20 introduction of floating brush park triyanto
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INTRODUCTION OF FLOATING BRUSH PARK FISHERY
(RASAU TERAPUNG) TO ANTICIPATE WATER LEVEL FLUCTUATION IN
CAPTURE FISHERY MANAGEMENT IN LAKE MANINJAU,WEST SUMATRA
Triyanto1)
, Dede Irving Hartoto1)
, Sutrisno2)
, Agus Hamdani2)
and Sulastri1)
1)
Research Center for Limnology-LIPI2)Research Station for Limnology-LIPI
Email: [email protected]
ABSTRACTThe floating brush park namely rasau terapung was introduced to anticipate the fluctuation of
water level in Lake Maninjau during August to December 2010. This was a collaboration of fourof fishermen groups. The construction was employing bamboos which were filled with branches
of tree, coconut leaves and bamboo sticks. The size was 5x5 m2
using floating plastic drums. The
construction of rasau enabled it to move along water fluctuation. A number of rasau terapungwere 38 units located around the lake. It would function after residing in the water for a month.
Some of aquatic vegetations and some of invertebrate organisms were attached in rasau
terapung. Therefore the fishes could be attracted and stayed in rasau terapung area. Fish
production in rasau terapung was 97-117 kg (0.6-0.8 kg/m2). Not only had the fish production
increased, but also the daily fish catch of fishermen around the rasau terapung had risen.
Keyword: water level fluctuation, floating brush park, Lake Maninjau
INTRODUCTION
LakeManinjau is one of the inland waters located in the province of West Sumatra. It is
a tecto-volcanic lake with an area of 9737.5 ha, and maximum depth 165 m. Lake
Maninjau has good potencies for fisheries. Fishery activities in Lake Maninjau are
mostly aquaculture and capture fisheries. Capture fishery of Lake Maninjau has an
economic contribution to the people. Some types of native fish of Lake Maninjau have a
high economic value, such as bada (Rasboraargyrotaenia), rinua, gariang (Tor soro),
barau (Hampala macrolepidota), and asang (Osteochilus haselti). They are often
included in targeted fish by fishermen. Fishing gear used is also quite varied consisting
of nets, fishing rods, scoop and trap, and rasau. Based on data from the West Sumatra
provincial fisheries department in 2003, it was recorded that the production of capture
fisheries in Lake Maninjau reached 111.7 tons (Triyanto et al. 2007).
Rasau is commonly known as traditional FADs that serves to collect fish in
fishing activities by fishermen of Lake Maninjau for a long period.Rasau was made
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from a collection of wooden twigs, and midrib of palm trees embedded in the edge of the
lake. The use of this rasau is effective enough to help fishermen catch fish in thelake. Based on the information of fisherman that used rasau, fish catch around rasau can
reach 1-2 kg/day or depend on the number of fish that gather at these rasau areas. Fish
production on a similar system called the brush park which varies between 0.01 to 3.8
kg/m2/year (ICLARM-GTZ, 1991; Welcomme and Kapetsky, 1981 in Herb et al. 2003).
Fish capture system with rasau is less used.Rasau that exist at this time are not
functioning optimally, due to fluctuations in lakes water level which is high.
Fluctuations in water level of Lake Maninjau appear at an elevation of 462-464 m asl
(Fakhrudin et al. 2002). When low water level occurs, rasau is on the top of water
surface so that its function as a means of collecting fish is ineffective. In addition as a
means of collecting fish, rasau has ecological function because it can be the protected
areas, where spawning and foraging exist. Ecological function is the result from the
formation of the food chain systems that supports life functions for fish communities. Its
placement on the edge of the lake is to support the role of productivity in the littoral
waters of the lake.
Introduction of rasau float is one of the efforts made to anticipate fluctuations in
water level in order to enhance fisheries production and improve the productivity of the
littoral zone. This paper submits the introduction of rasau terapung conducted in
August-December 2010 with the purpose of estimating rasau production and
composition of fish catches using rasau terapung.
MATERIALS AND METHODS
Rasau terapung (FBPF: Floating Brush Park Fishery) introduced, was a collection ofsticks made of wood and bamboo and was placed and tied in a square frame size of 5x5
m2
made of bamboo.Rasau framework consists of 4 pieces of plastic drum that served
as a buoy (Figure 1). On the basis was laid pieces of bamboo or concrete pipes.
Placement rasau terapung (Figure 2) was located on the edge of the lake at a depth of 2-
5 m with ballast anchors so that the movement rasau can follow the movement of lakes
water level.Rasau terapung was made of 38 pieces placed in four locations around Lake
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Maninjau, namely location 1: Tampang River (10 pieces), location 2: Sigiran (10
pieces), location 3: Rangeh River (6 pieces): and location 4: Batang River (12 pieces).Introduction ofrasau terapung was done by direct engagement with groups of
fishermen in Lake Maninjau.Rasau terapung management system conducted jointly was
carried out, by dividing into three parts ofrasau region, namely rasaulindung/rasau for
conservation (3 pieces), rasauproduksi/rasau for production (6 pieces) and rasau
sosial/rasau for social purpose(1 piece). Fishing was allowed only on rasau production
and rasau social. Catching fish was done after seeing the condition of many fish
collected in the area ofrasau. The fish caught were weighed and identified to determine
its species.
RESULTS AND DISCUSSION
Description of Lake Maninjau
Lake Maninjau is surrounded by hills located at Tanjung Raya District, West Sumatera.
Lake Maninjau is a volcano-tectonic lake. Since it was used for power generation in
1983, lake-water discharge system was unnatural. For the purposes of hydro electric
power, there have been built a DAM at the outlet of Lake Maninjau. The DAM is
located on the River Antokan which has an altitude of 462 m asl. DAM is raising the
water level of the lake from 462 m asl to 464 m asl (Fakhrudin et al. 2002). With the
operation of hydro electric power, the lake water level fluctuations are also influenced
by the operational activities of the turbine in the electricity production process.
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20 cm
bamboo
Bundles of
branches of
bamboo, and
coconut leaf
line and anchor (6 mm)
concrete pipe
with holes
water surface
plastic drum (floating
drum)
Figure 1. Specification ofrasauterapung: FBPF, size 5x5 m2
Location of RasauTerapung
Map of Lake Maninjau
Location 1
Location 2
Location 4
Location 3
Location of RasauTerapung
Map of Lake Maninjau
Location 1
Location 2
Location 4
Location of RasauTerapungLocation of RasauTerapung
Map of Lake Maninjau
Location 1
Location 2
Location 4
Map of Lake ManinjauMap of Lake Maninjau
Location 1
Location 2
Location 4
Location 3
Figure 2. Placement location ofrasau terapung in Lake Maninjau
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Lake Maninjau has been experiencing eutrophication mainly due to the input of
organic load from the floating cage net fishery activities (Sulastri, 2001; Triyanto et al.2007). The transparency of waters is very low with the range of 1-2 m. The level of light
penetration is reduced due to algae bloom due to the enrichment processes that occurs in
Lake Maninjau. According to Meutia et al. 2003 low levels of light penetration is
thought to have caused several species of aquatic plants in littoral area and is reduced
and even no longer exist as small jariamun (Najas sp.) and big jarimun (Potamogeton
sp.). Lake water level fluctuation can also cause death to aquatic plants that exist,
because of the effect on drying time in the littoral area of the lake. Diminishing water
plants in the littoral area of the lake can cause a decrease in the level of productivity of
the lake waters. According to Zalewski (1998) littoral lake is a habitat for many kinds of
aquatic organisms and plays an important role in supporting the productivity of lake
waters. Littoral zone may also function in the improvement of water quality conditions
in shallow lakes area (Numazawa et al. 2008).
Fisheries rasau and problems
Fisheries rasau is one of local wisdom that utilizes high-productivity waters in the
littoral area of the lake.Rasau placed on the edge of the lake serves as a shelter can
entice the fish to congregate in or around the area of rasau (Figure 3). This fishing
method is quite effective to help fisherman around the lake to get the daily catch of fish,
without damaging the habitat and water of the lake.
Figure 3. Traditional rasau in Lake Maninjau made from a collection of wooden twigs
and branches of coconut trees, located on the beach of the lake.
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The use of traditional rasau has not been optimal when, the rasau physically
are not submerged in the water. The placement of a static traditional rasau at the beachof the lake causes rasau always on the edge of the lake without being immersed by
water. Thus, the functional of traditional rasau is highly dependent of the lake water
level when normal. A water level fluctuation in the lake now highly affects on
traditional rasau function, so the method of fishing using this system is gradually
reduced.
Rasau terapung and management
Rasau terapung was developed based on the problems that occur in traditional rasau
whose function depends on the water level of the lake when it reaches ideal condition for
rasau so that it is always immersed in the water. A technical requirement of rasau
terapung is as follows:
1. the rasau should float so that it remains submerged in water according to water
level
2. it has a binding anchor heavy enough so it does not move
3. It has ecological structure (shade structure from excessive water temperature: the
sticks above the surface; trappers and retaining structures: a collection of twigs
and branches; structure where attached algae: a string of ropes and leafs.
4. if necessary, the addition of additional elements may be applied such as :
Lights: mounted at night to gather zooplankton and aquatic insects which will
attract fish to come because of the food source.
Place as a stimulant advent of artificial food fish.
Aquatic plants: helping the bio-ecology to improve the condition of waters inthe area ofrasau.
Introduction ofrasau terapung directly involved fishermen groups on several
locations in Lake Maninjau. This means that the rate of adoption to the fishermen could
take place quickly, considering that they have known natural rasau fishery system
properly. Placement of the rasau terapung on the shores of the lake with a depth of 2-5
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m. Management of the rasau terapung was conducted jointly by groups of fishermen so
that supervision and treatment could be more effective.Management of the rasau terapung was divided into three parts, namely the
production rasau (6 pieces), protection rasau (3 pieces) and social rasau (1 piece)
technically the rasau system (10 pieces of rasau) named Rasau Limnotek 7.0.
Placement of protection rasau was in between or in the middle of the rasau terapung
area, with the parallel patterns to the shoreline or circular system (Figure 4). Catching
fish was done when the rasau terapung had been in the lake for 1 month for minimum
period. The next catching was periodically followed by, in accordance to mutual
agreement and the conditions of existence of the fish in the area of rasau terapung. The
fish caught were in the area of production rasau and social rasau, while forprotection
rasau were left as a conservation for the existing fish community. The existence of fish
in the protection rasau areas were expected to maintain fish stocks in the waters. The
fish yielded from the social rasau were used for groups of fishermen for any purpose.
The fish yielded from the production rasau were used to increase the income of group
members. In addition to fishing on the rasau terapung area, every member of the
fishermen was allowed to fish individually near area of rasau terapung. Whereas the
other fishermen who were not members of the fishermen groups, could still catch fish
around the area of rasau terapung at a minimum distance of 50 m, or by mutual
agreement. The rasau terapung thatmanaged by groups of fishermen could be seen in
Figure 5.
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(A) (B)
Production
Rasau
Production
Rasau
Production
Rasau
Production
Rasau
Production
Rasau
Social
Rasau
Protection
Rasau
Protection
Rasau
Production
Rasau
Protection
Rasaushoreline
Production
Rasau
Production
Rasau
Production
Rasau
Production
Rasau
Production
Rasau
Social
Rasau
Protection
Rasau
Protection
Rasau
Production
Rasau
Protection
Rasau
Production
Rasau
Production
Rasau
Production
Rasau
Production
Rasau
Production
Rasau
Social
Rasau
Protection
Rasau
Protection
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Production
Rasau
Protection
Rasaushoreline
Production
Rasau
Production
Rasau
Production
Rasau
Production
Rasau
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SocialRasau
Protection
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Protection
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Protection
Rasaushoreline
ProductionRasau
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Production
Rasau
Production
Rasau
SocialRasau
Protection
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Protection
Rasau
Protection
Rasaushoreline
ProductionRasau
(B)
Figure 4. Pattern of placement the rasau terapung in Lake Maninjau (A. Circular
pattern; B. Parallel to the shoreline)
Figure 5. Rasau terapung managed by one group of fishermen at Sigiran in Lake
Maninjau
Production and composition of fish caught on rasau terapung
Production of rasau was determined based on fish catch directly in the area of
productionrasau. The fish catched by nets with encircle the net in rasau area. The fish
stayed in rasau should be out of the rasau. Fish yielded from twice capture were
obtained respectively at 98 and 117 kg, or the fish production level reached 0.6 to 0.8
kg/m2. The fish commonly caught were culture fish, such as carp (Cyprinus carpio) and
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tilapia (Oreochromis niloticus). The catch and composition of fish caught were
presented in Table 1 and 2.
Table 1. Species composition and total fish catch on production rasau at location 1 in
October 19, 2010.
No. Fish Species (local name) Number
(pieces)
Total
Weight (kg)
Size
(gr)
1. Pangasius sp. Patin 1 3 3000
2. Hampala macrolepidota Barau 12 2 50-150
3. Oreochromis niloticus Nila 18 23 250-1500
4. Cyprinus carpio Mas 30 62 1000-2000
5. Oxyeleotris marmorata Betutu 12 5 100-250
6. Chana striata Gabus 1 2 2000
7. Osphronemus goramy Gurame 2 1 500
8. Rasbora argyrotaenia Bada - - -
Total 98
Table 2. Species composition and total fish catch on production rasau at location 4 in
December 11, 2010.
No. Fish Species (local name) Total
Weight (kg)
Size
(gr)
1. Hampala macrolepidota Barau 5 750
2. Oreochromis niloticus Nila 65 250 1000
3. Cyprinus carpio Mas 30 250 1000
4. Oxyeleotris marmorata Betutu 3 250 5000
5. Osteochilus haselti Asang/Nilem 3 300 -700
6. Osphronemus goramy Gurame 2,5 3000
7. Rasbora argyrotaenia Bada 7,5 10
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8. Clarias sp. Lele 1 1000
Total 117
Fish harvest was still constrained by an effective technique for catching fish in
rasau. According to the fishermen, there were still a lot of fish that could not be caught
in rasau and the production might have reached twice than that of the captured
fish. When viewed from the composition of fish catches, fish caught were dominated by
carp and tilapia. Both of these fish were the commodity that a lot of fish reared in
floating net cages. By using this rasau, fish that escaped from the cages would be easy
to collect in rasau terapung area. While barau fish, patin/catfish and gabus/snake head
were native fish of the lake. Those fish were predatory fish that generally ate small fish
settled in the rasau area and beyond. In addition to the catch of rasau managed by
groups, fishermen catch around the rasau was also increased, in number. And the length
of time to catch fish became increasingly shorter. However, to calculate how much profit
they had earned by rasau terapung system on their daily catch was still under further
review. As a comparison of fish production in Bangladesh River utilizing shelter from
aquatic plants fish production reached 750 kg/ha/year, equivalent to 0.075 kg/m2/year
(Ahmed and Akhter, 2008). While the fish production in Lake Malawi with brush park
system over the past five months, reached 0.07 to 1.27 kg/m2 (Jamu et al. 2003).
Rasau terapung system is also a substrate for the growth ofjariamun, a species
of aquatic plants that lives in bottom in the littoral area of the lake (Fig. 6). Jariamun
(Najas sp and Potamogeton sp) is an aquatic plant that can be used as food by
herbivorous fish and a place to lay eggs or hiding places of any kind of fish in the
lake. Jariamun can grow under rasau within depth depending on the level of lightpenetration needed and is always immersed in water. Jariamun has ecological function
as a plant nutrient absorber, water purifier and a habitat for small fish. However its
population is reduced due to pollution, water level fluctuations and environmentally
destruction as the effect of fishing activities.
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Figure 6. Aquatic plants (Jariamun:Najas sp and Potamogeton sp.) attached in to rasau
terapung.
CONCLUSION
Rasau terapung is effective to anticipate fluctuations in water level of the lake. Its
function as a means of collecting fish can take up the production level approximately 0.6
to 0.8 kg/m2. In addition, this rasau may act as fish attractor/collector as well as
artificial habitat for many aquatic organisms.
ACKNOWLEDGEMENTS
Acknowledgements submitted to the XIII-LIPI IPTEKDA Program 2010, which had
funded this activity and to the group of fishermen in Lake Maninjau who had provided
respectable help during this research.
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