Summary of thesis on doctor of Philosophy in Biology: Fish resources in ecosystems in coastal areas of Quang Nam-Da Nang

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Provide data on fishery resource exploitation status and their characteristics, and ecological – connectivity of important fishery resource, this is the basis for proposing fishery management solutions in the coastal of Quang Nam - Da Nang.

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Nội dung Text: Summary of thesis on doctor of Philosophy in Biology: Fish resources in ecosystems in coastal areas of Quang Nam-Da Nang

VIET NAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY ……..….***………… NGUYEN THI TUONG VI FISH RESOURCES IN ECOSYSTEMS IN COASTAL AREAS OF QUANG NAM – DA NANG PROVINCES Major: Hydrobiology Code: 62 42 01 08 SUMMARY OF THESIS ON DOCTOR OF PHILOSOPHY IN BIOLOGY NHA TRANG – 2017
The dissertation was completed at: - Institute of Oceanography – Viet Nam Academy of Science and Technology - Department of Science and Marine Technology – Graduate University of Science and Technology – Viet Nam Academy of Science and Technology Scientific Supervisors: 1. Assoc. Prof. Dr. Vo Si Tuan 2. Dr. Nguyen Van Long Institute of Oceanography – Viet Nam Academy of Science and Technology 1st Reviewer: Assoc. Prof. 2nd Reviewer: Assoc. Prof. 3rd Reviewer: Assoc. Prof. The thesis had been defended at: - Institute of Oceanography, No.01 Cau Da, Nha Trang City, Khanh Hoa Province - At hour , Date 201 The thesis can be found at: - General Sciences Library of Ho Chi Minh City - Library of Graduate University of Science and Technology – Viet Nam Academy of Science and Technology - Library of Institute of Oceanography – Viet Nam Academy of Science and Technology
1 INTRODUCTION 1. Preface Fisheries management policy is increasingly focused on protecting ecosystems and individual fish resource groups. The first idea of ecosystem-based fisheries management was mentioned in the Stockholm Declaration in 1972, but until 2003 the FAO officially published a publication dealing with the ecosystem approach in The Ecosystem Approach to Fisheries (EAF) or the Ecosystem-Based Fishery Management (EBFM). This is a new approach and effective way of management. One of the concepts put into use is the ecological - connectivity. Sheaves (2009) defines ecological - connectivity as the movement of organisms from one habitat to another by the seasonal to complete their life cycle. With an ecosystem-based fisheries management approach, understanding the ecological - connectivity of the important fish resource will enhance ecosystem management and, at the same time, emphasize that in a marine protected area It is necessarily includes many of the inhabitants. Vietnam coastal has the distribution of tropical ecosystems such as coral reefs, mangrove forests and seagrass beds. Like many other countries in the world, the deterioration of ecosystems and the deterioration of coastal resources have been occurring at fast pace in many places over the last few decades. This is due to overexploitation and lack of understanding of marine ecosystems as well as concern for immediate benefits without paying attention to long-term ecological consequences. There have been many studies of fisheries resources in coastal ecosystems as a basis for proposing management solutions, but studies often focus on the fishing industry structure, productivity, groups of main species and the change of resources under human impact. In recent years, there have been some marine areas that have applied ecosystem-based fishery management approaches such as Phu Quoc or some coastal habitats in the South China Sea, but this approach is still unexplored. There is still a lack of scientific basis, especially the data on ecological - connectivity . Therefore, many of the current fisheries management documents is only focus on the size of the fish, the size of the net or harvesting season. There are almost no clear,
2 specific rules for the protection of spawning, nurseries areas or habitats that play an important role in the life cycle of important species. The coastal areas of Quang Nam-Da Nang have a diversified distribution of typical marine ecosystems such as soft bottom, seagrass beds, coral reefs, estuaries and mangrove forests. These ecosystems are also under pressure from over-exploitation and exploitation by destructive fishing gears. The protection and management of coastal resources in the Quang Nam-Da Nang coastal zone has been difficult by the delimitation of marine management boundaries based only on geographic features, administrative, rather than ecological, biological features. Therefore, the study on fish resource characteristics and ecological-connectivity of important fishery resource in Quang Nam- Danang coastal is a solid scientific basis for proposing ecosystem- based management solutions. So we do the thesis: " Fish resources in ecosystems in coastal areas of Quang Nam-Da Nang." 2. The objectives of the thesis Provide data on fishery resource exploitation status and their characteristics, and ecological – connectivity of important fishery resource, this is the basis for proposing fishery management solutions in the coastal of Quang Nam - Da Nang. 3. The contents of the thesis 1 - Basic characteristics of ecosystems and fish resources. 2 - Analyze and compare fish resources characteristics among ecosystems. 3 - Ecological – connectivity of the orange-spotted spinefoot (Siganus guttatus) in coastal habitats. 4 - Analyze the impacts in fisheries management. 5 - Propose solutions for fishery management related to ecosystems. 4. The significance of the thesis To provide data on fish resources, propose solutions to improve the management effectition and utilization of fish resources in the coastal ecosystems of Quang Nam-Da nang. NEW FINDINGS OF THE THESIS 1. The thesis is considered to be the most comprehensive and complete analysis of ecosystem characteristics, species diversity and status of fish
3 resource exploitation related to ecosystems in coastal coastal Quang Nam- Danang. 2. Specifically, this is the first study to discover and examine the ecological connectivity of the orange-spotted spinefoot (Siganus guttatus) in different ecosystems through outlining the life cycle of the fish from juvenile to adult. Accordingly, the seed stock in the Thu Bon estuary and the adult species in the coral reefs of Da Nang and Cu Lao Cham belong to the same population.This is the scientific basis for proposing ecosystem- based solutions for fisheries management. 3. It is the first study to propose ecosystem-based solutions for fisheries management in the coastal areas of Quang Nam-Da Nang. CHAPTER 1: OVERVIEW 1.1. Fisheries studies in the world 1.1.1. Exploitation status Fisheries studies in the world mainly focus on the current status of fishing, including the following main directions: (1) Quantification of fish yield ( 2) Main resource species groups, (3) Fish biology (4) Fisheries management. In the above research directions, output statistics and stock estimation are one of the main fisheries research directions, conducted to assess the current status of marine fisheries exploitation in each area and from which make comparisons or forecasts, warn the world fisheries trends to ensure that resources are properly exploited. The methods commonly used in stockpiling are hydrodynamic methods, mesh-traction methods, capture fish yield conversion methods, or the method of establishing the relationship between yield and biological productivity. Beside the direction of research statistical yield, estimation of reserves and fluctuations of fish resources, research direction the main source species groups also receive the attention of many scientists. Studies on yield statistics, fish stocks estimates and fluctuations, and major resource groups are conducted to develop fisheries management policies so that appropriate harvesting can be ensured sustainable development. At present,
4 management is increasingly focused on protecting individual ecosystems and groups of fish resources. 1.1.2. Ecological-connectivity The idea of fishery management based on ecosystems appeared in 1972 but until 2003 the FAO officially published an ecosystem approach to fisheries management. One of the key sources of data for this approach is the understanding of the life cycle linkages of fisheries resource in the ecosystems. Research on the migration of life-spanning fish species related to coastal habitats such as coral reefs, seagrass beds and mangrove forests, is of great importance in finding the necessary habitat of fish. The role of coral reefs, seagrass beds and mangroves varies different each other in the every stage in their life cycle. Some species of fish involve reefs migrating to coastal breeding grounds, where they disperse eggs into water, usually at the outlet end of the reef (towards the sea) and then eggs and larvae float into the area. Water settled on seagrass beds, mangroves in mangroves. Research on ecological-connectivity between coral reefs and seagrass beds in the Karimunjawa Marine Reserve (Indonesia) (2012) shows that 66/212 fish species are divided into four ecological groups: seagrass, nursing fish, wide distribution fish and coral reef fish. Coral reef fish and nursing fish are found on coral reefs and there is a transition between coral reef habitats and seagrass beds. Wide distribution fish groups is high density from coral reef to seagrass beds. Honda et al. (2013) study the ecological linkages of fish species in coastal ecosystems in the Philippines from 2010 to 2012, showing that 85.6% of fish species use two habitats during their life cycle, some species many habitats such as Lutjanus monostigma or Parupeneus barberinus use all three coral reef habitats, seagrass beds and mangroves in their life cycles. In ecological - connectivity studies, population genetics is a common tool used to identify population linkages. In the last few decades, advances in molecular genetic research have had a significant impact on population genetics research, contributing to the problem of resource management. 1.2 Fish resource studies in Viet Nam Statistics of marine fisheries studies in Vietnam show that the following research directions are available:
5 - Find out the fishing area, determine the yield, stock and harvesting potential. - Distribution and fluctuation of fish in relation to some environmental characteristics, fluctuation in yield and composition of fish caught. - Biology of economic fish species and scientific basis for reasonable exploitation - Assess the status of fish resources under the influence of nature and people. - An integrated assessment of the resources, the situation of fishing in different marine areas and the list of fish species in Vietnam's. It can now be seen that most of the studies focus only on general assessments of resources, some of the resource studies, but most of them only list the species composition and some comments on the types of sources testimonials. Although a number of studies have been conducted for individual populations, these results are mainly focused on assessing the productivity and yield of small pelagic fish species in whole sea. The study of marine ecosystems in Vietnam is more interested in later studies than in the study of resources and has only been investigated since 1954. After recognizing the importance of ecosystems, especially coastal ecosystems such as mangrove forests, coral reefs and seagrass beds, studies on fish resources in ecosystems are also be interested. However, these studies mainly record the presence of a number of economic fish species, analyze the species diversity, recently began to refer to the exploitation status and assess the extent of decline resources and solutions for sustainable use have not yet been fully researched on fish stocks (main beneficiaries, yields, catch yields, harvest seasons, distribution, etc.) in ecosystems. Especially, to date, almost no research has been done on the ecological connectivity of fish resources in coastal of Vietnam. 1.3 The coastal of Quang Nam-Da nang The coastal areas of Quang Nam - Da Nang have three main fishing areas: Cu Lao Cham, Thu Bon and Da Nang. Cu Lao Cham archipelago belongs to Tan Hiep commune, Hoi An city, Quang Nam province. It consists of 8 islands located 15 km from Thu Bon estuary. The DaNang coastal has a coastline of 89 km, adjacent to the northern island of Cu Lao Cham. In these marine areas, studies on fish resources are limited to assessing the exploitation status and listing of key species groups in each
6 of the areas, there are no studies on resource characteristics and ecological – connectivity. CHAPTER 2: MATERIALS AND METHODS 2.1. SUBJECTS AND TIME AND LOCATION 2.1.1 Subject Fish resources and the status of management, exploitation and use. 2.1.2. Geographical location of research area The thesis focuses on three major ecosystems in coastal areas from Da Nang to Quang Nam: Danang coastal areas (including Son Tra Peninsula and Danang Bay), Cu Lao Cham Archipelago and Thu Bon estuary. 2.1.3. Time of the stydy From February 2011 to September 2016. 2.2. METHODS 2.2.1. Study specific characteristics of fish resources and ecosystems 2.2.1.1 Habitat characteristisc Synthesized from the study of the authors. 2.2.1.2. Composition of fish species Buiding the fish species list from two material sources: from secondary sources and from the results of additional research on the fish species of the thesis. - Fish sample survey Collect samples from all fishing trades at fish markets. - Fish classification According to the documents of: Nguyễn Khắc Hường (2001), Nguyễn Khắc Hường and Trương Sĩ Kỳ (2007), Vương Dĩ Khang (1963), Nguyễn Văn Lục et al. (2007). Đỗ Thị Như Nhung (2007), Nguyễn Nhật Thi (2000, 2008), Nguyễn Hữu Phụng (2001), , Allen et al. (1997, 2003), Carpenter and Niem (1999a; 1999b; 2001a; 2001b), Kuiter and Helmut (2007), Kuiter & Tonozuka (2001), Matsuura et al. (2000), Kimura and Matsuura (2003), Matsuura and Kimura (2005), Nakabo (2002), Randall et al. (1990), 沈世杰 (Shen) (1993).
7 2.2.1.3 Fish resources specific characteristics Information on fisheries resources was collected following method in "Survey coastal resources with the participation of the community" by Walters et al. (1998) and in Vo Si Tuan (2013). - Field survey + Collecting samples to determine the main source of income From the main source list obtained from the results of the community consultation, species identification will be carried out by accompanying the fishermen at the fish catch market. + Collection of seed and identification of breeding grounds Going with fishermen to the area of seedling exploitation, determination of seedling boundaries sites by Garmin GPS map 76CSx. Fish seed collection in the Danang Bay, Thu Bon estuary are of the species Serranidae, Lutjanidae and Siganidae. 2.2.2 Analysis and comparison of fishery resources among ecosystems 2.2.2.1. Analysis of biodiversity indicators Analyze the structure of fish fauna through various indicators using the Primer 6.0 software. Similarity index according to the formula of Bray- Curtis (1957). Margaret Richards (1958). Similarity index Sorensen, 1948 (Ks). Principal component analysis (PCA) analysis using CANOCO software ver. 4.5. 2.2.2.2. Analysis of ecological characteristics Division of fish ecological groups based on Froese and Pauly's (2008) salinity and habitat adaptation. 2.2.2.3. Resource characteristics Analyze, compare and evaluate the characteristics of some fishery resources in three ecosystems in the study area and collect samples for understanding the current status of some fish groups related to coastal livelihoods. 2.2.3 Ecological – connectivity 2.2.3.1. Collected sample for size-structure study of Siganus guttatus The total number of individuals recorded was 3,878 in Cu Lao Cham, Thu Bon and Da Nang estuaries. 2.2.3.2. Collection of DNA analysis samples A total of 35 individual in these three area were collected in 2014 for DNA analysis.
8 - DNA analysis The fin were sent to the Marine Biodiversity Center (MARBEC) - Université Montpellier II, France. 2.2.4. Document on the status of exploitation Data sources on the number of vessels and machine capacity and annual production are collected from the reports of the local authors. In addition, information on harvesting status was collected by the author through community consultation and field surveys in the study areas. CHAPTER 3: RESULTS AND DISCUSSION 3.1. BASIC CHARACTERISTICS OF ECOLOGICAL SYSTEMS AND FISH RESOURCES 3.1.1. DaNang 3.1.1.1. Characteristics of habitat Coral reefs in Da Nang sea area is not large, with 191 species of hard coral reefs, covering about 104.6 ha. The only seagrass are distributed in Bai Son (Son Tra peninsula in the south of Son Tra Peninsula) with an area of over 10 hectares. Seaweed carpets dominated by Sargassum and Rosenvingea apricots are estimated at 26.2 ha. It can be said that the Danang coastal region has a diversity of tropical coastal habitats but these habitats do not play a key role in generating biological productivity for the Danang coastal zone, depending on the productivity of the coastal area. the two estuaries of the Han River and the Cu De River, the sandy bottom and the muddy bottom of the bay. The ecological characteristics of the Danang coastal zone are soft bays, the presence of coral reef and seagrass habitats making the bay highly ecologically diverse. 3.1.1.2. Composition of fish Combining the fish species composition of the additional surveys and species lists previously published by the authors in this area, the thesis synthesizes the composition of fish species in coastal Danang including 425 species of 230 varieties, 95 families and 18 order . The results of the surveys of the dissertation have added to 29 species of Da Nang, belongs to 24 genera, 20 families and 7 order. 3.1.1.3. Fish resources characteristics
9 a. Commercial fishery resources There are 18 species of fish in 6 families that are considered as the main source of income for the Danang fishing community. In order of economic value: the group of fishermen brought the highest income, followed by peanuts, anchovies, carp, mackerel, tuna and rabbit fish, sausages (Table 3.1). Especially, the fish ear of 8-10 years ago is a significant source of income to Da Nang fishermen (Vo Si Tuan, 2002). However, in recent years, the production of this fish has declined. Table 3.1. The main fish resources in coastal of Danang Pos Scientific Name Pos Scientific Name (1) Muraenesocidae (4) Siganidae 1 Muraenesox bagio (Hamilton, 1822) 10 Siganus canaliculatus (Park, 1797) (2) Engraulidae 11 Siganus fuscescens (Houttuyn, 1782) 2 Encrasicholina heteroloba (Rüppell, 1837) 12 Siganus guttatus (Bloch, 1787) 3 Encrasicholina punctifer Fowler, 1938 (5) Trichiuridae 4 Stolephorus commersonnii Lacepède, 1803 13 Trichiurus lepturus Linnaeus, 1758 (3) Carangidae (6) Scombridae 5 Atule mate (Cuvier, 1833) 14 Auxis rochei (Risso, 1810) 6 Caranx ignobilis (Forsskål, 1775) 15 Rastrelliger kanagurta (Cuvier, 1816) 16 Scomberomorus 7 Decapterus kurroides Bleeker, 1855 commerson (Lacepède, 1800) 17 Scomberomorus guttatus (Bloch & 8 Decapterus macrosoma Bleeker, 1851 Schneider,1801) 9 Decapterus maruadsi (Temminck & Schlegel, 1843) 18 Thunnus tonggol (Bleeker, 1851) Estimates of yield and income of major sources in 2011 show that the income from cutlassfish (Trichiurus lepturus) and pike congers (Muraenesox bagio) brings the largest revenue, followed by scad, anchovy, mackerel, tuna and group of golden rabbit fish, orange-spotted spinefoot fish (Siganidae) (Table 3.2). Table 3.2. Estimate yield and revenue of major sources 2011 Yield Revenue Pos Major sources Tons % Million VND % 1 Trichiurus lepturus 378 13 45.360 35 2 Muraenesox bagio 260 9 23.400 18 3 Carangidae 1.140 40 17.100 13 4 Engraulidae 670 24 16.750 13 5 Scombridae 176 6 16.720 13 6 Siganidae 198 7 10.593 8 Total 2.822 129.923 100
10 b. Fish seed resources There are seven species that are exploited by fishers for sale to commercial fishpond households (Table 3.3). Table 3.3. Fish seed stocks are exploited at Danang coastal Pos Scientific Name Pos Scientific Name (1) Serranidae (3) Siganidae Epinephelus awoara (Temminck & Siganus guttatus (Bloch, 1787) 1 5 Schlegel, 1842) 2 Epinephelus coioides (Hamilton, 1822) (4) Lutjanidae Epinephelus malabaricus (Bloch & 3 6 Lutjanus johnii (Bloch, 1792) Schneider, 1801) Epinephelus trimaculatus (Valenciennes, 4 7 Lutjanus russellii (Bleeker, 1849) 1828) (3) Siganidae The results of size survey showed that fish fingerlings exploited in the coastal reefs of Da Nang have different length depending on the species ranging from 44-148 mm. The seed of orange-spotted spinefoot fish were sampled at a minimum length of 60 mm, averaging 85 mm, the 90mm group was dominant, and the largest individual was 140 mm in size. The results of public consultation and size survey have not seen the group of Lutjanus or Serranidae less than 40 mm at Da Nang coastal. 3.1.2. Cu Lao Cham 3.1.2.1. Characteristics of habitat Coral reefs are the most important and popular habitat at Cu Lao Cham MPA. A total of 277 species of hard coral reefs are estimated at 311.2 ha. Beside the widely distributed coral reefs, Cu Lao Cham is also characterized by the existence of many reefs in deep water of 25-40 m, where many coral do not create reefs. In the White Rock and Mui Tho area there are reefs with an area of about 6 ha (Nguyen Van Long et al., 2008). Seagrass are distributed only on the west coast of Cu Lao Cham Island, and there are five seagrass species in which halophila is considered to be the most common. Total seagrass area is 50 ha. Seaweed beds include 76 species, Sargassum and Rosenvingea are considered important habitats for fish, especially rabbitfish. It is estimated that there are about 10 tons of dry Sargassum on total of 8 seaweed beds in Cu Lao Cham.
11 It is possible to compare the distribution area of coastal inhabitants of Cu Lao Cham with Da Nang through Table 3.4. Table 3.4. Distribution of habitats of Danang and Cu Lao Cham. Habitat Reefs in Coral reef Seagrass Seaweed Deep cleft deep water (ha) (ha) (tons dry) (m) Place (ha) Da Nang 104,6 10 55 0-30 Cu Lao Cham 311,2 50 10 6 0-60 It can be said that the Cu Lao Cham sea area is directly affected by the sea with coral reefs being the most important habitat creating the ecological characteristics of the whole sea, which determines the biology community in this area. 3.1.2.2. Composition of fish Combining the fish species of the additional surveys and species lists of the published authors noted the composition of the Cu Lao Cham fish species including 452 species of 178 genera, 66 families and 15 orders. Thus, the thesis has added to the research for Cu Lao Cham sea areas 5 species of 4 genera, 3 families and 2 orders. 3.1.2.3. Fish resources characteristics It has been identified that 14 species in 6 fish families are the main source of Cu Lao Cham (Table 3.5). Table 3.5. The main fish resources of Cu Lao Cham marine area. Pos Scientific Name Pos Scientific Name (1) Muraenesocidae 8 Siganus guttatus (Bloch, 1787) 1 Muraenesox bagio (Hamilton, 1822) (5) Trichiuridae (2) Clupeidae 9 Trichiurus lepturus Linnaeus, 1758 2 Sardinella gibbosa (Bleeker, 1849) (6) Scombridae 3 Spratelloides delicatulus (Bennett, 1832) 10 Auxis rochei (Risso, 1810) Spratelloides gracilis (Temminck & 4 11 Rastrelliger kanagurta (Cuvier, 1816) Schlegel,1846) Scomberomorus commerson (Lacepède, (3) Leiognathidae 12 1800) Scomberomorus guttatus (Bloch & 5 Leiognathus equulus (Forsskål, 1775) 13 Schneider,1801) (4) Siganidae 14 Thunnus tonggol (Bleeker, 1851) 6 Siganus canaliculatus (Park, 1797) 8 Siganus guttatus (Bloch, 1787) 7 Siganus fuscescens (Houttuyn, 1782) (5) Trichiuridae
12 Estimated yield and revenue of the six main fish resource groups in Cu Lao Cham are shown in Table 3.6. Table 3.6. Estimate yield and revenue of major sources 2011 Yield Revenue Pos Major sources Tons % Tons % 1 Trichiurus lepturus 198,6 39 23.832 61 2 Muraenesox bagio 58,4 12 5.256 13 3 Siganidae 88,2 17 5.832 14 4 Leiognathus equulus 57,5 11 1.725 4 5 Scombridae 22 4 1.710 4 6 Clupeidae 96,4 17 964 2 Total 516,7 100 40.172 100 Sample 96 individual of fish species related to coral reefs from fish catching sites to assess the size of the harvest (Figure 3.2). Length of grouper species are generally concentrated in the small group of species, some of the larger species are also of medium size undifferentiated species such as Epinephelus awoara, E. coioides. Rabitfish are medium in size over 175mm, relatively smaller than the average common size of the species (200mm). The survey results show that there is no fishing seed in this area. 3.1.3. Thu Bon estuary 3.1.3.1. Characteristics of habitat Mangrove are the speciality habitats of the Thu Bon estuary, with the dominant mangroves tree being Nippa fructicans of the Palmae palm family. The total area currently distributed in the Thu Bon estuary is over 80 ha. The seagrass of the Thu Bon estuary are distributed mainly in Cam Thanh commune and there are only two species: Halophila beccarii and Zostera japonica. Zostera japonica is the most important, occupying most of the dunes. The area of the whole area is about 30 ha, of which the most concentrated and most important habitat is Go Hi and Ba Bon is in Cam Thanh commune. Mangroves are the most important habitat in the Thu Bon estuary. The presence of seagrass adds to the richness of the estuarine ecosystem. Characteristics of seagrass in the Thu Bon estuary is characterized by very high seasonal fluctuations. Seagrass beds develop very well in the dry season when the salinity is over 15 ‰. In rainy season,
13 the body of seagrass will be rot (Nguyen Huu Dai, 2008), so that seagrass- related organisms will also have seasonal fluctuations. 3.1.3.2. Composition of fish Combining the fish species of the additional surveys and the species list of the published authors recorded the composition of the fish species in the Thu Bon estuary including 182 species of 110 genera, 55 families and 15 orders ( The thesis has added 70 species belonging to 57 genera, 37 families and 12 orders). 3.1.3.3. Fish resources characteristics There are 15 species have been identified, of which 3 are belong to the Perciformes family and 1 belong to the Mugiliformes family as the main source of Thu Bon estuary (Table 3.7). Table 3.7. The main fish resources of Thu Bon estuary. Pos Scientific Name Pos Scientific Name (1) Mugilidae 8 Acanthopagrus berda (Forsskal, 1775) 1 Chelon melinopterus (Valenciennes, 1836) 9 Acanthopagrus latus (Houttuyn, 1782) 2 Moolgarda pedaraki (Valenciennes, 1836) (4) Gobiidae Acentrogobius caninus (Cuvier & 3 Moolgarda cunnesius (Valenciennes, 1836) 10 Valenciennes, 1837) (2) Gerreidae 11 Acentrogobius nebulosus (Forsskål, 1775) 4 Gerres erythrourus (Bloch, 1791) 12 Glossogobius giuris (Hamilton, 1802) Oxyurichthys ophthalmonema 5 Gerres japonicus Bleeker, 1854 13 (Bleeker, 1856) 6 Gerres longirostris (Lacepède, 1801) 14 Oxyurichthys papuensis (Valenciennes, 1837) Oxyurichthys tentacularis 7 Gerres oyena (Forsskål, 1775) 15 (Valenciennes, 1837) (3) Sparidae Estimated yield and revenue of the six main fish resource groups in Thu Bon estuary are shown in Table 3.8. Table 3.8. Estimate yield and revenue of major sources 2011 at Thu Bon estuary. Yield Revenue Major sources Pos Tons % Tons % 1 Gobiidae 102 42 8.670 36 2 Mugilida 65 27 8.125 33 3 Gerreidae 60 24 4.800 20 4 Sparidae 18 7 2.700 11 Total 245 100 24.295 100
14 Fishing season in Thu Bon estuary usually takes place year-round or lasts for several months, not divided into 2 main and secondary seasons or northeast monsoon and southwest monsoon. b. Fish seed resources Five species belong to four families in the Perciformes family have been identified as the main source of fish seed harvested in Thu Bon estuary (Table 3.9). Among them, grouper currently has 3 species are commonly exploited, in which Epinephelus coioides (fishermen known as black grouper) account for over 90%, grouper Blee-ker and gnats account for nearly 10%, the rest are other grouper species only occasionally caught. Some species in the family of rabbit fish, red snapper and brown fish each have only 1 species being exploited as breeds. Table 3.9. Fish seed resources are exploited in Thu Bon estuary. Pos Scientific Name Pos Scientific Name (1) Serranidae 4 Lutjanus argentimaculus (Forsskal, 1775) 1 Epinephelus coioides (Hamilton, 1822) (3) Siganidae 2 Epinephelus malabaricus (Bloch & 5 Siganus guttatus (Bloch, 1787) Schneider, 1801) 3 Epinephelus bleekeri (Vaillant, 1878) (4) Scatophagidae (2) Lutjanidae 6 Scatophagus argus (Linnaeus, 1766) 3.2. ANALYSIS AND COMPARISON CHARACTERISTICS OF FISH RESOURCE IN ECOSYSTEMS 3.2.1. Feature of species composition 3.2.1.1. Fish composition between the three ecosystems Composed of fish species in the above three ecosystems, including 747 species of 318 genera, 106 families, 20 orders. Compared to the total number of fish species in the three area, Cu Lao Cham has the most diverse species, with 452 species (60.5% of total species); Da Nang: 425 species (56.9%); Thu Bon esturary: 182 species (24.4%). Cu Lao Cham and Da Nang are rich in habitats such as coral reefs, seagrass, rocky tidal areas and sandy tidal areas, soft bottoms (sandy mudflats, sand bottoms) ... However, the distribution habitat of Cu Lao Cham is much larger than that of Da Nang, which makes the Cu Lao Cham sea a richer variety of habitats than Da Nang leads to species diversity is also higher. Compared to the Thu Bon River estuary with two habitats characterized by mangroves and seagrass , it
15 is possible to see the Cu Lao Cham and Da Nang seas with a greater diversity of habitats than the Thu Bon estuary. Diversity of habitat determines species diversity. 3.2.1.2. Species composition and species richness among the three ecosystems The Bray-Curtis similarity index of species composition in the three areas shows that the Da Nang and Cu Lao Cham have the highest similarity of 44.2%, followed by Thu Bon and Da Nang by 36.2%, Thu Bon and Cu Lao Cham are lowest at only 15.8%. Group analysis shows that the species composition of the three areas formed into two groups: Cu Lao Cham and Da Nang, Thu Bon formed a separate group. Analysis of the Sorensen homology index (1948) also showed that the level of closeness in species composition in Da Nang and Cu Lao Cham was the highest at 44.2%; followed by Da Nang and Thu Bon with 36.2% and Cu Lao Cham and Thu Bon with the lowest 15.8%. 3.2.1.3. Adaptability by salinity and habitat The fish salinity adaptability in Cu Lao Cham, Da Nang and Thu Bon estuaries was markedly different, fish composition in Thu Bon and Da Nang estuaries formed many adaptive wide salt fish groups, consists of 4 groups: marine, brackish-fesh, brackish-marine, and fresh-brackish-marine; Cu Lao Cham are only three groups (marine, brackish-fesh, and fresh-brackish- marine), only the brackish group does not exist in all three areas. The habitat adaptability in the three areas is also markedly different among fish groups, the composition of the fish species in Cu Lao Cham, Da Nang and Thu Bon shows the habitat adaptability. It is quite wide with the presence of all five groups of fish (bottom fish, shoreline, offshore, coastal and coral reef fish). It can be said that habitat adaptation is seen in the group of fish that are closely associated with the dominant reef in Cu Lao Cham, Da Nang, and bottom fish and coastal fish dominate the Thu Bon estuary. 3.2.2. Resource characteristics 3.2.2.1. Main component of resources A list of main resource groups in the three coastal areas of Quang Nam- Da Nang was compiled (Table 3.10).
16 Table 3.10. The main resource groups in the three study areas Pos Cu Lao Cham Thu Bon Da Nang 1 Muraenesox bagio Mugilidae Muraenesox bagio 2 Siganidae Gerreidae Engraulidae 3 Leiognathus equulus Sparidae Carangidae 4 Clupeidae Siganidae 5 Trichiurus lepturus Gobiidae Trichiurus lepturus 6 Scombridae - Scombridae There is a similarity in the main resource composition between the two areas of Da Nang and Cu Lao Cham: two areas have four in six 6 groups of fish is the same, they are: Trichiurus lepturus, Muraenesox bagio, Siganidae and Scombridae. Carangidae also has an important role for Danang fishermen. Thu Bon estuary have four main groups of fish resources: Gobiidae, Mugilidae, Sparidae and Sparidae because these are true river fish species that are suitable for the Thu Bon estuary. It can be said that species diversity is related to the diversity of habitats, but the nature of the resources depends on ecosystem characteristics. 3.2.2.2. Source of fish seed Comparing the composition, yield and revenue of seed fish sources of Thu Bon estuary and Da Nang show that the characteristics of seed sources differ significantly (Table 3.11). Table 3.11. Composition, yield and revenue of fish seed sources in Da Nang and Thu Bon estuary in 2011. Yield Revenue Total Area Seed fish (tons or (milion (milion individual) VND) VND) Da Nang Serranidae 5.500 50 50 Siganus guttatus 24 tons 3.600 Thu Bon Serranidae 26.000 95 3.815 Lutjanus argentimaculus 22.000 70 Scatophagus argus 10.000 50 Compared with the Thu Bon estuary, the yield and revenue of seed sources in Da Nang are almost negligible, only 1.3% (50 million / 3.815 million). The distribution of seed sources in the Thu Bon estuary is determined through consultation and field surveys (Figure 3.1).
17 Figure 3.1. Distribution areas of groupers, orange-spotted spinefoot and snapper in Thu Bon estuary according to the results of community consultation. The results of the field survey showed that the area where many species belonged to snapper, grouper, and orange-spotted spinefoot are sandbanks, seagrass and nipa, especially there is Go Hi seagrass (Figure 3.2). Figure 3.2. Distribution of S.guttatus in the Go Hi seagrass. 3.2.2.3. Size of some fisheries resources related to coastal livelihoods A preliminary assessment of the size of groupers and juveniles was clearly visible in terms of fish size across the three seas. In the sea areas of Danang and Cu Lao Cham, the smallest size of groupers and juveniles is 60 mm, while in the Thu Bon estuary is 20-30 mm. Studies have shown that the S.guttatus is a multi-habitat, coral-reef-related and mangrove-based riverine habitat, with a low salt tolerance. Mother fish enters the tidal estuary, juveniles settle in seagrass (Susilo, 2009) (Ayson, 2014). Thu Bon estuary along with coral reefs in Cu Lao Cham and Da Nang are full of
18 essential habitats in the life span of the this fish, thus finding out the ecological – connectivity of this fish species in the coastal inhabitants of Quang Nam-Da Nang are nessecsary. In the present context, when studying the migration of S.guttatus in the world is very difficult, the study of size and genetic linkage is a useful tool for understanding the ecological linkage of the most important resource of this sea. 3.3 ECOLOGICAL – CONNECTIVITY OF THE ORANGE- SPOTTED SPINEFOOT (Siganus guttatus) IN COASTAL HABITATS 3.3.1. Size structure Considering the proportions of the size groups of orange-spotted spinefoot populations over time, from the first month of appearance of the Thu Bon River estuary (July 2014) to June 2015 in all three regions: Thu Bon estuaries, Cu Lao Cham and Da Nang can see the growth trend and movement of size groups (Figure 3.3). Figure 3.3 shows that July is the smallest fish size in the Thu Bon estuary (21-40 mm), which predominates over 70% of the breeding stock, continuing to August size 41-60 mm and less than 20 mm but small ratio. This shows that there were spawnings scattered before the rainy season in July and August. In September, the rate of 21-40 mm group decreased sharply, from over 70% to less than 20% demonstrates the results of seedling operations focused on this size group; Groups of sizes 41-60 mm represent the highest rate, signaling the end of the period, but there are still late spawning in the group of 21-40 mm in size, less than 20% in fish stocks. From October to January next year there are almost no more melon size fishes, the highest proportion and the largest size is 81-100 mm group. These are the survivors left after the breeding operation continues to growing. From September, the sea areas of Danang and Cu Lao Cham have appeared in size 61-120 mm but very low (less than 5%), this is the smallest fish size in the two seas. In november, december the proportion of this group of fish is increasing in Cu Lao Cham and Da Nang, while in Thu Bon it is supplemented by the smaller size group (41-60 mm) but the proportion of fish size 61 -140 mm hardly increased. In march, april, may and june of the following year, almost no more fishing activities in Thu Bon. This can be explained as follows: Thu Bon breeders reach the size of 61 mm, they begin to migrate from the Thu Bon to the next inhabitants of the life cycle