Otolith chemical fingerprints of skipjack tuna (Katsuwonus pelamis) in the Indian Ocean: First insights into stock structure delineation

PLoS One. 2021 Mar 29;16(3):e0249327. doi: 10.1371/journal.pone.0249327. eCollection 2021.

Abstract

The chemical composition of otoliths (earbones) can provide valuable information about stock structure and connectivity patterns among marine fish. For that, chemical signatures must be sufficiently distinct to allow accurate classification of an unknown fish to their area of origin. Here we have examined the suitability of otolith microchemistry as a tool to better understand the spatial dynamics of skipjack tuna (Katsuwonus pelamis), a highly valuable commercial species for which uncertainties remain regarding its stock structure in the Indian Ocean. For this aim, we have compared the early life otolith chemical composition of young-of-the-year (<6 months) skipjack tuna captured from the three main nursery areas of the equatorial Indian Ocean (West, Central and East). Elemental (Li:Ca, Sr:Ca, Ba:Ca, Mg:Ca and Mn:Ca) and stable isotopic (δ13C, δ18O) signatures were used, from individuals captured in 2018 and 2019. Otolith Sr:Ca, Ba:Ca, Mg:Ca and δ18O significantly differed among fish from different nurseries, but, in general, the chemical signatures of the three nursery areas largely overlapped. Multivariate analyses of otolith chemical signatures revealed low geographic separation among Central and Eastern nurseries, achieving a maximum overall random forest cross validated classification success of 51%. Cohort effect on otolith trace element signatures was also detected, indicating that variations in chemical signatures associated with seasonal changes in oceanographic conditions must be well understood, particularly for species with several reproductive peaks throughout the year. Otolith microchemistry in conjunction with other techniques (e.g., genetics, particle tracking) should be further investigated to resolve skipjack stock structure, which will ultimately contribute to the sustainable management of this stock in the Indian Ocean.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Indian Ocean
  • Otolithic Membrane / chemistry*
  • Trace Elements / analysis
  • Tuna*

Substances

  • Trace Elements

Grants and funding

This research was funded by the European Union (Grant number S12.697993) and the FAO/IOTC, within the framework of a collaborative project (GCP/INT/233/EC – Population structure of IOTC species in the Indian Ocean) between FAO/IOTC and CSIRO Oceans and Atmosphere, AZTI, Institut de Recherche pour le Développement (IRD), and Indonesia’s Center for Fisheries Research (CFR). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The views expressed herein can in no way be taken to reflect the official opinion of the European Union. The first author was funded by a Ph.D. research grant from the Department of Agriculture, Fisheries and Food Policy from the Basque Government (Convocatoria ayudas de formación a jóvenes investigadores y tecnólogos 2017).