Distribution, abundance, and life history traits of the blue swimming crab Portunus segnis (Forskål, 1775) in the Saudi waters of the Arabian Gulf

The blue swimming crab, Portunus segnis (Forskål, 1775), formerly known as P. pelagicus (Linnaeus, 1758) has become a major fishery resource in the Gulf. Yet, there are no regional studies on the stock population dynamics and life history processes of this species. Considering the extreme oceanographic features of the Gulf (high salinity and high temperature variations), which is hypothesized to cause fast growth of P. segnis, a study was conducted to determine the abundance/biomass distribution of its stocks, growth rates, and sexual maturation in the territorial Saudi waters in the Arabian Gulf. The study was based on trawling surveys, landing sites monitoring, and records of fisheries catch and efforts and juvenile habitat surveys. The spatial distribution patterns supported by generalized linear model indicated the occurrence of P. segnis in the nearshore shallow waters, and its absence from the offshore deeper waters, attributed to the variability of environmental conditions including salinity, temperature, and trophic resources. Manifa, one of the productive areas in the northern Saudi waters of the Gulf, had high abundance of the crab. In agreement with the hypothesis, the growth rate of the Saudi P. segnis was found to be the higher (2.12 K year ⁻¹) compared to other parts of the Gulf (1.1–1.7 K year ⁻¹) or other sea areas of tropical regions (0.95–1.68 K year ⁻¹). The study shows that P. segnis can spawn throughout the year, with at least three peaks: winter, late spring–early summer, and autumn. The L_50% record obtained in this study with females (127 mm) and males (125 mm) are larger than those reported with the same species from other parts of the Gulf (113 mm) or with other congeneric blue species crabs reported from other tropical regions (61–113 mm). The present study provided basic data to develop a management strategy for the fishery of P. segnis in the region.