As climate change progresses, sea turtle nesting beaches are warming and producing increasingly more female-skewed hatchling sex ratios. Whether or not this translates to lower reproductive success depends on the breeding ecology of males. However, given the difficulty in finding and sampling males, the role of males in sea turtle reproductive dynamics is not yet well understood. Specifically, the mating function, or the relationship between the operational sex ratio (the proportion of adults that are available to breed that are male) and reproductive success (in this case, defined as emergence success), is unknown. A two-sex, age-based population dynamics model was constructed to explore the survival probabilities of a green turtle (Chelonia mydas) population within 3 lifespans (255 years) into the future, under different temperature change scenarios and with different mating functions. Nesting and genetic data collected across three and a half field seasons from Fernando de Noronha, Brazil were incorporated into the model, with other demographic parameters borrowed from previous studies on the same population and filled in with data from the geographically closest population as needed. Preliminary results show that as changes in incubation temperatures increase, persistence requires that individual males are able to fertilize a larger proportion of breeding females. Furthermore, microevolution of the thermal reaction norm is unlikely to sufficiently increase the probability of population persistence for moderate to severe thermal scenarios. These simulations, when paired with ecological and genetic analyses, will help to bound realistic sea turtle mating functions and further quantify the probability of population persistence in a changing climate, while informing research and conservation priorities.

Temperature has a profound influence on various life history parameters across taxonomic groups. In sea turtles, which exhibit temperature-dependent sex determination, rapidly changing global temperature ranges pose a significant threat to the viability of populations by producing heavily female-biased sex ratios. Globally, population sex ratios of sea turtles have been studied extensively, enabling the tracking and prediction of changes through decades. However, the east coast population of olive ridleys in India, considered genetically significant, remains grossly understudied. In this study, we modeled the relation between nest temperature and sex ratios in the region from primary data on hatchling sex at Rushikulya from 2008-2023 based on the histology of ~1200 hatchlings from >100 nests. We then predicted historical sex ratios at arribadas for the past 50 years at two important mass nesting sites, Gahirmatha and Rushikulya. Additionally, we forecasted future sex ratios for arribadas with varying phenology under different models of climate change.

Our results indicate that at Rushikulya, the primary sex ratios are female biased (71%), with occasional years producing a high proportion of male hatchlings (65%) across the season. The pivotal temperature was found to be 29.4℃, established by modeling hatchling sex ratios and nest temperatures. The results of the historical analysis indicate a progressive female bias in sex ratios at arribadas in Gahirmatha over the past four decades, while sex ratios remain stable but slightly female biased in Rushikulya. Notably, we also observed a shift in nesting phenology, with the occurrence of arribada increasing towards warmer months in Gahirmatha over the last 40 years. For future predictions, we used climate models under 4 different scenarios (SSP 126, 245, 370, and 585) to predict potential sex ratios at two-decade intervals until 2100. The predicted climate warming, coupled with a potential shift in arribada phenology, predicts a strong feminization of the population under the business-as-usual and extreme scenarios at all timescales in the future. Therefore, while the population is currently stable or increasing, climate change still poses a considerable threat, especially given that there are no beaches further North along this coast for future colonization.

Trends in abundance are generally the most straightforward indicators of population status, but robust estimates can be difficult to obtain. When clear information on abundance is elusive, other demographic indicators may provide key insight into population trajectories. Here, we present long-term patterns in size structure, i.e. body size distributions, for a green turtle (Chelonia mydas) foraging aggregation in the eastern North Pacific. We use measures of carapace length collected during 1990–2023 to make inferences into coincident population dynamics at San Diego Bay, California, USA. Our data show that mean body size increased over roughly the first two decades of monitoring, but has declined since. Finer exploration of size distributions through time suggests that this recent trend is explained by increases in the recruitment of young individuals. Green turtle foraging populations in California largely originate from multiple source rookeries in Mexico, and we relate patterns in foraging size structure to trends in nesting abundance at the most significant rookery known in the Eastern Pacific: Colola Beach, Michoacán, Mexico. Together, these lines of evidence (foraging size structure and nesting trends) point to a notable rebound for a regional population at risk of collapse as recent as two decades ago. Given an apparent increasing population trajectory in Southern California, we explore local historical context to attempt to compare current population status to an uncertain, pre-Anthropocene baseline. We ask: Are foraging abundances returning to states exhibited before human harvesting, or are we witnessing completely new patterns? Available historical records, such as news articles and archaeological evidence from indigenous peoples, do not provide any evidence for a significant presence of green turtles. Thus, we conjecture that we may be entering “new territory,” with green turtles showing the potential to reach levels never before seen in California.

Rekawa rookery, located on the south coast, is the largest sea turtle rookery in Sri Lanka, visited by all five species that nest in Sri Lanka (Green turtle, Leatherbacks, Loggerheads, Hawksbills and Olive ridleys). The in-situ nest protection programme at Rekawa was initiated in September 1996, and nesting data was collected throughout the year along a 2km stretch of beach. Nine hundred seventy-three egg clutches were observed from September 1996 to August 1997, and only 375 egg clutches were observed from September 2009 to August 2010 (about 96% were green turtles), suggesting a >60% decline in the turtle population nesting at Rekawa. At least three decades before 1996, we suspect nearly all freshly laid eggs in Rekawa were harvested for human consumption. Therefore, we presume that there has been little or no recruitment into the Rekawa population for at least 30 years before 1996. However, there were 1,730 egg clutches (Green - 1,690, Olive ridley - 40) recorded at the Rekawa beach in 2020, 1,538 egg clutches were recorded (Green - 1,511, Olive ridley – 26, Leatherback - 1) in 2021and 1,771 egg clutches in 2022 (Green - 1,698, Olive ridley – 72, Leatherback - 1). This is over 70% increase in egg clutches compared to 1996/1997 and over 400% increase compared to 2009/2010. So, it can be concluded that the Rekawa nesting turtle population remarkably increased compared to the population in the late nineties. If the turtle hatchlings released after 1996 represented a restart of turtle recruitment, we suspect they began returning to Rekawa as nesting adults.

Introduction & Objectives:
Declines in the average body size of nesting sea turtles of various species have been documented around the world, with the cause attributed to a combination of ecological and demographic factors. Declines in ocean productivity may cause slower growth rates possibly resulting in smaller size at onset of sexual maturity. Conservation efforts may lead to larger nesting populations comprising higher proportions of smaller neophytes. More turtles might also increase competition for food. Our study examines long-term trends in body size of nesting hawksbills and the demographic factors that may be responsible for observed trends.

Methods: Daily beach surveys incorporating near-saturation flipper tagging, curved carapace measurements (CCL), and egg counts have been conducted at Cousine Island since 1992. We calculated the proportion of neophyte versus remigrant turtles each year, the relationship between CCL and clutch size, adult growth rates, and temporal trends in both body size (CCL) and nesting activity. We included CCL data collected at adjacent Cousin Island prior to 1998 in our analyses.

Results: Mean annual CCL declined significantly at 0.05 cm^-yr between 1974 and 2022 when data from both Cousine and Cousin were considered. Considering Cousine data alone during 2002-2022, however, the downward trend in CCL of 0.02 cm^-yr in the general population was not statistically significant. When neophyte and remigrant turtles were considered separately, neophyte CCL declined significantly at 0.19 cm^-yr, while remigrant CCL increased significantly at 0.12 cm^-yr. Clutch size was positively correlated with CCL, and annual egg clutch numbers increased significantly during 1992-2002. The number of neophyte females in the population fluctuated over time, while that of remigrant turtles increased during the same period. The mean annual CCL growth rate of individual mature females breeding at Cousine was 0.18 cm^-yr.

Conclusions: We conclude that at Cousine Island the declining trend in CCL over time was caused by a continuous decline in mean CCL of neophyte females over time, combined with increasing numbers of smaller neophytes. Declines in CCL of neophyte females are likely to produce smaller clutches in those individuals but this negative impact on reproductive output is appears to be offset by the benefits to the population that legal protection affords turtles at Cousine Island and the wider Seychelles. Strict conservation measures enable neophyte females not only to survive their first nesting season, but also to return to breed as remigrant females during multiple subsequent nesting seasons. As they age, the females get bigger and produce larger egg clutches. Over time, with reduced mortality, the numbers of remigrant females that nest each year tend to increase along with the contribution individual remigrant females make to reproductive output, even though neophyte body size is in decline.