Spatio-Temporal Distribution Patterns And Habitat Suitability Of Fish Spawning Grounds In The Yantai-weihai Offshore Waters

Historically,there was one important spawning ground of Scomber japonicus in the Yantai-Weihai offshore waters.Due to be determined as the main breeding migration channel of fish for most of the breeding stocks migrating from the Yellow Sea to the Bohai Sea in the spring,and also as the feeding ground when the adults and juveniles migrate out of the Bohai sea in summer and autumn,the Yantai-Weihai offshore waters was considered as an unstable spawning ground,so it has not been well studied in recent years.In order to find out the status of fish spawning grounds in Yantai-Weihai offshore waters,monthly spawning ground survey was carried out in this area from April to September in2020.Based on the survey data including fish eggs,larvae and juveniles,surface and bottom temperature,surface and bottom salinity,water depth,chlorophyll,zooplankton,phytoplankton and nutrient,the spatio-temporal distribution of early life stage of fish resources,the monthly turnover of community structure,and the suitable spawning habitats of main spawning species were comprehensively analyzed by spatial interpolation,cluster analysis,non-metric multi-dimensional scale ranking,similarity analysis,and redundancy analysis（RDA）.The spatio-temporal changes of spawning ground of Engraulis japonicus and Scomber japonicus,and the biological characteristics of age 0 Scomber japonicus in Yantai-Weihai offshore waters were investigated.Generalized additive model based on Tweedie distribution（Tweedie-GAM）was established to evaluate the effects of environmental factors on eggs abundance of Engraulis japonicus and Scomber japonicus.The major habitat factors was plotted to interpret the optimal spawning habitat using the Kriging interpolation method.The spawning habitat suitability index model（HSI）of Engraulis japonicus and Scomber japonicus was constructed,based on the sea surface temperature and salinity,and the scientific evaluation was carried out on the suitability in spawning grounds of Engraulis japonicus and Scomber japonicus during the peak spawning period.The main conclusions are as follows:（1）Status of fish spawning grounds in Yantai-Weihai offshore waters and suitable spawning habitats for major species.52 species of fish eggs and larvae were totally collected in the Yantai-Weihai offshore waters from April to September in 2020,including33 7038 eggs of 33 taxas and 2122 larvae of 28 taxas.The main spawning season is from May to June,with 24 taxas spawned then,which accounting for 98.32%species of the whole year.The main spawning ground located at the area north of the coastline from Taozi Bay to Jiming Island.Engraulis japonicus,Scomber japonicus,Scomberomorus niphonius,Cleisthenes herzensteini,Seriola lalandi,Callionymus beniteguri,Sillago japonica,Acanthopagrus schlegelii,Cynoglossus joyneri and Saurida elongata were the main spawning species.The community structure of fish eggs and larvae presented obvious annual variance on monthly basis in the Yantai-Weihai offshore waters.Apart from August and September,which is the end of the spawning season,the monthly species turnover rates were all over 50%,with average dissimilarities between communities of fish eggs and larvae in adjacent months no less than 73%.The results of RDA showed that variation in SST,SBT,SSS and depth in the Yantai-Weihai offshore areas affacted fish spawning activities significantly.The suitable spawning habitat of Engraulis japonicus,Scomber japonicus,Scomberomorus niphonius,Seriola lalandi,Cleisthenes herzensteini and Callionymus beniteguri was the areas with low SST and SBT,and high SSS.The suitable spawning habitat of Pseudopleuronectes herzensteini was the shallow waters with low SST and SBT,and high SSS.The suitable spawning habitat of Acanthopagrus schlegelii was the shallow waters with low SST.The suitable spawning habitat of Cynoglossus joyneri was the areas with high SST and SBT,and low SSS.The suitable spawning habitat of Saurida elongata was the medium shallow waters with high SBT and low SSS.The suitable spawning habitat of Sillago japonica was the bottom waters with high SBT.（2）Spatio-temporal variation of the spawning grounds of Engraulis japonicus and Scomber japonicus and the biological characteristics of age 0 juveniles of Scomber japonicus.In the Yantai-Weihai offshore waters,Scomber japonicus began to spawn in the late April.The spawning period of Scomber japonicus basically ended in mid-to-late July,and the peak spawning period was from late May to late June.From April to July,the center of gravity of Scomber japonicus spawning ground generally moved from the western and southern coastle waters to the eastern and northern distant waters.The main spawning ground of Scomber japonicus covered the area between 121°30’?122°15′E and37°30′?38°00’N.Engraulis japonicus began to spawn in the late April,the spawning period basically ended in late August,the main spawning period is from May to July,and the peak spawning period is from late May to late June.From April to September,the center of gravity of Engraulis japonicus spawning ground moved from the central and southern coastal waters to the northern and eastern distant waters.The main spawning ground of Engraulis japonicus was distributed in the area at 120°45’～122°30’E,north of the coastline from Penglai to Jiming Island,and the center of Engraulis japonicus spawning ground was located in the area north of the coastline from Laishan to the junction of Yantai and Weihai.In mid-July 2020,9192 age 0 juveniles of Scomber japonicus were collected from the Yantai-Weihai offshore waters,with fork lengths ranging from 66 to 128 mm and body weights ranging from 1.5 to 24 g.Age 0 juveniles were mainly distributed in the sea area north of Taozi Bay and the sea area north and east of the coastline from Chengshanjiao to Sanggou Bay.The relationship between fork length and body mass was W=2×10^-7 FL^3.776（R=0.9431）,which indicated positive allometric growth pattern.In late August,190 age 0 Scomber japonicus juveniles were collected with fork length ranging from 90 to 207 mm and body weight ranging from 8to 65 g.Age 0 juveniles were mainly distributed in the area north of the coastline from Muping to Jiming Island.（3）The correlation between the abundance of Engraulis japonicus and Scomber japonicus eggs and the main environmental factors in the Yantai-Weihai offshore waters.The Tweedie-GAM models showed that sea surface temperature（SST）,Engraulis japonicus egg abundance,ocean current velocity and sea surface salinity（SSS）were significant factors affecting the spawning selection of Engraulis japonicus in the Yantai-Weihai offshore waters,with explained deviance rates of 54.6%,17.8%,4.0%and 1.7%,respectively.Suitable spawning habitat of Scomber japonicus in the Yantai-Weihai offshore waters was areas with SST between 16.3?21.8oC,SSS between 32.1?32.9,and with low ocean current velocity and high Engraulis japonicus egg abundance.SST,SSS,sea surface chlorophyll a concentration（SCHLA）and ocean current velocity were significant factors affecting the spawning selection of Engraulis japonicus,with explained deviance rates of 43.1%,7.9%,7.7%and 2.1%,respectively.The suitable spawning environment for Engraulis japonicus was the sea surface temperature with SST between 15.7?22.3℃,SSS between 31.6?32.9,low SCHLA and low ocean current velocity.（4）Spawning habitat suitability evaluation of Engraulis japonicus and Scomber japonicus in the Yantai-Weihai offshore waters during the peak spawning period.From the end of May to the beginning of June,the high HSI areas of the Engraulis japonicus spawning grounds were mainly distributed in the coastal area from Penglai to Taozi Bay,the distant waters north of the coastline from Laishan to Muping and from the junction of Yantai and Weihai to Jiming Island.The high HSI areas of Scomber japonicus spawning grounds were mainly distributed in the coastle waters from Laishan to Jiming Island.At the end of June,the high HSI areas of Engraulis japonicus spawning ground decreased slightly and were no longer located in the coastal waters.The high HSI areas of the Scomber japonicus spawning ground were reduced to the northern boundary of the surveyed sea area north of the junction of Yantai and Weihai.The northern sea area from Laishan to Muping was the high value center for HSI of the spawning grounds of Engraulis japonicus and Scomber japonicus in May.In conclusion,the Yantai-Weihai offshore waters and adjacent sea areas is still one of the important fish spawning grounds in the Yellow Sea.With abundant spawning species and considerable fish egg abundance,it is the important recruitment of fishery resources.The fishery management in the Yantai-Weihai offshore waters should pay attention to its dual attributes as a key migratory channel and an important spawning area,and fully consider the concentrated distribution of early fish resources in the areas northern of Yantai and Weihai from May to July.According to the spatio-temporal distribution of spawning grounds of different fish species,strategies with species-specific early life history integration should be formulated to achieve better conservation and restoration of fishery resources.This study provides highly time-sensitive informations on early life stages of fishes in the Yantai-Weihai offshore waters so and its environmental factors.Research results involved would contribute to the research of fish community structure in early life stages,the recruitment mechanism,and the migration route of marine fishes in the Yellow Sea and Bohai Sea.All these could provide an ecological basis for the delineation of marine aquatic germplasm resources protection zones,the planning of species and areas for enhancement and release,and the formulation of conservation strategies for marine fishes in early life stages and their spawning grounds in the Yellow Sea and Bohai Sea.