First Satellite Tracks Of South Atlantic Sea Turtle ‘Lost Years’: Seasonal Variation In Trans-Equatorial Movement

In the South Atlantic Ocean, few data exist regarding the dispersal of young oceanic sea turtles. We characterized the movements of laboratory-reared yearling loggerhead turtles from Brazilian rookeries using novel telemetry techniques, testing for differences in dispersal during different periods of the sea turtle hatching season that correspond to seasonal changes in ocean currents. Oceanographic drifters deployed alongside satellite-tagged turtles allowed us to explore the mechanisms of dispersal (passive drift or active swimming). Early in the hatching season turtles transited south with strong southward currents. Late in the hatching season, when currents flowed in the opposite direction, turtles uniformly moved northwards across the Equator. However, the movement of individuals differed from what was predicted by surface currents alone. Swimming velocity inferred from track data and an ocean circulation model strongly suggest that turtles’ swimming plays a role in maintaining their position within frontal zones seaward of the continental shelf. The long nesting season of adults and behaviour of posthatchlings exposes young turtles to seasonally varying ocean conditions that lead some individuals further into the South Atlantic and others into the Northern Hemisphere. Such migratory route diversity may ultimately buffer the population against environmental changes or anthropologic threats, fostering population resiliency

Effects of temperature and demography on the phenology of loggerhead sea turtles in Brazil

Climate change affects the spatial distribution and timing of seasonal events (i.e. phenology) of species. The phenology of ectotherms, such as sea turtles, is strongly influenced by rising temperatures associated with climate change, since most of their life history traits are dependent on temperature. Most studies on the phenology of sea turtles report changes in the duration and an earlier onset of the nesting season in response to warmer temperatures. However, inconsistencies remain among and within species in the direction and the strength of their responses. Some authors suggested that sea turtles’ nesting phenology is triggered by a cue perceived before migration, whereas others suggested that environmental conditions at nesting sites are more important. Here, using nesting data collected over 26 nesting seasons, we tested whether the nesting phenology of loggerhead turtles Caretta caretta in Brazil is triggered by either temperature or demography, and if this occurs at nesting or foraging sites. We found that the onset of the nesting season was triggered by temperature at an important foraging site, while the duration of the nesting season was linked to the size of the nesting population. Our results suggest that loggerhead turtles respond to an environmental cue perceived at foraging sites before they start migrating. This finding will allow future research to assess the vulnerability of sea turtles in the context of climatic change by considering environmental conditions at foraging sites

Spatio-temporal variation in the incubation duration and sex ratio of hawksbill hatchlings: implication for future management

Climate change poses a unique threat to species with temperature dependent sex determination (TSD), such as marine turtles, where increases in temperature can result in extreme sex ratio biases. Knowledge of the primary sex ratio of populations with TSD is key for providing a baseline to inform management strategies and to accurately predict how future climate changes may affect turtle populations. However, there is a lack of robust data on offspring sex ratio at appropriate temporal and spatial scales to inform management decisions. To address this, we estimate the primary sex ratio of hawksbill hatchlings, Eretmochelys imbricata, from incubation duration of 5514 in situ nests from 10 nesting beaches from two regions in Brazil over the last 27 years. A strong female bias was estimated in all beaches, with 96% and 89% average female sex ratios produced in Bahia (BA) and Rio Grande do Norte (RN). Both inter-annual (BA, 88 to 99%; RN, 75 to 96% female) and inter-beach (BA, 92% to 97%; RN, 81% to 92% female) variability in mean offspring sex ratio was observed. These findings will guide management decisions in Brazil and provide further evidence of highly female-skew sex ratios in hawksbill turtles

The effıcıency of phenologıcal shıfts to buffer the effects of warmıng temperatures on hatchıng success and sex ratıo of loggerhead sea turtles

39th Annual Symposium on Sea Turtle Biology and Conversation, 18-23 February 2019, Charlston, SC, USA

The climatic debt of loggerhead sea turtle populations in a warming world

Phenological shifts, by initiating reproductive events earlier, in response to advanced seasonal warming is one of the most striking effects currently observed in wild populations. For sea turtles, phenological adjustment to warming conditions could be the most effective short-term adaptation option against climate change. We calculated future phenological changes required in seven important loggerhead (Caretta caretta) nesting populations to continue achieving a high hatching success and a sex ratio that lies within current ranges. Considering temperature-mediated phenological changes, we found that most populations (six out of seven) will not be able to keep pace with a warming climate. Under an optimistic climate warming scenario (RCP4.5), these populations will face a climatic debt, that is, a difference between required and expected phenological changes, and warming will substantially reduce hatching success and induce a feminization of hatchlings, which may jeopardize their reproductive sustainability. Our approach offers the possibility to quantify the efficiency of phenological shifts in oviparous reptiles by considering physiological, developmental and phenological processes