Stock distribution of a new record species Nemipterus mesoprion in offshore northern South China Sea

Nemipterus mesoprion has been identified as a new recorded species Nemipterus in Chinese waters in recent years, but there is little understanding of its resource status. Thus, based on the fishery resources data from the bottom-trawl survey in the offshore northern South China Sea during four seasons of 2014−2015, we analyzed the relationship between the body length and body mass for N. mesoprion population, and explored its stock distribution and spatial pattern by using spatial statistics method. The body length-mass relationship for N. mesoprion samples exhibited a significant power function with R² greater than 0.96, which had no difference between sexes. Besides, the population tended to follow an isometric growth pattern as the estimated parameter b was about three. In terms of temporal scale, the stock distribution showed a seasonal variation with the greatest biomass in summer and the smallest in spring for both the stock density and abundance. Generally speaking, its stocks were small, and the average stock density and abundance in four seasons were 0.41−2.29 kg·km⁻² and 44.38−147.69 ind·km⁻², respectively. In the aspect of spatial distribution, N. mesoprion was mostly distributed in Beibu Gulf, especially for the high-stock zone in northern area of 20°N. The result for standard deviational ellipse indicates that the main distribution direction of N. mesoprion in four seasons was counterclockwise (from quasi-north-south to northwest-southeast then to northeast-southwest), and the population distribution pattern followed a trend of aggregation to dispersion. The seasonal change in gravity center for both stock density and abundance was towards northward and then southeast.