Natal homing in juvenile loggerhead turtles (Caretta caretta)

Abstract

Juvenile loggerhead turtles (Caretta caretta) from West Atlantic nesting beaches occupy oceanic (pelagic) habitats in the eastern Atlantic and Mediterranean, whereas larger juvenile turtles occupy shallow (neritic) habitats along the continental coastline of North America. Hence the switch from oceanic to neritic stage can involve a trans-oceanic migration. Several researchers have suggested that at the end of the oceanic phase, juveniles are homing to feeding habitats in the vicinity of their natal rookery. To test the hypothesis of juvenile homing behaviour, we surveyed 10 juvenile feeding zones across the eastern USA with mitochondrial DNA control region sequences (N = 1437) and compared these samples to potential source (nesting) populations in the Atlantic Ocean and Mediterranean Sea (N = 465). The results indicated a shallow, but significant, population structure of neritic juveniles (PhiST = 0.0088, P = 0.016), and haplotype frequency differences were significantly correlated between coastal feeding populations and adjacent nesting populations (Mantel test R2 = 0.52, P = 0.001). Mixed stock analyses (using a Bayesian algorithm) indicated that juveniles occurred at elevated frequency in the vicinity of their natal rookery. Hence, all lines of evidence supported the hypothesis of juvenile homing in loggerhead turtles. While not as precise as the homing of breeding adults, this behaviour nonetheless places juvenile turtles in the vicinity of their natal nesting colonies. Some of the coastal hazards that affect declining nesting populations may also affect the next generation of turtles feeding in nearby habitats.

Assignment of nesting loggerhead turtles to their foraging areas in the Northwest Atlantic using stable isotopes

“…The use of foraging grounds adjacent to natal nesting areas has been suggested previously for large juvenile loggerheads in the NWA by mixed stock analysis of mitochondrial DNA haplotypes for aggregations of juveniles along the U. S. east coast (Bowen et al 2004). The stable isotope approach used in our study allowed us to sample adult female loggerheads at various nesting areas-where they are more easily accessiblewithout having to sample turtles at the different foraging areas to reveal a similar pattern of foraging ground segregation.…”

Lost at sea: genetic, oceanographic and meteorological evidence for storm-forced dispersal

“…Our focal species, the loggerhead sea turtle (Caretta caretta), is one of the most well-studied of sea turtle species. After emerging from nests, hatchling loggerhead sea turtles enter the sea and the juveniles then spend several years in the open ocean, followed by a transition from pelagic to neritic habitats when individuals are around 40-50 cm in size [23], although exceptions to this general life cycle have been found [24]. Pelagic juveniles are therefore of relatively small size, and still subject to any oceanographic and meteorological forces that may alter their direction of dispersal in the open seas.…”

Population structure and conservation implications for the loggerhead sea turtle of the Cape Verde Islands

“…While North Atlantic and Mediterranean loggerhead turtles are a relatively well-studied systems in population genetics and connectivity research Encalada et al 1998;Laurent et al 1998;Bowen et al 2004Bowen et al , 2005Carreras et al 2006Carreras et al , 2007Lee 2008), key gaps in sampling still remain. The second largest nesting aggregation of the globally endangered loggerhead sea turtle (IUCN 2007) in the Atlantic Ocean is found at the Cape Verde Islands, which is also the only major rookery in Western Africa for this species.…”

“…However, loggerhead turtles born at Florida (USA) rookeries are known to inhabit the pelagic zone of the North Atlantic gyre system for several years (Carr 1986). Next, an unknown proportion of juvenile turtles recruits to neritic habitats closer to their natal beaches, a behaviour known as juvenile natal homing (Bolten 2003;Bowen et al 2004), while others continue to feed in the high seas (Musick and Limpus 1997). Both pelagic and neritic feeding grounds are usually ''mixed stocks'' drawn from various different rookeries Laurent et al 1998;Bowen et al 2004;Bass et al 2004;Carreras et al 2006).…”

“…Next, an unknown proportion of juvenile turtles recruits to neritic habitats closer to their natal beaches, a behaviour known as juvenile natal homing (Bolten 2003;Bowen et al 2004), while others continue to feed in the high seas (Musick and Limpus 1997). Both pelagic and neritic feeding grounds are usually ''mixed stocks'' drawn from various different rookeries Laurent et al 1998;Bowen et al 2004;Bass et al 2004;Carreras et al 2006). At sexual maturity, some adults switch from subadult to adult foraging habitats (Bolten 2003).…”