The characteristics of spatio-temporal distributions of fish resources in the Danjiangkou Reservoir based on hydroacoustic assessment

为了解丹江口水库鱼类时空分布特征及资源现状，分别于2022年6—9月和2023年6—9月采用水声学探测和多网目复合刺网取样相结合的方式，对丹江口水库鱼类群落进行调查。调查期间共采集鱼类5目10科53种，其中2022年采集鱼类5目10科41种，䱗（Hemiculter leucisculus）、蒙古鲌（Culter mongolicus）、银鮈（Squalidus argentatus）和似鳊（Pseudobrama simoni）为优势种；2023年采集鱼类5目10科45种，蒙古鲌、䱗为优势种。水声学探测结果表明，鱼类平均密度、规格（目标强度）、生物量均具有明显的时空异质性：时间上，2023年丹江口水库鱼类平均密度（(8779±143) ind./hm）和生物量（(60.57±1.21) kg/hm）均显著高于2022年（(3827±96) ind./hm和 (37.76±0.95) kg/hm），2023年鱼类平均目标强度（(-56.25±0.16) dB）显著小于2022年（(-55.12±0.13) dB）；水平分布上，2022年和2023年湖北库区鱼类平均密度、目标强度、生物量均高于河南库区；垂直分布上，鱼类主要集中在30 m以上水层。刺网定量采样数据与水声学探测结果基本一致：时间上，2023年全库刺网平均单位努力捕捞量高于2022年，2023年全库刺网渔获物平均全长显著小于2022年；水平分布上，2022年和2023年湖北库区刺网渔获物平均全长、单位努力捕捞量均高于河南库区。本研究首次评估了丹江口水库鱼类资源时空分布特征，结果可为水源地保护、禁渔效果评估和水库优化调度提供基础数据支撑。;To quantify the spatiotemporal distributions and biomass of fish resources in the Danjiangkou Reservoir, the investigations of the fish assemblage were conducted by the combination of hydroacoustic detection and multi-mesh gillnet sampling between June and September 2022, and between June and September 2023. During 2022 and 2023, a total of 53 fish species were collected, belonging to 5 orders and 10 families. In 2022, a total of 41 fish species were collected, among which Hemiculter leucisculu, Culter mongolicu, Squalidus argentatus and Pseudobrama simoni were dominant. In 2023, a total of 45 fish species were collected, among which Culter mongolicu and Hemiculter leucisculu were dominant. The average densities, sizes (target strengths) and biomasses of fish assemblage from hydroacoustic data showed obvious spatial and temporal heterogeneities. In terms of temporal distributions, the average fish density ((8779±143) ind./ha) and biomass ((60.57±1.21) kg/ha) in 2023 were significantly higher than those in 2022 ((3827±96) ind./ha and (37.76±0.95) kg/ha) (P＜0.01), while the average target strength in 2023 ((-56.25±0.16) dB) was significantly lower than that in 2022 (((-55.12±0.13) dB). In terms of horizontal distributions, the average densities, target strengths, and biomasses of fish assemblage in the Hubei region were consistently higher than those in the Henan region both in 2022 and 2023. In terms of vertical distributions, fish were mainly concentrated in the water layer above 30 m. The quantitative sampling data of gillnets were consistent with the results of hydroacoustics. In terms of temporal distributions, the average value of catch per unit effort of the whole reservoir in 2023 was higher than that in 2022, while the average value of fish total length was on the contrary. In terms of horizontal distributions, the average values of fish total length and catch per unit effort of the Hubei region were all higher than those of the Henan region both in 2022 and 2023. This study evaluated the characteristics of spatial-temporal distributions of fish resources in the Danjiangkou Reservoir for the first time, and the results could provide basic data support for water source protection, fishing ban effect assessment, and reservoir optimization operation.