Relationship between tropical cyclones and the distribution of sea turtle nesting grounds

Aim This study examines the relationship between the distribution of existing sea turtle nesting sites and historical patterns of tropical cyclone events to investigate whether cyclones influence the current distribution of sea turtle nesting sites. The results, together with information on predicted cyclone activity and other key environmental variables, will help in the identification and prediction of future nesting sites for sea turtles as changes to the coastal environment continue. Location Queensland, Australia. Methods We used data on the nesting distribution of seven populations of four species of sea turtles [green (Chelonia mydas), flatback (Natator depressus), hawksbill (Eretmochelys imbricata) and loggerhead (Caretta caretta)] from the eastern Queensland coast, and tropical cyclone track data from 1969 to 2007 to explore the relationship between (1) sea turtle nesting phenology and cyclone season, and (2) sea turtle nesting sites and cyclone distribution. Furthermore, using two green turtle populations as a case study, we investigated the relationship between cyclone disturbance and sea turtle reproductive output, nesting site and season. Bootstrapping was used to explore if current sea turtle nesting sites are located in areas with lower or higher cyclone frequency than areas where turtles are currently not nesting. Results All populations of sea turtles studied here were disturbed by cyclone activity during the study period. The exposure (frequency) of tropical cyclones that crossed each nesting site varied greatly among and within the various sea turtle populations. This was mainly a result of the spatial distribution of each population’s nesting sites. Bootstrapping indicated that nesting sites generally have experienced lower cyclone activity than other areas that are available for nesting. Main conclusions Tropical cyclones might have been sufficiently detrimental to sea turtle hatching success on the eastern Queensland coast that through a natural selection process turtles in this region are now nesting in areas with lower cyclone activity. Therefore, it is important that future studies that predict climate or range shifts for sea turtle nesting distributions consider future cyclone activity as one of the variables in their model.     

Predaceous ants, beach replenishment, and nest placement by sea turtles

Ants known for attacking and killing hatchling birds and reptiles include the red imported fire ant (Solenopsis invicta Buren), tropical fire ant [Solenopsis geminata (Fabr.)], and little fire ant [Wasmannia auropunctata (Roger)]. We tested whether sea turtle nest placement influenced exposure to predaceous ants. In 2000 and 2001, we surveyed ants along a Florida beach where green turtles (Chelonia mydas L.), leatherbacks (Dermochelys coriacea Vandelli), and loggerheads (Caretta caretta L.) nest. Part of the beach was artificially replenished between our two surveys. As a result, mean beach width experienced by nesting turtles differed greatly between the two nesting seasons. We surveyed 1,548 sea turtle nests (2000: 909 nests; 2001: 639 nests) and found 22 ant species. S. invicta was by far the most common species (on 431 nests); S. geminata and W. auropunctata were uncommon (on 3 and 16 nests, respectively). In 2000, 62.5% of nests had ants present (35.9% with S. invicta), but in 2001, only 30.5% of the nests had ants present (16.4% with S. invicta). Turtle nests closer to dune vegetation had significantly greater exposure to ants. Differences in ant presence on turtle nests between years and among turtle species were closely related to differences in nest placement relative to dune vegetation. Beach replenishment significantly lowered exposure of nests to ants because on the wider beaches turtles nested farther from the dune vegetation. Selective pressures on nesting sea turtles are altered both by the presence of predaceous ants and the practice of beach replenishment.     

Nest site selection of loggerhead sea turtles: The case of the island of Zakynthos, W Greece

The sandy beaches of Zakynthos Island support the largest single nesting aggregation in the Mediterranean Region of the endangered loggerhead turtle Caretta caretta. The present study attempts to determine possible correlations between a series of habitat variables and nest site selection. Nesting activities, including total and nesting emergences were examined in response to the recorded biotic and abiotic variables. The results of the analysis indicate that beach width is the most critical habitat variable affecting nest site selection. Further analysis of nesting performance implies that sea turtles use multiple environmental cues for nest site selection during the different steps of the nesting processes such as emergence from the surf and nesting. Nevertheless, we caution that a detailed study needs to be conducted over a more extensive period of time to verify these suggestions.     

Microclimate modelling of beach sand temperatures reveals high spatial and temporal variation at sea turtle rookeries

The continual development of ecological models and availability of high-resolution gridded climate surfaces have stimulated studies that link climate variables to functional traits of organisms. A primary constraint of these studies is the ability to reliably predict the microclimate that an organism experiences using macroscale climate inputs. This is particularly important in regions where access to empirical information is limited. Here, we contrast correlative models based on both ambient and sea surface temperatures to mechanistic modelling approaches to predict beach sand temperatures at depths relevant to sea turtle nesting. We show that mechanistic models are congruent with correlative models at predicting sand temperatures. We used these predictions to explore thermal variation across 46 mainland and island beaches that span the geographical range of sea turtle nesting in Western Australia. Using high resolution gridded climate surfaces and site-specific soil reflectance, we predict almost 9 °C variation in average annual temperatures between beaches, and nearly 10 °C variation in average temperatures during turtle nesting seasons. Validation of models demonstrated that predictions were typically within 2 °C of observations and, although most sites had high correlations (r² > 0.7), predictive capacity varied between sites. An advantage of the mechanistic model demonstrated here is that it can be used to explore the impacts of climate change on sea turtle nesting beach temperatures as, unlike correlative models, it can be forced with novel combinations of environmental variables.     

Climate change and sea turtles: a 150-year reconstruction of incubation temperatures at a major marine turtle rookery

Sea turtles show temperature dependent sex determination. Using an empirical relationship between sand and air temperature, we reconstructed the nest temperatures since 1855 at Ascension Island, a major green turtle (Chelonia mydas) rookery. Our results show that inter‐beach thermal variations, previously ascribed to the albedo of the sand, which varies hugely from one beach to another, have persisted for the last century. Reconstructed nest temperatures varied by only 0.5 °C on individual beaches over the course of the nesting season, while the temperature difference between two key nesting beaches was always around 3 °C. Hence inter‐beach thermal variations are the main factor causing a large range of incubation temperatures at this rookery. There was a general warming trend for nests, with a mean increase in reconstructed nest temperatures for different months of between 0.36 and 0.49 °C for the last 100 years.     

Assessing climate change associated sea‐level rise impacts on sea turtle nesting beaches using drones,photogrammetry and a novel GPS system

Climate change associated sea‐level rise (SLR) is expected to have profound impacts on coastal areas, affecting many species, including sea turtles which depend on these habitats for egg incubation. Being able to accurately model beach topography using digital terrain models (DTMs) is therefore crucial to project SLR impacts and develop effective conservation strategies. Traditional survey methods are typically low‐cost with low accuracy or high‐cost with high accuracy. We present a novel combination of drone‐based photogrammetry and a low‐cost and portable real‐time kinematic (RTK) GPS to create DTMs which are highly accurate (<10 cm error) and visually realistic. This methodology is ideal for surveying coastal sites, can be broadly applied to other species and habitats, and is a relevant tool in supporting the development of Specially Protected Areas. Here, we applied this method as a case‐study to project three SLR scenarios (0.48, 0.63 and 1.20 m) and assess the future vulnerability and viability of a key nesting habitat for sympatric loggerhead (Caretta caretta) and green turtle (Chelonia mydas) at a key rookery in the Mediterranean. We combined the DTM with 5 years of nest survey data describing location and clutch depth, to identify (a) regions with highest nest densities, (b) nest elevation by species and beach, and (c) estimated proportion of nests inundated under each SLR scenario. On average, green turtles nested at higher elevations than loggerheads (1.8 m vs. 1.32 m, respectively). However, because green turtles dig deeper nests than loggerheads (0.76 m vs. 0.50 m, respectively), these were at similar risk of inundation. For a SLR of 1.2 m, we estimated a loss of 67.3% for loggerhead turtle nests and 59.1% for green turtle nests. Existing natural and artificial barriers may affect the ability of these nesting habitats to remain suitable for nesting through beach migration.     

Estimating the Effect of Beach Nourishment on Caretta caretta (Loggerhead Sea Turtle) Nesting

Caretta caretta (loggerhead sea turtle) nesting activity was recorded daily during three seasons prior to and two seasons immediately following a beach nourishment (replenishment) project in Palm Beach County, Florida. Surveys were done at the nourished beach (Jupiter/Carlin) and at two natural beaches (Juno and Tequesta). The size of the nourishment effect on nesting activity was estimated using Before‐After‐Control‐Impact Paired Series (BACIPS) models. Nesting declined by 4.4 to 5.4 nests km ^{? 1} day ^{? 1} on the nourished beach compared to the two natural beaches in the first season after nourishment. At the same time, false crawls (FC, non‐nesting crawls) increased by 5.0 to 5.6 FC km ^{? 1} day ^{? 1} on the nourished beach. In the second season following nourishment, nesting was reduced by 0.5 to 1.6 nests km ^{? 1} day ^{? 1} on the nourished beach compared to the two natural beaches. The increase in false crawl frequency in the second season following nourishment was 0.7 to 0.9 FC km ^{? 1} day ^{? 1}.These results suggest that beach nourishment significantly decreased loggerhead sea turtle nesting during the first season following the project. However, the size of the effect, in terms of nesting frequency and false crawl frequency, was much reduced by the second season following nourishment.     

Orientation and behaviour of hatchling green turtles (Chelonia mydas) in the sea

To investigate the initial stage of the ‘lost-year puzzle’ of sea turtle ecology, both hatchlings from the natural nesting groung at Tortuguero, Costa Rica and hatchlings from Tortuguero eggs that had hatched in a beach on Bermuda were tracked individually after their departure from these beaches. Of the Bermuda beach most were tracked by swimmers equipped with face mask and flippers and followed by a boat. Tracking off Tortuguero was done by an observer in a following boat. The data showed that non-random departure courses were maintained even when swimming hatchlings and moved over the horizon from all fixed objects on the shore. Observations were made on swimming and diving behaviour and on predator relationships of travelling turtles. The procedures described are useful research techniques and will be used for more extensive tracking in future seasons.     

Using historical data to assess the biogeography of population recovery

Historical ecology research is valuable for assessing long‐term baselines, and is increasingly applicable to conservation and management. In this study, we describe how historical range data can inform key aspects of protected species management, including evaluating conservation status and recovery, and determining practical management units. We examine contemporary (1973–2012) and historical (1250–1950) data on nesting beach distributions for green sea turtles Chelonia mydas in the Hawaiian Islands. Green turtle populations in Hawai‘i declined until federal and international protections began in the 1970s, but over the past four decades one index population has shown encouraging increases and broader recovery has been inferred. We find that 80% of historically major nesting populations are extirpated, or have heavily reduced nesting abundances in comparison with current estimates. Furthermore, historical nesting areas were not geographically isolated, but distributed across the archipelago. In comparison, today more than 90% of green turtle nesting in Hawai‘i occurs at a single site that is vulnerable to sea level rise. This research suggests that assessing recovery without historical data on spatial patterns may overlook important ecological dynamics at the popu lation or ecosystem level, which can result in improper or inadequate conservation assessments and recovery targets.     

Sea Turtle Nesting as a Process Influencing a Sandy Beach Ecosystem

Sea turtle egg mortality, egg predation, and small organisms associated with turtle nests were studied at Playa Ostional, Costa Rica. Sites with concentrated sea turtle nesting were compared with solitary nesting sites as a function of place and time based on ANOVA, Akaike's Information Criterion, and Bayesian analyses. Results indicate that sea turtle egg mortality was significantly associated (P < 0.005) with flowing water that erodes or saturates nesting sites, and with overlapped nesting in which sea turtles disturb each other's nests. Sarcophagid and calliphorid fly larvae (Bayesian prior = 1.19; posterior = 2.27), fungi (prior = 1.14; posterior = 1.92), mites (prior = 0.51; posterior = 1.15), and several other types of small organisms increased in number after turtle egg laying (N= 303 nests; 34,451 turtle eggs). During peak sea turtle nesting periods, visitation to nesting sites by poachers and vertebrate predators was high, and relative number of nests disturbed by these predators was low (P < 0.02). In multimodel analysis, the three most parsimonious models were: (1) turtle egg mortality and distance from mean high tide; (2) turtle egg predation and distance from mean high tide; and (3) turtle egg mortality and nesting density, with Akaike weights of 0.224, 0.203, and 0.153 respectively. Intensive sea turtle nesting might result in upwelling and turnover of nesting debris and nest organisms, and may influence biotic community structure of sandy beach ecosystems.     

Influence of sea turtle nesting on hunting behavior and movements of jaguars in the dry forest of northwest Costa Rica

Jaguars (Panthera onca) are opportunistic predators that prey on large profitable prey items, such as sea turtles at nesting beaches. Here, we use jaguar and sea turtle track-count surveys, combined with satellite telemetry of one jaguar, to evaluate whether jaguar hunting behavior and movements are influenced by seasonal sea turtle nesting in the Sector Santa Rosa of Área de Conservación Guanacaste in northwest Costa Rica. We used generalized linear models to evaluate the effect of moon phase and sea surface temperature on olive ridley (Lepidochelis olivacea) and green turtle (Chelonia mydas) nesting abundance, as well as the combination of these predictors on the frequency of jaguar predation activity (proximity to nesting beaches) and movements. For home-range size and location analyses, we calculated kernel density estimates for each season at three different temporal scales. Sea turtle nesting season influenced jaguar activity patterns, as well as sea turtle abundance was related to jaguar locations and predation events, but jaguar home-range size (88.8 km² overall) did not differ between nesting seasons or among temporal scales. Environmental conditions influenced sea turtle nesting and, as a consequence, also influenced jaguar movements and foraging activity. Our study defined the home range of a female jaguar in the tropical dry forest and its relationship to seasonally abundant turtles. Additional information related to the effect of tourism on jaguar–sea turtle interactions would improve conservation of these species at unique nesting beaches in the area.     

Climate change resilience of a globally important sea turtle nesting population

Few studies have looked into climate change resilience of populations of wild animals. We use a model higher vertebrate, the green sea turtle, as its life history is fundamentally affected by climatic conditions, including temperature‐dependent sex determination and obligate use of beaches subject to sea level rise (SLR). We use empirical data from a globally important population in West Africa to assess resistance to climate change within a quantitative framework. We project 200 years of primary sex ratios (1900–2100) and create a digital elevation model of the nesting beach to estimate impacts of projected SLR. Primary sex ratio is currently almost balanced, with 52% of hatchlings produced being female. Under IPCC models, we predict: (a) an increase in the proportion of females by 2100 to 76%–93%, but cooler temperatures, both at the end of the nesting season and in shaded areas, will guarantee male hatchling production; (b) IPCC SLR scenarios will lead to 33.4%–43.0% loss of the current nesting area; (c) climate change will contribute to population growth through population feminization, with 32%–64% more nesting females expected by 2120; (d) as incubation temperatures approach lethal levels, however, the population will cease growing and start to decline. Taken together with other factors (degree of foraging plasticity, rookery size and trajectory, and prevailing threats), this nesting population should resist climate change until 2100, and the availability of spatial and temporal microrefugia indicates potential for resilience to predicted impacts, through the evolution of nest site selection or changes in nesting phenology. This represents the most comprehensive assessment to date of climate change resilience of a marine reptile using the most up‐to‐date IPCC models, appraising the impacts of temperature and SLR, integrated with additional ecological and demographic parameters. We suggest this as a framework for other populations, species and taxa.     

Stormy oceans are associated with declines in sea turtle hatching

Many sea turtle populations are below 10% of their pre-Columbian numbers [1-4]. Though historic and systematic over-exploitation is the principal cause of these declines, sea turtles face similar threats today. Adults and juveniles are actively hunted and commercial fisheries catch them incidentally. Nesting suffers from beach development, egg poaching and the poaching of nesting females. Accompanying these familiar hazards is the largely unknown consequences of recent climate change. Here we report monitoring surveys from the Dry Tortugas National Park (DTNP, 24.64N 82.86W), Florida, and show that hurricanes and other storm events are an additional and increasing threat to loggerhead turtle (Caretta caretta) and green sea turtle (Chelonia mydas) nesting. Both species are listed by the US Endangered Species Act and the IUCN considers them 'endangered'.     

Antigua revisited: the impact of climate change on sand and nest temperatures at a hawksbill turtle (Eretmochelys imbricata) nesting beach

Whether a turtle embryo develops into a male or a female depends, as with many other reptiles, on the temperature during incubation of the eggs. With sea turtles, warm temperatures produce 100% females. Therefore, global warming has the potential to drastically alter their sex ratios. Air temperatures on Antigua have increased by 0.7°C over the last 35 years. Measurements in both the sand and the clutches laid by hawksbill turtles (Eretmochelys imbricata) at Pasture Bay, Antigua, show that for important parts of the nesting season temperatures are already above the level producing 50% of each sex (pivotal level). Comparisons are made to sand temperature measurements taken on this beach in 1989 and 1990. It is estimated that fewer males were produced in 2003 than in the previous years. Recommendations are made for close monitoring of the fertility of eggs and for research on any turtles nesting at cooler times of year.     

Effects of Beach Nourishment on Sea Turtles: Review and Research Initiatives

Beach nourishment is an engineering solution to erosion of beaches. As in any restoration project, the goals of beach nourishment are the restoration of habitat to promote survival of plants and animals and to maintain aesthetically pleasing sites for humans. Unfortunately, beach nourishment sometimes alters parameters of the natural beach, decreasing the reproductive success of sea turtles. Engineers have recognized this problem and are working to improve nourishment practices. Biologists must specify problems incurred by sea turtles as a result of beach nourishment so that they may be addressed. A review of the literature on sea turtles and beach nourishment found certain problems repeatedly identified. For nesting females, characteristics induced by nourishment can cause (1) beach compaction, which can decrease nesting success, alter nest-chamber geometry, and alter nest concealment, and (2) escarpments, which can block turtles from reaching nesting areas. For eggs and hatchlings, nourishment can decrease survivorship and affect development by altering beach characteristics such as sand compaction, gaseous environment, hydric environment, contaminant levels, nutrient availability, and thermal environment. Also, nests can be covered with excess sand if nourishment is implemented in areas with incubating eggs. The extent and implication of each problem are discussed, and future research initiatives are proposed.     

Bioko: critically important nesting habitat for sea turtles of West Africa

We evaluate the conservation status and threats faced by sea turtle nesting populations at Bioko Island, Equatorial Guinea (Central Africa). Beaches were monitored to obtain a detailed sea turtle nest census and, where possible, tagging of adult females was undertaken. Four sea turtle species were found nesting in the area: the green turtle (Chelonia mydas), the leatherback (Dermochelys coriacea), the olive ridley (Lepidochelys olivacea) and the hawksbill (Eretmochelys imbricata); with the former two species nesting in regionally important numbers. Nesting activity was concentrated between November and February, with a peak in December–January. Tagging and recapture of green turtles in two consecutive seasons suggested an estimated 560 (interquartile range: 420–1,681) and 414 (interquartile range: 190–1,255) nesting females in the area, respectively. Estimated numbers of nesting leatherbacks ranged from 123 to 215 and 243 to 293 in the first and second season, respectively. The other two species were less abundant (olive ridley: 19–29 and 28–43; hawksbill: 4–10 and 2 turtles). Data were compared with more recent surveys in the area and contextualised with information on human related threats. Despite the size of nesting stocks, ongoing permitted and illegal take of adult turtles at the nesting site constitutes a serious threat for these breeding aggregations. Additionally, tag returns from throughout the Gulf of Guinea suggest that the level of take in regional fisheries may also be a major threat.     

The role of geomagnetic cues in green turtle open sea navigation

Background

Laboratory and field experiments have provided evidence that sea turtles use geomagnetic cues to navigate in the open sea. For instance, green turtles (Chelonia mydas) displaced 100 km away from their nesting site were impaired in returning home when carrying a strong magnet glued on the head. However, the actual role of geomagnetic cues remains unclear, since magnetically treated green turtles can perform large scale (>2000 km) post-nesting migrations no differently from controls.

Methodology/Principal Findings

In the present homing experiment, 24 green turtles were displaced 200 km away from their nesting site on an oceanic island, and tracked, for the first time in this type of experiment, with Global Positioning System (GPS), which is able to provide much more frequent and accurate locations than previously used tracking methods. Eight turtles were magnetically treated for 24–48 h on the nesting beach prior to displacement, and another eight turtles had a magnet glued on the head at the release site. The last eight turtles were used as controls. Detailed analyses of water masses-related (i.e., current-corrected) homing paths showed that magnetically treated turtles were able to navigate toward their nesting site as efficiently as controls, but those carrying magnets were significantly impaired once they arrived within 50 km of home.

Conclusions/Significance

While green turtles do not seem to need geomagnetic cues to navigate far from the goal, these cues become necessary when turtles get closer to home. As the very last part of the homing trip (within a few kilometers of home) likely depends on non-magnetic cues, our results suggest that magnetic cues play a key role in sea turtle navigation at an intermediate scale by bridging the gap between large and small scale navigational processes, which both appear to depend on non-magnetic cues.     

Pleistocene paleogeography and sea levels on the Cayman Islands,British West Indies

The sea level high, 120 000 to 130 000 years ago, did not lead to the complete inundation of Grand Cayman. Deposition associated with that highstand, which produced the limestones of the Ironshore Formation, occurred in small embayments on the south, east, and north coasts and in a large lagoon that covered the central and western parts of Grand Cayman. Limestones in the western part of that lagoon contain tidal (?) channels and large scour surfaces which resulted from storm activity. Overlying the lagoonal deposits are limestones that were deposited on a high-energy, prograding beach. These successions occur 2 to 7 m above present day sea level. Evidence obtained from wave-cut notches and the sedimentology of the Ironshore Formation on each of the Cayman Islands indicates that the late Pleistocene highstand was about 6 m above present day sea level. By comparing the present day elevations of the features used to determine this position, it is evident that Grand Cayman, Cayman Brac, and Little Cayman have not undergone independent vertical movement over the last 125 000 years.     

Do female green turtles (Chelonia mydas) exhibit reproductive seasonality in a year-round nesting rookery?

In circumglobal populations of sea turtles, little nesting activity occurs during cold seasons when the sand temperature on a nesting beach is inappropriate for successful egg incubation. However, it is not known whether reproductive seasonality also occurs in year-round nesting rookeries where the sand temperature may be suitable throughout the year. Therefore, we examined the hypothesis that female turtles exhibit reproductive seasonality even in a year-round nesting population. To determine whether the time of nesting of individuals fluctuates between successive nesting seasons, a year-round nesting rookery of green turtles Chelonia mydas at Huyong Island, Thailand, was patrolled on foot every night for 3190 consecutive days, and nesting females were identified using microchips and metal tags. The date of first nesting within a season for an individual (nesting date) was considered the nesting season of each individual. We identified 94 females and 463 nests (including 47 unidentified nests) during the survey. Nesting dates were distributed throughout the year. Nineteen turtles remigrated to the nesting beach, and the nesting dates of the remigrated females occurred in the same seasons. This indicates that females have a fixed individual nesting season even in a year-round nesting rookery. The year-round nesting of green turtles may be attributed to a wide variation in the nesting seasons of individuals. Satellite tracking revealed that the mean travelling duration of post-nesting migrations in this population was 13.5±6.1 days. The proximity of locations for reproduction and feeding may also play an important role in sustaining year-round nesting in this population.     

Forecasting the viability of sea turtle eggs in a warming world

Animals living in tropical regions may be at increased risk from climate change because current temperatures at these locations already approach critical physiological thresholds. Relatively small temperature increases could cause animals to exceed these thresholds more often, resulting in substantial fitness costs or even death. Oviparous species could be especially vulnerable because the maximum thermal tolerances of incubating embryos is often lower than adult counterparts, and in many species mothers abandon the eggs after oviposition, rendering them immobile and thus unable to avoid extreme temperatures. As a consequence, the effects of climate change might become evident earlier and be more devastating for hatchling production in the tropics. Loggerhead sea turtles (Caretta caretta) have the widest nesting range of any living reptile, spanning temperate to tropical latitudes in both hemispheres. Currently, loggerhead sea turtle populations in the tropics produce nearly 30% fewer hatchlings per nest than temperate populations. Strong correlations between empirical hatching success and habitat quality allowed global predictions of the spatiotemporal impacts of climate change on this fitness trait. Under climate change, many sea turtle populations nesting in tropical environments are predicted to experience severe reductions in hatchling production, whereas hatching success in many temperate populations could remain unchanged or even increase with rising temperatures. Some populations could show very complex responses to climate change, with higher relative hatchling production as temperatures begin to increase, followed by declines as critical physiological thresholds are exceeded more frequently. Predicting when, where, and how climate change could impact the reproductive output of local populations is crucial for anticipating how a warming world will influence population size, growth, and stability.