Untitled - About the Philippines

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Overview of Aquaculture in the Philippines as run-off which is both harmful to fish and humans. Indiscriminate use of such chemicals and the potential hazard to human health and possibility of bacterial resistance development are major concerns. Dependence on raw (trash) fish and fish meal. The dependence of cultured fish on wild-caught fish is astounding. Fish oil and fish meal, which are essential ingredients of feeds, ultimately come from wild stocks. Studies have shown that 1/3 of all wild-caught fish is used to make feed for aquaculture. On average, it can take 5-12 kg of feed to produce 1 kg of finfish such as grouper, snapper, and seabass (www.wwf.org). Based on PHILMINAQ’s estimates, about 160,000 tons of wildfish/ feeds are wasted in tilapia pens, cages, and ponds while more than 160,000 tons are wasted for bangus culture. While some argue that trash fish is not suitable for human consumption, in less developed countries such as the Philippines, even trash fish is eaten. Furthermore, these small fish species have vital roles in the ecosystem mainly as food for larger species of fish. – Alteration of physical environment. The nets of cages, pens, and associated moorings change the environment by preventing efficient water exchange and changing the current patterns caused by friction to the water currents. Friction from the nets can alter the residence time of water in a bay. Sometimes these structures can also cause obstruction to navigation routes and migration paths of different species of fish. Feed wastage. There is still significant feed wastage in aquaculture and this excess feed does not get consumed and goes into the environment, which can have significant impacts. Some of the feed is in the form of dust that is too small to be eaten by the fish, some feed gets lost through over feeding of the fish, or if the feed pellets are the wrong size for the fish. Excess pellets settle to the sediments where they may be consumed by wild fish, consumed by benthic organisms or breakdown into nutrients by benthic assimilation. To be discussed Release of wastes. Aquaculture, like any other animal production activity, produces wastes in the form of particulate (mainly the uneaten food and faeces) and soluble substances (excreta) which increase biochemical oxygen demand, nitrates and phosphates in receiving waters. The risk of negative impacts of aquaculture wastes is greatest in enclosed waters or sites with poor water exchange rates such as in slow moving rivers, lakes and shallow bays. In these conditions, aquaculture production can lead to a build up of organic sediments and addition of nutrients to the water column. This, in turn, can lead to secondary effects such as eutrophication, algal blooms and low dissolved oxygen levels. A summary of environmental impacts associated with the culture of specific species is shown in Table 5. 15
Managing aquaculture and its impacts: a guidebook for local governments Table 5. Environmental impacts associated with specific cultured species Cultured species Seaweeds Mussel and oyster Abalone Sea urchins Mudcrab Shrimps Specific environmental impact Benign, generally, but absorption of nutrients from the sea may cause changes to marine ecosystem structure and function, alteration of currents and increasing shading of bottom environments. Nutrient stress, perhaps caused by too much seaweed culture in an area, has also been implicated in ‘ice-ice’ disease Shading of coral reefs and use of mangrove poles for stakes Mussel and oyster farming also result in increased biodeposition of wastes on the seabed, the resulting organic enrichment inducing changes in sediment chemistry and biodiversity. Increased dissolved and solid nutrient wastes Negligible yet Over-harvesting of wild juveniles, clearing of mangrove areas, and wastes; may be mitigated with development of hatchery technology P. vannamei Risk of escape and threat to local biodiversity and ecosystems P. monodon Badly sited ponds and overfeeding result to discharge of large quantities of wastes that are poorly dispersed and can lead to self-pollution. Effluents from shrimp ponds are high in both dissolved and particulate nitrogen and phosphorus which elevates nutrient levels in receiving waters and promotes eutrophication. Antimicrobials, once widely used by the industry in order to try to control disease, were discharged with wastewater into the environment where potentially they promoted the development of antibiotic-resistant strains of bacteria. They are now used in much smaller quantities. Milkfish Tilapia Overfishing of wild fry Adapted from Draft Final Report, ADB ADTA 4805 In brackishwater ponds, intensification of production methods can result in greater production of wastes which unless intercepted and treated (filter traps, settlement ponds, biofiltration beds), are discharged into the coastal environment causing eutrophication and self-pollution problems in some areas of the country (e.g., Bolinao). A chronic problem in milkfish pond culture is the resident mud snail, which can multiply to very high numbers and compete with milkfish for natural food. Eradication has often been through the application of banned organotin compounds that are toxic to other aquatic organisms and have food safety implications. Fishpens in freshwater environment result in net nutrient loss In cages, eutrophication caused by uneaten food and fish excreta, sedimentation and in cases of overstocking, fish diseases and fish kills Environmental impacts of too many ponds sited in the wrong place, intercepting or abstracting too much water and releasing untreated, nutrient-rich pond effluents and sediments during harvesting Organic loadings (waste feed and fish excreta) that inevitably result from cage aquaculture cause eutrophication, as manifest by higher phytoplankton biomass and primary productivity and depletion of dissolved oxygen and accumulation of H2S in bottom waters. Under certain conditions – cooling of surface water following rain, for example, or the draw-down of a reservoir – up-welling of bottom water to the surface can occur resulting in fish kills. 16
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