Data from: The staircase chart: visualising vertical and cross-shelf movements and dispersal of early-life fish, applied to Japanese jack mackerel

1.    Marine fish dispersal during early life stages is
a critical process that affects population connectivity and dynamics, yet
individual-level field observations remain difficult. This limits our
ability to identify the factors controlling the dispersal process,
including the active swimming of larvae and pelagic juveniles. Here, we
propose a method to reproduce ontogenetic vertical and horizontal
movements of fish on continental shelves. The approach combined
high-resolution profiles of oxygen stable isotope values (δ18O) from
otoliths, hydrodynamic simulations, and a hidden Markov model. The shelf
environment was compressed into a representative cross-section, in which
fish movements were predicted by analysing temperature and salinity
distributions in relation to otolith δ18O. Applying the method to Japanese
jack mackerel in the East China Sea shelf revealed general ontogenetic
vertical migration and variable cross-shelf movements. Twelve fish
collected from the southern to northern shelves originated mainly from the
southern outer shelf, which is influenced by the northward-flowing
Kuroshio current. Fast growers in the first 30 days moved to the inner
shelf earlier and stayed south, while others remained in the outer shelf
were transported to the northern shelf. These findings indicate that
horizontal movements, potentially influenced by active swimming, play an
important role in the retention and dispersal of fish that spawn at shelf
edges. This novel method can greatly advance our understanding of marine
fish dispersal and improve conservation efforts.