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Status of blue swimming crab (Portunus segnis) stock in the waters of Persian Gulf and Oman Sea (Hormuzgan Province)
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Tooraj Valinassab1   , Arezoo Vahabnezhad , Mohammad Darvishi , Behnam Daghoghi |
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Abstract: (8 Views) |
Introduction
The blue swimming crab (Portunus segnis) is a commercially significant decapod species in the Persian Gulf and Oman Sea, particularly along the southern coasts of Iran. Among the family Portunidae, P. segnis stands out due to its abundance and economic value. Historically misidentified as P. pelagicus, recent morphological and genetic studies (Lai et al., 2010) have confirmed its presence and dominance in the region. The species is widely distributed across the western Indian Ocean, the Red Sea, Mediterranean Sea, and West African coasts (Hasan and Noël, 2008). Despite its importance, sustainable exploitation of P. segnis remains a challenge due to increasing fishing pressure and environmental changes. Previous studies (Safaei, 2013; Giraldes et al., 2016; Yeşilyurt et al., 2022) have explored its population dynamics, reproductive biology, and growth patterns, revealing significant regional variations. Notably, invasive populations in the Mediterranean exhibit higher growth rates compared to native populations in the Persian Gulf, likely due to ecological factors such as predator pressure and food competition. This study aims to assess the biological status and exploitation levels of P. segnis in Hormuzgan Province, Iran. It seeks to estimate key population parameters, evaluate mortality rates, and propose management strategies for sustainable harvesting. This study is designed to address three key questions: First, what are the growth and mortality characteristics of P. segnis in the southern waters of Iran? Second, how do these biological traits compare with the global populations of the species? Third, what management strategies are essential to prevent overexploitation? By combining extensive field observations with advanced modeling techniques, the research presents a comprehensive picture of the population structure and exploitation status of P. segnis. The integration of biological indicators with fisheries data not only deepens scientific understanding of the species in the region but also provides a practical framework for localized resource management.
Methodology
The study was conducted over a 12-month period from September 2023 to August 2024. Monthly samples of P. segnis were collected from major landing sites in Kong, Qeshm, Bandar Abbas, and Sirik. Each month, 40–50 individuals were randomly selected and subjected to biometric analysis. Carapace width (CW) was measured using digital calipers (±0.01 cm), and body weight was recorded with precision scales (±0.01 g). Sex determination was based on abdominal morphology. Growth patterns were analyzed using the von Bertalanffy growth model via ELEFAN I (Pauly, 1998) in TropFishR. The relationship between CW and weight was modeled using the equation W= aCWᵇ, with regression parameters estimated separately for males and females. Growth type (isometric vs. allometric) was determined using Pauly’s t-test. Mortality rates were estimated using Pauly’s empirical formula for natural mortality (M), catch curve analysis for total mortality (Z), and the difference method for fishing mortality (F=Z–M). Exploitation rate (E=F/Z) and optimal biological reference points (Fopt, Flimit) were calculated following Patterson (1992). Cohort analysis and length-frequency distributions were used to identify age classes and recruitment patterns. Maximum Constant Yield (MCY) was estimated using Welch’s method (2002), incorporating 10-year average catch data and environmental variability indices. All statistical analyses were performed in R.
Results
A total of 2,042 P. segnis specimens (1,025 males, 1,017 females) were analyzed. Carapace width ranged from 4 to 19 cm in males and 5 to 17 cm in females, with a mean CW of 12.1 cm for males and 11.4 cm for females. The most frequent size class was 10–12 cm, accounting for 43% of the population. Statistical analysis confirmed significant sexual dimorphism in size (p<0.05). The CW–weight relationship showed allometric growth, with males exhibiting higher weight at equivalent CW than females. Regression equations were W=0.0667CW3.13 for males and W=0.0902CW2.72 for females, with R² values of 0.90 and 0.88, respectively. Sex ratio analysis across months revealed near parity (1:1), with minor fluctuations. Only in September 2024 did females significantly outnumber males (p<0.05). Seasonal trends indicated peak abundance of mature individuals from December to May, while juveniles dominated from June to September. Growth parameters estimated via von Bertalanffy model were: CW∞=17.85 cm, K=0.79 yr⁻¹, t₀=–0.51 yr, and Φ′=2.14. These values suggest rapid growth and high turnover. Mortality rates were Z=1.91 yr⁻¹, M=1.60 yr⁻¹, F=0.31 yr⁻¹, and E=0.16, indicating low fishing pressure relative to natural mortality.
Optimal exploitation benchmarks were Fopt=0.80 and Flimit=1.05.
The estimated MCY for Hormuzgan waters was 276 tons, based on a 10-year average catch and environmental index c=0.7. Cohort analysis revealed four distinct age classes, with recruitment peaking in April and growth slowing from September to November.
Conclusion and discussion
The findings underscore the ecological and economic importance of P. segnis in southern Iranian waters. Despite its commercial value, the species faces threats from habitat degradation and unregulated fishing. The observed low exploitation rate (E=0.16) suggests current fishing pressure is below biological limits, offering a window for proactive management. Seasonal growth patterns and recruitment dynamics highlight the need for temporal fishing regulations. The presence of juveniles during summer months suggests that restricting harvest during this period could enhance stock sustainability. Additionally, the allometric growth pattern and sexual dimorphism in size warrant gear modifications to reduce bycatch and protect smaller individuals. Comparative analysis with global studies (Josileen and Menon, 2007; Dineshbabu et al., 2008; Mehanna et al., 2013) showed regional differences in growth rates and CW∞, likely due to gear selectivity, sampling methods, and ecological conditions. For instance, CW∞ in Oman was 10.3 cm for males, while in India it reached up to 22.3 cm. Recommendations include implementing minimum legal-size limits, enhancing data collection on catch and effort, and promoting selective fishing gear. Establishing marine protected areas during peak spawning seasons could further safeguard reproductive stocks.
Conflict of interest
The authors declare no conflict of interest related to the conduct or publication of this research. |
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| Keywords: The authors declare no conflict of interest related to the conduct or publication of this research. |
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Full-Text [PDF 856 kb]
(5 Downloads)
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Type of Study: Research |
Subject:
ارزيابي ذخاير و پويايي جمعيت
Received: 2025/09/9 | Accepted: 2025/12/31
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