Measuring energy expenditure in sub-adult and hatchling sea turtles via accelerometry

Measuring the metabolic of sea turtles is fundamental to understanding their ecology yet the presently available methods are limited. Accelerometry is a relatively new technique for estimating metabolic rate that has shown promise with a number of species but its utility with air-breathing divers is not yet established. The present study undertakes laboratory experiments to investigate whether rate of oxygen uptake ( o ₂) at the surface in active sub-adult green turtles Chelonia mydas and hatchling loggerhead turtles Caretta caretta correlates with overall dynamic body acceleration (ODBA), a derivative of acceleration used as a proxy for metabolic rate. Six green turtles (25–44 kg) and two loggerhead turtles (20 g) were instrumented with tri-axial acceleration logging devices and placed singly into a respirometry chamber. The green turtles were able to submerge freely within a 1.5 m deep tank and the loggerhead turtles were tethered in water 16 cm deep so that they swam at the surface. A significant prediction equation for mean o ₂ over an hour in a green turtle from measures of ODBA and mean flipper length (R² = 0.56) returned a mean estimate error across turtles of 8.0%. The range of temperatures used in the green turtle experiments (22–30°C) had only a small effect on o ₂. A o ₂-ODBA equation for the loggerhead hatchling data was also significant (R² = 0.67). Together these data indicate the potential of the accelerometry technique for estimating energy expenditure in sea turtles, which may have important applications in sea turtle diving ecology, and also in conservation such as assessing turtle survival times when trapped underwater in fishing nets.     

Clinical Pathology Reference Intervals for an In-Water Population of Juvenile Loggerhead Sea Turtles (Caretta caretta) in Core Sound,North Carolina,USA

The loggerhead sea turtle (Caretta caretta) is found throughout the waters of the Atlantic, Pacific, and Indian Oceans. It is a protected species throughout much of its range due to threats such as habitat loss, fisheries interactions, hatchling predation, and marine debris. Loggerheads that occur in the southeastern U.S. are listed as “threatened” on the U.S. Endangered Species List, and receive state and federal protection. As part of an on-going population assessment conducted by the National Marine Fisheries Service, samples were collected from juvenile loggerhead sea turtles in Core Sound, North Carolina, between 2004 and 2007 to gain insight on the baseline health of the threatened Northwest Atlantic Ocean population. The aims of the current study were to establish hematologic and biochemical reference intervals for this population, and to assess variation of the hematologic and plasma biochemical analytes by season, water temperature, and sex and size of the turtles. Reference intervals for the clinical pathology parameters were estimated following Clinical Laboratory Standards Institute guidelines. Season, water temperature, sex, and size of the turtles were found to be significant factors of variation for parameter values. Seasonal variation could be attributed to physiological effects of decreasing photoperiod, cooler water temperature, and migration during the fall months. Packed cell volume, total protein, and albumin increased with increasing size of the turtles. The size-related differences in analytes documented in the present study are consistent with other reports of variation in clinical pathology parameters by size and age in sea turtles. As a component of a health assessment of juvenile loggerhead sea turtles in North Carolina, this study will serve as a baseline aiding in evaluation of trends for this population and as a diagnostic tool for assessing the health and prognosis for loggerhead sea turtles undergoing rehabilitation.     

Evidence for an asymmetrical size exchange of loggerhead sea turtles between the Mediterranean and the Atlantic through the Straits of Gibraltar

The permanent eastward current at the Straits of Gibraltar may trap small Atlantic loggerhead sea turtles (Caretta caretta) inside the western Mediterranean until their swimming and diving skills improve enough to allow them counter-current swimming abilities through the current. A captivity experiment with twelve loggerhead sea turtles (straight carapace length or SCL range: 25.3-48.0 cm) revealed that the average critical velocity of this species within the considered length range was 0.38 ± 0.16 m s^− 1 or 1.01 ± 0.24 bl s^− 1. As a consequence, loggerhead sea turtles are predicted to require a minimum SCL of 36.0 cm to swim counter-current through the Straits of Gibraltar, where the water velocity ranges 0.31-0.37 m s^− 1. Genetic analysis of 105 specimens using one mitochondrial marker and seven microsatellites, as well as the recapture of three tagged individuals, support this conclusion; all Mediterranean individuals found in the Atlantic side of the Straits were not smaller than 36.0 cm SCL and the average length (47.3 cm SCL) was significantly higher than that of the Mediterranean turtles in the Mediterranean side of the Straits (31.6 cm SCL). Furthermore, the average length of the turtles of any origin moving from the Mediterranean to the Atlantic was much larger than 36.0 cm (SCL: 54.5 cm SCL), which may indicate the intervention of a different, yet unidentified mechanism restricting east-westward movement. The Algerian current, running along northern Africa, may at least partially explain the delayed departure of loggerhead sea turtles from the Mediterranean Sea to the Atlantic Ocean, as it would force the eastward drift of loggerheads occupying the southwestern Mediterranean. Exchange through the Straits is asymmetrical, and Atlantic turtles are found to enter the Mediterranean at a length of about 20.5 cm. However, once in the Mediterranean they would be retained there for up to 7.9 years, due to the surface circulation pattern. This increases the time span at which turtles are exposed to a high mortality rate, caused by fishing.     

BIODIVERSITY RESEARCH: Fidelity to foraging sites,consistency of migration routes and habitat modulation of home range by sea turtles

Aim Resources can shape patterns of habitat utilization. Recently a broad foraging dichotomy between oceanic and coastal sites has been revealed for loggerhead sea turtles (Caretta caretta). Since oceanic and coastal foraging sites differ in prey availability, we might expect a gross difference in home‐range size across these habitats. We tested this hypothesis by equipping nine adult male loggerhead sea turtles with GPS tracking devices. Location National Marine Park of Zakynthos (NMPZ) Greece, central and eastern Mediterranean (Adriatic, Ionian and Aegean seas). Methods In 2007, 2008 and 2009, Fastloc GPS‐Argos transmitters were attached to nine male loggerheads. In addition, a Sirtrack PTT unit was attached to one male in 2007. Four of the turtles were tracked on successive years. We filtered the GPS data to ensure comparable data volumes. Route consistency between breeding and foraging sites of the four re‐tracked turtles was conducted. Foraging site home range areas and within site movement patterns were investigated by the fixed kernel density method. Results Foraging home range size ranged between circa 10 km² at neritic habitats (coastal and open‐sea on the continental shelf) to circa 1000 km² at oceanic sites (using 90% kernel estimates), the latter most probably reflecting sparsely distributed oceanic prey. Across different years individuals did not follow exactly the same migration routes, but did show fidelity to their previous foraging sites, whether oceanic or neritic, with accurate homing in the final stages of migration. Main conclusions The broad distribution and diverse life‐history strategies of this population could complicate the identification of priority marine protected areas beyond the core breeding site.     

Venous blood gases and lactates of wild loggerhead sea turtles (Caretta caretta) following two capture techniques

During summer of 2001, venous blood gases were determined in loggerhead sea turtles (Caretta caretta) captured by trawl (n = 16) in coastal waters of South Carolina and Georgia (USA) as part of a sea turtle census program and captured in pound nets (n = 6) in coastal North Carolina (USA) during a study of sea turtle population biology. Trawls were towed for 30 min, so turtles captured were forcibly submerged for < or = 30 min. Pound nets are passive gear in which fish and sea turtles are funneled into a concentrated area and removed periodically. Sea turtles in pound nets are free to surface and to feed at will. Blood was obtained from the dorsal cervical sinus as quickly as possible after landing on the boat (range 2-10 min trawl, 1-2 min pound net) and at 30 min after landing just prior to release. Blood gases including pH, partial pressures of O2 and CO2 (pO2, pCO2), and lactate were measured within 10 min. Instrument measurements for pH, pO2, and pCO2 made at 37 C were corrected to cloacal temperature and HCO3- was calculated from temperature-corrected pH and pCO2. Venous blood pH and bicarbonate were higher, and pO2 and lactate were lower from pound net-captured turtles compared to trawl captured turtles at the initial sampling time. In pound net turtles, pH and bicarbonate declined and lactate increased during 30 min on deck. In trawled sea turtles, venous blood pH increased and pCO2 and pO2 decreased during the 30 min on deck. Both capture systems caused perturbations in blood gas, acid-base, and lactate status, though alterations were greater in trawl captured turtles.     

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

The 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.     

Estimating At-Sea Mortality of Marine Turtles from Stranding Frequencies and Drifter Experiments

Strandings of marine megafauna can provide valuable information on cause of death at sea. However, as stranding probabilities are usually very low and highly variable in space and time, interpreting the results can be challenging. We evaluated the magnitude and distribution of at-sea mortality of marine turtles along the Pacific coast of Baja California Sur, México during 2010–11, using a combination of counting stranded animals and drifter experiments. A total of 594 carcasses were found during the study period, with loggerhead (62%) and green turtles (31%) being the most common species. 87% of the strandings occurred in the southern Gulf of Ulloa, a known hotspot of loggerhead distribution in the Eastern Pacific. While only 1.8% of the deaths could be definitively attributed to bycatch (net marks, hooks), seasonal variation in stranding frequencies closely corresponded to the main fishing seasons. Estimated stranding probabilities from drifter experiments varied among sites and trials (0.05–0.8), implying that only a fraction of dead sea turtles can be observed at beaches. Total mortality estimates for 15-day periods around the floater trials were highest for PSL, a beach in the southern Gulf of Ulloa, ranging between 11 sea turtles in October 2011 to 107 in August 2010. Loggerhead turtles were the most numerous, followed by green and olive ridley turtles. Our study showed that drifter trials combined with beach monitoring can provide estimates for death at sea to measure the impact of small-scale fisheries that are notoriously difficult to monitor for by-catch. We also provided recommendations to improve the precision of the mortality estimates for future studies and highlight the importance of estimating impacts of small–scale fisheries on marine megafauna.     

Characterizing watercraft-related mortality of sea turtles in Florida

Mortality from being struck by a motorized watercraft is considerable for many aquatic vertebrates around the world, including sea turtles. We studied stranded (i.e., dead, sick, or injured) sea turtles found in Florida, USA, during 1986–2014 and identified those with sharp force or blunt force injuries indicative of a vessel strike. About a third of stranded loggerheads (Caretta caretta), green turtles (Chelonia mydas), and leatherbacks (Dermochelys coriacea) had a vessel-strike injury (VSI). The frequency of this injury was lower but still substantial for stranded Kemp's ridleys (Lepidochelys kempii; 26.1%) and hawksbills (Eretmochelys imbricata; 14.8%). Over the study period, the annual number of stranded loggerheads, green turtles, and Kemp's ridleys with a VSI increased as did the annual number of vessels registered in Florida. Eighty-one percent of the stranded turtles with a VSI were found in the southern half of Florida and 66% of those were found along the southeast coast. By coastal county, the proportion of stranded sea turtles with a VSI was positively related to the mean annual number of registered vessels. The percentage occurrence of a VSI was highest for adult loggerheads, green turtles, and leatherbacks, and reproductively active individuals appeared to be particularly vulnerable to these injuries. We conducted necropsies on 194 stranded sea turtles with a VSI and concluded that this injury was the cause of death or the probable cause of death in ≥92.8% of these cases. During 2000–2014, we estimate that the mean annual numbers of stranded sea turtles that died from a VSI were 142–229 loggerheads, 101–162 green turtles, 16–32 Kemp's ridleys, 4–6 leatherbacks, and 2–4 hawksbills. Considering that only about 10–20% of sea turtles that died likely washed ashore, the overall annual mortality may have been 5–10 times greater than that represented by strandings. Most of the significant clusters of stranded sea turtles with a VSI occurred at inlets or passes and the probability that a stranded sea turtle had a VSI decreased with increasing distance from inlets or passes, navigable waterways, and marinas. We suggest focusing initial management efforts on reducing watercraft-related mortality for all sea turtle species around 8 inlets in southeast Florida, reproductively active loggerheads and green turtles along the coast of southeast Florida, and Kemp's ridleys and adult male loggerheads at passes along the coast of southwest Florida. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. The Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society     

Propofol anesthesia in loggerhead (Caretta caretta) sea turtles

Rapid, safe, and effective methods of anesthetic induction and recovery are needed for sea turtles, especially in cases eligible for immediate release. This study demonstrates that intravenous propofol provides a rapid induction of anesthesia in loggerhead (Caretta caretta) sea turtles and results in rapid recovery, allowing safe return to water shortly after the procedure. Forty-nine loggerhead sea turtles were recovered as local fishery by-catch in pound nets and transported to a surgical suite for laparoscopic sex determination. Treatment animals (n = 32) received 5 mg/kg propofol intravenously (i.v.) as a rapid bolus, whereas control animals (n = 17) received no propofol. For analgesia, all animals received a 4 ml infusion of 1% lidocaine, locally, as well as 2 mg/kg ketoprofen intramuscularly (i.m.). Physiologic data included heart and respiratory rate, temperature, and a single blood gas sample collected upon termination of the laparoscopy. Subjective data included jaw tone and ocular reflex: 3 (vigorous) to 0 (none detected). Anesthetic depth was scored from 1, no anesthesia, to 3, surgical anesthesia. Turtles receiving propofol became apneic for a minimum of 5 min with a mean time of 13.7 +/- 8.3 min to the first respiration. Limb movement returned at a mean time of 21.1 +/- 16.8 min. The treatment animals were judged to be sedated for approximately 30 min (mean anesthetic depth score > or = 1.5) when compared to controls. Median respiratory rates for treatment animals were slower compared to controls for the first 15 min, then after 35 min, they became significantly faster than the controls. Median heart rates of control animals became significantly slower than treatment animals between 40 and 45 min. Physiologic differences between groups persisted a minimum of 55 min. Possible explanations for heart rate and respiratory rate differences later in the monitoring period include a compensatory recovery of treatment animals from anesthesia-induced hypoxia and hypercapnia or, alternatively, an induced response of the nonsedated control animals. The animals induced with propofol were easier to secure to the restraint device and moved less during laparoscopy. In conclusion, propofol is a safe and effective injectable anesthetic for use in free-ranging loggerhead sea turtles that provides rapid induction and recovery.     

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.

Skeletochronological estimation of age and growth of loggerhead sea turtles (Caretta caretta) in the western South Atlantic Ocean

Age and growth are important parameters for better understanding of life history and population dynamics of animal species, as well as for formulating management strategies. However, these data are difficult to obtain for sea turtles because of overall slow growth, delayed maturation and highly migratory behaviour. The loggerhead sea turtle, Caretta caretta, is a widely distributed species, globally listed as endangered. Although the species has been well‐studied in some regions, little is known about various aspects of its biology in other populations, such as those in the waters of the western South Atlantic Ocean, especially outside nesting areas. To address age and growth, loggerhead turtles found dead stranded on the northern coast of the state of Rio Grande do Sul during a period of 16 years (1994–2010) were utilized for estimation of age and growth rates using skeletochronology. The individuals analyzed were predominantly neritic juveniles, ranging from 53 to 101 cm curved carapace length (CCL; mean = 71 cm), with estimated ages between 10 and 29 years (mean = 15 years). Mean estimated annual growth rate was 2.1 cm CCL year^?1 (1.9 cm SCL yr^?1), showing large variation among individuals and between successive years in the same individual. Generalized additive mixed models analysis indicated that growth response was influenced by age, CCL and year. The results demonstrated that the southern coast of Brazil is an important area for the development of neritic juveniles of this species, which appear to recruit to this region beginning at about 12 years of age and sizes greater than 55 cm CCL.     

Relationship between tropical cyclones and the distribution of sea turtle nesting grounds

Aim This study examines the relationship between the distribution of existing sea turtle nesting sites and historical patterns of tropical cyclone events to investigate whether cyclones influence the current distribution of sea turtle nesting sites. The results, together with information on predicted cyclone activity and other key environmental variables, will help in the identification and prediction of future nesting sites for sea turtles as changes to the coastal environment continue. Location Queensland, Australia. Methods We used data on the nesting distribution of seven populations of four species of sea turtles [green (Chelonia mydas), flatback (Natator depressus), hawksbill (Eretmochelys imbricata) and loggerhead (Caretta caretta)] from the eastern Queensland coast, and tropical cyclone track data from 1969 to 2007 to explore the relationship between (1) sea turtle nesting phenology and cyclone season, and (2) sea turtle nesting sites and cyclone distribution. Furthermore, using two green turtle populations as a case study, we investigated the relationship between cyclone disturbance and sea turtle reproductive output, nesting site and season. Bootstrapping was used to explore if current sea turtle nesting sites are located in areas with lower or higher cyclone frequency than areas where turtles are currently not nesting. Results All populations of sea turtles studied here were disturbed by cyclone activity during the study period. The exposure (frequency) of tropical cyclones that crossed each nesting site varied greatly among and within the various sea turtle populations. This was mainly a result of the spatial distribution of each population’s nesting sites. Bootstrapping indicated that nesting sites generally have experienced lower cyclone activity than other areas that are available for nesting. Main conclusions Tropical cyclones might have been sufficiently detrimental to sea turtle hatching success on the eastern Queensland coast that through a natural selection process turtles in this region are now nesting in areas with lower cyclone activity. Therefore, it is important that future studies that predict climate or range shifts for sea turtle nesting distributions consider future cyclone activity as one of the variables in their model.     

Helminth component community of the loggerhead sea turtle, Caretta caretta, from Madeira Archipelago, Portugal

The helminth fauna of pelagic-stage loggerhead sea turtles, Caretta caretta, is still poorly known. Here, we describe the helminth-component community of healthy, free-ranging juvenile loggerhead sea turtles captured in the waters around Madeira Island, Portugal. Fifty-seven were used in this study. The esophagus, stomach, intestine, liver, gallbladder, spleen, kidneys, trachea, bronchi, urinary bladder, heart, left and right aortas, and coelomic cavity were macroscopically inspected; organs and tissues were removed and washed through a sieve. A search for parasites was made using a stereoscopic microscope; recovered parasites were fixed and stored in 70% alcohol until staining and identification. Prevalence, mean intensity, and mean abundance values were recorded. In total, 156 parasite specimens belonging to 9 species were found: nematodes included Anisakis simplex s.l. (larvae) and an unidentified species; digenetic trematodes present were Enodiotrema megachondrus, Rhytidodes gelatinosus, Pyelosomum renicapite, and Calycodes anthos; acanthocephalans included Bolbosoma vasculosum and Rhadinorhynchus pristis; a single cestode, Nybelinia sp., was present. Parasite infections were found to have both low prevalences and intensities. Possible reasons for this include the oligotrophic conditions of the pelagic habitat around Madeira; a 'dilution effect' because of the vastness of the area; and the small size, and thus ingestion rate, of the turtles. Results are discussed in terms of the various turtle populations that may use the waters surrounding Madeira. This work provides valuable information on the parasite fauna of a poorly known stage in the life of loggerhead sea turtles, thereby filling a fundamental gap with regard to features of the parasite fauna in this species.     

The pineal-paraphyseal complex of sea turtles. I. Light microscopic description

The pineal-paraphyseal complex of sea turtles is an impressively large structure which projects dorsally and anteriorly above the prosencephalon. The complex was examined by light microscopy in several age classes of green sea turtles (Chelonia mydas) and from juvenile loggerhead turtles (Caretta caretta). The paraphysis is extensively fused to the distal portion of the pineal body, suggesting an interrelated function for these two tissues. No duct or canal was observed connecting the pineal lumen to the third ventricle. Two pineal cell types are described which appear to correspond to the neuroglial supportive cells and the secretory rudimentary photoreceptor cells of other amniotic vertebrates. A possible luminal secretion in the form of apical protrusions is produced by the latter cell type. No typical photoreceptive outer segments were observed.     

Histochemical and immunohistochemical studies of the gonads and paramesonephric ducts of male and female hatchlings of loggerhead sea turtles (Caretta caretta)

The sex of neonatal sea turtles is difficult to determine, because neonates lack heteromorphic sex chromosomes and dimorphic external characteristics; internal dimorphic morphology is defined at hatching. We used histochemical staining and made measurements in the gonads and paramesonephric ducts (PD) of both sexes to determine structural differences in female and male loggerhead sea turtle (Caretta caretta) hatchlings. We detected differences in the gonads and PD between the sexes including the amounts of mucopolysaccharides, collagen and elastic fibers. We determined that the thickness of the gonadal cortex and the diameter of the PD lumen are reliable sex-specific characteristics. We also assessed immunolocalization of aromatase, an enzyme complex that converts androgens to estrogens, and found differences in the localization and intensity of aromatase immunostaining in the gonads and PD of female and male hatchlings. Comprehensive studies of the sexual differences of sea turtles are important for conservation programs.     

Visual spectral sensitivity of hatchling loggerhead (Caretta caretta L.) and leatherback (Dermochelys coriacea L.) sea turtles,as determined by single-flash electroretinography

Electroretinographic recordings were made from hatchling loggerhead and leatherback sea turtle eyecup preparations to generate dark-adapted spectral sensitivity curves. Both species were maximally sensitive to wavelengths between 500 and 540 nm, with a secondary peak near 380 nm. The spectral sensitivity curve for leatherbacks was attenuated at the long wavelength end of the spectrum relative to that of the loggerheads. This difference may reflect adaptations to lighting available at the relatively shallow (loggerhead) versus deeper (leatherback) sites where each species forages. The broad spectrum of wavelengths detected by both species (near UV to yellow–orange) indicates that vision is likely mediated by more than one photopigment, potentially rendering these turtles capable of color vision.     

Impacts of a geotextile container dune core on marine turtle nesting in Juno Beach,Florida, United States

Hard armoring technologies (e.g. rock revetments and seawalls), which are installed to protect homes from beach erosion, can diminish the aesthetics and amenity of the beach. Over time, these structures cause beach narrowing and often prevent marine turtle access to nesting habitat altogether. An alternative armoring technology, known as geotextile dune core systems (or geocores), has been developed and implemented to protect inland infrastructure from beach erosion, yet there remains an absence of research on possible effects on marine turtles. In this study, we examined the impacts of a geocore installed on Juno Beach, Florida, United States in February 2014 on loggerhead (Caretta caretta) and green turtle (Chelonia mydas) nesting success, hatching success, and emergence success. A before‐after‐control‐impact paired series design evaluated the difference in nesting success per week for the impact and control sites 4 years before (2010–2013) and 4 years after (2014–2017) the installation of the geocore. Neither loggerhead nor green turtle nesting success was significantly different after the installation of the geocore; however, when analyzing loggerhead crawls that came to within 5 m of the geotextile bags, nesting success decreased. Neither hatching nor emergence success was significantly different after the installation of the geocore for either species. Our results suggest that geocores may minimally affect loggerhead and green turtles and provide a suitable restoration technique for homeowners facing beach erosion.     

Survival of Pelagic Juvenile Loggerhead Turtles in the Open Ocean

Abstract: We deployed pop-up archival transmitting tags on 15 loggerhead sea turtles (Caretta caretta) that had been lightly hooked in the United States pelagic longline fishery and on 10 loggerheads that we dip-netted off the surface to serve as controls in the North Atlantic Ocean. We received data from tags of 10 lightly hooked turtles and 7 control turtles. We used data transmitted by the tags in a known-fate model to estimate annual survival rates and determine if there were differences in survival between the 2 groups. The best model indicates there is no difference in survival between the lightly hooked and control turtles, and the estimated annual survival rate was 0.814 (95% CI = 0.557-0.939). Our results suggest that when all fishing gear is removed lightly hooked turtles may not suffer any additional mortality relative to control turtles.     

GLOBAL PHYLOGEOGRAPHY OF THE LOGGERHEAD TURTLE (CARETTA CARETTA) AS INDICATED BY MITOCHONDRIAL DNA HAPLOTYPES

Restriction-site analyses of mitochondrial DNA (mtDNA) from the loggerhead sea turtle (Caretta caretta) reveal substantial phylogeographic structure among major nesting populations in the Atlantic, Indian, and Pacific oceans and the Mediterranean sea. Based on 176 samples from eight nesting populations, most breeding colonies were distinguished from other assayed nesting locations by diagnostic and often fixed restriction-site differences, indicating a strong propensity for natal homing by nesting females. Phylogenetic analyses revealed two distinctive matrilines in the loggerhead turtle that differ by a mean estimated sequence divergence p = 0.009, a value similar in magnitude to the deepest intraspecific mtDNA node (p = 0.007) reported in a global survey of the green sea turtle Chelonia mydas. In contrast to the green turtle, where a fundamental phylogenetic split distinguished turtles in the Atlantic Ocean and the Mediterranean Sea from those in the Indian and Pacific oceans, genotypes representing the two primary loggerhead mtDNA lineages were observed in both Atlantic–Mediterranean and Indian-Pacific samples. We attribute this aspect of phylogeographic structure in Caretta caretta to recent interoceanic gene flow, probably mediated by the ability of this temperate-adapted species to utilize habitats around southern Africa. These results demonstrate how differences in the ecology and geographic ranges of marine turtle species can influence their comparative global population structures.     

Sea turtle species vary in their susceptibility to tropical cyclones

Severe climatic events affect all species, but there is little quantitative knowledge of how sympatric species react to such situations. We compared the reproductive seasonality of sea turtles that nest sympatrically with their vulnerability to tropical cyclones (in this study, “tropical cyclone” refers to tropical storms and hurricanes), which are increasing in severity due to changes in global climate. Storm surges significantly decreased reproductive output by lowering the number of nests that hatched and the number of hatchlings that emerged from nests, but the severity of this effect varied by species. Leatherback turtles (Dermochelys coriacea) began nesting earliest and most offspring hatched before the tropical cyclone season arrived, resulting in little negative effect. Loggerhead turtles (Caretta caretta) nested intermediately, and only nests laid late in the season were inundated with seawater during storm surges. Green turtles (Chelonia mydas) nested last, and their entire nesting season occurred during the tropical cyclone season; this resulted in a majority (79%) of green turtle nests incubating in September, when tropical cyclones are most likely to occur. Since this timing overlaps considerably with the tropical cyclone season, the developing eggs and nests are extremely vulnerable to storm surges. Increases in the severity of tropical cyclones may cause green turtle nesting success to worsen in the future. However, published literature suggests that loggerhead turtles are nesting earlier in the season and shortening their nesting seasons in response to increasing sea surface temperatures caused by global climate change. This may cause loggerhead reproductive success to improve in the future because more nests will hatch before the onset of tropical cyclones. Our data clearly indicate that sympatric species using the same resources are affected differently by tropical cyclones due to slight variations in the seasonal timing of nesting, a key life history process.