Effects of Antarctic sea ice variations-driven seawater cooling on habitat pattern of Argentine shortfin squid Illex argentinus in the southwest Atlantic Ocean

Abstract:

Based on the fisheries data from January to April 2013-2017, as well as the environmental data including the sea ice extent data in the Antarctica and sea water temperature data at depths of 54 m, 96 m, 193 m on the fishing ground, with the habitat suitability index (HSI) as an indicator of the habitat condition of Illex argentinus and variation of the areas with HSI>0.6 indicating the changes of suitable habitats, this study examined the relationship between sea ice extent and sea water temperature at different layers, and evaluated the influences of Antarctic sea ice variations-driven seawater cooling on HSI of I. argentinus in the Southwest Atlantic Ocean. Significant monthly variations were exhibited in the Antarctic sea ice extent, vertical water temperature and HSI of I. argentinus. A positive correlation was found between Antarctic sea ice extent and sea water temperature at different layers. The habitat quality of I. argentinus in the year with high sea ice extent was better than that in the year with low sea ice extent. Under the scenarios of vertical water temperature decreasing by 0.1, 0.3, 0.5 and 1.0 ℃ caused by the Antarctic sea ice melting, results suggested that with the decrease of vertical water temperature, spatio-temporal habitat pattern of I. argentinus showed significant changes. Suitable habitats of I. argentinus slightly enlarged with vertical water temperature decreasing no more than 0.5 ℃; while it clearly reduced under the scenarios of vertical water temperature decreased by 1.0 ℃. Large difference was found in the suitable habitats within different regions in the southwest Atlantic Ocean. Suitable habitat tended to move into the waters of the Exclusive Economic Zone (EEZ) off Argentina, and the percentage of suitable habitats within the EEZ off Argentina dramatically increased. Suitable habitats in the high seas had no evident changes. However, suitable habitats within the EEZ of Falkland Islands suffered great decrease. Our findings suggested that the great decreases of vertical water temperature induced by the sea ice melting in the Antarctica would lead to the inshore-ward movement of suitable habitats of I. argentinus off Argentina, while the suitable habitats would greatly decline within the EEZ of Falkland Islands.