Spatial and temporal distribution of Sthenoteuthis oualaniensis in the Northwest Indian Ocean during different life stages of cyclonic eddies

Mesoscale eddies, particularly cyclonic eddies (CEs), are known to influence the abundance and distribution of purpleback flying squid (Sthenoteuthis oualaniensis) resources in the northwest Indian Ocean. Sthenoteuthis oualaniensis is a short-lived species and is sensitive to environmental changes. The evolution of CEs is accompanied by structural and energetic transformations, exerting varying impacts on the local marine environment. However, the response of S. oualaniensis to these evolving CEs remains unclear. Therefore, this study analyzed the changes in basic eddy characteristics during CEs evolution and the environmental changes (sea surface temperature, chlorophyll-a concentration, and dissolved oxygen concentration at 150 m depth) driven by CEs. Combined with a habitat suitability index (HSI) model, the distribution of S. oualaniensis during the different life stages of CEs was analyzed. The results showed that the CEs experienced three stages: the early stage, the mature stage and the aged stage. At different stages, the parameters of CEs exhibited distinct distribution patterns. As the eddy evolved, the gravity center of S. oualaniensis abundance in latitude and longitude exhibited a movement trajectory similar to the eddy center. The environmental changes driven by this evolution process influenced the distribution of S. oualaniensis, and the maximum suitable habitat area was generated during the CEs mature stage. These results show that the evolution of CEs significantly affects the habitat distribution of S. oualaniensis in the northwest Indian Ocean.