ISTS Symposium43 Program/Agenda

After hatching, sea turtles disappear into the ocean, remaining unseen until many years later when they return to natal regions where that may reproduce, but also risk interaction with fishing gear, or other coastal threats. Within the sea turtle community, this period at sea is commonly referred to as the “Lost Years”. Until recently, the very small sizes and prolonged dispersal phases of juveniles posed many challenges for the development of satellite tracking studies. Recent advances in tag miniaturization technologies and data compression algorithms have enabled researchers to undertake groundbreaking studies on the movements and dispersal of early-stage turtles. Among others, new tags equipped with solar energy cells and pressure sensors have prolonged tracking durations and provided first-ever dive data for early-stage leatherback sea turtles for periods of a few days to a few weeks.

This study harnessed an unprecedented dataset gathered since 2022 from 36 early-stage juvenile leatherbacks satellite tagged and released off eastern Florida and western Thailand. The turtles from Florida were neonates with straight carapace lengths (SCL) ranging from 7.4-9.7 centimeters and weights ranging from 75-146 grams. The turtles from Thailand were considered juveniles with SCLs ranging from 22.0-36.0 centimeters and weights ranging from 1,075-3,857 grams. Microsatellite tags, manufactured by Lotek Wireless Inc., were attached using neoprene or elastane fabric pads secured with suture anchors and adhesives. The smallest turtles were equipped with K4H 130B tags (2.9g; 26x14.7x7.7mm), while the larger turtles used K4G 132A tags (12.1g; 47.7x30x21.9mm). Tags attachment methods and performances were detailed in Candela et al. (2024).

Tag-derived data (e.g., location data and vertical behavioral metrics), including time distribution at depth, daily maximum depth, and time underwater, present an opportunity to examine intricate relationships between diving behavior and other variables. We analyzed tracking durations, carapace lengths, physical variables of the dynamic marine environment of the Gulf Stream and within the Andaman Sea (e.g., water temperature, significant wave height, chlorophyll-a concentration), using a suite of remotely sensed and modeled data.

Despite the apparent limitations due to reduced tracking durations, the findings derived from this novel dataset reveal that Florida neonates mostly (>90%) remained in the upper 10 meters of the ocean but were capable of much deeper dives to 75 meters or more. In contrast, the larger and older Thailand juveniles, spent more time at depth and reached daily depths near 100 meters, with an impressive 184 meters dive recorded.

Our analysis revealed for both size classes clues to progressive adaptations for open ocean life (vertical behavior changes over time elapsed since release), optimization of swimming conditions (behavior shifts apparently linked to changes in the sea state), and possibly thermoregulatory behaviors, better marked in the large turtles released off Thailand. Our study promises to offer new insights into adaptative strategies and survival mechanisms employed by early-life stage turtles, effectively demystifying the earliest phases of the "Lost Years". This research informs sea turtle conservation and management by providing guidelines for reducing bycatch in fisheries or identifying critical habitats requiring protection during poorly understood early life stages.

This work presents the preliminary results of an innovative approach to monitor captive-reared loggerhead turtles (Caretta caretta) after their release into the ocean, to evaluate the habitats used and the influence of oceanographic parameters. The two loggerhead turtles included in the study were reared under similar controlled conditions for 14 years, under exhaustive and regular monitoring. After their release in Cofete beach, Fuerteventura (Canary Islands, Spain), both turtles, tracked with satellite devices equipped with sensors (temperature and pressure), explored two different habitats, the open ocean in the North Atlantic, and coastal environments in Western Africa, both characterized by pronounced thermal gradients and biologically productive upwelling systems. The combination of telemetry data, real-time data collected by sensors (temperature and deep), and remotely-sensed environmental variables—such as sea surface temperature, chlorophyll-a and satellite altimetry- enabled a detailed analysis of their habitat use, diving patterns, and reliance on ocean currents for navigation, revealing how these behaviors are influenced by the oceanographic context. The findings highlight the value of animal-borne telemetry sensors to gather specific insights critical for conservation strategies and efforts worldwide for this endangered species.

After establishing a local population of juvenile green sea turtles through the identification of individual head scale patterns in a project started in June 2020, further research is being conducted examining their behaviors. Starting in September 2024, we began quantifying behavior through observations at Camachee Cove Marina and Conch House Marina, located in St. Augustine, Florida along the Intracoastal Waterway. Observations were recorded regarding feeding, time spent in the area, and social behavior as individuals grazed along the floating docks of marinas. Green sea turtles were located in the marina and given one minute to acclimate to human presence. Then, we observed the turtle from the floating docks for 10 minutes and recorded the number of breaths, interaction with other turtles, swimming behavior, and feeding using tallies. Social behavior with other juveniles includes pursuing, biting, feeding adjacently, circling, etc. Thus far, the primary behavior observed is feeding: 50% of the time feeding behavior is observed, turtles are grazing along floating docks. However, they are also seen feeding on floating material and growth on boats. From our observations, we calculated that they take one breath about every 2 minutes. Of all our turtle encounters, 29.4% of the time the sea turtles were observed in groups of at least two turtles, and the dominant group behavior observed was pursuing another turtle. Further data is being collected as this is an ongoing project and these are the preliminary findings. This information can help better understand juvenile green sea turtle behavior and their usage of man-made structures in marinas.

Juvenile green sea turtles (Chelonia mydas) inhabit sabellariid worm rock reefs along Florida’s southeastern coast. These shallow nearshore reefs provide foraging habitat and shelter for juvenile green turtles until they approach maturity and migrate to deeper foraging grounds. Artificial reefs are common along Florida’s coast and provide similar resources (food and shelter), however there is limited research on how green turtles use these structures compared to natural reefs. This study examines green turtle utilization of a 500-meter artificial breakwater constructed in 2020 to mitigate shoreline erosion near the St. Lucie Nuclear Power Plant in St. Lucie County, Florida. This shallow breakwater mirrors the shelter and foraging opportunities of the adjacent natural reefs. From 2020 to 2023, we conducted 13 Distance Sampling surveys using five fixed transects along the breakwater and a natural reef 1 km south of the breakwater, a known juvenile green turtle habitat. A total of 264 turtles were observed during these surveys with only 15 (5.7%) recorded at the breakwater site. Despite this artificial structure’s proximity to an established green turtle foraging area at the worm rock reef site, the breakwater exhibited significantly lower turtle densities. This suggests that, even after three years post-deployment, the artificial habitat may not fully meet the ecological needs of juvenile green turtles. The lack of observed residency or increase in turtle abundance at the breakwater, despite anticipated food availability as the structure matured, contrasts with findings from other artificial structures like fishing piers and jetties, where turtle presence implies an attractant effect. In this case, the physical presence of the artificial structure alone appears insufficient to draw turtles at a comparable rate to the nearby natural reef habitat.

Understanding the spatial dynamics of marine animals is essential for developing effective conservation strategies, including the design of marine protected areas (MPAs). Spatial use by marine animals changes over time, influenced by life stages, habitat variability, and individual plasticity. The hawksbill turtle (Eretmochelys imbricata), classified as critically endangered in the IUCN RedList, exemplifies a species with complex spatial ecology.

Between 2015 and 2023, 20 juvenile hawksbill turtles (mean CCL (±SD) = 56.1 ± 9.9 cm, range 41.0 - 71.0 cm) were tagged at five contrasted neritic sites around Reunion Island in the Southwest Indian Ocean. The tags recorded precise locations at decametric-level resolution over extended periods (mean = 7 months; SD = 4 months). Notably, seven of these tags were recovered (35 %), yielding additional location data beyond those received via the Argos satellite network (1.5–2.5 times more locations). The recovery of tags also allowed to access high temporal resolution records (3–10-second intervals) of wet/dry switch activity, a proxy for surface time, which has not been previously exploited in studies. Our analyses focused on daily and seasonal variations in spatial use, home range, surface time patterns, and nocturnal clustering, considering individual characteristics (size and site). We addressed three key questions: (1) How does spatial use vary on a daily scale? (2) How do movements and spatial use evolve over longer temporal scales (monthly to seasonal)? (3) What are the advantages and limitations of Fastloc tracking in ecological studies?

Juvenile hawksbills exhibited site-specific variation in home range, influenced by habitat type, particularly the presence of reef platforms. Temporal stability in home range indicated consistent habitat preferences across seasons. However, wet/dry switch data revealed distinct seasonal basking behaviors, with increased surface time during early mornings in winter, likely related to thermoregulation (sea temperature range: 23–28°C). Nocturnal clustering showed that individuals favored a limited number of night sites, with strong preferences for sites closest to their daily core habitat. Additionally, more than half of the turtles undertook exploratory movements (1–5 km) beyond their home ranges, generally returning within the same day. Two individuals demonstrated long-distance migrations (500 km and 2,000 km), highlighting long-range habitat shifts during immature stages. The recovery of tags also enabled an evaluation of the relationship between data volume and home range quality, identifying a minimum number of locations required for accurate home range estimation and showing how daily surface time patterns influence GPS location volume. These findings enhance our understanding of juvenile hawksbill spatial ecology, providing critical insights to inform conservation strategies for Reunion Island and the broader region.

Like most species of hard-shelled sea turtles, oceanic post-hatchling hawksbill turtles return to nearshore environments as small juveniles. Upon arrival, they distinguish themselves from the other species by maintaining a close association with coral reef habitats, in which they are believed to play an important ecological role. Since hatchling dispersal patterns throughout the Caribbean basin are largely dictated by oceanic currents, mixed-stock foraging aggregations of juveniles are a common outcome. In some cases these aggregations can be located quite a distance from the turtles’ points of origin. It has been known for some time that an aggregation of primarily immature hawksbill turtles resides on a roughly 500 km long barrier reef system that lines Florida’s SE coast. Previous investigations have characterized a portion of the population in the northern part of the reef system that was dominated by larger individuals (mean straight carapace length 56.6cm), but were unable to identify recruitment sites for small juveniles first arriving from the oceanic environment. To better understand the abundance, distribution, and dispersal patterns of the region’s neonate hawksbills, approximately 300 hours of in-water surveys were conducted across 70 reef sites in The Florida Keys National Marine Sanctuary (FKNMS) from Key Largo through the Marquesas Keys. The Sanctuary protects over, 7,500 sq. km of marine habitats in the waters of Monroe County, Florida, including the southernmost terminus of the SE Continental Reef Tract. Over a ten-year period, 61 hawksbill turtles were hand captured, weighed, measured, and sampled, in some cases multiple times. A combination of Restriction Site-Associated DNA sequencing (RADSeq) and mitochondrial DNA (mtDNA) analyses were used to identify the likely origins of each turtle and to describe the demographic history, gene flow, and effects of female-mediated dispersal on the population structure of Florida’s hawksbill aggregation. Additionally, we attempted to link genetic origin to fine-scale variations in morphology, growth, and distribution among individuals in the study. Based on the mean body size (38.1 ± 10.2 cm SCL) of the turtles found on the shallow reefs of FKNMS, we hypothesize that the southern portion of the Reef Tract represents a likely entry point to Florida’s reef system for successive generations of young hawksbills that originate from many distinct source rookeries around the Caribbean, particularly nesting beaches along the east coasts of central and south America. Though logistically difficult to obtain, particularly over large, functionally meaningful spatiotemporal ranges, data concerning the relative abundance, habitat use, growth rates, and spatial ecology of immature turtles are vitally important to inform overall recovery efforts.