Space-time characteristics of fishery resources of the Dolphin Provincial Nature Reserve of the Yangtze River in Zhenjiang based on acoustic survey

LI Peijie;WANG Shaogen;LIN Danqing;PAN Jie;LIU Yan;ZHU Xiaofeng;LIU Kai;Experimental Station for Scientific Observation of Fishery Resources and Environment in the Lower Reaches of the Yangtze River, Ministry of Agriculture and Rural Affairs; Freshwater Fishery Research Center, Chinese Academy of Fishery Sciences;The Management Office of Yangtze River Dolphin Nature Reserve in Zhenjiang;

fish resource assessment;;acoustic survey;;nature reserve;;target strength;;Yangtze River dolphin

The Dolphin Provincial Nature Reserve of the Yangtze River in Zhenjiang was approved and established by the Jiangsu Provincial People's Government in 2013, optimizing the functional area of the reserve in 2014. The area has wide and rich aquatic biological resources and is a natural spawning and feeding ground for fish. Fishes are the main bait for the finless porpoise. In the context of gradual improvement of the aquatic environment in the Yangtze River Basin and effective control of human activities, the change in fish stock is the most important factor affecting the distribution, activities, and reproduction of the Yangtze finless porpoise. Over time, human activities have affected aquatic systems, such as river dams, fish populations, and water quality. The aquatic biodiversity of this area has continued to decline, and biological conservation is imperative. Thus, timely and accurate assessment of the temporal and spatial distribution of fishery resources is of great significance for protecting the aquatic environment. Acoustic assessment of fishery resources is a technology that has been gradually developed and improved in China over the past 40 years. Compared with the traditional net fishing assessment method, this method is highly efficient and fast, does not damage fishery resources, can be used to sample a large area, allows for the collection of abundant real-time spatial and temporal data, and has been widely applied. In this study, we conducted acoustic surveys four times in 2018, The amplitude of variation of the density of fish resources was 0.090–0.575 ind/m~2, and the mean value was 0.286 ind/m~2. The density of fish stocks was the highest in July and the lowest in January. The spatial distribution also changed significantly with seasons. In July and October, the resource density of the south and north branches of Hechangzhou was significantly higher than that upstream and downstream of Hechangzhou. However, in January and April, the resource density was higher upstream and downstream of Hechangzhou than in the branches. The single target strength was a unimodal distribution in the survey areas, mainly –59.5 to –53.5 dB. The single target was concentrated in the 10–40 m layer of water in spring,autumn, and winter, whereas it was concentrated in the 5–20 m layer of water in summer. Based on the investigation and evaluation of fishery resources of the Yangtze River Dolphin Provincial Nature Reserve in Zhenjiang, the basic information on fishery resources could be determined, and the quality of habitat of the finless porpoise can be increased over time. Thus, our results provide a scientific basis for the management of the reserve and the implementation of scientific management and protection. In the acoustic assessment, the distribution of the integral values of the catch is the key link. Limited by survey conditions on the Yangtze River, no simultaneous trawl surveys were conducted in this study, and the estimated fishery resource density may have contained certain errors.However, it likely had little effect on the relationship between the temporal and spatial distribution of fish. In future research, acoustic surveys should be supplemented by multiple survey methods and comprehensive observation to improve the accuracy of acoustic assessments of fishery resources.