PHYSICAL IMPACTS
was no active government support. Upon the creation of the BFAR in the late 1940s, funds for pond construction became available (mainly through international loans).
Mangroves were considered ‘valueless land’ (as quoted from Carbin 1948 as cited by Primavera 1995) at that time and conversion to brackish-water milkfish pond was deemed a more useful alternative. Thus began the accel- erated conversion of mangroves to brackish-water ponds at a rate of 5,000 ha/year in the 1950s and 1960s. Con- version slowed down to 800 ha/year in the 1970s when mangrove areas were placed under the joint jurisdiction of the fisheries and forestry bureaus and there was a move to- ward conservation. As the technology for shrimp culture developed, more mangroves were converted into ponds.
The host of ecosystem services provided by man- groves which turned out to be far more valuable was left unaccounted for during the initial period of conversion into ponds. It was only with the establishment of set parameters for valuation of various ecosystem services that it now has become apparent that mangroves, left as is, have far more economic, environmental, and bio- logical benefits than converting them to fishponds, and not the ‘valueless land’ they were deemed to be.
Mangrove ecosystem-derived services include (a) interception of land-derived nutrients, pollutants, and suspended matter before these reach deeper water (Tam and Wong 1999); (b) export of materials that support nearshore food webs including shrimps (Sase- kumar et al. 1992); (c) protection of vulnerable coastal areas from storm surges that have recently destroyed local communities in the country (Kathiresan and Ra- jendran 2005; Alongi 2008); (d) prevention of coast- al erosion through sediment stabilization (Marshall 1994); and (e) nursery and spawning areas for a variety of commercially important fish, shellfish, and molluscs (Sasekumar et al. 1992). With the loss of mangroves, important subsidies to subsistence uses and ecological, economic, and conservation uses are also lost. It is in- teresting to note that the decrease in mangrove areas in various countries is inversely correlated with an increase in GDP but not generally correlated with population (Valiela, Bowen, and York 2001).
4.1.2 Eutrophication
Eutrophication results from the heavy inputs of nutri- ents in the aquatic environment, mainly from uncon- sumed feeds, aquatic animal wastes, and other inputs into the aquatic system to boost production. A study on nitrogen and phosphorus utilization of formulated feeds under controlled laboratory conditions shows that an equivalent of only 33 percent of nitrogen and 29 percent of phosphorus is retained in fish (as bio- mass) and the rest is lost through fecal and urinary excretion (Cuvin-Aralar 2003). Since this was done in the laboratory, the feed ration was visibly consumed by the fish with some unquantified, but considered, minor nutrient losses through leaching.
Feed conversion rates vary with species, feeding strategy, and feeding management. Overfeeding results in high feed conversion ratios (FCRs) with excess nutrients entering the culture environment as organic sediments or dissolved nutrients in the water column. Nitrogen and phosphorus loading rates from one ton of shrimp harvest have ranged from 10 to 117 kg of nitrogen and 9 to 46 kg of phosphorous, depending on FCR (White et al. 2008).
Table 13 shows model estimates of amounts of nitrogen and phosphorus released to the aquatic environment from aquaculture as a function of FCR.
David et al. (2009) documented the increasing nutrient flux in sediment cores from aquaculture activi- ties in a number of marine aquaculture sites in the Phil- ippines: Honda Bay and Malampaya Bay in Palawan,
Table 13: Estimated organic matter and nutrient loading for one ton of harvested shrimp released at different FCRs
FCR Organic matter
kg/ton Nitrogen
kg/ton Phosphorus kg/ton
1 500 26 13
1.5 875 56 21
2 1,250 87 28
2.5 1,625 117 38
Source: Asian Shrimp Culture Council 1993, as cited by White et al. 2008.
Manila Bay, Bolinao in Pangasinan, and Milagros Bay in Masbate. The sites have varying degrees of aquacul- ture activity. Results show a narrow concentration range for nitrogen from older core samples when compared to newer ones. On the other hand, phosphorus showed significantly higher levels in younger or more recently deposited sediments. Sediments deposited years ago and older had 20 ppm phosphorous. On the other hand, a 2–3-fold increase in phosphorous levels was noted in sediments deposited within the last 15 years. Phospho- rous sediment profiles reflected the intensity of aqua- culture activities in the different sites. Honda Bay and Malampaya Sound in Palawan are sites where aquacul- ture activities had lower aquaculture intensity. Manila Bay has about 39 km2 of fish cages which are adjacent to urban centers. Bolinao has more than 1,100 fish cages, mainly milkfish (Chanos chanos), and Milagros Bay is a developing aquaculture site with shellfish as the ma- jor product. Phosphorous concentrations in these sites ranged from 10 to 90 ppm. Table 14 summarizes the phosphorous values obtained for the study sites.
A study is currently being undertaken by the National Fisheries Research and Development Institute (NFRDI) on nutrient buildup from aquaculture ponds in the provinces of Bulacan, Bataan, Cavite, and Pam- panga and the National Capital Region, all surround- ing Manila Bay.
An indirect impact of eutrophication is mass fish kill. Mass fish kill is a common occurrence in aqua- culture operations in the Philippines and has incurred huge financial losses for the aquaculture investor. In La- guna de Bay, 60 percent of mass fish mortalities record- ed between the 1970s and the late 1990s were attribut- ed to low dissolved oxygen, secondary to massive algal bloom due to eutrophication (Cuvin-Aralar 2001). The cause of massive algal bloom is excess nutrients in the lake, which in turn is due to eutrophication as has been discussed in the previous section. More recent incidents of mass fish kills in different regions of the country were also documented by the BFAR from 2005 to 2014 (Bantaya, pers.comm.). Of the more than 300 inci- dents of mass fish kills, almost 40 percent were because of poor water quality due to dissolved oxygen depletion and elevated ammonia. A number of instances of oxy- gen depletion were due to algal blooms. Interestingly, a few incidents of mass fish mortalities were also reported as being caused by agricultural pollution run-offs into inland waters with aquaculture activities. In Bolinao, Pangasinan, an important site for milkfish aquaculture, the site has experienced environmental changes due to these mariculture activities which release organic mat- ter from unconsumed feed and fecal material that ac- cumulate in the sediment. A massive fish kill incident in 2002 occurred in the area associated with the bloom of a dinoflagellate, accompanied by a <2 mg/l dissolved oxygen level. Increase in nutrient levels over a 10-year period (1995–2005) in the area has been reported (Mc- Glone et al. 2008). Ammonia has reportedly increased by 56 percent, nitrite by 35 percent, nitrate by 90 per- cent, and phosphate by 67 percent as the waters became increasingly eutrophic.
Taal Lake has multiple uses and benefits such as for open water fisheries, commercial aquaculture, recre- ational activities, navigation routes, and water source.
Of particular interest are immense aquaculture activities in the lake that started in the 1980s through which ti- lapia (Oreochromis niloticus) and milkfish (Chanos cha- nos) culture was introduced (Papa and Mamaril 2011).
The proliferation of fish pens and cages has affected the Table 14: Comparison of phosphorus
values from marine aquaculture sites in the Philippines
Site Characteristics P-range, ppm
Malampaya Sound
Capture fisheries; shellfish culture
15–85 Honda Bay Less aquaculture development 22 (average) Manila Bay 39 km2 of fish cages 20–60 Bolinao Bay 1,100 fish cages (milkfish) 20–90 Milagros Bay Developing aquaculture site;
mainly shellfish
15–40
Baseline Value 15–20
Source: David et al. 2009.
water quality of the lake. It is estimated that 64 percent of the nitrogen and 81 percent of the phosphorus con- tents of fish feed are released into the lake environment (Edwards 1993). Yambot (2000) calculated that for ev- ery 1.5 tons of fish feed given, 16 kg of phosphorus is released into Taal Lake waters. Further, the excess fish feed and fish feces contribute to the increased organic material that settles at the bottom of the lake. Decom- position of this organic matter releases hydrogen sulfide (H2S) and other toxic gases (White et al. 2008).
Significant fish kill occurrences in Taal Lake have created major economic setbacks in the area. One noteworthy incident was the 2011 massive fish kill that disrupted the socioeconomic activities in the lake, with recorded losses of approximately PHP 140 million. The event was attributed to an interplay of factors such as lake overturn, water pollution, change in season (that is, from summer to rainy season), changes in wind stress, and intermittent rainfall (BFAR 2011).
From 1998 to 2011, lake overturn and pollution are the major causes of reported fish kill in Taal Lake (Figure 38) (Magcale-Macandog et al. 2013). Increase in wind turbulence and low atmospheric temperature cools the lake water surface layer (epilimnion) and
erodes the thermal stratification of the water column (Balistrieri et al. 2006; Caliro et al. 2008; Marti-Car- dona et al. 2008). In combination with the pressure of strong winds, mixing of water occurs. This transports the low dissolved oxygen and reduced chemical sub- stances such as hydrogen sulfide (H2S), nitrite (NO2), and ammonia (NH3) from the lake bottom to the wa- ter surface, as well as mixes them in localized portions of the lake. The lake then goes into a state of hypoxia characterized by low dissolved oxygen, that is, below 2 mg/L. This undesirable water quality subsequent to lake overturn triggers fish kills in Taal Lake.
4.1.3 Contamination from Toxic and Hazardous Substances of Aquatic Products
A survey of specifically selected antibiotic and pesticide residues in Philippine aquaculture and fishery prod- ucts was conducted recently by Coloso, Catacutan, and Arnaiz (2015) from samples of tilapia, milkfish, sea bass, snapper, grouper, rabbitfish, carp, catfish, silver perch, tiger shrimp, white shrimp, and freshwater prawn. Some of the sampled fish tested positive for the antibiotic
Figure 38: Occurrences of fish kill in Taal Lake due to various factors including lake overturn, population, oxygen depletion, sulfur upwelling, and timud infestation based on BFAR announcements and reports from 1998 to 2011
Wind direction (degrees) Wind velocity (mps)
200
0 120 80 100 60 40 20 140 160 180
3.0
0 1.0 0.5 1.5 2.0 2.5
15
0 5 0 20 25 30 35 40 45 50 55 60
Wind direction Fish kill due to pollution Wind velocity Fish kill due to lake overturn Fish kill due to timud infestation Fish kill due to oxygen depletion Fish kill due to sulfur upwelling
Sources: BFAR and PAGASA; Graph by Magcale-Macandog et al. 2013.
OTC and oxalinic acid (OXA) as well as for organo- chlorine pesticides (OCP) for both high-value and low- value fish commodities. OXA and OTC were the most common antibiotic residues found and methoxychlor for OCP from Luzon, Visayas and Mindanao. OXA in Penaeus vannamei sample from Mindanao was found to exceed the maximum residue limit (MRL, based on Japan Food Chemical Research) and Permissible Expo- sure Limit (PEL, based on the Occupational Safety and Health Administration based in the United States). In one sample of freshwater prawn Macrobrachium species from Luzon, the level of Endosulfan I (0.0144 ppm) was considered harmful based on PEL (0.00642) and
MRL (0.005). Endrin ketone (0.02582 ppm) was also detected from the same prawn sample, although no PEL and MRL is as yet established (Table 15).
4.2 Impact of Diversification of Culture