The Growth And Distribution Of The Age 0 Group Pacific Cod(gadus Macrocephalus Tilesius) In The Yellow Sea And Its Relationship With Environmental Factors

Pacific cod Gadus macrocephalus is distributed around the rim of the North Pacific Ocean,and it's considered as an ecologically important species.Fish growth is the core of fish physiology and ecology,and the habitat conditions?spawning time,water depth and water temperature?of Pacific cod spawning and nursing ground vary among different geographic groups.Studies on the biological characteristics and distribution patterns of age 0 group Pacific cod would helpful in the understanding of cod population dynamics.Based on the data collected during the fishery resources surveys carried out in June,August,October and December 2016,the growth of the age 0 group Pacific cod in the Yellow Sea was studied.The Generalized Additive Model?GAM?and Random Forest were used to analyze the distribution characteristics and their relationship with environmental factors of the age 0 group Pacific cod.This paper aims to provide reference for the population dynamics,resource conservation and sustainable utilization of Pacific cod?Gadus macrocephalus Tilesius?in the Yellow Sea.The main results of this study are listed as follows:1.The mean body length of the age 0 Pacific cod in June was 6.66 cm,the average body weight was 4.3 g,and the dominant body length was 5.0-7.0 cm,representing around 50%of the total;The mean body length of the age 0 Pacific cod in August was 12.41cm,the average body weight was 23.2 g,and the dominant body length was 11.0-13.0cm,representing around 55.6%of the total;The mean body length of the age 0 Pacific cod in October was 15.51cm,the average body weight was 58.5g,and the dominant body length was 15.0-17.0cm,representing around33.3%of the total;The mean body length of the age 0 Pacific cod in December was 18.29 cm,the average body weight was 83.5g,and the dominant body length was 17.0-19.0cm,representing around 53%of the total.According to the relationship between body length and body weight of the age 0 Pacific cod,the Allometric factor b was 3.3161.There were significant differences(t=12.31>t_0.05=1.96)between the Allometric factor b and 3 by T test?Pauly?,and the result indicated that the age 0 Pacific cod was allometric.Growth rate of the body weight was not equal to the body length,and the weight gain was faster.2.The age 0 group Pacific cod in the Yellow Sea were distributed in the waters with bottom salinity range of 31.7 to 33.3psu,with bottom water temperature range from 6.6 to 12.1?and with depth range of 35.8 to 87.2m.The favorite sediment in the nursery habitats was fine silty sand and soft clay mud.In terms of the distribution of the age 0 Pacific cod,it was mainly concentrated in the East and southeast of the Shidao,and a few in the east of Yanwei fishing ground,to a great extent,which coincided with the spawning ground.In addition,the age 0group Pacific cod were distributed in the Yellow Sea Cold Water Mass with low water temperature.The seasonal variation in the distribution pattern of the age 0 group Pacific cod was trickily synchronized with the seasonal variation of the Yellow Sea Cold Water Mass.3.GAM results showed that the environmental factors which had significant effects?P<0.05?on the ecological density of the cod juvenile were in the order of bottom water temperature,sediment and bottom salinity,while the depth,prey density and competing species density had no significant influence on the juvenile density.According to the relative importance of the environmental factors calculated by the random forest model,the results showed that the environmental factors of the Pacific cod nursing ground were determined by the bottom temperature,prey density,competing species density,depth,sediment and bottom salinity in turn.4.In the horizontal direction,there was no significant difference in the habitat distribution of juvenile and adult Pacific cod.However,in a vertical direction,the water layer in which the juvenile cod live was different from that in which the adult Pacific cod live.Compared to adults,the juvenile cod habitat was shallow.