The journey a hatchling undertakes after entering the ocean is a long and dangerous one full of challenges and a lot of travelling. It all starts when hatchlings emerge from their eggs in the sand and then head to sea. They tend to return to near-shore environments as young juveniles after approximately 7 years leaving us with a large gap known as the lost years. Tracking these little hatchlings is a difficult task and for a long time little was known regarding where they go and how they travel. However, technology has now allowed us to improve our understanding of movement patterns and mechanisms hatchlings utilise in their early life stages.
Even though many of the studies primarily focus on the Atlantic population, some work has been done on hatchling movements in the Mediterranean. Because young turtles have limited swimming capabilities distribution simulations primarily see them as passive drifters relying on ocean currents for movement. These simulations have deduced that hatchlings from the Levantine and South-Central Mediterranean tend to remain in the same area whereas Ionian hatchlings disperse into other areas such as into the Adriatic and the South-Central Mediterranean. Recent findings have however shown that hatchling trajectories can differ from the simulations, highlighting the importance of even limited directional swimming paired with other environmental conditions.
In ocean basins like the Atlantic it was long thought that gyres were the main route of transport for hatchlings and juveniles. Nevertheless, telemetry studies have revealed that young turtles do often leave the gyres aggregating in areas with a lot of algae mats which are used as a shelter. This further gave rise to the thermal niche hypothesis as the temperature in these algal mats differs from that of the surrounding. By associating in a warmer environment, hatchlings are able to increase their rate of feeding and consequently their growth rates making them less susceptible to predators.
In conclusion, we do not know the precise location of all the nursery grounds, neither how exactly hatchlings get there. In order to determine a hatchlings/young juveniles’ trajectory, further telemetry studies that assess the importance of a range of different factors have to be performed which will eventually allow us to ‘find’ the lost years.
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Abalo-Morla, S., Marco, A., Tomás, J., Revuelta, O., Abella, E., Marco, V., Crespo-Picazo, J., et al. 2018. Survival and dispersal routes of head-started loggerhead sea turtle (Caretta caretta) post-hatchlings in the Mediterranean Sea. Marine Biology. 165(3).
Casale, P. and Mariani, P., 2014. The first ‘lost year’ of Mediterranean sea turtles: dispersal patterns indicate subregional management units for conservation. Marine Ecology Progress Series, 498: 263-274.
Mansfield, K.L., Wyneken, J., Porter, W.P. and Luo, J. 2014. First satellite tracks of neonate sea turtles redefine the ‘lost years’ oceanic niche. Proceedings of the Royal Society B: Biological Sciences, 281.