The spatial niche and differentiation of major fish species in the waters east of the Zhoushan Islands in spring and autumn

: Based on data from the fishery resources survey in the waters east of the Zhoushan Islands in April (spring) and October (autumn) in 2018, the index of relative importance was used to determine the importance of various fish species in the survey area. The niche breadth and overlap of major fish species were examined using the mean crowding, Shannon, and Pianka indices. Our results showed that there were 10 and 12 major fish species in spring and autumn, respectively. The niche breadth of major fish species in spring and autumn were 0.06–2.01 and 0.34–2.19, respectively, indicating differences between the two seasons. Larimichthys polyactis was the only wide-niche species ( B i ≥ 2.0) in spring, whereas four were found in autumn: Johnius grypotus , Miichthys miiuy , Larimichthys polyactis, and Amblychaeturichthys hexanema . There were six medium-niche species (2.0> B i ≥ 1.0) in both spring and autumn, whereas there were three narrow-niche species (1.0> B i >0) in spring and two in autumn. The degree of niche overlap was unbalanced in the two seasons. There were 20 pairs of species with significant overlap in the spring niche, accounting for 44.44% of the total number of pairs, with a relatively high degree of overlap. Conversely, the major fish species overlap in autumn was low, with 16 pairs of species with significant overlap, accounting for only 24.24% of the total number of pairs. Redundancy analysis (RDA) showed that tem-perature and salinity were the factors directly affecting the distribution of the major fish species, though depth was also an important factor affecting the obvious niche differentiation of major fish species in spring and autumn.