The orange-spotted grouper (Epinephelus coioides) is a valuable food fish. To support the sustainable management of orange-spotted grouper fisheries, it is important to determine the optimum catchable size. The purpose of this study was to determine an optimal catchable size for the orange-spotted grouper stock in Kwandang Bay, North Gorontalo District, Indonesia. The Catchable size was determined based on the size at first sexual maturity, fecundity, and reproductive potential. The study was conducted from December 2016 to November 2017. The size at first sexual maturity was estimated based on the examination of gonads from 141 specimens, while fecundity was estimated based on a sample of 40 female fish with ripe gonads. The mean total length (TL) at first maturity was 40 cm. Fecundity ranged from 30,526 - 1,395,846 eggs with a mean of 687,025 eggs. The reproductive potential was highest in the size range of 55-64 cm TL. The recommended size for orange-spotted grouper is above 64 cm, to enable females to attain their maximum level of egg production before capture and thus contribute to maintaining the stock.

Abstract. Achmad DS, Gani S, Ardiansyah W, Mokoginta MM, Nurdin MS, Jompa J, Indrianti MA, Achmad N. 2022. Population dynamics of reef fish in the Kwandang Bay, Sulawesi Sea, Indonesia. Biodiversitas 23: 5217-5226. The grouper stocks in Kwandang Bay, Sulawesi Sea, Indonesia, are dominated by orange-spotted grouper (Epinephelus coioides) and coral trout (Plectropomus leopardus). However, the Kwandang Bay grouper fishery is currently experiencing serious challenges due to population decline resulting in a decline in both the average size of fish caught and the production volume. This study was conducted in Kwandang Bay, Sulawesi Sea, from January to December 2021. The population dynamics parameters estimated were growth, recruitment, mortality, exploitation rate and yield per recruit. The results showed that the total length (TL) of E. coioides and P. leopardus ranged from 16.50-101 cm and 17.90-60 cm, respectively, with Von Bertalanffy K-coefficients of 0.38 and 0.69, respectively. Recruitment occurred during most of the year, with respective recruitment value ranges of 0.99-17.11% and 0.08-19.22%. Natural and fishing mortality was 0.69/year-1 and 0.87/year-1 for E. coioides, 1.16/year-1 and 1.47/year-1 for P. leopardus. Beverton and Holt yield per recruit analysis indicated recruitment overfishing of both E. coioides and P. leopardus. Fishing regulations are needed to maintain a sustainable grouper fishery, including a 25% reduction in fishing vessels and gear, to enable the groupers of Kwandang Bay to spawn at least once during their life cycle.

Blue swimming crab (Portunuspelagicus) is aeconomical valuable fisheries importantcommodity  due to the high demand and availability jobs created for the fishermen. Due to their high demand blue swimming crab heavily exploited from Salemo Island. This study aimed at comparing the sex ratio and the size at first maturity of blue swimming crab caught in mangrove ecosystems, coral reefs, and seagrass. Sex ratio was analyzed using chi square test and the size at first maturity was analyzed using the Spearman-Karber formula. The results showed the sex ratio ofmales and femalessmall crab caught in every ecosystem is balanced. The size at first maturity of blue swimming crab caught in mangrove, seagrass and coral reefs, each to the male 81,08 mm, 102,36 mm and 102,87 mm in width and size of female 94,54 mm, 83,35 mm, 98,31 mm width. In a reference to government regulations, the blue male swimming crab caught in the coral reef and seagrass ecosystems have yet to size at first maturity is allowed to be captured. Keywords: blue swimming crab, sex ratio,size at first maturity, Salemo Island

Highlight Research There are 26 species identified to be originated from the bay, which the highest diversity in Indonesia Six species found in Kwandang Bay is showing trends of decreasing populations and two species vulnerable based on IUCN conservation list Growth model and Fulton condition factor determined for 14 species indicates that they live in a good state of well beings in the bay The models and condition factors also reflect the adequate food resources required for grouper growth which makes Kwandang Bay as a good habitat for groupers   Abstract Grouper fishery has been the source of income for 3,700 fishermen in Kwandang Bay. Since 2017, grouper populations in Kwandang have been depleting due to the absence of management. This research aimed to analyze species composition, length-weight relationship, and condition factor of the groupers. Samples were collected from fishers who caught the fish using traps, speargun, and handline. Samples were identified through a method by Heemstra and Randall, while the length-weight relationship was estimated using log-linear regression and t-test. The number of specimens identified during January - December 2021 was 1,571 individuals. Research showed that those samples consisted of 26 species under eight genera. Six species found in Kwandang Bay were showing trends of decreasing populations and two species were vulnerable based on the IUCN conservation list. Length-weight relationship analysis of 14 grouper species resulted in b value ranging from 1.6359 to 3.4417 and R2 ranges from 0.7718 to 0.9858. A significant test at a 95% confident interval showed that 14 species had an isometric growth pattern. Fulton condition factors show that Kwandang Bay is an essential habitat for groupers, and the bay can support the fish growth due to the adequate food availability.

Orange-spotted grouper is one of the coral reef fish has the economic value and exploited by local fisherman. Information about the size structure and sex ratio are urgent to formulate a policy for sustainability. This research aims to analyze the size structure and sex ratio of the orange-spotted grouper in Kwandang Bay. The research was conducted from December 2016 to November 2017. Sampling is carried out twice a month for one year. The total sample of orange-spotted grouper used for the analysis of the sex ratio was 149 individuals. Sample of orange-spotted grouper collected from fish landed and middlemen (grouper traders) at the Kwandang Fishing Port. Data analysis applying chi-square. The results show that males bigger than females. The sex ratio of orange-spotted grouper is 87.25 % female, 7.38 % male, and 5.37 % hermaphrodites. Orange-spotted grouper dominated by females and undergoes a gonad differentiation to male (protogynous hermaphrodite). It is concluded that The size of the male orange-spotted grouper is larger than that of the female grouper. The caught orange-spotted grouper is dominated by the female phase and undergoes a differentiation of the gonad from female to male (protogynous hermaphrodite)