Migration And Distribution Of Anchovy In Yellow Sea And Its Relation With Environmental Factors

Japanese anchovy (Engraulis japonicus) is a connecting link species in marine ecosystem ,and hence a key fish in the China-GLOBEC program.For the popurse of studying the main feature of the key physical process and its influence on ecosystem, a series of integrated mult-disciplinary survey of the anchovy were carried out during winter from 2001-2003 and summer in 2000 and 2001.Based on the data from the surveys refered above,the migration and distribution pattern of the anchovy and its relation with environmental factors are analysed.During winter migration,in November ,the Yellow Sea Cold Water Mass(YSCWM) dominate the distribution of Japanase anchovy,main aggregation of the anchovy is located in the edge of Yellow Sea Cold Water Mass.In January,the anchovy assembled along the warm tongue formed by the invasion of Yellow Sea Warm Current(YSWC), total biomass of anchovy in January is obvious larger than that in November owing to the migration of anchovy in Bohai Sea.Temperature and salinity ,which have a remarkable influence on the migration and distribution of anchovy,make function of drive force.The anchovy will change their distribution pattern with the variation of the environmental factors to keep themselves in a comfortable habitat.When the hydrological factors have uniform vertical struture,the anchovy concentrated in the area of optimal temperature (11 oC -12 oC),when the water is still stratified, the anchovy tend to distribute in water volume with optimal temperature . In this paper, we give a preliminary description of the physical factors's influence on the behavior and distribution of anchovy using a indicator named environmental fitness. The indicator takes temperature and salinity as parameter and represent the habitat is whether suitable for anchovy or not. The fitness of the surveyed sea area is calculated and has a good match with the distribution of anchovy. The anchovy will concentrated in sea area with high fitness and be seldom found in area with low fitness. Especially ,when the water is still stratified ,the distribution of fitness can clearly indicate the influence of the environment on the anchovy. In the area occupied by Yellow Sea Cold Water Mass, the fitness is rather low all the time , it suggest that the area taken up by Yellow Sea Cold Water become a barrier to the migration of anchovy. Instead of coming cross the Yellow Sea Cold Water, the anchovy probably migrate along the edge of Yellow Sea Cold Water. The distribution of anchovy spawning stock in southern water to Shandong Peninsula is mainly controlled by Qingdao Cold Water Mass. The anchovy concentrated along the edge of Qingdao Cold Water Mass, and were seldom found in center area. In spawning season(June),the anchovy distribute in the area with a depth no more than 30m, in bottom of which lies strong ocean front. The target temperature for spawning anchovy stock is much higher than that for anchovy in winter migration. The favorite temperature for anchovy spawning stock is about 18 oC -21 oC at surface layer and 17 oC -20 oC at bottom layer. In May, the anchovy assembled in the edge of Qingdao Cold Water Mass, with temperature of 11 oC -16 oC. The distribution of anchovy in May match the distribution of fitness quite well, while in June, the distribution of anchovy is quite different from the fitness. It has close relation to gonad development and the anchovy egg's survival temperatue.