the biology and fishery of mud crab, genus scylla in east ... biology and fishery of mud crab,...

THE BIOLOGY AND FISHERY OF MUD CRAB, GENUS Scyllu IN EAST MALAYSIA

MHD. IKHWANUDDIN @ POLITY BIN ABDULLAH

A thesis submitted in fulfilment of the requirements for the Degree of Master of Science (Aquatic Science)

Institute of Biodiverhty and Environmental Conservation UNIVERSITI MALAYSIA SARAWAK

2001

Administrator

ACKNOWLEDGEMENTS

First I would lrke to extend my sincere thanks to my advisor Prof. Dr. Steve Oakley for his comments, advice and encouragement throughout this study. I thank Prof. Dr. Ghazally Isrnail, Deputy Vice Chancellor, UNIMAS as my co-advisor and Mr. William Chang Wei Say, former Director of Agriculture Department, Sarawak for grating me permission to hrther nly studies at UNIMAS. I thank also the following groups and individuals who have contributed significantly to the successes of my research;

Inland Fisheries, Agriculture Department, Sarawak (Mr. Choong Ee Hock, Mr. Hariffin Awg. Bini, Mr. Fakhmddin Bokhari and all other Fisheries Officers) for their moral support. Sematan Fisheries Station, Agriculture Department, Sarawak (Mr. Ahmad Besar, Mr. Aken Jetom, Mr. Abd. Nasir, Mr. Awg. Jali and all station staffs) for assisting me in the laboratory and field works. The people of Sematan (Mr. Jol Sahak, Mr. Awg. Marikan, Mr. Saileh and Mr. Hipni 501) for their help in crab fishing and sampling. Instibte of Biodiversity and Environmental Conservation (IBEC), UNIMAS (Dr. Nicolas Pilcher, Dr. Stuart J. Davies, Dr. Indra Das Neil, Mr. Anthony Kong, Mr. Bujang and Miss Norzian) for creatlng a great environment and sharing the ideas to finish ths thesis. Faculty of Resource Science and Technology, UNIMAS for giving permission to use the faculty laboratory. South East Asian TCE Project (Prof. Dr. Don Macintosh, Mr. Tan Cheng Kiat, Mr. Standly Tan and Mr. Hakon) for their moral support. Malaysian Meteorological Department, Sarawak, for providing the rain data. Marine Fisheries Department, Sarawak, for providing the annual fisheries statistics. Muhandis Industrial Services Sdn. Bhd. (Mr. Dokanaer Kasto and Mr. Lii-oilg Yu) for their help in typing and printing the final thesis submission. I would like especially to thank my colleagues at IBEC, UNIMAS for their knowledge and enthusiasm: Yong A1 Hua, Charmine, Khairul Adha Rahim, Layang Unam Norashidah Hashim, Supian Zulkifli, Hardy, Alexander and Chung.

I gratefully acknowledge sources of funding, the Tunku Abdul Rahrnan Scholarship, Sarawak Foundation, IRPA Grant, Ministry of Science, Technology and Environment and DANCED of the South East Asian TCE Project.

Last but not least appreciation must be expressed to my wife; S ~ t i Natrah Mohd. Noor, my sons; Mhd. Naimullah, Mhd. Fadhillah and Mhd. Aslah, my daughters; Siti Nur Dhiya and Siti Nur Ain and my parents; Kria Sebulok and Nanti Tap01 for their moral support and sacrifices throughout the preparation of this thesis.

TABLE OF CONTENTS

TITLE PAGE

ACKNOWLEDGEMENTS

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF APPENDICES

ABSTRACT (ENGLISH)

ABSTRAK (BAHASA MALAYSIA)

CHAPTER 1

GENERAL INTRODUCTION

1.1 Genetics and biology 1.1.1 Taxonomy 1.1.2 Species distribution 1.1.3 Reproductive biology

1.2 Ecology and natural resources 1.2.1 Natural distribution and movement 1.2.2 Feeding pattern 1.2.3 Natural resources

1.3 Brood stock and seed production 1.3.1 Brood stock 1.3.2 Larval rearing

1.3.2.1 Food and feeding 1.3.2.2 Physico-chemical condition 1.3.2.3 Provision of substrates 1.3.2.4 Hygiene and quarantine protocols 1.3.2.5 Rearing system

1.3.3 Nursery 1.4 Aquaculture production system

1.4.1 Fattening operations 1.4.2 Growout operations 1.4.3 Recommendations related to aquaculture production

1.5 Trade and economics 1.5.1 Trade 1.5 "2 Economics

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1.6 Summary 1.7 General objective 1.8 General methods

1.8.1 Study site 1.8.2 Taxonomic status 1.8.3 Crab morphometrics 1.8.4 Sexes 1.8.5 Statistical analyses

CHAPTER 2

REPRODUCTIVE BIOLOGY OF MUD CRAB, GENUS ScyZZa

2.1 Introduction 2.2 Materials and methods

2.2.1 Study site 2.2.2 Crab samples 2.2.3 Size at maturity 2.2.4 Size at mating 2.2.5 Ovarian development stage 2.2.6 Female Maturity Index (FMI) 2.2.7 Gonadosomatic Index (GSI) 2.2.8 Fecundity

2.3 Results 2.3.1 Size at maturity in females 2.3.2 Size at maturity in males 2.3.3 Size at mating in females 2.3.4 Size at mating in males 2.3.5 Gonad maturity condition related to females maturity index (FMI) 2.3.6 Ovarian development 2.3.7 Annual periodicity of female reproduction 2.3.8 Fecundity

2.4 Discussion

CHAPTER 3

POPULATION DYNAMICS AND ECOLOGY OF MUD CRAB, GENUS Scylla


3.2.1 Study site 3.2.2 Crab samples 3.2.3 Tagging equipment and techniques

3.2.4 Sampling technique 3.2.5 Tag retaining and size after moulting

3.3 Results 3.3.1 Crabs capture and distribution

3.3.1.1 Distribution of crabs caught 3.3.1.2 Size frequency of crabs captured 3.3.1.3 Catch per unit effort (CPUE) 3.3.1.4 Tagged crabs recaptured

3.3.2 Crabs movements 3.3.2.1 Distance moved by tagged crabs 3.3.2.2 Population exchange within the sample site

3.3.3 Crabs growth 3.3.3.1 Growth per moult and retention of T-bar tags 3.3.3.2 Natural growth

3.3.4 Marked crabs caught outside the sample site 3.3.4.1 Caught during the biological survey 3.3.4.2 Caught by local fishermen

3.3.5 Environmental variables 3.4 Discussion

CHAPTER 4

TRACKING THE MOVEMENT OF MUD CRAB, GENIJS Scylla


4.2.1 Study site 4.2.2 Crab samples 4.2.3 Maturity condition 4.2.4 Tracking system 4.2.5 Telemetry system field trial 4.2.6 Tracking methods

4.3 Results 4.3.1 Telemetry system field trial 4.3.2 Tracking in the small mangrove channel 4.3.3 Tracking in the main estuary channel 4.3.4 Tracking in the estuary mouth 4.3.5 Movement pattern

4.4 Discussion

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CHAPTER 5

POPULATION ESTIMATE OF THE MUD CRAB, GENUS Scylla FROM MARK- RECAPTURE METHODS


5.2.1 Study site 5.2.2 Crab samples 5.2.3 Tagging equipment and sampling techniques 5.2.4 Population estimators

5.3 Results 5.3.1 Area covered by crabs population 5.3.2 Population estimate

5.3.2.1 All crabs combine population 5.3.2.2 S. tranquebaricu population 5.3.2.3 S. olivucea population

5.3.3 Population density 5.4 Discussion

CHAPTER 6

THE SEASONAL STUDIES OF THE MUD CRAB, GENUS ScylZa FISHERY IN SARAWAK


6.2.1 Study site 6.2.2 Crab samples 6.2.3 Fishing Catch Per Unit Effort (CPUE) trend

6.3 Results 6.3.1 Taxonomic status 6.3.2 The carapace width(CW)-body weight(BW) relationship 6.3.3 Monthly sizelspecies distribution 6.3.4 Sex ratio 6.3.5 Fishing Catch Per Unit Effort (CPUE) trend 6.3.6 Mean monthly total rainfall 6.3.7 Mud crab landing in Sarawak

6.4 Discussion

CHAPTER 7

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MUD CRAB, GENUS Scylla FISHERY IN BRUNEI BAY, NORTH WEST OF BORNEO

7.1 Introduction 162 7.2 Materials and methods 162

7.2.1 Study site 162 7.2.2 Crab samples 163

7.3 Results 163 7.3.1 Taxonomic status 163 7.3.2 Size distribution 165 7.3.3 Mean monthly total rainfall 167

7.4 Discussion 169

CHAPTER 8

FIRST RECORD MUD CRAB, Scyllaparamamosain FROM NORTH BORNEO


8.2.1 Study site 8.2.2 Crab samples

8.3 Results 8.3.1 Marudu Bay 8.3.2 Banggi

8.4 Discussion

CHAPTER 9

GENERAL DISCUSSION

REFERENCES

APPENDICES

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LIST OF TABLES

Table 1.1. Morphological characters useful in determining species identity of adult mud crab, genus Scylla (Keenan et. ai., 1998)

Table 1.2. Size when 50% of crab are at maturity in Scylla spp. from various localities

Table 1.3. Size at maturity based on three different criteria in female Scyllu spp. from various localities

Table 1.4. Size at maturity based on three different criteria in male ScylZa spp. from various localities

Table 1.5. Comparative data of spawning activity of Scylla spp. from various localities

Table 1.6. Larval food regimes used to rear Scylla spp. larvae in various localities

Table 1.7. Physico-chemnical conditions used in the culture of Scylla larvae in various localities

Table 1.8. Details of production parameters for floating base fattening system in South East Asia

Table 1.9. Details of production parameters for pond base fattening system in South East Asia

Table 1.10. Details of production parameters for crab growout culture system in South East Asia

Table 1.1 1. Cost and Returns analysis of different culture system of mud crab (reproduced from Abgayani, 1998)

Table 2.1. Description of stages of ovarian development in Scylla species

Table 2.2. Size at maturity and mating in female crabs (cm)

Table 2.3.Length frequency of female crab size at maturity

Table 2.4. Size at maturity in male crabs (cm)

Table 2.5. Length frequency of male crab size at maturity

Table 2.6.Length frequently of female crab size at mating

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Table 2.7. Size at mating in male crabs (cm)

Table 2.8. Length frequency of male crab size at mating

Table 2.9. Female maturity index (FMI) reflecting the different stages of gonadal development, S olivacea

Table 2.10. Female maturity index (FMI) reflecting the different stages of gonadal. development, S. tranquebarica

Table 2.1 1. Female GSI values by carapace width(cm)

Table 2.12. Monthly mean, maximum and minimum values of GSI for female crab, S. olivacea

Table 2.13. Monthly mean, maximum and minimum values of GSI for female crab, S. tranquebarica

Table 2.14. Mean, standard deviation, maximum and minimum values of crab eggs; and ovigerous female crab CW

Table 2.15. Size when 50% of crab at maturity based on two different criteria in Scylla sp, from various localities

Table 2.16. Size at maturity based on three different criteria in female Scylla spp. from various localities

Table 2.17. Size at maturity based on three different criteria in male Scylla spp. from various localities

Table 2.18. Comparative data of spawning activity of Scylla spp. from various localities

Table 3.1. Ten stations at the study site

Table 3.2. Summary of the results from 32 sampling trips in the study site

Table 3.3. Distribution of S. olivacea caught in the study site

Table 3.4. Distribution of S. tranquebarica caught in the study site

Table 3.5. Size frequency of crabs captured in study site by sexes

Table 3.6. Size frequency of crabs captured at the study site in mangrove and channel habitat

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Table 3.7. CPUE details during the biological sampling for 11 months, Sept. 1998-July 1999, at the study site

Table 3.8. Mean monthly CPUE during the biological sampling for 11 months, Sept. 1998-July 1999, in the study site

Table 3.9. Recaptured rate of crabs in the study site

Table 3.10. No. of tagged crabs recaptured frequency in the study site

Table 3.11. Mean distance between release and recapture site of crabs which had moved within the study site

Table 3.12. Furthest recapture position for tagged crabs within the study site

Table 3.13. S. olivacea; Distance between release and recapture sites of crabs at liberty for varying time periods in the study site

Table 3.14. S. tranquebarica; Distance between release and recapture sites of crabs at liberty for varying time periods in the study site

Table 3.15. Recapture zones of crabs tagged in the study site. Crabs recapture outside the study areas are not included

Table 3.16. Percentage of crabs retain tag after moult for tagged crabs in the laboratory

Table 3.17.Crabs growth per moult by species in the laboratory 86

Table 3.18. Growth of crabs between time of tagging and last recapture in the study site 87

Table 3.19. Sampling trips to catch the marked crabs (with T-bar tag) outside the study site 88

Table 3.20. Details of the sampling trips at the Sematan estuary (river mouth) 89

Table 3.2 1. Recapture of marked crabs (with T-bar tag) and berried female by local fishermen 90

Table 3.22. Water salinity and temperature details during the biological sampling for 11 months, Sept, 1998-July 1999, in the study site 90

Table 3.23. Mean monthly water salinity and temperature during the biological sampling for I 1 months, Sept. 1998-July 1999, in the study site

Table 4.1. Size, sex and species of crabs used and the tracking study site

Table 4.2. Pulses signal from sonic tag 3.5m deep under water at different hydrophone position

Table 4.3. Pulses signal from ultrasonic tag at different depth position inside the mud bottom, under water, with hydrophone 3.5m on top of the sonic tag

Table 4.4. Pulses signal from ultrasonic tag, 3.5m deep under water at different hydrophone distance

Table 4.5. Summary of results obtained by tracking 10 crabs. Tracking duration, duration after 48 hours, gross distance and average ground speed

Table 4.6. Summary of results obtained by tracking 6 crabs. Crab movement direction with or against water current

Table 4.7. Summary of results obtained by tracking 6 crabs. Net distance, gross distance and straightness index

Table 5.1. Mean, maximum, minimum and standard deviation of distance moved (m) by tagged crab within the mangrove channel (data reproduced from chapter 3)

Table 5.2. Mark-recapture data for a series of 32 sanlples of all crabs combined population in mangrove channel of Sematan mangrove forest

Table 5.3. Population estimates derived from data in table 5.2 of all crabs combined population from mangrove channel of the study site in Sematan mangrove forest by use of the Jolly-Seber model of population estimation

Table 5.4. Mean, maximum, minimum and standard deviation of population estimates derived from data in table 5.3 of all crabs combined population from mangrove channel of the study site in Sematan mangrove forest by use of the Jolly-Seber model of population estimation

Table 5.5. Mark-recapture data for a series of32 samples of S. tranquehlzrica population in mangrove channel of Sematan mangrove forest

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Table 5.6. Population estimates derived from data in table 5.5 of S. tranquebarica population from mangrove channel of the study site in Sematan mangrove forest by use of the Jolly-Seber model of population estimation 140

Table 5.7. Mean, maximum, minimum and standard deviation of population estimates derived from data in table 5.6 of S. tranquebarica population from mangrove channel of the study site in Sematan mangrove forest by use of the Jolly-Seber model of population estimation 14 1

Table 5.8. Mark-recapture data for a series of 32 samples of S. olivacea population in mangrove channel of Sematan mangrove forest 142

Table 5.9. Population estimates derived from data in table 5.8 of 8. olivacea population from mangrove channel of the study site in Sematan mangrove forest by use of the Jolly-Seber model of population estimation

Table 5.10. Mean, maximum, minimum and standard deviation of population estimates derived from data in table 5.9 of S, olivacea population from mangrove channel of the study site in Sematan mangrove forest by use of the Jolly-Seber model of population estimation 146

Table 5.1 1. The population density of mud crab through out the study period from 32 samples within the study site 146

Table 6.1. Percentage of mud crab species composition sampled (14,000 crabs) from June, 1998-July, 1999 for Sematan

Table 6.2. Relationship between Body weight and carapace width of mud crab species sampled from Sematan 150

Table 6.3. Sex ratio within the small mangrove and main estuary channel of mud crab species sampled

Table 6.4. Sarawak mud crab landing by gear and year (Quantity in metric tonnes)

Table 7.1. Sarawak mud crab landing by fishing districts and year (Quantity in metric tonnes)

Table 7.2. Species distribution of mud crab sampled from Brunei Bay 164

Table 7.3. Length frequency distribution for mud crab, S. olivacea sampled from Brunei Bay (n male=95; n female=78) 165

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Table 7.4. Length frequency distribution for mud crab, S. tranquebarica sampled from Brunei Bay (n male=277; n fernale=130)

Table 7.5. Means, standard deviations(SD), ranges and samples number(n) of carapace width(cm) of the fishery catch from Brunei Bay

Table 7.6. Percentage of mature crab sampled for B~unei Bay

Table 7.7. Miri Airport monthly total rainfall (millimeter)-Data from Malaysia Meteorological Service, Sarawak

Table 8.1. Mud crab species composition in crabs fishery in Marudu Bay

Table 8.2. Length frequency distribution for S. olivacea sampled in Marudu Bay

Table 8.3. Length frequency distribution for S. tranguebarica sampled in Marudu Bay

Table 8.4. Length frequency distribution for S. paramamosain sampled in Marudu Bay

Table 8.5. Length frequency distribution of crab caught in Marudu Bay

Table 8.6. Means, standard deviations (SD), ranges and samples number (N) of carapace width (cm) of the fishery catch from the Marudu Bay

Table 8.7. Mud crab species composition sampled in July, 1999 for Banggi

Table 8.8. Length frequency distribution for S. tranquebarica sampled in July, 1999 for Banggi

Table 8.9. Means and standard deviation (SD) of mud crab species from Sematan, Brunei Bay, Marudu Bay and Banggi

Table 8.10. Locations of S. paramamosain which have been positively identified from the Indo-pacific region

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LIST OF FIGURES Page

Figure 1.1. Drawings of part of carapace of Scylla species showing diagnostic taxonomic features: (A) S. serrata, male; (B) S. tranquebarica, male; (C) S. paramamosain, male; (D) S. olivacea, male (Kennan et al., 1998)

Figure 1.2. Drawings of right cheliped of Scylla species showing diagnostic taxonomic features: (A) S. serrata, male; (B) S. tranquebarica, male; (C) S. paramamosain, male; (D) S, olivaceu, male (Keenan et al., 1998)

Figure 1.3. Photographs of adult female S. serrata showing diagnostic features: high, bluntly pointed frontal lobe spines; pairs of large spines obvious on carpus and propodus; polygonal pattering clearly present on all appendages. Top figure - dorsal, bottom figure - frontal. Photo : Queensland Museum. (Keenan, 1999)

Figure 1.4. Photographs of adult male S. tranqueharica showing diagnostic features: moderate, blunted frontal lobe spines; pairs of large spines obvious on carpus and propodus; polygonal pattering present on last two pairs of legs, weak or absent on other appendages. Top figure - dorsal, bottom figure - frontal. Photo : Queensland Museum. (Keenan, 1999)

Figure 1.5. Photographs of adult male S. paramamosain showing diagnostic features: moderately high, pointed and triangular frontal lobe spines usual; pairs of large spines obvious on propodus, on carpus inner spine absent and outer spine reduced; polygonal pattering present on last two pairs of legs, weak or absent on other appendages. Top figure - dorsal, bottom figure - frontal. Photo : Queensland Museum. (Keenan,1999)

Figure 1.6. Photographs of adult male S. olivucea showing diagnostic features: low and rounded frontal lobe spines; pair of reduced spines obvious on propodus, on carpus inner spine absent and outer spine reduced; polygonal pattering absent from all appendages. Top figure - dorsal, bottom figure - frontal. Photo : Queensland Museum. (Keenan, 1999)

Figure 1.7. Mud crab (S. olivacea) inner section before dissecting the carapace and removing gonads (reddish orange colour) to calculated the drained ovary weight for Gonad somatic Index (GSI), Photo: A. M. Ikhwanuddin

Figure 1.8. Berried female mud crabs (Scylla serrata) commonly carry between 2-5 million eggs. Photo: Glen Smith. (Williams et al., 1999)

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Figure 1.9. Close up of 12-day-old eggs (-330pm diameter) attached to setae, showing pigmentation of eyes and body. Note undeveloped egg in the centre of the photograph. Photo: David Mann. (Williams et al., 1999)

Figure 1.10. Newly hatched first zoeal stage (Zl) of S, serrata next to unhatched egg. Photo: David Mann. (Williams et al., 1999)

Figure 1.1 1. The fifth zoeal stage (Z5) of S. serrata. The Z5 stage appears between days I1 and 14 of the culture cycle at 28 '~ . Photo: David Mann. (Williams et al., 1999)

Figure I . 12. Megalopae metamorphose from the Z5 stage, developing large claws. During the megalopal stage they change from a planktonic to a benthic existence. Photo: David Mann. (Williams et al., 1999)

Figure 1.13. The first crab stage (C1) of S. serrata, after metamorphosis &om the megalopal stage. Photo: David Mann. (Williams et al., 1999)

Figure 1.14. 'Clean' recirculation system for rearing mud crab larvae. (Mann et al., 1999)

Figure 1.15. Flow-through system for rearing mud crab larvae. (Holliday, 1986, cited by Fielder and Heasman, 1999)

Figure 1.16. Top figure: Crab fattening in floating cages at Sematan, Sarawak, East Malaysia. Bottom figure: Harvesting of crabs after fattening periods. Photo: A. M. Ikhwanuddin

Figure 1.17. Top figure: Crab fattening in pond at Samarahan, Sarawak, East Malaysia. Bottom figure: Fattening pond with mound of earth in the centre which can be used by crab for burrowing and shelter. Photo: A. M. Ikhwanuddin

Figure 1.18. Top figure: Intensive pen culture within the crab enslosures at Sematan, Sarawak, East Malaysia. Bottom figure: Close up of the pen cuJture system with high fencing, perimeter plank walk, perimeter drainage and mangrove vegetation in the centre of the pen. Photo: A. M. Ikhwanuddin

Figure 1.19. Map of Sematan river estuary

Figure 1.20. Diagram of carapace width (CW) which is the distance between tips of the ninth antero-lateral spines of the carapace

Figure 1.2 1. Diagram how to differentiate male and female crabs

Figure 2.1. Mature female with widening and darkening of the abdomen (Top position crab). The other two females is the immature female (Bottom position crabs). Photo: A. M. Ikhwanuddin

Figure 2.2. Length frequency of female crabs at maturity

Figure 2.3. Female crab size at maturity

Figure 2.4. Length frequency of male crabs at maturity

Figure 2.5. Length frequency of female crabs at mating

Figure 2.6. Female crab size at mating

Figure 2.7. Length frequency of male crabs at mating

Figure 2.8. Male crab size at mating

Figure 2.9. Effect of size on gonadal development of mature female S. olivacea. Histogram shows percentage of crabs with gonads in each stage of development

Figure 2.10. Effect of size on gonadal development of mature female S. tranquebarica. Histogram shows percentage of crabs with gonads in each stage of development

Figure 2.1 1. Seasonal changes in the proportion of mature female S. olivacea with ovaries in various stages of development

Figure 2.12. Seasonal changes in the proportion of mature female S. tranquebarica with ovaries in various stages of development

Figure 2.13. Monthly mean GSI for female crab S. olivacea

Figure 2.14. Monthly mean GSI for female crab S. tranquebarica

Figure 2.15. Relationship between fecundity and carapace width for S. olivacea

Figure 3.1. Map of main study site, Tanjung Beluku river

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Figure 3.2. Diagram of collapsible crab trap which were of the same type commonly used by the local crab fishermen in Sematan. Chopped fish (small shark) were placed in the centre of the trap as bait. Photo: A. M. Ikhwanuddin

Figure 3.3. Top figure: The anchor T-bar tags were inserted with a Dennision tagging gun into the posterior margin of the crab's body, between the carapace and abdomen. Bottom figure: The tag Insertion was put in slightly off-centre to avoid damaging the dorsal abdominal artery and also to avoid tag loss at moult. Photo: A. M. Ikhwanuddin

Figure 3.4. The distance betmeen the sampling stations within the mangrove channel of the study site

Figure 3.5. Size frequency of S. olivacea captured at the study site by sexes

Figure 3.6. Size frequency of S. tranquebarica captured at the study site by sexes

Figure 3.7. Size frequency of S. olivacea captured at the study site in mangrove and channel habitats

Figure 3.8. Size frequency of S. tranquebarica captured at the study site in mangrove and channel habitats

Figure 3.9. The monthly mean CPUE at the study site

Figure 3.10. Frequency of tagged crab recaptures at the study site

Figure 3.1 1. Relationship between day of tagginglrecapture tagged crabs and carapace width (Natural growth trend of S, olivacea in the wild)

Figure 3.12. Relationship between day of tagginglrecapture tagged crabs and carapace width (Natural growth trend of S. tranquebarica in the wild)

Figure 3.13. The monthly mean salinity at the study site

Figure 3.14. The monthly mean temperature at the study site

Figure 4.1. The position of the hydrophone from the ultrasonic tag during the telemetry system field trial

Flgure 4.2. Photograph of the ultrasonic tag was attached to the mid-dorsal carapace surface of a crab during the study. Photo: A. M. Ikhwanuddin

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Figure 4.3. Tracking the ultrasonic tag crab in the mangrove channel. Photo: A. M. Ikhwanuddin

Figure 4.4. Tracking the movement of crab no. 1 (S. olivacea; male; 1 1.7cm CW). Tracking site: Small channel of Tanjung Beluku River (Off Sematan River)

Figure 4.5. Tracking the movement of crab no. 2 (S. olivacea; male; 12.2cm CW). Tracking site: Small channel of Tanjung Beluku River (Off Sematan River)

Figure 4.6. Tracking the movement of crab no. 4a (S. tranquebarica; female; 12.5cm CW). Tracking site: Small channel of Tanjung Beluku River (Off Sematan River)

Figure 4.7. Tracking the movement of crab no. 4b (S. tranquebarica; female; 12.5cm CW). Tracking site: Small channel of Tanjung Beluku River (Off Sematan River)

Figure 4.8. Tracking the movement of crab no. 5 (S. tranquebarica; female; 12.9cm CW). Tracking site: Main channel of Sematan River

Figure 4.9. Tracking the movement of crab no. 6 (S. tranquebarica; female; 10.8cm CW). Tracking site: Main channel of Sematan River

Figure 4.10. Tracking the movement of crab no. 7 (S. tranquebarica; berried female; 12.lcm CW). Tracking site: Main channel of Sematan River

Figure 4.1 1. Tracking the movement of crab no. 8 (S, olivacea; female; 11.2cm CW). Tracking site: Main channel of Sematan River

Figure 4.12. Tracking the movement of crab no. 9 (S. tranquebarica; female; 11.7cm CW). Tracking site: Sematan River Estuary

Figure 4.13. Tracking the movement of crab no. 10 (S. tranquebarica; female; 14.0cm CW). Tracking site: Sematan River Estuary

Figure 4.14. Frequency of speed of movement in 30 minute intervals by four crabs (crab no. 5 ,6 ,7 & 8) in the main estuary channel

Figure 4.15. Frequency of speed of movement in 1 hour intervals by two crabs (crab no. 9 & 10) in the estuary mouth

Figure 4.16. Distance moved by crab no. 5

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Flgure 4.19. Distance moved by crab no. 8


Figme 4.2 1. Distance moved by crab no. 10

Figure 5.1. Illustration diagrams how to estimated the total area covered by the mud crabs within the study site

Figure 6.1. Mud crab species composition in samples for commercial fishers catches (14,000 crabs) (June, 1998-July, 1999)

Figure 6.2. Morphometric relationship between body weight and carapace width of S. olivacea female

Fig~re 6.3. Morphometric relationship between body weight and carapace width of S. olivacea male

Figure 6.4. Morphometric relationship between body weight and carapace width of S. tranqueharica female

Figure 6.5. Morphometric relationship between body weight and carapace width of S. tranquebarica male

Figure 6.6. Size frequency distribution for S. olivacea sampled for commercial fishers catches from Sematan (June, 1998-July, 1999)

Figure 6.7. Size frequency distribution for S. tranquebarica sampled for commercial fishers catches from Sematan (June, 1998-July, 1999)

Figure 6.8. Abundance of mature S. olivacea sampled from June, 1998-July, 1999

Figure 6.9. Abundance of mature S. tranquebarica sampled from June, 1998-July, 1999

Figure 6.10. Abundance of female S. olivucea sampled from June, 1998-July, 1999

Figure 6.1 1. Abundance of female S. tranquebarica sampled from June, 1998-July, 1999

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Figure 6.12. Mean monthly total rainfall for Sematan from 1987-1998 (12 years)

Figure 6.13. Monthly total rainfall for Kuchtng Division (Sematan) throughout the study period, from June, 1998-July, 1999

Figure 6.14. Sarawak mean and percentage mud crab landing by month from 1990-1 997

Figure 6.1 5. Sarawak mud crab landing by fishing traps from 1990- 1997

Figure 7.1. Map of Brunei Bay showing the study site

Figure 7.2. Species distribution of mud crab sampled from Brunei Bay

Figure 7.3. Length frequency % of mud crab S. olivncea, sampled from Brunei Bay

Figure 7.4, Length frequency % of mud crab S. tranquebnrica, sampled from Brunei Bay

Figure 7.5. Monthly total rainfall for the study site (Miri Airport) for 1997



Figure 8.1. Map of the study sites, Marudu Bay and Banggi Island

Figure 8.2. Mud crab species composition in crab fishery in Marudu Bay

Figure 8.3. The size distribution of mud crabs caught in Marudu Bay

Figure 8.4. Length frequency distribution for S. tranquebarica sampled in July, 1999 for Banggi

LIST OF APPENDICES

nth) by species by months

e daily CPUE and tidal fluctuation

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Page

ABSTRACT

The study was conducted to determine the biological information and fishery statistics of mud crab, genus Scylla in selected mangrove ecosystems within East Malaysia. The main study site was the Sematan mangrove forest with three other minor study sites; Brunei Bay, Marudu Bay and the Island of Banggi. The important biological information and fishery statistics on mud crab examined was; the size at maturity and mating for both crab sexes; the gonadal development including the annual breeding periodicity and fecundity of the female crabs; the crab distribution, the crab home range and the crab natural growth rate within the mangrove ecosystem; the crab movement within the mangrove ecosystem; the crab population size; and the taxonomic status, carapace width-weight relationship, monthly size and species distribution, sex ratio and fishing catch per unit effort of the mud crabs sampled from the Sematan mangrove forest. For other study sites, data such as taxonomic status, carapace width-weight relationship, monthly size and species distribution, sex ratio and fishing catch per unit effort of the mud crabs was also examined. The recent taxonomic work by Keenan et al., (1998) was used to determine the mud crab species within the study.

Studies shows that, the size when female crab were sexually mature for Scylla serrata has a larger size compare to the two Scylla sp. in the study. The study also shows that mature S. tranquebarica is more larger than S. olivacea. The size distribution of crabs caught in the study sites shows that most of the samples were consisted of much larger and mature crabs. The study shows that the population of both Scylla spp. in the study is reproductive throughout the year with spawning peak activity during the warmer months. The study shows that the channel and the mangrove habitats in the intertidal area are the habitat type for S. olivacea. Where as the subtidal area and the channel habitat of the intertidal area are the habitat type for S. tranquebarica. The population density of mud crabs in Sematan were 262.2m2 per crab for S. tranquebarica and 137.5m2 per crab for S. olivacea. The study shows that mud crab is a nocturnal animal with night feeding activity. The study shows that S. tranquebarica do migrated offshore during spawning season, the same manner with S. serrata but not for S. olivacea. The mean CPUE was 0.3kglpot or 1.9crabdpot for Sematan and 0.24kg/pot or 1.0 crab/pot for Brunei Bay. The biological studies of the mud crab fishery in Sematan shows that S. olivacea is the most abundant species caught (77.64%) with S. tranquebarica (21.91%) and S. paramamosain (0.45%) is the other species caught. The mud crab fishery survey done in Brunei Bay shows that only two species of S. tranquebarica (70.2%) and S. olivacea (29.8%) was measured. The fishery catches from the Marudu Bay, shows that S. tranquebarica (67.6%), S. paramamosain (24.7%) and S. olivacea (7.8%) was measured. But the fishery catches from Banggi, shows that only S. tranquebarica was measured in the samples. This establishment of the biological and fishery data on mud crab, genus Scylla in East Malaysia is important for conservation and effective management of mud crab resources and their fishing in the regions.

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ABSTRAK

Kajian telah dijalankan untuk menentukan maklumat biologi dan statistik perikanan ketam bakau, genus Scylla di ekosistem hutan bakau yang terpilih di Malaysia Timur. Kawasan kajian utama ialah Hutan Bakau Sematan dengan tiga kawasan kajian sampingan lain; Teluk Brunei, Teluk Marudu dan Pulau Banggi. Maklumat biologi dan stastistik perikanan yang penting bagi ketam bakau yang dikaji adalah; saiz matang dan mengawan bagi kedua-dua jantina ketam; perkembangan gonad termasuk jangkamasa pembiakan tahunan dan kesuburan ketam betina; taburan ketam, jarak kediaman ketam dan kadar tumbesaran semulajadi ketam dalam ekosistem hutan bakau; pergerakan ketam dalam ekosistem hutan bakau; saiz populasi ketam; status taksonomi; Hubungan Lebar cengkarang-Berat ketam, taburan saiz bulanan dan spesis, nisbah jantina dan Hasil Tangkapan Per Unit Usaha bagi sampel ketam bakau dari Hutan Bakau Sematan. Bagi kawasan kajian lain, data seperti status taksonomi, Hubungan Lebar cengkarang-Berat ketam, taburan saiz bulanan dan spesies, nisbah jantina dan Hasil Tangkapan Per Unit Usaha juga dikaji. Kerja taksonomi yang terbaru oieh Keenan et al., (1998) digunakan untuk menentukan spesies ketam bakau semasa kajian.

Kajian menunjukkan bahawa saiz apabila ketam betina matang bagi Scylla serrata adalah lebih besar dibandingkan dengan dua spesies Scylla dalam kajian. Kajian juga menunjukkan bahawa S. tranquebarica matang lebih besar daripada S. olivacea. Saiz taburan ketam yang ditangkap dari kawasan kajian menunjukkan kebanyakan sampelnya terdiri daripada ketam besar dan matang. Kajian menunjukkan bahawa populasi kedua-dua spesies Scylla dalam kajian adalah subur sepanjang tahun dengan kemuncak aktiviti pembiakan semasa bulan kemarau. Kajian menunjukkan bahawa habitat terusan dan bakau dalam kawasan 'intertidal' adalah jenis habitat S. olivacea. Kawasan 'subtidal' dan habitat terusan di dalam kawasan 'intertidal' adalah jenis habitat bagi S. tranquebarica. Kepadatan populasi ketam bakau di Sematan adalah 262.2m2 per ketam bagi S. tranquebarica dan 137.5m2 per ketam bagi S. olivacea. Kajian menunjukkan bahawa ketam bakau adalah haiwan 'nocturnal' dengan aktiviti pennakanan pada waktu malam. Kajian menunjukkan bahawa S. tranquebarica boleh berhijrah ke luar persisiran pantai semasa musim pembiakan, sama seperti S. serrata tetapi tidak bagi S, olivacea. Purata Hasil Tangkapan Per Unit Usaha adalah 0.3kghubu atau 1.9 ketarnhubu bagi Sernatan dan 0.24kghubu atau 1.0 ketarnlbubu bagi Teluk Brunei. Kajian biologikal bagi perikanan ketam bakau di Sernatan menunjukkan bahawa S. olivacea adalah spesies yang paling banyak ditangkap (77.64%), S. tranquebarica (21.91%) dan S. paramamosain (0.45%). Survei perikanan bagi ketam bakau yang dilakukan di Teluk Brunei menunjukkan hanya dua spesies iaitu S. tranquebarica (70.2%) dan S. olivacea (29.8%) sahaja yang diukur. Tangkapan perikanan dari Teluk Marudu menunjukkan S. tranquebarica (67.6%), S. paramamosain (24.7%) dan S. olivacea (7.8%) sahaja yang diukur. Tetapi tangkapan perikanan dari Banggi menunjukkan bahawa hanya S. tranquebarica sahaja yang diukur dalam sampel. Pengurnpulan data biologikal dan perikanan bagi ketam bakau, genus Scylla di Malaysia Timur adalah penting bagi pemuliharaan dan pengurusan efektif sumber ketam bakau dan perikanan di rantau ini.

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General Introduction

CHAPTER 1

GENERAL INTRODUCTION

1.1 Genetics and biology

1.1.2 Taxonomy

Over the last few years it has become widely recognised that the mud crabs of the Indo- Pacific region belong to more than one species of the genus Scylla (Serene, 1952; Stephenson and Campbell, 1960; cited by Keenan et al., 1998; Estanlpador, 1949; Kathirvel and Srinivasagam, 1992; Fuseya and Watanabe, 1996; Overton et al., 1997). The original descriptions of mud crab only identified one species, but use different species names (Forskal, 1775; Dana, 1852, cited by Alcock, 1899). The first study to revise the taxonomy was by Estampador (1949) who recognised three species in the genus, Scylla serrata, S. oceanica and S, tranquebarica and one variant, S. serrata var. paramamosain. Estampador's work was also supported by Serene (1952), cited by Overton (1999), based on a similar study in Vietnam. Despite Estampador's classification, all four morphs of the Scylla have been known for many years as S. serrata in the fisheries and aquaculture industry and in scientific publications (Fortes, 1999). This is because, there was considerable confusion regarding the taxonomy of species in the genus, Scylla. Studies by Stephenson and Campbell (1960); Stephenson (1972); cited by Overton (1999), all suggested that the racial variation seen in Scylla is not substantial enough to establish separate species. In Indian waters several authors recognised two species in the genus, Scylla: S. oceanica and S. serrata (Kathirvel, 1981 cited by Kathirvel and Srinivasagam, 1992), S. serrata and S. serrata serrata (Radhakrishnan and Samuel, 1982 cited by Kathirvel and Srinivasagam, 1992) and S. tranquebarica and S. serrata (Joel and Sanjeevaraj, 1983, cited by Kathirvel and Srinivasagam, 1992).

As pointed out by Keenan et al., (1998) an understanding of the taxonomy of Scylla populations throughout the Indo-pacific is central to the development of a successful aquaculture industry, as well as improved wild-stock management of the different types. It has been recognised that the uncertainty of genetic relationship and taxonomic details of the genus, Scylla is a primary constraint to the management of the wild fishery and development of aquaculture (Angell, 1992; Brown, 1994, cited by Keenan, 1999).

The recent research by Keenan and co workers in the South East Asia region presented convincing arguments for the recognition of three species in the genus, Scylla serrata, S. olivacea and S. tranquebarica (Keenan et al., 1995; Keenan et al., 1996). Subsequent studies have also recognised an additional new species identified as S. paramamosain (Keenan et al., 1998; Keenan, 1999). For the first time, species names can be used with confidence from the solid taxonomic studies of Keenan and co-workers, the morphological characters used to determine species identity are shown in Table 1.1 (Keenan et al., 1998; Keenan, 1999) and Figure 1.1 to Figure 1.6.

the biology and fishery of mud crab, genus scylla in east ... biology and fishery of mud crab,...

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