Effects of Interspecific Competition on Habitat Shifts of Sardinops melanostictus (Temminck et Schlegel, 1846) and Scomber japonicus (Houttuyn, 1782) in the Northwest Pacific

As economically important sympatric species in the Northwest Pacific, the Japanese sardine (<i>Sardinops melanostictus</i>) and Chub mackerel (<i>Scomber japonicus</i>) exhibit significant biological interactions. Understanding the impact of interspecies competition on their habitat dynamics can provide crucial insights for the sustainable development and management of these interconnected species resources. This study utilizes fisheries data of <i>S. melanostictus</i> and <i>S. japonicus</i> from the Northwest Pacific, collected from June to November between 2017 and 2020. We integrated various environmental parameters, including temperature at different depths (0, 50, 100, 150, and 200 m), eddy kinetic energy (EKE), sea surface height (SSH), chlorophyll-a concentration (Chl-a), and the oceanic Niño index (ONI), to construct interspecific competition species distribution model (icSDM) for both species. We validated these models by overlaying the predicted habitats with fisheries data from 2021 and performing cross-validation to assess the models' reliability. Furthermore, we conducted correlation analyses of the habitats of these two species to evaluate the impact of interspecies relationships on their habitat dynamics. The results indicate that, compared to single-species habitat models, the interspecific competition species distribution model (icSDM) for these two species exhibit a significantly higher explanatory power, with <i>R</i>² values increasing by up to 0.29; interspecific competition significantly influences the habitat dynamics of <i>S. melanostictus</i> and <i>S. japonicus</i>, strengthening the correlation between their habitat changes. This relationship exhibits a positive correlation at specific stages, with the highest correlations observed in June, July, and October, at 0.81, 0.80, and 0.88, respectively; interspecific competition also demonstrates stage-specific differences in its impact on the habitat dynamics of <i>S. melanostictus</i> and <i>S. japonicus</i>, with the most pronounced differences occurring in August and November. Compared to <i>S. melanostictus</i>, interspecific competition is more beneficial for the expansion of the optimal habitat (HIS ≥ 0.6) for <i>S. japonicus</i> and, to some extent, inhibits the habitat expansion of <i>S. melanostictus</i>. The variation in migratory routes and predatory interactions (with larger individuals of <i>S. japonicus</i> preying on smaller individuals of <i>S. melanostictus</i>) likely constitutes the primary factors contributing to these observed differences.