Oceanic Influences on Mud Crab (Scylla olivacea) Reproductive Traits: A Comparative Study Across the Indian and...

Scylla olivacea is a commercially important species in the Indo-Pacific region, currently facing growing pressures from anthropogenic stressors. This study compares populations from the Indian Ocean (Andaman Sea) and the Pacific Ocean (Gulf of Thailand) to assess how different oceanic region and seasonal conditions influence key reproductive traits. By examining parameters such as sex ratio, size at first maturity, fecundity, and gonadosomatic index (GSI), the study aims to identify the differences that can inform targeted and sustainable management strategies. Crab samples were collected monthly from five sampling sites along the coast of the Indian Ocean (Ranong, Satun and Trang provinces) and the Pacific Ocean (Pattani and Surat Thani provinces) using traditional crab traps by local fishermen from April 2022 to May 2023 and subsequently analyzed in the laboratory. Results indicated that crabs from Ranong province, the Indian Ocean, exhibited smaller body sizes and values of most reproductive parameters (p < 0.01). The fecundities were 1.03 × 106 and 1.49 × 106 for crabs from Ranong and Pattani provinces, respectively. Positive relationships were found between internal carapace width (ICW), carapace length (CL), abdomen width (AW), and body weight (BW) with ovary weight (OW). Mature females, based on gonad development stages III and IV, were present year-round at both oceanic coasts. Peak abundances were found in November at both sites. High GSI levels were recorded in April and June for Ranong province (3.05 ± 1.97 to 10.97 ± 1.96) and February and June for Pattani province (3.19 ± 1.72 to 10.52 ± 1.71). The estimated sizes at maturity (M50) for female/male of S. olivacea varied across locations with smaller sizes observed from the Indian Ocean viz., 78.0/83.1 mm, 64.0/79.2 mm and 81.9/80.6 mm in the provinces of Ranong, Satun and Trang, respectively and 92.3/93.2 mm and 96.9/96.8 mm in Pattani and Suratthani, respectively. The sex ratio also indicated variations across region, with male:female ratios of 1:0.92, 1:0.78, 1:0.77 and 1:1 in the provinces of Pattani, Ranong, Satun and Trang. It is thus concluded that the oceanic region affects reproductive characteristics of S. olivacea and these findings can be applied to highlight the importance of localized management strategy for a sustainable use of mud crab resources.