Reply to Safina and Walter et al.: Multiple lines of evidence for size-structured spawning migrations in western Atlantic bluefin tuna

Richardson, David E.; Marancik, Katrin E.; Guyon, Jeffrey R.; Lutcavage, Molly E.; Galuardi, Benjamin; Lam, Chi Hin; Walsh, Harvey J.; Wildes, Sharon; Yates, Douglas; Hare, Jonathan A.

doi:10.1073/pnas.1607666113

Cited by 5 publications

(3 citation statements)

References 8 publications

(12 reference statements)

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“…Tagging information further revealed that mature size fish occurred in the Slope Sea in spring and summer coinciding with the spawning season estimated for the found larvae (Galuardi et al., 2010), and age‐structure spawning in the western Atlantic has been hypothesized based on tagging, longline catch data and reproductive studies data, meaning that younger fish would preferably spawn in the Slope Sea and only bigger fish would spawn in the Gulf of Mexico (Richardson et al., 2016a). The implications of Slope Sea spawning generated debate and controversy (Richardson et al., 2016b; Safina, 2016; Walter et al., 2016), with one of the key unknowns being the connectivity between the Slope Sea and the other two spawning grounds. In addition, some studies found evidence of migratory changes in ABFT, including the re‐colonization (Aarestrup et al., 2022; Horton et al., 2020; Nøttestad et al., 2020) and even expansion (Jansen et al., 2021) of its geographic range.…”

Section: Introductionmentioning

confidence: 99%

Unidirectional trans‐Atlantic gene flow and a mixed spawning area shape the genetic connectivity of Atlantic bluefin tuna

Díaz‐Arce,

Gagnaire,

Richardson

et al. 2023

Molecular Ecology

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The commercially important Atlantic bluefin tuna (Thunnus thynnus), a large migratory fish, has experienced notable recovery aided by accurate resource assessment and effective fisheries management efforts. Traditionally, this species has been perceived as consisting of eastern and western populations, spawning respectively in the Mediterranean Sea and the Gulf of Mexico, with mixing occurring throughout the Atlantic. However, recent studies have challenged this assumption by revealing weak genetic differentiation and identifying a previously unknown spawning ground in the Slope Sea used by Atlantic bluefin tuna of uncertain origin. To further understand the current and past population structure and connectivity of Atlantic bluefin tuna, we have assembled a unique dataset including thousands of genome‐wide single‐nucleotide polymorphisms (SNPs) from 500 larvae, young of the year and spawning adult samples covering the three spawning grounds and including individuals of other Thunnus species. Our analyses support two weakly differentiated but demographically connected ancestral populations that interbreed in the Slope Sea. Moreover, we also identified signatures of introgression from albacore (Thunnus alalunga) into the Atlantic bluefin tuna genome, exhibiting varied frequencies across spawning areas, indicating strong gene flow from the Mediterranean Sea towards the Slope Sea. We hypothesize that the observed genetic differentiation may be attributed to increased gene flow caused by a recent intensification of westward migration by the eastern population, which could have implications for the genetic diversity and conservation of western populations. Future conservation efforts should consider these findings to address potential genetic homogenization in the species.

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Section: Introductionmentioning

confidence: 99%

Unidirectional trans‐Atlantic gene flow and a mixed spawning area shape the genetic connectivity of Atlantic bluefin tuna

Díaz‐Arce,

Gagnaire,

Richardson

et al. 2023

Molecular Ecology

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“…Tagging information further revealed that mature size fish occurred in the Slope Sea in spring and summer coinciding with the spawning season estimated for the found larvae (Galuardi et al 2010), supporting the hypothesis of spawning strategy in the western Atlantic. The implications of Slope Sea spawning generated debate and controversy (Richardson et al 2016b, Safina 2016, Walter et al 2016, with one of the key unknowns being the connectivity between the Slope Sea and the other two spawning grounds. In addition, some studies found evidence of migratory changes in ABFT, including the return to (Horton et al 2020, Nøttestad et al 2020, Aarestrup et al 2022) and even expansion (Jansen et al 2021) of its geographic range.…”

Section: Introductionmentioning

confidence: 99%

Unidirectional trans-Atlantic gene flow and a mixed spawning area shape the genetic connectivity of Atlantic bluefin tuna

Díaz-Arce¹,

Gagnaire

Richardson³

et al. 2023

Preprint

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The commercially important Atlantic bluefin tuna (Thunnus thynnus), a large migratory fish, has experienced notable recovery aided by accurate resource assessment and effective fisheries management efforts. Traditionally, this species has been perceived as consisting of eastern and western populations, spawning respectively in the Mediterranean Sea and the Gulf of Mexico, with mixing occurring throughout the Atlantic. However, recent studies have emerged challenging this assumption by revealing weak genetic differentiation and identifying a previously unknown spawning ground in the Slope Sea used by Atlantic bluefin tuna of uncertain origin. To further understand the current and past population structure and connectivity of Atlantic bluefin tuna, we have assembled a unique dataset including thousands of genome-wide Single Nucleotide Polymorphisms (SNPs) from five hundred larvae, young of the year and spawning adult samples covering the three spawning grounds and including individuals of other Thunnus species. Our analyses support two weakly differentiated but demographically connected ancestral populations that interbreed in the Slope Sea. Moreover, we also identified signatures of introgression from albacore into the Atlantic bluefin tuna genome, exhibiting varied frequencies across spawning areas, indicating strong gene flow from the Mediterranean Sea towards the Slope Sea. We hypothesize that the observed genetic differentiation may be attributed to increased gene flow caused by a recent intensification of westward migration by the eastern population, which could have implications for the genetic diversity and conservation of western populations. Future conservation efforts should consider these findings to address potential genetic homogenization in the species.

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“…Together with past lines of evidence from tagging, histology, and reproductive hormones, an alternate hypothesis of bluefin life history was put forward: that both the eastern and western stocks exhibit maturity at 3-5 years of age, but that younger western bluefin spawn in the Slope Sea until they reach a size where the longer migration to the Gulf of Mexico is favorable (Richardson et al 2016a). The younger bluefin that are hypothesized to occupy the Slope Sea during the spawning season were estimated, as a spawning class, to have a higher biomass than the older bluefin that occupy the Gulf of Mexico, which in combination with the larval abundances in the Slope Sea led to the classification of this region as a third major spawning ground (Richardson et al 2016a(Richardson et al , 2016b.…”

Section: Introductionmentioning

confidence: 99%

Support for the Slope Sea as a major spawning ground for Atlantic bluefin tuna: evidence from larval abundance, growth rates, and particle-tracking simulations

Hernández

Richardson

Rypina

et al. 2022

Can. J. Fish. Aquat. Sci.

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Atlantic bluefin tuna (Thunnus thynnus) are commercially and ecologically valuable, but management is complicated by their highly migratory lifestyle. Recent collections of bluefin tuna larvae in the Slope Sea off northeastern United States have opened questions about how this region contributes to population dynamics. We analyzed larvae collected in the Slope Sea and the Gulf of Mexico in 2016 to estimate larval abundance and growth rates and used a high-resolution regional ocean circulation model to estimate spawning locations and larval transport. We did not detect a regional difference in growth rates, but found that Slope Sea larvae were larger than Gulf of Mexico larvae prior to exogenous feeding. Slope Sea larvae generally backtracked to locations north of Cape Hatteras and would have been retained within the Slope Sea until the early juvenile stage. Overall, our results provide supporting evidence that the Slope Sea is a major spawning ground that is likely to be important for population dynamics. Further study of larvae and spawning adults in the region should be prioritized to support management decisions.

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Reply to Safina and Walter et al.: Multiple lines of evidence for size-structured spawning migrations in western Atlantic bluefin tuna

Cited by 5 publications

References 8 publications

Unidirectional trans‐Atlantic gene flow and a mixed spawning area shape the genetic connectivity of Atlantic bluefin tuna

Unidirectional trans‐Atlantic gene flow and a mixed spawning area shape the genetic connectivity of Atlantic bluefin tuna

Unidirectional trans-Atlantic gene flow and a mixed spawning area shape the genetic connectivity of Atlantic bluefin tuna

Support for the Slope Sea as a major spawning ground for Atlantic bluefin tuna: evidence from larval abundance, growth rates, and particle-tracking simulations

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