Browsing by Author "Joydas, Thadickal V."
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- Distribution, abundance, and life history traits of the blue swimming crab Portunus segnis (Forskål, 1775) in the Saudi waters of the Arabian GulfPublication . Rabaoui, Lotfi; Yacoubi, Lamia; Lin, Yu-Jia; Joydas, Thadickal V.; Maneja, Rommel H.; Dagoy, Joshua; Qurban, Mohammad A.; Roa-Ureta, RubenThe blue swimming crab, Portunus segnis (Forskal, 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. (c) 2021 Elsevier B.V. All rights reserved.
- Diversity, distribution, and density of marine mammals along the Saudi waters of the Arabian Gulf: update from a multi-method approachPublication . Rabaoui, Lotfi; Roa-Ureta, Ruben; Yacoubi, Lamia; Lin, Yu-Jia; Maneja, Rommel; Joydas, Thadickal V.; Panickan, Premlal; Gopalan, Jinoy; Loughland, Ronald; Prihartato, Perdana K.; Qassem, Ali; Hikmawan, Tyas I.; Diaz Lopez, Bruno; Qurban, Mohammed A.Despite the important role of marine mammals in marine ecosystems and the imperative for their conservation, there is still a great lack of information on the diversity, distribution, and density of these animals in the Saudi waters of the Arabian Gulf. To fill this gap, an integrative data-collection approach including fishermen’s questionnaires, opportunistic sighting reports, and directed boat-based surveys, was undertaken between 2016 and 2020, leading to the first scientific report of marine mammal diversity, distribution, and density in the region. The results of the different approaches carried out during the study confirmed a high diversity of cetaceans on the west coast of the study area, with bottlenose dolphins (Tursiops aduncus), humpback dolphins (Sousa plumbea) and dugongs (Dugong dugon) as the most common species. While the two dolphin species were found to be widely distributed in both coastal and offshore waters, D. dugon appears to occur exclusively in coastal waters in the southern part of the study area, mainly in the Gulf of Salwah. The presence of both species of dolphins increased during the summer months and in the vicinity of the numerous oil and gas facilities in this region. The distribution of the observed dolphins was found mostly within a 10–20 km radius around each facility. Other cetacean species observed less frequently in the area include Bryde’s whale (Balaenoptera edeni), killer whale (Orcinus orca), common dolphin (Delphinus delphis) and finless porpoise (Neophocaena phocaenoides). Regarding the density of marine mammals in the region, boat-based surveys confirmed the results of fishermen’s questionnaires and reports of opportunistic sightings, with bottlenose and humpback dolphins being the most abundant species. These results provide a baseline for policies oriented to the conservation of mammals in the Saudi waters of the Arabian Gulf.
- Ecology, life history, and fisheries potential of the flathead lobster (Thenus orientalis) in the Arabian GulfPublication . Rabaoui, Lotfi; Yacoubi, Lamia; Lin, Yu-Jia; Joydas, Thadickal V.; Qurban, Mohammad A.; Premlal, Panickan; Gopalan, Jinoy; Nazeer, Zahid; Vijayakumaran, Manambrakat; Khan, Syed Ajmal; Roa-Ureta, RubenThis study, which included examination of the distribution and life history and a stock assessment of the flathead lobster (Thenus orientalis), is the first of its kind in the waters of Saudi Arabia in the Arabian Gulf, also known as the Persian Gulf. The flathead lobster is widely distributed in this region, although it is more abundant in the central and northern Arabian Gulf. Carapace lengths at 50% and 95% maturity are 59 and 65 mm for females and 58 and 71 mm for males. The fecundity of 4 berried females ranged from 26,000 to 76,000 eggs per spawning, and the fertilization rate exceeded 97%. Length-frequency data were consistent with just 2 cohorts, indicating that this species has a short life span and high growth coefficient (K=0.846 year(-1)). Large fishing boats (called dhows) accounted for more than 98% of the total landings. Estimates of natural mortality rates from use of generalized depletion models have high statistical precision and a magnitude compatible with short life history. In addition, abundance levels estimated with the depletion model are sufficient to support a sustainable small-scale fishery either as bycatch of shrimp trawlers or as a resource targeted with specialized gear. A targeted fishery for flathead lobster could be set during the off months of the shrimp trawl fishery (February-July), reducing interference with the reproduction cycle.