The main objective of this study is to investigate the differences in the abundance of free-swimming school and associated school of Katsuwonus pelamis influenced by environmental and other population factors. This study utilized the production statistics from 2011 to 2020, combined with marine environmental factors （SST, SSS, Chl.a）, the CPUE data for yellowfin tuna and bigeye tuna in the Western and Central Pacific Ocean are used as other population factors.A generalized additive model （GAM） was used to analyze the two fish populations separately, and the final model was confirmed through the akaike information criterion.The results indicate that other population factors had the most significant influence on both school types, and the explanatory deviation rates were 31.40% and 67.00%. For free-swimming schools, longitude and month were significant besides other population factors, and their interpretation deviation rates were 4.15% and 4.14%. Among the environmental factors, SST was the most important, with an explanatory deviation rate of 3.90%, followed by SSS with an explanatory deviation rate of 3.78%, and Chl.a had a lesser impact, with an explanatory deviation rate of only 1.40%. For associated schools, month and longitude were significant, and their interpretation deviation rates were 20.70% and 10.60%. Among the environmental factors, SSS was the most influential, with an explanatory deviation rate of 8.37%,while Chl.a and SST had lesser impacts,with explanatory deviation rates of 1.13% and 0.19%.It is concluded that the effects of other population factors should be considered in the future fishery forecasting models.With the aim of providing a reference for future research in the field of tuna purse-seine fisheries and for the scientific identification of fishing grounds.