20 Introduction of Floating Brush Park Triyanto

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Proceedings National Symposium on EcohydrologyJakarta, March 24, 2011

267

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


Location 1

Location 2

Location 4

Location of RasauTerapungLocation of RasauTerapung


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

Rasau

Production

Rasau

Protection

Rasaushoreline

Production

Rasau

Production

Rasau

Production

Rasau

Production

Rasau

Production

Rasau

SocialRasau

Protection

Rasau

Protection

Rasau

Protection

Rasaushoreline

ProductionRasau

Production

Rasau

Production

Rasau

Production

Rasau

Production

Rasau

Production

Rasau

SocialRasau

Protection

Rasau

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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20 Introduction of Floating Brush Park Triyanto