Population parameters of several groupers (Famili Serranidae) in Labuan Bajo waters, East Nusa Tenggara

Labuan Bajo has a fertile aquatic ecosystem, one of them is the coral reef ecosystem. This condition happened because of the supply of nutrients that are carried through Indonesia Through Flow and the local upwelling phenomena. Various species of reef fish of various sizes have been caught in Labuan Bajo waters. In general, the type of reef fish that dominates is grouper fish catch by using handline fishing gear. Furthermore, there is damage that occurs in the coastal ecosystem causes changes in ecological functions and disrupted ecosystem benefits. In addition, pressure from overuse did not provide opportunities for resources to carry out recovery makes the condition of resource stocks threatened. This study aims to determine the parameter aspects of the population of several types of grouper fish in Labuan Bajo waters. The types of grouper studied included Plectropomus leopardus, P. maculatus, P. oligacanthus, and Variola albimarginata. Data collection was carried out by enumerators from April to August 2019 which included the daily data on the length and weight distribution of groupers. Length-frequency distribution data is analyzed by estimating fish population parameters using the Electronic Length Frequency Analysis (ELEFAN I) program which is packaged in the FAO-ICLARM Stock Assessment Tool II (FiSAT II) software. The results of the analysis showed the equation of growth parameters for Von Bartalanffy for P. leopardus is Lt = 89.06(1-e−0.24(t+0.52)); P. maculatus is Lt = 76(1-e−0.54(t+0.23)); P. oligacanthus is Lt = 72.32(1-e−0.66(t+0.19)); and V. albimarginata is Lt = 45(1-e−0.51(t+0.29)). The length at first birth of each species is Lt=0 P. leopardus = 10.45 cm, Lt=0 P. maculatus = 8.88 cm, Lt=0 P. oligacanthus = 8.52 cm, and Lt=0 V. albimarginata = 6.19 cm. Meanwhile, the exploitation rate (E) of P. leopardus, P. maculatus, P. oligacanthus, and V. albimarginata were 0.81; 0.53; 0.45; and 0.70.


Introduction
Labuan Bajo waters mostly have coral reef ecosystems. The major fisheries activities that develop in that area are coral reef fisheries. As an ecosystem that is directly connected to the Indian Ocean, Labuan Bajo has more or less the same oceanographic conditions. The geographical location of the Indian Ocean waters has a very high dynamics of water mass variability because it's influenced by water mass intrusion from other regions such as the Indonesian Through Flow (ITF) and is also influenced by global climate anomalies such as El-Nino Southern Oscillation (ENSO) [1]. In addition, the occurrence of an upwelling phenomenon that occurs in the east monsoon brings a supply of nutrients from the deep layers to the surface [2;3;4]. This condition also brings the supply of nutrients to Labuan Bajo so that this area has very fertile water conditions. Based on the statistical data of West Manggarai District in 2018, coral reef fishes, which consisted of several types of groupers catch by using handline, contributed 18-21% of the total production. Furthermore, several environmental problems that have become the attention include climate change issues, shoreline changes, land-used shifting, and overfishing will affect the sustainability of fisheries resources. Afterward, the occurrence of degradation of coastal and marine ecosystems such as mangroves, coral reefs, and seagrasses also affects the dynamics of the population of fish resources and the environment. This event has been indicated by several general problem trends, such as catch declining, longer distances to the fishing ground, and smaller length of first catch and maturity in several types of economically important fish species, like groupers. The damage that occurs to coastal and marine ecosystems, in this case, causes the ecological functions and economic benefits of these ecosystems to be disrupted, while excessive use pressures and do not provide opportunities for resources to self-recover, make the condition of resource stocks threatened from sustainability [5]. This study aims to determine the aspects of population parameters of several types of groupers in the waters of Labuan Bajo.

Location
The data was collected with the locations around Labuan Bajo waters, East Nusa Tenggara in April -August 2019. Daily length-weight data was obtained from the handline fishing boat that landed on Selayar Island, Labuan Bajo. Data recording is carried out by enumerators who have been previously appointed.

Data Collection
Data collection was carried out randomly following standard sampling procedures in the field [6]. Measurement aspects include total length (cm), fork length (cm), and individual weight (grams). The type of fish taken was focused on the type of grouper (Family Serranidae), which are Plectropomus leopardus, P. maculatus, P. oligacanthus, and Variola albimarginata.

Data Analysis
The length-frequency distribution data were analyzed using fish population parameter estimation analysis consisting of L∞, K, t0, Z, M, F, and E values using the Electronic Length Frequency Analysis (ELEFAN I) program which is packaged in the FAO-ICLARM Stock Assessment Tool II (FiSAT II) software [7]. In general, the theory regarding the analysis is: 2.3.1. Growth Estimation. Estimation of growth parameters was carried out using the growth formula Von Bertalanffy Lt = L∞ (1 − − ( − 0) ) [8]. From Von Bertalanffy's growth equation, the formula can be manipulated into a= L∞*(1 -b), with K and L∞ are constants, a and b are constants if t is a constant. The growth parameters k and L∞ are derived from: Furthermore, to determine to use Pauly formula [9]: Log (-t0) = -0,3922 -0,2752 (Log L ∞) -1,038 (Log K) with: L∞ : length asymptotic (cm) K : growth rate coefficient (year) t0 : the theoretical age of the fish when the length is equal to zero (year) 2.3.2. Mortality Estimation. According to [9], fish natural mortality is also influenced by environmental temperature. Various relationships can be seen from the length growth data with multiple According to [8], information on mortality rates is very important in analyzing the dynamics of an exploited population and stock size. The mortality rate can be estimated using the equations proposed by Beverton and Holt. Total mortality can be estimated by the average length (L) of the catch of a fish population, with the following equation: with : Z : total mortality rate (year) K : growth coefficient L∞ : length asymptotic (cm) L : average length of fish caught L 1 : the minimum size of fish caught According to [9], to calculate the rate of exploitation (exploitation ratio) the following formula is used:

Size Distribution
The size distribution of Plectropomus leopardus or known as leopard coral grouper ( Figure 1

Population Parameter Estimation
Estimation of population parameter calculations was carried out using the FiSAT II software. The parameters analyzed include L∞ (asymptote length), K (growth coefficient), t0 (theoretical age), Z (total mortality rate), M (natural mortality rate), F (fishing mortality rate), and E (exploitation rate). The results of the analysis of growth parameters following the Von Bartalanffy (VB) growth formula (Table 1) describe the relationship between length increase (Lt) over time (t). Based on the results of the analysis, it is known that Lt=0 (length of first birth) of each species is Lt=0 P. leopardus = 10.45 cm, Lt=0 P. maculatus = 8.88 cm, Lt=0 P. oligacanthus = 8.52 cm, and Lt=0 V. albimarginata = 6.19 cm ( Figure 5).  Furthermore, based on satellite data, the average sea surface temperature of Labuan Bajo waters is 28.27 o C with a standard deviation of 0.95 o C [10]. Thus, the results of the analysis regarding the mortality rate and exploitation rate are attached in Table 2. Based on the comparison of M and F values, it can be seen that the exploitation rate (E) for P. leopardus, P. maculatus, and V. albimarginata exceeds the Eopt = 0.5, so their status is in a fully exploited condition. Meanwhile, the value of the exploitation rate of P. oligacanthus is E = 0.45, or almost in a fully exploited condition if not managed properly.

Discussion
Plectropomus leopardus. The Lmax value of the research results is the same as the size ever found in East Indian waters of 75 cm [11], but smaller than have been found in Asia Pacific waters, which is 120 cm [12]. Based on the Von Bartalanffy equation, the L∞ value of the research results is greater than [13], which is 62.16 cm in Karimun Jawa, Indonesia; and [14] namely 63.01 cm and 50.5 cm in Coron and Guiuan waters, Philippines. K values is bigger (0.10 and 0.0088) than research results. The value of K can illustrate that Plectropomus sp. has a slow growth rate compared to other types of groupers. The speed of fish growth can show the condition of the waters and the abundance of food in there [15]. Furthermore, the t0 value of the research results is greater when compared to the case study [13;14], which is -1.37 years and -4.41 years. The characteristics of coral grouper are slow growth, long lifespan, and slow natural mortality rate [16;17]. Therefore, coral grouper has a high mortality rate and susceptibility to fishing pressure so that the possibility of overfishing conditions is increasing. Fish mortality is divided into natural mortality (M) or mortality due to age, competition, predation, and disease; and fishing mortality (F) or mortality due to fishing activities. Fishing mortality (F) is a function of fishing effort. If we compare the natural mortality rate and the fishing mortality rate, it's shown that F>M so that E>Eopt=0.5 so that the condition is already in fully exploited status. The results of the study [13;14] have values of E = 0.13 and E = 0.78 -0.81. From both cases, it can be seen that there are Plectropomus maculatus. The Lmax research value comparison of P. maculatus with the case study [11] in East Indian waters, which is 125 cm, has a smaller value. Meanwhile, when compared with [18] in the waters of Cendrawasih Bay, Papua, 48.5 cm, has a greater value. The differences were caused by the geographic location and environmental condition. Furthermore, the L∞ in Karimun Jawa [13] is 92.56 cm with K = 0.10/year and t0 = -1.21 years. Then the L∞ in Saleh Bay waters, West Nusa Tenggara [19] was 76.55 cm with K = 0.10/year and t0 of -1.34 years. As a comparison, it can be seen that the value of L∞ is varying while the values of K and t0 are lower than the results. This condition was occurred due to differences in the latitude of geographical location, environmental factors, and food availability [20;8]. Then, based on the results of the analysis, E = 0.53 indicates overfishing pressure. This condition also occurs in several other places [13;19]. Excessive fishing pressure can cause growth and recruitment overfishing [21;22].
Plectropomus oligacanthus. As we compared the result with case studies in Cendrawasih Bay waters [18] and East India waters [11], the Lmax value of P. oligacanthus varied with the Lmax values in both locations were 48.5 cm and 75 cm. The difference in size caught often occurs because of differences in fishing gear and fishing locations. Furthermore, based on the case study [13], the parameter values for the population of P. oligacanthus were L∞ = 67.93 cm, K = 0.13, and t0 was -1.05 years. This value is greater when compared to the results of the study. Meanwhile, the value of the exploitation rate is not much different, E= 0.51 (slightly exceeds Eopt). If we have good management, these conditions can be recovered at the optimum point of exploitation so that the resource can be sustainable. Where possible, a combination of no-take marine reserves, market-based management approaches, and allocation or resurrection of property rights systems are recommended to complement conventional fishery management actions that limit catch and effort. Additional investment in aquaculture propagation is also needed to reduce fishing pressure on wild stocks and support management initiatives. This global synthesis of information on the biology, fisheries, and management of Plectropomus will assist in guiding future management actions that are trying to address a range of stressors including fishing, reef habitat degradation, and the escalating effects of climate change [23]. Based on [24;25], the open-closed season and changes in catch size have a positive impact on increasing grouper biomass.
Variola albimarginata. The results from [26] stated that the Lmax of V. albimarginata in Indonesian waters was 65 cm. As well as the case study [11] in East Indian waters Lmax = 60 cm. Both values are greater than the Lmax of the research results. Furthermore, the results of the study of population parameters [27] in the waters of the Great Barrier Reef Australia are L∞ = 31.5 cm, K = 0.51. This value is lower than the research study. Meanwhile, the L∞ and K values of V. albimarginata found in the waters of Lihir Island, Papua New Guinea [28] were 24.4 cm and 0.97/year, respectively. This value is also lower than the results of the study. Furthermore, based on the comparison of F and M values, it is known that the exploitation rate of V. albimarginata is in the fully exploited condition. Management that involves the community was needed through increasing community knowledge and awareness regarding grouper resource conservation efforts as part of grouper management co-management.