TRANSATLANTIC DEVELOPMENTAL MIGRATIONS OF LOGGERHEAD SEA TURTLES DEMONSTRATED BY mtDNA SEQUENCE ANALYSIS

Abstract

Molecular markers based on mitochondrial (mt) DNA control region sequences were used to test the hypothesis that juvenile loggerhead sea turtles (Caretta caretta) in pelagic habitats of the eastern Atlantic are derived from nesting populations in the western Atlantic. We compared mtDNA haplotypes from 131 pelagic juvenile turtles (79 from the Azores and 52 from Madeira) to mtDNA haplotypes observed in major nesting colonies of the Atlantic Ocean and Mediterranean Sea. A subset of 121 pelagic samples (92%) contained haplotypes that match mtDNA sequences observed in nesting colonies. Maximum likelihood analyses (UCON, SHADRACQ) estimate that 100% of these pelagic juveniles are from the nesting populations in the southeastern United States and adjacent Yucatan Peninsula, Mexico. Estimated contributions from nesting populations in south Florida (0.71, 0.72), northern Florida to North Carolina (0.19, 0.17), and Quintana Roo, Mexico (0.11, 0.10) are consistent with the relative size of these nesting aggregates. No contribution was detected from nesting colonies in the Mediterranean (Greece) or South Atlantic (Brazil), although samples sizes are insufficient to exclude these locations with finality. The link between west Atlantic nesting colonies and east Atlantic feeding grounds provides a more complete scientific basis for assessing the impact of subadult mortality in oceanic fisheries. Demographic models for loggerhead turtles in the western Atlantic can now be improved by incorporating growth and mortality data from juvenile turtles in pelagic habitats. These data demonstrate that the appropriate scale for loggerhead turtle conservation efforts is vastly larger than the current scale of management plans based on political boundaries.

The geomagnetic environment in which sea turtle eggs incubate affects subsequent magnetic navigation behaviour of hatchlings

“…This direction is consistent with the migratory path of the turtles in this geographical area [9,10]. …”

“…Turtles initially swim eastward to the Gulf Stream current, where many become entrained in the North Atlantic Subtropical Gyre, the circular current system that flows around the Sargasso Sea [8,9]. Many loggerheads migrate across the Atlantic and back before eventually returning to the North American coast [9,10].…”

Conservation implications of complex population structure: lessons from the loggerhead turtle (Caretta caretta)

“…(1998). Corresponding information for feeding populations is available in Bolten et al . (1998), Bowen et al .…”

“…This migratory marine reptile has two distinct juvenile stages, the first being an oceanic stage after hatching (Carr 1987; Bolten 2003a). For post‐hatchling turtles departing the nesting beaches of the northwestern Atlantic, this oceanic habitat extends from the Grand Banks (Newfoundland, Canada) to the Azores and Madeira, as well as the Mediterranean Sea (Bolten et al . 1998; Laurent et al .…”

“…In order to resolve the conservation implications of complex population structure, here we assemble loggerhead genetic data from three previously published surveys of North Atlantic populations, and an unpublished thesis. These studies include mtDNA data for oceanic juveniles ( N = 455: Bolten et al . 1998; LaCasella et al .…”