Size at sexual maturity and body size composition of mud crabs Scylla spp. caught in Don Sak, Bandon Bay, Gulf of Thailand

Abstract

Size at sexual maturity and body size composition of mud crabs Scylla spp. were examined as the basis for settling a minimum landing size as a fishing regulation in Don Sak, Bandon Bay, Gulf of Thailand, which has suffered serious mangrove habitat degradation. Mud crabs were caught using baited traps and gill nets. Hooked metal rods were also used to lever the crabs out of their burrows inside the mangroves. Two mud crab species, S. paramamosain and S. olivacea, occur in the bay; S. paramamosain is the dominant species, accounting for 87% of the samples. The size at which 50% of the S. paramamosain females reached maturity (SM 50 ) was estimated as an external carapace width (ECW) of 112.0 mm based on the morphology of the abdomen. Allometric changes in the crushing chelae height to ECW ratio suggested that the SM 50 of S. paramamosain males occurred at 106.4 mm ECW. The body size composition revealed that mainly immature mud crabs were exploited in Don Sak. To maintain a sustainable fishery for mud crabs, fishing regulations-including a minimum landing size based on the SM 50 estimates-are essential, as is habitat restoration.

PENGGUNAAN BENTUK DAN POSISI CELAH PELOLOSAN PADA BUBU LIPAT KEPITING BAKAU (Shape and Position Escape Gap Application of Collapsible Mud Crab Trap)

“…Tongdee (2001) menyatakan bahwa ukuran lebar karapas kepiting bakau saat matang gonad di Ranong Thailand berkisar 70-100 mm, Hamasaki et al (2011) mengemukakan bahwa kepiting bakau di Teluk Bandon Thailand dengan lebar karapas 72-111 mm merupakan individu yang belum dewasa. Wijaya et al (2010) melaporkan bahwa di Kutai Timur ukuran kepiting matang gonad memiliki lebar karapas > 100 mm.…”

Fishery biology of mud crabs Scylla spp. at Iriomote Island, Japan: species composition, catch, growth and size at sexual maturity

“…Female mud crabs can be assigned to one of the following three maturity classes based on abdominal shape: mature females with broad U-shaped abdominal flaps, immature females with narrow abdominal flaps, and prepubertal females with intermediate abdominal shapes between immature and mature forms [8]. However, Hamasaki et al [14] suggested that the intermediate-form females should be treated as premature because of their low reproductive ability. Therefore, to estimate the maturity size of S. serrata in this study, only two groups (mature and immature) were considered, and prepubertal females were considered immature.…”

“…Pre-and post-copulatory mate guarding of females by males also occurs in mud crabs [35]. The morphometric maturity of males was estimated by the ratio of chela height to body size [8,14,36]. Allometric relationships between ECW (x) and CH (y) were examined for males according to Sampedro et al [37] and Corgos and Freire [38].…”

“…Mud crabs are acknowledged for their commercial importance as food, and overfishing of mud crab species has been observed at varying levels in different countries in accordance with the development of both national and international markets [4]. Mud crab overfishing has resulted in the decreased size and abundance of mud crabs in many fisheries, making them an increasingly scarce resource throughout the Indo-Pacific region [4][5][6][7][8][9][10][11][12][13][14][15][16]. Fishing regulations, such as prohibiting the capture of immature crabs, should be indispensable for sustainable utilisation of mud crab resources [5,8,14].…”

“…Recently, taxonomy of the genus Scylla has been resolved as four distinct species, i.e., S. serrata (Forskål), S. tranquebarica (Fabricius), S. olivacea (Herbst) and S. paramamosain Estampador by Keenan et al [2] based on both morphometric and genetic characteristics. Since then, biological and ecological studies in relation to fisheries have focused on individual mud crab species in several countries and regions [3][4][5][6][7][8][9][10][11][12][13][14][15][16], including Japanese waters [3,18,19,[24][25][26]. In Japan, S. serrata, S. paramamosain and S. olivacea inhabit coastal inlets and support commercially important fisheries on a local scale in warm temperate zones, including Lake Hamana in Shizuoka Prefecture and Urado Bay in Kochi Prefecture, where several studies have been conducted to reveal the species composition of the catch and growth of mud crabs [25,26].…”