Spatial distribution of Larimichthys polyactis juveniles in the southern 

Yellow Sea and northern East China Sea in summer

Abstract: Small yellow croaker Larimichthys polyactis is an economically important species in Chinese offshore ecosystem. Juvenile is in an important period of transition from larvae to adult. This stage is not only different from the characteristics of high natural mortality and fluctuating abundance in the early life history period, but also different from the higher feeding capacity and environmental adaptation of adults. Juveniles have different preferences for the choice of living environment.The abundance and spatial distribution of the juvenile are crucial to the population dynamics and they are sensitive to environmental factors. Therefore, studying the geographic distribution pattern of juvenile populations and their dominant factors will help to clarify their selection patterns for the living environment. Larimichthys polyactis has obvious cluster habit and migration characteristics. It does seasonal migration throughout the year between spawning grounds, feeding grounds and wintering grounds. During feeding periods, it is mainly distributed in warm water control areas or marginal areas of warm water areas. The western part of Dasha fishery is the largest feeding ground for Larimichthys polyactis in the east Yellow Sea. At present, the research on Larimichthys polyactis populations at home and abroad mainly focuses on juveniles and juvenile populations, mixed feeding populations, and adult overwintering populations. There are few related studies on juvenile feeding populations alone. Generalized additive model (GAM) is a nonparametric generalized multiple linear regression method proposed by HASTIE. It can flexibly describe the response of species to environmental factors and predict the relationship between multiple independent variables and dependent variables, and can well analyze the relationship between fishery resources and multiple environmental factors in fisheries.In order to understand the spatial distribution characteristics of Larimichthys polyactis juveniles ，a survey was conducted in the southern Yellow Sea and northern East China Sea (30°30′N35°00′N, 120°00′E127°00′E) in August 2019 to explore the relationship between the quantity distribution of Larimichthys polyactis juveniles and related environmental factors. Three generalized additive models (GAM) were compared. The fitting effect and predictive ability of Delta GammaGAM were better than that of TweedieGAM and Delta LognormalGAM. For Delta GammaGAM, the root mean square error was 12 014.43, the Pearson correlation coefficient was 0.461, and Spearman’s rank correlation coefficient was 0.699. The distribution of Larimichthys polyactis showed a high degree of autocorrelation in space, and was concentrated in the area of 32°N34°N and 122°E124°E, and diminishingly diffused from the center. According to the models, the distribution of Larimichthys polyactis juveniles was only significantly related to water depth with a negative linear relationship, which explained the nearshore distribution preference of Larimichthys polyactis juveniles.

Keywords: Larimichthys polyactis juveniles; generalized additive model; environmental factors; southern Yellow Sea