Gillnets selectivity and effectivity for controlling invasive fish species in Lake Matano, South Sulawesi

Abstract

Lake Matano is one of the ancient lakes in East Luwu Regency, South Sulawesi, which has uniqueness and high endemicity for freshwater fishes. The presence of invasive alien fishes there can threaten the existence of endemic fishes. This study aimed to investigate the selectivity and effectiveness of the use of gillnets on several mesh sizes for controlling the population of invasive alien fishes in Lake Matano, South Sulawesi. Sampling was conducted in May, October, November 2015 and February, July, November 2016 using monofilament experimental gillnets with various mesh sizes (0.75, 1.0, 1.5, 2.0, 2.5, 3.0 inches) and twine (D = 0.15, 0.20, 0.25 mm). The mesh size of 1.5, 2.0, and 2.5 inches could catch flowerhorn cichlid as the dominant and invasive alien fish with little chance to catch native fishes in Lake Matano. The selectivity factor (SF) for the mesh size of 1.5, 2.0, and 2.5 inches was 3.02. The average catch size of flowerhorn cichlid captured by the mesh size of 1.5. 2.0, and 2.5 inches were 11.5, 15.3, and 19.2 cm, respectively. The yarn diameter did not significantly affect flowerhorn cichlid capture (P <0.05). However, the mesh size of 1.5 inches was significantly different (P>0.05) to other mesh sizes. For effectiveness, gillnet was better to operate in littoral areas of lakes, especially in the location associated with the sand substrate with macrophytes. The operation of the gillnet in Lake Matano needs to be regulated in terms of location and setting time to minimize the capture of fish species other than flowerhorn cichlid.
Keywords: flowerhorn cichlid, gillnet selectivity, invasive species, Lake Matano, Louhan

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Gillnets selectivity and effectivity for controlling invasive fish species in
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International Conference on Tropical Limnology 2019
IOP Conf. Series: Earth and Environmental Science 535 (2020) 012039
IOP Publishing
doi:10.1088/1755-1315/535/1/012039
1
Gillnets selectivity and effectivity for controlling invasive fish
species in Lake Matano, South Sulawesi
A A Sentosa* and D A Hedianto
Research Institute for Fish Resource Enhancement, Jalan Cilalawi No. 1 Jatiluhur Purwakarta
West Java 41152 Indonesia
* Corresponding author
agusarifinsentosa7@gmail.com
Abstract. Lake Matano is one of the ancient lakes in East Luwu Regency, South Sulawesi,
which has uniqueness and high endemicity for freshwater fishes. The presence of invasive
alien fishes there can threaten the existence of endemic fishes. This study aimed to investigate
the selectivity and effectiveness of the use of gillnets on several mesh sizes for controlling the
population of invasive alien fishes in Lake Matano, South Sulawesi. Sampling was conducted
in May, October, November 2015 and February, July, November 2016 using monofilament
experimental gillnets with various mesh sizes (0.75, 1.0, 1.5, 2.0, 2.5, 3.0 inches) and yarn
thickness (D = 0.15, 0.20, 0.25 mm). The mesh size of 1.5, 2.0, and 2.5 inches could catch
flowerhorn cichlid as the dominant and invasive alien fish with little chance to catch native
fishes in Lake Matano. The selectivity factor (SF) for the mesh size of 1.5, 2.0, and 2.5 inches
was 3.02. The average catch size of flowerhorn cichlid captured by the mesh size of 1.5. 2.0,
and 2.5 inches were 11.5, 15.3, and 19.2 cm, respectively. The yarn diameter did not
significantly affect flowerhorn cichlid capture (P <0.05). However, the mesh size of 1.5 inches
was significantly different (P>0.05) to other mesh sizes. For effectiveness, gillnet was better to
operate in littoral areas of lakes, especially in the location associated with the sand substrate
with macrophytes. The operation of the gillnet in Lake Matano needs to be regulated in terms
of location and setting time to minimize the capture of fish species other than flowerhorn
cichlid.
Keywords: flowerhorn cichlid, gillnet selectivity, invasive species, Lake Matano, Louhan
1. Introduction
Malili Lakes Complex is an ancient lake complex located in East Luwu regency, South Sulawesi,
consisting of several lakes such as Lake Matano, Mahalona, Towuti, Wawontoa/Lantoa, and Masapi
[1,2]. Lake Matano has an area of 164 km2 with a maximum depth of 590 m and an altitude of 382 m
above the sea level [3,4]. Lake Matano has a very high conservation value because it has much
endemic fish and other aquatic species [5,6].
One of the problems found in Lake Matano that threaten fish biodiversity is the introduced invasive
species. According to Herder et al. [7], fourteen species were found in Lake Matano during the
research on 2000-2012. The occurrence of flowerhorn cichlid, locally known as louhan, is increased,
and the fish tend to be invasive. Almost 35% of freshwater fishes extinction is caused by habitat
changes or loss, 30% by alien fishes introduction, 4% due to excessive exploitation, and by other

International Conference on Tropical Limnology 2019
IOP Conf. Series: Earth and Environmental Science 535 (2020) 012039
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doi:10.1088/1755-1315/535/1/012039
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factors such as pollution, water use competition, and global warming. The introduction of alien fish
species into freshwater ecosystems can have profound consequences, including loss of species
diversity, extinction of endemic species, distortion of food web function, and changes to ecosystem
productivity [8–15].
Lake Matano has 18 endemic fishes species that are generally dominated by family
Telmatherinidae and Gobiidae [16,17]. The occurrence of alien fishes in Lake Matano has widely
reported, and the invasive alien fishes are expected to have a negative impact because it will threaten
the existence of native or endemic fishes [5,18,19]. Therefore, it is necessary for controlling invasive
alien fishes, especially for flowerhorn cichlid in order to maintain biodiversity and endemicity of
fishes in Lake Matano. Donaldson and Cooke [20] reported that capture technique is one of the
methods for controlling invasive fish based on the selectivity of fishing gear. Next, this study aims to
analyze the selectivity and effectiveness of the use of gillnets on several mesh sizes for controlling the
population of invasive alien fishes, especially the flowerhorn cichlid in Lake Matano, South Sulawesi.
2. Methods
The research was conducted in May, October, November (2015) and February, July, November (2016)
in Lake Matano, East Luwu Regency, South Sulawesi. Data were collected at 17 stratified random
sampling stations [21] (figure 1).
Figure 1. Sampling station in Lake Matano.
Fishing experiments were conducted by installing experimental gillnets for four hours during the
day in the littoral zone (<100 m towards the shore). The gillnets used were made from monofilaments
with specific mesh size, i.e. 0.75; 1.0; 1.5; 2.0; 2.5; 3.0 and 3.5 inches. Experimental fishing was also
conducted in the limnetic area (depth >20 m) to determine the distribution patterns of flowerhorn
cichlid horizontally and vertically. The yarn diameter size (D) was also used with certain variations,
i.e., 0.15; 0.20; and 0.25 mm to analyze the effectiveness of flowerhorn cichlid fishing as an invasive
fish in Lake Matano. Identification of flowerhorn cichlid referred to Herder et al. [7], Hildebrand [22],

International Conference on Tropical Limnology 2019
IOP Conf. Series: Earth and Environmental Science 535 (2020) 012039
IOP Publishing
doi:10.1088/1755-1315/535/1/012039
3
Kullander [23], and the Fishbase [24]. The total length (TL) of fish samples were measured using a
measuring board with a precision of 0.1 cm.
The analysis for controlling invasive alien species (IAS) was conducted based on a gear selectivity
approach using gillnets. Estimation of gillnet selectivity was conducted using the logistic model (Holt
model) by the normally distributed for capture selection curve [25]. The assumptions for this model
are:
a. Fish caught gilled (fish caught just behind the operculum) and wedged (fish caught around the
body as far as the dorsal fin).
b. The optimum length of fish caught from the selection curve is proportional to the mesh size.
c. Both the selection curves of two mesh sizes have the same standard deviation.
d. Both mesh size has the same fishing power.
e. The formula for this model is:
2
2
()
exp 2*
LL Lm
Ss

−
=

(1)
Lmi = SF*mi (2)
where:
SL = points of the selection curve
L = the median of the fish length
Lm = the optimum length of the fish that can be caught
S = standard deviation
SF = selection factor
m = number of fish caught at Li
The effectiveness of gillnets was analyzed using a Randomized Block Design [26]. The group
approaches analyzed was a certain group of mesh sizes (1.5, 2.0, and 2.5 inches) and difference of
yarn thickness (D) (0.15 mm, 0.20 mm and 0.25 mm) with 12 times repetition. The hypothesis tested
was the effect of treatment of difference of mesh size and yarn diameter to the catch as follows:
H0 : µ1 = µ2 = µn (treatment has no effect on flowerhorn cichlid catch)
H1 : µ1 ≠ µ2 ≠ µn (at least one treatment where µn ≠ 0
The F test (ANOVA: Two-Factor Without Replication) was used following Least Significant
Difference (LSD) test to determine the significance of the controlling treatment for flowerhorn cichlid
by the formula:
.
0.05/ 2, 2
()
dfw MSw
LSD t n
=
................................................. ................... (2)
where,
LSD = Least Significant Difference
t0.05 = critical value from the t-distribution table (α = 0.05)
dfw = degree of freedom
MSw = mean square within, obtained from the results of the ANOVA test
n = number of replication
3. Results
3.1. Distribution of the Flowerhorn Cichlid as Invasive Alien Fishes
The flowerhorn cichlid caught in Lake Matano had a total length ranging from 4.2 to 22.4 cm. The
fish was caught on particular mesh sizes (1.0; 1.5 and 2.0 inches) and the yarn thickness. The 0.75-
inch mesh size caught a high amount of native fish species, especially for Telmatherina spp. (Opudi),

International Conference on Tropical Limnology 2019
IOP Conf. Series: Earth and Environmental Science 535 (2020) 012039
IOP Publishing
doi:10.1088/1755-1315/535/1/012039
4
while the mesh size > 2.5 inches had a deficient number of catches. The sufficient mesh size for
capturing flowerhorn cichlid but low for native fishes was 1.5, 2.0 and 2.5 inches, while mesh size of
≤ 1.0 inches was poorly used for flowerhorn cichlid control because it profoundly caught the native
fishes (figure 2).
Figure 2. Catch distribution of flowerhorn cichlid based on mesh size in Lake Matano.
The observed research stations were divided into the dominant bottom characteristics of the waters,
i.e., rocks, sand, mud, and aquatic plants (dominant species of submerged water plants). Based on the
substrate characteristics, the division of each type of substrate was divided into 4. The sand substrate
that was overgrown with submerged water plants consists of Matano Village, Ontalo Island, Petea,
Kupu-Kupu Beach; the rock-sand substrates consist of Soroako, Rusunawa, Nuha, Impian Beach; the
sandstone substrate consists of Otuno, Woiso, Ensa, Tapuntole, Neowi; and the sandy mud substrate
consists of Tanah Merah.
The horizontal distribution of flowerhorn cichlid was very high (> 60%) in Matano Village, Ontalo
Island, Kupu-Kupu Beach, Soroako, Impian Beach, and Petea 2 (figure 3). However, in Petea 1 and
Otuno region adjacent to the outlet area had a relatively low abundance of flowerhorn cichlid (<30%).
An attempt by experimental fishing for investigating vertical distribution of flowerhorn cichlid showed
decreasing of total catch with increasing depth [27] (figure 4). However, the flowerhorn cichlid with
bigger body size was found at > 15 m depth.

International Conference on Tropical Limnology 2019
IOP Conf. Series: Earth and Environmental Science 535 (2020) 012039
IOP Publishing
doi:10.1088/1755-1315/535/1/012039
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Figure 3. Horizontal distribution of flowerhorn cichlid in Lake Matano
Figure 4. Vertical distribution of flowerhorn cichlid in Lake Matano [27].
3.2. Selectivity and effectiveness of gillnets
The flowerhorn cichlid controlling as invasive alien fish in Lake Matano was effectively carried out
using the fishing method. A fishing gear that had the capability of capturing flowerhorn cichlid in
large quantities and selectively without the risk and the great opportunity for native fishes was gillnets.
The gillnets selectivity was analyzed for mesh size of 1.5, 2.0, and 2.5 inches.
The selectivity factor (SF) for the three mesh sizes was 3.02. The 1.5-inch mesh size had an
optimal for flowerhorn cichlid captured at 11.5 cm TL, 2.0 inches for 15.3 cm TL, and 2.5 inches for
19.2 cm TL (figure 5). A significant mesh size that could catch a lot of flowerhorn cichlid but a few
for native fishes and captured flowerhorn cichlid before mature or spawn (Lm) was 1.5 inches mesh
size. The length at maturity (Lm) for female and male flowerhorn cichlid was 12 cm and 14.2 cm,
respectively.

International Conference on Tropical Limnology 2019
IOP Conf. Series: Earth and Environmental Science 535 (2020) 012039
IOP Publishing
doi:10.1088/1755-1315/535/1/012039
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Figure 5. Gillnets selectivity for flowerhorn cichlid in Lake Matano.
The study of fishing effectiveness with different yarn diameter (D = 0.15, 0.20, 0.25 mm) and
various mesh size using ANOVA & LSD test showed that the yarn diameter did not significantly
affect the flowerhorn cichlid fishing (P<0.05). However, the mesh size of 1.5 inches was significantly
different (P>0.05) to other mesh sizes.
4. Discussion
The flowerhorn cichlid had spread and could be caught in all the waters of Lake Matano, especially in
the littoral area. This result showed the distribution data and the adaptation level of the flowerhorn
cichlid in Lake Matano. However, in Petea which is the region adjacent to the outlet area had a
relatively low abundance, similar to Herder et al. [7]. The flowerhorn cichlid was able to be adapt in
all types of habitat characteristics and various types of substrates, especially it on the sand bottom
substrate and overgrown with submerged water plants where the fish abundantly found [7,27,28].
The efforts to prevent and control invasive alien fish species (IAS) require the involvement of
various parties in synergy through strong cross-sectoral coordination at the national level.
Government supported the research and development related to IAS impacts, such as impact
mitigation methods, is also needed. Therefore, it was necessary to build the complete system
information for IAS distribution and circulation, threat detection and attacks as well as for controlling
and eradicating the IAS.
Complete system information is needed to build basic data on the spread and distribution, threat
detection, and the negative impact of IAS. The basis of prevention and IAS control has been stated in
the Regulation of the Minister of Marine Affairs and Fisheries Number: PER.17/MEN/2009
concerning Prohibition of Import of Several Fish Species from Overseas into the Territory of the
Republic of Indonesia. On the other hand, comprehensive prevention and control measures against the
IAS have not been visible, either by governments, universities, private institutions, NGOs or the
communities themselves. The level of public understanding of the dangers and threats of IAS needs to
be improved.
Based on our studies conducted in 2015-2016, we propose some concepts, techniques of
management, and control for the IAS population in the Lake Malili Complex, especially in Lake
Matano, to be utilized by the relevant stakeholders. The efforts needed for managing fisheries,
especially related to the IAS, are as follows:
1. There is a need for synergy between the Center for Conservation of Natural Resources of South
Sulawesi Province, Ministry of Environment and Forestry, as the management authority of Lake
Matano, and the Office of Marine and Fisheries of East Luwu Regency, as the supervisor and the

International Conference on Tropical Limnology 2019
IOP Conf. Series: Earth and Environmental Science 535 (2020) 012039
IOP Publishing
doi:10.1088/1755-1315/535/1/012039
7
surrounding community as the lake water users, to control flowerhorn cichlid population by
capture continuously.
2. The flowerhorn cichlid can be caught and controlled using gillnets. The gillnet specifications used
are made from monofilament yarn with 1.5-inch as an optimal mesh size for capturing them. The
yarn thickness can be adjusted because it did not affect the catch significantly.
3. An intensive fishing effort can be conducted, especially in the flowerhorn cichlid spawn season, at
the beginning of the rainy season.
4. The flowerhorn cichlid fishing shall be done in areas with sand substrate and overgrown with
aquatic plants and high anthropogenic activity.
5. The capture shall be done in the littoral area (<100 m to the lake), done during the day because the
endemic crabs would be highly caught in the night.
The prevention efforts for reducing IAS in Lake Matano must be a concern for some point as
follows:
1. Fish cultivation at the surrounding of Lake Matano needs to be supervised to prevent the
unintentional release of introduced culture fishes such as carp fish, tilapia, and catfish to Lake
Matano as those fishes can proliferate and potential to be an invasive alien species.
2. We need to educate the community about the importance of species biodiversity and endemicity in
Lake Matano and the negative impact of IAS.
3. In order to stimulate flowerhorn cichlid fishing activities, the local governments (i.e., Provincial or
District Government, The Office of Marine and Fisheries, and other relevant agencies) need to
hold a massively flowerhorn cichlid fishing activity as it was done in 2014.
4. The local government and relevant stakeholders issue some regulations in prevention efforts by
prohibiting the introduction of alien fish species and providing the rule of law and punishment.
Socialization to the people needs to be intensified for the effectiveness of the regulations that have
been made.
5. It is necessary to determine a conservation area for the native fishes species from Lake Matano.
Areas that can be proposed as conservation areas are Woiso, Neowi, Tapuntole, Enda and Otuno
based on criteria low abundance of IAS from this research.
5. Conclusion
An effective mesh size gillnet for controlling flowerhorn cichlid in Lake Matano is 1.5 inches. The
thickness of the yarn did not significantly affect for flowerhorn cichlid fishing. For effectiveness,
gillnets are better to operate in littoral areas of lakes, mainly associated with the sand substrate with
macrophytes and more anthropogenic activities. The operation of the gillnet in Lake Matano needs to
be regulated in terms of location and setting time to minimize the capture of fish species other than
flowerhorn cichlid.
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Acknowledgments
This paper was a contribution of the research project titled: "Controlling Invasive Alien Fishes Species
(IAS) in Lake Matano, Malili Lake Complex, South Sulawesi" for years 2015-2016 in Research
Institute for Fish Resource Enhancement and Conservation (RIFEC). The authors thank all parties for
their support and valuable idea for this paper.