长江天鹅洲故道“四大家鱼”种质资源天然生态库建库可行性研究

FEASIBILITY STUDIES ON GENETIC CONSERVATION OF CHINESE CARPS IN SWAN OXBOW OF THE CHANGJIANG RIVER

天鹅洲故道水面面积为１３．７—３０．０ｋｍ２。据１９９１—１９９４年的调查，该故道具有以下优良性状：（１）水质好，溶解氧为５．７—１０．５ｍｇ／ｍｌ，透明度为０．３—１．７５ｍ。（２）水生生物丰富，共有１６门，３０６种。（３）鱼类种类繁多，计有９目１８科７７种。（４）家鱼资源丰富，性状优良。每年７—８月约有近２０万尾鲢、鳙、草、青鱼苗种进入故道育肥，其渔获量在７万ｋｇ左右；生长参数的比较分析证明，故道里的“四大家鱼”维持了其在长江的优良生长特性。总之，天鹅洲故道是建立鲢、鳙、草鱼、青鱼种质资源生态库的理想的自然场所。若把最初捕捞年龄从目前的１龄提高到３龄，把捕捞死亡率从０．６降低到０．３—０．５，并设置有效的拦鱼设备，预期可年产１０万ｋｇ或３—４万尾后备亲鱼。存在问题是：（１）竭泽而渔。对进入故道育肥的“四大家鱼”和就地繁生的鱼类的过度捕捞。（２）渔民过多。在故道打鱼为生的近５００渔民，转业困难，使该故道渔业生产处于恶性循环之中。这些问题如不解决，种质资源库势难建立。此外，从长远发展看，长江三峡高坝建成后，宜昌江段产卵场可能消失，以及故道的牛轭湖化，对天鹅洲故道作为种质资源天然生态库的影响都不容忽视。

The SWan OXbow is One of the three existing oxbows along the ChangjiangRiver.Based on the study from 1991 to 1994,the following advantages have been found:(1)good water quality,no solution,DO2 5.7 10.5mg/ml,transparency 0.3 1.75m.(2)abundant hydro-organisms,16 Phylums, 306 species.(3) rich fish species,9 orders,18 famlies,77 species.(4) plentiful Chinese carps(silver carp,high、ad carp, grass carp and blackcarp)with excellent aquaculture performances.During July-August, there are about200,000fry-fingerlings of Chinese carps immigrated ftom Changjlang River into the Oxbowfor feeding,resulting in a harvest of 70,000kg. The comparison on growth performance ofChinese carps between the Oxbow and the River indicats that the carps in Oxbow maintainthe excellent performance as the River stoops.Generally,the Swan Oxbow Is an ideal location for setting up a genetic conservation area for the Chinese carps.If the age at nrst capture could be raised from 1 to 3 years old,and the fishing mortality could be decreased from0. 6 to 0.3 0.5,100,000kg or 30,000 40,000 broodfish would be obtained per year.Theexisting major problems as obstacles for establishing the genetic conservation area are:(1)extremely heavy overfishing,of the immigrated Chinese carps and other local fishes withinone growing season.(2)The employment problem.There are about 500 fishermen living onfishing in Oxbow,it is difficult to shift them ftom fishing to other jobs.For long term,themajor threat will be from:when the Three Gorges Dam, is to be built the Yichang spawninggtound Will disappear,and the Oxbow Will transform to an isolated lake. In this case, SwanOxbow will lose its ecological-geographical advantages as a genetic conservation.