A new paper published in the international peer-reviewed journal Animals has shed light on new technologies to track sea turtles during their so-called “lost years”. Led by Tony Candela, oceanographer and marine ecosystem modeler at Mercator Ocean, the study describes the results of 3 years of experiments in which scientists equipped 160 young specimens of 4 different sea turtle species with novel microsatellite tags. These experiments are part of a larger project called “Lost Years Initiative” led by Upwell, an NGO based in California.  Despite the consequent reduction in power supply and transmission capabilities that followed the miniaturisation, the study has showed that these tags can represent useful tools for tracking sea turtles in the first 10-20 years of their lives, when their small size and cryptic behaviours prove challenging to successful tracking efforts. Observation data collected through microsatellite tagging technology has the potential to complement and improve existing numerical models, further empowering researchers to learn about juvenile sea turtles and their behaviours.  

The lost years: a crucial phase in the lifespan of sea turtles 

If on one hand satellite tags are excellent tools for monitoring adult sea turtles over vast distances and extended periods, tracking young turtles remains a significant challenge. The difficulty arises especially because juvenile sea turtles have smaller carapaces and exhibit behaviours that still raise many questions within the ocean science community. This challenging phase in their development is often referred to as the “lost years”, representing a gap of information of about 10-20 years in the life of the turtle. 

After hatching, sea turtles venture into the open sea, where they face numerous threats to their survival. During this early stage of their lives, sea turtles are a few centimetres long and possess poor swimming skills, making them highly vulnerable to many predators.  

However, this phase is crucial for the overall survival of the species for several reasons. Among others, the mortality of young turtles directly reduces the number of future adults, hindering the population’s ability to reproduce. Additionally, adult turtles often settle in areas they visited during their early life stages. By tracking young turtles, scientists can gain valuable insights into their future migration paths and destinations. 

Understanding these “lost years” is therefore essential to improving marine conservation efforts. By learning more about this critical phase, researchers can help developing more effective strategies to protect sea turtles throughout their entire lifecycle. 

Satellite tagging for young sea turtles: new technology brings hope, but challenges remain 

Published on the scientific journal Animals, the paper “Novel Microsatellite Tags Hold Promise for Illuminating the Lost Years in Four Sea Turtle Species”* sheds light on a new miniaturised tracking technology that could finally allow researchers to uncover the migration patterns and environmental interactions of sea turtles in the early stages of their lives. Miniaturising tags presents numerous challenges. Factors such as robustness, hydrodynamic cost, and durability must be carefully weighed against adequate power supply and reliable data storage and transmission capabilities that effectively allow tags to fulfil their intended purpose.  

The study was conducted on young specimen of 4 different sea turtle species: juvenile loggerhead (Caretta caretta), green (Chelonia mydas), Kemp’s ridley (Lepidochelys kempii) and leatherback turtles (Dermochelys coriacea). Turtles were equipped either with solar-powered or non-solar powered tags and were then released in four different locations of the North Atlantic Ocean: Jekyll Island (GA, USA), Eastern Florida (FL, USA), Grand Cayman (Cayman Islands), and the Azores, (Portugal).  

Overall, the authors were satisfied with the transmission capabilities observed during the 3-year study. The experiments conducted provided encouraging results in terms of transmission capabilities, since the microsatellite tags deployed showed satisfying signals in terms of quality and regularity, with relatively few missed transmission windows, especially among solar-powered tags.  

The miniaturisation of tags still poses technological challenges, which the authors identified more in the robustness of the tags and their attachment than in the duration of their battery. Throughout the study, some devices stopped transmitting signals and causes may have different origins, from tag detachment due to the sea turtles’ growth or their interactions with the environment (some sea turtles scratch their carapace on rocks or the seafloor) to substantial diving habits and attacks by predators.  

According to Tony Candela, lead-author of the paper, “confirming that new microsatellite tags can provide transmission with regularity and quality, the study gives to the global scientific community insights about the benefit of new miniaturisation technologies to track young sea turtles, but low transmission power and robustness brought by the miniaturisation process still represent the main challenges.” 

Microsatellite tags and numerical models: two complementary instruments  

In the study “Dispersal of juvenile leatherback turtles from different Caribbean nesting beaches: A model study” published in 2022, Tony Candela and our expert oceanographer Philippe Gaspar, in collaboration with George L. Shillinger from the non-governmental organisation Upwell, presented a numerical model where juvenile leatherback turtles dispersed under the combined effect of Ocean currents and habitat-driven swimming movements. While the turtles passively drift with Ocean currents, they actively swim towards favourable habitats, rich in food and with suitable water temperatures. 

This numerical model complemented the data on the “lost years” of leatherback sea turtles obtained through satellite tracking technology, the authors argued. Today, as described in the new study, the successful miniaturisation of satellite tags can further improve the tracking efforts to understand the behaviour of young sea turtles and consequently feed more data into the numerical model. 
 
“Numerical models are theoretical, while microsatellite tags provide ‘real’ information. We can use numerical models to complete the gaps of satellite-based observation and, conversely, real data can validate our numerical models” explained Tony Candela, adding: “Satellite-based tracking is very useful to Mercator Ocean to calibrate numerical models and keep expanding Ocean knowledge for a healthier Ocean”. As indeed, sea turtles are bio-indicator species whose presence, absence, abundance, or health status provides information about the quality of the environment in which it lives. Essentially, if sea turtles are thriving, it indicates that the Ocean is thriving. 

Additional Resources 

• Read the full paper “Novel Microsatellite Tags Hold Promise for Illuminating the Lost Years in Four Sea Turtle Species” 

• Access the paper “Dispersal of juvenile leatherback turtles from different Caribbean nesting beaches: A model study” 
• Read our article on juvenile leatherback turtles and numerical models 
• Learn more about the “Lost Years Initiative” led by Upwell 

*This study is supported by Mercator Ocean International, Upwell and Aquarium La Rochelle