromis niloticus (L.) to determine effects of the different N-P ratios on the utilization of phytoplankton by fish. The fish were fed isonitrogenously and ration ranged from maintenance requirement for the first week to 3 times maintenance requirement for the succeeding weeks. Results showed that green algae, particularly the Chlorococcales group, dominated all the cultures. This was followed by diatoms. The blue-green algae consisted the third group in all treatments. Gross energy, crude protein, crude fat, neutral detergent fiber and crude ash content of the phytoplankton harvest did not vary significantly among treatments. However, crude protein expressed as percentage of organic matter was significantly higher in the treatment using 12N: 1P compared to those cultured in lower N-P ratios. Nile tilapia fed phytoplankton from 12N: 1P and 6N: 1P ratios showed significantly better growth than those fed with phytoplankton cultured in the lowest N-P ratio.
  • Conference paper

    Sustainable development of Philippine lake resources: an agenda for research and development. 

    RDI Guerrero - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    There are 59-70 lakes in the Philippines. With the exception of Laguna de Bay and Lake Taal, little is known about Philippine lakes although they contribute as much as 15% to the total annual fisheries production of the country. There is need for an integrated basin approach for the sustainable management of Philippine lake resources. Among the research strategies recommended for sustainable management of Philippine lakes are: (1) studies on lake fisheries resources - fish stock assessment, effects of fishing and other human activities on lake productivity, the biology of major aquatic species, and the carrying capacity of lakes; and (2) lake management studies - the rational use of lakes, strengthening management, enforcement and institutional mechanisms, and socio-economics focused on the users of lakes.
  • Conference paper

    Managing 'sinirapan' Mistichthys luzonensis Smith in Lake Buhi, Camarines Sur: Insights from its biology and population dynamics. 

    VS Soliman & MFHA Sergio - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    The population dynamics and related aspects of the biology of 'sinarapan' Mistichthys luzonensis Smith, the world's smallest commercial fish, are used as basis in formulating management strategies for this goby in Lake Buhi, Camarines Sur. Mesh size limit (4.1mm) and catch limit, estimated through length-based analytic fishery methods, are proposed. Yield-per-recruit analysis using length-frequency data for 11 months provided the quantitative indices used in estimating fishing limits. Closed season for 'sinarapan' was established from temporal pattern of recruitment and the reproductive biology of the species. Much of the data on 'sinarapan' came from studies in Lake Manapao. To improve the recruitment success of 'sinarapan', a habitat enhancement scheme in Lake Buhi is hereby recommended.
  • Conference paper

    Some limnological features of the northern shore areas of Volcano Island, Lake Taal. 

    NC Lopez, SN Javier & AC Mamaril - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    Physico-chemical and biological features of the northern shore areas of Volcano Island, Lake Taal observed at monthly intervals from four stations during the period 1994 and 1996 indicate varied microhabitats inhabited by a variety of plants and animals. Physico-chemical characteristics of surface waters were: temperature, 28-35°C; dissolved oxygen content, 3.5-6.2 ppm; pH, 7.5-8.9; salinity, 0-24 ppt; and conductivity, 1.6-4.3 S cm-1. Substratum types were mainly sandy with pebbles or rocks or sandy-muddy. Characteristic submerged plants were the eelgrass Vallisneria gigantea and filamentous green algae. In the eelgrass region, atyid shrimps, mostly Ciridina gracilirostris, commonly occur. Snails such as Melanoides costellaris and Terebia granifera were the most abundant benthic animals collected. Other invertebrates identified from core samples were Corbicula manilensis, annelids, crustaceans and chironomid larvae.
  • Conference paper

    Preliminary observations on the diel feeding patterns of Nile tilapia Oreochromis niloticus (L.) in Laguna de Bay, Philippines, with the aid of the computer model MAXIMS. 

    H Richter, U Focken, K Becker, CB Santiago & WB Afuang - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    Nile Tilapia, Oreochromis niloticus, cultured in cages in Laguna de Bay, were sampled on two occasions in 1995, each time over a 24-hour cycle. The weights of stomach content were averaged and analysed with the computer model MAXIMS. The model predicted that, in May, larger fish feeding on natural food alone fed continuously from dawn to dusk, ingesting 4.9 to 5.4% of their body weight (wet weight basis) whereas smaller fish had two feeding periods per day, from sunrise to mid-morning and again from mid-afternoon until after sunset, ingesting between 13.0 and 13.7%. In August, fish were given supplemental feed that ran out around mid-day, after which they continued to ingest natural food. The fish ingested 3.8 to 4.0% supplemental feed and 4.4 to 4.7% natural food per day. In May, most of the stomach contents consisted of the blue-green alga Anabaena spiroides, whereas in August, the natural food was made up principally of detritus. On the basis of these findings, it is recommended that supplemental feed be given in several doses spread throughout the day.
  • Conference paper

    Translocation of the clupeid Sardinella tawilis to another lake in the Philippines: A proposal and ecological considerations. 

    AC Mamaril - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    The dwindling commercial catch of Sardinella tawilis (Clupeidae), locally known as 'tawilis', reported in recent years by local fisher folk in Lake Taal, Batangas, Philippines, could be a result of the interaction of factors such as over fishing, destructive fish-capture techniques, changes in water quality, and others. Like the rest of the handful of endemic freshwater fish species in the Philippines, S. tawilis is threatened with depletion of its stocks, if not with extinction in the near future. A conservation strategy that could be considered is the translocation of 'tawilis' to another lake in the Philippines, whose ecological features closely resemble those of Lake Taal and where 'tawilis' would receive socio-economic and cultural acceptability. Cases of clupeid introductions - natural and man-made, successes and failures - are presented from published literature. Special attention is given to the case of a well-planned trans-country (Thailand-to-Indonesia) attempt to introduce a clupeid fish. The broader questions of biodiversity, endemicity, conservation, and fish community structure in Lake Taal (and elsewhere) must be underpinned by sound basic taxonomy and ecology.
  • Conference paper

    Assessment of local government's implementation of open access policy in Taal Lake, Philippines: Effects on lake conservation and management. 

    MT Mercene-Mutia - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    The effects of local government's implementation of the current national policy on open access in municipal fisheries are assessed in terms of their impact on the fishery resources of Taal Lake. Local officials and fisherfolk were interviewed and their responses were analyzed for trends in perceptions on how local open access policies affect fishing practices and productivity in the lake. A policy matrix containing certain areas of concern of local governments related to sound decisionmaking on lake fishery was designed.

    The study shows that local government implementation of open access policy in Taal Lake tends to have negative effects on the lake's fisheries. Open access allows for the unregulated entry of fishing practices like fish cage culture which tend to increase the pollution load in the lake. Pollution due to fish farming in cages seems to even exceed loads from domestic wastes and agricultural runoff. While fish cages flourished in the lake, the income of small fisher folk has declined because of dwindling catch from capture fisheries.

    It is recommended that national government agencies (e.g., Department of Agriculture, Bureau of Fisheries and Aquatic Resources, Department of Environment and Natural Resources) should forge an agreement with local government units for a continuing assessment of the fishery resources in Taal. This needs to be coupled with technical assistance to undertake sustained efforts to improve the conservation, productivity and management of the lake's aquatic resources. There is also a need to increase the budgetary allocations for new research and extension activities to address problems and issues of the fishery sector in the lake and for upgrading the capability of local and sectoral policy and decision makers on the lake's fisheries.
  • Conference paper

    Bathymetry and hydrobiology of Lake Mahagnao, Leyte. 

    RA Francisco, MR Pundavela, JM Granali, LA Tumabiene, JP Alpino & VV Elmido - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    Lake Mahagnao in Burauen, Leyte (10° 52.15' N and 124° 51.32' E) lies 26 m above sea level. It is surrounded by a mountain range that includes a dormant twin volcano. A bathymetric survey established 122 sampling stations using Global Positioning System. The stations formed transect lines across the lake. A bathymetric map of Lake Mahagnao was generated with the use of the SURFER software. Lake Mahagnao has a shoreline of 15,590 m and surface area of 15.75 ha. The deepest portion of the lake is 18.75 m. The mean pH of the water is 6.58; water surface temperature, 27oC; and water visibility, 1.64 m. Eighty-one species were identified as primary producers. Station 5, the deepest portion of the lake, had the highest phytoplankton density at 4,716 cells/ml and Station 2 had only 634 cells/ml. Cyanobacteria were the most abundant in all the sampling stations.
  • Conference paper

    An ecological assessment of seven major lakes in the Philippines. 

    MT Zafaralla - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    An ecological assessment was done on the seven major lakes in the Philippines, namely; Laguna de Bay, Taal, Naujan, Lanao, Mainit, Buluan, and Bato. The assessment was based largely on secondary data and some primary data. The ecological parameters considered for each lake were focused on published information as well as those unpublished but were made accessible to the author by researchers and agencies of government. The different lakes are classified into three ecological categories, namely; critically degraded, degraded, threatened, and underdeveloped. Where adequate data on a lake is available, emphasis is also given on the examination of the nature of land use, lake development measures, climatic variations in terms of rainfall, and ecological conditions in the lake as they affect fish production. Finally, lake specific and general recommendations are forwarded for management purposes.
  • Conference paper

    A modelling of eutrophication in Laguna de Bay as a tool for rational resources management. 

    I Mitsumoto & AE Santiago - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    A lake model originally developed for Shin-Nippon Meteorological and Oceanographical Consultants Co., Ltd (METOCEAN) was used with modification to simulate the water quality of Laguna de Bay. The METOCEAN model made use of the 1984 meteorological and water quality data collected from different local government agencies. Hydraulic modeling was applied to obtain basic circulation patterns which the water quality modeling was based upon. Results of the hydraulic modeling suggests that steady backflow of saltwater from Pasig River reaches deep inside the bottom layer of the lake although the lake water flows out through the Pasig River. Thus, the water quality model for Laguna de Bay focused on the unique role of the salt water intrusion in limiting phytoplankton productivity. The effect of saltwater intrusion was simplified as the change of depth of euphotic zone in the lake water estimated from the Secchi disc transparency. For simplicity and expandability of the model as a predicting tool, Secchi disc transparency was the only forcing function considered in the study.

    Modelling resolution of water quality has 4 boxes horizontally and 3 levels vertically. Calibration of the water quality model was carried out by running the model repeatedly until satisfactory agreement with measured data was obtained under average wind condition (Eastern wind, 1.5 m/sec.) Other wind directions including no wind condition were also tested to see the effect of wind on water quality. Validation of the water quality model was done for 1985 to 1988 as continuing simulation from the calibration in 1984 under the average wind condition. Then simulation of the condition of the lake from 1991 to 1995 based on the 1984 data used in the calibration was tried changing only the Secchi disc transparency data.

    Initial results of the water quality model differentiated conditions with and without saltwater intrusion. Without saltwater backflow, higher concentration of total inorganic nitrogen and inorganic phosphorus and low dissolved oxygen especially in the bottom layer are predicted. Under this condition, release of large amounts of nutrients in the sediments is expected to be dominant source of total inorganic nitrogen in the lake. The study is the first attempt to model the lake. The model still needs calibration and validation with measured values of recent years before adapting its usefulness as a tool for predicting water quality of Laguna de Bay.
  • Conference paper

    The status of tilapia aquaculture in Lake Sebu, South Cotabato. 

    ZM Beniga - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    Tilapia culture in Lake Sebu started in the early 1970's and is now considered the backbone of the economy and major driving force of the development of the Municipality of Lake Sebu. About 19% of Lake Sebu's 354 ha water area is used for aquaculture. The present tilapia production system is not as intensive as in other lakes in the country. The daily 3-ton tilapia harvest is marketed in the different towns within the province and in neighboring provinces. Municipal Ordinance 01, Series of 1994 regulates fish cage establishment within the lake. The local government unit launched a semi-annual 'Oplan Linis', a clean up operation to remove floating debris, water hyacinth, and other vegetation along the lakeshore. Reforestation has been implemented as part of the watershed management program. For centralized marketing and effective collection of revenues, a fish port was opened in January 1997. The tilapia industry in Lake Sebu is now confronted with several setbacks. Poor-quality seeds require a longer culture period and, despite higher inputs, still result in low production. Fish kills, locally termed 'kamahong', are becoming more frequent and devastating. Market competition is another problem. Producers of intensively fed tilapia from Lake Sebu have to contend with a large volume of unfed and low priced tilapia from Lake Buluan (Lutayan area).
  • Conference paper

    Fish culture in cages in Lake Danao, Cebu. 

    SN Tanduyan & PC Bontia - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    Lake Danao is a picturesque inland body of water having an area of 685 ha located in the municipality of San Francisco in Pacijan Island, Camotes, Cebu. At the middle of the lake is a circular islet with an area of one acre. This lake is a potential area for cultivation of fishes in pens and cages. To date there are only two agencies which use the lake for fish production, namely; the Department of Agriculture Regional Office No 7 Carmen-Lake Danao Fishery Complex Research Outreach Station and the CSCST-Fishery and Industrial College, San Francisco, Cebu. The following are the ranges of selected water quality parameters: salinity, 0-0.5 ppt; water temperature, 27-29 °C; pH, 8.5-9. The lake has no definite inlet and outlet of water and is free from pollutants. The water is clear with assorted vegetation. The soil is coarse, silty and sandy. The present study has shown the feasibility of growing tilapia in cages in Lake Danao.
  • Conference paper

    Biological monitoring in west bay, Laguna Lake: Phytoplankton composition and water pollution. 

    JC Francisco & TR Perez - 2001 - SEAFDEC Aquaculture Department; Philippine Council for Aquatic and Marine Research and Development; Bureau of Fisheries and Aquatic Resources
    Phytoplankton composition and density were studied in three (3) stations in West Bay, Laguna Lake. Blue-green algae and diatoms were the most abundant in terms of cell density. Green algae had the most number of species. Diatoms predominated in the early parts of the year, under intense light conditions. Pulses of green algae were evident toward the end of the year, under high nitrogen concentrations. BIP (Biological Index of Pollution) values were very much affected by seasonal variations in the phytoplankton community.

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