BU R&D Journal 24 (1): 67-81, July 2021 | ISSN (Print): 0016-4139 journal.bicol-u.edu.ph | ISSN (Online): 2719-082X doi: 10.47789/burdj.mbtcbbgs.20212401.11

The Eel Fishery in Tributaries Along Lagonoy Gulf: Implications for Management and Conservation

Plutomeo M. Nieves1,*, Antonino B. Mendoza Jr.1, Raul G. Bradecina2, John Christopher C. Nolial1, Niño C. Celestial1, Satoshi Kubota3, and Katrina L. Canon3 1Bicol University Tabaco Campus, Tabaco City, Albay, Philippines 2Partido State University, Goa, Camarines Sur, Philippines 3Laboratory of Molecular and Cellular Biology, Kochi University, Kochi Japan *Corresponding author: [email protected]

Abstract

This study provides a discussion of the eel fishery in the tributaries and rivers along Lagonoy Gulf primarily to formulate management and conservation strategies supportive of the economic potentials and sustainability of the resources. Data collection employed key informant interview and focus group discussion to collect fishery-based data together with the collection of 300 samples per month. Caudal cutaneous pigmentation method was used in species identification. GIS map was prepared to identify the potential eel habitats. The species composition across the study area include: Anguilla marmorata (89.80%), A. bicolor pacifica (10.10%) and A. japonica (0.10%). The wide-distribution of A. marmorata could be explained by the fastness of leptocephalus metamorphosis. Two gears type were identified: modified fyke net was mainly used in glass eel collection while the remaining gears for adult eel. Post-harvest practices are similar to milkfish. Finding showed no clear indication of the status and trend of the fishery. Supply and value chain is limited to 30 collectors, 93 fishers and 5 traders, their number increases proportionately in-line with increasing catch. Estimated annual production for glass eel is 4,626 kg - 1,386 kg valued at ₱9.4M to ₱12.67M and about 325MT to 81.3 MT adult eel annually valued at ₱23.3M to ₱6.6M. Policies and strategies supportive of economic potential of eel resources are recommended alongside the development of sustainable management interventions to sustain the fishery. Further study on species identification using a combination of morphological and molecular technique is recommended.

Keywords: modified fyke net, ichthyotoxic plant, caudal cutaneous pigmentation, and glass eel

Introduction markets are Japan, South Korea and China, where eels are perceived as delicacies and a source of stamina. The Philippines is one of the few areas in the world Unfortunately, the country’s shipments of live eels in where high-value species of eels such as Anguillids (true 2014 valued at $34.87 million declined (5,142. MT) from eels) and Monopterus (paddy eels) thrive. The Philippines about $38.29 million (5,455.26 MT) worth of live eels is also home to five of the only 16 eel species in the exported in 2013 (Business Mirror, February 24, 2015). world, namely, Anguilla marmorata (Giant Mottled Eel), Despite this, the BFAR expects demand for Philippine live Anguilla bicolor pacifica (Indian Short-finned Eel), Anguilla eels to remain high. luzonensis (Luzon Mottled Eel), Anguilla celebesensis Watanabe and Miller (2012) comprehensively (Celebes Long-finned Eel) and the Anguilla japonica describe the species, geographic distribution, habitat, (Japanese eel) (Ame et al.., 2013). and conservation of freshwater eels. Freshwater eels of From an economic standpoint, eels have a huge the genus Anguilla are widely distributed throughout global market with a good export price of $15,000 in the many parts of the world and consist of 16 species. European market in 2010 (Crook, 2014). For this reason, Three of the species are divided into separate subspecies many people and entrepreneurs are into catching and that have different morphological characteristics and trading Anguilla along major tributaries in the Cagayan geographic ranges. The morphology of all anguillids is River from Lal-lo to Gonzaga in Cagayan. The major generally similar, but is divided into four groups based BU R&D Journal, Vol. 24, July 2021 ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: Implications for Management and Conservation journal.bicol-u.edu.ph on taxonomic differences in terms of body markings, anguillid species, particularly larval transport and glass maxillary bands of teeth, the position of the dorsal fin, eel recruitment. The major threat facing all freshwater and the number of vertebrae. Five are temperate and eel species in the Philippines is the growing exploitation 11 tropical but all are catadromous with their offshore and associated illegal trade of glass eels for aquaculture spawning areas located at tropical latitudes. programs in East Asian farms. Fishing for glass eels has been driven by market value resulting in relatively high Anguillid species vary in maximum body size and in levels of exploitation. Without hard evidence on the the sizes of their species ranges, with A. marmorata being population dynamics of eel, it is difficult to quantify the one of the largest species with the widest geographic influence of these threats to the species as a whole. distribution, while species such as A. borneensis and A. dieffenbachii have restricted geographic distributions. The rivers and tributaries along Lagonoy Gulf (LG) Some species have single spawning areas and panmictic in Eastern Philippines is a potential freshwater settlement spawning populations, but others have multiple area for migrating eels because its location receives water populations, such as A. marmorata, which is present from the Pacific Ocean through the North Equatorial in three different ocean basins. Anguilla japonica is a Current (NEC) and Kuroshio Current that transport temperate catadromous species mainly distributed in larvae from the major spawning grounds of tropical eels Taiwan, China, Korea and Japan; mature males spawn in the western waters of the Mariana Islands. This project in the western waters of the West Mariana Ridge explored the fishery for catadromous freshwater eel (Tsukamoto, 1992; Han et al., 2012). After hatching, the resources along tributaries and rivers in LG with the hope larvae passively drift from the spawning ground by way of managing the stock and enhancing the livelihood of the of the North Equatorial Current (NEC) and the Kuroshio people depending on the fishery. Without science-based at depths typically between 50 and 150 m from 4-6 information, the threat of overexploitation, illegal trade, months before reaching the East Asian coast (Han et al., recruitment and migration, and climate change cannot be 2012). The larvae then metamorphose to glass eel and adequately addressed. It also provides a comprehensive adopt sheltering behavior to escape from oceanic current, account of the eel fishery in LG. This consists of the and actively swim toward the nearby estuaries and rivers potential migration and settlement areas of the eels, the for growth (Tesch, 2003). All anguillid species enter species composition of eels found, the collection gears freshwater for their juvenile growth period, but many used, the post-harvest practices, including the marketing remain in estuaries, brackishwater lakes or lagoons and and trade. The general aim was to describe the full range some may not enter freshwater. In freshwater, anguillids of activities of the eel fishery and to explore the economic live in rivers, streams and lakes, but the degree of use of benefits within sustainable levels. different habitats ranging from small streams far inland to the estuary appears to vary among species. Some eels The project’s primary goal was to generate even switch between habitats, moving back downstream science-based information as input in the formulation to the estuary to complete their juvenile growth period. management and conservation strategies supportive Their unique catadromous life history has made them to the economic potentials and sustainability of the eel vulnerable to the effects of dams that block their fishery in the tributaries and rivers along Lagonoy Gulf. migrations, pollutants, parasites, viruses and overfishing. Specifically, it sought to: (1) identify eel fishing grounds in Changes in conditions in the ocean also influence their tributaries along LG; (2) determine species composition recruitment success in terms of their larval feeding or and abundance of eel caught; (3) determine eel catching transport success. Glass eels are best observed in areas gears and efficiency; (4) determine post-harvest handling closer to the spawning site and from offshore waters practices and (5) determine supply and value chain for which are less disturbed by environmental factors. eels from the study sites in LG. According to Han and colleagues (2016), glass eels hide in the seabed during the day and rise up to the surface at night. The arrival peaks occurred during all lunar periods Materials and Methods except the full moon period as in the case of A. marmorata or other eel species occurring in the Philippines due to Sampling Area. The study covers the provinces the influence of Kuroshio Current. bordering LG which include the provinces of Albay, Camarines Sur and Catanduanes (Figure 1). The As with many anguillid eels, there are threats during identification of sampling sites within the sampling the transitional phases of their life histories. Climate area was accomplished using snowballing technique in change plays a vital role in fluctuations of abundance in coordination with Municipal Agriculture’s Office (MAO)

68 BU R&D Journal, Vol. 24, July 2021 Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Implications for Management and Conservation journal.bicol-u.edu.ph of the concerned LGU, project partners such as Partido shown in Table 1. Sample collection was done at evening State University (ParSU), Catanduanes State University flood tide during the new moon phase. (CatSU) and relevant contacts (eel gatherers, fishers and traders) involved in eel fishery. The criterion used This coincides with the upstream migration of includes: the river or tributary’s connection to LG waters, glass eel (Arai, 2016). Glass eels were packed in a styro the existence of eel resources, and eel fishers including box with ice for subsequent species identification in the buyers in the site. As such, Comoun/Balza River in laboratory. Adult eels were identified based on coloration Malinao, Albay, Sabang-Lagonoy River in Camarines (with or without) and type of fins (long or short). All Sur, and Bato River in Catanduanes were the selected datasets were analyzed descriptively and data presented sampling sites for the study. in tabular or graphical format. The abundance of glass eel species for each province was expressed as the percentage Identification of Potential Eel Fishing Grounds. of a single species over the total number of eels collected The identification of potential eel fishing grounds made for each site. The difference in the abundance of each use of a similar approach as in the selection of sampling species across the three major fishing grounds was sites in the sampling area. Site validation and direct identified through ANOVA and Tukey’s Test at 0.05% observation of the existence of the eel fishery was also level of significance. conducted. Catching Gears and Efficiency. The inventory of To map out the location of the potential eel fishing eel fishing gears was collected from 37 key informants. grounds and the extent of the river system, the expert The interview guide focused on a series of questions service of a professional GIS preparer was outsourced such as the names of eel fishing gears owned, stage to prepare the GIS map showing the potential eel fishing of eels (glass eels or adult eels) and quantity caught, grounds as shown in Figure 2. other species and quantity caught, and time of fishing operation. The collected information was sorted and Species Composition and Abundance. Species classified based on the mode of gear operation or gear identification and abundance was accomplished by type (active or passive), gear description, and operation. collecting 300 glass eel samples per month using modified The catch composition by gear was derived from the fyke net across sampling areas and identified using catch information. Catch efficiency by gear was measured Caudal Cutaneous Pigmentation Method by Shirotori in terms of the number of individual species caught. and colleagues (2016) and Han and colleagues (2012) as Data validation was accomplished through Focus Group

Figure 1. Location map of Lagonoy Gulf, Philippines (13.25°-13.80°N,123.50°- 124.25°E) showing the areas bordering the Gulf and the sampling areas in Comun/Balza River in Malinao, Albay; Sabang-Lagonoy River in Camarines Sur, and Bato River in Catanduanes.

69 BU R&D Journal, Vol. 24, July 2021 ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: Implications for Management and Conservation journal.bicol-u.edu.ph

Table 1. The species identification chart for glass eel based on Shirotori annd colleagues (2016) and Han and colleagues (2012)

Species Caudal Pigmentation Description Illustration A. marmorata With caudal pigmentation but not touching the end/tip of the tail; inner pigmentation is scattered

A. bicolor pacifica With caudal pigmentation that extends to the tip/end of the tail

A. japonica No caudal pigmentation

A. luzonensis The same with A. marmorata, however, inner pigmentation are rigid and not scattered

Discussion (FGD). presentation of policy recommendations relative to the management and conservation strategies supportive Post-Harvest Handling Practices. Data on the of the economic potentials and sustainability of the eel post-harvest handling of glass eels accomplished through fishery. KI interview of 30 glass eel fishers and 5 eel traders. Information on eel post-harvest handling practices during collection, after collection, upon landing, during conditioning, during packaging, and during transport Table 2. Identified Potential Eel Fishing Grounds by was collected. Data validation was accomplished through Province along Lagonoy Gulf FGD. Data collected was sorted and analyzed descriptively and translated into graphs and tables. Province Municipality Fishing Ground Supply and Value Chain. Datasets for supply and Camarines Sagñay Sagñay River value chain were collected similar to the methods used Sur San Jose Sabang-Lagonoy in gear inventory and post-harvest handling practices. A River1 total of 128 key informants participated, consisting of 30 Lagonoy Lagonoy River glass eel collectors, 93 adult eel fishers, and 5 eel traders. Presentacion Pili River The key informant’s actual involvement in the fishery and their knowledge about eel resources, the fishery and Albay Malinao Comun/Balza River2 marketing well justify their participation. The questions posted include the volume of harvest both during peak Tiwi Taki River and lean season, the price during peak and lean season, Malilipot Malilipot River and the expenses incurred during peak and lean season. Bacacay Bacacay River On the other hand, questions for the traders include the Sto. Domingo Maangot River quantity traded during peak and lean season, the price during peak and lean season, and the expenses incurred Catanduanes Virac Pajo River during peak and lean season. Data generated was sorted San Andres Mayngaway River and analyzed descriptively and presented in tabular 3 format. Bato Bato River San Miguel Bato River Other Activities. Eel fora participated in by Panganiban Panganiban River key LGU officials, ParSU, CatSU, fishers and traders’ 1 2 3 informants and other stakeholders were conducted in Sampling site in Camarines Sur; Albay and Catanduanes Albay, Camarines Sur and Catanduanes to disseminate study output and validate information including the

70 BU R&D Journal, Vol. 24, July 2021 Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Implications for Management and Conservation journal.bicol-u.edu.ph

Results and Discussion

Potential Eel Migration and Fishing Sites

Thirteen potential eel migration and settlement sites (Table 2) were identified. River deltas are the usual glass eel collection sites while the upstream portion of the river is the fishing ground for adult eels. This is expected because catadromous eels migrate to freshwater bodies to spend their adult life. In Taiwan, the entire shoreline A is used for glass eel collection using fry dozer attached to a specifically designed motorized flatboat (Figure 3) compared to the usual mouth of the river as fishing ground for glass eels in the Cagayan River including in rivers in LG.

The Geographic Information Systems (GIS) maps showing the potential eel collection and fishing grounds in Albay, Camarines Sur and Catanduanes are shown in Figures 2A-C. In Albay (Figure 2A), migration path originates from the Pacific through the influence of NEC and Kuroshio Current that enters the gulf from Maqueda Channel and between Catanduanes and Rapu- Rapu Island. Migrating eels can settle into inland bodies of water via three major rivers which include Comun/ B Balza River in Malinao, Malilipot River in Malilipot, and Bacacay River in the municipality of Bacacay.

In Camarines Sur (Figure 2B), the nearest entry point is Maqueda Channel via Sabang-Lagonoy River in the municipalities of San Jose and Lagonoy. An annual inundation in this river during the rainy season allows better eel dispersion and food availability. In addition, Sagñay River in Sagñay and Pili River in Presentacion are also known eel fishing areas and settlement sites for species with faster metamorphosis because of its direct access to Lagonoy Gulf. C

In Catanduanes (Figure 2C), the river system is most advantageous for migrating eel seeking to settle in freshwater habitat being close to the Pacific Ocean where the known tropical eel spawning ground in the western waters of Marianas is located. Hence, the higher probability for migrating eels to settle in their rivers and tributaries. In addition, oceanic migration is also influenced by the NEC and Kuroshio Current since both Figure 2. (A) GIS map of potential eel collection and current moves closer to the island. It should be noted fishing grounds in Albay; (B) GIS map of potential eel that the entry points of glass eels and elvers as well as collection and fishing grounds in Camarines Sur; (C) GIS the exit point of silver (mature) eels are very accessible to map of potential eel collection and fishing grounds in the seas and ocean waters, as shown in Figure 2C. Aside Catanduanes from Bato and Panganiban rivers, Pajo River in Virac and Mayngaway and Mayngaway River in San Andres also contribute to the eel population.

71 BU R&D Journal, Vol. 24, July 2021 ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: Implications for Management and Conservation journal.bicol-u.edu.ph

Table 3. Species identified from samples collected in rivers along the gulf using caudal pigmentation

Species Composition (%) Species Albay Cam Sur Cat LG A. marmorata 87.50 82.30 99.70 89.80 A. bicolor pacifica 12.40 17.50 0.30 10.10 A. japonica 0.10 0.30 0.00 0.10

Figure 3. Motorized flatboat equipped with fry-dozer for glass eel collection in Taiwan contention was supported by the study of Ahmad and Lim (2006) in Peninsular Malaysia, where A. bengalensis bengalensis was misidentified as tropical mottled eel (A. The value of GIS map can be gleaned from the marmorata). After reexamination of a number of key perspective of locating the potential sites for eel resources characteristics of the preserved specimen, it turned out and the extent of eel dispersion in freshwater settlement as A. bengalensis bengalensis (Arai, 2014). The species areas along Lagonoy Gulf. While the above-mentioned misidentification was attributed to insufficient data rivers are potential eel habitats, the evaluation of the from analysis using morphological characteristics, thus, biological integrity of these rivers that determines the supporting the contention of Watanabe and colleagues diversity and abundance of the many aquatic species, (2005) that identification of eels at the species level including catadromous eels, is beyond the scope of the using solely visual observation is difficult because study. of their similarities and overlapping morphological characteristics (Ege, 1939; Arai, 2016). Hence, molecular It is also common knowledge that various natural identification was found suitable for precise species and human-induced perturbations are present in many identification (Sugeha et al., 2008) despite the need for areas bordering Lagonoy Gulf. In Albay, rivers are a large number of samples to clarify genetic variations frequently threatened by volcanic eruptions and flash among and within species to be able to identify each of floods, which practically damage the river ecosystem the specimens at the species level (Watanabe et al., 2005). and morphology. Informal settlers along riverbanks Therefore, a combination of morphological and molecular contribute domestic waste and sewerage resulting in techniques is crucial in species identification. aquatic pollution, while road development alters the eel habitat. Similarly, rivers and tributaries are also The distribution of eel species by province is shown threatened by agricultural development, flooding and in Figures 4, 5 and 6. The wide distribution of A. marmorata domestic pollution, particularly in built-up areas close to is evident in all provinces all year-round. A. bicolor pacifica these rivers. is also found across provinces in smaller numbers (Table 3) with peaks noted in August and November for Albay Species and Composition and Camarines Sur, respectively. In Catanduanes, A. bicolor pacifica was noted only in October and December. Collected glass eel samples subjected to caudal Meanwhile, A. japonica was found only in November in cutaneous pigmentations methods (Han et al., 2012) Camarines Sur and Albay. The differences in seasonal resulted to 89.80% A. marmorata (Giant Mottled Eel), occurrence across sites can be explained by the fact that 10.10% A. bicolor pacifica (Indian Short-finned Eel) and while eel species may share the same spawning ground in 0.10% A. japonica (Japanese eel) species composition the NEC to the west of Mariana Island (Han et al., 2012; (Table 3). However, analysis of variance in terms of A. Kuroki et al., 2012; Han et al., 2016), their distribution marmorata occurrence by province showed no significant and spawning vary (Han et al., 2012; Han et al., 2016) difference (p>0.05). depending on the season or months. Moreover, Arai It should be noted that identifying these species and colleagues (1999), Schmidt (1925) and Tsukamoto (1992) reported that the duration of oceanic migrations at the glass eel level is complex (Yoshinaga et al., 2014). Watanabe and colleagues (2005), mentioned that not of tropical eels seems to be related to the distance and all morphological differences are accurate measures of complexity of the oceanic current system between the species distinction due to overlapping distribution. This spawning ground and the river habitats.

72 BU R&D Journal, Vol. 24, July 2021 Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Implications for Management and Conservation journal.bicol-u.edu.ph

The common sizes of glass eels are: 4.1 cm to 7.0 cm in length and weight ranging from 0.05 g to 0.21 g. The number of individuals per kilogram glass eels is about 4,000 to 6,000 individuals. The length of the glass eel varies by province—in Camarines Sur, are slightly longer (5.2cm - 7.0 cm) than those lengths in Albay (5.3 - 6.7), while shorter (4.1 - 5.1 cm) in Catanduanes in the same collection time. Samples of glass eels from Comun/Balza River are shown in Figure 7.

Figure 7. Glass eels caught from Modified Fyke Net in Comun/Balza River

marmorata across sampling areas in LG is similar to the abundance and distribution pattern of freshwater eels with abundance index of 96.62% for A. marmorata and 3.26% for A. bicolor pacifica in Pangi River, Maitum, Species composition and distribution in Albay Figure 4. Sarangani Province, reported by Valdez and Castillo (2016). The widespread species distribution of A. marmorata throughout the Philippine archipelago was also noted by van Herwaarden (2003), Aoyama and colleagues (2015), Shirotori and colleagues (2016), and the Inland Fishery Resources Development and Management Department. This could be attributed to the faster-growing leptocephalus at metamorphosis which determines the dispersal range of eel and therefore must be able to settle in the nearest freshwater environment Figure 5. Species composition and distribution in for their early growth phase (Cheng & Tzeng, 1996; Camarines Sur Tzeng, 2010). Anguilla bicolor pacifica constitutes the second important species in LG. It occurred in all provinces in smaller percentages, with Catanduanes having significantly the lowest compared with Albay and Camarines Sur. Meanwhile, a significant difference in the number of A. bicolor pacifica was revealed by ANOVA (p<0.05). Tukey’s Test uncovered that there is a significant difference between the number of A. bicolor pacifica in Catanduanes against Albay and Camarines Sur. On the other hand, A. bicolor pacifica from Camarines Sur against Figure 6. Species composition and distribution in Albay shows no significant difference (p>0.05). Catanduanes van Herwaarden (2003) noted that A. bicolor pacifica inhabits the southern part of Luzon, the Visayas This finding is in agreement with the reported total and Mindanao. The occurrence of A. bicolor bicolor in length of tropical eel of larvae rarely exceeding 60 mm (6.0 Philippine waters is sympatric with A. bicolor pacifica and cm) TL, and often smaller than 50 mm (5.0) TL (Jespersen A. marmorata was reported by Jamandre and colleagues 1942; Marui et al., 2001; Arai et al., 2001; Aoyama, 2003; (2007). To distinguish one from the other, Aoyama and co- Kuroki et al., 2006). workers (2007), Arai and co-workers (1999) and Aoyama and colleagues (1999) hypothesized that A. bicolor bicolor The noted wide occurrence and abundance of A.

73 BU R&D Journal, Vol. 24, July 2021 ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: Implications for Management and Conservation journal.bicol-u.edu.ph may spawn in the Indian Ocean and A. bicolor pacifica is necessary. In some areas, it is used together with tuba may spawn in the Pacific Ocean from eastern Indonesian or tubli to ensure catch. A variant of the spear gun is the clade. spear locally known as Piltik (Figure 7C). The gear is operated by an individual using a spear with two or more The occurrence of A. japonica in LG, although with prongs (1m in height). The basic components are prong, rarity, may require molecular technique for precise species rubber and bamboo with flashlight as accessory for night identification (Sugeha et al., 2008). It should be noted operation. Prongs used in spears are made of iron nails or that the species is known to have longer metamorphosis, pointed metal rods. The operation is similar to spear guns so they will migrate further and settle much later in but normally used in shallow water areas. Push net locally freshwater habitat than those with faster metamorphosis known as sudsod, is a gear that measures 1.0 m (H) x 1.15 which need freshwater environment early on (Cheng & m (W), with different shapes (circular & rectangular), sizes Tzeng, 1996; Tzeng, 2010). In this regard, a combination and materials, and generally made of split bamboo and of morphological and molecular techniques is crucial steel bar (Figure 7D). Normally, operation is done during for precise species identification. It should be noted that daytime in shallow waters or even turbid waters. Thus, A. japonica is valued most for its popularity and price it disturbs infaunal and infloral community in riverbeds. as an aquaculture species as it performs better in terms Electro-fishing gear is made from assembled battery of growth and survival rates (Nielsen & Prouzet, 2008). packs containing high voltage current used to electrocute Historically, Asian eel farms in mainland China, Japan, fishes (Figure 7E). It consists of a battery, wire, metal, bag/ Korea and Taiwan used A. japonica glass eels. However, box, scope net, and bamboo or pipe. The gear is illegal and the declines in A. japonica recruitment, combined with destructive to all aquatic organisms within the radius of the apparently cheap and abundant supplies of other electrical field. species, caused a change in sourcing over the last decades. The declining population of the annual recruitment Passive gears are usually in the form of traps and of A. japonica glass eels led Japanese farms to look for pots made mainly from local materials such as bamboo, alternative species for importation from the late 1960s vines, and synthetic netting materials. These gears are (Tsunogai, 1997). Nevertheless, A. japonica still remains generally fixed in place and rely on the migrating target the preferred species for consumption in Japan (Crook, species to enter the gear designed with easy entrance and 2014). Alarmingly, this species is currently listed under difficult exit. The modified fyke net (MFN) known locally endangered species on the IUCN Red List for Threatened as Kubong, is the main collecting gear for glass eel made species due to concerns that a variety of threats, including of fine mesh-net (Figure 7-F). It has two 8 m long wings overexploitation, are causing decline in natural stocks 1.15 m (H), 10 m (L) with a 2.5 m catching bag and at least (Jacoby & Gollock, 2014; Jacoby et al., 2014). 7 bamboo poles as support. They are set in two ways— stationary and by dragging. Normally, this collecting gear Eel Catching Gears and Efficiencies is operated by two to three fishers during the evening high tide for about two to three hours during the new Gear Types. Eel fishing gears, consisting of active moon and first quarter. The same observation was and passive gears, are usually made from traditional (i.e. reported by Valdez and Castillo (2016) that freshwater bamboo and rattan) and modern netting materials. In eels are more abundant during the new moon phase than addition, extracts from ichthyotoxic or poisonous plants the full moon phase. This is because, freshwater eels are are used with the fishing gears. Active gears are designed more seen during dark hours such as the new moon. In to chase and capture target and non-target species singly addition, glass eels prefer to migrate during those times, or in combination with bait or ichthyotoxic plants. These suggesting that the lunar phase has a strong effect on the include spear, spear gun, push net, and electro-fishing inshore migration mechanism of glass eels at the river gear. mouth.

Hook and line (Banwit), consists of a combination Scoop net is used to collect trapped glass eels in the of lines and hook (with single or multiple hooks) with catching bag or funnel. Rock Mounds (locally Patambak natural baits (Figure 7A). The hook size determines the or Hilay in Albay; Gango in Cam Sur) is an aggregating size of the catch. Spear gun (Pana) is designed to launch device that makes use of stone piles with a net flooring a spear at a fish, powered by the rubber (Figure 7B). The (Figure 7G). Rock mound is usually 0.5 to 1.3m high basic components are spear (75-80 cm), a stock or barrel depending on the water depth at lowest tide. This is set in and a handle or grip containing a trigger mechanism. the morning in a shallow-stony water area and harvested For a successful catch, the identification of eel burrow the next day or after a week by raising the four tips of

74 BU R&D Journal, Vol. 24, July 2021 Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Implications for Management and Conservation journal.bicol-u.edu.ph the net flooring and the stone removed slowly to gather bag net, push net, and dip net B-gillnet (Philippines) the fish into the net. Fish traps (Bubo), occur in different (Siriraksophon , 2014). shapes and sizes. It is made of split bamboo separated by narrow interspaces braided together by the strands of Ichthyotoxic plants are toxic to fish; examples of cane (Figure 7H). Traps may have single or multi-opening, commonly used plant species are “Tuba-tuba” (Jatropha with inwardly projecting bamboo splits permitting curcas), “Tubli” (Derris spp.), and “Bayati” (Anamirta entry of fish without any means to escape. These traps cocculus Linn.). Plant extracts from ichthyotoxic plants are placed underwater with or without baits. Normally, (i.e. rotenone and curcin) and other substances that are this is set in place at night and harvested the following applied raw or processed, that can kill, stupefy, disable morning. Variation of the trap is a bamboo filter trap fish and other aquatic animals are commonly used for locally known as Ansag, an indigenous trap built for fishing. The fruit, roots or stem is mashed and the extract volume fishing (Figure 7I). This trap is designed to take is applied in an area in the water to stupefy fish for easy advantage of the high water level during the rainy season. catching. Although fishes are killed with the poison, they The trap catches various fish species filtered into the are not poisonous when consumed by humans. In some traditional and intricate structure that allows the fishers countries, stupefying the fish by ichthyotoxic plants is a to conveniently wait for fish to arrive and be handpicked. tribal practice (Ravikumar et al., 2015). However, using this method of harvesting is also strictly prohibited These findings are consistent with the survey in some countries because of damaging consequences conducted by SEAFDEC in January 2014 that indicated of its use to the fish and the ecosystem. In LG, the use that the most common gears used to catch Anguilla spp. of ichthyotoxic plants may have been the cause of the in the Southeast Asian countries are: traps (Indonesia, deterioration of the biological integrity of many rivers Myanmar, Philippines, Thailand); scoop net (Indonesia); and tributaries. hook-and-line (Indonesia, Philippines); fyke net,

Figure 7. Different types of gear. A - Hook and Line (banwit), B - Spear gun (pana), C - Spear (piltik), D - Push net (sudsod), E - Electro-fishing gear, F - Modified fyke net (kubong), G - Earth mounds (patambak/hilay), H - Bamboo traps (bubo), I - Bamboo filter trap (ansag)

75 BU R&D Journal, Vol. 24, July 2021 ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: Implications for Management and Conservation journal.bicol-u.edu.ph

Catch Composition. Result obtained on glass eel gathering showed that modified fyke net is the main collecting gear used for catching 81.5% of glass eels. The remaining percentage consists of by-catch and discards such as milkfish (9.18%), shrimp (5.88%), crescent perch (1.93%), pipefish (0.73%), freshwater crab (0.43%) and swamp eel (0.34%). Since the fishery is new in that study area, no production record is available, making it difficult to determine facts and figures about the fishery for management and conservation purposes. The issue of by- Catch Efficiency by Gear Type catch and discards is also alarming since it contributes to Figure 11. the decline of non-target species and the shifts in species dominance and the occupation of certain ecological Post-harvest Handling Practices niches can be partly due to discarding (Alverson et al., 1994). In the production of quality seed stock like glass eel, Table 4 presents the catch composition by gear types post-harvest handling is critically important. Normally, for adult eel harvesting obtained from KI interview. collection is done at evening flood tide during the new Among the gears, electro-fishing had the most number moon which coincides with the upstream migration of of species (16 species) and most number of individuals glass eel (Arai, 2016). The post-harvest handling flow caught (3,107), indicative of its destructive potential. It chart is shown in Figure 8. From collection, the larvae are should be noted that electric gears are prohibited under handled with care to prevent physical damage and stress. Republic Act 8550 as amended by RA 10654 not only Once landed, they go through a series of steps before because of its destructive effect to aquatic resources but delivery to the next market chain; only active glass eels also to users. Other fishing gear registering better harvest are acceptable in the market. by species and volume are in the order of push net, spear, Temperature is maintained at 26-29°C to avoid spear gun, traps, and hook and line. mortalities (Nielsen & Prouzet, 2008) and limit weight loss and pigmentation, which are important indicators Catch Efficiency. For glass eel collection, modified fyke net is the most efficient gear but its operation is of quality and market preference. It should be noted that limited to a specific lunar cycle which coincides with the transparent glass eels are preferred than dark pigmented glass eel migration. On the other hand, for gears designed ones (Nielsen & Prouzet, 2008). Conditioning prior to to catch adult eels, the catch efficiency measured by the transport includes a 24-hour starvation and reducing number of individuals caught regardless of species per water temperature to reduce stress during a long distance gear showed that electro-fishing gear is the most efficient transport. Baliao and colleagues (1998) reported that (Figure 19). The least efficient is hook and line and traps. reduction of water temperature to less than 5°C/hr in However, in terms of catching target species (eels), traps the holding tanks of grouper fry prior to transport down and pots were more efficient (25.09%), followed by hook to 18°C, prevent temperature shock and stress during and line (24.18%) and spear gun (10.89%). This could be transport. After the pre-conditioning period, sorting and attributed to the selective gear design resulting in better culling of glass eels is done to remove weak or wounded and bigger catch. By design, traps are actually constructed glass eels. If unsold after harvest, gatherers keep them for to catch bigger fish, while for hook and line, the size of about two to four days or more depending on the glass the hook determines the size of the catch. Spear gun eels’ condition, market prices and transport availability on the other hand, is generally selective by operation (Nielsen & Prouzet, 2008). and is expected to capture bigger fish. According to These post-harvest handling practices evolved from Holden (1991), the efficiency of the local fishers could the techniques and experiences of milkfish (Chanos chanos) be improved by the introduction of a few selected types fry industry and from those introduced by consolidators of gears; unfortunately many of these materials also and other buyers outside the region. Some traditional compete with modern gears when used in the same type knowledge is also incorporated (i.e. salinity shocking of water bodies. and use of clay pot). Being a potential aquaculture species and export commodity of economic importance, further improvement on post-harvest handling is recommended.

76 BU R&D Journal, Vol. 24, July 2021 Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Implications for Management and Conservation journal.bicol-u.edu.ph

Table 4. Catch Composition by Gear Type used for Adult Eels

Push Net Trap/Pot Electro-fishing Hook & line Spear gun Spear Species Comp. F* % F* % F* % F* % F* % F* % Brackish water shrimp - - - - 406 13.07 - - - - 231 15.90 FW Crab 83 7.66 65 11.25 137 4.41 ------FW Prawn 108 9.96 44 7.61 512 16.48 - - - - 408 28.00 FW shrimp 60 5.54 - - 213 6.86 ------Crescent Perch ------103 12.75 - - Adult Eel 71 6.55 145 25.09 199 6.40 103 24.18 88 10.89 67 4.60 Swamp eel 47 4.34 34 5.88 138 4.44 15 3.52 77 9.53 62 4.26 Loach goby 68 6.27 - - 196 6.31 ------Broad head sleeper - - - - 223 7.18 - - - - 124 8.51 Round goby 19 1.75 - - 221 7.11 - - - - 246 16.90 Tilapia 157 14.50 120 20.76 442 14.23 160 37.56 168 20.79 98 6.73 Carp 13 1.20 61 10.55 89 2.86 66 15.49 99 12.25 37 2.54 Mosquito fish 98 9.04 ------Mudfish 11 1.01 50 8.65 65 2.09 32 7.51 78 9.65 24 1.65 Catfish 4 0.37 25 4.33 53 1.71 21 4.93 37 4.58 48 3.29 Climbing perch 31 2.86 12 2.08 72 2.32 8 1.88 111 13.74 83 5.7 Gourami 12 1.11 - - 93 2.99 ------Trumpet snail 133 12.30 ------Nerite snail 169 15.60 ------Snake turtle - - 22 3.81 48 1.54 21 4.93 47 5.82 29 1.99 Total 1084 100 578 100 3107 100 426 100 808 100 1457 100 *F= frequency count

Figure 8. Post-harvest handling practices flow chart

77 BU R&D Journal, Vol. 24, July 2021 ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: Implications for Management and Conservation journal.bicol-u.edu.ph

Supply and Value Chain Analysis of the Eel Fishery Glass eels are sold to traders outside the province, while adult eels are sold domestically for food. The supply The eel fishery in the LG revolves around the unique chain is relatively short and can only be traced from biology and abundance of the resource. The abundance of eel fishers and collectors. Eel glass collectors spend an eel is dependent on the supply of migrating larvae from average of ₱ 866-₱ 1,049 in fishing operations and earn the wild, natural as well as fishing mortalities in addition net revenue ranging from ₱2,783-₱11,718 during lean to natural processes. Current available information and peak months, respectively. Meanwhile, traders spend on eel fishery does not reveal a clear status and trend. a monthly average of ₱949.30 to ₱6,419.30. They may There are few players participating in the business of eel have a net loss of ₱1,155 or earn a net monthly benefit of fishery. Of the 128 key players identified, 30 are glass ₱36,851. Likewise, the adult eel fishers’ average monthly eel collectors, 93 are adult eel fishers and only five are expenses ranges from ₱230-₱424 with a net loss of ₱ 165 traders. The number of active glass eel gatherers appears and a net benefit of ₱6,256. to increase proportionately with the increasing catch and presence of buyers. Given the benefits and incentives derived from the eel fishery annually, there is a need to develop policies Seeds stock collection is mainly from modified fyke and strategies that will ensure the conservation and nets with six operations per year with a mean harvest of management of eels as a resource while maximizing the 1.0-4.0 kg/trip during peak months and 0.5-1.0 kg/trip economic potential. during lean months. Comparatively, in Cagayan River, the mean annual glass eel catch per fishermen ranged from 2.7 kg in 2009 to 15.2 kg in 2012 and is expected to Conclusion and Recommendations increase to as much as 10‐29 kg per gatherer (Ame et al., 2013). This could be because eel gatherers in the study The eel fishery in LG revolves around A. marmorata, area are totally new to the industry. In addition, glass eel A. bicolor pacifica in addition to the rare occurrence of A. collection is also restricted under Fisheries Administrative japonica. The dispersal and distribution of these species are Order No. 242 that prescribes a size limit of 15 cm for determined by the rate of leptocephalus metamorphosis eels designated for export to prevent a possible collapse and the influence of the NEC and Kuroshio Current that in the wild population due to indiscriminate gathering, facilitate its dispersion. A total of 10 types of collecting resulting in the reduction of the volume of export. gears were identified in addition to three ichthyotoxic plants. Glass eel is mainly collected using modified fyke Glass eel prices range from ₱2,000 to ₱10,000 net coinciding with the eel migration at the evening tide per kg during peak and lean months, respectively. The during the new moon to last quarter phase of the moon estimated production and value of traded glass eels and for two to three hours fishing operation. Adult eels are adult eels during peak and lean seasons across provinces exploited mainly for food using traditional fishing gears. is presented in Table 5. On the basis of traded value, the glass eel fishery in LG is worth ₱9.40-12.69M at a price Post-harvest handling practices evolved from range of ₱ 2,000-10,000 per kg. This translates to an practices in the milkfish fry industry. No record of annual estimated annual income of ₱313,800-423,000 per glass production statistics is available that indicate trends and eel collectors in the study area. status of the fishery. The hidden supply and value chain is characterized by limited players, a short supply chain, and On the other hand, the annual adult eel production unstable market. It is therefore imperative that policies from hook and line, traps and pots, spear gun including the and strategies that enhance and maximize the economic illegal electro-fishing gear is estimated at 81,358-325,541 potential of the eel resources must be developed along with kg valued at ₱6.64M-23.35M annually at ₱210-₱ kg development of sustainable management interventions (Table 5). The estimated catch is about 4-7 kg/trip during to sustain the fishery. To achieve this, the following peak months, and 0.07-2.0 kg/trip during lean months. policy recommendations is hereby suggested: (1) massive Adult eel fishers make 4 to 12 maximum operations IEC campaign together with strict law enforcement of during peak months, and one to six operations during fisheries and environmental law; (2) further study using lean months. No recorded annual production statistics Polymerase Chain Reaction–Restriction Fragment is available that show catch per unit effort (CPUE) as an Length Polymorphism; (3) verification studies along indicator of abundance. post-harvest technology and collecting gears for glass eels to improve catch efficiency and minimize by-catch; Marketing of eels in general is an unstable market (4) test fishing along the shoreline for glass eel; (5) and dependent on the season and availability of buyers.

78 Table 5. Estimated Monthly and Annual and Value of Traded Glass Eel and Adult Eel across provinces

Price Per Kilo Production per month (kg) Annual Production (kg) Value Traded Monthly Value Traded Annually Stakeholder/ Province Peak Lean Peak Lean Peak Lean Peak Lean Peak Lean Glass Eel Collectors Cam Sur 2,000 10,000 720 180 4,320 1,080 1,440,000 1,800,000 8,640,000 10,800,000 Albay 3,500 6,500 18 18 108 108 63,000 117,000 378,000 702,000 Catanduanes 2,000 6,000 33 33 198 198 66,000 198,000 396,000 1,188,000 Grand Total 771 231 4,626 1,386 1,569,000 2,115,000 9,414,000 12,690,000 Adult Eel Fishers Cam Sur 240 320 1,395.3 109.8 3,953 1,098 83,715 8,784 837,150 87,840 Albay 210 240 11,930 2,868 310,010 80,260 835,100 2,229,440 21,700,700 6,420,800 Catanduanes 280 320 1,157.80 160.95 11,578 1,,609.5 81,046 12,876 810,460 128,760 Grand Total 14,483.1 3138.8 325,541 81,358 918,815 251,100 23,348,310 6,637,400 BU R&D Journal, Vol. 24, July 2021 ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: Implications for Management and Conservation journal.bicol-u.edu.ph exploring the development of value-added products for of Kuroshio Science, 7(1):41-48 adult eel; and (6) the development of nursery and grow- out technologies. Arai, T., Limbong, D., Otake, T., & Tsukamoto, K. (1999). Metamorphosis and inshore migration of tropical eels Anguilla spp. in the Indo-Pacific. Marine Ecology Progress Series, 182, 283-293. Acknowledgment Arai, T., Limbong, D., Otake, T., & Tsukamoto, K. (1999). Metamorphosis and inshore migration of tropical eels This project is funded by DOST-PCAARRD and Anguilla spp. in the Indo-Pacific. Marine Ecology Progress implemented by Bicol University Tabaco Campus, in Series, 182, 283-293. cooperation with the LGUs of Albay, Camarines Sur and Catanduanes, and Partido State University and Arai, T. (2014). First record of a tropical mottled eel, Anguilla Catanduanes State University. We also acknowledge bengalensis bengalensis (Actinopterygii: Anguillidae) from the cooperation of BFAR-5, the concerned LGUs’ the Langkawi Islands, Peninsular Malaysia, Malaysia. Agriculture and Fisheries staff, and all project participants Marine Biodiversity Records, 7, e38. and cooperators. Special acknowledgement is accorded to Arai, T. (2016). Biology and ecology of Anguillid eels. CRC Kochi University, Japan, and to Dr. Satoshi Kubota and Press, Taylor and Francis Group, LCC, page 297. Ms. Katrina L. Canon for their support in the training on basic molecular techniques. Arai, T. (2016). Taxonomy and distribution. Biology and ecology of anguillid eels, 1-20.

Baliao, D. D., De los Santos, M. A., Rodriguez, E. M., & Ticar, References R. B. (1998). Grouper culture in brackishwater ponds. Aquaculture Department, Southeast Asian Fisheries Ahmad, A., & Lim, K. K. P. (2006). Inland fishes recorded from Development Center. the Langkawi Islands, peninsular Malaysia. Malayan Nature Journal, 59(1), 103-120. Business Mirror, February 24, 2015. PHL’s live eel exports declined by 5.7 percent in 2014–BFAR. Aoyama, J., Mochioka, N., Otake, T., Ishikawa, S., Kawakami, Y., Castle, P., Nishida, M., & Tsukamoto, K. (1999). Cheng, P. W., & Tzeng, W. N. (1996). Timing of metamorphosis Distribution and dispersal of anguillid leptocephali in and estuarine arrival across the dispersal range of the the western Pacific Ocean revealed by molecular analysis. Japanese eel Anguilla japonica. Marine Ecology Progress Marine Ecology Progress Series, 188, 193-200. Series, 131, 87-96.

Aoyama, J., Wouthuyzen, S., Miller, M. J., Inagaki, T., & Crook, V. (2014). Slipping away: international Anguilla eel trade Tsukamoto, K. (2003). Short-distance spawning migration and the role of the Philippines. TRAFFIC and ZSL, UK, of tropical freshwater eels. The Biological Bulletin, 204(1), 1-54. 104-108. Ege, V. (1939). A revision of the genus Anguilla Shaw. Dana Rep, Aoyama, J., Wouthuyzen, S., Miller, M. J., Minegishi, Y., Kuroki, 16, 8-256. M., Suharti, S. R., Kawakami, T., Sumardiharga, O. & Fw, T. (2003). The eel. Blackwell Science, Oxford, England, Tsukamoto, K. (2007). Distribution of leptocephali of the 2993, 408. freshwater eels, genus Anguilla, in the waters off west Sumatra in the Indian Ocean. Environmental biology of Han, Y. S., Zhang, H., Tseng, Y. H., & Shen, M. L. (2012). Larval fishes, 80(4), 445-452. Japanese eel (Anguilla japonica) as sub‐surface current bio‐tracers on the East Asia continental shelf. Fisheries Aoyama, J., Yoshinaga, T., Shinoda, A., Shirotori, F., Yambot, Oceanography, 21(4), 281-290. A. V., & Han, Y. S. (2015). Seasonal Changes in Species Composition of Glass Eels of the Genus Anguilla (Teleostei: Han, Y. S., Lin, Y. F., Wu, C. R., Iizuka, Y., Castillo, T. R., Anguillidae) Recruiting to the Cagayan River, Luzon Yambot, I. U., Mamalangcap, M.D., & Yambot, A. V. (2016). Island, the Philippines1. Pacific Science, 69(2), 263-270. Biogeographic distribution of the eel Anguilla luzonensis: dependence upon larval duration and oceanic currents. Alverson, D. L., Freeberg, M. H., Murawski, S. A., & Pope, J. Marine Ecology Progress Series, 551, 227-238. G. (1994). A global assessment of fisheries bycatch and discards (Vol. 339). Food & Agriculture Org.. Jacoby, D. and Gollock, M. (2014). Anguilla bicolor, Anguilla celebesensis, Anguilla japonica, Anguilla luzonensis and Ame, E. C., Ayson, J. P., & Ame, R. B. (2013). Status of Elvers Anguilla marmorata. The IUCN Red List of Threatened Fisheries in Cagayan Province, Luzon, Philippines Journal Species. Version 2014.2: www.iucnredlist.org

80 BU R&D Journal, Vol. 24, July 2021 Nieves et al.: The Eel Fishery in Tributaries Along Lagonoy Gulf: ISSN (Print): 0016-4139 | ISSN (Online): 2719-082X Implications for Management and Conservation journal.bicol-u.edu.ph

Jacoby, D., Casselman, J., DeLucia, M., Hammerson G.A., & Research in Indonesia, 33(2), 129-138. Gollock, M. (2014). Anguilla rostrata. The IUCN Red List of Threatened Species. Version 2014.10: www.iucnredlist. Tsukamoto, K. (1992). Discovery of the spawning area for org. Japanese eel. Nature, 356(6372), 789-791.

Jamandre, B. W. D., Shen, K. N., Yambot, A. V., & Tzeng, W. N. Tsunogai, H. (1997). History of aquaculture and current (2007). Molecular phylogeny of Philippine freshwater eels situation. In: Lecture of fish culture 7 eel. Inaba S., Matsui Anguilla spp.(Actinopterygi: Anguilliformes: Anguillidae) I., Aoe H., Tunogai H. (eds), 9th edition, Midori-Shobo, inferred from mitochondrial DNA. The Raffles Bulletin of Tokyo, Japan, pp. 22-29. Zoology, 14, 51-59. Tzeng, W. (2010). Biology of Japanese eel Anguilla japonica: Jespersen, P. (1942). Indo-Pacific leptocephaids of the genus from larval dispersal to migratory life history Anguilla. Systematic and biological studies. Dana-Rep evolution. Proceedings of International Symposium on Carlsberg Found, 22, 1-128. Eel Culture and Trade: Sustainable Aquaculture and Marketing Prospects of Eels. PHILSCAT, Central Luzon Kuroki, M., Aoyama, J., Miller, M. J., Wouthuyzen, S., Arai, T., & State University Science City of Munoz, Nueva Ecija, Tsukamoto, K. (2006). Contrasting patterns of growth and Philippines. February 5, 2010. migration of tropical anguillid leptocephali in the western Pacific and Indonesian Seas. Marine Ecology Progress Valdez, A.S.M. & Castillo, T.R. (2016). Abundance and Series, 309, 233-246. Distribution of Freshwater Eels in Pangi R i v e r , Maitum, Sarangani Province. Journal of Aquaculture Kuroki, M., Miller, M. J., Aoyama, J., Watanabe, S., Yoshinaga, T., Research and Development, 7(2). & Tsukamoto, K. (2012). Offshore spawning for the newly discovered anguillid species Anguilla luzonensis (Teleostei: van Herwaarden, H.C.M. (2003). Eel culture in the Philippines. Anguillidae) in the Western North Pacific. Pacific Science, Aqua crop aquaculture consultancy service. 66(4), 497-507. Watanabe, S., Aoyama, J., Nishida, M., & Tsukamoto, K. (2005). Marui, M., Arai, T., Miller, M. J., Jellyman, D. J., & Tsukamoto, A molecular genetic evaluation of the taxonomy of eels K. (2001). Comparison of early life history between New of the genus Anguilla (Pisces: Anguilliformes). Bulletin of Zealand temperate eels and Pacific tropical eels revealed Marine Science, 76(3), 675-690. by otolith microstructure and microchemistry. Marine Ecology Progress Series, 213, 273-284. Watanabe, S. & Miller, M.J. (2012). Species, Geographic Distribution, Habitat and Conservation of Freshwater Nielsen, T., & Prouzet, P. (2008). Capture-based aquaculture of Eels, In book: Eels: Physiology, Habitat and Conservation, the wild European eel (Anguilla anguilla). Capture-based Chapter: Species, Geographic Distribution, Habitat and aquaculture. Global overview. FAO Fisheries Technical Conservation of Freshwater Eels, Editors: S. Nakashima, Paper, (508), 141-168. M. Fujimoto, pp.1-44.

Ravikumar, T., Dam-Roy, S., Krishnan, P., Sankaran, M., Yoshinaga, T., Aoyama, J., Shinoda, A., Watanabe, S., Azanza, & Sachithanandam, V. (2015). Traditional usages of R. V., & Tsukamoto, K. (2014). Occurrence and biological ichthyotoxic plant Barringtonia asiatica (L.) Kurz. by the characteristics of glass eels of the Japanese eel Anguilla Nicobari tribes. Journal of Marine and Island Cultures, japonica at the Cagayan River of Luzon Island, Philippines 4(2), 76-80. in 2009. Zoological Studies, 53(1), 1-6.

Schmidt, J. (1925). The breeding places of the eel. Ann. Report Smithonian Inst., 1924, 279-316.

Shirotori, F., Ishikawa, T., Tanaka, C., Aoyama, J., Shinoda, A., Yambot, A. V., & Yoshinaga, T. (2016). Species composition of anguillid glass eels recruited at southern Mindanao Island, the Philippines. Fisheries science, 82(6), 915-922.

Siriraksophon, S., Ayson, F. G., & Sulit, V. T. (2014). Potentials and prospects of Southeast Asian eel resources for sustainable fisheries and aquaculture development. Fish for the People, 12(2), 7-13.

Sugeha, H. Y., Suharti, S. R., Wouthuyzen, S., & Sumadhiharga, K. (2008). Biodiversity, distribution and abundance of the tropical anguillid eels in the Indonesian waters. Marine

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