三峡蓄水后长江口凤鲚汛期生物学特征及捕捞量变动

FLUCTUATION OF BIOLOGICAL CHARACTERISTICS AND YIELD OF COILIA MYSTUSIN FISHING SEASON AFTER IMPOUNDMENT OF THE THREE GORGES DAM IN YANGTZE RIVER ESTUARY

分别在长江南支南门至新河水域、北港水域和圆沙至九段沙水域设置调查断面，对三峡蓄水后（2003～2011年）长江口凤鲚汛期生物学特征、渔汛特征及捕捞量进行了持续调查，并将之与蓄水前（1997～2002年）调查数据进行了对比研究。调查期内凤鲚汛期绝对怀卵量变幅为3404~26850粒，平均为11554粒；相对怀卵量变幅为347～1582粒／g，平均为783粒／g；卵径变幅为0．53～1．06mm，平均为0．78mm。凤鲚全长变幅为139～155mm，平均为146mm；体长变幅为123～137mm，平均为129mm；体重变幅为12．O～15．8g，平均为13．6g；丰满度系数变幅为0．387～0．466，平均为0．442。2003～2011年凤鲚全长小于140mm的个体所占比例均值为36．91％，140～180mm的个体占比为57．06％；体重小于12g的个体占比为39．57％，12～20g的个体占比为45．34％。长江口凤鲚渔汛出现时水温通常介于17~C～20℃，5月中下旬至6月中旬为旺汛期，各年5月捕捞量占比变幅为30．59％～83．76％，平均为61．17％。调查期间长江口凤鲚汛期捕捞船数量变幅为63～278艘，平均为141艘；单船全汛捕捞量变幅为367．9～5023．5妇，平均为2441．2kg；汛期总捕捞量变幅为23．2--1256．9t，平均为422．3t。三峡蓄水后长江口凤鲚渔获规格和捕捞量均出现了不同程度的下降，与历史记录相比，其资源几近枯竭，捕捞价值基本丧失。建议立即对凤鲚实施禁捕，并尽快建立繁殖场和越冬场保护区。

During 2003--2011,total three investigating sections including waters of Nanmeng port to Xinhe port with central position in 121~26r06＂E longitude and 31~33＇41＂N latitude, waters of North channel en- trance with central position in 122~00~42＂E longitude and 31~21＇54＂N latitude and waters of northern Jiudu- ansha with central position in 122~00＇42＂E longitude and 31~21~54＂N latitude were set in southern branch waters of Yangtze River estuary. In these sections, four to six ships were arranged every year to research fishery resource of Coilia mystus in fishing season. Based on the investigations, the studies were carried out for biological characteristics, fishing features and annual yield of Coilia mystus, and comparative study with the similar research during 1997--2002 was also performed. The results showed that absolute fecundity in fishing seasons from 2003 to 2011 ranged from 3 404 to 26 850 individuals,and the average amount was 11 554 individuals; the relative fecundity ranged from 347 ind./g to 1 582 ind./g, and the average amount came to 783 ind./g;the diameter of mature eggs fluctuated between 0.53 mm and 1.06 turn,with the aver- age value reaching 0.78 ram. In aforesaid period,total length of sampling groups ranged from 139 mm to 155 ram,and the mean data was 146 mmlstandard length ranged from 123 mm to 137 ram,and the mean value was 129 ram;body weight ranged from 12.0 g to 15.8 g,and the mean data was 13.6 g;the coefficient of fullness ranged from 0. 387 to 0. 466,and the mean data was 0. 442. From 2003 to 2011,full length of 36.91% random collecting samples were less than 140 mm,and 57.09% individuals ranged from 140 to 180 mm. In the same period, body weight of 39.57~ samples were less than 12 g, while 45.34~ individuals were 12--20 g. At the beginning of the fishing season,water temperature usually fluctuated from 17~C to 20~C. The peak fishing season period mainly occurred in later May until the middle of June,and the catch proportion in May of total catch in fishing seasons fluctuated from 30.59% to 83.76%, with the average number reaching 61.17%. Fishing ships ranged from 63 to 278 with the average of 141 were used during the investigation and the catch per unit effort ranged from 367.9 kg to 5 023.5 kg with the average of 2 441.2 kg. Total catch in Yangtze River estuary ranged from 23.2 t to 1 256.9 t. The result showed that the downward trend of biological characteristics and annual yield could be easily found after impoundment of the Three Gorges Dam. Compared with the historical data,it could be easily concluded that the Coilia mystus fishery resource is coming to be exhausted,and its fishing value is coming to be lost. Under the un- favorable background, only if the subjective factors with negative influence were improved as soon as possi- ble, resource of Coilia mystus could gain adequate space and time. In the end, protecting proposals were also given, such as making policy of fishing forbidden and establishing protection zones.