This study was conducted to analyze the effects of a citizen science angling program on the biomass and individual body size of the invasive species Micropterus salmoides (largemouth bass) in Samga Reservoir, Songnisan National Park. Currently, M. salmoides is a representative invasive alien species that threatens freshwater biodiversity worldwide due to its strong carnivory and high reproductive capacity (Lowe et al., 2000). In particular, adult bass, as apex predators, prey on native fish, leading to a decline in indigenous species diversity and abundance (Ko et al., 2008). While previous removal efforts in national parks have primarily focused on the ‘number of individuals’ as a measure of performance, actual predation pressure on ecosystems is determined more by biomass and body size than by numerical abundance (Hixon et al., 2014). Analysis of capture data collected from May to September in 2021 and 2022 revealed that the mean daily catch significantly increased from 80.3 individuals in 2021 to 155.6 individuals in 2022 (p < 0.05). Conversely, the mean individual weight significantly decreased from 250.7 g to 164.3 g (p < 0.01). However, there was no statistically significant difference in the total daily biomass removed between the two years (p > 0.05). These findings suggest that continuous angling pressure is effective in reducing the mean body weight of captured bass. As larger individuals generally exhibit greater reproductive contribution and stronger predation capability, their removal has ecological impacts that extend beyond simple numerical reduction (Hixon et al., 2014; Mittelbach and Persson, 1998). Therefore, future management strategies should shift their focus from simple numerical removal to biomass reduction, as this approach may be more effective in alleviating predation pressure on the ecosystem.