Tempo-Spatial Distribution of an Endangered Fish Species, Threadfin Porgy Evynnis cardinalis (Lacepède, 1802), in the Northern South China Sea

Accurate information on the temporal and spatial distribution of fish stocks is necessary for informed management and conservation of fisheries resources. We report on the temporal and spatial variation in biomass and density of a hitherto little-studied species of commercial importance, the threadfin porgy Evynnis cardinalis, it was listed as endangered (EN) in a recent International Union for Conservation of Nature (IUCN) red list, on the northern South China Sea continental shelf, using data collected during fisheries surveys from 2014 to 2015. Seasonal variation in the frequency of occurrence of E. cardinalis in trawl samples on this shelf was highest during summer (68.57%) and lowest during winter (31.43%). Average biomass was highest in autumn (33.05 kg·km−2) and density was highest in spring (936 ind·km−2). The highest annual average biomass (41.6 kg·km−2) and density (1021 ind·km−2) occurred off Shantou, and the lowest occurred off Zhanjiang (7.2 kg·km−2 and 165 ind·km−2, respectively); seasonal patterns in density are more similar in waters off Yangjiang and Shantou than elsewhere. The highest annual average biomass occurred at 40 m depth (56.9 kg·km−2), and the highest annual average density (1084 ind·km−2) occurred at 30 m depth. Density of E. cardinalis varied with depth, with lower densities occurring in shallow and deeper waters, and higher densities at intermediate depths.