Changes in tropical tuna abundances and forage community characteristics affected by climatic variations in the western Indian Ocean

Abstract

Yellowfin tuna (YFT) and bigeye tuna (BET) are economically significant species in the Indian Ocean. However, previous studies on the interactions between tunas and their prey have primarily focused on the Pacific and Atlantic Oceans, with limited research in the Indian Ocean. This study applied standardized catch per unit effort (CPUE) data to compare the spatial distributions of these tunas with their forage communities, which are impacted by climate change and fishing activities. The analysis identified two regions: area A, which showed a high CPUE overlap (> 80% grid) for both YFT and BET, and area B, which was dominated by high YFT CPUEs but had less overlap with BET. In area A, cross-wavelet analysis revealed that both YFT and BET were significantly and positively correlated with forage species such as Scombridae and Carangidae. In contrast, YFT in area B was primarily associated with Loliginidae, Sergestidae, and Mollusca, with varying correlations over time. The impacts of climate variability also differed regionally. In area A, the Dipole Mode Index (DMI) positively influenced tunas and their primary prey, whereas sea surface temperature (SST) showed a negative correlation. Conversely, YFT in area B was positively correlated with SST and the Oceanic Ni & ntilde;o Index (ONI) but negatively correlated with DMI. These findings highlight the complex, region-specific interactions between tunas and their ecosystems in the Indian Ocean.