Genetic connectivity between Atlantic bluefin tuna larvae spawned in the Gulf of Mexico and in the Mediterranean Sea

Carolina Johnstone; Montse Pérez; Estrella Malca; José María Quintanilla; Trika Gerard; Diego Lozano-Peral; Francisco Alemany; John Lamkin; Alberto García; Raúl Laiz-Carrión

doi:10.7717/peerj.11568

Genetic connectivity between Atlantic bluefin tuna larvae spawned in the Gulf of Mexico and in the Mediterranean Sea

PeerJ. 2021 Jun 14:9:e11568. doi: 10.7717/peerj.11568. eCollection 2021.

Authors

Affiliations

¹ Centro Oceanográfico de Málaga, Instituto Español de Oceanografía, Consejo Superior de Investigaciones Científicas, Fuengirola, Málaga, Spain.
² Centro Oceanográfico de Vigo, Instituto Español de Oceanografía, Consejo Superior de Investigaciones Científicas, Vigo, Pontevedra, Spain.
³ Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, Florida, United States of America.
⁴ Southeast Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Miami, Florida, United States of America.
⁵ Centro de Supercomputación y Bioinnovación, Servicios Centrales de Apoyo a la Investigación, Universidad de Málaga, Málaga, Spain.
⁶ International Commision for the Conservation of Atlantic Tunas, Madrid, Spain.

Abstract

The highly migratory Atlantic bluefin tuna (ABFT) is currently managed as two distinct stocks, in accordance with natal homing behavior and population structuring despite the absence of barriers to gene flow. Larval fish are valuable biological material for tuna molecular ecology. However, they have hardly been used to decipher the ABFT population structure, although providing the genetic signal from successful breeders. For the first time, cooperative field collection of tuna larvae during 2014 in the main spawning area for each stock, the Gulf of Mexico (GOM) and the Mediterranean Sea (MED), enabled us to assess the ABFT genetic structure in a precise temporal and spatial frame exclusively through larvae. Partitioning of genetic diversity at nuclear microsatellite loci and in the mitochondrial control region in larvae spawned contemporarily resulted in low significant fixation indices supporting connectivity between spawners in the main reproduction area for each population. No structuring was detected within the GOM after segregating nuclear diversity in larvae spawned in two hydrographically distinct regions, the eastern GOM (eGOM) and the western GOM (wGOM), with the larvae from eGOM being more similar to those collected in the MED than the larvae from wGOM. We performed clustering of genetically characterized ABFT larvae through Bayesian analysis and by Discriminant Analysis of Principal Components (DAPC) supporting the existence of favorable areas for mixing of ABFT spawners from Western and Eastern stocks, leading to gene flow and apparent connectivity between weakly structured populations. Our findings suggest that the eastern GOM is more prone for the mixing of breeders from the two ABFT populations. Conservation of this valuable resource exploited for centuries calls for intensification of tuna ichthyoplankton research and standardization of genetic tools for monitoring population dynamics.

Keywords: Eastern Gulf of Mexico; Fish spawning; Fisheries management; Larval fish; Microsatellite loci; Mitochondrial control region; North Western Mediterranean; Population structure; Thunnus thynnus; Western Gulf of Mexico.

Grants and funding

This collaborative study was supported by “ECOLATUN” PROJECT CTM2015-68473-R (MINECO/FEDER) funded by Spanish Ministry of Economy and Competitiveness; “TUNAGEN” project funded by Instituto Español de Oceanografía (IEO); and “BLUEFIN” project financed by IEO and Balearic Island Observing and Forecasting System (SOCIB). This research was funded by NASA (NNX11AP76G S07), the NOAA National Marine Fisheries Science Service through the Southeast Fisheries Science Center, as well as by the Cooperative Institute for Marine and Atmospheric Studies under Cooperative Agreement NA15OAR43200064 at the University of Miami, Miami, FL, USA. There was no additional external funding received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.