International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 04, April 2019, pp. 174-181, Article ID: IJCIET_10_04_019
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=04
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
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Scopus Indexed
EXPLOITATION RATE OF MEAT OYSTER
(CRASSOSTREA GIGAS) AGAINST THE
DYNAMICS OF ITS POPULATION IN THE
COASTAL AREA OF BANDA ACEH
Lili Kasmini, Miswar Budi Mulya*, Ternala Alexander Barus
Department of Biology, Faculty of Mathematics and Natural Sciences,
Universitas Sumatera Utara, Medan, Indonesia
M. Ali Sarong
Faculty of Teacher Training and Education, Universitas Syiah Kuala,
Banda Aceh 23111, Indonesia
*Corresponding Author
ABSTRACT
Research on the rate of exploitation ofmeat oyster especially Crassostrea gigas to
the dynamics of its population has been conducted in Banda Aceh, Aceh Province. This
study was conducted in 6 months starting from July to December 2017. Surveys and
activities were conducted in two locations: Tibang and Ulee lheue, where samples were
collected at least 150 samples per location per month. Data collection was done by line
transect method. Total samples of oyster collected 1800 samples, where all samples fall
into the adult category. The long frequency value was dominated by 40-50 mm long
class with estimated age of 1 year oyster. Analysis of the rate of mortality showed the
total mortality rate (Z) reached 7.22year-1, natural mortality rate (M) 1.27year-1, the
catching mortality rate (F) 5.95year-1 and the exploitation rate (E) 0.82year-1. Based on
the data of the rate of exploitation indicates that the activity of oyster catching has been
included in overexploitation category.
Keywords: exploitation, oyster, Crassostrea, sample
Cite this Article: Lili Kasmini, Miswar Budi Mulya, Ternala Alexander Barus and
M. Ali Sarong, Exploitation Rate of Meat Oyster (Crassostrea Gigas) Against the
Dynamics of its Population in the Coastal Area of Banda Aceh. International Journal
of Civil Engineering and Technology, 10(04), 2019, pp. 174-181
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editor@iaeme.com
Exploitation Rate of Meat Oyster (Crassostrea Gigas) Against the Dynamics of its Population in
the Coastal Area of Banda Aceh
1. INTRODUCTION
Crassostrea gigas belongs to one tropical species that has a high economic value and very
substantial to socio-economic community of coastal fishermen (Ferreira et al., 2006). The
province of Aceh has 5 species of meat oysters consisting of 2 genera, namely from the genus
Ostrea and the genus Crassostrea, consisting of C. virginica, C. gigas, C. iridescens, C.
angulata and O. edulis (Octavina et al., 2014) . One of the most common species found based
on that study wasC. gigas.
Oysters consume food by means of a filter feeder, in which the preferred predominant food
are phytoplankton and organic matter (Adite et al., 2013). The oyster in reproductive cycle acts
as protrandous hermaphrodite, meaning every oyster begins with male sex and can turn into a
female a few years later if the environment is favorable for breeding (Westphal et al., 2015).
Oyster habitat is dominated by rocks or hard substrate as a place to attach to oyster shells,
whereas on mud substrate, the oyster is difficult to live (Escapa et al., 2004).
Until recently, research on Crasostrea sp. related to the rate of exploitation has not been
done in Aceh nor in Indonesia. The research that has been done in the world on oysters is
mostly focused on biological aspects, such as oyster gametogenesis (Dheilly, et al., 2012),
genetic aspects of oysters (Wu et al., 2013; Klinbunga et al., 2005), reproduction of oysters
(Guo and Allen, 1994; Keightley et al., 2015), study of morphological character of oyster
(Ferreira et al., 2006) and identification of oyster stomach contents (Astuti et al., 2001).
Further studies have been conducted in Aceh, including analysis of heavy metal content in
oysters (Sarong et al 2015, Astuti et al 2016), community structure of meat oysters (Fadli et al.
2012, Octavina et al., 2014), long association weight and oyster condition factors (Octavina et
al., 2015; Kasmini et al., 2018). But research on the rate of oyster exploitation has never been
done, so it is important to do as stock assessment, especially for conservation efforts and oyster
cultivation in the future.
2. RESEARCH AND METHODS
2.1. Location and time
Surveys and sampling were conducted in 6 months starting from July to December 2017.
Sampling was conducted in 2 locations, Tibang and Ulee Lheue, where each location was
divided into 3 sampling stations.
Table 1. Location and coordinates of the study
Locations
Tibang
Ulee Lheue
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Coordinates
5033’36.7” N,
95017’22.8” E
5033’21.0” N,
95017’11.7” E
5033’01.6” N,
95017’09.5” E
5035’25.1” N,
95021’03.5” E
5035’47.0” N,
95020’50.8” E
5035’36.2” N,
95020’44.4” E
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2.2. Data retrieval
Surveys and observations were conducted every month, where samples are collected at least
150 samples per location of data collection. Data collection was done by line transect method.
The samples collected were separated and then measured in length and weight. Long
measurements were performed using a digital caliper (Precision Measuring Error = 0.01 mm)
and weight measurements were made using digital scales (Pocket Scale, MH-Series, Error =
0.01 g).
2.3. Data Analysis
2.3.1. Long frequency distribution
Suspected group size was done by doing analysis of the long frequency.The frequency of the
oyster length taken was distributed into several groups with the assumption of normal data
distribution. The long frequency distribution was obtained by determining the class interval,
mean grade, and the frequency in each length group (Komala et al., 2011).
Growth analyzes, especially the dynamics of oyster populations was done using Von
Bentalaffy growth method. The analysis included frequency of length, age prediction, mortality
rate (total mortality, natural, catch and exploitation) and recruitment process. The data collected
during the next 6 months of research were analyzed using the FISAT II (FAO-ICLARM Stock
Assessment Tools-II) program.
Oyster growth was analyzed using the Von Bertalanffy (Sparred and Venema 1999)
equations as follows:
Lt = L∞ (1 − exp−𝑘(𝑡−𝑡𝑜) )
Where Lt = length of oyster at age t (mm); L∞ = infinitive length (mm); K = growth
coefficient per day; t0 = alleged theoretical age of oysters at length zero.
2.3.2. Mortality rate
The analysis of the total mortality rate (Z), the natural mortality rate (M), the catching mortality
rate (F) and the rate of exploitation (E) calculated using the FISAT II program refer to the Jons
/van Zalinge Plot for Estimation of Z plot model by entering the L∞ and K. The equation used
to determine the value of natural mortality rate (M) is referring to Pauly (1980):
Log (M) = -0.0066-0.279Log(L∞)+0.6543Log(K)+0.4634Log(T)
Where M = natural mortality rate; L∞ = infinitive length; K is the growth coefficient; T =
mean water temperature.
The optimum length of the caught oyster (Lopt) is calculated by the equations referring to
Froese and Binohlan (2000):
Lopt = 3*L∞/(3+M/K)
Where Lopt = optimum length of the captured oyster; M = natural mortality rate; L∞
=infinitive length; K is the growth coefficient.
The analysis of recruitment pattern was done by using FISAT II program with the type of
analysis choice of recruitment pattern. As in the growth parameter of inputs and graph, the
value entered was the value of L∞, K and t0.
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Exploitation Rate of Meat Oyster (Crassostrea Gigas) Against the Dynamics of its Population in
the Coastal Area of Banda Aceh
3. RESULTS/AND DISCUSSION
3.1. Length Frequency
Individu (N)
Based on the analysis of oyster population dynamics data, the frequency of the lengths found
was dominated by the oyster size of 40-50mm at both study sites (Tibang and UleeLheue).
The number of samples found dominated by of 40-50 mm class of length, reached 689
samples (38.28%) of a total of 1800 oyster samples. The second dominant sample was in the
30-40 mm in length with the number of 544 samples (30.22%), followed by the 50-60 mm
class of length with the sample taken was 322 samples (18.44%) as shown in Figure 1.
689
800
544
600
332
400
200
96
90
37
4
4
3
0
0
1
0
Class of Length (mm)
Figure 1. Graphic of length frequency based on oyster length classes at both locations
The growth rate analysis of Von Bentalaffy Growth Function (VBGF) showed the
predominantly caught oysters estimated at one year (Figure 2).Furthermore in the first 2 years
seen on the VBGF growth chart that the oyster grows rapidly (optimal), but in the next year the
rate of growth slows down.
Figure 2. Graphic of growth of Von Bentalaffy Growth Function (VBGF) oyster at Tibang and
UleeLheue sites
3.2. Mortality
The analysis of the rate of mortality of the oysters showed that the total mortality rate (Z)
reached 7.22year-1 (Figure 3a), the natural mortality rate (M) 1.27 year-1, the catching mortality
rate (F) 5.95year-1 and the exploitation rate (E) 0.82year -1 (Table 2). The Z value is caused by the
capture and death of oysters in nature. Furthermore, the value of M due to disease and the age
of old oysters. The F value was determined by the catch of the oysters being carried out in
nature.
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Based on the data of exploitation rate showed that the activity of oyster catching has been
included in the category of over exploitation (overfishing). This is indicated by the rate of
exploitation (E) of 0.82year-1 (Figure 4.8a) or 82% of oyster deaths due to capture, while the
sustainable limit should be 0.50year-1 (Table 2). Therefore, capture strategies and management
need to be established to keep the oyster population sustainable in the future.
Table 2. Population dynamics growth parameters
No
Parameter
Results
1
Infinitive length (L∞)
141.75 mm
2
Optimum length of the captured oyster (Lopt)
45.72 mm
3
Growth coefficient (K)
1.1year-1
4
Total mortality rate (Z)
7.22year-1
5
Natural mortality rate (M)
1.27year-1
6
Catching mortality rate (F)
5.95year-1
7
Rate of exploitation (E)
0.82year-1
Furthermore, based on the VBGF chart showed that the rate of oyster death predominantly
occurs at the time of the oyster 1 year old (Figure 2). The optimum length of capture (Lopt)
occurred at 45.72 mm (Table 2), which, according to the VBGF graph (Figure 2), was estimated
at the size of the 1 year oldoyster. Based on the probability analysis that with increasing size
the odds of oysters being captured are higher (Figure 3b).
Figure 3. Graph (a) mortality rate and
(b) probability of oyster capture
3.3. Recruitment
The results of oyster recruitment pattern analysis indicate that the oyster spawning throughout
the year. However, in certain months the recruitment process occurs very little, that was in
January and December (Figure 4). The peak of recruitment occurs twice, in June and August
(Figure 4).
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Exploitation Rate of Meat Oyster (Crassostrea Gigas) Against the Dynamics of its Population in
the Coastal Area of Banda Aceh
Figure 4. Oyster recruitment rate chart, where J is January, F is February, M for March, and the next
following month for a year.
The results showed that the total mortality rate (Z) reached 7.22 year-1 (Figure 3a), natural
mortality rate (M) 1.27year-1, the catching mortality rate (F) 5.95year-1 and the rate of exploitation
(E) 0.82year-1 (Table 2). The natural mortality rate consists of three phases, namely the initial
phase, the phase of stable death, and the phase of death by aging (Chen and Watanabe, 1989).
The mortality rate is related to the ability of a species to perform the recruitment process in
order to maintain the stability of the dynamics of its population in the future (Fogarty et al.,
1991).
If an organism has a high recruitment capability, then the organism has the ability to
maintain its population stability in nature (Bakun and Broad, 2003).But unlike oysters, fish
have depensatory dynamics where the ability of recruitment is low due to difficulty to find fish
pairs which used to be called as allee effect (Myers et al., 1995). While oyster reproductive
activity (recruitment) is done by removing eggs and sperm into the waters randomly when
stimuli to spawn are detected (Westphal et al., 2015).
The results of the exploitation rate analysis indicate that oysters at two research sites
(Tibang and UleeLheue) have been over-exploited, whereas based on E 0.82year-1 the
explanation of oyster death from catching activity reaches 82% or exceeds the sustainable limit
value of 50% (Mullon et al ., 2005) (Table 2). Excessive exploitation of an organism despite
its potential to recover, will require a long time and consistent management consistency to
preserve its sustainability (Hutchings, 2000). Furthermore, this overexploitation is directly
related to the declining population of an organism in nature, which will affect the ability of
recruitment to be low (Myers et al., 1997). This abundance and diversity is highly dependent
on its tolerance and its sensitivity to environmental change (Harahap A et al., 2018)
This will affect the future sustainability of the population of a future organism related to
the conservation aspect (Forgaty et al., 1991), therefore management is required in order for
the existence of exploitation (oyster) organisms to remain stable. However, obstacles found in
the field show that the understanding of oyster fisherman is very low on eco-catching ecofriendly, so comprehensive socialization related to the importance of proper oyster fishing
management needs to be done. Another factor that becomes an obstacle is the exploitation of
oysters that plays the most substantial role in the social and economic aspects of fishing
communities (Post et al., 2002).
The dominance of caught oysters was seen in the size the length of 40-50 mm (Figure 1).
This is consistent with the optimum catch length (Lopt) analysis results that obtained at the size
of 45.72 mm (Table 2). Thus based on the predominantly caught oyster size estimated to be 1
year old (Figures 2 and 3a). But overall 1800 samples of captured oysters were estimated to be
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Lili Kasmini, Miswar Budi Mulya, Ternala Alexander Barus and M. Ali Sarong
1-3 years old. According to Westphal et al. (2015), the Genus Crassostreafirst reproduces
(spawning) at 20 mm in size. Thus all the oysters exploited in the estuary Tibang and
UleeLheuewas already in the adult category.These results indicate that the rate of exploitation
occurs highest in the adult group of oysters, so that if exploitation is not stopped, the ability of
oyster recruitment will continue to decline.
5. CONCLUSION
It can be concluded that oyster exploitation (C. gigas) in the Tibang and UleeLheue coastal
area have exceeded the overexploitation limit, which may affect the dynamics of the
population.The entire oyster caught (1800 samples) included in the adult category, with an
estimated age of 1-3 years. Oyster recruitment activities occur throughout the year, but
overfishing will affect the ability of oyster recruitment thus the number of oyster population
continues to decline throughout the year.
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