STUDIES ON FISH BEHAVIOUR IN RELATION TO NET
TRANSPARENCY OF MILLENNIUM GILLNET OPERATION IN
BONDET WATERS, CIREBON
CAROLINA CATUR RAKHMADEVI HALUAN
STUDIES ON FISH BEHAVIOUR IN RELATION TO NET
TRANSPARENCY OF MILLENNIUM GILLNET OPERATION IN
BONDET WATERS, CIREBON
CAROLINA CATUR RAKHMADEVI HALUAN
Thesis
As one of the requirements for a master degree in Marine Technology
at Fisheries Utilization Department
GRADUATE SCHOOL
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
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ABSTRACT
Carolina Catur Rakhmadevi Haluan. Studies on Fish Behaviour in Relation to Net Transparency of Millennium Gillnet Operation in Bondet Waters, Cirebon. (Supervised by Ari Purbayanto and M. Fedi A. Sondita)
The millennium gillnet was recently adopted by Cirebon fishermen. Its use has been spread to other areas. Research on this type of gear is rare. The objectives of this research were: (1) to investigate the effects of net transparency on fish behaviour in relation to net panel of millennium gillnet; and (2) to obtain information on catch composition and capture process of millennium gillnet. This research consisted of laboratory experiment and field experiment. The laboratory experiment was conducted from August 2005 to March 2006 at Fish Behaviour Laboratory, Tokyo University of Marine Science and Technology. The field experiment was carried out in October to November 2006 in waters off Cirebon. The result concludes that: (1) net transparency affected the Japanese Jack mackerel behaviour in relation to contrast colour of the net panel; (2) the effect of usage - reduced transparency on mackerel behaviour was not significant; (3) catch of millennium gillnet in the field was dominated by threadfins (71.29%); and (4) capture condition of the catch of millennium gillnet was dominated by gilled and wedged.
ABSTRAK
Carolina Catur Rakhmadevi Haluan. Studi Tingkah Laku Ikan Terkait dengan Transparansi Jaring pada Pengoperasian Gillnet Millennium di Perairan Bondet, Cirebon. Dibimbing oleh Ari Purbayanto dan M. Fedi A. Sondita
Gillnet millennium diadopsi oleh nelayan Cirebon yang kemudian penggunaannya telah menyebar ke berbagai daerah di Indonesia. Penelitian mengenai jaring ini masih belum banyak dilakukan. Hal tersebut mendorong penulis untuk melaksanakan penelitian mengenai jaring millennium yang bertujuan untuk: (1) menyelidiki pengaruh transparansi panel jaring millennium terhadap tingkah laku ikan; (2) memperoleh informasi mengenai komposisi hasil tangkapan dan proses tertangkapnya ikan oleh jaring ini. Penelitian ini terdiri atas penelitian laboratorium dan eksperimen penangkapan. Penelitian pengaruh transparansi jaring dilaksanakan pada bulan Agustus 2005-Maret 2006 di Laboratorium Tingkah Laku Ikan, Tokyo University of Marine Science and Technology. Penelitian mengenai komposisi hasil tangkapan dilaksanakan pada bulan Oktober-November 2006 di perairan Cirebon. Berdasarkan hasil penelitian, diperoleh kesimpulan bahwa: (1) transparansi jaring berpengaruh terhadap tingkah laku ikan kembung Jepang terhadap warna kontras; (2) efek dari penurunan transparansi yang diakibatkan oleh pemakaian jaring adalah tidak signifikan; (3) hasil tangkapan jaring millennium didominasi oleh ikan kuro (71.29%) dan tangkapan lain sebagai hasil tangkapan sampingan; dan (4) cara tertangkapnya ikan oleh jaring millennium secara dominan terjerat pada insang (gilled) dan
wedged.
STATEMENT ON SOURCES DECLARATION
I declare that this thesis, with a titled: Studies on Fish Behaviour in Relation to Net Transparency of Millennium Gillnet Operation in Bondet Waters, Cirebon is my own work assisted by advisory committee and has not been submitted in any form for another degree or diploma to any university or other institution of tertiary education. The source of information cited from previous publications are mentioned on text and listed in references section at the end of this thesis.
Bogor, August 2007
LEGALIZATION
Title of Thesis : Studies on Fish Behaviour in Relation to Net Transparency of Millennium Gillnet Operation in Bondet Waters, Cirebon
Name : Carolina Catur Rakhmadevi Haluan
NIM : C551040131
Approved by Advisory Committees
Dr. Ir. Ari Purbayanto, M.Sc Dr. Ir. M. Fedi. A. Sondita, M.Sc Chairman Member
Authorized by
Marine Technology Study Program The Dean of Graduate School Chairman,
BIOGRAPHY
The author was born in Bogor, June 13, 1983, as third daughter of John Haluan and Unmiati. Her life was spent mostly in Bogor. She graduated from Mardi Yuana 1 Elementary School in 1994, Mardi Yuana 2 Middle School in 1997, and Bogor Public 1 High School in 2000. She continued her study to Bogor Agricultural University and then graduated in June 2004 from Fisheries Utilization Department. She was one of the top ten graduates of Faculty of Marine Science and Technology.
In 2004, she continued her study to graduate program majoring on Marine Technology Study Program. In 2005, she received Japan Student Services Organization (JASSO) scholarship for one year student exchange program at
Tokyo University of Marine Science and Technology (TUMSAT).
In Marine Technology Student Association of Bogor Agricultural University, she became the first secretary in 2006-2007 periods. At spare time, she loves to do traveling, Balinese dancing, and reading novels. She graduated from Marine Technology Graduate Program with a thesis, titled: The Studies on Fish Behaviour in Relation to Net Transparency of Millennium Gillnet Operation in Bondet Waters, Cirebon.
FOREWORD
The adoption of fishing technology always gives impacts to the area where the technology is adopted. The impacts are potential to produce advantages or disadvantages to the local fisheries society, especially the fishermen. It all depends on the various aspects such as, well community acceptance, profitability, practicality, affordability, and environmental friendly.
Millennium gillnet, is a case of adoption of fishing gear technology by local fishermen in Cirebon, West Java. The gear has been well accepted but some improvements may be needed to increase its effectiveness.
This thesis is hopefully could explain some researches result on the development of the adopted fishing gear, in this case the millennium gillnet. This
is necessary for the sustainability of gillnet fishery in North Coast Java.
ACKNOWLEDGEMENTS
I wish to express my deep gratitude to numerous people who have assisted me throughout my studies, include:
1. The Advisory Committee, Dr. Ir. Ari Purbayanto M.Sc. and Dr. Ir. M. Fedi A. Sondita M.Sc for their guidance and supervisions during the course of this study.
2. The Head of Fish Behavior Laboratory, Tokyo University of Marine Science Technology: Prof. Dr. Takafumi ARIMOTO for discussion and assistance during my stayed in Japan as exchange student in 2005.
3. The Head of Marine Technology Study Program: Prof. Dr. Ir. John Haluan, M.Sc for his support, discussion and corrections on my thesis.
I also deliver many thanks to:
1. Prof. Dr. Ir. Daniel R. Monintja for his wise words and encouragement.
2. Family: Papa (John Haluan) and mama (Unmiati), my sisters (Ka Eunice and Ka Aris) and brothers (Firman and Samuel) for standing by me and giving me encouragement on finishing this thesis. For my personal editor, Andreas Adoe for the support and English editing of this thesis.
3. Mr. Sadiki and family, and all millennium gillnet fishermen for the cooperation and information during my stayed in Cirebon.
4. The Head Division of Cirebon Regency Fisheries and Marine Affairs Agency, Mrs. Lucia Cipto Astuti, SE, MP.
5. The member of Marine Tecnology Study Program of 2004 and 2005, Pak Cua, Pak Ismawan, Bu Riena, Bu Lisa, Mba Anti, Bang Djabal, Bang Irham, Hasan, Alfa, Bu Siti, Pak Cecu, Pak Syawal, Pak Is, Pak Imran, Sylvia, Mba Dian, Bang Ongge, Dame and Mba Lia for their warm friendship.
6. The member of Fish Behavior Laboratory, Tokyo University of Marine Science and Technology: Akiyama sensei, Inada sensei, Ozawa san, Nopporn san, Korn san, Ibnu san, Hayashi san, Miyagi san, Tsukada san, Takeuchi san, Yachii san, Kabaya san and also best gratitude for my tutor, Yanase san.
TABLE OF CONTENTS
Page
LIST OF TABLES ... vi
LIST OF FIGURES ... vii
LIST OF APPENDIX ... viii
1 INTRODUCTION... 1
1.1 Background ... 1
1.2 Problem Formulation ... 2
1.3 Objectives ... 4
1.4 Benefits ... 4
1.5 Hypothesis ... 4
1.6 Conceptual Framework ... 4
2 LITERATURE REVIEW... 6
2.1 The Description of the Gillnet... 6
2.2 Capture Conditions of Gillnet ... 9
2.3 The Fish Behaviour in Relation to Gillnet ... 10
2.4 Factors Affecting the Efficiency of Gillnet in Relation to Fish Behaviour ... 14
3 RESEARCH METHOD ... 17
3.1 Fish Behaviour Study ... 17
3.1.1 Time and location ... 17
3.1.2 Fish behaviour in relation to contrast colour net panel ... 17
3.1.2.1 Materials and instruments ... 17
3.1.2.2 Research procedure ... 20
3.1.2.3 Data analysis ... 20
3.1.3 Fish behaviour using specific white panels ... 21
3.1.3.1 Materials and instruments ... 21
3.1.3.2 Research procedure ... 23
3.1.3.3 Data analysis ... 25
Page
3.2.2 Materials and equipments ... 25
3.2.3 The methods of collecting data ... 26
3.2.4 Research method ... 26
3.2.5 Assumptions ... 27
3.2.6 Operation method ... 29
3.2.7 Data analysis ... 30
4 RESULTS ... 31
4.1 Brief History of Millennium Gillnet ... 31
4.2 Fish Behaviour Study ... 32
4.2.1 Fish behaviour in relation to contrast colour net panel ... 32
4.2.1.1 Net colour transparency ... 34
4.2.1.2 Fish behaviour in relation to netting panel ... 34
4.2.2 Behaviour experiment using specific white net panels ... 34
4.2.2.1 Mesh passing reaction of fish ... 36
4.2.2.2 Behaviour of fish in relation to net colour ... 39
4.3 Capture Process Experiment ... 40
4.3.1 Catch composition ... 40
4.3.2 Capture conditions ... 41
5 DISCUSSIONS ... 43
5.1 Behaviour Study ... 43
5.1.1 Fish behaviour in relation to contrast colour net panel ... 43
5.1.2 Behaviour experiment using specific white net panels ... 45
5.2 Capture Process Experiment ... 48
6 CONCLUSIONS AND RECOMMENDATIONS ... 52
6.1 Conclusions ... 52
6.2 Recommendations ... 52
REFERENCES ... 53
APPENDIX ... 57
LIST OF TABLES
Page 1 Instruments for the contrast colour net panel experiment ... 18 2 Instruments for the fish behaviour using specific white panels ... 22 3 Materials for the experimental fishing ... 25 4 Description of the millennium gillnet used in the experimental
fishing operations in Cirebon ... 27 5 Signification level of comparison proportion among three types of
net panel ... 34 6 Species composition in percentage and total length (TL) of fish
LIST OF APPENDIX
Page
1 The map of experimental fishing operation ... 57
2 The average length and body girth of Japanese Jack mackerels ... 58
3 The average water temperature and salinity during experiment ... 59
4 Frequency and proportion of fish passing through the netting panel of contrast colour net panel ... 60
5 Frequency and proportion of fish passing through the netting panel of behaviour experiment using specific white panels ... 61
6 Statistical test of frequency of fish passing through the net ... 62
7 Capture conditions of threadfins (Polynemus spp.) ... 64
8 Fish caught by millennium gillnet ... 65
9 Millennium gillnet catch ... 67
LIST OF FIGURES
Page
1 The systematic diagram of this research ... 5
2 Capture conditions of a same sized fish by gillnets of different mesh size (Sparre and Venema, 1999) ... 10
3 Japanese Jack mackerels (Trachurus japonicus)... 17
4 Instruments used in the contrast colour net panel experiment ... 19
5 The design of the experimental tank ... 20
6 Equipments used during the behaviour experiment ... 23
7 Acclimatization process (from top view) ... 24
8 Conditioned behaviour (from top view) ... 24
9 Fishing boat of millennium gillnet used in the experimental fishing .... 27
10 Design of the millennium gillnet in Bondet Waters, Cirebon ... 28
11 Deployment of the marking buoy in the afternoon ... 29
12 Shooting net piece by piece ... 29
13 The last hauling process (in the late afternoon) ... 30
14 Comparison among the fish passing through the net panel on voluntary behaviour ... 32
15 Comparison among the fish passing through the net panel on conditioned behaviour ... 33
16 Comparison of fish passing through the net panel ... 35
17 Proportion of fish passing through the net ... 36
18 Contact and non-contact reaction of fish passing through old white net panel ... 37
19 Contact and non-contact reaction of fish passing through new white net panel ... 38
20 Contact and non-contact reaction of fish passing through white dyed net panel ... 38
21 Proportion of fish passed through the net colour ... 39
22 Captured position of threadfins on class range (cm) ... 41
1 INTRODUCTION
1.1Background
The development of fishing technology in Indonesia can not be separated from the progress of fishing science, including the knowledge of gear and catch. The knowledge of catch includes the study of fish as the main catch, using the fish behaviour approach. Knowledge on fishing gear and its catch is important to understand capture process applied.
Gillnet is a type of common fishing gear in Indonesia, including the north
coast of Java Sea. Various types of gillnet using local names are popular among fishermen in the north coast of Java Sea, especially in Cirebon.
Commonly, gillnets in the north coast of Java Sea are used to catch pelagic fish. Fridman (1986) notes that pelagic fish commonly swim in massive school and usually active on daytime. This type of fishes are intensively using their sense of sight on predation (Gunarso, 1985).
The development of gillnet fishing technology in the north coast of Java Sea has been enriched by adoption of foreign technology. Around the year of 2000, the millennium gillnet adopted from South Korea was introduced in Gebang Mekar Village, Cirebon. This gear was introduced by local fishermen who had visited South Korean fishing industry. Soon, the use of this gillnet expanded to Mertasinga Village, Cirebon through a short training held by the local Fisheries and Marine Affairs Agency. Nowadays, the existence of this net is spreading to other areas in the north coast Java Sea (Indramayu) as well as Semarang (Central Java) and Pontianak (West Borneo).
The underwater transparency of millennium gillnet is believed by fishermen to give effect on the number of fish caught. Net with less transparent should be less contrast to its environment, and then it is less visible to the fish which become more easily to be caught by the net if the fish passing through the net. In contrary, if the fish are attracted by the net during capture process, the net should be
Millennium gillnet has replaced the use of nylon gillnet that used before by fishermen to catch the same target of fish of same average size. The difference between nylon gillnet and millennium gillnet is on the webbing material and net colour. The nylon gillnet is made of nylon multifilament, while the millennium gillnet is made of multi-monofilament. The nylon gillnet colour is dark blue while the millennium gillnet colour is white transparent. According to Hovgard and Lassen (2000), nylon multi-monofilament made of a number of monofile nylon thread or monofilaments in parallel. Multi-monofilament nets are generally considered to be the most efficient as the use of thin parallel threads make the net softer than the monofilament or multifilament (Hovgard and Lassen, 2000). It makes the multi-monofilament nets more flexible underwater.
Even though this type of gillnet has been accepted and well implemented in Cirebon, the information of its use for catching pelagic fish, the capture process of this gillnet, and the effect of its net transparency is very limited. Therefore it is necessary for understanding the catch performance and improving the effectiveness of millennium gillnet.
1.2 Problem Formulation
Principally, gillnet is wall or compounds of net which set out in particular pattern to barrier the school of fish in order that fish are gilled, tangled or trapped (Sainsbury, 1996). To improve its catching efficiency, there are some major parameters of gillnet to be considered (i.e., colour of netting, dimension of material, types of netting material and hanging ratio) (Hovgard and Lassen, 2000). On the millennium gillnet, transparency (or colour) is believed to affect the catch efficiency and effectiveness. In gillnet fishery, transparency influences the visibility of this gillnet underwater, therefore less noticeable is necessary. Salmon drift gillnet has less transparency than flying fish drift gillnet since it using the nylon monofilament, while flying fish gillnet using the multifilament net (Nomura, 1985).
water. They further inferred that the visibility of nets depends on both the water colour and the colour of the seabed. Cui et al. (1991) used the light intensity thresholds as an indicator of the fishing power of different coloured nets by comparing mackerel (Scomber scrombus) behaviour towards different coloured twine. Considerable differences in colour selection thresholds observed for both a thin monofile thread and a thicker multifilament thread.
As new adopted gear, analysing a factor affecting the effectiveness on catch, in this case the net transparency is considered necessary. In order to analyse the net transparency; in relation of fish as catch target, some approaches should be conducted. The study of behaviour often becomes the best way on analysing these problems (e.g. Wardle et al. 1991, Cui et al. 1991). Knowledge of fish behaviour, in relation to captures, can be acquired in different ways. Laboratory studies informs that the fish behaviour patterns towards the gear or representations of gear-related stimuli can be described, and general behaviour relevant to the fish capture process such as the swimming capacities of different species, can be studied (Ferno and Olsen, 1994).
Meanwhile, as first step to understand the catch performance of millennium gillnet, the study of capture process is needed. This become necessary since the information regarding this gillnet, which it was used from the first time until recent years is still limited. The capture process of gillnet can be determine according to the ways of fish being retained in the net. The fish can be captured by being gilled, wedged, snagged and entangled (Hovgard and Lassen, 2000).
For that reason, some studies are needed to understand the effect of transparency on fish behaviour towards net panel. Not just the effect of transparency, some studies are also needed to obtain some information regarding the capture process of millennium gillnet as the way to understand the catch performance of this net.
1.3Objectives
The research objectives are:
(1) To investigate the effects of the net transparency on fish behaviour in relation to the net panel of millennium gillnet.
(2) To obtain the information on catch composition and capture process of millennium gillnet.
1.4Benefits
The research result can be beneficiary for understanding millennium gillnet in Cirebon, regarding:
(1) The effects of transparency on the fish behaviour in relation to the net panel of millennium gillnet.
(2) The catch composition and capture process of millennium gillnet.
1.5 Hypothesis
Hypothesis of this research is the net transparency affects the behaviour of fish in relation to net panel of millennium gillnet.
1.6 Conceptual Framework
The millennium gillnet effectiveness in Cirebon is believed to be affected by the net colour or transparency and fish performance (Figure 1). Two methods of investigation were used to understand both factors. The transparency factor was investigated in the experiment of fish behaviour towards contrast colour panel and
Millennium gillnet effectiveness in Cirebon
Affected by colour transparency Affected by fish performance
Investigated through fish behaviour in relation to net panel
Investigated by fishing experiments operations
Fish behaviour on contrast color
Fish behaviour on specific white panel
(Old white net, new white net and black
painted)
(Old white net, new white net and white
painted )
Descriptive analysis through percentage of
catch composition Capture process and catch composition
One Way Anova Two Way Anova
•
Recommendation the effective and efficient colour of millennium gillnet•
•
Information of catch composition and capture processFigure 1. The systematic diagram of this research
2 LITERATURE REVIEW
2.1 The Description of the Gillnet
Gillnet is a wall of netting which may be set at or below the sea surface, on the sea bed, or at any depth between. Fish are caught by gilled, or by entangled as they attempt to pass through the net, which may be classified as a gillnet, tangle net or trammel net depending on the manner in which the net is constructed and the way the netting is hung (Sainsbury, 1996).
True gillnets are simply used to catch fish with body size of almost uniform
since the mesh size matched to the fish’s girth: the mesh size used depends on the species and size range being targeted. The net is constructed so that the meshes are virtually square in shape and large enough that the fish can get its head through, but not its body, so that it becomes caught by at the gill cover on attempting to back out. These nets are used for a wide range of species including small pelagic, cods and haddock, bass, and salmon (Sainsbury, 1996).
Trammel nets are constructed of three panels of netting attached to the same framing ropes. A middle sheet of webbing of small, loosely hung mesh is rigged between outside walls of large mesh. A fish striking from either side passes through the large outer mesh web and hits the small mesh netting which is carried through the openings of the other large mesh webbing to form a sack or pocket in which fish is entrapped (Sainsbury, 1996).
In North Sulawesi, Indonesia several types of gillnets are operated (i.e. drift gillnet, bottom gillnet, semi-encircling gillnet and shark gillnet) in artisanal fisheries. Drift gillnet mostly used nylon monofilament. The mesh size was ordinarily 1.75 inches; length of float line was about 40 to 80 m and 70 number of mesh depth. The catch species were flying fish (Cypsolurus sp.), needle fish (Tylosurus sp.), barracuda (Sphyraena sp.) and sardine (Sardinella sp.) (Reppie and Lalamentik, 1999).
Bottom gillnet is almost the same as the drift gillnet, the difference between them just on the sinking force and buoyancy ratio, where the sinking power of the bottom gillnet is much bigger than its buoyancy, because it should laid stable on the bottom. The catch consist of Acanthurus sp., yellow tail (Caesio sp.), black pomfret (Formio sp.), grouper (Epinephelus sp.), Chaetodon sp., emperor (Lethrinus sp.), slip mouth (Leigonathidae) and trevally (Caranx sp.) (Reppie and Lalamentik, 1999).
Semi encircling gillnets utilizing the onshore migration behaviour of fish in the tidal waters. The net material was nylon monofilament 1.75 inches, float line
about 90 m in length and 23 number mesh depth, sinking force much larger than its buoyancy. The catch species were slip mouth (Leigonathidae), Lutjanus sp.,
Caranx sp., Lates sp., Lethrinus sp., Tylosurus sp., Pomadasys sp., Sphyraena sp. and Mugil sp (Reppie and Lalamentik, 1999).
Shark gillnet was just a simple deep bottom gillnet for demersal species, included shark. This gillnet used to catch two specimen of “living fossil” coleacanth (Latimeria chalumnae) in Menado Tua Dua. The mesh size limited to 5, 5.5 and 8 inches since only this size was available in the local market (Reppie and Lalamentik, 1999).
Most of gillnet experiments in Indonesia studied the selectivity of types of gillnet, such as drift gillnet, bottom gillnet and also trammel net. One of the examples of gillnet experiment in Indonesia was conducted in Pelabuhan Ratu, West Java to determine selectivity of sweeping trammel net for banana prawn (Penaeus merguensis) using five types of trammel net which different in their nominal inner mesh (i.e. 38.1, 44.5, 50.8, 57.2, and 63 mm) (Yokota et al., 2003). The curve of selectivity resulted to a peak of 3.8 prawn length to mesh size (l/m)
with 50% selection range of the relative efficiency of 3.7. The right side of the selectivity curve was skewed (i.e. the right side of curve decline slightly), indicating that the selectivity of sweeping trammel net for banana prawn was not high, especially for large individual. However, the reliability of the result was considered low due to large residual squares between the experimental and the estimated values.
Research in selectivity and escape mechanism of tiger prawn was carried out through simulated capture using trammel net at shrimp pond in Lampung District (Purbayanto et al., 2007). The size selectivity research was conducted to compare performance of catching efficiency and size selectivity of black tiger shrimp caught by trammel net (inner net of monofilament nylon 1.25, 1.50, 1.75, 2.00 inch mesh size). The result showed that trammel net with inner net of monofilament nylon has relatively high catching efficiency especially for catching large size shrimp compared with multifilament nylon. The size selectivity for monofilament nylon net was lower than multifilament nylon. Black tiger shrimp escapes through the mesh net when encountering the net and finding a space on
the inner net which is larger than the shrimp body for escaping.
Some other gillnet studies was conduct in Cirebon to investigate the effect of differences of hanging ratio on catching swimming crab (Portunus pelagicus) in Bondet Waters, Cirebon (Ansharullah, 2004; Firmansyah, 2004). They used 5 different size of hanging ratio (0.42, 0.44, 0.46, 0.50, and 0.48). The result showed no differences of hanging ratio towards the swimming crab, but they give recommendation of using hanging ratio of 0.42 since it had less mesh size than the others.
catch. He assumed the morphology of catch (compressed or not compressed) affected the result. It also proved that hanging ratio affecting the selectivity.
2.2 Capture Conditions of Gillnet
The capture conditions of gillnet were defined according to the ways of fish being retained in the net. The fish can be captured in gillnet by being:
(1) Gilled, when the fish is meshed immediately behind the gill cover (Figure 2). (2) Wedged, when the fish is meshed around the body somewhere behind the gill
cover. Wedging is hardly distinguishable from gilled when the maximal girth is found at a position close to the gill cover (Figure 2).
(3) Snagged, when the fish is attached to the netting at the head region. This catch process is the most common for species with protruding maxilla or pre opercula (Figure 2).
(4) Entangled, when the fish is wrapped into the netting, held by pockets of netting or attached to the net by teeth, fins, spines or other projections. Fish that are already caught by other catch processes may subsequently be wrapped
into the netting while struggling to free themselves (Figure 2).
Baranov (1914) as cited by Ferno and Olsen (1994) has distinguished three different ways of fish being retained by gillnet, which are:
(1) Gilled, if the fish entering a mesh and being unable to back out because the mesh is behind the gill cover.
(2) Wedged, if the fish is being held tightly by a mesh around the body.
(3) Tangled, if the fish does not penetrate a mesh but is caught in the net by teeth, maxillaries or other projections.
Figure 2. Capture conditions of a same sized fish by gillnets of different mesh size (Sparre and Venema, 1999)
On sweeping trammel net, the fish captured by snagged, gilled, entangled and pocketed. Snagged, when the fish was held by a mesh along the head part from the operculum to the front part of the dorsal fin. Entangled, when one part of the fish body (teeth, maxillaries, fins and other projections) was held by a mesh or entirely the fish body was wrapped tightly by the nets. And pocketed, when the fish was entrapped in the pocket formed by loose inner net without necessarily entangling or penetrating the net (Purbayanto et al., 1999).
From the result of capture conditions of trammel net in Tateyama Bay, Chiba Prefecture, Japan in June to September 1995 showed that a small Japanese whiting was mostly gilled, while medium and large fish were mostly pocketed. The by-catch species were mostly entangled in the net (Purbayanto et al., 1999).
2.3 The Fish Behaviour in Relation to Gillnet
towards gear is become the interesting objects to investigate by researchers. Not only fish being the experiment objects but also some of species of crustaceans, such as lobsters, crab, and shrimps (Nomura, 1991).
Some observe that if a fish encounters a gillnet, it stops its movement temporarily, but in shallow water, if the net swing because of waves and tilts to the front, the fish follow the net and, when the net swings back, the fish gets its head caught in a mesh of the net. Generally, fish seem to lack the faculty of judgement but it is known that there are certain patterns in the behaviours of fish that react reflexively to the gears (Nomura, 1991).
A survey on the distribution of spot lined sardines enmeshed in midwater gillnets shows that they were more often caught on the sinker side regardless of the length of the barrel ropes by which the net is suspended from the sea surface. This seems to indicate that when the sardines encountered the net, they had been panicked into starting a downward escape immediately before they were enmeshed. Therefore, fishermen adjust their ropes so that the centre of the width of the net will be somewhat deeper than the water depth in the centre of the fish
group detected by the fish finder (Nomura, 1991).
In laying the net, the direction in which the net extends is at an acute angle to the direction of movement of the school (which is believed to be the opposite to the direction of the tidal current) and the net is placed at a suitable distance from the school. It is desirable to time net casting so that the school will encounter the net immediately on completion the net’s descent after proceeded straight ahead during the length of time the net takes to sink to a depth of 40-50 m after it is cast. This exemplifies the technique of operating nets according to the behaviours of fish (Nomura, 1991).
Lobsters get entangled in bottom gillnet as they leave their reefs on dark nights to feed. They are not caught on moonlit nights because they are timid. If a lobsters contact gillnet, it cleverly passed through the gap under the sinker and escapes to the opposite side. If the surplus buoyancy is too great, the meshes open up and the lobster passes through the mesh by bringing its antennas down on its back (Nomura, 1991).
From the knowledge of how a lobster reacts to a net, if composing a bottom gillnet with 10.5 cm meshes and a net depth of not more than 60 cm, then it is important not only to reduce the size of the floats and enable the buoyancy to be applied evenly in order to minimize the gap under the sinker; and it is also important to cut surplus buoyancy as much as possible and adopt rather large shrinkage. If this is done, about half of the net depth is in the state of crawling on the sea bottom. So, when a lobster retreats after the contact of its antennas with the net, the net entangles it if any part of its body is caught by the net. This is how lobsters are netted.
The fish behaviour also influenced the availability of fish stock. The horizontal and vertical distribution of fish may vary seasonally and change from year to year. Such variations in fish distribution cause changes in availability of fish to all types of fishing gear including gillnet. Seasonal changes in distribution, e.g. those caused by spawning migration, are well known for several marine fish (Ferno and Olsen, 1994).
Seasonal changes in availability due to spawning and feeding migrations are
often predictable and this source of variability in stock assessment may be minimized by conducting the assessment surveys in the same areas and periods every year. Annual changes in area and vertical distributions have been documented for cod (Godo and Wespestad, 1993 cited by Ferno and Olsen, 1994) and these are a source of uncertainty that is difficult to correct for. Changes in fish availability will affect abundance estimates based on gillnet survey data in a similar way.
speed of young perch (Perca fluviatilis) feeding upon small Daphnia was more than twice that of perch feeding upon chironomid larvae (Persson, 1987 cited by Ferno and Olsen, 1994). It is also likely that the speed of cod is lower when they are searching for benthic fauna than when feeding for active prey such as herring (Clupea harengus) and capelin (Mallotus villosus).
External factors, such as temperature also influence the catch rate of gillnets. Temperatures has a significant influence on swimming capabilities such as speed and duration (Wardle, 1993 cited by Ferno and Olsen, 1994). He (1991) as cited by Ferno and Olsen (1994) found that cod of 36-42 cm length had a reduction in maximum sustainable swimming speed of 56% when the water temperature was reduced from 5 to 0oC, and the author suggested that temperature may have severe impact on gillnet catches. As activity falls with decreasing temperature, the number of encounters with gillnets may be reduced. Secondly, a reduction in swimming speed may increase the ability of fish to react visually and turn away before coming into contact with the gillnet.
There may be differences in activity between sexes, especially during the
spawning season, which may affect the catch composition of passive fishing gear, including gillnet. In a comparison between catches of cod taken by gillnet, longline and purse seine during the spawning season, differences in the sex ratio between the three types of fishing gear were obtained. The purse seine catches assumed to give a nearly correct picture of the fish present because of the sex ratio was 50:50, while for gillnet the sex ratio was 60% males and 40% females, and for longline the ratio was 40% males and 60% females. Rollefsen (1953) as cited by Ferno and Olsen (1994) suggested, on the basis of observations in aquaria, that male cod are more aggressive and therefore more likely to encounter the net and be caught. Furthermore, a female fish which is just hovering about may very well not only avoid the risk of running into a net, but also have more time to investigate edible objects. This may be the reason why females are more frequently caught on longlines. Surveys during the spawning season should thus be avoided, in order to obtain representative samples of both sexes.
Ideally, the probability of encountering passive fishing gears should be independent of fish density. However, fishing experiments with gillnets in four
lakes with different stock levels of brown trout (Salmo trutta) have shown the catchability decreased with increasing population level (Borgstrom, 1992 cited by Ferno and Olsen, 1994). The author excluded saturation as a possible cause and indicated that the results could be explained by a decline in swimming activity with increasing density of fish as a result of reduced availability of food. Dickson (1989) as cited by Ferno and Olsen (1994) also indicated that mobility of cod decreased as stock level rose. When stock level was low, cod were schooling in small number at dawn and not schooling at dusk, while at higher stock level there was no distinct aggregation. The mobility due to schooling and not schooling increased the chance of encounter with gillnets.
In relation of mesh sizes of gillnet, Rudstam et al. (1984) as cited by Ferno and Olsen (1994) stated that the increase in efficiency with increasing mesh size could be explained by the variations in swimming distances. As swimming speed increases with fish size (Wardle, 1993 cited by Ferno and Olsen, 1994), the number of encounters of fish encounters with the net increases. Borgstom (1989) as cited by Ferno and Olsen (1994) suggested that the rise in efficiency with mesh
size found for roach could not be explained only by differences in swimming speed, but also by the greater visibility of smaller meshes. Selectivity experiments are usually carried out using different mesh sizes, but the researchers close to keep the twine diameter constant. This means that neither the open area ratio nor the bulk of their nets could be held constant.
In relation to visibility of gillnet, the studies of the reaction of mackerel (Scomber scrombus) to different materials in tank experiments showed that multifilament thread was detected by mackerel at much lower light intensities than monofilament (Cui et al., 1991).
2.4 Factors Affecting the Efficiency of Gillnet in Relation to Fish Behaviour
Hamley (1975) and Dickson (1989) as cited by Ferno and Olsen (1994) discussed features of gillnets which influence catching efficiency and selectivity, such as colour, mesh size, twine material and thickness, and construction of the net. On this paper, the discussion will be stressed on features that relates to the visibility of gillnet.
Gillnet is a stationary gear and the catch depends on the net generating a minimum of stimulation which might provoke avoidance responses. Observations of ultrasonically tagged American shad (Alosa sapidisimma) in the vicinity of driftnets have shown that fish can possess a remarkable ability to avoid the nets (Legget and Jones, 1971 cited by Ferno and Olsen, 1994). Experimental studies in tanks strongly indicate that before fish are caught in the net, the visual stimulus of the net is the key factor that determines whether or not fish react (Cui et al., 1991). Gillnets become invisible at certain threshold light intensities that are related to colour, net, material and turbidity (Dickson, 1989 cited by Ferno and Olsen, 1994).
Net factories produce gillnets of different colours, and fishermen choose nets with a colour which they believe will make the nets as invisible as possible
for a specific season and area (Ferno and Olsen, 1994). Several experiments have been carried out to investigate the effect of different colours on catch rates of fish in gillnets. The experiments by Jester (1973) as cited by Ferno and Olsen (1994) showed that gillnet colour had either a positive or negative effects on catch rates, depending on the species. However, it is not possible to draw any general conclusion about colour and visibility from these experiments, since it is the luminance of the net relative to the background which is the key factor in net visibility. Wardle et al. (1991) have pointed out that the colour of gillnet should be matched to the sea bed to make them as invisible as possible. Ferno and Olsen (1994) suggest that since water colour can vary, colour in material adds a complication that could be avoided by careful selection of a neutral grey with a density that results in a good match with the water background.
In addition of colour, thread twine thickness and type of material determine net visibility; thinner twines are less visible than thicker ones. Since the fish is not expected to sense the net existence, it would be preferable to choose thin twines.
However, very thin twine can easily break by larger fish, so that thickness must be adapted to the species and size of fish.
The efficiency of gillnets has greatly increased with the introduction of less visible synthetic fibres, especially transparent polyamide monofilaments, which have replaced natural fibres. Polyamide thread is the dominant material used in gillnets today in the western hemisphere. Four different types of polyamide thread are in use, twisted multifilament, monofilament, monotwine (3-strand monofilament) and multi-monofilament. Comparative fishing experiment shown that multifilament gillnets are less efficient than nets of monofilament materials (Washington, 1973; Hylen and Jacobsen, 1979 cited by Ferno and Olsen, 1994).
3 RESEARCH METHOD
3.1 Fish Behaviour Study
3.1.1 Time and location
The fish behaviour study was conducted in Fish Behaviour Laboratory, Tokyo University of Marine Science and Technology in August – September 2005 (fish behaviour towards contrast colour net panel) and December 2005 – March 2006 (fish behaviour study using specific white net panel).
3.1.2 Fish behaviour in relation to contrast colour of the net panel
3.1.2.1 Materials and instruments
Materials and instruments used in the behavioural study towards contrast
[image:34.595.107.500.84.842.2]colour panel are shown in Table 1 and 2. Japanese Jack mackerels was used as test fish (Figure 3). The reason of this is that these fish are a type of pelagic fish and which is target catch of millennium gillnet.
Figure 3. Japanese Jack mackerels (Trachurus japonicus)
The Japanese Jack mackerels used in the experiment was in healthy condition. The average fork length of this fish was around 13-15 cm within maximum body girth (Gmax) was around 12.7-13 cm.
Three net panels used as treatment of transparency (i.e. old white, new white,
minimize cost.
Table 1. Instruments for the contrast colour net panel experiment
No. Instruments Function
1. 2. 3. 4. 5. 6. 7. 8.
3 net panels (old, new and black painted) (46x53 cm) framed by PVC 16 mm (Figure 4).
Forcing panel
Experimental tank (200x100x50 cm) filled with sea water 30 cm in height (Figure 4).
Video recording system (Figure 4), consisted of:
• 8 mm Sony handy-cam
• underwater camera
• multi-viewer
• monitor
• VHS video cassettes (60 minutes)
Thermometer
Lux meter
Digital camera Stopwatch
Research instrument
As the treatment behaviour Fish tank
Recording the fish swimming and behaviour
Measuring the water temperature Measuring the light intensities Documentation
Counting time needed for fish on entering the net
50 cm
A
B
100 cm
1. old white, 2. black, 3. new white
46 cm
53 cm 200 cm
Underwater CCD camera
Sony 8 mm handycam
Monitor Multi
viewer player Video
7.5 cm 10 cm
VI D EO OBSERVATI ON SYSTEM
EX PERI M EN TAL TAN K
N ET PAN EL
[image:36.595.108.479.78.480.2]M e sh siz e
Figure 4. Instruments used in the contrast colour net panel experiment
The old net was considered less transparent than the new gillnet, whether it would affect the behaviour of fish on passing through the net panel is one of the objectives that will be analyzed. Black painted net panel is representation of nylon gillnet, which most has dark in colour (dark blue). The panel without net were used as control of fish passing through the net.
The using of forcing panel was considered as treatment of conditioned behaviour. Meanwhile, the voluntary behaviour was considered as treatment without the use of forcing panel. The reason of doing the behaviour treatment was to understand the behaviour of fish towards netting panel with or without any obstruction. The net panel was placed on 50 cm from starting point of swimming of the experimental tank (area A) which is located in the right side (Figure. 5).
1. VOLUNTARY
CON TROL:
PAN EL
W I TH OUT
A N ET
2. CONDITIONEDT
TRREEAATTMMEENNTT11 TTRREEAATTMMEENNTT 22
Net panel
A B
A B
Net panel
Forcing panel (Old white, black,
new white)
NET PANEL COLOUR
[image:37.595.116.511.86.346.2](Old white, black, new white)
Figure 5. The design of the experimental tank
3.1.2.2 Research procedure
1) The fish were acclimatized for 3 days in the experimental tank.
2) At the beginning of the experiment, fish were allowed to swim freely for about 10 minutes.
3) The net panel were set; each replicates was done for 15 minutes.
4) Randomization of net panels sequence was using RANDBETWEEN on MS-EXCEL.
5) The behaviour toward net panel and number of fish passing through the net were recorded on VHS video cassettes using video recording system.
3.1.2.3 Data analysis
The number of individual passing each of net panel presented in chart.
Statistical test for significant difference (α=0.05) between the number of
3.1.3 Fish behaviour using specific white panels
The fish behaviour using specific white panels was conducted to follow up the result of the fish behaviour towards contrast colour panel. From the result of contrast colour panel experiment, there was an effect of colour (i.e. old white, new white, and black painted) on behaviour of fish passing through the net panel. Moreover, the comparison between the new white and black painted net panel estimated was the highest (further explanation is on results and discussions).
Since it was the highest, then it estimated that black painted or contrasting colour was more visible to fish than old white and new white. It means that fish suppose to recognize more of the existence of this net panel.
Furthermore, on further study, the comparison between each net panel will be focused and specified only for the old white net and new white net with an addition of the white dyed net. The reason of using the white dyed net was to add more choices on white transparency.
3.1.3.1 Materials and instruments
The fish used in this study was the same than that on contrast colour panel experiment which was Japanese Jack mackerels. The difference was only in number, totally 24 fish.
The instruments that was used in this study was also similar than that on contrast colour net panel experiment. The things that make this experiment difference than that on the contrast colour net panel experiment was that this experiment was using larger experimental tank which separated in the middle of the experimental tank by the use grey PVC separator (Table 2). The purpose of this action was to larger the swimming track of fish than that on the contrast colour net panel experiment.
Table 2. Instruments for the fish behaviour using specific white panels
No. Instruments Function
1. 2. 3. 4. 5. 6. 7. 8.
3 net panels (old, new and white painted) (46x53 cm) framed with PVC 16 mm. Grey PVC separator (200x50 cm) was put in the middle of test tank to allow fish swim circling. Other separators placed both in the right and left of test tank, were used as temporary holding tank (Figure 6).
Herding panel (Figure 6).
Experimental tank (400x100x50 cm) filled with sea water at 40 cm in height (Figure 6).
Video recording system (Figure 6), consisted of: Victor GY-DY 500 DV
8 mm Sony handy cam Underwater camera Multi-viewer Monitor
Mini DV cassettes (80 minutes) Thermometer
Lux meter
Digital camera Stopwatch
Research instrument
Herding the fish swimming Fish tank
Recording the fish swimming and behaviour
Measuring the water temperature Measuring the light intensities Documentation
Figure 6. Equipments used during the behaviour experiment
3.1.3.2 Research procedure
For preparation, about 10 Jack mackerels that were used as experimental fish were released from the keeping tank in the morning. They were let to swim voluntarily and get used with the test channel. At night fish were preserved in the temporary holding area. The experimental protocol of this behavioural research is mentioned below.
1) Before starting the experiment, fish were acclimatized to swim in circling movement for 1 hour. The 16 mm diameter of PVC pipe and 125 cm length used to lead the school of fish moving circling, then pass the panel without a net that was set already (Figure 7).
Panel without a net K eep in g ar e a K eep in g ar e a Lead Lead Panel without a net K eep in g ar e a K eep in g ar e a Lead Lead
Figure 7. Acclimatization process (from top view)
2) After 1 hour acclimatization, the trials were started, the netting panel was set then the water temperature and light intensity was measured. Time for each trial of behaviour was 20 minutes. There were 10 replicates of each trial using 3 different types of net (new white, old white, white dyed) and panel without a net as control.
3) The black herding panel were set one area A-C. The setting time of the herding panel on each area was 1 minutes, after that the time will be counted precisely (Figure 8). The swimming behaviour of each trial was recorded on mini DV. Ne t pane l K eep in g ar e a Ke epi n g ar e a Herding panel Herding panel
A
B
C
1 ‘ 1’ 1’ Ne t pane l K eep in g ar e a Ke epi n g ar e a Herding panel Herding panelA
B
C
1 ‘ 1’ 1’Figure 8. Conditioned behaviour (from top view)
4) These procedures will be repeated with 3 different netting panels (new white,
3.1.3.3 Data analysis
The number of fish passing through the different colour of mesh panel, the time elapsed and mesh passing behaviour on each trial was analyzed on Sony Mini DV on frame- by frame basis. Each is expressed on a proportion of the number of fish passed through the test channel in 20 minutes observation period to the control attempt. The using of statistics method of One Way Anova is necessary to see the significance different of mesh passing behaviour.
3.2 Capture Process Experiment
3.2.1 Time and location
Experimental fishing operations were conducted in October-November 2006 in Bondet Waters, Cirebon Regency using a commercial fishing unit. The map of experimental fishing operation is on Appendix 1.
3.2.2 Materials and equipments
Millennium gillnet catch was the research objects of this study. The catch of
millennium gillnet was measured its length and weight by the help of ruler and weight scale. Nylon string was used to help measuring the maximum body girth (Gmax) as shown in Table 3.
Table 3. Materials for the experimental fishing
No. Materials Function
1 2 3 4 5 6
Millennium gillnet catch
Fishing provision (fresh water, rice, and fuel) Ruler (height max 5 m)
Weight scale (weight max 5 kg) Nylon string
Digital camera
Research object Provision of fishing Measuring the total length Measuring the weight of catch Measuring the maximum body girth Tool of documentation
Millennium gillnet and fishing boat are used in the fishing experiments. The fishing boat was used to transport the fishermen to fishing area and the millennium gillnet is used as the fishing gear. They are both the most important
factors of fishing activity as well as the importance of fishermen as the actors of this activity.
3.2.3 The methods of collecting data
The data recorded in each operation were fishing operation method, time duration for each operation stage and catch number in millennium gillnet according to the captured conditions (snagged, gilled, wedged and entangled) with reference to the species and size. Ten replicates were done and each replicate presented by one fishing operation (setting-hauling). The total length and body girth of fish caught will be measured to the nearest centimetre.
Some interviews with the millennium gillnet fishermen were conducted to collect some information about the development of the millennium gillnet in Cirebon.
3.2.4 Research method
The millennium gillnet used in this experiment was 804 m long. The body
net consists of 12 pieces of net, measuring 67 m long and 7.8 in depths for each piece. The net webbing was nylon multi-monofilament, with mesh size of 4 inch, respectively. The hanging ratio of the web was 0.45.
Figure 9. Fishing boat of millennium gillnet used in the experimental fishing
Table 4. Description of the millennium gillnet used in the experimental
fishing operations in Cirebon
No Items Specifications
1
2 3 4
5
Body net
Number of net units Float line
Float
Sinker
Nylon, 4 inch mesh size in stretch measure, white transparent in colour, 41 meshes deep, 4248 meshes long, 0.45 of hanging ratio.
12 pieces (804 m long and 7.8 m deep). PE 50 mm diameter, 804 m long
Cylindrical plastic, 13.4 cm diameter, 38.5 cm long, 576 pieces, and 126 cm of each float distance.
Cylindrical cement, 10 cm diameter, 3.2 cm width, 1 kg each, 101 pieces, 8 m of each sinker.
3.2.5 Assumptions
The assumptions used in the experimental fishing were: 1) The possibility of each individual to be caught is the same.
2) The external factor caused by oceanography conditions (i.e. current, tides, temperature, salinity, turbidity) are considered not significant among research nets.
Figure 10. Design of the millennium gillnet in Bondet Waters, Cirebon
50.00 PE 12 50.00 PE
1400 Pb 1000 g R 650 tex
E = 0.45 5 (x 2)
PA multi monofilament/ folded monofilament
3.2.6 Operation method
1) In the afternoon, around 3 p.m., the fishing boat started the fishing operation and arrived at the location around 4 p.m. Setting process was done on the seabed upright the coastal line by deploying the marking buoy (Figure 11), then piece by piece of the net while the boat moves forward (Figure 12).
[image:46.595.165.454.232.404.2]Figure 11. Deployment of the marking buoy in the afternoon
Figure 12. Shooting net piece by piece
2) The net were soaked underwater around 2-3 hours. After the soaking time ended, the net then piled up on the deck for subsequent operations. The catch number counted and catch size were measured (Figure 13).
Figure13. The last hauling process (in the late afternoon)
3.2.7 Data analysis
4 RESULTS
4.1 Brief History of Millennium Gillnet
Millennium gillnet was introduced in Mertasinga Village, Bondet through a short training held by the Fishing Utilization Section of local Fisheries and Marine Affairs Agency in 2002. The first introduction in Cirebon was probably in Gebang Mekar Village on the year of 2000-2001. It was introduced by Gebang Mekar fishermen who just returned from South Korea from a fishing contract.
No one knew who was the first person who named this gillnet as a
millennium gillnet. The name of “millennium” probably came from the year 2000, a period of time when this gillnet was first introduced in Cirebon. The name was probably also came from the colour of net material which is white transparent and looked shinning, at the beginning of its use.
This gillnet was a popular gillnet used in South Korean and Cirebon fishermen tried to adopt the use of this gillnet to the local artisanal fisheries. As soon as the use of this gillnet started to raise, the local net factory, PT ARIDA made this gillnet in mass production. Many of millennium gillnets used in Cirebon was produced by PT ARIDA.
Fishermen usually bought this gillnet from the local market or stores, since they can not order this net directly from the producer, PT ARIDA because of the requirement of minimum order. Koperasi Unit Desa (KUD), the local fisheries cooperative society, helped the fishermen on ordering this gillnet to the producer by collecting the need of this net until reached the minimum order. But recently, most of the fishermen started to use the second hand or used gillnet instead of new gillnet in order to minimize the cost.
The tight competition among the swimming crab fishermen is made the income of the fishermen decreasing. Many of the swimming crab fishermen switched their job then became a millennium gillnet fishermen because of the good prospect of this gillnet. This was because of a successful introduction and
implementation of this net among Cirebon’s fishermen.
(West Borneo) and was operated to an industrial fishing. But in Cirebon, most of the millennium gillnet fishermen are the artisanal fishermen.
4.2 Fish Behaviour Study
4.2.1 Fish behaviour in relation to contrast colour net panel
From the result of the experiment, the largest frequency of fish entering the new white was on the conditioned behaviour (106 fish), while fish tend to enter the old white panel on the voluntary behaviour (101 fish). On the other hand, the frequency of fish entering both panel (old white and new white) were higher than the frequency of fish entering black panel. From the proportion of fish passing through net, the highest frequency of average was on the new white in voluntary behaviour (0.577). Frequency of fish entered black panel less than the new and old white panel.
w w w
y
±
S
E
*
Note: *) Significant among 3 net panels
Figure 14. Comparison among the fish passing through the net panel on voluntary behaviour
From Figure 14, the comparison of fish passing through the net panel on voluntary behaviour was significant to the other net panels. This probably was due to the white nets, either old white or new white were less visible than the black net.
control. The control was the frequency of fish passing through the panel without a net.
In voluntary behaviour, the fish was less active than the conditioned behaviour. This probably because of none of stimulus is used to stimulate the fish of not avoiding to pass through the net panel. The use of forcing panel to minimize the swimming area of fish in area B was very helpful to makes the fish swim more active.
w w w
y
±
S
E
Figure 15. Comparison among the fish passing through the net panel on conditioned behaviour
From Figure 15 above, the comparison of fish passing through the net panel on conditioned behaviour was not significant. The fish becoming more active than if it was in voluntary because of the use of forcing panel. This made the frequency of passing in each of net panel of conditioned behaviour increasing, especially in both white nets (old white and new white). The frequency of passing in both white nets (i.e. the old white net and new white net) was higher than the black net, with the highest frequency was in old white net. It showed that the fish was actually avoiding the contrast colour.
4.2.1.1 Net colour transparency
From the result of TWO-WAY ANOVA (α= 0.05), the net colour
transparency between old white, new white and black painted has significant difference.
Table 5. Signification level of comparison proportion among three types of
net panel
Net colour Old white Black painted New white
Old white 0.072 0.967
Black painted 0.049*
New white
Notes: *) significant in p<0.05
Table 5 shown the signification level to compare the proportion among three types of net panel in voluntary behaviour. According of the signification level between the three netting panel, it showed that the comparison between the new white and black painted was the most significant.
4.2.1.2 Fish behaviour in relation to netting panel
The behaviour of fish recorded on video tape were (1) Japanese Jack mackerels tend to swim in circling movement around and near the mesh panel with their school; (2) After succeed passing the mesh and entering the other side of experimental tank, they tend to return to the previous side, and joined their school; (3) Japanese jack mackerel was able to see net barrier on their swimming movement, but intend to pass; (4) Japanese jack mackerels was avoiding the black panel.
4.2.2 Behaviour experiment using specific white net panels
From the result of the experiment, most of fish was to keep clear the mesh
As the result of the frame on frame analysis on mini DV, Japanese Jack mackerel did the reaction behaviour when they recognized the existence net panel on their swimming movement, stop first, and tried to pass the net panel, either way they avoiding the net panel and just swimming in circling. The Jack mackerels were not very active in voluntary unless they were given some stimulus, for example to herd their swimming movement, the treatment that was given as conditioned behaviour on this experiment.
w w w w y
y
±
S
E
Figure 16. Comparison of fish passing through the net panel
The proportion of the frequency of passing in Figure 16 derived from the frequency of fish passing through each net panel divided into frequency of fish passed through control. The control was the frequency of fish passing through the panel without a net.
The result of the experiment showed that the frequency of passing among white nets is not significant; it means that there is no effect of transparency among three types of white nets. It makes that operating old white net or new white net considering similar in fish to pass. If this result will be implemented on the habit
of fishermen, the use of old white net considering fine to the fishermen in order to minimize the cost, as long as the web is less of damages and still in good condition.
w w w w y
Figure 17. Proportion of fish passing through the net
Figure 17 showed that in 10 trials of this behavioural experiment, the frequency of fish passing was fluctuated. This was because of the natural
behaviour of this fish that sometimes very active but sometimes inactive. It was very difficult to maintain the fish in stable condition in each trial, even though external factors that probably could influence the experimental result such as illumination, temperature, time of food giving are being controlled.
From this result, it can be derived that animal including also fishes, have their inactive period and active period of swimming, in this case the swimming of passing through the net. This result only try to described the activity of fish during each trial, but from statistical test it can be inferred that if the net transparency of a net panel less visible, then the more fish passing through it.
4.2.2.1 Mesh passing reaction of fish
From the result of one way ANOVA on old white, new white and white dyed net panel showed that most fish could pass through the mesh without any contact. Most fishes always try to keep clear on netting panel then try to pass through the netting panel. It means that non contact behaviour is significant behaviour reaction in all of netting panel used on the experiment.
%
*
Figure 18. Contact and non-contact reaction of fish passing through old white net panel
Figure 18, 19, and 20 are proportion of fish passed through the netting panels (old white, new white and white dyed). The value of proportion derives from the frequency of fish passed the net with or without contact divided total number of fish passed through the net. From the three panels used on the experiment, old white netting panel has the largest number proportion on non-contact reaction on passing. That is considering because most fish could be able to pass this net without any contact, if it compares within the others.
Figure 19. showed that most of fish could be able to pass the old white net without any contact (12.032%). It means that non-contact behaviour was dominant against contact behaviour. This happen because of the hanging ratio of the netting panel (0.65) and the mesh perimeter that used in the experiment was bigger than in the real fishing operation (hanging ratio around 0.4-0.45).
%
[image:55.595.102.497.65.829.2]*
Figure 19. Contact and non-contact reaction of fish passing through new white net panel
Figure 19 above showed that most of fish could be able to pass the new white net without any contact (8.999%). It means that non-contact behaviour was
dominant against contact behaviour. This happen because of the hanging ratio of the netting panel (0.65) and the mesh perimeter that used in the experiment was bigger than in the real fishing operation (hanging ratio around 0.4-0.45).
% *
Figure 20 showed that most of fish could be able to pass through the white dyed netting panel without any contact (7.185%). It means that non-contact behaviour was dominant against contact behaviour. This happen because of the hanging ratio of the netting panel (0.65) and the mesh perimeter that used in the experiment was bigger than in the real fishing operation (hanging ratio around 0.4-0.45).
The reason of using bigger hanging ratio in behaviour study is to avoid fishes got injured when they were passing the mesh, so the behaviour of passed could be observed. In actual fishing operation, the fish suppose to get caught by the net, and then the hanging ratio and mesh perimeter considered being smaller.
4.2.2.2 Behaviour of fish in relation to net colour
Proportion of fish passed through different colour of mesh panels is shown in Figure 21. As we could see from the figure, old white net has the highest proportion of fish passed through the mesh. Wardle et al. (1991) stated that the net colour appearance underwater was affected by many factors, at low intensities
gillnets made by fine twines chosen to be relatively invisible to the fish. If the luminance of an object matches the luminance of the background then the object will see as invisible.
w w w
w y
%
Figure 21. Proportion of fish passed through the net colour
With one way Anova, the significance of the influence of colour on the frequency of fish passed through the mesh showed no significance different. All of the net panels are considered to have capability of facilitating fish to pass and the old white net panel is the highest. This means that fish was avoiding the more visible white transparency.
4.3 Capture Process Experiment
4.3.1 Catch composition
The catch composition of millennium gillnet dominated by threadfins (Polynemus spp.) for 71.287% of catch. While by-catch were consists of striped catfish eel (Plotosus lineatus), spotted catfish (Arius maculatus), great barracuda (Sphyraena barracuda), triple tail (Labotes surinamensis), barramundi (Lates calcarifer), blue spotted snapper (Lutjanus rivulatus), silver pomfret (Pampus argentus), stingray (Dasyatis spp.), garfish (Hemirhampus spp.) and shark (Charcarinus spp.).
Table 6. Species composition in percentage and total length (TL) of fish
caught by millennium gillnet
No English name Scientific name TL (cm) Number of
catch Catch (%)
1 Threadfins * Polynemus spp. 34-73 72 71.287
2 Striped catfish eel * Plotosus lineatus 32-82 11 10.891
3 Spotted catfish * Arius maculatus 44-53 7 6.931
4 Great barracuda Sphyraena barracuda 89-94 2 1.980
5 Triple tail Labotes surinamensis 45-57 2 1.980
6 Barramundi * Lates calcarifer 63-72 2 1.980
7 Blue spotted snapper * Lutjanus rivulatus 30 1 0.990
8 Silver pomfret * Pampus argentus 30 1 0.990
9 Rayfish * Dasyatis spp. 180 1 0.990
10 Garfish Hemirhampus spp. 78 1 0.990
11 Shark Charcarinus spp. 58 1 0.990
Total 101 100
Note: *) demersal fish
This was because fishermen operated the millennium gillnet in the shallow waters of Bondet Waters around 7-10 m of depth and the distance of fishing operation just around 0-12 miles from the coastal zone. Since the body net was around 7.8 m of depth then the demersal species were caught by this gillnet.
If this gillnet were operated in deeper and further waters area, the catch were dominates by pelagic species, such as barred Spanish mackerel, frigate tuna, sailing fish, etc as seen in Karangsong, Indramayu. In Indramayu, millennium gillnet is operated in industrial scale, not the artisanal fishery. They using larger fishing boat (around 20 GT) and operates in the ocean and waters more than 12 miles. The period of fishing ope
