Hue discrimination in hatchling loggerhead turtles (Caretta caretta caretta)

Hatchling Atlantic loggerhead turtles (Caretta caretta caretta) were successfully trained to discriminate between broadband hues to obtain food when spatial, intensity, and other confounding cues were randomized with respect to the correct choice. Possible hue preference, the relation of these results to sea-orientation, and the suitability of these animals as subjects in behavioural studies are discussed.     

Neurological disease in wild loggerhead sea turtles Caretta caretta

Beginning in October 2000, subadult loggerhead sea turtles Caretta caretta showing clinical signs of a neurological disorder were found in waters off south Florida, USA. Histopathology indicated generalized and neurologic spirorchiidiasis. In loggerhead sea turtles (LST) with neurospirorchiidiasis, adult trematodes were found in the meninges of the brain and spinal cord of 7 and 3 affected turtles respectively, and multiple encephalic intravascular or perivascular eggs were associated with granulomatous or mixed leukocytic inflammation, vasculitis, edema, axonal degeneration and occasional necrosis. Adult spirorchiids were dissected from meningeal vessels of 2 of 11 LST brains and 1 of 10 spinal cords and were identified as Neospirorchis sp. Affected LST were evaluated for brevetoxins, ciguatoxins, saxitoxins, domoic acid and palytoxin. While tissues from 7 of 20 LST tested positive for brevetoxins, the levels were not considered to be in a range causing acute toxicosis. No known natural (algal blooms) or anthropogenic (pollutant spills) stressors co-occurred with the turtle mortality. While heavy metal toxicosis and organophosphate toxicosis were also investigated as possible causes, there was no evidence for their involvement. We speculate that the clinical signs and pathologic changes seen in the affected LST resulted from combined heavy spirorchiid parasitism and possible chronic exposure to a novel toxin present in the diet of LST.     

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.     

Orientation and swimming behavior of hatchling loggerhead turtles Caretta caretta L. during their offshore migration

Loggerhead turtle Caretta caretta L. hatchlings emerging from nests on the eastern coast of Florida swim offshore toward the Florida Current. Part of the trip is accomplished during an initial 20-h period of swimming (the “frenzy”); the remainder may take a day or more of oriented swimming. Swimming speeds are slower than those of green turtles Chelonia mydas L. Hatchlings are well oriented in an offshore direction when released into the ocean during the day or night. Completion of a crawl down the beach or a plunge into the surf are unnecessary for proper orientation. Immediately after entering the ocean at night, responses to light appear essential for oriented swimming. However, present hypotheses based upon phototropotaxis may not account for orientation later in the migration.     

An unsuccessful attempt to elicit orientation responses to linearly polarized light in hatchling loggerhead sea turtles (Caretta caretta)

Sea turtles undertake long migrations in the open ocean, during which they rely at least partly on magnetic cues for navigation. In principle, sensitivity to polarized light might be an additional sensory capability that aids navigation. Furthermore, polarization sensitivity has been linked to ultraviolet (UV) light perception which is present in sea turtles. Here, we tested the ability of hatchling loggerheads (Caretta caretta) to maintain a swimming direction in the presence of broad-spectrum polarized light. At the start of each trial, hatchling turtles, with their magnetic sense temporarily impaired by magnets, successfully established a steady course towards a light-emitting diode (LED) light source while the polarized light field was present. When the LED was removed, however, hatchlings failed to maintain a steady swimming direction, even though the polarized light field remained. Our results have failed to provide evidence for polarized light perception in young sea turtles and suggest that alternative cues guide the initial migration offshore.     

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.     

Clutch size for Mediterranean loggerhead turtles (Caretta caretta)

We investigated the number of eggs laid and the total clutch volume for loggerhead turtles ( Caretta caretta L.) nesting on the Greek island of Cephalonia (38° 09' N, 20° 33' E) during 1990. Both the number of eggs laid and clutch volume were positively related to female body size, and the mean explained variation for these relationships (36·6% and 37·7%, respectively) were not significantly different. Clutch volume decreased as the season progressed because individuals laid successively smaller clutches. The inter-nesting interval (range 15–19 days) did not significantly influence the number of eggs laid or clutch volume. For individuals seen laying more than once, female size in combination with the number of a clutch in relation to all the clutches observed for that individual, together explained 65·5% of the variation in clutch volume.     

Exceptional growth rates of captive loggerhead sea turtles,Caretta caretta

Twelve loggerhead sea turtle hatchlings (Caretta caretta) were removed from a nest site (A) at the Back Bay National Wildlife Refuge (U.S. Fish and Wildlife Service), Virginia Beach, VA. Hatchlings were distributed among study participants, and raised in captivity for a period of two years. Growth of the loggerheads was recorded weekly by straight-line caliper measurements of carapace lengths as well as measurements of total weights. Growth rates from the present study were much greater than those measured in previous studies. Mean weights for Nest A turtles at 1.5 years ranged from 10.3 to 17.6 kg, with one exceptional individual reaching 20.0 kg. The data from this study provide new insights into the early growth potential of loggerhead sea turtles. How this accelerated development may affect sexual maturity and post-release viability remain to be determined. © 1993 Wiley-Liss, Inc.     

Swimming behaviour and dispersal patterns of headstarted loggerhead turtles Caretta caretta

Swimming behaviour and dispersal patterns were studied in headstarted loggerhead turtles Caretta caretta which were released at three different sites on the Caribbean island of Curaçao (Netherlands Antilles) and at one site on the neighbouring island of Klein Curaçao, after 1–2.5 yrs of captivity. Turtles were tagged and followed up to a distance of 6125 m offshore, using a boat with a Global Positioning Unit. The released turtles reverted to typical hatchling behaviour and showed an offshore migration almost perpendicular to the coastline. No significant differences were found in directional swimming among the four sites. The turtles swam almost continuously about 30 cm under the water surface; their mean overall swimming speed was higher than in adult wild loggerheads suggesting a 'frenzy'-like swimming stage. The turtles exhibited diving behaviour, and the dive frequency and duration was comparable to that of similar-sized (wild) turtles. The present study demonstrates that upon release the headstarted loggerheads behave naturally and show dispersal patterns similar to wild hatchling turtles. The fact that the released turtles were still able to show offshore directional swimming suggests that the headstarting did not affect their short-term orientation abilities.     

Heavy metals in tissues of loggerhead turtles (Caretta caretta) from the northwestern Adriatic Sea

Thirty-five specimens of Caretta caretta were collected dead along the Adriatic Sea coast from the Po Delta to the Reno mouth (Italy). Turtles were classified into four size categories ranging from 24.5 to 74 cm, by measuring the minimum straight-line carapace length (MSCL). Cd, Cu, Fe, Mn, Ni, and Zn levels were assessed in liver, lung, muscle and adipose tissue. Cd, Cu and Fe mainly accumulated in the liver (8.9, 23.7 and 1180 mg/kg dry mass [d.w.], respectively), and Mn in the lung (29.5 mg/kg d.w.). Levels of Ni were higher in adipose (22 mg/kg d.w.) than other tissues, while Zn concentrations were higher in muscle (about 140 mg/kg d.w.). Negative correlations with size were established for Zn in liver and Cu in adipose tissue, while positive correlations were observed for Mn and Ni in adipose tissue. Metal concentrations did not differ between males and females, nor between individuals found stranded and those victims of by-catch. On average, Cd, Cu, Mn and Ni concentrations in our specimens were higher than in loggerhead turtles and other species living in other areas. We hypothesize that trace metals could be used as "acquired markers" to help investigate migration routes of C. caretta.     

Mating‐induced ovulation in loggerhead sea turtles,Caretta caretta

Mating‐induced ovulation is common in mammals, but has been rarely described in other taxa. Observations of several mature female loggerhead sea turtles, Caretta caretta, held in captivity seemed to indicate that ovulation did not occur in the absence of a male. This study was designed to determine whether this was an effect of captivity or an effect of the absence of a male. Two mature female loggerheads were followed over six annual reproductive cycles. Ultrasound exams were performed approximately every 2 weeks to follow the development of follicles in the ovaries. During the first two seasons, no male was present, in the next two seasons, a mature male was present without mating, and in the final two seasons a mature male was present, mating with one or both females. When no male was present or when present without mating, ovarian follicles developed to full size, but ovulation did not occur and the follicles gradually began to decrease in diameter and undergo changes evident on ultrasound. In the fifth season, only one of the females mated, dropping two eggs after 7 days, and continued to oviposit throughout the following months (total 275 eggs). The unmated female did not ovulate, showing the same pattern as earlier seasons. In the final season, both females mated and ovulated, dropping eggs for the next four months (total 539 eggs). The following year, no males were present and neither female ovulated. This study provides clear evidence that ovulation in loggerhead sea turtles is induced by mating. Zoo Biol 27:213–225, 2008. © 2008 Wiley‐Liss, Inc.     

Salt gland adenitis as only cause of stranding of loggerhead sea turtles Caretta caretta

The present study describes pathological and microbiological findings in 9 stranded loggerhead sea turtles Caretta caretta, whose only observed lesion was bilateral purulent salt gland adenitis. Histological lesions ranged from the presence of abundant eosinophilic material associated with bacterial colonies in the lumen of the central ducts of the glandular lobules to the destruction of the glandular tissue and presence of abundant eosinophilic material composed of heterophils and cell debris, lined by multinucleated giant cells. Aeromonas hydrophila, Staphylococcus sp., and Vibrio alginolyticus were the bacteria most frequently isolated. Plasma concentrations of sodium and chloride and plasma osmolality from 2 turtles suffering from salt gland adenitis were, respectively 45.7, 69.2, and 45.7% higher than the mean value for healthy turtles. These cases suggest that failure to maintain homeostasis due to severe lesions in the salt glands can cause stranding and/or death of loggerhead sea turtles.     

Female loggerhead sea turtles (Caretta caretta L.) rarely remate during nesting season

The goal of this study was to assess the consequences of single versus multiple paternity by identifying paternity of clutches per female to identify whether there were detectable costs or benefits. Multiple mating can occur when the benefits of mating outweigh the costs, but if costs and benefits are equal, no pattern is expected. Previous research on loggerhead sea turtle (Caretta caretta) populations found male‐biased breeding sex ratios and multiple mating by many females nesting in southwestern Florida. A sample of nesting loggerhead females who laid more than one nest over the course of the season and a subset of their hatchlings were examined from 36 clutches in 2016 on Sanibel Island, Florida. Males that fathered hatchlings in the first clutch sampled were identified in subsequent clutches. Interestingly, 75% of the females analyzed had mated singly. No male was represented in more than one female's clutches. The results suggest that females likely mate at the beginning of the season and use stored sperm for multiple clutches. Evidence for mating between laying events was limited. There was no consistent pattern across the subsequent multiple paternity clutches, suggesting benefits to loggerhead females likely equal their costs and subsequent mating is likely determined by female preference.     

Gastrointestinal helminth community of loggerhead sea turtle Caretta caretta in the Adriatic Sea

We analysed the intestinal helminth community of 70 loggerhead sea turtles Caretta caretta with a curved carapace length ranging from 25 to 85.4 cm, recovered dead in neritic foraging habitats in the Adriatic Sea in 1995 to 2004. The overall prevalence of infection was high (70.0%), with a mean abundance of 36.8 helminth parasites per turtle. Helminth fauna comprised 5 trematodes (Calycodes anthos, Enodiotrema megachondrus, Orchidasma amphiorchis, Pachypsolus irroratus, Rhytidodes gelatinosus) and 3 nematodes (Sulcascaris sulcata, Anisakis spp., Hysterothylacium sp.), with 6 taxa specific for marine turtles. In terms of infection intensity and parasite abundance, O. amphiorchis was the dominant species (mean intensity: 49.8; mean abundance: 12.8), followed by R. gelatinosus (30.5 and 8.3, respectively) and P. irroratus (23.5 and 7.0, respectively), while larval Anisakis spp. exhibited the highest prevalence (34.3%). The intensity of helminth infection ranged from 1 to 302 (mean: 52.6 ± 69.1) and was not correlated with the size of turtles; this relationship held for all species, except R. gelatinosus (rS = 0.556, p < 0.05). In comparison to other marine habitats, the helminth community of Adriatic loggerheads is characterised by higher species diversity (Shannon-Wiener H' = 1.58) and evenness (E = 0.76), and lower dominance values (Berger-Parker d = 0.35), which can be attributed to the life history and feeding ecology of sea turtles in recruited neritic grounds and the diversity of their benthic prey.     

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.     

Visual acuity thresholds of juvenile loggerhead sea turtles (Caretta caretta): an electrophysiological approach

Visual evoked potentials measure dynamic properties of the visual system by recording transient electric responses of neural tissue identified to correspond to a specific visual stimulus, such as light or a striped grid. In this study, visual evoked potentials were used to test the visual acuity of juvenile loggerhead sea turtles (Caretta caretta) in water. Subject animals were fitted with a Plexiglas goggle filled with filtered seawater. Stimuli of black and white striped gratings were presented to the turtles using a slide projector directing an image onto a screen via a rotatable mirror that shifted the striped pattern laterally one-half cycle. Bioelectric activity was collected using a digital averaging computer and subdermal platinum electrodes, implanted under the head scutes directly above the optic nerve and the contralateral optic tectum. To isolate the response signal from the noise, signal averaging techniques were used when collecting visual evoked potentials. The resulting response waveforms included a robust positive-negative compound that was used to track the turtle's response to visual stimulation. Acuity thresholds for these sea turtles, which were derived from linear regressions analysis of the positive-negative compound amplitudes versus stripe size, ranged from 0.130 to 0.215. This acuity level is comparable to other inshore, shallow water marine species.     

Helminth communities of loggerhead turtles (Caretta caretta) from Central and Western Mediterranean Sea: The importance of host's ontogeny

We investigated the factors providing structure to the helminth communities of 182 loggerhead sea turtles, Caretta caretta, collected in 6 localities from Central and Western Mediterranean. Fifteen helminth taxa (10 digeneans, 4 nematodes and 1 acanthocephalan) were identified, of which 12 were specialist to marine turtles; very low numbers of immature individuals of 3 species typical from fish or cetaceans were also found. These observations confirm the hypothesis that phylogenetic factors restrict community composition to helminth species specific to marine turtles. There were significant community dissimilarities between turtles from different localities, the overall pattern being compatible with the hypothesis that parasite communities reflect the ontogenetic shift that juvenile loggerheads undergo from oceanic to neritic habitats. The smallest turtles at the putative oceanic, pelagic-feeding stage harboured only the 2 digenean species that were regionally the most frequent, i.e. Enodiotrema megachondrus and Calycodes anthos; the largest turtles at the putative neritic, bottom-feeding stage harboured 11 helminth taxa, including 3 nematode species that were rare or absent in turtles that fed partially on pelagic prey. Mean species richness per host was low (range: 1.60–1.89) and did not differ between localities. Variance ratio tests indicated independent colonization of each helminth species. Both features are expected in ectothermic and vagrant hosts living in the marine environment.