Transport of Scomber japonicus Larvae in Different Kuroshio Paths Investigated by a Coupled Ocean–Biophysical Model

The transport and distribution of Scomber japonicus larvae significantly affect their habitat and population dynamics. Understanding these processes is crucial for developing effective fishing and conservation strategies. However, the interannual variability of the Kuroshio path introduces both complexity and uncertainty. This study implemented a coupled ocean–biophysical model to simulate and analyze the transport of S. japonicus larvae in the Pacific Ocean south of Japan across three Kuroshio path modes, including the offshore non-large-meander (ONLM), nearshore non-large-meander (NNLM), and typical large-meander (TLM) paths. Two transport scenarios, passive drift (PD) and active swimming (AS), were considered in the simulations. The simulated results presented a comprehensive analysis of the distribution, connectivity, and transport distances of S. japonicus larvae. These findings highlighted the significant influence of biological behavior on larval transport, notably reducing transport distances and shifting the distributions northward. This allowed larvae to actively migrate to areas with higher zooplankton aggregation. Larvae released from the western and nearshore spawning grounds around Southern Kyushu–Shikoku were mainly transported to the central nursery region between 132.5° E and 140° E, whereas larvae released from the eastern spawning grounds were mainly distributed in the eastern nursery region east of 140° E near the Kuroshio Extension. These patterns suggest that nursery areas 2 and 3 may warrant further attention in future spatial management assessments, particularly when considering larval transport under different Kuroshio path modes. This study provides valuable insights into the transport and distribution mechanisms of S. japonicus larvae, offering critical guidance for the conservation of fishery resources and the promotion of sustainable fishery management.