Seasonal variation in habitat distribution of Liparis tanakae in the northern East China Sea and southern Yellow Sea

northern East China Sea and southern Yellow Sea%Liparis tanakae%habitat suitability index%environmental factors%seasonal variation

In order to understand the ecological characteristics of Liparis tanakae,fisheries resource surveys were conducted in the northern East China Sea and southern Yellow Sea for four seasons during 2018-2019.The data of surface water temperature(SST),surface salinity(SSS),bottom water temperature(SBT),bottom salinity(SBS),water depth and fishery resource density were collected,and a study on seasonal changes in habitat suitability of Liparis tanakae was conducted.First,the total variance contribution rates of environmental factors calculated from the boosted regression tree(BRT)model were weighted respectively to surface water temperature,surface salinity,bottom water temperature,bottom salinity and water depth of Liparis tanakae habitat in each season,then seasonal suitability index curves of Liparis tanakae for different environmental variables were plotted;next,cross-validation was used to evaluate the predictive performance of HSI model computed using arithmetic mean method(AMM)and HSI model computed using geometric mean method(GMM)to determine the optimal model;finally,the habitat index of Liparis tanakae was mapped and seasonal variation of its optimal habitat was determined.The results showed that in spring,summer and autumn,sea bottom temperature was the most important environmental factor affecting the suitable habitat of Liparis tanakae.The contribution rate was 84.05%,54.60%and 60.74%respectively.In winter,the most important environmental factor was surface water temperature(34.71%),the second was surface salinity(23.18%),and the third was bottom water temperature(22.63%).According to the results of the suitability curve of environmental factors,the bottom water temperature of the most suitable habitat for Liparis tanakae was 9.60-11.37 ℃ in spring,7.64-10.46 ℃ in summer and 7.64-10.46 ℃ in autumn,the temperature of the bottom layer was 8.92-9.92 ℃,and that of the surface layer was 9.82-12.34 ℃ in winter.Cross validation resultus showed that spring and summer selected AMM algorithm,autumn and winter selected GMM algorithm and weighted HSI model to study their habitat suitability.The area of the optimal habitat(HSI≥0.7)of Liparis tanakae showed a certain change with seasons.The area was smaller in spring,summer and autumn,accounting for 13.43%-23.53%of the total study sea area.Compared with other seasons,the optimal habitat area in winter expanded significantly,accounting for 45.31%of the research sea area.In summer and autumn,the variation of the optimal habitat of Liparis tanakae with seasons is basically the same as its migration route,but it is different in winter.The bottom temperature in summer and autumn is an important influencing factor.During this period,the nearshore water temperature is relatively high,forming a dense isotherm in the southwest of the Yellow Sea,which hinders the distribution of Liparis tanakae in the nearshore.In winter,with the decrease of water temperature,Liparis tanakae migrates from the central deep water area in the southern Yellow Sea to the northern part of the East China Sea and the central part of the Yellow Sea,and the range of optimal habitats expands significantly compared with other seasons.