Event Abstract

Natal signatures in otoliths of young-of-the-year yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tuna from the Indian Ocean

  • 1 Marine Research Division, Centro tecnológico experto en innovación marina y alimentaria (AZTI), Spain
  • 2 UMR5254 Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux (IPREM), France

Yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tuna are the main target species of tropical tuna fisheries in the Indian Ocean. The intensive exploitation of these species has aroused concerns regarding the best approach towards the responsible management of the fishery. Although the understanding of the population structure of a species is essential to infer how a species may respond to human exploitation, to date no scientific information exists on whether these species constitute single or several populations in the Indian Ocean. Among the available techniques for stock discrimination, the examination of the chemical composition of otoliths (i.e. hard-calcareous structures that are found in the inner ear of the fish) has the potential to offer insights into the range of movement and stock structure of a species. Here, we investigated for differences in the chemical composition of yellowfin and skipjack tuna captured among 4 major areas in the Indian Ocean: Northwest Indian Ocean, Mozambique Channel, Maldivian archipelago and northern Indonesia (Figure 1). To reduce the risk that collected individuals moved out from the area where they were originated prior to the sampling, only smallest individuals available (<37 cm and <35 cm in the case of yellowfin and skipjack tuna, respectively) were selected. Therefore, the otolith collection used in this study was comprised of young-of-the-year (YOY) yellowfin (n=100) and skipjack (n=100) tuna otoliths collected across the Indian Ocean between mid-March to mid-August 2018 and mid-March to mid-April 2019. Using a laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS), four 44 µm diameter spots were ablated in the core region of the otolith (which represent the natal signature of the fish). The first ablation spot was always placed in the narrowest part of the otolith section (where the primordium is assumed to be), followed by 3 spots placed at 50, 100 and 200 µm distance respectively. Trace element concentrations of selected elements (Li, Mg, Mn, Sr, Ba, Fe and Zn) were measured at each spot. The obtained results were used to investigate three main questions. First, we tested for potential ontogenetic variations on otolith elemental concentrations during fish early life by comparing intra-group variability at each spot. These will be useful for selecting the optimal portion of otolith to be used as indicator of natal origin. Second, we seek for interannual variability in the chemical signatures of samples collected at the same area in consequent years. This clarification can inform about the importance of age-class matching when using the baseline YOY signature to estimate the origin of juvenile and adult yellowfin and skipjack tuna. Third, differences in otolith elemental signatures among the four nursery regions were tested using both univariate and multivariate statistical methods. Additionally, a random forest (RF) classification analysis was used to test if individuals could be correctly classified to their capture locations. Overall, these results will contribute to delineate a natal origin signature baseline for yellowfin and skipjack tuna in the Indian Ocean, which will posteriorly be useful to study the degree of mobility and provenance of older individuals (e.g. connectivity between different regions, homing behaviour of spawning individuals…). These results will provide first insights into potential differences between fish belonging to different areas, increasing our understanding on the population structure and connectivity of these species. Ultimately, this information will be necessary for delineating realistic stock structure scenarios and for the identification of appropriate stock units for the sustainable management of yellowfin and skipjack tuna in the Indian Ocean.

Figure 1


Authors want to thank all the scientific observers on board for their assistance in sample collection. This work has been developed within the framework of the FAO funded project "Population Structure of IOTC Species in the Indian Ocean: estimation with next-generation sequencing technologies and otolith micro-chemistry". This work was supported by a grant of the Department of Agriculture, Fishing and Alimentation from the Basque Government to Iraide Artetxe-Arrate for her doctoral work.

Keywords: Yellowfin (Thunnus albacares), Skipjack (Katsuwonus pelamis), Tropical tuna, Otolith microchemistry, Natural tracer, Indian Ocean, Stock structure

Conference: XVI European Congress of Ichthyology, Lausanne, Switzerland, 2 Sep - 6 Sep, 2019.

Presentation Type: Oral


Citation: Artetxe-Arrate I, Fraile I, Pecheyran C and Murua H (2019). Natal signatures in otoliths of young-of-the-year yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tuna from the Indian Ocean. Front. Mar. Sci. Conference Abstract: XVI European Congress of Ichthyology. doi: 10.3389/conf.fmars.2019.07.00086

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Received: 31 May 2019; Published Online: 14 Aug 2019.

* Correspondence: Miss. Iraide Artetxe-Arrate, Marine Research Division, Centro tecnológico experto en innovación marina y alimentaria (AZTI), Pasaia, Spain, i.artetxe73@gmail.com