象山港日本对虾增殖放流的效果评价

日本对虾是中国近海重要的增殖品种,2010年象山港分两批次放流日本对虾苗种约1.67亿尾。通过对放流苗种存活状况、洄游分布、生长特性及回捕情况的跟踪调查,对象山港日本对虾的增殖效果做出初步评价。结果表明:(1)日本对虾放流苗种在8月中旬成为补充群体,集中于港区底部进行索饵育肥;9月中旬,第1、2批放流苗种的平均体长分别达到95.4 mm和71.4 mm,成活率分别约为0.79%和1.06%;10月上旬,随着港区水温降低,增殖苗种资源量锐减。(2)协方差分析表明:日本对虾增殖群体和自然群体的体长-体重关系存在显著性差异,增殖群体的体征状况明显优于自然群体。(3)日本对虾放流苗种在港区主要为桁杆拖虾和地笼网渔业所利用,在港区滞留期间,回捕率约为0.25%。总结发现:栖息地破坏及放流苗种的过早利用是制约象山港日本对虾增殖效果的重要因素,优化增殖策略、保护港区生态环境应是今后港区增殖工作的重点。

Stocking effectiveness of hatchery-released kuruma prawn Penaeus japonicus in the Xiangshan Bay, China

Stock enhancement is a fisheries management approach involving the release of hatchery organisms to increase abundance and commercial landing of natural fish or invertebrate population.Kuruma prawn Penaeus japonicus is one of the most important fishing and cultured crustaceans in China coast,and thus is listed as one of the important target species for stock enhancement.In 2010,a total of about 167 million hatchery kuruma prawn juveniles(body length ≥ 11.0 mm) were released through two phases into the Xiangshan Bay,Zhejiang Province.The first batch of 30.68 million prawn juveniles were released on July 6,while the second batch of about 135.9 million prawn juveniles were released on July 15—16.In order to evaluate the potential effectiveness of the stock enhancement program,the present study monitored survival,growth rate,and migratory pattern of the hatchery-released kuruma prawn in the bay through recapture method monthly.It was necessary for assessing the stocking effectiveness to distinguish the released individuals from natural partners.It was found that there were obvious differences in hatching time and body size between the natural and hatchery kuruma prawn juveniles,and thus we could use cohort analysis with the least-squares method to identify released hatchery individuals in the study.The results indicated that the released prawns mainly inhabited in inner or middle part of the Bay where the sediments were sandy or sandy-mud substratum.The released juvenile prawns started recruiting to the fishery in mid/late August,and then it might migrate from the Bay to coastal open water for overwintering in October.In mid-September,the released prawns reached the mean body length of 95.4 mm and 71.4 mm,with the survival rate of 0.79% and 1.06%,respectively,for the first and second batch.The relative abundance of the released prawns in the total catch was 14.0% and 84.2%,respectively,for the first and second batch.The exponents for the body length-body weight relationships differed significantly(P < 0.05) between released and natural stock,with greater value for the released stock,which showed that released individuals were more robust than natural ones.During the fishing season,it was found that lots of released prawns were caught by local fishermen through small beam trawls and fish traps within the bay.During the study period from late August to early October,a total of about 420,600 released prawns were collected,representing the mean recapture rate of about 0.25%.In general,the effectiveness of the stock enhancement program did not satisfy with the desired aim due to the low survival and recapture rate of released juvenile prawns.The low stocking effectiveness might be resulted from habitat destruction and ineffective release strategies.In future,optimizing release strategy and restoration of nursery habitats should be essential for promoting the stocking effectiveness of kuruma prawn in the bay.We recommended three optimal measures for the stock enhancement program: 1) the large-sized kuruma prawn juveniles were proposed to be released,2) the best release site should be located in the inner part of the bay,and 3) the release date should be April in advance,which would prolong growth period of kuruma prawn juveniles in the bay and increase the efficiency of the stock enhancement programs.