Pen-fish-farming development in east Taihu Lake and its effects on lake environment

Abstract

东太湖是太湖东南部一个草型湖湾,面积131.25km²,水草丰盛,水质良好,渔业资源丰富,但由于多种原因,捕捞渔业产量仅有1700t/a左右.自80年代以来兴起的围栏养殖渔业到1992年时已发展到1007.9hm²的规模和1870t的总产量,年产值1485.23万元,利润率达45.1%。与此同时,也引起了634.4hm²水生植被的毁坏和水质污染等环境生态负效应。在现行的三种围养模式中,大网围放牧式养殖因过低的生产能力和破坏大面积水生植被而应予以淘汰;小网围精养具有较高的经济效益.但由于污染较严重,应限制其规模并调整其分布以减轻污染程度;网围养蟹以其高利润率和轻污染及对水生植被破坏较轻而具有较大的发展潜力,应予科学引导.同时探讨青虾等的养殖技术以增加水产品的多样性。;East Taihu Lake, belonging to part of Taihu Lake, is located in the southern Yangtze River delta. It is a shallow lake with a mean depth of 1.07 m, a surface area of 131.25 km², and 124.9 km² of aquatic vegetation. Although sufficent dissolved oxygen, mesotrophic water and annual mean temperature of 17.1℃ might bring high potential fish productivity to the lake, yet the natural fishing yield has been still keeping at about] 700t/a. Pen fish farming began in 1984 and developed very rapidly in the last decade. By 1992, it had reached 1 007.9 hm² in total area, 1870t in total yield, 14.85 million RMB Yuan in output value and got a profit rate as high as 45.1%. At the same time, it had destroyed 634.4 hm² of aquatic vegetation and produced 185.64 t of nitrogen, 22.7 t of phosphorous and a large amount of organic pollutants to the lake. Large-scale pen fish farming should be forbidden because it may destroy large area of aquatic vegetation (367.4 hm²) and lead to very low fish yield (128.7 t) and output value (0.63 million RMB Yuan). Small-scale pen fish farming destroyed less aquatic vegetation (267 hm²) but gave much more higher fish yield (1662 t) and output value (8.15 million RMB Yuan). About 31644 t of aquatic macrophyte was harversted from the lake and used as fish food, and 2869 t of grain and grass was also added in. It caused a total pollution load of 170.73 t in nitrogen and 20.74 t in phosphorous for the lake as a result of which for every 1000 RMB Yuan of profit 542.8 fcg nitrogen and 65.9 kg phosphorous Co the iake, so that small pen fish farming should be limited and carefully managed. Crab culture gave high output value (16245 RMB Yuan/hm²) and the highest profit rate (58.6%), and brought about much less pollutants to the lake and had less effect on the aquatic vegetation. Detailed studies are needed to improve crab culture technique and promote its development in East Taihu Lake.