The Spatial and Temporal Distribution of Bigeye Tuna and Yellowfin Tuna in the Northwest Indian Ocean and Their Relationship with Environmental Factors

The Northwestern Indian Ocean (NWIO) serves as a primary fishing ground for tuna longline fisheries, with bigeye tuna (<i>Thunnus obesus</i>) and yellowfin tuna (<i>Thunnus albacares</i>) constituting the main target species. Investigating their spatiotemporal distribution and relationship with environmental factors is of significant importance for fishery management and fishing. This study analyzed and compared the distribution patterns and environmental preferences of these two species across different depth layers, based on fisheries scientific survey data collected during the 2023/2024 and 2024/2025 fishing seasons. Key findings include: The hook rate in 2023/2024 was higher than in 2024/2025, and the hook rate for <i>T. obesus</i> exceeded that of <i>T. albacares</i>. <i>T. obesus</i> were predominantly concentrated within 63° E-69° E and 7° N-9° N, while <i>T. albacares</i> exhibited a broader yet more dispersed distribution range. <i>T. obesus</i> primarily occupied depth layers of 130-140 m (12.20%), 180-190 m (9.76%), and 270-280 m (9.76%). <i>T. albacares</i> were mainly found at 110-120 m (15%), 140-150 m (15%), and 200-210 m (15%). Both species exhibit distinct spatial clustering patterns, and their hotspot distribution areas are, respectively, 63° E-69° E, 5° N-10° N and 64° E-68° E, 0° N-4° N. Correlation analysis revealed significant relationships between <i>T. obesus</i> distribution and latitude, zooplankton abundance, water temperature at various depths, and chlorophyll a concentration. Our research provides reference for understanding the distribution of <i>T. obesus</i> and <i>T. albacares</i> across different water layers and their habitat preferences, laying a scientific foundation for achieving sustainable utilization of both species.