First integrated analysis of acoustic, biological, and environmental factors influencing tropical tuna in the western Indian Ocean

Understanding the spatial dynamics of tuna fisheries in relation to prey biomass and environmental variability is crucial for sustainable management in the Indian Ocean; however, the direct links between tuna catches and prey biomass remain insufficiently resolved. This study examined the relationships between prey biomass and catches of skipjack, bigeye, and yellowfin tuna, together with their spatial and environmental drivers in the western Indian Ocean, by integrating acoustic surveys (38 kHz), zooplankton sampling, Indian Ocean Tuna Commission catch records, and satellite- and in situ -derived environmental data. Temperature, salinity, dissolved oxygen, and chlorophyll- a were analyzed at upper (47.4 m) and lower (130.7 m) depths of the thermocline. Tuna catches were highest in equatorial and northwestern regions, coinciding with elevated prey biomass, increased zooplankton density, and favorable environmental conditions. Catch patterns revealed depth-dependent environmental preferences, with warmer and more productive conditions favored at 47.4 m and cooler, high-salinity, and low-productivity conditions at 130.7 m, along with a pronounced spatial structure characterized by persistent high-catch zones in the northern and western regions. Despite limitations in sampling resolution and reliance on fishery-dependent data, this integrated approach provides valuable insights for ecosystem-based management of tropical tuna fisheries under changing oceanographic conditions.