Therefore, for the management of the Pacific herring, which migrates to coastal waters, it is very important to protect their spawning grounds. Identifying the number of adult fish in the spawning grounds and the ecological characteristics of spawned eggs and hatched larvae and estimating the initial recruitment accurately will directly contribute to more effective management of fisheries resources, the maintenance of local fisheries, and increased fishery yields. Jinhae Bay in South Gyeongsang Province is a known spawning ground for the Pacific herring and Pacific cod (_Gadus macrocephalus_) in Korea. During the month of January, which is the main spawning period, it is prohibited to catch the Pacific cod, a high-value fish species, while no regulations are in place for the Pacific herring. The Pacific herring, being one of the most important links in the marine food chain, is highly correlated with the domestic catches of the Pacific cod, a large cold-water fish species [7]. There have been various studies on the early life stages of the Pacific herring using collection and observation techniques, including the distribution of spawning grounds in Jinhae Bay [8], larval diet [9], and estimation of spawning periods, through scuba observation [10]. However, there has been insufficient research on continuous spatiotemporal distributions using acoustic methods for the spawning habits of adult fish and larval behavior in Jinhae Bay. The acoustic method yields objective and continuous data for all water layers. Therefore, with the acoustic characteristics of the dominant fish species, it is possible to estimate the spatiotemporal distribution and the existing amounts of major fish species in the survey area. Other countries perform hydroacoustic surveys of various migratory fishes such as the Alaskan cod, Bering Sea pollock, Peruvian anchoveta, and sardine on a regular basis. Korea has published limited research results on the distribution and current amounts of major fish species using acoustic equipment in Asan Bay in South Chungcheong Province (anchovies), Tongyeong in South Gyeongsang Province, Yeosu in South Jeolla Province, and the waters near Jeju and around artificial reefs installed in coastal areas [11; 12; 13]. In addition to spatial research using acoustic methods, the movement patterns of fishes and fluctuations in zooplankton have been studied through limited-time or long-term monitoring using moored acoustic equipment such as multi-beam image sonar, acoustic zooplankton fish profiler, and acoustic Doppler current profiler, owing to the advancement of technology [14; 15; 16]. In addition, a moored scientific echosounder operated by an internal battery was installed and operated at the bottom of the sea to receive acoustic data on marine organisms on the water layers, so that continuous data, including day/night and seasonal fluctuations in fish and zooplankton and spawning or wintering grounds for fish [17; 18], can be obtained in limited areas of water. In ship-based acoustic surveys of fish spawning grounds in particular, the risk of missing the exact spawning time due to changes in the spawning period caused by fluctuations in the marine environment or changes in the survey schedule resulting from sea conditions can be minimized by installing a moored echosounder in the sea [18]. As a result of egg and larval surveys using nets in 2015 and 2016, Jinhae Bay was confirmed as an important spawning ground for the Pacific herring, which plays a pivotal role in the marine food chain [8]. After hatching, young Pacific herring appeared in the eastern waters of Chilcheon Island in the north of Geoje Island, South Gyeongsang Province, the nearby waters of Jam Island, and the southwestern waters of Jinhae Bay, depending on the tidal current of the bay [8].