Juvenile Loggerhead Turtles Research Articles

MODELING LOGGERHEAD TURTLE MOVEMENT IN THE MEDITERRANEAN: IMPORTANCE OF BODY SIZE AND OCEANOGRAPHY

Adapting state-space models (SSMs) to telemetry data has been helpful for dealing with location error and for modeling animal movements. We used a combination of two hierarchical Bayesian SSMs to estimate movement pathways from Argos satellite-tag data for 15 juvenile loggerhead turtles (Caretta caretta) in the western Mediterranean Sea, and to probabilistically assign locations to one of two behavioral movement types and relate those behaviors to environmental features. A Monte Carlo procedure helped propagate location uncertainty from the first SSM into the estimation of behavioral states and environment--behavior relationships in the second SSM. Turtles using oceanic habitats of the Balearic Sea (n = 9 turtles) within the western Mediterranean were more likely to exhibit "intensive search" behavior as might occur during foraging, but only larger turtles responded to variations in sea-surface height. This suggests that they were better able than smaller turtles to cue on environmental features that concentrate prey resources or were more dependent on high-quality feeding areas. These findings stress the importance of individual heterogeneity in the analysis of movement behavior and, taken in concert with descriptive studies of Pacific loggerheads, suggest that directed movements toward patchy ephemeral resources may be a general property of larger juvenile loggerheads in different populations. We discovered size-based variation in loggerhead distribution and documented use of the western Mediterranean Sea by turtles larger than previously thought to occur there. With one exception, only individuals > 57 cm curved carapace length used the most westerly basin in the Mediterranean (western Alborán Sea). These observations shed new light on loggerhead migration phenology.

Trends in catch rates of sea turtles in North Carolina, USA

Sea turtles captured in pound nets during the autumn and early winter in the Pamlico- Albermarle Estuarine Complex, North Carolina, USA, were sampled 1995-1997 and 2001-2003 to monitor trends in catch rates during their autumn emigration from the temperate sounds. Juvenile loggerhead turtles Caretta caretta were the most frequent species encountered, followed by green turtles Chelonia mydas and Kemp's ridley turtles Lepidochelys kempii. Several different subpopula- tions with origins throughout the western North Atlantic were represented on these foraging grounds. The catch rates of loggerhead turtles increased significantly at a rate of 13% yr -1 . Despite annual increases in the major contributing nesting beach populations in excess of 10% yr -1 , we did not detect a trend in catch rates for either green or Kemp's ridley turtles, perhaps due to low statisti- cal power. There was a significant increase in size of loggerhead turtles over time. We also detected a significant difference in annual size distributions of green and Kemp's ridley sea turtles, but there was no discernable pattern. We conclude that long-term studies on the sea turtles' foraging grounds, at multiple sites, are needed to monitor the status of sea turtle populations.

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.

Summer Abundance Estimates of Caretta caretta (Loggerhead Turtles) in Core Sound, NC

Abstract We estimated summer abundance of juvenile Loggerhead Turtles at our study site in Core Sound, NC with a Horvitz-Thompson type estimator, which uses count data and recapture probability to estimate abundance. Abundance ranged from 192 (95% CI = 88–1047) to 633 (95% CI = 219–1047) turtles over the six years of this study. These results provide preliminary estimates of juvenile Loggerhead Turtle abundance during the summer in Core Sound.

SUCCESSIVE CHANGES OF HEMATOLOGIC CHARACTERISTICS AND PLASMA CHEMISTRY VALUES OF JUVENILE LOGGERHEAD TURTLES (CARETTA CARETTA)

Hematologic characteristics and plasma chemistry values of juvenile loggerhead turtles (Caretta caretta) from the ages of 1 mo to 3 yr were obtained to establish baseline values. Five clinically normal loggerhead turtles were selected from the same clutch and raised in an indoor artificial nesting beach. Blood samples were successively collected and examined for various blood characteristics for a maximum total of 15 times. Hematologic characteristics, including packed cell volume, white blood cell counts, and white blood cell differentials; and plasma chemistry values, including total bilirubin, total protein, albumin, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, gamma-glutamic transpeptidase, creatinine, blood urea nitrogen, uric acid, alkaline phosphatase, amylase, triglyceride, total cholesterol, ionized sodium, ionized potassium and ionized chlorine, were measured. These results were used to establish a hematology and blood chemistry baseline for captive juvenile loggerhead turtles and will aid in their medical management.

Effects of transients on estimating survival and population growth in juvenile loggerhead turtles

Population growth and annual survival of juvenile loggerhead turtles Caretta caretta were investigated in North Carolina using mark-recapture techniques. Lack of fit of the models employed caused us to reject the obtained estimates and led us to suspect that many loggerhead turtles were transient in the study area. We estimated apparent survival and the proportions of residents and transients. Transients represented approximately 75% of newly captured individuals captured at our study site. When transients were taken into account, apparent survival of residents increased from between 0.36 and 0.74 to 0.81. Our study highlights the need to consider the presence of transients when interpreting the results of loggerhead monitoring studies.

Sex ratios of juvenile loggerhead sea turtles Caretta caretta in the Mediterranean Sea

Species with environmental sex determination may have sex ratios different from 1:1, and so sex ratio is an important variable in studies on the population dynamics of these species. This is particularly important for the endangered sea turtles, in order to understand the possible effects of human impacts and conservation measures. Unfortunately, only adults show an evident external sexual dimorphism, so that sex ratio data are difficult to obtain and are limited for the juvenile class, which represents the largest part of a population. Here we present the first extensive assessment of sex ratio of juvenile loggerhead turtles (Caretta caretta) in the Mediterranean Sea. A total of 310 dead turtles from four different areas were sexed by direct examination of gonads, the most reliable sexing method. Females were 54.2% of the whole sample, and no significant differences were found between the study areas. However, this value cannot be ascribed to a single population, because specimens from different nesting sites, both within and outside the Mediterranean, share the same foraging areas and each population may potentially contribute with a different sex ratio. Although we found an unbiased sex ratio, when other information from the region about distribution, mixed stocks, and sex ratios are considered, actually present results are compatible with a hypothetical scenario in which a majority of females are produced in the Mediterranean nesting beaches.

Natal origin of loggerhead turtles, Caretta caretta, in the neritic habitat off the Italian coasts, Central Mediterranean

Shallow (neritic) waters close to the Italian coasts (Central Mediterranean Sea) are frequently visited by foraging loggerhead turtles, but the nesting populations which rely on this area have not been determined. To estimate the rookery origins of this feeding cohort, mitochondrial DNA control region sequences were analysed from 106 juvenile loggerhead turtles and compared to those published for key nesting populations in the Atlantic and Mediterranean regions using a Bayesian based stock analysis program. Six distinct haplotypes were detected, of which two have previously been reported from both Mediterranean and Atlantic nesting beaches and one only from Atlantic nesting populations. The remaining three haplotypes could not be assigned to a rookery of origin. Mixed stock analysis indicated that the waters along the Southern Italian coasts are utilised primarily by Mediterranean nesting populations, with approximately 68% of the individuals provided by the genetically homogeneous Greece/South eastern Mediterranean nesting aggregate and 23% by the Turkish management unit. 7% of the loggerhead turtles were assigned to Atlantic stock. Our results suggest that only a small proportion of the Atlantic juveniles which enter the Mediterranean to forage in its pelagic waters utilise also the neritic areas along the Italian coasts. This is consistent with theory of juvenile homing, according to which oceanic stage juveniles preferentially recruit to neritic developmental habitats within their natal region, and implies that the elevated human-induced mortality occurring in this area impacts almost exclusively the smaller and demographically more vulnerable Mediterranean loggerhead turtle stock.

Western Mediterranean immature loggerhead turtles: habitat use in spring and summer assessed through satellite tracking and aerial surveys

An aerial survey was conducted in early spring 2002 over the continental shelf of the Balearic Archi- pelago to study the distribution of neritic loggerhead turtles. Furthermore, five juvenile loggerhead turtles (straight carapace length (SCL) range 37.1-48.7 cm), were instrumented with transmitters and monitored during 2003 by satellite tracking to study habitat use over a broader geographical range. The distribution of the turtles over the continental shelf matched habitat availability, as defined by depth. However, those tracked by satellite spent most of the time in the oceanic waters of the Algerian basin and generally avoided continental shelf areas. In these turtles, average speed of travel and mean cosine of turning angle did not significantly differ between habitats, indicating that avoidance of shelf areas is not due to active habitat selection. On average, tracked turtles spent 35.1±19.7% of the time at the surface, although surface time was much greater in the turtle with the shortest carapace length, suggesting that this individual had limited swimming capacity. We conclude that the transition between passive drifting and active habitat selection occurs at an SCL of about 40 cm. The turtles followed tracks that matched pre- vailing currents, but on some occasions they also swam upstream. Hence, the distribution of late juvenile log- gerhead turtles in the southern and central western Mediterranean may reflect a combination of passive drifting and active habitat selection.

Natal homing in juvenile loggerhead turtles (Caretta caretta)

Juvenile loggerhead turtles (Caretta caretta) from West Atlantic nesting beaches occupy oceanic (pelagic) habitats in the eastern Atlantic and Mediterranean, whereas larger juvenile turtles occupy shallow (neritic) habitats along the continental coastline of North America. Hence the switch from oceanic to neritic stage can involve a trans-oceanic migration. Several researchers have suggested that at the end of the oceanic phase, juveniles are homing to feeding habitats in the vicinity of their natal rookery. To test the hypothesis of juvenile homing behaviour, we surveyed 10 juvenile feeding zones across the eastern USA with mitochondrial DNA control region sequences (N = 1437) and compared these samples to potential source (nesting) populations in the Atlantic Ocean and Mediterranean Sea (N = 465). The results indicated a shallow, but significant, population structure of neritic juveniles (PhiST = 0.0088, P = 0.016), and haplotype frequency differences were significantly correlated between coastal feeding populations and adjacent nesting populations (Mantel test R2 = 0.52, P = 0.001). Mixed stock analyses (using a Bayesian algorithm) indicated that juveniles occurred at elevated frequency in the vicinity of their natal rookery. Hence, all lines of evidence supported the hypothesis of juvenile homing in loggerhead turtles. While not as precise as the homing of breeding adults, this behaviour nonetheless places juvenile turtles in the vicinity of their natal nesting colonies. Some of the coastal hazards that affect declining nesting populations may also affect the next generation of turtles feeding in nearby habitats.

Tag recoveries of the loggerhead sea turtle Caretta caretta in the eastern Adriatic Sea: implications for conservation

Data on tag recoveries of 31 adult female and two juvenile loggerhead turtles (Caretta caretta) along the eastern Adriatic coast were analysed. All adult females originated from Mediterranean nesting areas: 29 from Greece, one from Cyprus and one from Turkey. This is the largest aggregation of long-distance tag recoveries in the Mediterranean for the loggerhead population nesting in Greece. The short period elapsed between the last observation of some turtles on the nesting beach and their recovery suggests the existence of a migratory pathway from the Ionian Sea into the Adriatic. Recoveries of some turtles within a period of a year indicate that loggerheads reside in the Adriatic for some time, suggesting that some individuals may demonstrate a level of site fidelity for these marine habitats. The high concentration of tag returns in the shallow northern Adriatic highlights this region as an important feeding habitat, for the population nesting in Greece in particular. The Ionian–Adriatic loggerheads form an important management sub-unit for this nesting population.

The dual function of the lung in chelonian sea turtles: buoyancy control and oxygen storage

Chelonian sea turtles use their lung as a buoyancy organ and as the major oxygen store when diving, and hence, buoyancy regulation and oxygen consumption can be expected to interact. The buoyancy of seven juvenile loggerhead turtles, Caretta caretta, was determined by measuring directly their underwater weight ( M uw) while they were resting on a freely suspended weighing platform at a depth of 80 cm. Underwater weight was recorded continuously for 2 days for each turtle, followed by another 2 days measurements during which the turtles carried lead weights attached to their carapace, and finally, a last day of measurement after the weights had been removed. Total duration of resting dives ( t r), buoyancy ( F B), total resulting force acting on the resting turtle ( F res) and body volumes were derived from the M uw data. Turtles were slightly negatively buoyant when resting ( F res=−0.2943 to −0.981 N kg −1) and M uw increased significantly throughout each apnoeic period, meaning that the turtles progressively lost buoyancy. Pulmonary gas loss was calculated from the rate at which buoyancy decreased, which was significantly slower during the first half of the dive than during the second half of the dive. Resting oxygen consumption rates ( V O 2 ) were calculated from these data assuming that the pulmonary gas loss represents oxygen consumption from the lung. The V O 2 obtained in this way (1.69–4.86 ml O 2 min −1) corresponded well with other published and V O 2 measured previously on loggerhead turtles in the same facility. Using oxygen from the lung affects buoyancy and may have impacts on the diving behaviour.

Origin of juvenile loggerhead turtles (Caretta caretta) in a tropical developmental habitat in Caribbean Panamá

AbstractMaximum likelihood mixed stock analysis was used to identify the natal origin of immature loggerhead turtles (Caretta caretta) in a tropical developmental habitat in Caribbean Panamá. Approximately 65–70% of the loggerhead turtles in Chiriquí Lagoon originate from South Florida nesting beaches, and the other 30–35% originate from Mexico. Haplotype frequencies of the Chiriquí Lagoon loggerhead population are significantly different from those observed in the pelagic environment in the eastern Atlantic, and estimated nesting beach contributions to Chiriquí Lagoon are significantly different from values expected if recruitment were based solely on the size of nesting populations. These observations suggest that dispersal of loggerheads into benthic developmental habitats from the pelagic environment is not random. The occurrence of US and Mexican loggerheads in tropical developmental habitats has not been previously recognized. Exploitation and other mortality factors operating in the Caribbean area must be taken into account in demographic models and management plans for these two populations. This exploitation could be particularly important for the small, demographically vulnerable Mexican population and for other small populations for which no genetic data are currently available.

Feeding ecology of the loggerhead turtle Caretta caretta in the western Mediterranean

AbstractWe studied the feeding ecology of juvenile loggerhead turtles Caretta caretta in the western Mediterranean based on the contents of the digestive tract of 54 turtles (range of CCL: 34–69 cm) seized in Barcelona (Spain) in 1991. Turtles had been captured in fishing trawls, but specific information about dates and localities is not available. Despite this limitation, we obtained interesting evidences about the foraging strategies of loggerheads, with potentially important conservation implications. We report 33 new taxa in the diet. Results indicated that western Mediterranean loggerheads feed in an opportunistic way. Numerically, fish made up the most important prey group, followed by pelagic tunicates, crustaceans, molluscs and other invertebrates. The importance of fish as a food resource has been rarely reported, and several lines of evidence indicated that fish were possibly consumed as discarded by‐catch. This raises the question over whether or not western Mediterranean fisheries are an important food source for juvenile loggerheads. The number and diversity of prey increased with turtle size, this may reflect the lack of prey selectivity of juvenile loggerheads coupled with a higher retention of food remains in larger turtles. Discounting prey that could be consumed as discarded by‐catch, dietary data suggest that most, if not all, loggerheads of our sample were captured in neritic habitats. However, many turtles contained remains of both pelagic and benthic‐demersal prey. These observations support the existence of an intermediate neritic phase in loggerheads' developmental shift from pelagic–oceanic to benthic–neritic foraging habitats, as previously suggested. During this phase, loggerheads would feed upon both pelagic and benthic prey.

Molecular evidence of male-biased dispersal in loggerhead turtle juveniles

Serum testosterone levels and mtDNA haplotypes were obtained from 65 juvenile loggerhead turtles ( Caretta caretta, L.) incidentally caught in the central Mediterranean. The group of specimens carrying a haplotype specific for the northwest Atlantic had higher testosterone levels, and so included more males, than the other one. Since primary sex ratios of northwest Atlantic colonies are strongly skewed towards females, results indicate a male bias among Atlantic turtles entering the Mediterranean. This demonstrates for the first time a sex-biased dispersal of specimens in the pelagic phase, an important factor to be considered in conservation programs.

Demographic composition of the feeding population of juvenile loggerhead sea turtles (Caretta caretta) off Charleston, South Carolina: evidence from mitochondrial DNA markers

To determine the origin of juvenile loggerhead turtles (Caretta caretta) that occupy the Charleston Harbor Entrance Channel at Charleston, South Carolina, USA, mitochondrial DNA restriction-fragment length polymorphisms from this feeding population were compared to haplotypes from candidate nesting populations. Previous studies have defined two major nesting populations in the southeastern USA, one corresponding to Florida and the other to Georgia/South Carolina. These nesting populations are distinguished by both unique haplotypes and frequency distributions of common haplotypes. The frequency distribution of haplotypes in the juvenile feeding-ground population was significantly different from both nesting populations, implying that the feeding aggregate is drawn from two or more nesting populations. Assuming that these turtles are derived exclusively from rookeries in the southeastern USA, a maximum likelihood estimator indicates that approximately half are from the Florida rookery and half are from the northern (Georgia/South Carolina) rookery complex. Because 91% of nesting in the southeastern USA occurs in Florida rookeries and 8% in the northern complex, the 50:50 ratio indicates that juvenile turtles from Georgia and South Carolina tend to feed preferentially near their respective rookery locations. Human encroachment on this feeding habitat may pose an especially high risk to the smaller Georgia/South Carolina rookeries.

Trans-Pacific migrations of the loggerhead turtle (Caretta caretta) demonstrated with mitochondrial DNA markers.

Juvenile loggerhead turtles (Caretta caretta) have recently been documented in the vicinity of Baja California and thousands of these animals have been captured in oceanic fisheries of the North Pacific. The presence of loggerhead turtles in the central and eastern North Pacific is a prominent enigma in marine turtle distribution because the nearest documented nesting concentrations for this species are in Australia and Japan, over 10,000 km from Baja California. To determine the origin of the Baja California feeding aggregate and North Pacific fishery mortalities, samples from nesting areas and pelagic feeding aggregates were compared with genetic markers derived from mtDNA control region sequences. Overall, 57 of 60 pelagic samples (95%) match haplotypes seen only in Japanese nesting areas, implicating Japan as the primary source of turtles in the North Pacific Current and around Baja California. Australian nesting colonies may contribute the remaining 5% of these pelagic feeding aggregates. Juvenile loggerhead turtles apparently traverse the entire Pacific Ocean, approximately one-third of the planet, in the course of developmental migrations, but mortality in high-seas fisheries raises concern over the future of this migratory population.

Podoceru Chelonophilus (Amphipoda: Podoceridae) Associated with Epidermal Lesions of the Loggerhead Turtle, Caretta Caretta (Chelonia)

Examination of a small sample of Podocerus chelonophilus found clustered around mucus-exuding epidermal lesions of juvenile loggerhead turtles (Caretta caretta) collected off Madeira revealed the presence of fibrous material in the gut contents. The absence of planktonic remains suggested that these amphipods had been exploiting turtle material directly.With the exception of the Cyamidae (whale lice), rather few amphipod taxa consistently live in association with marine vertebrates. Sea turtles, however, have been recorded carrying gammaridean and caprellidean epibionts by Caine (1986), who reported eight gammaridean species (including two domicolous fouling species) from nesting loggerhead turtles in Florida.

Preliminary studies on the growth and food consumption of the juvenile loggerhead turtle ( Caretta caretta L.) in captivity

The effects of temperature and food ration on the growth of juvenile loggerhead turtle, Caretta caretta L. were examined in relation to body weight under controlled conditions in the laboratory. With increasing food ration there was increasing growth rate. The best daily growth rate at 20°C water temperature was 1.87%. Basal metabolism was reached at a daily feed rate of 1.01% body weight at 20.5°C derived from a formula for growth, namely g = Af − B where g = 0.62 f − 0.63.

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.