A Review of Sarda sarda Population Structure Using the Mitochondrial Control Region as a Genetic Marker

Abstract

The Atlantic bonito (Sarda sarda) is an epipelagic and neritic marine fish that inhabits most of the Mediterranean and the Atlantic’s coasts. It is one of the most important species of small tuna in these areas due to its economical and nutritional value. Despite its importance, more genetic information about it and its population structure is required for a better understanding of this species and possible future management approaches. Here, a review on previous data belonging to the “Laboratori d’Ictiologia Genètica” of the University of Girona was made through different genetic and statistical tests. The resulting sample size consists of almost 1000 individuals of S. sarda, being to our knowledge the most extensive study of this species to date, encompassing almost all species distribution. Results demonstrate a high molecular variability for Atlantic bonito throughout studied locations and correlate with a division on two highly differentiated phylogenetic clades that have already been described in previous studies. These clades appear to be more abundant in some locations, Clade 1 in the Atlantic side of the African coast and the eastern Mediterranean and Clade 2 in the North-West Atlantic and the Western Mediterranean. Clade 1 individuals’ haplotypes are more similar between them but experience an uneven spread throughout locations, whereas Clade 2 experiences the opposite phenomenon. Population structure was clearly defined for S. sarda as North-West Atlantic, African Coast and the Mediterranean Sea. Mediterranean structure (with Portugal included) was divided in the Western Mediterranean, the Eastern Mediterranean, and Malta, these results, however, did not prove conclusive enough and more experimentation in that particular field is required, mainly increasing sample size in the Eastern Mediterranean, specifically the Marmara Sea. Evidence also challenged the hypothesis of the Strait of Gibraltar constituting a biogeographical barrier and chronological genetic drift, in spite of that, evidence in favour of geographical genetic drift was found for Atlantic bonito. To our understanding, this work could improve fishery management in the future for S. sarda due to the amount of genetical information and characterization it provides on this species alongside strong and robust evidential data to support it