Ecological niche differentiation and Mixed-Schooling behavior of Auxis Thazard and Auxis Rochei in the Indian ocean

Abstract

Understanding the behavioral and ecological dynamics of sympatric tuna species is vital for sustainable marine resource management. This study investigates the mixed-schooling behavior and environmental niche differentiation between Auxis thazard (frigate tuna) and Auxis rochei (bullet tuna) in the Indian Ocean. Despite frequent observations of mixed-species schools, driven by their phylogenetic proximity and ecological similarities, these species demonstrate notable differences in multidisciplinary habitat preferences. approach A integrating environmental data, and statistical modeling was employed. Key ecological drivers —including sea surface and bottom temperatures, salinity, primary productivity, dissolved oxygen, and distance to land—were analyzed across A. thazard and A. rochei occurrence points from 2020 to 2024. Generalized Additive Models (GAMs) revealed significant environmental predictors for both species, with A. thazard occupying rather than complete ecological equivalence. The findings highlight the complex interplay between shared behaviors and environmental partitioning in pelagic tunas and underscore the value of integrating spatial analysis and ecological modeling to inform ecosystem-based fisheries management. This study contributes to a nuanced understanding of species interactions in tropical marine ecosystems, with implications for biodiversity exploitation. conservation and sustainable Keywords: Auxis thazard, Auxis rochei, mixed schooling behavior, environmental niche differentiation, Indian ecosystems. I. a broader ecological niche, particularly in offshore, cooler, and well oxygenated waters. In contrast, A. rochei was more associated with warmer, saline, nearshore environments. Habitat Suitability Predictions using Environmental Niches (HSPEN) and spatial probability mapping confirmed these distinctions, while Schoener’s D index (0.62) and Principal Component Analysis indicated moderate niche overlap. Mixed-schooling is thus interpreted as a function of behavioral plasticity and opportunistic overlap during foraging and reproduction, rather than Ocean pelagic INTRODUCTION Species belonging to the genus Auxis, specifically Auxis thazard (frigate tuna) and Auxis rochei (bullet tuna), are small pelagic scombrids widely distributed across tropical and subtropical oceans, including the Indian Ocean. These species are ecologically important as mid-trophic level predators, playing a key role in marine food webs, and they are of considerable economic value to artisanal and small-scale fisheries across the Indo Pacific region. Despite their size, their ecological impact is significant, particularly due to their abundance and foraging behavior. complete ecological equivalence. Generalized Additive Models revealed that A. thazard occupies deeper, cooler offshore waters (mean depth 316.5 m, SST 26.29°C), while A. rochei prefers shallow, warmer nearshore environments (mean depth 22.5 m, SST 28.16°C). Schoener's D index of 0.62 indicated moderate niche overlap, suggesting that mixed schooling represents opportunistic behavioral plasticity rather than complete ecological equivalence. The findings highlight the complex interplay between shared behaviors and environmental partitioning in pelagic tunas and underscore the value of integrating spatial analysis and ecological modeling to inform ecosystem-based fisheries management. This study contributes to a nuanced understanding of species interactions in tropical marine ecosystems, with implications for biodiversity exploitation. conservation and sustainable exploitation.