Differences in habitat variability of the northwestern Indian Ocean’s Sthenoteuthis oualaniensis in response to ENSO events

In order to explore the influence of environmental factors and ENSO events on the habitat of Sthenoteuthis oualaniensis in the northwestern Indian Ocean, this study examined these effects across various seasons. Utilizing production and fishing data of S. oualaniensis collected from September 2021 to May 2024 in the specified region, coupled with marine environmental factor data, we conducted multicollinearity diagnostics and employed the generalized additive model to filter environmental factors and establish a habitat suitability index model with seasonal-specific weights. Based on model performance, optimal models for each season were chosen and validated. Furthermore, these optimal models were utilized to forecast the habitats suitability of S. oualaniensis, enabling a comparative analysis of the spatiotemporal distribution differences of these habitats during El Niño, La Niña, and normal conditions. The findings reveal that the Catch Per Unit Effort (CPUE) of S. oualaniensis in the northwestern Indian Ocean positively correlates with latitude in autumn and winter, but negatively in spring. In contrast, CPUE exhibits a positive correlation with longitude throughout the year. Notably, the environmental factor with the highest weight in the optimal model varies seasonally: eastward current velocity for autumn, sea surface temperature for winter, and chlorophyll-a concentration for spring. Validation results indicate that the prediction accuracy of the optimal models for each season surpasses 70%, with accuracy in spring exceeding 95%. During La Niña events, the habitat area of S. oualaniensis in the northwestern Indian Ocean expands significantly, whereas during El Niño events, it diminishes and shifts northward. The habitat's migration east or west is contingent upon the monsoon wind direction, specifically westward in winter and eastward in spring. This study offers valuable insights into the effects of environmental factors and ENSO events on S. oualaniensis in the northwestern Indian Ocean across different seasonal timescales, ultimately contributing to the sustainable utilization of this species.