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Catch field surveys were conducted by on-boarding both for small-scale and commercial-scale boats in the upper Gulf of Thailand in 2006-07. The small-scale operates inshore (0.5-3.0km) by one man operation, with individual pot setting of 295-367 pots/boat. The commercial-scale operates offshore (>3km) by 5-8 crews with long-line type setting of 1,687-2,120 pots/boat. The catches were analyzed in CPUE, catch composition, bycatch and discard by number. They were also compared from the view point of operation strategies as fishing ground, method, soaking time, etc. Average CPUE for the small- scale was 2.81 crabs/pot, which was much higher than the commercial-scale of 0.26 crabs/pot. Catch composition of blue swimming crab for small-scale accounted for 72.4-91.3% while 21.2-51.6% for commercial-scale of total catch. ...

Blue swimming crabs (BSC) (Portunus pelagicus) fisheries in Southeast Sulawesi waters have experiencing huge pressure, however studies on their reproductive biology were limited. The objective of the study was to find out the growth model, size at the first maturity, fecundity, and sex ratio disparity of BSC. The samples were collected monthly during June 2014 - April 2015 using gillnets, crab pots or hand-picking. Berried females were collected for fecundity (F) analysis. Relationship between weight (W) and carapace width (CW) were analyzed using a simple linear regression. The CW size of the first maturity was pointed out at 50% of frequency cumulative (CW50), while relationship between F and CW was analyzed following F = a*CWb. Sex ratio of both sexes was tested using the Chi-square (α = 0.05). The result shows growth model of both sexes was “allometric” (b < 3) following equation of W = -1.6181 + 0.0224*CW for males and W = -1.7909 + 0.0238*CW for female. The relationship between F and CW was F = 80.443e0.0236 CW (r = 0.7679). This organism produces high fecundity as its biology reproductive strategy to maintain its population. Males and females attaine the first maturity at CW50 of 11.957 cm and 10.802 cm, respectively. The sex ratio generally females preponderate over males, however, the Chi-square test was not significantly different. Factors affecting sex ratio disparity were mainly locations (water quality), migration and distribution patterns according to sex, sampling method, gears catchability, mortality and growth, reproduction activities, and CW sizes.

จากการศึกษาการแพร่กระจายขนาดของปูม้าจากเครื่องมือประมงประเภทอวนลากและอวนรุนในน่านน้ำไทย ซึ่งปรกอบด้วย เรืออวนากขนาดใหญ่ (ความยาวมากกว่า 14 เมตร) เรืออวนลากแคระ (ความยาวน้อยกว่า 14 เมตร) และเรืออวนรุน พบว่า อัตราการจับปูม้าของเรือประมงอวนลากขนาดใหญ่แยกตามจังหวัดที่สุ่มตัวอย่าง คือ นครศรีธรรมราช สงขลา ปัตตานี สตูล และภูเก็ต มีค่าเท่ากับ 0.081 0.063 0.053 0.891 และ 0.324 กิโลกรัมต่อชั่วโมง ตามลำดับ ...

Ernawati T, Sumiono B, Madduppa H. 2017. Reproductive ecology, spawning potential, and breeding season of blue swimming crab (Portunidae: Portunus pelagicus) in Java Sea, Indonesia. Biodiversitas 18: 1705-1713. The blue swimming crab (Portunidae: Portunus pelagicus) is one of the most economically important fisheries species in Indonesia. Little is known about their reproductive ecology and key biological characteristics. This study aimed to investigate population biology and reproductive ecology (Carapace’s width to weight relationship, growth, natural mortality, size at first maturity and at first captured, Spawning Potential Ratio (SPR), and breeding season) of P. pelagicus at six important landing sites around the Java Sea (Jakarta, Cirebon, Demak, Rembang, Sumenep, and Sampit) from January 2014 to January 2015. Monthly data were collected by fishers at each landing sites, with a total of 14,408 individuals being measured. The study found that males were heavier than females and the smallest mean of individuals’ height belonged to Jakarta compared to other locations. The growth parameters varied at the different locations. Crabs could grow up to 100 mm in 10 months with the maximum age being less than three years. The growth rate (K) of more than 1 indicated a fast-growing crustacean with a short lifespan. The lowest carapace width at first capture (L c ) for the BSC was obtained from crabs caught using a bottom gillnet landed in Jakarta, followed by dredged crabs in Cirebon. The mean carapace width at first maturity (L m ) in the Java Sea was 10.6 cm, with the lowest L m of female crabs being landed in Cirebon and the highest in Sampit. The Spawning Potential Ratio (SPR) ranged from 11% to 24% and the selectivity curve for the BSC fishery at each landing sites is positioned well to the right of the generic maturity curve, except in Demak, suggests that the operation enables almost all crabs to mature and spawn before entering the fishery. The collapsible trap was the most selective gear, with an average catch of 112 mm across at all landing sites, and the least selective was in trawls. Therefore consideration needs to be given to the different gear types used to catch crabs to leave smaller crabs in the water longer to grow to maturity. Considering its fast growth and peak season (February-April and August-October), a short-period is recommended at some sites that have been over-exploited to rebuild a broodstock to support the long-term sustainability of this species.