Dataset: Biometrics, identifications, and isotopic values of larval fish and isotopic values of zooplankton from samples collected on R/V Roger Revelle cruise RR2201 (BLOOFINZ-IO) in Argo Basin region off Northwest Australia from January to March 2022

Larval tuna were collected in 2022 during BLOOFINZ-IO cruise RR2201 aboard R/V Roger Revelle (Landry et al., 2024). Plankton nets (Bongo-90 with 500-micrometer (μm) mesh) were utilized for ichthyoplankton sampling and the procedure was described in Malca et al., 2025. Larvae were identified at sea utilizing morphological, meristic, and pigmentation characteristics (Nishikawa, 1985; Nishikawa and Rimmer 1987). A subset of tuna larvae were identified and preserved at -80 degrees Celsius (°C) at sea and were processed for morphometrics, genetics, SIA, and aging in the IEO-CSIC laboratories in Malaga, Spain. Shipboard identifications were confirmed using: i) a multiplex PCR to distinguish SBT (Thunnus maccoyii) from yellowfin (T. albacares), albacore (T. alalunga), bigeye (T. obesus), and skipjack (K. pelamis) tunas (see Malca et al., 2025); ii) mitochondrial cytochrome c oxidase subunit I (COI), and iii) high-resolution melting (HRM) techniques (Malca et al., 2025).

Coupled to the Bongo-90 net system, a Bongo-25 (25-centimeter (cm) diameter) plankton net was fitted with 200 and 55 μm mesh nets to simultaneously target meso- and micro-zooplankton, respectively. A mechanical flowmeter (2030, General Oceanics) was placed in the center of all plankton nets to calculate the volume of water filtered (cubic meters) by each net. Plankton samples from the 200-μm net (hereafter meso-zooplankton) were divided into two aliquots using a Folsom plankton splitter, with half preserved in 95% ethanol and the other half frozen at −80°C. Microzooplankton (samples from 55-μm mesh net) were first poured through a 200-μm mesh sieve to remove larger zooplankton and debris, then filtered onto 55-μm mesh and frozen at −80°C (Laiz-Carrión et al., 2015). Each meso- and micro-zooplankton sample was freeze-dried for 48 hours at −20°C, and weighed to the nearest 1 microgram (μg). Dry weight (DW) biomass values were standardized to milligrams per cubic meter (mg m−3) using the volume filtered by the plankton nets.

Laboratory analysis at the Málaga Oceanographic Center (IEO-CSIC) was conducted by first measuring standard length (SL, mm) with Image J 1.44a software (USA National Institute of Health) and DW (mg, nearest 1 μg) after freeze-drying for 24 hours. Larvae were classified as preflexion and postflexion based on the degree of notochord flexion observed on a digitized and calibrated image of each larva (Kendall et al., 1984). Next, otoliths were removed and age estimations were conducted following the protocols described by Malca et al., 2023. Natural abundances of N (δ15N) and C (δ13C) were measured using an isotope-ratio spectrometer (Thermo-Finnigan Delta-plus) coupled to an elemental analyzer (FlashEA1112, Thermo-Finnigan) at the Instrumental Unit of Analysis of the University of A Coruña. Ratios of 15N/14N and 12C/13C were expressed in conventional delta notation (δ), relative to the international standard, Atmospheric Air (N2), and Pee-Dee Belemnite (PDB), respectively, using acetanilide as standard. The analysis precisions for δ15N and δ13C were 0.11‰ and 0.14‰, respectively, based on the standard deviation of internal references (repeatability of duplicates).

Additional details regarding the survey (RR2201 cruise) can be found in the cruise report found in the link: http://hdl.handle.net/1834/43464.