Can leftovers from predators be reliably used to monitor marine turtle hatchling sex-ratios? The implications of prey selection by ghost crabs

In marine turtles, the sex of an individual is determined by temperatures experienced during embryonic development. Gonad histological observation is still the only reliable way to determine hatchling sex, hampering the study of reproduction and of the demographic consequences of context-dependent sex-ratios, a subject of interest in a warming planet. We investigated whether hatchling remains from predation by Ocypode cursor can be used to estimate sex-ratio trends in a green turtle rookery at Poilão, Guinea-Bissau (10°52′N, 15°43′W). Sex could be readily determined in 77 and 79% of the predated hatchlings in 2008 and 2009, respectively. By comparing hatchlings killed by crabs, hatchlings accidentally dying on the reefs, and live hatchlings, we show that ghost crabs select the smaller prey, but do not select according to hatchling sex, which is explained by the lack of hatchling size dimorphism in this population. The proportion of male hatchlings was 0.45 ± 0.06 and 0.15 ± 0.06 for early and late-season clutches, respectively, these differences most likely being explained by rainfall. Using leftovers from predation by crabs may be a good solution to non-invasively monitor broad trends in sex-ratios of sea turtles.     

The effect of incubation temperature on hatchling quality in the olive ridley turtle, Lepidochelys olivacea, from Alas Purwo National Park, East Java, Indonesia: implications for hatchery management

Nest protection through egg relocation from natural nests into protected hatcheries is a common practice used at rookeries around the world to increase hatchling recruitment into sea turtle populations. However, rarely have the impacts of this practice on hatchling recruitment and quality been assessed. This study investigated the influences of the thermal nest environment of olive ridley turtles Lepidochelys olivacea on emergence success and quality of hatchlings of hatchery nests in Alas Purwo National Park, East Java, Indonesia (2009 and 2010 nesting seasons). Nest temperatures above 34?°C for at least 3 consecutive days during incubation in the hatchery resulted in decreases in emergence success and locomotor performance of hatchlings. The use of the hatchery is recommended due to extremely high predation rate of nests left on the beach; however, altering hatchery management practice by spacing nests one meter apart and providing shade should improve hatchery outcomes now and into the future.     

Emergence pattern of loggerhead turtle (<Emphasis Type="Italic">Caretta caretta</Emphasis>) hatchlings from Kyparissia Bay,Greece

The present study describes the emergence pattern of loggerhead sea turtle hatchlings (Caretta caretta) from a nesting beach in Kyparissia Bay (Greece). We try to establish the role played by hatchling biometry, nest relocation and distance from nest to the sea on this emergence pattern. We surveyed a total of 32 nests, and found long emergence periods (mean = 6.7 nights). The majority of emergences occurred at night, mainly between 0030 and 0100 hours, and in small groups. Most of the hatchlings emerged from the nests the first night. We found no clear trend when we studied the effect of hatchling biometry between successive emergence days. We also found that relocation of the nests did not significantly affect the emergence pattern. However, we noted that in the relocated nests, hatchlings emerged in smaller groups. Emergence periods were inversely related to distance from the sea. In short, factors such as climate conditions, relocation and nest distance to the sea appear to have some effect on the emergence pattern. Therefore, they should be taken into account in both biological studies and management plans for sea turtle nesting beaches. Our results suggest leaving an extended period between the first emergence of hatchlings and the excavation of nests by researchers in future studies in the area.     

Discrimination of ocean wave features by hatchling loggerhead sea turtles, Caretta caretta

At the beginning of their offshore migration, hatchling sea turtles orient directly into oceanic waves as they swim away from land. Recent experiments have demonstrated that hatchlings swimming underwater can determine the propagation direction of waves by monitoring the circular movements they experience as waves pass above. During July and August 1993, we studied how loggerhead sea turtle hatchlings (Caretta caretta L.) from the east coast of Florida, USA, responded to a range of wave parameters. We constructed a wave simulator to reproduce in air the circular movements that normally occur beneath small ocean waves. Hatchlings suspended in air and subjected to these orbital movements attempted to orient into simulated waves when periods and amplitudes were similar to those found near the Florida coast. Orbital movements with longer periods (greater than 10 s), however, failed to elicit responses. The results demonstrate that hatchling loggerheads can distinguish between waves with different periods and amplitudes, and that Florida hatchlings respond most strongly to orbital movements closely resembling those of waves that occur near their natal beach. Received: 28 May 1996 / Accepted: 17 September 1996     

Modelling the fate of marine turtle hatchlings

The SLIM oceanographic model was used to examine the fate of hatchling flatback turtles (Natator depressus) in the first two weeks of their dispersal starting at Wild Duck Island, a major turtle-nesting site in the central Great Barrier Reef region of Australia. We ran simulations to investigate the effects of spring versus neap tides, hatchling's swimming behaviour during their first three days at sea, and the location of nesting beaches. The model predicted that up to 50% of the turtle hatchlings entering the sea from the windward, southern beach remained after 14 days in shallow, nearshore waters, irrespective of tides and swimming. These waters are turbid and may be inhospitable to hatchlings. In contrast >80% of hatchlings dispersing from the leeward, northern beach were dispersed to deeper water (10-40 m) in a quasi-stationary dispersion core centred around 10 km north of the nesting beach after 14 days and the offshore spread of the turtle plume was enhanced by the hatchling's seaward swimming during the first three days. This was due to the presence of a coastal boundary layer and a stagnation zone around the northern side of island, but not the southern side. The model confirmed that dispersal from eastern Queensland flatback turtle rookeries is restricted to the lagoons and coastal waters, and that water circulation and hatchling's swimming control dispersion. The model explains why more turtles nest on the northern than the southern side. This study highlights the usefulness of oceanographic models to increase knowledge about a cryptic life stage of marine turtles.     

Locomotion performance of green turtle hatchlings from the Heron Island Rookery,Great Barrier Reef

Locomotion performance plays a vital role in determining hatchling green turtle Chelonia mydas survival in the first few hours after emerging from their nests as hatchlings crawl and swim the gauntlet of predators before reaching the relative safety of the open ocean. Previous laboratory based constant incubation experiments found incubation temperature to influence the size and swimming performance of hatchling green turtles. Here we examine the morphology and crawling and swimming performance of hatchling green turtles as they emerge from nests on Heron Island rookery in the southern Great Barrier Reef to test the hypothesis that nest temperature in the field can influence these attributes. We found inter-nest differences in hatchling mass and dimensions, and that hatchling mass was not correlated with nest temperature. However, hatchlings from warmer nests had smaller carapace dimensions than hatchlings from cool nests suggesting that more yolk was converted to hatchling tissue during embryonic development in cool nests. There was considerable intra- and inter-nest variation in both crawling and swimming performance of hatchlings. Hatchlings from cool nests tended to be faster crawlers than hatchlings from warm nests, but the thrust produced during swimming was not correlated with nest temperature. During the 4 h swimming trial, hatchlings swimming effort decreased significantly during the first 3 h but swimming effort remained relatively constant for the last 1 h. Individual hatchling crawling and swimming performances were not correlated with each other. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Compression of home ranges in ghost crabs on sandy beaches impacted by vehicle traffic

Animal movement is a pivotal element of many ecological processes, and on ocean-exposed sandy shores, ghost crabs (genus Ocypode) undertake extensive nocturnal forays on the beach surface. Because crab populations are also threatened by vehicle traffic, indicators that can detect sublethal effects before population declines are manifest are important. To this end, we tested on a barrier island in Eastern Australia whether movement patterns of crabs respond predictably to disturbance by vehicles; this was done by tracking (using the spool-and-line technique) crabs at night in beach sections open and closed to traffic. Beach traffic not only halved population densities of crabs on the unvegetated beach seawards of the dunes, but it also fundamentally changed crab behaviour and movement: individuals from beach areas rutted by tyre tracks travelled shorter distances in a more erratic zigzag pattern, and they had significantly compressed home ranges. Such behavioural changes linked to human pressures could be well suited as an early warning signal for wider negative ecological impacts (as demonstrated by reduced abundances). They also emphasize the need to incorporate sublethal effects into the assessment and management of ecological changes resulting from beach recreation.     

草甘膦铵盐暴露对乌龟胚胎发育、孵出幼体运动及学习表现的影响

草甘膦暴露可能对某些水生动物具有致死及亚致死毒性,但未见有涉及龟鳖类动物的行为毒理学的研究报道。用不同浓度草甘膦铵盐处理孵化中的乌龟卵来检测草甘膦暴露对其胚胎发育、孵出幼体大小、翻身能力以及空间学习能力的影响。结果表明,2～2 000 mg·L~(-1)浓度范围内的草甘膦铵盐暴露并不会影响乌龟卵孵化成功率、胚胎发育速率以及孵出个体的体质量和翻身时间,但对孵出幼体的空间学习能力产生一定影响。较高浓度的草甘膦铵盐暴露会导致孵出幼体的觅食时间延长、觅食过程中的运动距离增大。因此,胚胎期草甘膦铵盐暴露可能对乌龟孵出幼体的后续生长和存活有一定的负面效应。     

Breeding biology of the green turtle,Chelonia mydas, (Reptilia: Cheloniidae) on Wan-An Island,Peng-Hu Archipelago,Taiwan. I. Nesting ecology

The nesting season of the green turtle, Chelonia mydas on Wan-An Island, Peng-Hu Archipelago, Taiwan extended from early June to early October in both 1992 and 1993. Turtles nested on 9 of the 11 beaches on the island. The average inter-nesting interval was 14.9 d. A close relationship between the first reemergence time and the tidal cycle was found in the present study. The mean straight carapace length of the adult female was 96.6 cm. Female turtles produced from one to nine egg clutches; the average clutch size was 113 eggs. The mean egg size was 46.9 mm in diameter and 22.7 g in weight. The average incubation period was 49.3 d. The sediment characteristics of the beaches on the island are well within the incubation requirements for green turtle nesting. The average hatching success was 70%, but was lower in the artificial nest. The average size for hatchlings was 46.9 mm in straight carapace length and 22.7 g in body weight. The health of the hatchling is influenced by the adult female size, the nesting depth and the precipitation during incubation.     

Effects of Organized Turtle Watches on Loggerhead (Caretta caretta) Nesting Behavior and Hatchling Production in Florida

To evaluate the effects of organized turtle watches on female sea turtles and their eggs, we quantified nesting behavior and hatchling production of loggerhead turtles ( Caretta caretta ) in south Brevard Country, Florida, U.S.A. We compared the duration of five phases of nesting behavior, the directness of the turtle's return path, rate of travel during return crawl, hatching success, and hatchling emergence success between experimental and control turtles. Experimental turtles nested while observed by an organized turtle watch group consisting of at least 15 people; control turtles were not observed by a turtle watch group. Experimental turtles spent significantly less time camouflaging nest sites than did control turtles. The duration of the other four phases of nesting behavior were not significantly different between the two groups. Experimental turtles also traveled less-direct paths during return crawls, although their rates of travel were not significantly different from those of control turtles. Hatching success and hatchling emergence success were not significantly different between experimental and control turtle nests in either year. Although turtle watch groups influenced nesting behavior, they were not found to be detrimental to hatchling production. Florida's turtle watch program is a means for garnering public support for sea turtle conservation through education, and it should continue.     

Magnetic orientation by hatchling loggerhead sea turtles (Caretta caretta) from the Gulf of Mexico

Loggerhead sea turtle hatchlings emerge from nests on either the east or west coast of the South Florida peninsula and then migrate offshore in opposite directions. Under laboratory conditions, magnetic cues induce east coast hatchlings to swim in directions that promote their transport by oceanic surface currents, such as the North Atlantic gyre. However, the surface currents used by west coast hatchlings are unknown. We examined the responses of west (Sarasota) hatchlings to magnetic cues in the Gulf of Mexico, the Florida Straits, and the Gulf Stream to determine their (1) likely migratory routes (2) orientation where currents lead into the Atlantic Ocean, and (3) orientation adjacent to Florida’s east coast. The results suggest that migration inside Gulf waters may be circuitous, that the turtles respond appropriately to enter Atlantic waters, and that orientation along Florida’s east coast probably promotes transport by the Gulf Stream into the North Atlantic gyre.     

Hitchhikers reveal cryptic host behavior: new insights from the association between Planes major and sea turtles in the Pacific Ocean

Studies that incorporate information from habitat-specific ecological interactions (e.g., epibiotic associations) can reveal valuable insights into the cryptic habitat-use patterns and behavior of marine vertebrates. Sea turtles, like other large, highly mobile marine vertebrates, are inherently difficult to study, and such information can inform the implementation of conservation measures. The presence of epipelagic epibionts, such as the flotsam crab Planes major, on sea turtles strongly suggests that neritic turtles have recently occupied epipelagic habitats (upper 200 m in areas with >200 m depth) and that epipelagic turtles spend time at or near the surface. We quantified the effects of turtle species, turtle size, and habitat (neritic or epipelagic) on the frequency of epibiosis (F ₀) by P. major on sea turtles in the Pacific Ocean. In neritic habitats, we found that loggerhead (F ₀ = 27.6 %) and olive ridley turtles (F ₀ = 26.2 %) host crabs frequently across a wide range of body sizes, and green turtles almost never host crabs (F ₀ = 0.7 %). These results suggest that loggerheads and olive ridleys display variable/flexible epipelagic-neritic transitions, while green turtles tend to transition unidirectionally at small body sizes. In epipelagic habitats, we found that loggerheads host crabs (F ₀ = 92.9 %) more frequently than olive ridleys (F ₀ = 50 %) and green turtles (F ₀ = 38.5 %). These results suggest that epipelagic loggerheads tend to spend more time at or near the surface than epipelagic olive ridleys and green turtles. Results of this study reveal new insights into habitat-use patterns and behavior of sea turtles and display how epibiont data can supplement data from more advanced technologies to gain a better understanding of the ecology of marine vertebrates during cryptic life stages.     

A little movement orientated to the geomagnetic field makes a big difference in strong flows

Whilst a range of animals have been shown to respond behaviourally to components of the Earth’s magnetic field, evidence of the value of this sensory perception for small animals advected by strong flows (wind/ocean currents) is equivocal. We added geomagnetic directional swimming behaviour for North Atlantic loggerhead turtle hatchlings (Caretta caretta) into a high-resolution (1/4°) global general circulation ocean model to simulate 2,925-year-long hatchling trajectories comprising 355,875 locations. A little directional swimming (1–3 h per day) had a major impact on trajectories; simulated hatchlings travelled further south into warmer water. As a result, thermal elevation of hatchling metabolic rates was estimated to be between 63.3 and 114.5% after 220 days. We show that even small animals in strong flows can benefit from geomagnetic orientation and thus the potential implications of directional swimming for other taxa may be broad.     

Deforestation: risk of sex ratio distortion in hawksbill sea turtles.

Phenotypic sex in sea turtles is determined by nest incubation temperatures, with warmer temperatures producing females and cooler temperatures producing males. The common finding of highly skewed female-biased hatchling sex ratios in sea turtle populations could have serious repercussions for the long-term survival of these species and prompted us to examine the thermal profile of a relatively pristine hawksbill nesting beach in Guadeloupe, French West Indies. Data loggers placed at nest depth revealed that temperatures in the forested areas were significantly cooler than temperatures in the more open, deforested areas. Using these temperatures as a predictor of sex ratio, we were able to assess the relative contributions of the different beach zones to the primary sex ratio: significantly more males were likely to be produced in the forested areas. Coastal forests are therefore important male-producing areas for the hawksbill sea turtle, and this has urgent conservation implications. On Guadeloupe, as on many Caribbean islands, deforestation rates are high and show few signs of slowing, as there is continual pressure to develop beachfront areas. The destruction of coastal forest could have serious consequences both in terms of local nesting behavior and of regional demography through the effects on population sex ratios. Human alterations to nesting habitat in other reptile taxa have been shown to modify the thermal properties of nest sites in ways that can disrupt their ecology by allowing parasite transmission, increasing vulnerability to climate change, or rendering existing habitat unsuitable.     

Dispersal,population structure and burrow shape of Ocypode cursor

The distribution of the sand crab Ocypode cursor (L.), as indicated by the number of burrows, was studied for 2 years in a 50×50 m sand beach area in northern Israel. A definite relationship was established between the distribution pattern from the seashore inwards towards the sand dunes, and the degree of sand moisture as it changed seasonally. During autumn, more crabs were found at a distance of 15 to 25 m from the sea where sand moisture was about 14%. At the beginning of winter crabs dispersed evely, disappearing with advancing winter. Crabs reappeared in spring, although in smaller numbers, dispersing in a pattern similar to that in autumn. At the beginning of summer and later on, more crabs appeared and concentrated closer to the sea (5 to 10 m). The population structure was analysed directly by measuring the crab's dimensions, and indirectly by counting burrows and measuring the diameter of their openings. Direct analysis revealed two distinct sizeage groups: smaller crabs 0.5 to 3 cm long, and larger ones over 4 cm long. The smaller burrows were inhabited by the first group and were mostly found closer to the sea; the second group was found more landwards. Three main types of burrow shapes are described.     

The nesting of the Pacific ridley turtle Lepidochelys olivacea on Playa Nancite,Costa Rica

A study of the nesting of the Pacific ridley turtle Lepidochelys olivacea was undertaken in Costa Rica on Playa Nancite — one of two beaches on which the authors had, the previous year, discovered large nesting aggregations of this species. During the 3 1/2-month period of this study, approximately 288,000 turtles nested on the 1300 m-long beach. About 99% of these nested during 3 periods of mass-nesting (arribadas). The predictability of the arribadas was investigated by observing and recording environmental parameters with which they may be correlated. The mass-nesting phenomenon, aspects of nesting behavior, and the adaptive advantages of mass-nesting are discussed. During the period of study, nearly 2,000 turtles were tagged, 102 of which were subsequently recovered. Carapace lengths and widths of 251 tagged turtles were measured. The emergence of hatchlings was recorded daily and, from these data, the incubation period and an indication of egg and hatchling survival was obtained. The activities of the various predators on eggs, hatchlings, and adults are described.     

Dune vegetation fertilization by nesting sea turtles

Sea turtle nesting presents a potential pathway to subsidize nutrient-poor dune ecosystems, which provide the nesting habitat for sea turtles. To assess whether this positive feedback between dune plants and turtle nests exists, we measured N concentration and delta15N values in dune soils, leaves from a common dune plant (sea oats [Uniola paniculata]), and addled eggs of loggerhead (Caretta caretta) and green turtles (Chelonia mydas) across a nesting gradient (200-1050 nests/km) along a 40.5-km stretch of beach in east central Florida, USA. The delta15N levels were higher in loggerhead than green turtle eggs, denoting the higher trophic level of loggerhead turtles. Soil N concentration and delta15N values were both positively correlated to turtle nest density. Sea oat leaf tissue delta15N was also positively correlated to nest density, indicating an increased use of augmented marine-based nutrient sources. Foliar N concentration was correlated with delta15N, suggesting that increased nutrient availability from this biogenic vector may enhance the vigor of dune vegetation, promoting dune stabilization and preserving sea turtle nesting habitat.     

Kinetics of uranium uptake by the crab Pachygrapsus laevimanus and the zebra winkle Austrocochlea constricta

The crab Pachygrapsus laevimanus and the zebra winkle Austrocochlea constricta were exposed for 40 d to uranium (1.5 to 10 mg l^-1) in continuous-flow sea water in separate starved and fed treatments, and the kinetics of uranium bioaccumulation were estimated from an exponential model. Starved and fed crabs took up U at a similar rate, which suggests that sea water was the major source of U to the crab; the fed crabs excreted U more rapidly than the starved crabs and this led to a lower net uptake of U by fed crabs. Fed and starved winkles took up U at similar rates and excreted it at similar rates, so the sea water was also the major source of U to winkles. Crabs took up more U than winkles; the concentration factors were 7 to 18 and 4, respectively. Uranium turnover was quite slow for both species (11 to 36 d) as it was also for winkle shells (6 d); this suggests that the rate-limiting processes which control turnover are biological (e.g. growth or tissue replacement) or physical (e.g. diffusion into the shell) rather than chemical (e.g. precipitation, adsorption or exchange). There was no effect of increasing U concentration in water on the U kinetic parameters.     

Hidden demographic impacts of fishing and environmental drivers of fecundity in a sea turtle population

Fisheries bycatch is a critical threat to sea turtle populations worldwide, particularly because turtles are vulnerable to multiple gear types. The Canary Current is an intensely fished region, yet there has been no demographic assessment integrating bycatch and population management information of the globally significant Cabo Verde loggerhead turtle (Caretta caretta) population. Using Boa Vista island (Eastern Cabo Verde) subpopulation data from capture–recapture and nest monitoring (2013–2019), we evaluated population viability and estimated regional bycatch rates (2016–2020) in longline, trawl, purse-seine, and artisanal fisheries. We further evaluated current nesting trends in the context of bycatch estimates, existing hatchery conservation measures, and environmental (net primary productivity) variability in turtle foraging grounds. We projected that current bycatch mortality rates would lead to the near extinction of the Boa Vista subpopulation. Bycatch reduction in longline fisheries and all fisheries combined would increase finite population growth rate by 1.76% and 1.95%, respectively. Hatchery conservation increased hatchling production and reduced extinction risk, but alone it could not achieve population growth. Short-term increases in nest counts (2013–2021), putatively driven by temporary increases in net primary productivity, may be masking ongoing long-term population declines. When fecundity was linked to net primary productivity, our hindcast models simultaneously predicted these opposing long-term and short-term trends. Consequently, our results showed conservation management must diversify from land-based management. The masking effect we found has broad-reaching implications for monitoring sea turtle populations worldwide, demonstrating the importance of directly estimating adult survival and that nest counts might inadequately reflect underlying population trends.     

Sand disposal of the painted ghost crab Ocypode gaudichaudii (Decapoda: Ocypodidae): A possible role in courtship

In 1991/1992, we studied the sand disposal behavior of the painted ghost crabs Ocypode gaudichaudii on the Pacific coast of Panamá. O. gaudichaudii either kick, dump or tamp sand they excavate from their burrows. Here we relate these three kinds of sand disposal to burrow structure and distribution, as well as to crab size and sex. Our objective was to determine whether tamping may be a male courtship signal. Burrows whose owners tamped sand were on average longer, deeper, and higher on the beach than were burrows whose owners kicked or dumped sand. Five burrow shapes were distinguished, with half-spiral and spiral shapes being most common among tamped burrows. All crabs excavated from tamped burrows were males. Tamped burrows peaked in abundance around full and new moons. These observations, together with what is known about mating and breeding behavior of other ghost crabs, suggest that tamping may be involved in O. gaudichaudii courtship.