DOI: 10.5061/dryad.79cnp5j0w
title: Geographic, seasonal and ontogenetic variations of δ15N and δ13C of Japanese sardine explained by baseline variations and diverse fish movements

description: Understanding and predicting variability in the stable isotope ratios of
 nitrogen and carbon (δ15N and δ13C, respectively) of small pelagic fish is
 crucial to enable isotopic studies of a variety of marine predators that
 feed on them. However, because the isotope ratios reflect plastic feeding
 habits and fish migration in addition to baseline variation, their
 predictions require a mechanistic understanding of how each factor
 contributes. Here, we investigated the habitat-wide variability of δ15N
 and δ13C of the Japanese sardine Sardinops melanostictus in the western
 North Pacific and its marginal seas (the East China Sea and the Sea of
 Japan). By combining this with the archived particulate organic matter
 (POM) dataset as a baseline, we aimed to understand how ecological
 processes and baseline fluctuations affect isotope ratios of the sardine.
 Both δ15N and δ13C of sardine showed significant geographical and seasonal
 trends, with higher values in southern nearshore areas, including the Seto
 Inland Sea, intermediate values in marginal seas and lower values in
 Pacific offshore areas. As the variations were largely consistent with the
 geographic and temporally integrated seasonal trends of isotope ratios of
 POM, respectively, the baseline variations are the main determinant of
 sardine isotope composition. The trophic levels of sardine are therefore
 not significantly different between regions, with possible minor increases
 in the southern nearshore area. Adults showed less geographic variation
 than larvae and juveniles, likely due to slower turnover periods and wider
 migration ranges. Although larval and juvenile isotope ratios in marginal
 seas mostly reflected the local baseline, those in the Pacific offshore
 often reflected the baseline in the neighbouring southern region,
 suggesting contrasting juvenile movements between regions. Our results
 suggest that the δ15N and δ13C of Japanese sardine strongly reflect
 baseline variations, but can also be influenced by life-stage- and
 region-dependent fish movements, thereby demonstrating both the
 possibility and difficulty of mechanistically modelling the isoscapes of
 lower trophic level species.
description: Tissues were freeze-dried and
 ground into powder. Lipids were extracted from all samples using a 2:1
 chloroform:methanol solution, freeze-dried again, and 800 μg of a
 subsample was extracted for isotope analysis. The
 δ<sup>15</sup>N and δ<sup>13</sup>C values of the
 samples were determined at Fisheries Resources Institute (Yokohama, Japan)
 or GeoScience Laboratory (Nagoya, Japan) using a continuous-flow stable
 isotope ratio mass spectrometer (IsoPrime100, Elementar, Stockton, UK;
 Delta Plus Advantage, Thermo Fisher Scientific, Waltham, Massachusetts,
 USA) coupled to an elemental analyser (vario MICRO cube, Elementar;
 FLASH2000, Thermo Fisher Scientific, Yokohama Japan). The
 δ<sup>15</sup>N and δ<sup>13</sup>C values were
 reported in δ-notation against the atmospheric N2 standard and the VPDB
 reference standard (Vienna Pee Dee Belemnite), respectively, and given as
 a ‰ value. Analytical accuracies were ± 0.2‰ for
 δ<sup>15</sup>N and δ<sup>13</sup>C in both
 laboratories. The agreement of the reported values between the two
 laboratories was tested using a blind standard (powder of fish eye lens)
 where the differences in the reported values for both
 δ<sup>15</sup>N and δ<sup>13</sup>C were less than
 the analytical precisions.
description: # Geographic, seasonal and ontogenetic variations of δ15N and δ13C of
 Japanese sardine explained by baseline variations and diverse fish
 movements
 [https://doi.org/10.5061/dryad.79cnp5j0w](https://doi.org/10.5061/dryad.79cnp5j0w) Newly obtained carbon and nitrogen stable isotope ratios of Japanese sardine muscles are reported. ## Description of the data and file structure The csv file contain all the data. Year, Month, date, Latitude (degrees North), Longitude (degrees East) of fish collection, carbon stable isotope ratio (VPDB permil, lipid extracted), nitrogen isotope ratio (V atmospheric N2 permil, lipid extracted), Standard Length (mm) and C/N ratio (lipid extracted) are reported.