_applied_  
_sciences_  
_Technical Note_  
**Small-Scale Spatiotemporal Pattern in the Spawning of Pacific Herring (_Clupea pallasii_) in the Jinhae Bay, Korea, Estimated Using Hydroacoustic Survey**  
**[PERSON] 1,*, [PERSON] 2, [PERSON] 3, [PERSON] 4, [PERSON] 4, [PERSON] 5, [PERSON] 1 and [PERSON] 1**  
1 Fisheries Resources Research Center, National Institute of Fisheries Science (NIFS), Tongyeong 53085, Korea; [EMAIL_ADDRESS] (K.H. ); [EMAIL_ADDRESS] (D.N.K.) 2 Jeju Fisheries Research Institute, National Institute of Fisheries Science (NIFS), Jeju 63038, Korea; cho22916 korea.kr  
3 South Sea Fisheries Research Institute, National Institute of Fisheries Science (NIFS), Yeosu 59780, Korea; [EMAIL_ADDRESS]  
4 Division of Marine Technology, Chonnam National University, Yeosu 59626, Korea; [EMAIL_ADDRESS] (K.L. ); [EMAIL_ADDRESS] (W.O.) 5 Distant Water Fisheries Resources Division, National Institute of Fisheries Science (NIFS), Busan 46083, Korea; [EMAIL_ADDRESS]  
*Correspondence: [EMAIL_ADDRESS]; Tel. : +82-55-650-2250  
**Abstract:** Acoustic surveys were used to locate coastal Pacific herring (_Clupea pallasii_) spawning grounds, and the spatial and temporal patterns of their spawning in Jinhae Bay, Korea were examined. We deployed mooring with a newly designed autonomous echosounder for ~70 days during the Pacific herring spawning season in Jinhae Bay, from January to April 2018. At the same time, ship-based acoustic surveys were conducted to identify the spatial distribution twice, at 38 and 120 kHz, onboard the fishing vessel in January and April 2018 in the bay. Fish school signals, including those from adult Pacific herring, are often detected through ship-based acoustic surveys in January, from outside the bay. In the spring, weak scattering signals from fish larvae and zooplankton were continuously detected inside the bay. Backscatter at the mooring in the center of Jinhae Bay was low from mid-January to early March, gradually increasing to higher levels until the end of March. The backscatter observed from the mooring correlated well with ship-based acoustic surveys in the center of the bay. This study proposes that the mooring type acoustic echosounder is a valuable tool for temporal abundance information and other aspects of fish behavior. **Keywords:** hydroacoustic survey; Jinhae Bay; _Clupea pallasii_; spawning grounds; spatiotemporal distribution  
**1. Introduction**  
A species of the herring family (belonging to the order Clupeiformes), Pacific herring (_Clupea pallasii_) is a cold-water fish that spawns and grows in the coastal waters of Korea, mostly during the winter season, and moves to the high-latitude Bering Sea as the water temperature rises due to seasonal changes [1]. While Korea recorded high catches of the Pacific herring until the 1970s, the amount of fishery resources plummeted due to overfishing and environmental pollution. However, since the early 2000s, catches of the Pacific herring have increased every year due to the improved management of fisheries resources [2,3]. These herring catches are related to climate change. The Pacific herring is in the migration path of the Tsushima Warm Current, which flowed in the East Sea to Uleung Basin in 1987 and 1988, where the water temperature increased from 3 \({}^{\circ}\)C to 4 \({}^{\circ}\)C from 0 to 75 m. However, the water temperature dropped from 5 \({}^{\circ}\)C to 1-2 \({}^{\circ}\)C at a depth of 200 m in 1992-1993 in the same area [4]. This may have led to an increase in the amount of the Pacific herring, a cold-water fish species moving from deep water. The domestic catch of the Pacific herring was recorded as 32,519 tons in 2017, of which 29,438 tons (more than 90%) was caught in the waters near South Gyeongsang Province. This is highly correlated with the species migration to spawning grounds, which are in Jinhae Bay and Nakdong River Estuary in South Gyeongsang Province where Pacific herring larvae are frequently observed from winter to spring [5; 6].