scholarly journals Open-sea migration of magnetically disturbed sea turtles

2000 ◽  
Vol 203 (22) ◽  
pp. 3435-3443 ◽  
Author(s):  
F. Papi ◽  
P. Luschi ◽  
S. Akesson ◽  
S. Capogrossi ◽  
G.C. Hays
Keyword(s):  
Magnetic Field ◽  
Chelonia Mydas ◽  
Brazilian Coast ◽  
Long Distance ◽  
Return Trip ◽  
Green Turtles ◽  
Ascension Island ◽  
Open Sea ◽  
Nesting Beaches ◽  
Feeding Grounds

Green turtles (Chelonia mydas) that shuttle between their Brazilian feeding grounds and nesting beaches at Ascension Island in the middle of the Atlantic Ocean are a paradigmatic case of long-distance oceanic migrants. It has been suggested that they calculate their position and the direction of their target areas by using the inclination and intensity of the earth's magnetic field. To test this hypothesis, we tracked, by satellite, green turtles during their postnesting migration from Ascension Island to the Brazilian coast more than 2000 km away. Seven turtles were each fitted with six powerful static magnets attached in such a way as to produce variable artificial fields around the turtle that made reliance on a geomagnetic map impossible. The reconstructed courses were very similar to those of eight turtles without magnets that were tracked over the same period and in the previous year, and no differences between magnetically disrupted and untreated turtles were found as regards navigational performance and course straightness. These findings show that magnetic cues are not essential to turtles making the return trip to the Brazilian coast. The navigational mechanisms used by these turtles remain enigmatic.

scholarly journals Oceanic Long-distance Navigation: Do Experienced Migrants use the Earth's Magnetic Field?

2001 ◽  
Vol 54 (3) ◽  
pp. 419-427 ◽  
Author(s):  
S. Åkesson ◽  
P. Luschi ◽  
A. C. Broderick ◽  
F. Glen ◽  
B. J. Godley ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Satellite Telemetry ◽  
Oceanic Islands ◽  
South Atlantic ◽  
Common Mechanism ◽  
Brazilian Coast ◽  
The South ◽  
Long Distance ◽  
Green Turtles ◽  
Ascension Island

Albatrosses and sea turtles are known to perform extremely long-distance journeys between disparate feeding areas and breeding sites located on small, isolated, oceanic islands or at specific coastal sites. These oceanic journeys, performed mainly over or through apparently featureless mediums, indicate impressive navigational abilities, and the sensory mechanisms used are still largely unknown. This research used three different approaches to investigate whether bi-coordinate navigation based on magnetic field gradients is likely to explain the navigational performance of wandering albatrosses in the South Atlantic and Indian Oceans and of green turtles breeding on Ascension Island in the South Atlantic Ocean. The possibility that magnetic field parameters can potentially be used in a bi-coordinate magnetic map by wandering albatrosses in their foraging area was investigated by analysing satellite telemetry data published in the literature. The possibilities for using bi-coordinate magnetic navigation varied widely between different areas of the Southern Oceans, indicating that a common mechanism, based on a bi-coordinate geomagnetic map alone, was unlikely for navigation in these areas. In the second approach, satellite telemetry was used to investigate whether Ascension Island green turtles use magnetic information for navigation during migration from their breeding island to foraging areas in Brazilian coastal waters. Disturbing magnets were applied to the heads and carapaces of the turtles, but these appeared to have little effect on their ability to navigate. The only possible effect observed was that some of the turtles with magnets attached were heading for foraging areas slightly south of the control turtles along the Brazilian coast. In the third approach, breeding female green turtles were deliberately displaced in the waters around Ascension Island to investigate which cues these turtles might use to locate and return to the island; the results suggested that cues transported by wind might be involved in the final stages of navigation.

scholarly journals Inter- and Intra-Beach Thermal Variation for Green Turtle Nests on Ascension Island, South Atlantic

1995 ◽  
Vol 75 (2) ◽  
pp. 405-411 ◽  
Author(s):  
Graeme C. Hays ◽  
Colin R. Adams ◽  
Jeanne A. Mortimer ◽  
J.R. Speakman
Keyword(s):  
Green Turtle ◽  
Chelonia Mydas ◽  
South Atlantic ◽  
Nest Temperature ◽  
Long Beach ◽  
Thermal Variation ◽  
Green Turtles ◽  
North East ◽  
Ascension Island ◽  
East Bay

Nest temperatures for green turtles (Chelonia mydas) nesting on Ascension Island, South Atlantic (7°57'S 14°22'W), were examined. Temperature probes were placed into nests on two beaches, Long Beach (26 nests) and North East Bay (8 nests). Within these beaches there was relatively little thermal variation (SD of nest temperature was 0.32°C for Long Beach and 0.30°C for North East Bay). To examine inter-beach thermal variation temperature probes were buried at 55 cm on 12 beaches. Inter-beach thermal variation was large and was related to the beach albedo with the darkest beach (albedo, 016) being 4.2°C warmer than the lightest coloured beach (albedo, 0.73).

scholarly journals The nesting success of green turtles on beaches at Kazanli, Turkey

Oryx ◽  
1992 ◽  
Vol 26 (3) ◽  
pp. 165-171 ◽  
Author(s):  
Stephanie J. Coley ◽  
Andrew C. Smart
Keyword(s):  
Nest Site ◽  
Chelonia Mydas ◽  
Nesting Success ◽  
Beach Erosion ◽  
Marine Turtle ◽  
Chemical Pollution ◽  
Turtle Species ◽  
Green Turtles ◽  
Nesting Beaches ◽  
Turkish Society

The green turtle Chelonia mydas is one of two marine turtle species to nest in Turkey. Its three main nesting beaches are in eastern Turkey, with possibly the densest congregation of nesting turtles in the Mediterranean being found at Kazanli. However, beach erosion, hatchling predation, agricultural encroachment and chemical pollution mean that the future of the Kazanli nest site is uncertain. The Turkish Society for the Protection of Nature (Dogal Hayati Koruma Dernegi) is making valiant efforts to protect all the turtle nesting beaches in Turkey but lacks detailed information on the numbers of nesting turtles on many beaches. This paper describes a short study of nesting turtles at Kazanli during 1990 and makes recommendations for the conservation of the nesting beach.

Sea Turtle Navigation and the Detection of Geomagnetic Field Features

1998 ◽  
Vol 51 (1) ◽  
pp. 10-22 ◽  
Author(s):  
Kenneth J. Lohmann ◽  
Catherine M. F. Lohmann
Keyword(s):  
Chelonia Mydas ◽  
Sea Turtle ◽  
Ocean Basin ◽  
Open Ocean ◽  
Continuous Series ◽  
Turtle Species ◽  
Green Turtles ◽  
Open Sea ◽  
Circular Current ◽  
Distant Target

The lives of sea turtles consist of a continuous series of migrations. As hatchlings, the turtles swim from their natal beaches into the open sea, often taking refuge in circular current systems (gyres) that serve as moving, open-ocean nursery grounds. The juveniles of many populations subsequently take up residence in coastal feeding areas that are located hundreds or thousands of kilometres from the beaches on which the turtles hatched; some juveniles also migrate between summer and winter habitats. As adults, turtles periodically leave their feeding grounds and migrate to breeding and nesting regions, after which many return to their own specific feeding sites. The itinerant lifestyle characteristic of most sea turtle species is thus inextricably linked to an ability to orient and navigate accurately across large expanses of seemingly featureless ocean.In some sea turtle populations, migratory performance reaches extremes. The total distances certain green turtles (Chelonia mydas) and loggerheads (Caretta caretta) traverse over the span of their lifetimes exceed tens of thousands of kilometres, several times the diameter of the turtle's home ocean basin. Adult migrations between feeding and nesting habitats can require continuous swimming for periods of several weeks. In addition, the paths of migrating turtles often lead almost straight across the open ocean and directly to the destination, leaving little doubt that turtles can navigate to distant target sites with remarkable efficiency.

Nesting of green turtles (Chelonia mydas) at Ascension Island, South Atlantic

2001 ◽  
Vol 97 (2) ◽  
pp. 151-158 ◽  
Author(s):  
Brendan J Godley ◽  
Annette C Broderick ◽  
Graeme C Hays
Keyword(s):  
Chelonia Mydas ◽  
South Atlantic ◽  
Green Turtles ◽  
Ascension Island

Reproductive investment by green turtles nesting on Ascension Island

1993 ◽  
Vol 71 (6) ◽  
pp. 1098-1103 ◽  
Author(s):  
Graeme C. Hays ◽  
Colin R. Adams ◽  
John R. Speakman
Keyword(s):  
Egg Size ◽  
Reproductive Investment ◽  
Chelonia Mydas ◽  
The Body ◽  
Adult Size ◽  
Green Turtles ◽  
Female Body Size ◽  
Ascension Island ◽  
Egg Chamber ◽  
The Relationship

Clutch sizes and egg sizes were measured for green turtles (Chelonia mydas) nesting on Ascension Island in the South Atlantic (7°57′S, 14 °22′W) in 1992. The mean number of eggs per clutch was 127.5 (SD = 22.9; n = 46 clutches). The number of eggs per clutch increased in larger turtles and declined as the nesting season progressed. Mean egg size was 45.5 mm (SD = 1.45 mm; n = 47 clutches). Three turtles laid significantly smaller eggs than the rest of the sample. When these three clutches were removed from the analysis, mean egg size increased in larger turtles. When the effect of female body size was removed there was no relationship between the number and size of the eggs in a clutch. The depth from the top to the bottom of the egg chamber, the depth from the top of the egg chamber to the topmost egg, and the depth of the body pit were all independent of adult size. Egg size varied systematically within clutches, the largest eggs being laid first and the smallest eggs last. This intraclutch variation in egg size had important consequences for the calculated gradient of the relationship between egg size and adult size.

Migration of green turtles (Chelonia mydas) from Australasian feeding grounds inferred from genetic analyses

2010 ◽  
Vol 61 (12) ◽  
pp. 1376 ◽  
Author(s):  
Kiki E. M. Dethmers ◽  
Michael P. Jensen ◽  
Nancy N. FitzSimmons ◽  
Damien Broderick ◽  
Colin J. Limpus ◽  
...  
Keyword(s):  
Anthropogenic Impacts ◽  
Geographic Distance ◽  
Chelonia Mydas ◽  
Breeding Population ◽  
Breeding Sites ◽  
Green Turtles ◽  
The North ◽  
Breeding Populations ◽  
The Impact ◽  
Feeding Grounds

Coastal seagrass habitats in tropical and subtropical regions support aggregations of resident green turtles (Chelonia mydas) from several genetically distinct breeding populations. Migration of individuals to their respective dispersed breeding sites provides a complex pattern of migratory connectivity among nesting and feeding habitats of this species. An understanding of this pattern is important in regions where the persistence of populations is under threat from anthropogenic impacts. The present study uses mitochondrial DNA and mixed-stock analyses to assess the connectivity among seven feeding grounds across the north Australian coast and adjacent areas and 17 genetically distinct breeding populations from the Indo-Pacific region. It was hypothesised that large and geographically proximate breeding populations would dominate at nearby feeding grounds. As expected, each sampled feeding area appears to support multiple breeding populations, with two aggregations dominated by a local breeding population. Geographic distance between breeding and feeding habitat strongly influenced whether a breeding population contributed to a feeding ground (wi = 0.654); however, neither distance nor size of a breeding population was a good predictor of the extent of their contribution. The differential proportional contributions suggest the impact of anthropogenic mortality at feeding grounds should be assessed on a case-by-case basis.

scholarly journals Orientation to Oceanic Waves by Green Turtle Hatchlings

1992 ◽  
Vol 171 (1) ◽  
pp. 1-13 ◽  
Author(s):  
KENNETH J. LOHMANN ◽  
CATHERINE M. FITTINGHOFF LOHMANN
Keyword(s):  
Green Turtle ◽  
Weather Conditions ◽  
Chelonia Mydas ◽  
Sea Turtle ◽  
Wave Direction ◽  
Physiological Mechanisms ◽  
Wave Propagation Direction ◽  
Green Turtles ◽  
Open Sea ◽  
Vertical Accelerations

Minutes after emerging from underground nests, hatchling green turtles (Chelonia mydas L.) enter the sea and begin a migration towards the open ocean. To test the hypothesis that migrating hatchlings use wave cues to maintain their seaward headings, we released turtles offshore during unusual weather conditions when waves moved in atypical directions. Hatchlings swam into approaching waves in all experiments, even when doing so resulted in orientation back towards land. These data suggest that green turtle hatchlings normally maintain seaward headings early in the offshore migration by using wave propagation direction as an orientation cue. Because waves and swells reliably move towards shore in shallow coastal areas, swimming into waves usually results in movement towards the open sea. The physiological mechanisms that underlie wave detection by sea turtle hatchlings are not known. Calculations indicate that, at the depth at which hatchlings swim, accelerations produced beneath typical waves and swells along the Florida coast are sufficient to be detected by the vertebrate inner ear. We therefore hypothesize that hatchlings determine wave direction while under water by monitoring the sequence of horizontal and vertical accelerations that occur as waves pass above.

scholarly journals Orientation and open-sea navigation in sea turtles

1996 ◽  
Vol 199 (1) ◽  
pp. 73-81 ◽  
Author(s):  
K Lohmann ◽  
C Lohmann
Keyword(s):  
Magnetic Field ◽  
Visual Cues ◽  
Sea Turtles ◽  
Positional Information ◽  
Sea Turtle ◽  
Compass Orientation ◽  
Loggerhead Sea Turtle ◽  
Open Sea ◽  
Nesting Beaches ◽  
Field Inclination

Loggerhead sea turtle hatchlings (Caretta caretta L.) emerge from underground nests, scramble to the sea and begin a transoceanic migration by swimming away from their natal beach and into the open ocean. Evidence suggests that hatchlings sequentially use three different sets of cues to maintain orientation during their initial migration offshore. While on the beach, hatchlings find the ocean by crawling towards the lower, brighter seaward horizon and away from the dark, elevated silhouettes of vegetation and dunes. Upon entering the ocean, turtles initially orient seawards by swimming into waves, which can be detected as orbital movements from under water. Laboratory experiments have demonstrated that turtles can transfer a course initiated on the basis of waves or visual cues to a course mediated by a magnetic compass. Thus, by setting a magnetic course on the basis of nearshore cues that indicate the seaward direction, hatchlings may continue on offshore headings after entering deep water beyond sight of land. Sea turtles may use the earth's magnetic field not only as a cue for compass orientation but also as a source of world-wide positional information. Recent experiments have demonstrated that loggerheads can detect subtle differences in magnetic field inclination and intensity, two geomagnetic features that vary across the surface of the earth. Because most nesting beaches and oceanic regions are marked by a unique combination of these features, these findings raise the possibility that adult sea turtles navigate using a bicoordinate magnetic map.

scholarly journals Isolation of fungal pathogens from eggs of the endangered sea turtle species Chelonia mydas in Ascension Island

2016 ◽  
Vol 97 (4) ◽  
pp. 661-667 ◽  
Author(s):  
Jullie M. Sarmiento-Ramirez ◽  
Jolene Sim ◽  
Pieter Van West ◽  
Javier Dieguez-Uribeondo
Keyword(s):  
Fungal Pathogens ◽  
Control Strategies ◽  
Chelonia Mydas ◽  
Sea Turtle ◽  
Emerging Pathogens ◽  
Potential Threat ◽  
Turtle Species ◽  
Ascension Island ◽  
Fusarium Falciforme ◽  
Nesting Beaches

Fungal emerging pathogens are one of the main threats for global biodiversity. Sea turtles do not seem to be an exemption, and recent studies on important nesting areas worldwide have shown that two fungal pathogens, i.e. Fusarium falciforme and Fusarium keratoplasticum, are involved in low hatching success in nests of sea turtle species. Although the presence of these pathogens has been detected in Ascension Island, there are no investigations on the distribution of these two pathogens in main nesting beaches in the island. In this study, we analysed 109 eggshells of the species Chelonia mydas from four nesting areas in Ascension Island. We have isolated and identified a total of 46 fungal isolates. A phylogenetic analysis, of the ITS nrDNA region, with a number of reference sequences of the Fusarium solani species complex, showed that 23 of these isolates corresponded to the pathogen F. keratoplasticum. The analyses on isolation frequency, that included other previously obtained isolates, i.e. 11 F. keratoplasticum and one F. falciforme, showed that F. keratoplasticum was the species most frequently isolated in Ascension Island and it was found in all nesting beaches, while F. falciforme was only isolated from Pan Am beach. When compared with other nesting areas worldwide, the abundance of F. keratoplasticum over F. falciforme was higher than any other nesting region tested. These findings are important in order to evaluate the potential threat of this pathogen to nests of the sea turtle population of Ascension Island, and to develop future control strategies.

Sign in / Sign up

Export Citation Format

Share Document