Living Together but Remaining Apart: Atlantic and Mediterranean Loggerhead Sea Turtles (Caretta caretta) in Shared Feeding Grounds

Abstract

Juvenile loggerhead sea turtles (Caretta caretta) from Atlantic nesting populations migrate into the western Mediterranean, where they share feeding grounds with turtles originating in the Mediterranean. In this scenario, male-mediated gene flow may lead to the homogenization of these distant populations. To test this hypothesis, we genotyped 7 microsatellites from 56 Atlantic individuals sampled from feeding grounds in the western Mediterranean and then compared the observed allele frequencies with published data of 112 individuals from Mediterranean nesting beaches. Mediterranean populations were found to be genetically differentiated from the Atlantic stock reaching the western Mediterranean (F(st) = 0.029, P < 0.001); therefore, the possible mating events between Atlantic and Mediterranean individuals are not sufficient to homogenize these 2 areas. The differentiation observed between these 2 areas demonstrates that microsatellites are sufficiently powerful for mixed stock analysis and that individual assignment (IA) tests can be performed in combination with mitochondrial DNA (mtDNA) analysis. In a set of 197 individuals sampled in western Mediterranean feeding grounds, 87% were robustly assigned to Atlantic or Mediterranean groups with the combined marker, as compared with only 52% with mtDNA alone. These findings provide a new approach for tracking the movements of these oceanic migrants and have strong implications for the conservation of the species.

Movement patterns of marine turtles in the Mediterranean Sea: a review

“…Since genetic flow from the Atlantic to the Mediterranean is estimated to be low, these Atlantic turtles are thought not to breed in the Mediterranean but to return to the Atlantic to breed (Carreras et al 2011). This hypothesis is corroborated by a few empirical findings: one loggerhead tagged in the western Mediterranean (Spain) was found in Cuba (Moncada et al 2010), one turtle tagged in the eastern Mediterranean (north Ionian Sea) was found on the coast of Portugal, just outside the Mediterranean (Argano et al 1992), and one turtle tagged in the central Mediterranean was found in North America (Casale et al 2013b).…”

A critical review of the Mediterranean sea turtle rescue network: a web looking for a weaver

“…The resident Mediterranean loggerhead population is genetically isolated (Carreras et al 2011) from individuals of the two Atlantic RMUs migrating to Mediterranean foraging grounds and is considered to face high threats (Wallace et al 2011). Bycatch rates are estimated at up to 200,000 loggerheads per year, leading to more than 50,000 deaths annually through direct interaction alone (Casale 2008, Lucchetti and Sala 2010, Casale 2011.…”

Mitochondrial DNA markers of loggerhead marine turtles (<em>Caretta caretta</em>) (Testudines: Cheloniidae) nesting at Kyparissia Bay, Greece, confirm the western Greece unit and regional structuring

“…The Mediterranean Sea hosts an independent regional management unit ) of loggerhead sea turtles, genetically separated from those in the Atlantic Ocean (Carreras et al 2011). Although individuals are found at sea throughout the region, regular nesting is concentrated in the eastern basin (Broderick et al 2002, Margaritoulis et al 2003, Casale and Margaritoulis 2010 with only sporadic nesting in the western basin (Delaugerre and Cesarini 2004, Bentivegna et al 2008, Tomás et al 2008, Casale et al 2012.…”