Adult Sea Turtles Research Articles

Efforts in the State of Qatar to conserve and monitor endangered marine turtles

Abstract Marine turtles are listed as endangered and they belong to Animal Kingdom phylum Chordata, class Reptilia and are descendants from early reptiles. Marine turtles are long-living and the females lay many eggs. Each year, thousands of hatchlings emerge from their nests along many coastlines across the world. Natural obstacles faced by young and adult sea turtles are numerous and on the increase, including natural predators and human exploitation. Unfortunately, only an estimated one in 1000 to 10000 will survive to adulthood. Together with marine biologists at Qatar University, studies on marine turtles in the State of Qatar were initiated in 2002, sponsored by Ras Laffan Industrial City. The outcome of the 2002 study provided the baseline data needed for subsequent studies. It has now been established that only one species of the endangered extant marine turtles, the Hawksbill turtle, nests in the Gulf area and in Qatar along the northeastern sandy beaches and islands (Ras Laffan, Fewairit, Al Maronah, Al Ghariyah, Jazirat Ras Rakan, Jazirat Umm Al Tays and Halul Island). Studies showed that Ras Laffan City is a major nesting area [No. of nests recorded since 2001: (2001: 74), (2002: 240), (2003:208), (2004: 190), (2005: 229), (2006:129), (2007:76), (2009: 72)]. An outcome of the studies since 2002 showed that females average clutch size varies between 65-78 eggs, which are incubated for 51-57 days in a nest temperature of 28.6⁰C – 33.3⁰C. Since 2009, efforts to monitor the nesting population along the Qatar coastline have started and the satellite tracking of females continues. This showed the females remain in the Gulf waters between Ras Laffan moving north (Kingdom Bahrain – Kingdom of Saudi Arabia) and south to the UAE. One tracked female travelled a maximum distance of 1917 km in 147 days. A number of females have been tagged to date, of which 3 tagged in 2005 returned to nest in 2009. Between 2009 and 2010 over 40 females were tagged.

Estimating demographic parameters for loggerhead sea turtles using mark–recapture data and a multistate model

AbstractThe survival for adult loggerhead sea turtles from a saturation tagging study on Bald Head Island, NC, USA, was estimated using a multistate model with unobservable states to relax assumptions that are violated when survival is estimated from multistate models and produce more accurate estimates of survival, recapture, and breeding transition probabilities. The influence of time, trap dependence, and low site fidelity to the study nesting beach on survival and recapture were examined. The best model given the data included an imprecise site‐fidelity effect on survival, constrained the reproductive cycle to 4 years, and contained a time effect on recapture rates. The estimate of annual survival for adult females was of 0.85, producing the highest estimate in the literature for loggerhead sea turtles. Multistate models should be applied to other nesting beach data for sea turtles to improve survival estimates and in turn the ability to model and manage populations.

Individual specialists in a generalist population: results from a long-term stable isotope series

Individual variation in resource use has often been ignored in ecological studies, but closer examination of individual patterns through time may reveal significant intrapopulation differences. Adult loggerhead sea turtles (Caretta caretta) are generalist carnivores with a wide geographical range, resulting in a broad isotopic niche. We microsampled scute, a persistent and continuously growing tissue, to examine long-term variation in resource use (up to 12 years) in 15 nesting loggerhead turtles. Using stable isotopes of nitrogen and carbon, we examined the resource use patterns (integration of diet, habitat and geographical location) and demonstrate that individual loggerheads are long-term specialists within a generalist population. We present our results in the context of a conceptual model comparing isotopic niches in specialist and generalist populations. Individual consistency may have important ecological, evolutionary and conservation consequences, such as the reduction of intraspecific competition.

Ontogenetic development of migration: Lagrangian drift trajectories suggest a new paradigm for sea turtles

Long distance migration occurs in a wide variety of taxa including birds, insects, fishes, mammals and reptiles. Here, we provide evidence for a new paradigm for the determinants of migration destination. As adults, sea turtles show fidelity to their natal nesting areas and then at the end of the breeding season may migrate to distant foraging sites. For a major rookery in the Mediterranean, we simulated hatchling drift by releasing 288 000 numerical particles in an area close to the nesting beaches. We show that the pattern of adult dispersion from the breeding area reflects the extent of passive dispersion that would be experienced by hatchlings. Hence, the prevailing oceanography around nesting areas may be crucial to the selection of foraging sites used by adult sea turtles. This environmental forcing may allow the rapid evolution of new migration destinations if ocean currents alter with climate change.

Ultrasound Imaging of the Inguinal Region of Adult Male Loggerhead Sea Turtles (Caretta caretta)

The biology and reproductive anatomy of male loggerhead sea turtles (Caretta caretta) have been difficult to study. The principle method for evaluation of the coelomic cavity in both adult and juvenile male sea turtles is celioscopy. The purpose of this study was to describe the technique and structures seen when scanning the inguinal region of live, wild-caught, adult male loggerhead sea turtles and to compare these findings to those resulting from celioscopy and necropsy. Twenty-one adult male loggerhead sea turtles were collected by trawling in the Cape Canaveral shipping channel in April 2007. All turtles were placed in dorsal recumbency and imaged with a Sonosite 180 Vet Plus (Sonosite, Inc., Bothell, Washington 98021, USA) and a microconvex, 4-7-MHz curvilinear array probe. The inguinal region was divided into four quadrants: cranial, lateral, medial, and caudal. Celioscopy was performed on 13 turtles, and biopsies were obtained of the testes and the epididymides to confirm correct identification of the structures. In the cranial aspect of the inguinal region, the urinary bladder and large and small intestines were identified. In the lateral inguinal region, the lung and kidney were seen. In the medial aspect of the inguinal region, the testis and epididymis were routinely identified. In the caudal aspect of the inguinal region, the coxofemoral joint was seen. A small learning curve was required; however, correlation with celioscopy and biopsy showed that consistent, repeatable identification of caudal coelomic structures was easily achieved. Ultrasound provided an inexpensive, rapid, noninvasive method to evaluate the reproductive anatomy of live-captured, male loggerhead sea turtles.

Ontogenetic changes in tracheal structure facilitate deep dives and cold water foraging in adult leatherback sea turtles

Adult leatherbacks are large animals (300-500 kg), overlapping in size with marine pinniped and cetacean species. Unlike marine mammals, they start their aquatic life as 40-50 g hatchlings, so undergo a 10,000-fold increase in body mass during independent existence. Hatchlings are limited to the tropics and near-surface water. Adults, obligate predators on gelatinous plankton, encounter cold water at depth (<1280 m) or high latitude and are gigantotherms that maintain elevated core body temperatures in cold water. This study shows that there are great ontogenetic changes in tracheal structure related to diving and exposure to cold. Hatchling leatherbacks have a conventional reptilian tracheal structure with circular cartilaginous rings interspersed with extensive connective tissue. The adult trachea is an almost continuous ellipsoidal cartilaginous tube composed of interlocking plates, and will collapse easily in the upper part of the water column during dives, thus avoiding pressure-related structural and physiological problems. It is lined with an extensive, dense erectile vascular plexus that will warm and humidify cold inspired air and possibly retain heat on expiration. A sub-luminal lymphatic plexus is also present. Mammals and birds have independently evolved nasal turbinates to fulfil such a respiratory thermocontrol function; for them, turbinates are regarded as diagnostic of endothermy. This is the first demonstration of a turbinate equivalent in a living reptile.

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.

A review of lethal and non-lethal effects of predators on adult marine turtles

Although predation is recognized as an important factor for sea turtles at early life history stages, the possible influences of predators on adult sea turtles have largely been overlooked. Indeed, because predation rates on adult turtles generally are low, it often is assumed that predators do not influence turtle behavior, affect population sizes, or structure sea turtle impacts on marine communities. Yet, sharks, killer whales and crocodiles may take adult turtles, and no sea turtle species is invulnerable. Furthermore, as long-lived animals, adult sea turtles are predicted to invest in anti-predator behavior even when predation risk is relatively low to avoid the reproductive costs of an early death. Several studies suggest that predators may influence behavior and habitat use of adult turtles. For example, in a pristine ecosystem in Australia green turtles, especially those in good body condition, avoid profitable feeding areas in order to be safe from tiger sharks. Such predation-sensitive foraging could lead to populations being partially regulated by synergistic effects of predation risk and food abundance. Indeed, observed rapid rebounds of sea turtle populations may have been facilitated by reductions in shark populations. Finally, if sea turtles modify their foraging habitat use in response to predators, the spatiotemporal pattern of turtle effects on their communities could be shaped by predators. Historical reconstructions of past turtle populations and conservation strategies aimed at increasing turtle populations must consider the possible effects of predators, including non-lethal ones. Future work should focus on gaining a broader understanding of the effects of predators across a range of sea turtle taxa and habitats.

Goal navigation and island-finding in sea turtles

Juvenile and adult sea turtles often navigate to specific feeding areas during long-distance migrations, and adults periodically return to particular geographic areas for mating and nesting. In addition, turtles displaced from feeding or nesting areas often home to the site of capture. Relatively little is known, however, about how turtles navigate to particular goal areas. Both juvenile and adult turtles use the Earth's magnetic field as a source of navigational information. Laboratory experiments have provided evidence that juvenile green turtles learn the magnetic topography of their feeding grounds and acquire a “magnetic map” that facilitates navigation toward particular locations. Adult green turtles displaced from nesting beaches on an island in the Indian Ocean showed diminished homing ability when magnets were attached to their heads, implying that mature turtles also exploit magnetic cues when navigating to islands or other specific destinations. Although geomagnetic information appears to be an important component of sea turtle navigation, it is unlikely to be the only cue used. Additional experiments in which nesting green turtles were displaced from islands have highlighted the possible involvement of local, non-magnetic cues in the final phase of island-finding. Thus, a reasonable hypothesis is that turtles use multiple cues to navigate in the marine environment, perhaps relying on a magnetic map to navigate into the vicinity of a distant target and then using non-magnetic cues to guide themselves to the final goal.

Important areas at sea for adult loggerhead sea turtles in the Mediterranean Sea: satellite tracking corroborates findings from potentially biased sources

Sea turtle populations worldwide suffer from reduced survival of immatures and adults due to fishery bycatch. Unfortunately, information about the whereabouts of turtles outside the breeding habitat is scarce in most areas, hampering the development of spatially explicit conservation plans. In the Mediterranean, recoveries of adult females flipper-tagged on nesting beaches suggest that the Adriatic Sea and Gulf of Gabès are important foraging areas for adults, but such information could be heavily biased (observing and reporting bias). In order to obtain unbiased data, we satellite-tracked seven loggerhead sea turtles after they completed nesting in the largest known Mediterranean rookery (Bay of Laganas, Zakynthos, Greece). Three females settled in the north Adriatic Sea, one in the south Adriatic Sea and two in the Gulf of Gabès area at the completion of their post-nesting migrations (one individual did not occupy a distinct foraging area). The concordance of tracking results with information from recoveries of flipper-tagged turtles suggests that the north Adriatic Sea and the Gulf of Gabès represent key areas for female adult Mediterranean loggerhead sea turtles.

Long-distance navigation in sea turtles

Adult sea turtles of several species migrate across vast expanses of ocean to arrive at specific nesting areas and feeding sites. Two hypotheses have been proposed to account for this remarkable navigation. The first is that chemical cues emanating from target areas guide turtles to their destinations. The second is that turtles can approximate their position relative to target regions using features of the earth's magnetic field. Because animals often rely on multiple cues while migrating, the two hypotheses are not mutually exclusive. Satellite tracking experiments have revealed that migrating turtles often swim directly to distant goals, even when traveling perpendicularly to water currents. Because animals usually change course frequently while seeking the source of a chemical plume, the consistency of headings casts doubt on the hypothesis that turtles follow such plumes over great distances. Chemical cues may nevertheless play a role in enabling turtles to recognize a target area in the final stages of a long migration. The magnetic navigation hypothesis is based on the finding that hatchling loggerhead turtles can detect two different features of the geomagnetic field (inclination angle and intensity) that vary across the earth's surface. Hatchlings from Florida, U.S.A., respond to magnetic features found along their migratory route by swimming in directions that may help keep them safely within the North Atlantic gyre, a circular warm-water current system favorable for growth and development. These results suggest that young turtles can derive positional information from features of the earth's field, and that such information may play an important role in guiding trans-oceanic migrations. Adults might also exploit geomagnetic features in long-distance navigation. In principle, turtles nesting on coastlines might locate the appropriate region by returning to an area marked by the intersection of the shoreline and a magnetic isoline (e.g., a particular inclination angle or intensity). Turtles that migrate to remote islands may be able to exploit bicoordinate magnetic maps for positionfinding, although secular variation and other factors may limit the conditions under which such a system can be used.

Orientation and open-sea navigation in sea turtles

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.

DETECTION OF MAGNETIC INCLINATION ANGLE BY SEA TURTLES: A POSSIBLE MECHANISM FOR DETERMINING LATITUDE

For animals that migrate long distances, the magnetic field of the earth provides not only a possible cue for compass orientation, but a potential source of world-wide positional information. At each location on the globe, the geomagnetic field lines intersect the earth's surface at a specific angle of inclination. Because inclination angles vary with latitude, an animal able to distinguish between different field inclinations might, in principle, determine its approximate latitude. Such an ability, however, has never been demonstrated in any animal. We studied the magnetic orientation behavior of hatchling loggerhead sea turtles (Caretta caretta L.) exposed to earth-strength magnetic fields of different inclinations. Hatchlings exposed to the natural field of their natal beach swam eastward, as they normally do during their offshore migration. In contrast, those subjected to an inclination angle found on the northern boundary of the North Atlantic gyre (their presumed migratory path) swam south-southwest. Hatchlings exposed to an inclination angle found near the southern boundary of the gyre swam in a northeasterly direction, and those exposed to inclination angles they do not normally encounter, or to a field inclination found well within the northern and southern extremes of the gyre, were not significantly oriented. These results demonstrate that sea turtles can distinguish between different magnetic inclination angles and perhaps derive from them an approximation of latitude. Most sea turtles nest on coastlines that are aligned approximately north&shy;south, so that each region of nesting beach has a unique inclination angle associated with it. We therefore hypothesize that the ability to recognize specific inclination angles may largely explain how adult sea turtles can identify their natal beaches after years at sea.

Surveys of the sea turtles of Angola

Five species of sea turtles have been reported from Angola (in decreasing order of abundance): leatherback Dermochelys coriacea, olive ridley Lepidochelys olivacea, green Chelonia mydas, loggerhead Caretta caretta, and hawksbill Eretmochelys imbricata. All have been reported to nest on Angolan beaches, although with varying frequency. Immature, subadult and adult sea turtles have been recorded foraging along the coastline of Angola and in bays which provide developmental habitats. Few data are available on the distribution and abundance of each species in these habitats. The level of exploitation of turtles in Angola is moderate, as no dedicated turtle fishery exists. If, however, exploitation is considered to include those turtles taken by incidental catch, it would be deemed heavy. All size classes of turtles and eggs of some species have been taken incidentally although it has been reported that eggs are deliberately hunted. Even though sea turtles have been protected under Angola's hunting laws since 1972, and a heavy fine has existed since that time to discourage exploitation, little enforcement has occurred.

Oxygen transport in the green sea turtle

Green sea turtles (Chelonia mydas) are well known as endurance swimmers and divers. Physiological correlates of these traits were studied in 9 adult sea turtles (mean body mass=87 kg) at a body temperature of 25°C. The respiratory properties of the blood were similar to those of other turtles except for a higher oxygen affinity (P50=18.2 Torr, pH 7.6), which may be an allometric function. Resting, systemic blood flow, calculated from the Fick principle was 21.5 ml·kg−1. min−1, similar to values reported for other turtles. Pulmonary blood flow, measured by mass spectrometry of acetylene uptake in the lungs was 24.0 ml·kg−1·min−1, not significantly different from the calculated systemic flow. Other evidence of a small (net) intracardiac shunt is the high arterial saturation (ca. 90%) of arterial blood. This distinctive feature of O2 transport inC. mydas provides an\([Ca_{O_2 } - C\bar \upsilon _{O_2 } ]\) content difference of 4.1 ml· dl−1. This results in a relatively low blood convection requirement at rest\(\dot Q_t /\dot V_{O_2 }\)=24.4 mlbtps·mlstpd−1), similar to that for many mammals. This would favor a high maximum O2 uptake, as measured by others in this species. The relatively high O2 affinity of blood in this species could be adaptive to “loading” O2 during intermittent breathing while swimming and to utilizing the lung O2 store during the progressive hypoxia of diving.

Oxygen affinity of sea turtle blood

The oxygen binding properties of whole blood in adult sea turtles (green, Chelonia mydas; loggerhead, Caretta caretta) were measured as a function of pH, and carbon dioxide partial pressure using the ‘Hemoscan Oxygen Dissociation Analyser’ with modifications that improved the performance of the method. Under approximately physiologicl conditions (25.7°C, P CO 2 = 37 Torr; pH 7.45) there is a marked affinity difference between the two species (green, P 50 = 29 Torr; loggerhead, 47 Torr). It is suggested that the large affinity difference between blood of green and loggerhead turtles may be related to differences in depths to which they typically dive. The Hill coefficient at 50% saturation is 2.4 in the green under these conditions, and 2.7 in loggerhead. Hill plots of both species curve upward and have significant regions with n approaching 1 at low saturation with the effect that the lower end of the binding curve is more hyperbolic than sigmoidal. The fixed acid and CO 2 Bohr effects in both species are strongly saturation dependent, being very low at low saturation and increasing markedly at higher saturation. The fixed acid Bohr effects are similar in the two species but the green is more sensitive to CO 2 at constant pH, and so has a larger CO 2 Bohr effect. The hyperbolic shape of the lower end of the binding curves, and low pH sensitivity in this region, would tend to favor oxygen loading during a dive, when lung Pa O 2 and blood pH are falling. These properties might therefore favor more complete utilization of the lung oxygen store. We suggest that diving vertebrates can usefully be divided into two groups, those that use the lung as the main oxygen store and those that use tissue (blood and myoglobin) stores.

Regulation of hemoglobin function and whole blood oxygen affinity by carbon dioxide and pH in the loggerhead (Caretta caretta) and green sea turtle (Chelonia mydas mydas).

The oxygen affinity of suspensions of erythrocytes from juvenile and adult loggerhead (Caretta caretta) and green sea (Chelonia mydas mydas) turtles decreased markedly with increasing concentrations of carbon dioxide (0 to near 15%) or hydrogen ion (pH 7.6 to pH 7.2). The P50's were higher with increases in pCO2, particularly at pH near 7.4, than were the P50's with increases in hydrogen ion concentration at any given CO2 concentration. Solutions of hemoglobins from the juvenile loggerhead (8-9 mos.) and green sea (10 mos.) turtles responded to 2, 3-DPG, ATP, or inositol-P5 when added at molar ratios of phosphate to hemoglobin of 4:1 and 20:1 in 0% and 6.29% CO2 but showed no decrease in oxygen affinity at these two CO2 levels in the green turtle when the molar ratio of phosphate to hemoglobin was 0.4. These compounds had little effect on the P50 of these hemoglobins in 14.6% CO2. The P50 of the adult loggerhead turtle hemoglobin did not increase in the presence of organic phosphates beyond the effect induced by CO2 alone. The P50 of hemoglobin from the adult green sea turtle increased only slightly when the molar ratio of phosphate to hemoglobin was 20:1 and at 0 and 6% CO2 concentration; little effect was observed at 14.6% CO2. These data demonstrate that blood oxygen affinities and hemoglobin function in these two species of marine turtles are altered significantly by CO2 and to a lesser degree by pH. It is suggested that such alterations may be of significance in vivo during prolonged diving when there are dramatic rises in blood pCO2 and [H+] and profound decreases in pO2.

Body Depth: An Indicator of Morphological Variation among Nesting Groups of Adult Loggerhead Sea Turtles (Caretta caretta)

Body Depth: An Indicator of Morphological Variation among Nesting Groups of Adult Loggerhead Sea Turtles (Caretta caretta)

Ventilation and gas exchange during rest and exercise in adult green sea turtles

Ventilation and metabolic rate were measured during exercise in adult female green turtles at Tortuguero, Costa Rica. Six turtles were studied at night on the beach while actively covering their nests. Five turtles, captured after nesting, were studied at rest, during 20 min of spontaneous activity, and during recovery from the activity. Arterial blood samples were obtained from the latter animals and analyzed for pH,\(P_{CO_2 } , P_{O_2 } \), O2 concentration and lactate concentration. Blood was obtained by heart puncture from 8 turtles immediately after nesting and analyzed for blood lactate. Active metabolism (\(\dot V_{O_2 } \)) in both groups was almost 10 times the standard resting value (0.024 l/kg·h). The increase in ventilation during exercise, due exclusively to higher breathing frequency, exceeded the increase in\(\dot V_{O_2 } \), so that the ratio\(\dot V_{E_2 } /\dot V_{O_2 } \) (the air convection requirement), more than doubled. The respiratory exchange ratio,\(\dot V_{CO_2 } /\dot V_{O_2 } \), that averaged 0.56 in the resting turtles, increased to 1.08 during exercise in the captured turtles and was 0.90 in the nesting animals. Arterial\(P_{O_2 } \) and O2 saturation remained unchanged during exercise, indicating efficient gas exchange in the lungs. Pre-exercise values of all variables were restored 1 h after the end of exercise. Blood acid-base changes associated with activity in the captive turtles were variable and not statistically significant, but suggested partially compensated metabolic acidosis. Lactate concentrations were significantly elevated in the nesting turtles.

THE GREEN SEA TURTLE, CHELONIA MYDAS (LINN.) IN MALAYA AND SARAWAK

THE GREEN SEA TURTLE, CHELONIA MYDAS (LINN.) IN MALAYA AND SARAWAK