Genetic and growth profiles of three specimens of swordfish (Xiphias gladius) tagged and recaptured in the North Atlantic

This paper presents an analysis of the genetic and growth patterns of three swordfish specimens (two males and one female) tagged with traditional tags and later recaptured over a period of time ranging from 2.7 to 5.4 years. Two of these specimens were tagged and recaptured in the NW Atlantic, while the third individual was tagged and recaptured in the NE Atlantic. These three specimens were genotyped for four micro-satellite loci and were analysed together with additional genotyped specimens from Atlantic and Mediterranean areas using a Bayesian cluster analyses. The results suggest that the three recaptured swordfish have a genetic profile that is characteristic of the Atlantic. The growth patterns were seen to differ in two of the specimens analysed (male and female): the male was assumed as a single ring pattern, while the female was assumed as a mostly double ring pattern. The age estimation of these two specimens according to these premises could be accommodated to previous growth studies. The third specimen which is known to be a male at least 6 years of age, tagged and recaptured in the NW Atlantic, was not possible to accommodate to previous growth studies. The examination of genetic data in combination with tagging-recapture information may facilitate the study of aspects related to individual and stock specific growth and elucidate the patterns of ring formation on the hard parts (spines). It would be advisable to enhance the tagging-recapture protocols of swordfish and to include the routine sampling of tissues and hard parts in all the recaptures made by the different fleets.