| The Chinese mitten crab (Eriocheir sinensis) is one of most traditional rare aquatic animals because of its delicious taste and rich nutrition. In China there are the Changjiang, Oujiang and Liaohe Chinese mitten crab populations, in which the Changjiang crabs have the highest yield and optimal quality. Since the1980s, due to the adverse impact of the engineering construction in the middle and lower reaches of the Changjiang River water system, water worsening environmental degradation as well as resources in long-term excessive use including pro-crab, crab fishing and Crab triple, the Changjiang Chinese mitten resources desreased rapidly. After spring closed season methods, proliferation discharge flow, germplasm resources establishment, the Changjiang crab resources have some recovery. In this study, from September2011to August2012, samples collected from Changshu section in the Changjiang River. population structure, biological characteristics, diet changes and population resourses were studied. Further population dynamics from2007to2011in the lower Changjiang River was also studied according to the monitoring data from the fishery resources environmental science observations of the lower reaches in the Changjiang River Ministry of Agriculture. The main results are list as follows.1.840Chinese mitten crab samples collected from September2011to2012August. Shell width of the catch groups ranged from11.82to80.00mm, the average shell width was35.32±11.32mm, the dominant shell width was between15and55mm, which occupied93.33%. Shell length ranged from10.81to76.00mm, the average shell length was32.03±10.44mm, advantage shell length group was between15and50mm, which occupied91.55%.Body weight of the catch groups was in the scope from0.7g to275.0g, the average weight was25.17±25.20g and advantage body weight was between0.7and50.0g, which occupied89.28%in the whole group. The month sex ratio (♀/♂) was0.44to1.68, no significant differences are found in the month sex ratio. According to the measured biological datas of the Chinese mitten crab, fitting relationship of body weight, shell width and shell length were as follows: shell length-body Weight:W♂=0.0007X29754(r2=0.9846) W♀=0.0010X28290(r2=0.9755); W=0.0008X29090(r2=0.9813); shell width-body weight:W♂=0.0004L3.0026(r2=0.9923); W♀=0.0006L2.9095(r2=0.9792); W=0.0005L2.9587(r2=0.9815); shell length-shell width:L♂=1.0938X+0.3746;(r2=0.9941); L♀=1.0628X+1.2454(r2=0.9890); L=1.0799X+0.7342(r2=0.9922);2. There were129full-stomach crabs for diet analysis from Changshu section. Stomach content analysis shows that there were aquatic vascular plants, algae, organic detritus distinguish objects, aquatic oligochaetes, the rotifers, nauplii and scale films. Statistic analysis showed that their appeare frequencies were71.3%,74.7%,87.6%,18.6%.1.6%,3.1%and0.8%respectively. The aquatic vascular plants included Phragmites australis, Spartina alterniflor and Scirpus triqueter and their frequencies were71.3%,19.4%and11.6%. Furthermore33genera and4phylum algae are identified, they were Cyanophyta (6genera), Chlorophyta (7genera), Bacillariophyta (19genera), Pyrrophyta (1case) and their frequencies were41.86%,27.91%,94.57%,0.78%respectively.3. Based on the biological characteristics datas collected from September2011to August2012in Changshu section of the Changjiang River. The growth and mortality of crabs were analysised, and the utilization resources were evaluated through the Beverton-Holt model. The results show that:(1) the Von Bertalaffy growth parameters L∞=93.5mm, K=1.1, t0=-0.171;(2) the total mortality coefficient Z=6.51, natural mortality coefficient M=2.12, and fishing mortality coefficient F=4.39, the exploitation rate E=0.67;(3) in the current fishing mortality coefficient, average select body length was28.89mm;(4) in the F constant state, according to Length-structure VPA method, the Changshu section catch quantities were2.1x106ind, annual average resources were2.23x107ind, about89.34t. The results showed that crabs were in excessive development state in present.4. The lower Changjiang river population dynamics results showed that the annual total and the end of flood season instantaneous catches changed from9.07to30.44t and from3.01to6.07t in Anhui province respectively, furthermore the total amount of resources changed12.09to36.5t. In Jiangsu province, total catches ranged from6.76to48.28t, the end of flood season instantaneous resources ranged2.85to1.19t, total amount of resources ranged9.88to55.92t. The total resources of the Changjiang River downstream changed from9.88to55.92t. Thanks to the proliferation of releasing and other resource protection measures, the lower reaches of the Changjiang River Chinese crab resources appear rebounded significantly since2006. While after gradually restored crab season began in2007, fishing intensity have begun tound. In order to maintain the sustainable development of the Chinese mitten crab, it is recommended to control the Chinese mitten mitten crab fishing intensity in flood season, the gradual reduction of the special fishing permit issued quantity, try to protect the pro-crab populations reach the breeding grounds, strict implementation of norms to ensure that releasing seed quality. |
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