Navigation and seasonal migratory orientation in juvenile sea turtles

Abstract

Juvenile loggerhead and green turtles that inhabit inshore waters of North Carolina, USA undertake long seasonal migrations, after which they often return to specific feeding areas. In addition, juvenile turtles are capable of homing to specific sites after being displaced. As a first step towards investigating the navigational mechanisms that underlie these movements, juvenile turtles were captured in coastal waters of North Carolina and displaced 30-167·km along circuitous routes while deprived of visual cues. At the testing location, turtles were tethered in a circular arena and permitted to swim while their orientation was monitored. Between May and September, when juvenile loggerhead and green turtles inhabit feeding areas along the North Carolina coast, turtles oriented in directions that corresponded closely with the most direct route back to their capture locations. During October and November, however, both loggerhead and green turtles oriented southward, a direction consistent with the migratory paths of turtles beginning their autumn migration. The results demonstrate for the first time that both homing and migratory orientation can be elicited in juvenile turtles under laboratory conditions in which orientation cues can be readily manipulated. In addition, the results provide evidence that juvenile loggerheads can assess their position relative to a goal using local cues available at the test site and are therefore capable of map-based navigation.

Use of multiple orientation cues by juvenile loggerhead sea turtlesCaretta caretta

“…Thus, the turtles used in our experiments probably included individuals motivated to move toward different seasonally appropriate destinations rather than toward a single goal. Recent experiments have confirmed that the orientation behavior of juvenile turtles tested in arenas does indeed change seasonally; turtles tested during summer oriented toward the locations where they were captured (presumably in an effort to return to their feeding areas), whereas turtles captured during the autumn migratory season swam predominantly southward (Avens, 2003; L. Avens and K. J. Lohmann, manuscript in preparation).…”

“…Under many circumstances, juvenile turtles displaced from their feeding grounds return to the areas where they were captured (Ireland, 1980;Musick and Limpus, 1997;Avens et al, 2003). Analyses of the directional headings of the 10 groups of turtles during their Day 1 trials suggested that many turtles attempted to home while tethered in the arena.…”

Green turtle Chelonia mydas mixed stocks in the western South Atlantic, as revealed by mtDNA haplotypes and drifter trajectories

“…Animals may transit be tween foraging areas depending on factors such as variations in current intensity, water temperature and food availability (Musick & Limpus 1997, Bass et al 2006). Avens & Lohmann (2004) studied displacements of juvenile green turtles in North Carolina, and reported that animals presented seasonal movements in order to stay in warmer waters. This behavior has also been observed in green turtles tagged in Uru guay, which display a pattern of in habiting lower latitudes in Brazil during colder periods (López-Mendilaharsu et al 2006).…”

Magnetic maps in animals: nature's GPS

“…Such turtles often show fidelity to specific foraging areas, returning to them reliably after long, seasonal migrations or experimental displacements (Ireland, 1980;Avens et al, 2003;Avens and Lohmann, 2004). How the turtles return to these foraging areas was investigated using juvenile green turtles Chelonia mydas captured in their feeding grounds near the central east coast of Florida.…”