DOI: 10.6084/m9.figshare.27850272
title: <b>Antarctic toothfish </b><b><i>Dissostichus mawsoni </i></b><b>in the South Orkney Islands: Using stable isotopes and otoliths to test current hypotheses about nursery areas and demographic units.</b>

description: This dataset contains stable isotope and elemental composition data from otoliths of Antarctic Toothfish (<i>Dissostichus mawsoni</i>) to investigate habitat use and connectivity between sub-populations in the CCAMLR area 48. The dataset includes measurements of stable isotopes (δ<sup>13</sup>C and δ<sup>18</sup>O) and elemental ratios (Li, Na, Mg, Cr, Mn, Sr, Sn, Ba) from otolith sections.<b>Isotopic Composition Dataset:</b>Powder samples (≥30 μg) from both the nuclear and marginal regions of otoliths were collected using a microdrill. These regions represent juvenile (0-540 μm from the core) and adult (255 μm from the edge) life stages. The stable isotope ratios of carbon (δ<sup>13</sup>C) and oxygen (δ<sup>18</sup>O) were analyzed at the University of Arizona Environmental Isotope Geochemistry Laboratory using an automated KIEL-III carbonate preparation device coupled with a Finnigan MAT 252 ratio-gas spectrometer. Otolith material was digested in vacuum with dehydrated phosphoric acid, at 70°C. The CO2 generated by this reaction was analysed to determine δ<sup>18</sup>O and δ<sup>13</sup>C. Results were expressed in parts per thousand (‰) relative to the standard Vienna Pee Dee Belemnite, VPDB, using international standards NBS‐19 and NBS‐18.<b>Columns in the Isotopic Composition File:</b><b>COD_LAB</b>: Laboratory code assigned to each sample for identification purposes.<b>ID_LANCE</b>: Identifier for each fishing or sampling event (e.g., tows).<b>YYYYMMDD</b>: Date of sampling, formatted as year-month-day (YYYY-MM-DD).<b>LATITUDE</b>: Latitude of the sampling location in decimal degrees.<b>LONGITUDE</b>: Longitude of the sampling location in decimal degrees.<b>SPECIES</b>: Taxonomic identification of the fish species.<b>LT</b>: Total length of the fish, measured in centimeters.<b>SEX</b>: Biological sex of the individual (e.g., 1: Male, 2: Female).<b>COHORT</b>: Estimated year of birth of the fish, calculated using the inverse function of the von Bertalanffy growth model (Horn, 2002).<b>OTOLITH_SECTION</b>: Section of the otolith analyzed (e.g., nuclear or marginal).<b>d13C</b>: Carbon stable isotope ratio (δ¹³C) is reported in permille (‰). Results were normalized to the Vienna Pee Dee Belemnite (VPDB) scale using the international standards NBS‐19 and NBS‐18.<b>d18O</b>: Oxygen stable isotope ratio (δ¹⁸O) is reported in permille (‰). Results were normalized to the Vienna Pee Dee Belemnite (VPDB) scale using the international standards NBS‐19 and NBS‐18.<b>Elemental Composition Dataset:</b>Elemental composition was analyzed at the Andean Geothermal Center of Excellence (FCFM), Universidad de Chile, using a 193 nm ArF laser ablation (LA) system (Photon Machines Analyte G2) coupled to an iCapQ ThermoScientific ICP-MS. Analyses followed a radial transect of spots from the primordium to the ventral edge of the otolith section, or to the dorsal edge when the ventral was not accessible. Spot spacing ranged from 93 to 97 μm to cover the entire transect, resulting in 14–24 ablations per otolith, depending on size.<br>Each ablation used a fluence of 5 J·cm⁻², a frequency of 10 Hz, and a duration of 30 seconds, reaching depths of 20–30 μm with an average spot diameter of 65 μm. Silicate glass reference material NIST SRM 612 served as the primary external standard, and USGS synthetic calcium carbonate MACS-3 was used for quality control. Calcium (Ca) was used as the internal standard, assuming a stoichiometric value of 38.8% CaO in the aragonite matrix. External standard measurements were performed before and after the ablation of each otolith.<br>Data obtained from the mass spectrometer were processed using the Iolite V2.5 software, employing the preset internal and external standard method ("Trace Elements IS" reduction scheme) <br><b>Columns in the Elemental Composition File:</b><b>COD_LAB</b>: Laboratory code assigned to each sample for identification purposes.<b>ID_LANCE</b>: Identifier for each fishing or sampling event (e.g., tows).<b>YYYYMMDD</b>: Date of sampling, formatted as year-month-day (YYYY-MM-DD).<b>LATITUDE</b>: Latitude of the sampling location in decimal degrees.<b>LONGITUDE</b>: Longitude of the sampling location in decimal degrees.<b>SPECIES</b>: Taxonomic identification of the fish species.<b>LT</b>: Total length of the fish, measured in centimeters.<b>SEX</b>: Biological sex of the individual (e.g., 1: Male, 2: Female).<b>COHORT</b>: Estimated year of birth of the fish, calculated using the inverse function of the von Bertalanffy growth model (Horn, 2002).<b>SECTION</b>: Region of the otolith analyzed, categorized as nuclear (near the core) or marginal (near the edge), based on the position of the laser ablation spots.<b>N_SPOT</b>: Position of the spot (ablation) analyzed within the otolith, indicating the sequential order of laser ablations along a radial transect from the core (primordium) to the edge of the otolith section.<b>Li7.Ca43</b>: Lithium-to-Calcium ratio (Li).<b>Na23.Ca43</b>: Sodium-to-Calcium ratio (Na).<b>Mg24.Ca43</b>: Magnesium-to-Calcium ratio (Mg).<b>Cr52.Ca43</b>: Chromium-to-Calcium ratio (Cr).<b>Mn55.Ca43</b>: Manganese-to-Calcium ratio (Mn).<b>Sr88.Ca43</b>: Strontium-to-Calcium ratio (Sr).<b>Sn120.Ca43</b>: Tin-to-Calcium ratio (Sn).<b>Ba138.Ca43</b>: Barium-to-Calcium ratio (Ba).