Thermal control of hatchling emergence patterns in marine turtles

The emergence patterns of green turtle (Chelonia mydas) hatchlings on two beaches on Ascension Island, South Atlantic were monitored and related to thermal patterns in the sand at 10, 20, 30 and 40 cm depth. A total of 6001 hatchlings were recorded emerging on Long Beach, and 3171 emerged on North East Bay during the study period. No significant difference was observed in the temporal pattern of hatchling emergence among nights, or between the two beaches. Hatchling emergence predominantly occurred at night with over 93% of hatchlings emerging during the hours of darkness. Almost all hatchlings emerging in daylight suffer predation by the Ascension frigatebird (Fregata aquila). Counts of frigatebirds both above the study beaches and offshore were highest just after sunrise, with a smaller peak prior to sunset, when frigatebirds were found to predate hatchlings emerging, crawling down the beach or detected in inshore waters. The likely thermal cues controlling hatchling emergence were investigated (temperature at different depths, thermal gradients in the sand and temperature change). The most plausible thermal factor appears to be the change of temperature at superficial sand depths, with hatchling emergence inhibited when subsurface sand temperatures were increasing. This simple mechanism is likely to ensure predominantly nocturnal hatchling emergence regardless of sand albedo, seasonality or latitude as long as night is relatively cooler than day.     

Natural beaches confer fitness benefits to nesting marine turtles

Coastal ecosystems provide vital linkages between aquatic and terrestrial habitats and thus support extremely high levels of biodiversity. However, coastlines also contain the highest densities of human development anywhere on the planet and are favoured destinations for tourists, creating a situation where the potential for negative effects on coastal species is extremely high. I gathered data on marine turtle reproductive output from the literature to determine whether coastal development negatively influences offspring production. Female loggerhead (Caretta caretta) and green turtles (Chelonia mydas) nesting on natural beaches (as opposed to beaches with permanent development) produce significantly more hatchling turtles per nest; all else being equal, females that successfully produce more offspring will have higher fitness than conspecifics producing fewer offspring. Thus, female marine turtles nesting on natural beaches probably have higher fitness than turtles nesting on developed beaches. Consequently, populations nesting on natural beaches may be able to recover more quickly from the historic population declines that have plagued marine turtles, and some species may recover more quickly than others.     

Post-nesting movements and submergence patterns of loggerhead marine turtles in the Mediterranean assessed by satellite tracking

Two female loggerhead turtles (Caretta caretta) were tracked, following nesting at Alagadi Beach (35°33′N, 33°47′E), Northern Cyprus, eastern Mediterranean for 60 and 82 days, respectively. The two individuals showed marked differences in their behaviour. Individual A was tracked to Syrian coastal waters, whereas individual B travelled around the coast of Northern Cyprus to a foraging site in the waters off the east coast of Northern Cyprus. Submergence durations varied markedly during different phases of the migration, suggesting coastal foraging/resting at certain stages en route with sustained directed travelling movements during initial coastal movements and open ocean crossing. Both turtles showed fidelity to foraging grounds for the duration of transmissions (Turtle A: 36 days; Turtle B: 58 days). In both cases, locations were centred in inshore waters although the two individuals exhibited quite different submergence patterns. Individual A carried out very short dives of typical duration <10 min, whereas Individual B carried out longer dives with typical duration >20 min. Diel differences in submergence duration at the foraging grounds suggested longer dives at night/early morning for both turtles. For Turtle A, there was a general reduction in submergence duration as the period of residence increased; a pattern that may have been related to increasing temperature experienced. The total distance travelled by the two turtles (320 and 227 km) was relatively short when compared to satellite tracking studies of conspecifics following nesting in South Africa and USA and tagging studies of nesting loggerhead turtles in Greece and Australia. It is hypothesized that short migratory distance may be correlated with both the small body size and the relatively high frequency of remigration in this population.     

Fidelity and over-wintering of sea turtles

While fidelity to breeding sites is well demonstrated in marine turtles, emerging knowledge of migratory routes and key foraging sites is of limited conservation value unless levels of fidelity can be established. We tracked green (Chelonia mydas, n=10) and loggerhead (Caretta caretta, n=10) turtles during their post-nesting migration from the island of Cyprus to their foraging grounds. After intervals of 2-5 years, five of these females were recaptured at the nesting beach and tracked for a second migration. All five used highly similar migratory routes to return to the same foraging and over-wintering areas. None of the females visited other foraging habitats over the study period (units lasted on average 305 days; maximum, 1356 days), moving only to deeper waters during the winter months where they demonstrated extremely long resting dives of up to 10.2h (the longest breath-holding dive recorded for a marine vertebrate). High levels of fidelity and the relatively discrete nature of the home ranges demonstrate that protection of key migratory pathways, foraging and over-wintering sites can serve as an important tool for the future conservation of marine turtles.     

Nest site fidelity and clutch frequency of loggerhead turtles are better elucidated by satellite telemetry than by nocturnal tagging efforts: Implications for stock estimation

Satellite telemetry and ground-based tagging studies are complementary methods to define the spatial and temporal patterns of nesting behavior by migratory sea turtles. Estimates of site fidelity and clutch frequencies are compared for satellite telemetry versus ground truth patrols over a 6 km stretch at a southwest Florida loggerhead (Caretta caretta) rookery. Site fidelity ranged from 1.9 km to 109.1 km for all nests deposited by a female within a season. The mean site fidelity was 28.1 km for all nests, but declined to 16.9 km if omitting the first nest. Nest frequency ranged from 2 to 8 nests per season, with a modal value of 5 nests. Satellite telemetry documented a mean nest frequency of 5.4 nests per female in comparison to 2.2 nests detected by monitoring patrols. The remigrant females had higher clutch frequency, were larger in size, and had higher site fidelity compared to newly tagged females. Satellite telemetry provided improved measurements of site fidelity and reveals a need for revised fecundity estimates. If measures of clutch frequency are representative of loggerhead assemblages nesting elsewhere within the South Florida grouping, the confidence bounds on Western Atlantic loggerhead stocks are approximately 32% lower than currently accounted for annual nesting individuals.     

Responses of hatchling sea turtles to rotational displacements

After emerging from underground nests, sea turtle hatchlings migrate through the surf zone and out to the open ocean. During this migration, both waves and water currents can disrupt hatchling orientation by unpredictably rotating the turtles away from their migratory headings. In addition, waves cause turtles to roll and pitch, temporarily impeding forward swimming by forcing the hatchlings into steeply inclined positions. To maintain seaward orientation and remain upright in the water column, hatchlings must continuously compensate for such displacements. As a first step toward determining how this is achieved, we studied the responses of loggerhead (Caretta caretta L.) sea turtle hatchlings to rotational displacements involving yaw, roll, and pitch. Hatchlings responded to rotations in the horizontal plane (yaw) by extending the rear flipper on the side opposite the direction of rotation. Thus, the flipper presumably acts as a rudder to help turn the turtle back toward its original heading. Turtles responded to rotations in the roll plane with stereotypic movements of the front flippers that act to right the hatchlings with respect to gravity. Finally, hatchlings responded to rotations in the pitch plane with movements of the hind flippers that appear likely to curtail or counteract the pitching motion. Thus, the results of these experiments imply that young sea turtles emerge from their nests possessing a suite of stereotypic behavioral responses that function to counteract rotational displacements, enable the animals to maintain equilibrium, and facilitate efficient movement toward the open sea.     

Tetranucleotide markers from the loggerhead sea turtle (Caretta caretta) and their cross-amplification in other marine turtle species

The loggerhead sea turtle (Caretta caretta) is a federally threatened species and listed as endangered by the World Conservation Union (IUCN). We describe primers and polymerase chain reaction (PCR) conditions to amplify 11 novel tetranucleotide microsatellite loci from the loggerhead sea turtle. We tested primers using samples from 22 females that nested at Melbourne Beach, Florida (USA). Primer pairs yielded an average of 11.2 alleles per locus (range of 4–24), an average observed heterozygosity of 0.83 (range 0.59–0.96), and an average polymorphic information content of 0.80 (range 0.62–0.94). We also demonstrate the utility of these primers, in addition to primers for 15 loci previously described, for amplifying microsatellite loci in four additional species representing the two extant marine turtle families: olive ridley (Lepidochelys olivacea), hawksbill (Eretmochelys imbricata), green turtle (Chelonia mydas), and leatherback (Dermochelys coriacea).     

Fuel use and corticosterone dynamics in hatchling green sea turtles (Chelonia mydas) during natal dispersal

During their natal dispersal hatchling sea turtles depart their nest, beach and inshore areas quickly to move into offshore developmental habitat using their finite energy stores. Patterns of fuel use and endocrine responses that could facilitate hatchling sea turtle dispersal activity are poorly understood. This study, examined aspects of intermediary metabolism by measuring plasma fuel use and an endocrine response of hatchling green turtles (Chelonia mydas) during terrestrial and aquatic activity coinciding with natal dispersal. Specifically, we measured plasma concentrations of glucose, non-esterised free fatty acids and protein to gauge the contributions of carbohydrate, lipid and protein metabolism for fuelling natal dispersal. In addition, we measured plasma levels of the steroid hormone corticosterone (CORT) a hormone implicated in regulating a number of metabolic events associated with migration and energy use in vertebrates. During terrestrial activity, hatchlings ascended through the sand from their nests and exhibited significant increases in plasma CORT and lactate indicating intense periods of anaerobic activity. During swimming, all plasma metabolites, with the exception of plasma protein, peaked between 1 and 4 h post-beginning swimming activity. Plasma CORT peaked at between 3 and 5 h of swimming activity. These plasma concentrations are consistent with intensive activity inducing catabolism of carbohydrate, lipid and protein stores to support prolonged activity. These results are similar to other vertebrates and suggest a relatively uniform cascade of physiological processes during such arduous migratory events.     

Discovery of a regular nesting area of loggerhead turtle <Emphasis Type="Italic">Caretta caretta</Emphasis> in southern Italy: a new perspective for national conservation

Loggerhead turtle Caretta caretta nesting in Italy had been reported to be limited to the Pelagian Islands and only sporadically elsewhere. As presence of loggerhead turtle nests had occasionally been reported (1988–1999) along about 200 km of the Ionian coast of Calabria, we carried out a project to assess the actual state of the nesting population between 2000 and 2004. We divided the coastline in two sectors (A: 52 km, and B: 146 km) that were monitored from mid-June to end of July for a total of n = 174 monitoring days and 1,813.6 km patrolled on foot with different intensities (extensive versus intensive). In sector B, through extensive monitoring we did not find any emergence tracks, but in sector A by intensive survey (2002–2004: one survey/3.64 days) we detected 3–8 nests/year. In total, 25 nests (both observed and reported), were recorded in our study area, and an assessment of a total of 15–16 nests/year was suggested. These figures, within the national scenario depicted from the review of known nesting events in the last 40 years (88 records concerning more than 143–144 nests), show that loggerhead turtle nesting has been underestimated in Italy, due to inadequate monitoring protocols, and that nesting is more frequent than expected (at least 30–40 nests/year). Conservation strategies in Italy should then focus not only on the reduction of mortality at sea, but also include large-scale actions to preserve scattered (but regular) nesting events.     

The dual function of the lung in chelonian sea turtles: buoyancy control and oxygen storage

Chelonian sea turtles use their lung as a buoyancy organ and as the major oxygen store when diving, and hence, buoyancy regulation and oxygen consumption can be expected to interact. The buoyancy of seven juvenile loggerhead turtles, Caretta caretta, was determined by measuring directly their underwater weight (M_uw) while they were resting on a freely suspended weighing platform at a depth of 80 cm. Underwater weight was recorded continuously for 2 days for each turtle, followed by another 2 days measurements during which the turtles carried lead weights attached to their carapace, and finally, a last day of measurement after the weights had been removed. Total duration of resting dives (t_r), buoyancy (F_B), total resulting force acting on the resting turtle (F_res) and body volumes were derived from the M_uw data. Turtles were slightly negatively buoyant when resting (F_res=−0.2943 to −0.981 N kg⁻¹) and M_uw increased significantly throughout each apnoeic period, meaning that the turtles progressively lost buoyancy. Pulmonary gas loss was calculated from the rate at which buoyancy decreased, which was significantly slower during the first half of the dive than during the second half of the dive. Resting oxygen consumption rates (V_O2) were calculated from these data assuming that the pulmonary gas loss represents oxygen consumption from the lung. The V_O2 obtained in this way (1.69-4.86 ml O₂ min⁻¹) corresponded well with other published and V_O2 measured previously on loggerhead turtles in the same facility. Using oxygen from the lung affects buoyancy and may have impacts on the diving behaviour.     

Molecular evidence of male-biased dispersal in loggerhead turtle juveniles

Serum testosterone levels and mtDNA haplotypes were obtained from 65 juvenile loggerhead turtles (Caretta caretta, L.) incidentally caught in the central Mediterranean. The group of specimens carrying a haplotype specific for the northwest Atlantic had higher testosterone levels, and so included more males, than the other one. Since primary sex ratios of northwest Atlantic colonies are strongly skewed towards females, results indicate a male bias among Atlantic turtles entering the Mediterranean. This demonstrates for the first time a sex-biased dispersal of specimens in the pelagic phase, an important factor to be considered in conservation programs.     

Establishing physiological blood parameters in the loggerhead sea turtle (Caretta caretta)

The loggerhead sea turtle (Caretta caretta), one of the three sea turtle species inhabiting the Mediterranean Sea, is an endangered species. However, although frequently treated in marine animal rescue centers, and the subject of several studies in literature, as yet, few studies have been conducted on large numbers of loggerhead sea turtles in order to establish physiological reference ranges that enable the identification of pathological values. The lack of studies on reference parameters probably depends on the fact that marine turtles treated in wildlife rescue centers are usually in a critical conditions, thus precluding the collection of data on healthy animals and compromising the reliability of any data obtained from them. The present biological study was therefore conducted in order to obtain a database from healthy animals in natural conditions. Serum biochemistry and serum protein electrophoresis were performed on blood samples obtained from 65 healthy adult loggerhead sea turtles captured and delivered to the Sea Turtle Rescue Center of Linosa (Italy); the blood samples were collected during the clinical examination of rescued animals. Laboratory analyses of serum samples were made in order to establish reference parameters, commonly required for laboratory diagnoses in mammals and diseased animals.

Allometric growth in juvenile marine turtles: possible role as an antipredator adaptation

Female marine turtles produce hundreds of offspring during their lifetime but few survive because small turtles have limited defenses and are vulnerable to many predators. Little is known about how small turtles improve their survival probabilities with growth though it is assumed that they do. We reared green turtles (Chelonia mydas) and loggerheads (Caretta caretta) from hatchlings to 13 weeks of age and documented that they grew wider faster than they grew longer. This pattern of allometric growth might enable small turtles to more quickly achieve protection from gape-limited predators, such as the dolphinfish (Coryphaena hippurus). As a test of that hypothesis, we measured how dolphinfish gape increased with length, reviewed the literature to determine how dolphinfish populations were size/age structured in nearby waters, and then determined the probability that a small turtle would encounter a fish large enough to consume it if it grew by allometry vs. by isometry (in which case it retained its hatchling proportions). Allometric growth more quickly reduced the probability of a lethal encounter than did isometric growth. On that basis, we suggest that allometry during early ontogeny may have evolved because it provides a survival benefit for small turtles.     

Multiple paternity assessed using microsatellite markers, in green turtles Chelonia mydas (Linnaeus, 1758) of Ascension Island, South Atlantic

Paternity was determined for three clutches and up to 20 offspring per clutch in the green turtle (Chelonia mydas) from Ascension Island, South Atlantic, using microsatellite markers. All three clutches were sired by at least two different males. The results were compared with those of previous studies of multiple paternity in turtles. No significant difference among studies was observed in the mean contribution of the males siring the largest proportion of progeny per clutch. The present study also provides evidence for segregation distortion (meiotic drive) in turtles.     

Comparative study on the fatty acid composition of two marine vertebrates: striped dolphins and loggerhead turtles

The fatty acid composition of total lipids extracted from seven different tissues (fat, liver, cerebrum, cerebellum, lung, kidney and muscle) of 10 striped dolphins (Stenella coeruleoalba) (weight 75.7±16.2 kg) found dead or moribund during a morbillivirus epizootic, and from two tissues (fat and liver) of 54 loggerhead turtles (Caretta caretta) (18.5±10.5 kg) seized dead after illegal capture, both from the Mediterranean Sea, have been determined by high resolution chromatography techniques. When comparing both species, fatty acid composition is surprisingly similar, with a predominance of the monoenoic followed by the saturated group of fatty acids, and a very close ratio of polyunsaturates n-3/n-6. The relatively high arachidonic acid content in the liver of the two marine species is remarkable. The similar diet can play an important role in these findings, but it is suggested that probably metabolic pathways and essential fatty acid requirements between both marine vertebrates are similar, more than is expected from their earlier filogenetic evolutionary divergence.     

Diving at the shallow end: Green turtle behaviour in near-shore foraging habitat

Green turtles Chelonia mydas of immature and adult size (n = 19, curved carapace length 49 to 118 cm) were equipped with time-depth recorders for short periods (≤ 7 d) to investigate diel and seasonal variation in diving behaviour. Research sessions were distributed over 2 years to cover seasonal variation in sea temperature from 14 °C to 30 °C. Diurnal dives were shallower and shorter than nocturnal dives, with diel patterns also evident in dawn and dusk peaks in occupation of depths within 1 m of the surface, elevated diurnal occupation of depths 1 to 2 m below the surface and elevated nocturnal occupation of depths > 2 m. Dive duration increased as sea temperature decreased, showing strong negative correlation by day and by night. Study turtles made resting dives that were 3 to 4 times longer in median duration, and six times longer in maximum duration, at cool temperatures than they were at warm temperatures, but there was no evidence of winter diapause or location shift to avoid cold water. The large majority of turtles spent 89 to 100% of their time at depths ≤ 5 m below the surface, three individuals did not exceed 3 m and the maximum depth recorded by any turtle was 7.9 m, although deeper water was available. Furthermore, the dive data indicated that study turtles collectively spent more than 80% of their time at charted (low tide) depths of 3 m or less, indicating that they consistently used the shallow margins of the bay where human activities tend to be concentrated, thereby potentially increasing their exposure to anthropogenic threats.     

Twelve new polymorphic microsatellite markers from the loggerhead sea turtle (Caretta caretta) and cross-species amplification on other marine turtle species

We describe 12 new polymorphic dinucleotide microsatellite loci and multiplex Polymerase Chain Reaction conditions from the loggerhead sea turtle Caretta caretta. Levels of polymorphism were assessed in 50 individuals from the nesting population of the Cape Verde Islands. Number of alleles ranged from 3 to 13 (average of 7.33) and the values of observed heterozygosities from 0.32 to 0.80 (average of 0.61). Cross-species amplification on three other marine turtles, Chelonia mydas, Eretmochelys imbricata and Dermochelys coriacea, revealed polymorphism and variability at eight, eleven and three loci, respectively.     

Metabolic heating in Mediterranean loggerhead sea turtle clutches

Offspring sex ratio is an important demographic parameter and, given its determination by incubation temperature in sea turtles, might be a key factor for their conservation under climate warming. An appealing approach to estimate hatchling sex ratios is to measure sand temperatures at nest depth and deduce hatchling sex ratios from a beforehand-established relationship of hatchling sex ratio and sand temperature. Such estimates will only be accurate though if metabolic heat produced by the embryos is considered. Judging whether metabolic heating has a potential effect on hatchling sex ratios without actually measuring temperature within clutches would greatly facilitate monitoring protocols. We tested for a relationship between the amount of metabolic heating and the number of developed embryos as well as clutch size in the largest known loggerhead sea turtle (Caretta caretta) population of the Mediterranean on Zakynthos (Greece). Temperatures were measured within 20 nests as well as at a reference site in the sand at nest depth. Metabolic heating was detected, but only during the last third of the incubation period did nests heat up considerably (1.6 °C on average) above the temperature of the surrounding sand. During the middle third of incubation, when sex is determined, the amount of metabolic heating was negligible. The amount of metabolic heating during the last third of the incubation duration was significantly correlated to the number of offspring developed to at least about 75% of incubation duration. This factor explained nearly 50% of variation in metabolic heating. Metabolic heating was also significantly correlated to clutch size. Given that clutch size within the Mediterranean is largest in Zakynthos loggerheads, we conclude that metabolic heating can be ignored in the estimate of hatchling sex ratios in Mediterranean loggerhead populations. These results thus provide the basis for a feasible monitoring of hatchling sex ratios in the loggerhead sea turtle in the Mediterranean.