Abstract:This study determined the particle release area based on the abundance data of largehead hairtail eggs obtained from the ichthyoplankton surveys in the coastal waters of the southern Yellow Sea (119°E-124°E, 33°N-37°N) conducted from 2018 to 2022. Subsequently, the Finite-volume Coastal Ocean Model (FVCOM) coupled with the Lagrangian particle tracking algorithm was employed to simulate the transport process of largehead hairtail larvae. The primary objectives were to investigate the spawning periods, spawning grounds, and nursery habitats of largehead hairtail in the southern Yellow Sea, and to assess the influence of oceanic conditions on the egg distribution and larval dispersion. The results indicated that largehead hairtail spawned in spring and summer in the southern Yellow Sea with the eggs appeared in May, July and August, and August was the peak spawning month. Largehead hairtail eggs were mainly distributed in 19-30 m waters in May, and 11-70 m waters in August. The sea surface temperature and sea bottom temperature for the presence of largehead hairtail eggs was 13.9-29.7 and 8.4-28.3 ℃ respectively. The Random Forest model analysis revealed that water temperature and depth were the main environmental factors affecting the abundance of largehead hairtail eggs. Particle tracking simulation experiments showed that the particles released in May mainly spread towards the northwest coastal area of the particle release area after 1-15 days (when the swim bladder has not formed and the larvae have no vertical migration behavior), and after 16-40 days(when the swim bladder has formed and the larvae have vertical migration behavior), the particles left the coastal area and spread eastward to the waters near a 50 m water depth. In July and August, before the occurrence of vertical migration behavior, larvae stayed in the near-bottom layer and most of them were transported from the release area to the nearshore waters； After that, larvae moved slightly from the near-shore aggregation area to the off-shore direction. Some of the individuals released in the offshore deep-water areas spread to the north and northeast in a short-distance, and the dispersal pattern did not change significantly in their whole larval stages. Aggregation areas of largehead hairtail larvae derived from field surveys in August were consistent with the results of particle transport simulation experiments. We thought that the season and spatial location of spawning, the diel vertical migration characteristics of larval fish, and the regional upwelling and frontal structure were the dominant factors that shape the transport pattern of largehead hairtail larvae. The results of the study provide a scientific basis for understanding the habitat selection mechanism of egg and larvae stages and early replenishment dynamics of this fish in the southern Yellow Sea, and help for the management and protection of largehead hairtail resources.
