Population structure of blackfin tuna (Thunnus atlanticus) in the western Atlantic Ocean inferred from microsatellite loci

Abstract

The blackfin tuna, Thunnus atlanticus, is a small tropical tuna exploited by recreational and commercial fisheries in various parts of its range. Information on stock structure is needed to develop management plans for this species but is currently lacking. In this work, 470 blackfin tuna from nine geographic populations were assayed at 13 homologous microsatellite markers to provide a first assessment of stock structure across the species range. The overall divergence among locality samples was very low (overall FST = 0.0004) indicating high connectivity of blackfin tuna across their range. No clear grouping of localities in differentiated units was inferred but structuring followed a weak isolation by distance pattern (r = 0.16, P = 0.032). Pairwise exact tests and spatial analysis of molecular variance suggested divergence of the sample collected offshore Baía Formosa (Brazil) possibly reflecting reproductive isolation of Brazilian populations from those in the Caribbean region and further north. Further study of the status of Brazilian populations and the transition between this region and the Caribbean is warranted. Cryptic subdivision within the Northern Hemisphere part of the range is possible and should be evaluated using increased marker density and a more comprehensive geographic coverage.

Differentiation of Spatial Units of Genus Euthynnus from the Eastern Atlantic and the Mediterranean Using Otolith Shape Analysis

“…This situation is not common in pelagic fish species and even less in tuna, since they tend to migrate over medium or long distances, both along coastal areas and on open sea [94][95][96][97]. There are cases of restricted geographic expansion in some tuna species in the Atlantic waters, such as Thunnus atlanticus, which is distributed exclusively in tropical and subtropical waters of the Western Atlantic Ocean, ranging from the mid-Atlantic region of the United States east coast to northern Brazil, including the Gulf of Mexico [98]. In the same way, Auxis thazard, although it can be found throughout the Atlantic Ocean, is not distributed along the Mediterranean Sea, where Auxis rochei is dominant [71].…”

Population structure and genetic diversity in wild dotted gizzard shad (Konosirus punctatus) revealed by microsatellite markers

“…Notwithstanding we cannot completely rule out that factors such as the Wahlund effect and selection might have resulted in heterozygote deficits, the presence of null alleles seems to be the most likely explanation for that. Besides, null alleles seem to be particularly common in populations with highly effective population sizes (Chapuis and Estoup, 2007), such as in commercially important fish (Song et al, 2019;Wang et al, 2021;Saillant et al, 2022). Even though null allele frequencies recorded at nine loci were > 0.1 (Table 1), these loci were retained in further analyses as they are unlikely to significantly bias the accuracy of assignment tests and the patterns of population differentiation (Carlsson, 2008).…”

Age, growth, and mortality of Blackfin Tuna in the Gulf of Mexico

“…Blackfin Tuna Thunnus atlanticus are the smallest of the eight true tunas and are distributed in tropical and subtropical waters of the western Atlantic Ocean (Doray et al 2004;Bezerra et al 2013;Saillant et al 2022), from the northeast coast of the United States to the southeastern coast of Brazil, including the Gulf of Mexico (GOM) and Caribbean Sea (Vieira et al 2005). While Blackfin Tuna receive considerably less pressure from global fisheries than larger Atlantic tunas (Bluefin Tuna, Yellowfin Tuna, and Bigeye Tuna; Rooker et al 2007;Lucena-Frédou et al 2021), they support locally important commercial and recreational fisheries, particularly at lower latitudes, and make up most of the artisanal catch in South America (Freire et al 2005) and the Caribbean (Taquet et al 2000;Doray et al 2004).…”

“…Blackfin Tuna are commonly targeted by the recreational rod-and-reel fishery in the GOM (Adams and Kerstetter 2014;Fenton et al 2015) because they are found closer to shore (Rooker et al 2013) and are thus the most accessible tuna to coastal anglers. With growing threats of overfishing and stock depletion of larger tunas, increased fishing pressure on the Blackfin Tuna population is expected , and indeed, recreational landings in the USA have increased by threefold since the 1980s (Saillant et al 2022). Despite the GOM being classified as an essential spawning and nursery ground for the species (Muhling et al 2017;, stock status for Blackfin Tuna remains uncertain, due in part to the lack of basic life history information .…”

“…2013; Cornic and Rooker 2018; Saillant et al. 2022), from the northeast coast of the United States to the southeastern coast of Brazil, including the Gulf of Mexico (GOM) and Caribbean Sea (Vieira et al. 2005).…”