Internesting Intervals Research Articles

Effect of water temperature on the duration of the internesting interval across sea turtle species

Sea turtles generally lay several clutches of eggs in a single nesting season. While a negative correlation between water temperatures and the time required between constitutive nesting events (termed the internesting interval) has been previously reported in loggerhead Caretta caretta and green turtles Chelonia mydas, it is not understood whether this relationship remains constant across other sea turtle species. Here, we expanded upon these previous studies on loggerhead and green turtles by using larger sample sizes and including data from species with a wider range of body-sizes; specifically: hawksbill Eretmochelys imbricata, leatherback Dermochelys coriacea, and olive ridley turtles Lepidochelys olivacea. In total, we compiled temperature data from biologgers deployed over internesting intervals on 23 loggerhead, 22 green, 7 hawksbill, 26 leatherback and 11 olive ridley turtles from nesting sites in 8 different countries. The relationship between the duration of the internesting interval and water temperatures in green and loggerhead turtles were statistically similar yet it differed between all other turtle species. Specifically, hawksbill turtles had much longer internesting intervals than green or loggerhead turtles even after controlling for temperature. In addition, both olive ridley and leatherback turtles exhibited thermal independence of internesting intervals presumably due to the large body-size of leatherback turtles and the unique capacity of ridley turtles to delay oviposition. The observed interspecific differences in the relationship between the length of the internesting interval and water temperatures indicate the complex and variable responses that each sea turtle species may exhibit due to environmental fluctuations and climate change.

Synchronised nesting aggregations are associated with enhanced capacity for extended embryonic arrest in olive ridley sea turtles

Sea turtle species in the genus Lepidochelys exhibit an unusual behavioural polymorphism, nesting in both aggregations and solitarily. Aggregated nesting events, termed ‘arribadas’, involve hundreds of thousands of females congregating at a single nesting beach over a few days to oviposit their eggs. Aggregate and solitary nesting behaviours are associated with distinct inter-nesting intervals, three and four weeks for non-arribada and arribada nesters respectively. Consequently, embryos are maintained in pre-ovipositional embryonic arrest in the hypoxic oviduct for different lengths of time depending on the mother’s reproductive behaviour. However, sea turtle embryos are limited in their capacity to remain in arrest and will subsequently die if held in hypoxia too long. Here, we tested whether embryos oviposited during arribada or non-arribada nesting differ in their capacity to be maintained in pre-ovipositional arrest. Olive ridley turtle (Lepidochelys olivacea) eggs from eight clutches (four from each nesting tactic) were divided among seven treatments after oviposition; normoxia (control; 21% O2), or hypoxia (1% O2) for 3, 3.5, 4, 8, 15 or 30 days, before being returned to normoxia. Arribada eggs were capable of extending pre-ovipositional arrest for longer, with some eggs from the 8- and 15-day hypoxia treatment still hatching while no non-arribada eggs hatched after more than four days in hypoxia. This difference in embryonic capacity to survive extended periods of arrest may be an important mechanism facilitating arribada behaviour by allowing longer inter-nesting intervals. Our finding provides an intriguing insight into the physiological mechanisms that are integral to this unique mass-nesting behaviour.

Diving behavior and thermal habitats of gravid hawksbill turtles at St. Croix, USA

Knowledge of an animal’s behavior during particular life history stages can provide insights into habitat selection, and this can have important conservation implications. Gravid hawksbill turtles spend the internesting interval resting on the seafloor, but their diving behavior has only been previously examined in shallow-water habitats. We examined depth use of gravid hawksbills in a location of variable bathymetry to determine if hawksbills engage in deeper diving if deeper waters are available. We attached archival time-depth recorders onto hawksbills nesting at Sandy Point National Wildlife Refuge, St. Croix, US Virgin Islands, where the neritic zone ends within 500 m of the shoreline. We recorded seven internesting intervals from five individuals. Internesting intervals were characterized by long dives (mean 24.2 ± SD 22.3 min) to a constant depth, consistent with seafloor resting in a spatially restricted residence area. There was little variation in the water temperatures at all depths occupied (mean 29.06 ± SD 0.43 °C). Two turtles attained the deepest recorded dives for gravid hawksbills (95.1 and 84.4 m) and sometimes remained at depths greater than 60 m for up to 30 min. Although we recorded instances of relatively deep diving for the species, the overall pattern of seafloor resting and infrequent diving was consistent with hawksbills in other ocean basins with different offshore habitats. We propose that benthic resting is common behavior for gravid hawksbills globally, and protection of benthic habitats near the nesting beach should be a management priority.

Daily Changes in the Blood Levels of Two Steroids and Other Biochemicals Related to Vitellogenesis and Eggshell Formation during Internesting Intervals in a Captive Female Loggerhead Turtle

Abstract: Blood levels of progesterone (P4), estradiol-17β (E2), calcium (Ca), triglyceride (TG), and total protein (TP) were monitored in a captive female loggerhead turtle throughout a nesting season that included three 13- or 14-d internesting intervals. We observed the turtle's ovaries to monitor the appearance of shelled eggs, using ultrasonography, and compared the results of blood analyses and ovary observations. The blood P4 level remained low (<0.2 ng/mL), with the exception of three sharp peaks (1.7, 2.2, and 4.2 ng/ mL) immediately after the initial three nestings. Eggshell formation occurred immediately after the P4 peaks. The blood Ca level gradually dropped to approximately 3.0 µmol/mL during each eggshell formation period but then recovered to approximately 3.7 µmol/mL prior to the next eggshell formation. The blood E2 level fluctuated between 44 and 299 pg/mL, but with two higher peaks (734 and 419 pg/mL) after eggshell formation in the first and second internesting intervals, respectively...

Tracking hawksbill sea turtles (Eretmochelys imbricata) during inter-nesting intervals around Barbados

Hawksbill sea turtles (Eretmochelys imbricata) nesting in Barbados (Needham’s Point, 13° 04′ 41.33′′ N, 59° 36′ 32.69′′W) were outfitted with GPS dataloggers over three breeding seasons (2008–2010) to track movement during inter-nesting intervals. Most females established spatially restricted resident areas up current and within 7 km of the nesting beach where they spent the majority of the inter-nesting interval. Females nesting earlier in the season settled on shallower sites. Only experienced remigrant turtles occupied the most distant resident areas. Females tracked for multiple inter-nesting intervals exhibited site fidelity, but the area contracted and the activity of females decreased with each successive interval. Hawksbills may trade off site characteristics with distance from the nesting beach and reduce activity over the course of the breeding season to optimise energy reserves during inter-nesting intervals.

Sperm Utilization Patterns and Reproductive Success in Captive Loggerhead Turtles (Caretta caretta)

Abstract We investigated the effects of the order of sequential matings in captive female loggerhead turtles (Caretta caretta) on the paternity of their successive clutches. Paternity analysis revealed that only 3 of the 7 successive clutches were multiply sired, although all egg-laying females were observed to copulate with multiple males prior to egg-laying. In multiply sired, successive clutches of particular females, the relative paternal contributions of different males did not vary, although some potentially successful matings were observed during internesting intervals. Prior to nesting periods, males showed mating in response to the female reproductive cycle in which the cumulative durations of mountings observed by highly sensitive cameras peaked at 21–40 days before any individual female laid her first clutch. A regression line between cumulative duration of mountings and relative parental contributions for 21–40 days before laying the first clutch fit a predictive equation for sperm competition...

Annual Frequency of Clutches of Pseudemys texana and Trachemys scripta at the Headwaters of the San Marcos River in Texas

I observed 215 nesting events of Pseudemys texana (134) and Trachemys scripta (81) from 25 April to 14 July 2008 on a golf course in Hays County, Texas. For P. texana, 111 (82.8%) nested one time, 21 (15.7%) nested twice, and 2 (1.5%) nested three times. For T. scripta, 53 (65.4%) nested one time, 24 (29.6%) nested twice, 3 nested three times (3.7%), and 1 nested four times (1.2%). Both species had an internesting interval of ca. 30 days between first and second clutches. Subsequent internesting intervals were shorter but samples were not sufficient to address whether this was fortuitous. On their first attempt, 82% of P. texana and 78% of T. scripta completed nesting. Nesting was diurnal with most activity occurring before noon. Neither distance to nesting site from water nor number of days from the first nesting event to the next nesting event varied with length of plastron.

Thermal and trophic habitats of the leatherback turtle during the nesting season in French Guiana

Understanding environmental cues determining behaviour and habitat use of species of conservation concern is crucial if one aims at implementing sustainable management of these natural resources. In this way, here, we investigate the thermal and trophic conditions encountered by the critically endangered leatherback sea turtle Dermochelys coriacea during its nesting season in French Guiana where high bycatch rates have been reported. Mean sea water temperatures obtained in situ by animal-borne recorders were 26.6 ± 0.7 °C in the water column, with all but one turtle remaining in water > 25 °C during the inter-nesting interval. In terms of prey availability, regular jellyfish stranding events were recorded during the nesting season, on a 1.25-km long section of the nesting beach. The occurrence of jellyfish was supported by benthic trawls performed on the continental shelf, with a total of 45.4 kg of jellyfish collected in 3.5 h exclusively in coastal waters 10 to 20 m deep where water transparency was between 0.8 and 3 m. This is consistent with the at sea distribution area of gravid leatherbacks during their inter-nesting intervals, as they spent almost 70% of their time diving in shallow (< 20 m deep) waters in front of the Maroni River estuary. In French Guiana, leatherback's gelatinous prey are thus present in very shallow water close to the nesting site and may be easily exploited by active gravid leatherbacks. This suggests that French Guiana female leatherbacks may be influenced by local trophic conditions and actively prospect productive areas overlapping with local fisheries ground.

Tracking leatherback turtles ( Dermochelys coriacea) during consecutive inter-nesting intervals: Further support for direct transmitter attachment

Over recent years there have been substantial efforts to record and interpret the post-nesting movements of leatherback turtles ( Dermochelys coriacea) breeding in tropical regions. Less well documented are the movements undertaken by individual turtles during the breeding season itself, or more specifically between sequential nesting events. Such movements are of interest for two reasons: (1) gravid female leatherbacks may range extensively into the territorial waters and nesting beaches of neighbouring countries, raising questions for conservationists and population ecologists; and (2) the magnitude of movements themselves help elucidate underlying reproductive strategies (e.g. whether to rest near to the nesting or forage extensively). Here, satellite relay data loggers are used (SRDLs) to detail the movements and behaviour of two female leatherback turtles throughout three consecutive inter-nesting intervals in the Commonwealth of Dominica, West Indies. Both near-shore residence and extensive inter-nesting movements were recorded, contrasting previous studies, with movements away from the nesting beach increasing towards the end of the nesting season. Using this behavioural study as a backdrop, the suitability of attaching satellite transmitters directly to the carapace was additionally explored as an alternative approach to conventional harness deployments. Specifically, the principal aims were to (1) gather empirical data on speed of travel and (2) assess dive performance (aerobic dive limit) to enable comparisons with turtles previously fitted with harnesses elsewhere in the Caribbean ( n = 6 turtles; Grenada, WI). This produced mixed results with animals bearing directly attached transmitters travelling significantly faster (55.21 km day − 1 ; SD 6.68) than harnessed individuals (39.80 km day − 1 ; SD 6.19); whilst no discernable difference in dive performance could be found between the two groups of study animals.

Dispersal and dive patterns in gravid leatherback turtles during the nesting season in French Guiana

We present the first combined analysis of diving behaviour and dispersal data collected from gravid leatherback turtles during 3 consecutive nesting seasons in French Guiana. In total, 23 turtles were fitted with Argos satellite transmitters and 16 individuals (including 6 that were concur- rently satellite-tracked) were equipped with an electronic time-depth recorder for single inter- nesting intervals, i.e. between 2 consecutive ovi-positions. The leatherbacks dispersed over the con- tinental shelf—from the coastal zone to the shelf break—and moved over 546.2 ± 154.1 km (mean ± SD) in waters of French Guiana and neighbouring Suriname. They mostly performed shallow (9.4 ± 9.2 m) and short (4.4 ± 3.4 min) dives with a slight diurnal pattern. They dived deeper as they moved away from the coast, suggesting that they were predominantly following the seabed. Inter-nesting intervals could be divided into 2 phases: the first comprised 75% of the time turtles spent at sea, dur- ing which they dived on average 47 min h -1 , while the second was characterised by lower and more variable diving effort as the turtles returned to shore. The extended movements of leatherbacks and the fine analysis of dive shapes suggest that, in French Guiana, leatherbacks may feed during the inter-nesting interval, probably to compensate for the energy costs associated with reproduction. Consequently, this critically endangered species is exposed to a high risk of interaction with local fisheries over the continental shelf.

Clutch Frequency in the Red-Eared Slider (Trachemys scripta elegans)

Clutch Frequency in the Red-Eared Slider (Trachemys scripta elegans)

Reptilian diving:highly variable dive patterns in the green turtle Chelonia mydas

Diving reptiles, unlike most diving birds and mammals, return infrequently to the surface to breathe. Spending the bulk of their lives underwater, they are likely to have developed a large variety of specific behavioural patterns different from those of their warm-blooded counterparts. However, for technical reasons, underwater behaviour of these aquatic reptiles remains poorly understood. In this study green turtles Chelonia mydas nesting on Cyprus (Eastern Mediterranean) were equipped with multi-channel data loggers monitoring diving behaviour and activity (via a logger-integrated 3-D compass which served as an activity sensor) during the inter-nesting interval. Data from 2 turtles for 2 consecutive inter-nesting intervals were available for detailed dive analysis. Both turtles showed highly variable dive patterns ranging from travelling subsurface dives to specific dive types such as U- (mainly resting and foraging dives), S- (a form of energy saving swimming) and V-dives. The green turtles stayed near the coast throughout the study, dived no deeper than ca 25 m, but remained underwater for up to ca 40 min. The recordings of the activity sensor revealed high activity levels (less than 20% resting d -1 ) during the whole inter-nesting period which was attributed to extensive foraging. The combination of both the activity data and the dive data showed that the turtles were engaged in travelling movements for 46 % of the inter-nesting time spent underwater, foraged for 34 % and rested for 12% of the time. We discuss the physiological, ecological and conservation implications of these results.

Reproductive Homing and Internesting Behavior of the Green Turtle (Chelonia mydas) at Ascension Island, South Atlantic Ocean

Female green turtles (Chelonia mydas) were tagged while nesting on the 32 cove-head beaches distributed in four clusters along the leeward shoreline of Ascension Island. The turtles showed high nesting site fidelity, returning to the same beach cluster during at least 70% of consecutive observed renesting emergences. Stronger site fidelity to beach clusters and also to points within the boundaries of a beach was more evident in emergences separated by less than 7 d (assumed to be repeated attempts to lay one clutch of eggs) than in nestings separated by longer time intervals, involving separate egg clutches. These differences correlate with predictable patterns of behavior observed in females, the movements of which were visually tracked during their internesting intervals. After successful oviposition, most of the tracked females traveled to a shallow area off the northwest coast of the island. Those that did not lay eggs remained in the vicinity of the beach just abandoned, traveling back and forth in nearshore waters until daylight when they moved into deeper water. The rates, patterns and periodicities of travel by Ascension turtles in their internesting habitat after successful and aborted nestings are compared with those of internesting female turtles at other breeding grounds; possible explanations for observed differences are discussed.