Genetic Identity of YOY Bluefin Tuna from the Eastern and Western Atlantic Spawning Areas

Abstract

We used 320 young-of-the-year (YOY) specimens of the highly migratory and overfished Atlantic bluefin tuna, Thunnus thynnus, Linnaeus 1758, to evaluate the hypothesis that Atlantic bluefin tuna comprises 2 stocks with spawning grounds in the Gulf of Mexico and in the Mediterranean Sea. Significant genetic differentiation at 8 nuclear microsatellite loci (F(ST) = 0.0059, P = 0.0005) and at the mitochondrial control region (Phi(ST) = 0.0129, P = 0.0139) was detected among YOY Atlantic bluefin tuna captured on spawning grounds in the Gulf of Mexico (n = 40) versus the western (n = 255) and eastern (n = 25) basins of the Mediterranean Sea. The genetic divergence among spawning populations, combined with the extensive trans-Atlantic movements reported for juvenile and adult Atlantic bluefin tuna, indicates a high degree of spawning site fidelity. Recognition of genetically distinct populations necessitates independent management of Atlantic bluefin tuna on spawning grounds and warrants evaluation of the level of mixing of populations on feeding grounds. The genetic pattern might not have been detected unless juvenile specimens or actively spawning adults had been sampled.

Otolith shape variation provides a marker of stock origin for north Atlantic bluefin tuna (Thunnus thynnus)

“…Analyses of DNA microsatellites (Carlsson et al 2007), mitochondrial DNA (Boustany et al 2008) and single nucleotide polymorphisms (Albaina et al 2013) all show significant genetic divergence of the two populations. In addition, there is evidence of genetic heterogeneity within the Mediterranean, and the existence of separate spawning populations in the western and eastern Mediterranean has been proposed (Carlsson et al 2004;Riccioni et al 2010).…”

Spatio-temporal population structuring and genetic diversity retention in depleted Atlantic Bluefin tuna of the Mediterranean Sea

“…The assessment of population dynamics, environmentally driven changes, and levels of exploitation in large pelagic fish is crucial for both stock management and conservation of marine ecosystems dominated by these oceanic top predators (6). Although fisheries still remain the chief source of data for assessing spatiotemporal population dynamics of these fish (7-10), whenever possible, their findings should be compared with those of fishery-independent approaches, such as genetic, electronic, and microchemical tagging experiments (11)(12)(13), to have more accurate data on the key features of population dynamics, such as spawning and migrations (10).…”

“…Microchemical signatures in otoliths of yearlings (i.e., young-of-the-year) unequivocally identified two main spawning areas [i.e., the Mediterranean Sea for the Eastern Atlantic population, the Gulf of Mexico for the Western Atlantic population (13)]. Because of high rates of natal homing of spawning adults to their native areas (95.8% for the Mediterranean Sea and 99.3% for the Gulf of Mexico) and limited and more complex movements in sexually mature ABFTs (11,17), the two populations show significant genetic divergence at both microsatellite (12) and mtDNA (18) loci. The two ABFT populations differ in size, with the eastern population approximately 10 times as large as the western population (19).…”

Fish Resources of the Gulf of Mexico

“…Large differences in growth, maturation, stock structure, and movement have been identified between the eastern and western Atlantic bluefin tuna. Genetic differentiation and natal homing behavior, observed in genetic and archival tagging studies, provide strong evidence for independence of the Gulf of Mexico and Mediterranean Sea Atlantic bluefin tuna stocks Carlsson et al 2007;Boustany et al 2008).…”

“…Atlantic bluefin tuna are highly migratory and experience large-scale, transoceanic movements between foraging and spawning grounds over a wide range of pelagic environments from warm tropical to subpolar waters of the North Atlantic Ocean (Figure 9.20) (Mather et al 1995;Collette et al 2001;Fromentin and Powers 2005), and the northern Gulf of Mexico is one of the spawning locations of Atlantic bluefin tuna (Table 9.15). Based on genetic and tagging studies, two separate stocks are defined with their separate spawning grounds in the Gulf of Mexico (western stock) and Mediterranean Sea (eastern stock), respectively Boustany et al 2007;Carlsson et al 2007). Information for the western stock or western Atlantic population of bluefin tuna is summarized in the tables and text that follow (Tables 9.15, 9.16, and 9.17).…”