Trans-Pacific dispersal of loggerhead turtle hatchlings inferred from numerical simulation modeling

We used Lagrangian numerical simulations to examine the trans-Pacific dispersal processes of loggerhead turtle hatchlings. Ten thousand simulated particles were released from each of the three nesting regions in Japan and tracked for 5 years. Results showed many particles moving eastward, drifting in the Kuroshio Current followed by the Kuroshio Extension Current. However, no particles reached Baja California, a known feeding area, through passive processes, indicating that trans-Pacific transportation requires active swimming by turtles. The duration of the trans-Pacific dispersal was estimated to be at least 1.6–3.4 years, with some turtles drifting in the Kuroshio Countercurrent and remaining in the western Pacific even after 5 years. This indicates that as revealed by previous genetic studies, not all loggerheads always disperse along a trans-Pacific route. The findings showed that survival and expected growth rates varied widely according to ambient temperatures during drifting, which in turn depended on nesting location.     

Satellite telemetry reveals behavioural plasticity in a green turtle population nesting in Sri Lanka

Satellite transmitters were deployed on ten green turtles (Chelonia mydas) nesting in Rekawa Sanctuary (RS-80.851°E 6.045°N), Sri Lanka, during 2006 and 2007 to determine inter-nesting and migratory behaviours and foraging habitats. Nine turtles subsequently nested at RS and demonstrated two inter-nesting strategies linked to the location of their residence sites. Three turtles used local shallow coastal sites within 60 km of RS during some or all of their inter-nesting periods and then returned to and settled at these sites on completion of their breeding seasons. In contrast, five individuals spent inter-nesting periods proximate to RS and then migrated to and settled at distant (>350 km) shallow coastal residence sites. Another turtle also spent inter-nesting periods proximate to RS and then migrated to a distant oceanic atoll and made forays into oceanic waters for 42 days before transmissions ceased. This behavioural plasticity informs conservation management beyond protection at the nesting beach.     

Are anthropogenic factors affecting nesting habitat of sea turtles? The case of Kanzul beach,Riviera Maya-Tulum (Mexico)

Marine coast modification and human pressure affects many species, including sea turtles. In order to study nine anthropogenic impacts that might affect nesting selection of females, incubation and hatching survival of loggerhead (Caretta caretta) and green turtle (Chelonia mydas), building structures were identified along a 5.2 km beach in Kanzul (Mexico). A high number of hotels and houses (88; 818 rooms), with an average density of 16.6 buildings per kilometer were found. These buildings form a barrier which prevents reaching the beach from inland, resulting in habitat fragmentation. Main pressures were detected during nesting selection (14.19% of turtle nesting attempts interrupted), and low impact were found during incubation (0.77%) and hatching (4.7%). There were three impacts defined as high: beach furniture that blocks out the movement of hatchlings or females, direct pressure by tourists, and artificial beachfront lighting that can potentially mislead hatchlings or females. High impacted areas showed lowest values in nesting selection and hatching success. Based on our results, we suggest management strategies to need to be implemented to reduce human pressure and to avoid nesting habitat loss of loggerhead and green turtle in Kanzul, Mexico.     

Migratory and reproductive movements of male leatherback turtles (<Emphasis Type="Italic">Dermochelys coriacea</Emphasis>)

The biology of the endangered leatherback turtle (Dermochelys coriacea) at sea is poorly understood. As research has been almost exclusively limited to studies of nesting females, the movements of male turtles and the timing and location of mating activity have remained unknown. We report on the first deployments of satellite tags on male leatherbacks. Male migration to and residency in waters adjacent low-latitude nesting beaches in the western Atlantic suggest that this is where mating occurs, and return migration to these areas reveals male fidelity for breeding sites. Rate of travel decreased markedly after arriving in coastal breeding areas, where males remained for up to 96 days before assuming northward migrations. The initiation of these northward migrations coincided with peak nesting activity in adjacent nesting colonies. Data from satellite-linked time-depth recorders attached to two males revealed diel dive patterns in breeding areas and marked differences in diving behaviour between migratory and breeding periods in one turtle. When male turtles were in waters adjacent nesting colonies, their movements differed from those reported for nesting females, with females ranging farther from shore. Our results suggest that male leatherbacks may be vulnerable to entanglement in coastal fishing gear in waters adjacent nesting beaches.Communicated by R.J. Thompson, St. Johns     

Migratory activity by hatchling loggerhead sea turtles (Caretta caretta L.): evidence for divergence between nesting groups

The South Florida subpopulation of loggerhead sea turtles (Caretta caretta L.) nests with great fidelity on either the southeast or the southwest coast of Florida, USA. The hatchlings that emerge from those nests must swim in opposite directions and search for different surface currents to migrate away from continental shelf waters. In this laboratory study, we compared the pattern of swimming activity shown by the hatchlings from each coast over the first 6 days of migration. Turtles from both coasts were equally active during their “frenzy” period (the first 24 h of swimming) and during the daylight hours of the 5 days that followed (the “postfrenzy” period). However, the west coast turtles were significantly more active than the east coast turtles during the nocturnal portion of the postfrenzy period. This difference may be related to the greater distance southwest coast turtles must negotiate to locate surface currents for transport out of the Gulf of Mexico and into the Atlantic Ocean basin. These differing behavioral strategies may be genetically determined, as similar correspondence between activity and distance is well known among migratory populations of birds and fish and is often based upon inherited programs of endogenously driven activity. Alternatively, behavioral differences between the two nesting groups could be a manifestation of phenotypic plasticity that arises as the hatchlings respond to unique environmental cues on each coast.     

Predicting the Impact of Sea-Level Rise on Caribbean Sea Turtle Nesting Habitat

Abstract:  The projected rise in sea level is likely to increase the vulnerability of coastal zones in the Caribbean, which are already under pressure from a combination of anthropogenic activities and natural processes. One of the major effects will be a loss of beach habitat, which provides nesting sites for endangered sea turtles. To assess the potential impacts of sea-level rise on sea turtle nesting habitat, we used beach profile measurements of turtle nesting beaches on Bonaire, Netherlands Antilles, to develop elevation models of individual beaches in a geographic information system. These models were then used to quantify areas of beach vulnerable to three different scenarios of a rise in sea level. Physical characteristics of the beaches were also recorded and related to beach vulnerability, flooding, and nesting frequency. Beaches varied in physical characteristics and therefore in their vulnerability to flooding. Up to 32% of the total current beach area could be lost with a 0.5-m rise in sea level, with lower, narrower beaches being the most vulnerable. Vulnerability varied with land use adjacent to the beach. These predictions about loss of nesting habitat have important implications for turtle populations in the region.     

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.     

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.     

Migratory activity by hatchling loggerhead sea turtles (Caretta caretta L.): evidence for divergence between nesting groups

The South Florida subpopulation of loggerhead sea turtles (Caretta caretta L.) nests with great fidelity on either the southeast or the southwest coast of Florida, USA. The hatchlings that emerge from those nests must swim in opposite directions and search for different surface currents to migrate away from continental shelf waters. In this laboratory study, we compared the pattern of swimming activity shown by the hatchlings from each coast over the first 6 days of migration. Turtles from both coasts were equally active during their “frenzy” period (the first 24 h of swimming) and during the daylight hours of the 5 days that followed (the “postfrenzy” period). However, the west coast turtles were significantly more active than the east coast turtles during the nocturnal portion of the postfrenzy period. This difference may be related to the greater distance southwest coast turtles must negotiate to locate surface currents for transport out of the Gulf of Mexico and into the Atlantic Ocean basin. These differing behavioral strategies may be genetically determined, as similar correspondence between activity and distance is well known among migratory populations of birds and fish and is often based upon inherited programs of endogenously driven activity. Alternatively, behavioral differences between the two nesting groups could be a manifestation of phenotypic plasticity that arises as the hatchlings respond to unique environmental cues on each coast.     

Patterns in the emergence of green (<Emphasis Type="Italic">Chelonia mydas</Emphasis>) and loggerhead (<Emphasis Type="Italic">Caretta caretta</Emphasis>) turtle hatchlings from their nests

The emergence patterns of both green (Chelonia mydas) and loggerhead (Caretta caretta) turtle hatchlings were observed in great detail over three seasons at Alagadi beach, northern Cyprus. In total, 38 green turtle and 50 loggerhead turtle nests were monitored, accounting for the emergence of 2,807 and 2,259 hatchlings, respectively. We quantified these emergences into 397 green turtle and 302 loggerhead turtle emergence groups. Overall, 85.0% of green turtle and 79.5% of loggerhead turtle groups emerged at night; these accounted for 85.5 and 90.8% of hatchlings, respectively. The remaining emergences were dispersed throughout the day for green turtle nests but confined to the morning in loggerhead turtle nests. Hatchling emergence from individual nests occurred over periods of between 1 and 7 nights, with most hatchlings typically emerging on the first night. Group sizes of green turtles emerging during the day were significantly smaller than those emerging at night. Hatchlings of both species that emerged from nests during the day had longer emergence durations than those that emerged from nests at night only.Communicated by R.J. Thompson, St. Johns     

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.     

Migration of green turtles <Emphasis Type="Italic">Chelonia mydas</Emphasis> from Tortuguero,Costa Rica

During 1955–2003, flipper tags were attached to 46,983 green turtles and ten turtles were fitted with satellite transmitters at Tortuguero, Costa Rica. Eight satellite-tracked turtles stayed within 135 km of the beach and probably returned to nest after release. The internesting area is more extensive than previously documented. Post-nesting migration routes of satellite-tracked turtles varied. Seven turtles swam close to the coast and three turtles swam through oceanic waters before moving toward nearshore areas. Sea surface height anomaly maps indicate that oceanic movements were consistent with the southwestern Caribbean gyre. Circling and semi-circling turtles could have been disoriented but submergence and surface times suggest they may have been feeding in Sargassum sp. concentrations. Rapid post-nesting migrations (mean 2.2 km hr⁻¹) ended on benthic feeding grounds in shallow waters (<20 m) off Belize (n=1), Honduras (n=1) and Nicaragua (n=8). The spatial distribution of migration end points (n=10) and tag returns (n=4,669) are similar. Fishermen in Nicaragua target green turtles along migratory corridors and on foraging grounds. Management efforts are urgently needed in Nicaragua, particularly in the high-density feeding areas south and east of the Witties (N14°09 W82°45). The proximity of foraging grounds to the nesting beach (mean 512 km) may permit female turtles to invest more energy in reproduction and hence the Tortuguero population may have greater potential for recovery than other green turtle nesting populations. Recovery of the Tortuguero green turtle population will benefit countries and marine ecosystems throughout the Caribbean, especially Nicaragua.     

Some observations of sea turtle nesting activity in Costa Rica

Low level aerial observations were used to obtain synoptic records of the distribution of sea turtle nesting activity along both coasts of Costa Rica. Pertinent environmental information was simultaneously recorded including beach characteristics, river effluents, and evidence of coastal currents. Other correlative information was obtained from detailed maps, current charts, and climatological data. On the Caribbean coast, as expected, green turtle (Chelonia mydas) nesting was concentrated on the beaches between the Tortuguero and Parismina Rivers. On the Pacific coast, two major nesting beaches for the Pacific ridley Lepidochelys olivacea were found, each having over 100 thousand turtles aggregated offshore during the peak period between September and November. Aggregations were present at least from July through December. Massed nesting occurs each year on these same beaches and the event is known as the salida de flota by the natives of Guanacaste Province. Numerous less important nesting beaches were also found. Nesting density did not correlate well with beach quality but, instead, appeared to be related to the proximity of the beach to offshore currents. Oceanic current systems apparently facilitate the transport of sea turtles to the general vicinity of the important nesting beaches on both coasts of Coata Rica.Contribution No. 1557 from the Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, USA.     

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.     

Tracking post-nesting movements of loggerhead turtles (Caretta caretta) with sonic and radio telemetry on the southwest coast of Florida, USA

Nine post-nesting loggerhead turtles (Caretta caretta) were tracked using sonic and radio telemetry. Tracking began immediately after the turtles left the beach and continued until contact was either lost or terminated. As sonic tags transmit continuously underwater, they were much more effective than the radio tags in determining the paths of the turtles. Radio tags transmit only at the surface and were useful in ascertaining submergence durations. For nine of the ten turtles tracked with sonic signals, the gross movement was away from the beach in a westerly direction. The tracking periods ranged from 3.35 to 8.25 h, while the straight-line movements ranged from 3.05 to 12.88 km, respectively. Sixty-seven percent of the submergence durations recorded were <3 min. This respiratory behavior suggests continuous swimming, and the paths of the turtles suggested directed movement offshore immediately after nesting. The gradual littoral slope and lack of nearshore structure in this part of the Gulf of Mexico could be contributing factors to the patterns of dispersal observed, as benthic structures provide resting and foraging habitat for loggerheads.     

Breeding biology of the green turtle, Chelonia mydas (Reptilia: Cheloniidae), on Wan-An Island, PengHu archipelago. II. Nest site selection

Nest site selection of the green turtles on Wan-An Island in the summer of 1996 was determined. Turtles (Chelonia mydas) laid on average one clutch for every three emergences. Even though the total track length was 115 m on average, individual lengths varied considerably depending on the nesting beach where the turtles emerged. Limited accessibility, i.e. adequate distance from the nearest village and a well-protected environment, make beaches A and D suitable nesting beaches for green turtles on Wan-An Island. Both total track and nesting track apexes were found clustered in the interface zone, and turtles preferred to reach the vegetation zone once they emerged from the sea. It is suggested that the turtles on Wan-An Island exhibit nest site selection behavior. Based on these results and the high nest site fidelity to their first nesting beach, conservation recommendations are proposed to the county and central governments for the preservation of nesting beaches in their natural state, by prohibiting illegal sand mining and properly controlling turtle watch groups on Wan-An Island. Received: 21 November 1997 / Accepted: 24 December 1998     

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.     

Putting Longline Bycatch of Sea Turtles into Perspective

Abstract:  Although some sea turtle populations are showing encouraging signs of recovery, others continue to decline. Reversing population declines requires an understanding of the primary factor(s) that underlie this persistent demographic trend. The list of putative factors includes direct turtle and egg harvest, egg predation, loss or degradation of nesting beach habitat, fisheries bycatch, pollution, and large-scale changes in oceanographic conditions and nutrient availability. Recently, fisheries bycatch, in particular bycatch from longline fisheries, has received increased attention and has been proposed as a primary source of turtle mortality. We reviewed the existing data on the relative impact of longline bycatch on sea turtle populations. Although bycatch rates from individual longline vessels are extremely low, the amount of gear deployed by longline vessels suggests that cumulative bycatch of turtles from older age classes is substantial. Current estimates suggest that even if pelagic longlines are not the largest single source of fisheries-related mortality, longline bycatch is high enough to warrant management actions in all fleets that encounter sea turtles. Nevertheless, preliminary data also suggest that bycatch from gillnets and trawl fisheries is equally high or higher than longline bycatch with far higher mortality rates. Until gillnet and trawl fisheries are subject to the same level of scrutiny given to pelagic longlines, our understanding of the overall impact of fisheries bycatch on vulnerable sea turtle populations will be incomplete.     

Satellite tracking reveals a dichotomy in migration strategies among juvenile loggerhead turtles in the Northwest Atlantic

Few data are available on the movements and behavior of immature Atlantic loggerhead sea turtles (Caretta caretta) from their seasonal neritic foraging grounds within the western north Atlantic. These waters provide developmental habitat for loggerheads originating from several western Atlantic nesting stocks. We examined the long-term movements of 23 immature loggerheads (16 wild-caught and seven headstart turtles) characterizing their seasonal distribution, habitat use, site fidelity, and the oceanographic conditions encountered during their migrations. We identified two movement strategies: (1) a seasonal shelf-constrained north–south migratory pattern; and (2) a year-round oceanic dispersal strategy where turtles travel in the Gulf Stream to the North Atlantic and their northern dispersal is limited by the 10–15°C isotherm. When sea surface temperatures dropped below 20°C, neritic turtles began a migration south of Cape Hatteras, North Carolina (USA) where they established fidelity to the waters between North Carolina’s Outer Banks and the western edge of the Gulf Stream along outer continental shelf. Two turtles traveled as far south as Florida. Several turtles returned to their seasonal foraging grounds during subsequent summers. Northern movements were associated with both increased sea surface temperature (>21°C) and increased primary productivity. Our results indicate strong seasonal and interannual philopatry to the waters of Virginia (summer foraging habitat) and North Carolina (winter habitat). We suggest that the waters of Virginia and North Carolina provide important seasonal habitat and serve as a seasonal migratory pathway for immature loggerhead sea turtles. North Carolina’s Cape Hatteras acts as a seasonal “migratory bottleneck” for this species; special management consideration should be given to this region. Six turtles spent time farther from the continental shelf. Three entered the Gulf Stream near Cape Hatteras, traveling in the current to the northwest Atlantic. Two of these turtles remained within an oceanic habitat from 1 to 3 years and were associated with mesoscale features and frontal systems. The ability of large benthic subadults to resume an oceanic lifestyle for extended periods indicates plasticity in habitat use and migratory strategies. Therefore, traditional life history models for loggerhead sea turtles should be reevaluated.     

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