长江禁捕后长江口刀鲚资源特征

研究于2019—2021年对长江口刀鲚(Coilia nasus)生物学、资源密度及其时空分布特征等展开调查,并结合刀鲚生产性捕捞退出前(2017—2018年)的调查结果,对长江禁捕后长江口水域刀鲚资源恢复效果进行了评估。结果显示, 2021年共采集刀鲚2895尾,抽样解剖1960尾,雌雄比为1.87:1,平均体长和平均体质量分别为(272±32) mm和(91.4±33.4) g,较2019—2020年分别增加4.41%和37.55%,较2017—2018年分别显著增加5.84%和22.85%(P<0.05);平均丰满度系数为0.44±0.10,较2019—2020年增加18.28%,较2017—2018年增加12.82%(P>0.05)。2021年日均调查尾数N_B和重量W_B分别为170尾/d和15.56 kg/d,较2019—2020年分别增长1.09倍和1.48倍;单网调查尾数N_t和重量W_t分别为50尾/网和4.56 kg/网,较2019—2020年分别增长1.24倍和1.69倍,...

CHARACTERISTICS OF COILIA NASUS RESOURCES AFTER FISHING BAN IN THE YANGTZE RIVER

Estuarine tapertail anchovy (Coilia nasus) is a valuable migratory fish species and the most representative species in the lower reaches of the Yangtze River, and its resource status have been attracted an increasing amount of attention. In order to effectively track and evaluate the recovery effects of C. nasus resource after the national fishing ban strategies, this study carried out an investigation on the spatial-temporal characteristics of biology and resource density of C. nasus in the Yangtze River estuary from 2019 to 2021 based on the survey results conducted before the withdrawal of productive fishing (2017—2018). The results showed that a total of 2895 C. nasus were collected, and 1960 were dissected in 2021, with a female to male ratio of 1.87﹕1. The mean body length of (272±32) mm and mean body weight of (91.4±33.4) g, increased by 4.41% and 37.55% compared with 2019—2020, and significantly increased by 5.84% and 22.85% compared with 2017—2018 (P<0.05), respectively. The mean fatness of 0.44±0.10 was 18.28% higher than that in 2019—2020 and 12.82% higher than that in 2017—2018 (P>0.05). In terms of resource density, the mean daily catch number (N_B) and weight (W_B) in 2021 were 170 ind./d and 15.56 kg/d, 1.09 times and 1.48 times higher than that in 2019—2020, respectively. The number (N_t) and weight (W_t) of single net were 50 ind./net and 4.56 kg/net, 1.24× and 1.69× increase compared with 2019—2020, respectively, and the resource density showed an increasing trend from 2019 to 2021. The migration time of C. nasus mainly occurred in March and April in 2020—2021, which was earlier than the peak of migration in 2019. The density of C. nasus in deep water was significantly higher than that in shallow water (P<0.05). Our study suggested that the recourses of C. nasus did not recover immediately in 2019 due to the influence of overfishing in the early stage and the fact that the other fishery production was not completely eliminated. Since January 1st, 2021, the implementation of fishing ban in key waters of the Yangtze River and the Yangtze River Estuary has reduced fishing pressure, and the population biological specifications and resource density of C. nasus in Yangtze River estuary have recovered significantly. The resource shows a good tendency towards recovery, highlighting the important role of the fishing ban management policy. This study suggested that long-term follow up monitoring should be carried out on representative migratory species such as C. nasus to obtain the resource characteristics during the period of fishing ban in the Yangtze River, and to support the assessment of fishing ban effect and biological integrity evaluation in the Yangtze River.