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 souther..., Juvenile T. japonicus were collected during a bottom trawl survey in the East China Sea conducted by the Japan Fisheries and Education Agency from May to June 2014. We analysed geographic differences in transport and migration by selecting otoliths from 12 juveniles at four stations with relatively large catches: Sts. S and C on the southern shelf and Sts. N-1 and N-2 on the northern shelf. Station St. N-2, near N-1, served to confirm regional movement differences. The extracted otoliths (sagittae) were cleaned, air-dried, and embedded in epoxy resin. To facilitate the observation of daily increments and subsequent micromilling, the otoliths were ground with sandpaper to expose the core, polished with an alumina polishing suspension (BAIKOWSKI International Corporation), and coated with nail polish. The daily increment widths were quantified from the core to edge using an otolith measurement system (RATOC System Engineering Co., Ltd.). As an indicator of the early life growth rate, the ..., # Data from: The staircase chart: visualising vertical and cross-shelf movements and dispersal of early-life fish, applied to Japanese jack mackerel Dataset DOI: [10.5061/dryad.v9s4mw77v](10.5061/dryad.v9s4mw77v) ## Description of the data and file structure ### Files and variables #### File: d18O_data.csv **Description:** Compiled otolith data ##### Variables * Station_original: Station ID in the original survey * Sta: Renamed station ID for this study * Original_ID: Fish ID in the original survey * ID: Renamed Fish ID for this study * Ind: Individual identifier * SL: Standard length at catch (mm) * OR: Otolith radius (um)  * Date_col: Date of collection * Date_hatch: Estimated hatch date * Drill_width: Width of micromilled area (um) * Drill_OR_e: Distance from the core to the outer edge of the milled area (um) * Drill_OR_m: Distance from the core to the centre of the milled area (um) * dph: Days post hatch corresponding to the outer edge of the milled area * dph_m: Median d..., ,