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.