Sea Turtle Nests Research Articles

Size scaling of sea turtle reproduction may reconcile fundamental ecology and conservation strategies at the global scale

AbstractAimThe body size of marine megafauna can influence population dynamics because larger females have disproportionally greater reproductive output. We explored how this size scaling relationship can affect predictions of population size structure in nesting sea turtles by combining a phylogenetically controlled meta‐analysis with a long‐term field nesting survey.LocationGlobal (meta‐analysis) and Malaysia (field survey).Time periodPresent.Major taxa studiedSea turtles.MethodsWe extracted body size and reproductive parameters of all sea turtle species from the literature and estimated the reproductive‐energy output using allometric models. We then examined the relationship between body size and the proportion of protected nesting beaches by country as an indicator of conservation efforts on body size. Long‐term monitoring (1993–2019) of body size and nesting data on green turtles (Chelonia mydas) from Redang Island (Malaysia) was used to examine temporal changes in body size and fecundity and to test whether the size scaling of fecundity was isometric (linear) or allometric (curvilinear).ResultsWe show that the total reproductive‐energy output of larger nesting females was, on average, disproportionately greater in all sea turtle species. We found no strong correlations for countries with a higher proportion of protected nesting sites with female size. Finally, we showed that scaling‐derived calculations of population‐level yearly reproductive output in the green turtle population from Redang Island were more accurate when using a hyperallometric (rather than an isometric) relationship at the individual level.Main conclusionsUnderstanding ecosystem function and conservation effort requires accurate predictions of population trends. Our findings highlight the necessity to account for scaling effects of body size in predicting anthropogenically mediated population shifts, and the need to protect large females in order to facilitate effective population replenishment.

Fusarium species isolated from post-hatchling loggerhead sea turtles (Caretta caretta) in South Africa

Species in the Fusarium solani species complex are fast growing, environmental saprophytic fungi. Members of this genus are filamentous fungi with a wide geographical distribution. Fusarium keratoplasticum and F. falciforme have previously been isolated from sea turtle nests and have been associated with high egg mortality rates. Skin lesions were observed in a number of stranded, post-hatchling loggerhead sea turtles (Caretta caretta) in a rehabilitation facility in South Africa. Fungal hyphae were observed in epidermal scrapes of affected turtles and were isolated. The aim of this study was to characterise the Fusarium species that were isolated from these post-hatchling loggerhead sea turtles (Caretta caretta) that washed up on beaches along the South African coastline. Three gene regions were amplified and sequenced, namely the internal transcribed spacer region (ITS), a part of the nuclear large subunit (LSU), and part of the translation elongation factor 1 α (tef1) gene region. Molecular characteristics of strains isolated during this study showed high similarity with Fusarium isolates, which have previously been associated with high egg mortality rates in loggerhead sea turtles. This is the first record of F. keratoplasticum, F. falciforme and F. crassum isolated from stranded post-hatchling loggerhead sea turtles in South Africa.

Resilient Eggs: Highly Successful Loggerhead Sea Turtle Nesting Sites Vary in Their Characteristics

Sea turtle nest success, defined as the number of eggs in a nest that successfully hatch and emerge, is closely linked to environmental conditions. Interacting biotic and abiotic factors influence hatching and hatchling emergence success. To date, combinations of multiple factors interacting together, which result in highly successful sea turtle nests are not well understood. Using 25 years of historic nest data and local expert experience, we identified five historically successful loggerhead (Caretta caretta) nesting beaches (hotspots) along the Florida (United States) Atlantic coast and measured nest environments along with the nest success. Principal component analysis was used to reduce 12 environmental variables so that the relative contributions of sand characteristics, nest temperatures, sand moisture, and nest location were considered. The nest environments differed among nesting beaches and were broadly segregated into two distinct climates: subtropical (hot and humid) and warm-temperate (warm and dry). We found that nests at subtropical sites, compared with warm-temperate sites, were characterized by environmental gradients in contrasting ways. Nest locations were predominantly mid-beach in subtropical sites but clustered at higher elevations and closer to the base of the dune at warm-temperate climate sites. Collectively, highly successful nest hotspots represent a mosaic of abiotic factors providing conditions that promote successful hatching and emergence. This new perspective on consistently successful loggerhead nesting beach traits demonstrate that the key traits of sea turtle nesting habitat vary with prevailing climate type and should be managed accordingly.

Surveys of the Angolan coast uncover the largest olive ridley sea turtle nesting population in the Atlantic and the largest non-arribada population globally

AbstractKnowledge of the abundance and distribution of species is important for designing and prioritizing conservation and management activities. Despite numerous existing studies on the distribution and status of sea turtles, we still lack knowledge about certain populations, especially in Angola, which is considered to be the southernmost range of nesting sea turtles in the eastern Atlantic. This study provides an overview of the status, size and distribution of the olive ridley sea turtle Lepidochelys olivacea population nesting along the coast of Angola, and its relevance in the context of other olive ridley turtle nesting populations in the Atlantic. Aerial and ground surveys were conducted along 1,410 km of Angolan coastline and daily beach monitoring over 53.9 km of seven permanent study sites at a range of latitudes during 2011–2020. Angola hosts the largest olive ridley turtle nesting population in the Atlantic, and the largest non-arribada population globally. Although the population appeared relatively stable, the pressures from various threats on land (e.g. consumption of turtles and eggs) and at sea (captures in fishing gear) necessitate the development of a comprehensive management plan, improved and strengthened legislation and law enforcement, and a cohesive approach to conserving all sea turtle species in Angola.

Why do sea turtle nests fail? Modeling clutch loss across the southeastern United States

AbstractUnderstanding the relative influence of environmental conditions and disturbance types on species' nest success is imperative to our estimation of current and future population trajectories of vulnerable species, especially ectotherms. The reproductive output of oviparous species is highly dependent on the location of a nest in terms of the environment experienced by incubating embryos and the risk of disturbance events. Climate change may present a particular danger to oviparous species because eggs cannot behaviorally regulate and avoid extreme temperatures. Hierarchical Bayesian models offer a powerful tool for utilizing available long‐term datasets to predict current and future species–environment relations in a manipulatable framework. We modeled the probability of depredation and inundation events occurring during incubation and how these disturbances, along with local climate, predict total clutch failure for loggerhead sea turtles (Caretta caretta) using a dataset of over 9000 nest inventories from five nesting areas that span the latitudinal extent of primary nesting locations in the United States. We found that nesting distance from the high waterline was important in determining the probability of inundation and depredation disturbance events, as well as clutch failure. Nests that experienced at least one inundation event were more likely to have no emergence than nests that experienced at least one depredation event, which may be the result of concerted efforts to control highly destructive nest predators in our study sites or the magnitude of inundation disturbances. Extreme high‐temperature events increased the probability of clutch failure, but the probability of clutch failure decreased with increasing average temperatures up to a critical threshold. The results of these models have clear implications for conservation management decisions on where to deploy predator deterrents and relocate nests, as well as the potential for predicting future changes in nest productivity across the broad nesting range of loggerhead sea turtles.

How well do embryo development rate models derived from laboratory data predict embryo development in sea turtle nests?

Development rate of ectothermic animals varies with temperature. Here we use data derived from laboratory constant temperature incubation experiments to formulate development rate models that can be used to model embryonic development rate in sea turtle nests. We then use a novel method for detecting the time of hatching to measure the in situ incubation period of sea turtle clutches to test the accuracy of our models in predicting the incubation period from nest temperature traces. We found that all our models overestimated the incubation period. We hypothesize three possible explanations which are not mutually exclusive for the mismatch between our modeling and empirically measured in situ incubation period: (1) a difference in the way the incubation period is calculated in laboratory data and in our field nests, (2) inaccuracies in the assumptions made by our models at high incubation temperatures where there is no empirical laboratory data, and (3) a tendency for development rate in laboratory experiments to be progressively slower as temperature decreases compared with in situ incubation.

Tidally-Driven Gas Exchange in Beaches: Implications for Sea Turtle Nest Success

Goforth, K.M. and Carthy, R.R., 2022. Tidally-driven gas exchanges in beaches: Implications for sea turtle nest success. Journal of Coastal Research, 38(3), 523–537. Coconut Creek (Florida), ISSN 0749-0208. The success of individual sea turtle nests is influenced by nest location on the beach and the resulting incubation environment. Several abiotic factors affect nest incubation, and thus nest success, but tides and gas exchange are two of the most important. The effects of tides on nest success have been well documented in regard to overwash and inundation events. However, the possible effect of tidally-driven gas exchange has received little attention. The incursion and retreat of the saltwater wedge may cause substantial movement of gases through the beach during the tidal cycle. This study quantifies the differences in tidally-driven gas exchange among beach types and shoreline elevation levels. Carbon dioxide (CO2) efflux was used as a means of measuring gas movement through the beach to examine tidal effects across different beach zones and among different beach types. CO2 efflux was measured throughout the tidal cycle at three distinct beaches (accreting, eroding, and nourished) at Cape San Blas, Florida. There was a general pattern of CO2 efflux rising and falling throughout the tidal cycle on each beach and a difference in the CO2 efflux observed among beaches and beach zones. Efflux patterns at the nourished and eroding beaches were similar, but the nourished beach exhibited a decreased and dampened CO2 efflux pattern throughout the course of the tidal cycle. Analyses of the hatchling turtle emergence success data from 2011 to 2014 for the three beaches found that emergence success differed among the three beaches. The highest emergence success was on the nourished beach, which exhibited a relatively consistent efflux pattern. These results suggest that tidally-driven gas exchange may have implications on nest incubation and survival and are a consideration in beach restoration management and best practices for coastline conservation.

Seasonal factors affecting sea turtle nesting in the Southeastern Caribbean Sea (Gulf of Paria, Venezuela)

The nesting characteristics (number of nests and eggs, time of year, nesting initiation, and nesting length) of leatherback (Dermochelys coriacea) and hawksbill (Eretmochelys imbricata) sea turtles of the southern Caribbean Sea (specifically in the Gulf of Paria in Venezuela), were examined in association with weekly precipitation averages and number of rainy days per week during the period between 2009 and 2018. We hypothesized about the influence of rainfall intensity and patterns as the main abiotic factor for sea turtle nesting. On average, leatherbacks preferred nesting during the drier season of each year (March, April, and May), while hawksbills nested during the rainy season (June to September). For both species, we found few significant correlations between the number of nests or clutch size (number of eggs per nest) and weekly averages of seasonal precipitation rates in the region. Average hawksbill clutch sizes were not correlated with average precipitation rates but were positively correlated with the number of rainy days per week (r=0.66, P≤0.05). Average hawksbill clutch sizes decreased each year on average (-3.3 eggs/year, r=-0.88, P≤0.001), which coincided with a negative long-term trend in the number of rainy days (-0.11 rainy days/week, r=-0.69, P≤0.05). During the study period, nesting activities for both leatherback and hawksbills started progressively later (0.9 and 0.6 weeks/year, respectively p≤0.05) and were shorter (-0.9 and -0.8 weeks /year, P≤0.1 and P≤0.05, respectively).

Sea Turtle Nesting: What Is Known and What Are the Challenges under a Changing Climate Scenario

The rate of climate change experienced globally in recent decades may compromise sea turtles’ survival; especially temperature increase, which is particularly fast, impacts life history characteristics, such as temperature-dependent sex determination (TSD), late maturity and sea turtles highly migratory nature. This review aims to identify and summarize the information that has been collected from 2009-2020 in order to aid future empirical studies that seek to fill these and other knowledge gaps, and subsequently assist conservationists in making multilevel decisions to protect sea turtle populations and species. In a summarized way the general knowledge acquired so far on the influence of environmental abiotic and biotic factors on nesting behaviour and hatching, emergence and survival successes of sea turtle hatchlings, was gathered. To accomplish this work, a search on Web of Science, Science Direct, NCBI/PubMed, and Google Scholar was carried out using the terms “sea turtles + climate change”. Published articles in the period 2009-2020 were selected, related to the nesting ecology of 5 species of sea turtles: Caretta caretta, Eretmochelys imbricata, Dermochelys coriacea, Chelonia mydas, Lepidochelys olivacea. Emphasis was also placed on geographical information and on population location (e.g. climatic conditions during the nesting season). These articles (N = 126) were analysed giving relevance to researcher’s data interpretations, comparisons with other researches, and the reached conclusions. An attempt was made to represent all 5 species of sea turtles when selecting articles on each of the environmental factors that influence sea turtle nesting: temperature, humidity, nesting substrate, gases, depth of the nest, sea surface temperature (SST), nest location on the beach, nesting phenology and geographic distribution of nesting habitats. The interaction between these parameters and their consequences on the terrestrial phase of reproduction are presented and discussed.

Direct and indirect pathways for environmental drivers of hatching success in the loggerhead sea turtle

Nest site selection has consequences for hatching success by mediating the temperature and moisture conditions that eggs experience during the incubation period. Understanding the potentially complex pathways by which nest placement influences these abiotic mediators, and therefore hatching success, is important for predicting which nests will be successful and which may require management action. We studied the effects of loggerhead sea turtle (Caretta caretta) nest site selection on hatching success by linking nest placement characteristics to hatching success through a structural equation model. We monitored 170 nests on Ossabaw Island, Georgia, during the summers of 2017 and 2018 and tracked nest conditions throughout the incubation period. Temperature had a complex effect on hatching success—nests had higher hatching rates if they were exposed to higher mean temperatures but also if they experienced both extremely high (>34°C) and extremely low (<26.5°C) temperatures, suggesting that temperature variability plays a role in determining nest outcomes beyond the mean temperature. Likewise, hatching success declined with a higher incidence of nests being inundated by tides. We found that nests placed at the highest elevations had the highest hatching success rates, likely because those nests had a much lower chance of being washed over by high tides and had higher mean temperatures. Nests were also more successful when placed in greater amounts of vegetation, again because vegetated nests were generally warmer and were associated with fewer washover events. These results shed light on the mechanisms behind selection for certain nest site characteristics and can guide the relocation of nests as a conservation action.

Sea Turtle Nesting Activity in Ghana, West Africa

The recovery of depleted sea turtle populations will require careful documentation of sea turtle reproduction sites and anthropogenic mortality risks throughout their known ranges. Although sea turtle nesting is well documented in many locations, there remains a paucity of data on the species and nesting ecology in western Africa. Here we provide the first longitudinal study of sea turtle nesting activity in Ghana. In decreasing order of abundance, we observed nesting olive ridley (Lepidochelys olivacea) (60 nests/yr), leatherback (Dermochelys coriacea) (17 nests/yr), and green (Chelonia mydas) sea turtles (2 nests/yr) along 3.7 km of beach. The primary nesting season for all species is September through January; however, olive ridley turtles sporadically nest throughout the year. Olive ridley nesting activity significantly declined during the study period (R2 = 0.53, p = 0.04). The primary risk factors for these animals are fishery bycatch, direct harvest of nesting females, and egg poaching.

The Atlantic Sargassum invasion impedes beach access for nesting sea turtles

One characteristic of global change is an increase in the frequency and magnitude of algae blooms. Although a large body of work has documented severe ecological impacts, such as mortality due to toxins or hypoxia, less research has described sublethal effects that may still affect population dynamics. Here, we focus on blooming Sargassum macroalgae in the North Atlantic and describe effects on nesting sea turtles. Since 2011, large masses of the algae have been inundating Atlantic nesting habitats. We documented the accumulation of Sargassum at Long Island, Antigua, and quantified effects on a rookery of hawksbill sea turtles (Eretmochelys imbricata). Using monitoring data from 2010 to 2019, we analyzed population- and individual-level patterns in nesting. Our results suggest that sea turtles respond to Sargassum at nesting beaches by shifting space use away from heavily impacted areas. We also tested for an effect on nesting success, but found no change in the years and areas most impacted by Sargassum. The algae may not increase the energetic costs of nesting after a turtle has emerged onto the beach, but we speculate that costs are imposed in algae-filled waters as turtles initially seek to emerge. As the Sargassum “invasion” continues, sea turtles at impacted sites will need to exhibit plasticity when choosing nesting sites, and nest densities may increase in areas with less Sargassum present. Individuals may also be required to expend more energy per nesting season. More broadly, this work demonstrates that algae blooms can have sublethal effects on fauna that affect population dynamics.

Nesting trends of olive ridley sea turtles Lepidochelys olivacea (Testudinata: Cheloniidae) on two beaches in Northwestern Mexico after 30 and 40 years of conservation

Introduction: Although olive ridley sea turtles (Lepidochelys olivacea) are the most abundant sea turtles in the world, quantitative information is scarce and unevenly distributed among regions. There are many management and conservation programs for this species, and assessments are necessary to identify nesting trends and effectively manage current conservation programs. PROTORMAR-UAS is a Research and Conservation program for the olive ridley turtle created by the Autonomous University of Sinaloa, Mexico. The program utilizes two biological stations: Santuario Playa Ceuta (SPC) and Playa Caimanero (PC). Objective: To evaluate the nesting trend of olive ridley turtles on two beaches in Northwestern Mexico and to predict prospective nesting trends for the next 30 years. Methods: Using annual nesting data collected over 40 years at SPC (1976-2016) and 30 years at PC (1986-2016), we evaluated nesting trends, hatching success, predation and poaching of olive ridley turtles on the two beaches in Northwestern Mexico. Then, prospective nesting estimates for the next 30 years were calculated predictive time series model. Results: A positive and significant correlation was identified between the number of annual nests and time for both beaches (rho = 0.850, P ≤ 0.01 for SPC; rho = 0.677, P ≤ 0.01 for PC); the average hatching success rates were 65.09 at SPC and 60.72 % at PC. The predictive time-series model indicated that the numbers of nests will continue to increase through 2045, increasing three-fold at SPC and six-fold at PC with respect to the last year of monitoring. Conclusions: There was a clear positive trend in the number of olive ridley sea turtle nests at both sites, which is consistent with trends found in other recent studies from the region. Therefore, we suggest that PC be designated a legally protected nesting area since it is located within the latitudinal limits of olive ridley nesting and given the need for resources for camp operation considering increased nesting and current problems with predation and poaching. Because in Mexico operating a nesting beach without any protection status implies not having a budget for its management.

Guide to Nesting Sea Turtles in Florida

Florida’s coastline provides critical habitat for sea turtle nesting, as it has for millions of years. Throughout the state, three of the seven species of sea turtles in the world have significant nesting populations. Loggerhead, green, and leatherback sea turtles use Florida’s beaches to lay nests each year. This publication provides information on the identification, nesting characteristics, and abundance of each of the common sea turtle species who nest in Florida.

Ancient Sea Turtle Nests!…from around the World!

Ancient Sea Turtle Nests!…from around the World!

Finding of a two-headed green turtle embryo during nest monitoring in Baa Atoll, Maldives.

Green sea turtles are one of the two species of marine turtles known to nest in the Maldives. The prevalent time of nesting seems to be inconsistent throughout the island nation. In this study, sea turtle nesting activity was monitored on the island of Coco Palm Dhuni Kolhu in Baa Atoll over a period of 12 months. A total of 13 nests were confirmed with a median hatching success rate of 89.58% as ascertained by nest excavation. In one of the nests, a severely deformed hatchling with polycephaly, an opening in the neck area and a lordotic spine was found, and we investigated in detail with radiographic images and a necropsy. Our findings support the importance of consistent nesting activity and nest monitoring efforts in the country as a basis for conservation efforts.

Genetic structure of olive ridley sea turtles (Lepidochelys olivacea) in Ghana, West Africa

Sea turtles migrate across ocean basins to reach foraging and breeding areas but still exhibit significant population structure across nesting beaches. Although five species of sea turtles nest in West Africa, the genetic structure of many species in this region has not been adequately explored. We investigated the diversity of mitochondrial and nuclear DNA for nesting olive ridley (Lepidochelys olivacea) turtles in two coastal communities (Mankoadze and Ada Foah) in Ghana that are approximately 160 km apart. Samples were collected during four nesting seasons: 2006, 2014, 2015 and 2016. Analysis of the control region of mtDNA (n = 45) revealed six variable positions defining five haplotypes, of which one was previously undescribed (Lo91). These findings are indicative of population expansion from a small ancestral population and support the scenario of colonization of the Atlantic via founder effect. Eleven microsatellite loci were used to analyze two years (2015 and 2016) from Mankoadze. We determined these nesting cohorts were not genetically distinct (FST = 0.025, P = 0.286) and can therefore be considered a single population. This population was compared to six females from Ada Foah across seven loci. Individuals from the two locations were less related than expected under a model of random chance, and showed signs of outbreeding, and reflected moderate variation between the two (FIS = -0.160, P = 1.00; FST = 0.104, P = 0.002). The structuring between locations indicate nesting individuals may utilize different migration routes, foraging grounds, or breeding grounds and that Ghana may serve as a transitional area between central and west African rookeries.

A test of the use of gray wolf (Canis lupus) urine to reduce coyote (Canis latrans) depredation rates on loggerhead sea turtles (Caretta caretta) nests

Loggerhead sea turtles (Caretta caretta) are currently listed as vulnerable, with a decreasing population trend, by the International Union of Conservation of Nature. From 2015 to 2019, coyotes (Canis latrans) depredated 24.12% of loggerhead nests on the night they were laid on South Island beach at the Tom Yawkey Wildlife Center, near Georgetown, SC, resulting in an estimated 3816 eggs lost each year. Over that time, a South Carolina Department of Natural Resources Turtle Technician Team patrolled the beach at dawn every morning to cage and catalog loggerhead nests and eggs but were unable to cost-effectively protect the nests the night the eggs were laid. To test a new method to dissuade coyote depredation, we used dispensers filled with gray wolf (Canis lupus) urine to simulate wolf activity on seven sections of the beach and left seven sections untreated as controls. We observed a significant reduction in depredation rates where urine was present relative to control areas (G-test adjusted with the Williams correction, G = 5.749, df = 1, p = 0.0165). The results suggest this may be an example of exploitative competition in the absence of interference competition. With daily teams already patrolling the beaches, using wolf urine as a deterrent could be an inexpensive, non-invasive way to reduce coyote depredation on loggerhead and other sea turtle nests elsewhere.

Understanding the coastal erosion vulnerability influence over sea turtle (Eretmochelys imbricata) nesting in NE of Brazil

Most of the studies on sea turtle nesting activity nowadays are focused on the impacts of climate change. However, there is a lack of studies gathering knowledge about the influence of coastal vulnerability to erosion and settlement to assess sea turtle nesting. This study aims to verify the influence of coastal erosion vulnerability over sea turtle nesting in five Brazilian Northeast beaches, in Pernambuco state, at Ipojuca coast. The main analyzed parameters were the urban settlement, coastal erosion indicators and the conservation status of the dunes by assessing shoreline change rates, backshore extension, vegetation cover and beaches morphodynamics associated aspects. Spearman’s rank correlation coefficient and tests of Kruskal–Wallis, Mann–Whitney, Shapiro–Wilk and Levene were employed as a set of statistical analyses. The results state that Eretmochelys imbricata is the predominant species that nests at the Ipojuca coast (93.2% of nesting females). There is a significant difference in the number of nests among the studied beaches (Kruskal–Wallis; p = 0.004). A strong and positive correlation between the backshore width and the number of nests was verified (Spearman’s rank correlation, rs = 0.881; p = 0.0002). The results indicate the preference for nesting on wave-dominated beaches, where the coastal reefs are absent and there is a well-developed backshore, mainly due to the lower urban settlement in these areas. Thus, efforts focused on preserving nesting beaches, especially those under high urbanization, are a key factor for sea turtle preservation.

Preserved food for snakes: predation on naturally made "pidan" eggs in sea turtle nests on the insular beach.

Several animal taxa store food for later consumption: for instance, squirrels and woodpeckers intentionally bury seeds into the soil and the trunk of a tree and consume them after a long period (Vander Wall 1990). However, exploitation of stored or preserved foods has never been reported in reptiles, although several species of snakes scavenge opportunistically on freshly dead animals such as road-killed vertebrates (DeVault and Krochmal 2002). During a long-term field study, we had opportunities to observe a snake (Lycodon semicarinatus) feeding at least nine months after the development of embryos had stopped, on unhatched sea turtle eggs laid in a nest in the sand (Fig. 1). The unhatched eggs appeared to have escaped decomposition under special conditions, similar to the traditional preserved food, "pidan" (known as century egg). Here, we report cases that snakes utilize naturally preserved foods.