山东半岛南部海域三疣梭子蟹增殖放流群体回捕率

根据2010年和2011年5-8月在山东半岛南部海域对三疣梭子蟹(Portunus trituberculatus)增殖放流前后分别进行的每年3个航次的对比调查结果,定量分析了三疣梭子蟹自然群体和增殖放流群体的数量,并根据三疣梭子蟹放流苗种数量和放流后捕捞产量,对三疣梭子蟹增殖放流群体回捕率进行分析.研究结果表明,2010年5月山东半岛南部海域三疣梭子蟹增殖放流前自然群体资源量很少,相对资源密度为0.90 ind/(站.h);在5-6月共放流苗种11 015.13万只,放流后10d左右资源量增加为26.08 ind/(站.h),放流群体所占的比例为96.55％;8月进行调查的相对资源密度为1.70 ind/(站.h),当年生群体数量占所有群体数量的比例为64.29％;9月、10月、11月秋汛期间捕捞产量为3 108 t,捕捞个体平均质量为232.3 g,增殖放流群体回捕率为7.54％.201 1年5月山东半岛南部海域三疣梭子蟹增殖放流前自然群体相对资源密度为1.70 ind/(站.h);在5-6月共放流苗种13 132万只,放流后10d左右资源量增加为29.15 ind/(站.h),放流群体所占的比例为94.17％;8月进行调查的相对数量为1.00 ind/(站.h),当年生群体数量占所有群体数量的比例为70.00％;9月、10月、11月秋汛期间捕捞产量为2 896 t,回捕个体平均质量为226.0 g,增殖放流群体回捕率为6.43％.除2011年胶州湾海域由于富营养化水质较差,以及其他因素对黄家塘湾海域的影响导致这两个放流点放流群体回捕率偏低外,2010年和2011年山东半岛南部放流海域整体水质良好,水温、透明度、盐度、营养盐比例、生物饵料等均比较适中,属于放流环境条件较佳的海域,比较适合三疣梭子蟹生长,放流群体回捕率整体上处于较高水平.

Recapture rates of swimming crabs (Portunus trituberculatus) released in the waters off southern Shandong Peninsula

  The demand for seafood is expected to rise substantially as both the standard of living and human population size continue to increase. Stock enhancement programs will likely help fill some of the projected gap in supply as well as replenish severely depleted or recruitment-limited fisheries. At present, stock enhancement programs have been widely implemented in the coastal waters of the Yellow Sea and Bohai Sea, China, including a program to enhance populations of the swimming crab (Portunus trituberculatus). However, little effort has been made to evaluate the effectiveness of these stock enhancement programs, particularly for species that are not suitable for physical tagging, such as the swimming crab. We conducted a quantitative analysis to assess the recapture rates of swimming crabs using survey data collected in May, June, July, and August of 2010 and 2011. We compared survey results before and after the release of swimming crabs in the waters off southern Shandong Peninsula. The wild population was relatively rare: only 0.9 individuals were caught per site per hour prior to release of cultured crabs in late May, 2010. Capture rates increased to 26.08 individuals per site per hour 10 days after the release of ~110.15 million seedling swimming crab, and the supplemented stock accounted for 96.55% of the total catch. The stock density was 1.70 individuals per site per hour during surveys in August, and the age-0 swimming crabs accounted for 64.29% of the total catch. The total yield of swimming crab was 3 108 tons in 2010, the average body weight was 232.3 g, and the recapture rate was 7.54%. In 2011, the density of the wild population of swimming crab was 1.70 individuals per site per hour before supplementation in late May, but increased to 29.14 individuals per site per hour 10 days after release of ~131.32 million seeding swimming crab, of which the supplemented stock accounted for 94.17% of the total catch. In August, the density had declined to 1.00 individual per site per hour and age-0 individuals represented 70.00% of the total catch. The total annual yield was 2 896 tons, the average body weight was 226.0 g, and the recapture rate was 6.43%. Our results suggest that the stock enhancement effort was more successful in 2010 than 2011. Our results also suggest that the water quality (temperature, transparency, salinity, nutrient composition and concentration) and food supply off southern Shandong Peninsula were suitable for stock enhancement of swimming crab, evidenced by the high recapture rates in 2010 and 2011. However, the poor water quality in Jiaozhou Bay and Huangjiatang Bay was associated with relatively low recapture rates.