Spatio-temporal variability of habitat distribution of Sthenoteuthis oualaniensis in South China Sea and its interannual variation

Based on the fishery data of Sthenoteuthis oualaniensis and three critical environmental factors including sea surface temperature (SST), Chlorophyll-a (Chl-a) and sea surface height (SSH), we developed an integrated habitat suitability index (HSI) model to examine the spatio-temporal distribution of potential habitat of S. oualaniensis in the South China Sea in spring and clarify the law of the spatio-temporal distribution of habitat of the fish. Results show that the SST and SSH on the fishing ground of S. oualaniensis were lower in the northern waters but higher in the southern waters. The Chl-a concentration was higher in the coastal waters but lower in the pelagic waters. The suitable habitats of S. oualaniensis in spring mainly distributed in the regions between 110°E and 119°E, and its spatial location was consistent of the overlapping areas among the suitable environmental ranges of the above-mentioned three factors. Besides, the HSI anomaly from 2014 to 2017 decreased gradually and showed interannual variability in space. Annually suitable range of each environmental factor exhibited a decreasing trend, and the unfavorable range of each environmental factor showed an increasing trend, leading to the contracted suitable habitats and enlarged unfavorable habitats for S. oualaniensis. The longitudinal and latitudinal distribution of suitable habitats of S. oualaniensis also showed significant interannual variability from year to year. The results indicate that the habitats of S. oualaniensis are closely associated with the environmental factors on their fishing ground; the variability of spatial and temporal of potential habi tat hotspots can be explained by the spatio-temporal distribution of environmental conditions.