Hydroacoustics-Based Study Of Fish Distribution Characteristics Of Yudong Reservoir And Its Related Factors

A reservoir is a man-made body of water formed by damming a river,situated between a lake and a river,with functions such as regulating water volume,flood control,irrigation,and power generation,which are of great significance to human society and economic development.At the same time,the construction and operation of reservoirs provide an environment for the survival and reproduction of fish,but the ecological system of reservoirs is relatively fragile.Human activities,such as over-fishing,water pollution,and water level regulation,can have adverse effects on the ecological system of reservoirs,resulting in a decrease in the number of fish and an im-balance in the ecological balance.Therefore,it is important to accurately assess fish resources and understand the relationship between fish distribution and environmental factors.Fisheries acoustics is a technology that applies acoustic principles to study fisheries resources.It can detect the location,quantity,size,and behavior of fish,as well as the physical characteristics of the underwater environment.It is an efficient means of evaluating fisheries resources,with advantages such as efficiency,speed,and no damage to biological resources.The diurnal and seasonal rhythms of fish may result in differences in acoustic detection results at different times.This has been con-firmed in many types of water bodies,but there is currently no research or reports on the timing of acoustic detection in deep water reservoirs on the plateau.This study took the Yudong Reservoir in Zhaotong City,Yunnan Province as the research object,con-ducted diurnal and nocturnal acoustic surveys in four seasons,clarified the appropriate detection time,analyzed the distribution of fish and environmental factors,and finally conducted a reasonable assessment of the fish resources in the reservoir.The specific research results are summarized as follows:1.In order to develop a suitable survey strategy for the Yudong Reservoir,this study conducted diurnal and nocturnal acoustic surveys in four seasons and found that the behavioral rhythm of fish can affect the accuracy of acoustic evaluation.The results showed that the average density detected at night was significantly higher than during the day,but the density of fish at night in summer was significantly lower than that in spring,autumn,and winter.In addition,the target strength detected during the day in summer was significantly higher than in the other seven surveys,which may have been due to differences in fish behavior resulting in incorrect judgments.Considering the results,acoustic surveys of the Yudong Reservoir should be conducted at night（except in summer nights）to obtain more accurate assessment results.2.This study used a combination of acoustic detection and environmental factor investigation to conduct a comprehensive investigation of the physical and chemical fac-tors,plankton,and fish distribution patterns in the Yudong Reservoir.Through Pear-son correlation and decision tree analysis,it was found that fish distribution was mainly positively correlated with dissolved oxygen and negatively correlated with NO₃^--N,while the decision tree analysis also indicated that water temperature and Total Ni-trogen（TN）were related to fish distribution to some extent.In terms of plankton,both Pearson correlation analysis and the decision tree analysis indicated that the den-sity of rotifers was the most important factor affecting fish distribution,followed by green algae and diatoms.In addition,Pearson correlation analysis also indicated that Cyanobacteria could affect fish distribution,but this was not reflected in the decision tree analysis.These results provide important references for further scientific manage-ment and protection of the Yudong Reservoir resources.3.A total of 13 fish species were collected in the Yudong Reservoir,with a total weight of 80,083.76 g and 483 individuals,belonging to 2 orders and 3 families,with Hypophthalmichthys molitrix and Acheilognathus macropterus as the dominant species,and Hypophthalmichthys nobilis,Cyprinus rubrofuscus,Rhodeus sinensis,Carassius auratus,Toxabramis swinhonis,and Ctenopharyngodon idella as common species,while Mylopharyngodon piceus,Tachysurus sinensis,Chanodichthys erythropterus,Pseudorasbora parva and Silurus asotus were rare species.The biomass of the Yudong Reservoir was calculated using the target strength-total length formula,the length-weight formula,and the biomass formula,and the fish density was approximately 1.7to 2.5（ind./m²）,the average biomass was between 4 to 5.06（g/m²）,and the total biomass was between 65,270.9 to 82436.4 kg.