Fishery biology of two crab species caught by offshore pots
ZHANG Jian，WANG Zhong－qiu，GUAN Wei－bing
Key Laboratory of Sustainable Exploitation of Oceanic Fisheries Resources，Ministry of Education，National Engineering Research Center for Oceanic Fisheries，Shanghai Ocean University，Shanghai 201306，China
Abstract: In order to investigate the fishery biological characteristics of main crab species caught in the offshore crab pot fisheries，4 trials in sea experiments with longlining pots were carried out from autumn in 2012 to winter in 2013 in the East China Sea.The fishery biological characteristics of swimming crab Portunus trituberculatus and redspotted swimming crab Portunus sanguinolentus，which dominated the catch，were measured and then analyzed.The results showed that there was larger population of crabs caught in autumn of 2012 and winter of 2013 than that caught in spring and autumn of 2013，larger in male crab than in female crab.The relationships between carapace width(CW）and body weight(W）of swimming crab and red spotted crab were expressed as W=5.077×10－4 CW2.533and W=1.388×10－4CW2.797，respectively.The female swimming crab caught in autumn and winter had gonad with stagesⅠ－Ⅲ，and male red spotted crab had gonad with stagesⅡ－Ⅴ phase，positive relationship of developmental stage with carapace width.The female red spotted crab caught in autumn and winter had gonad with stagesⅡ－Ⅲ，and male ones had gonad with stagesⅢ－Ⅴ.The swimming crab had condition factor of(5.65±0.94）g/mm3，with significantly negative correlated to carapace width.The red spotted crab had condition factor of(5.78±0.75）g/mm3.Compared to the previous study，the abnormal size frequencies，decrease in exponents of relationship between CW and W and condition factor reflected the possible trends of intensification of fluctuations in crab stock and population miniaturization，growth acceleration and development slowing down of crab individuals.It is suggested that the minimal catchable size of swimming crab be further studied in fisheries management.
2015, Vol. 30 
