Spatio-temporal and spatial distribution and biological characteristics 

of Larimichthys polyactis in Jiangsu sea area

Abstract: In order to further understand the temporal and spatial distribution characteristics and related patterns of Larimichthys polyactis in Jiangsu sea area timely and to manage the biological resource properly, data collected from four seasonal fishery resource surveys in Jiangsu sea area (31°45′N35°00′N,119°30′E125°00′E) from 2017 to 2018 were analyzed. The results showed that: 1) In spring, the average body length and average body weight of Larimichthys polyactis were at low values (78.96mm, 13.68g), while in autumn and winter, average body length (103.04mm in autumn, 96.20 mm in winter) and average body weight (19.62g in autumn, 16.35 g in winter) reached high values throughout the year after baited in summer. Sex maturity was the highest in spring, with 36.1% of samples still in the spawning stage, winter was the next. Sex maturity was the lowest in summer, all samples were at stage II. Feeding intensity was higher in spring and autumn than in summer and winter, it was mainly because parent fishes needed to replenish the energy loss after spawning in spring. The average feeding level of fishes reached the highest in autumn as the later stage of Larimichthys polyactis’s feeding stage. In summer, Larimichthys polyactis entered the feeding stage, the behavior of feeding just started, and the proportion of individuals with high feeding level was small. In winter, the temperature of Jiangsu sea area fell drastically, fishes were affected by the change of environment to reduce even stop feeding, then finding appropriate overwintering grounds became an urgent need. In terms of sex ratios, the ratio of male number to female number did not vary seriously over the four seasons and years, and there were more males than females, which was related to the recession of Larimichthys polyactis resources. 2)The spring spawning grounds of Larimichthys polyactis in Jiangsu sea area were mainly located in the adjacent waters north of the mouth of the Yangtze River (32°00′N33°15′N, 121°30′E122°15′E), the excellent location, rich food organism and good ecological environment were important reasons to attract parent fishes to spawn here; the summer feeding grounds were mainly located in the southern part of Dasha fishing ground (32°00′N33°00′N, 123°00′E124°30′E) and the northern outer waters of Lyusi fishing ground (33°30′N34°00′N, 121°30′E122°00′E). At this time, the feeding groups became disperse, the distribution range became wide and the stock density became significantly smaller than that in spring. In addition, the intensity of fish feeding became larger and the growth rate of fishes were significantly accelerated. The autumn feeding ground was located in the sea southeast of Lianqingshi sishing ground (34°00′N35°00′N, 122°30′E124°00′E), the size of fishes continued to increase, the feeding groups migrated to deep water area, the distribution range became more disperse than before, and the central area of resource density moved eastward to the deep water area in the northeastern Yellow Sea. Combined with environmental factors, it was found that the distribution of Larimichthys polyactis feeding grounds in Jiangsu sea area was more influenced by temperature factors and less influenced by salinity; the overwintering ground was located in the sea northeast of Dasha fishing ground (33°00′N35°00′N, 123°30′E124°30′E), with the fall of water temperature in Jiangsu sea area, Larimichthys polyactis migrated to the overwintering grounds off the southcentral Yellow Sea and off the northern East China Sea. Considering biological characteristics and resource density distribution together ,we inferred that: the center of Larimichthys polyactis overwintering grounds was not located in Jiangsu sea area(31°45′N35°00′N,119°30′E125°00′E). In addition, we found that the overwintering grounds shifted about one latitude to the northwest than before; 3)In spring, parent fishes with high sex maturity gathered to spawn and reared their young in waters near the Lyusi fishing ground, which located in the north of the Yangtze River mouth and along the offshore areas of Jiangsu Province, forming a high density area of Larimichthys polyactis; in summer and autumn, fish larvae with juveniles and adult fishes tended to disperse to bait, which were widely disperse in the research area with a clear tendency to move eastwards; the distribution of bait field was greatly affected by water temperature and less affected by salinity. In winter, Larimichthys polyactis migrated from the feeding grounds to the deep water of the outer wintering grounds(water depth range 36.435 m80.675 m); 4)Combined with the analysis of biological characteristics and resource density of Larimichthys polyactis samples, it was found that Larimichthys polyactis in Jiangsu sea area had the attributes of spawning, baiting and overwintering in deep water with seasonal changes, and the outline of reproduction and growth development system was relatively complete, so it could be inferred that there was a relatively stable dependence relationship between Larimichthys polyactis population and Jiangsu waters, which provided a theoretical basis for the conservation and rational exploitation of Larimichthys polyactis resources in Jiangsu sea area.

Keywords: Larimichthys polyactis； density index of resources； Jiangsu sea area； temporal and spatial distribution； biological characteristics