| With the people’s living standards improve and the continue increase of the population, the demand for seafood is expected to rise substantially. Although it remains to be seen that production from capture and stock enhancement can help ?ll the projected gap in supply additional ?sh except aquaculture, some successful cases like releases of cultured juveniles to replenish severely depleted or recruitment-limited ?sheries given us the very big confidence and encourages. In recent years, with increasing effects of human activities(overfishing) and environmentalchanges(pollution, habitat degradation) on marine ecosystem, combined with climate change, the fishery resource structure has beenchanged dramatically, characterized by unsustainability. In order to better understand the feeding habitats, recapture rates, current status and effectiveness of some important releasing species in the waters off Shandong Peninsula, the food composititon, feeding intensity and the trophic level of Penaeus chinensis and Liza haematocheila were studied based on stomach content analysis; the quantitative analysis has been used to assess the recapture rates of released swimming crab according to the three times surveys in every year of May, June, July and August 2010 and 2011 by comparing the survey results before and after releasing of swimming crab in the waters off southern Shandong Peninsula; andtheeffectiveness of stock enhancementof Penaeus chinensis was analyzedbased on the releasing data in the southern waters of Bohai Sea from Shandong Province in May and June, 2007-2013. The main resultswere as follows:Feeding habits of Penaeus chinensis of enhancement and releasing species in Bohai sea:Penaeus chinensis were important releasing species in the Bohai Sea. Based on the samples collected from bottom trawl surveys in the Bohai Sea,78 stomach samples of Penaeus chinensis with body lengths of 112~166mm in August, 2010. The results indicated that the food composition of Penaeus chinensiswere Bivalvia, Crustacea, Polychaeta, Gastropoda and Algae, of wich, Bivalviaaccountedfor 55.11% of the total foods, with frequency of occurrence of69.23%. Bivalvia larva was the most important species, accounting for 54.96% of the total foods, frequency of occurrence was 67.95%. Crustaceawas in second place, accounting for 44.32% of the total foods, with the frequency of occurrence of 49.99%.Ostracods accounted for 43.62% of the total foods with frequency of occurrence of 37.18%.Polychaeta, Gastropoda, and Algae had relatively lower numerical percentages, and frequency of occurrence.The trophic levelof Penaeus chinensis was 3.14, and the rate of feeding stomachs was 73.07%.The Recapture Rates of Released Portunus Trituberculatus in the Waters off Southern Shandong Peninsula:the quantitative analysis has been used to assess the recapture rates of released swimming crab according to the three times surveys in every year of May, June, July and August 2010 and 2011 by comparing the survey results before and after releasing of swimming crab in the waters off southern Shandong Peninsula. The results showed that there were few wildstock, only 0.9 individual were caught per site per hour before releasing in late May, 2010. When about 110.15 million seeding swimming crab released, 26.08 individual were caught per site per hour after around 10 days, and the released stock occupied 96.55%. The stock density reached 1.70 individual per site per hour during survey in August, and the 0-group swimming crab accounted for 64.29%. The total yield of swimming crab was 3108 tons in the year 2010, the average body weight was 232.3 g, then, the recapture rate was estimated to be 7.54%. In 2011, the density of wildstock of swimming crab was 1.70 individual per site per hour before releasing in late May, about 131.32 million seeding swimming crab were released, the density was 29.14 individual per site per hour afteraround 10 days, the released stock occupied 94.17% of total catch. The density was 1.00 fish caught per site per hour and the percentage of 0-group was 70.00% in the survey in Agust. The total yield was 2896 tons in the whole year, the average body weight was 226.0g, the recapture rate was estimated to be 6.43%. The effectiveness of stock enhancement of swimming crab in 2010 was better than that in 2011. By analysis, it indicated that the waters quality(temperature, transparency, salinity, nutrient composition and concentration) and food off Southern Shandong Peninsula were suitable for stock enhancement of swimming crab with high recapture rates in 2010 and 2011, except the low water quality of Jiaozhou bay and Huangjiatang bay with relatively low recapture rates.Current status and effectiveness of releasing Penaeus chinensis in the southern waters of Bohai Sea from Shandong province:Based on the releasing data of Penaeus chinensis in the southern waters of Bohai Sea from Shandong Province in May and June, 2007-2013, the effectiveness of stock enhancement was analyzed. About 610 million seeding Penaeus chinensis per year were released along the coastal waters off Binzhou, Dongying, Weifang and Laizhou. On average of 1430 fishing boats were used in fishing mainly on the released stock during open fishing season every year and the total yield of Penaeus chinensis was 7487.97 tons in seven years, the released stock occupied more than 90% of the total catch, and the production value reached about 783 million yuan RMB with a input-output ratio about 1:2. The stock enhancement of Penaeus chinensis has achieved the apparent ecological, economic and social benefits in Shandong Province. |
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