长江口溯河鳗苗开发率估算

利用长江口南支上段东风西沙调查站位(121°15′45′′E;31°40′18′′N)2015年度鳗苗捕捞数据,通过CPUE波动趋势分析,确定当年日本鳗鲡鳗苗溯河汛期特征;进而采用Leslie和Delury两种方法估算东风西沙站位鳗苗资源指标。结果显示,2015年度东风西沙站位出现6个明显的鳗苗补充汛期,两种方法估算的汛期波动规律一致。各汛期捕捞持续时间5~27 d,平均为10.17 d。Leslie法估算的各汛期捕捞开发率43.38%~96.30%,平均77.14%;Delury法估算结果为43.36%~105.37%,平均81.43%;均为较高水平。高开发率表明东风西沙水域樯张网作业方式致使溯河迁移鳗苗处于高度开发状态,减少溯河鳗苗数量,影响长江流域成鳗资源。Leslie法估算日捕捞死亡系数和日捕捞死亡率平均值分别为0.23和20.02%,均分别低于De Lury法估算平均值0.27和22.79%;捕捞死亡系数将为采用年渔获量估算鳗苗资源量提供基础数据。

AN ESTIMATE OF EXPLOITATION RATE OF ANGUILLA JAPONICA ELVERS UPSTREAM RUNNING ACROSS WATERS OF YANGTZE ESTUARY

Based on the daily catch data of Anguilla japonica elvers of DFXS station (121°15'45"E, 31°40'18"N) in the west waters of south branch of Yangtze Estuary from December 2014 to March 2015, the number of shoals immigrated upstream was determined by CPUE fluctuation analyses, and their resource indices were estimated by the Leslie method and Delury method. The present study indicated that there were six dominant elver shoals immigrated upstream, and these two methods were found to produce the same result of shoal fluctuant features in this period. The duration of fishing days for each shoal was different. The longest period lasted for 27 days, while the shortest one lasted only 5 days. The average fishing period was 10.17 days. Their exploitation rate estimated by the Leslie method reached 43.38%-96.30% with an average of 77.14%, and that estimated by the Delury method reached 43.36%-105.37% with an average of 81.43% of the initial immigrating population size. The exploitation rates of elvers in the DFXS station upstream were at high levels. High exploitation rates of elvers suggested that the approach of stake-set stow net in DFXS station waters reduced numbers of elver upstream and influenced adult resources of Anguilla japonica in the Yangtze Basin. The average daily fishing mortality coefficient and average daily fishing mortality rate of DFXS station waters estimated by Leslie method were 0.23 and 20.02%, respectively, lower than that estimated by the Delury method (0.27 and 22.79%, respectively). Fishing mortality coefficient is very useful for estimating Anguilla japonica elvers resources of waters of Yangtze Estuary.