Immature Green Turtles Research Articles

A Comparison of Immature Green Turtle (Chelonia mydas) Diets among Seven Sites in the Main Hawaiian Islands1

Understanding resource acquisition and feeding ecology of threatened species is integral to their conservation because diet is intimately linked with growth rate and reproductive output. We examined diets of immature green sea turtles, Chelonia mydas (L.), from seven sites on the islands of Hawai‘i, O‘ahu, Moloka‘i, and Lāna‘i in January and August 2003. Diet analysis was based on 191 samples collected from 181 live green turtles by stomach lavage. These samples were identified and quantified using dissection microscopy and the principles of microstereology. Diet of green turtles in the Main Hawaiian Islands was dominated by red algae, and diet items most commonly encountered were Acanthophora spicifera (an introduced species), Hypnea sp., Pterocladiella sp., and Cladophora sp. Sea grasses (Halophila hawaiiana and H. decipiens) were an important component of diet in turtles from Kāne‘ohe Bay. Content of green turtle diets differed among foraging grounds, and these differences may provide an insight into previously documented differences in turtle growth rates among sites.

Feeding ecology of the East Pacific green sea turtleChelonia mydas agassiziiat Gorgona National Park, Colombia

The diet of 84 East Pacific green turtles Chelonia mydas agassizii, captured in 2003 and 2004 at Gorgona National Park in the Colombian Pacific, was studied through analysis of lavage sam- ples collected from the lower oesophagus. We identified 5 food diet components, with rank in order of percent dry mass being: tunicates (Salpidae and Doliolidae), red mangrove fruits (Rhizophora mangle), algae (Rhodophyta, Chlorophyta, Cyanophyta), small crustaceans (shrimp larvae) and leaves (Ficus spp.). Three non-food diet items included coral fragments, shells, and sand/pebbles that were found in large amounts in most retrieved samples. Nutritional analyses were carried out to determine the contribution of diet components to the foraging turtles. Tunicates had the highest pro- tein value (438 g kg -1 ), followed by algae (174 g kg -1 ), leaves (170 g kg -1 ) and mangrove fruits (65 g kg -1 ). The frequency of retrieved components grouped in animal (including coral), vegetal and sand/pebbles categories did not vary between sampling seasons. The immature East Pacific green sea turtle population at Gorgona National Park showed an omnivorous behaviour, feeding on a range of animal and vegetal components with a bias towards tunicates (Salpidae and Doliolidae). In contrast to the generally herbivorous diet of juvenile green turtles (over 40 cm straight carapace length; SCL), Gorgona's immature population was composed of large juveniles, subadults and a few adults feeding mainly on animal matter. Mean SCL of 86 measured turtles was 58.4 ± 7.8 cm (ranging from 37.0 to 72.9 cm). Mean mass was 28.0 ± 10.7 kg (ranging from 7.5 to 50.5 kg). We speculate that this omniv- orous strategy of Gorgona's immature green turtles might provide energetic benefits for continuing long distance migrations to further developmental or mating grounds in the Pacific basin.

Identifying critical foraging habitats of the green turtle (Chelonia mydas) along the Pacific coast of the Baja California peninsula, Mexico

Abstract The conservation of highly mobile and migratory species remains one of the most serious challenges to resource managers. Intense mortality of immature green turtles has been identified at principal developmental–feeding habitats in Baja California, and is considered a great threat to the stability of the eastern Pacific population. Thus, coastal lagoons of the Baja California peninsula, such as Bahía Magdalena, have been identified as high priority areas for their protection. Conservation efforts to date have focused on creating a sea turtle refuge in the northwestern part of the bay, but this area may not be sufficient for protecting all of the critical feeding areas used by green turtles. The diet of green turtles was investigated through analysis of digestive tract contents from 24 green turtles that were drowned incidentally in fishing nets at feeding grounds in Bahía Magdalena and adjacent areas along the Pacific coast of the Baja California peninsula, Mexico. Mean straight carapace length (SCL) differed significantly between localities: mean: 55.5 cm (range: 47.7–76.9 cm, n=11) in Bahía Magdalena; mean: 67.7 >cm (range: 49–87 cm, n=11) in adjacent coastal waters. Green turtle diet consisted largely of marine algae and seagrasses, but food items varied spatially. The red algae Gracilaria pacifica, Gracilariopsis lemaneiformis and Hypea johnstonii were the most abundant diet items inside Bahía Magdalena, and the seagrass Phyllospadix torreyi was the most commonly ingested food in coastal areas outside of the bay. Results indicate that green turtles utilize spatially distinct foraging habitats within this region. Therefore, it is recommended that any design of protected areas for sea turtles in Bahía Magdalena should consider a regional approach instead of a local approach, taking into account the most important feeding areas used by green turtles at different life stages. Copyright © 2005 John Wiley & Sons, Ltd.

Depot fatty acid composition in immature green turtles ( Chelonia mydas) residing at two near-shore foraging areas in the Hawaiian Islands

The lipid content and fatty acid composition of depot fat were determined for 58 immature green turtles ( Chelonia mydas) residing at two near-shore foraging areas, Ahu-O-Laka, located in Kaneohe Bay on Oahu, and Kiholo Bay located on the island of Hawaii. Benthic flora at Kiholo was limited to a single algal species but included algae and seagrass at Ahu-O-Laka. Turtle straight carapace length ranged from 38.6 to 59.2 cm, suggesting that the sample set included new recruits to up to 12-year residents. Fatty acid data were analyzed using principal components analysis (PCA). PC1 accounted for over 50% of the variance. Turtles were generally delineated along PC1 by the length of time on benthic foraging grounds, with high (>0.75) negative loadings for the fatty acids 22:6n-3, 7M7H, t16:1n-10, 15:0, and 17:0 associated with relatively new recruits (suggesting a pelagic dietary source for these fatty acids) and high positive loadings for 12:0 and 14:0 associated with long-term residents. PC2 separated turtles primarily by capture location, with high positive loadings for 18:2n-6 and 18:3n-3 [the primary seagrass polyunsaturated fatty acids] associated with the Ahu-O-Laka turtles. Fatty acid profiles of turtles from both locations differed substantially from those of their benthic diets, suggesting considerable modification of dietary fatty acids and de novo biosynthesis.

Comparison of plasma androgen profiles in green and hawksbill sea turtles inhabiting Queensland waters

Investigations were made into profiles of plasma androgens (combined testosterone and 5α-dihydrotestosterone) in green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles inhabiting waters off Queensland, Australia. First, we documented the occurrence of sex-based and ontogenetic changes in plasma androgen of immature green and hawksbill turtles occurring in wild populations. Specifically, androgen levels are increased in pubescent individuals and adults of both species and sexes. Second, we measured seasonal variation in plasma androgen profiles of adult male green and hawksbill turtles. Third, we compared plasma androgens of post-nesting green and hawksbill turtles. As for previous studies on captive green turtles, our data indicate that wild populations of green turtles also show a prenuptial spermatogenic pattern, in which plasma androgen levels rise and peak prior to migration and courtship. However, our data from male hawksbill turtles are in contrast to this pattern and provide some evidence to suggest that a delayed phase shift may occur in this population. Unlike male green turtles, male hawksbill turtles in this study all showed signs of physiological preparation for breeding.

Oceanic survival and movements of wild and captive-reared immature green turtles ( Chelonia mydas) in the Indian Ocean

The ability of captive-reared turtles to survive in the wild is not precisely known, nor are movements of immature turtles in the open ocean. To provide information on these issues, a satellite tracking experiment was conducted in the western Indian Ocean to monitor oceanic movements of immature green turtles. Two wild turtles and four captive-reared individuals were tracked. The latter had been displaced after birth from nesting sites to a distant rearing site. Wild turtles survived after release, but did not move far away from release site. We hypothesize that this resident behaviour may be explained by stage-specific habitat requirements. Captive-reared turtles survived after release and migrated over thousands of kilometres. Among these, the oldest immature turtles retrieved the foraging sites of their native population, with movement patterns similar to those displayed by adults. Observed movements may be linked to hydrographic conditions such as general oceanic circulation, sea temperature and thermal fronts.

Survival probability estimates for immature green turtles Chelonia mydas in the Bahamas

Green turtles Chelonia mydas in the Atlantic undergo a complex series of development- al migrations, moving long distances among foraging grounds. The study of the ecology and demog- raphy of these foraging populations is hampered by a lack of estimates of survival probabilities for immature stages. In addition, for all species of sea turtles, estimates of survival probabilities have repeatedly been identified as the greatest requirement for improving models of population dynamics and plans for the management and conservation of these endangered and threatened species. We use data from long-term capture-mark-recapture studies of 2 sampling populations of immature green turtles in the Bahamas—Union Creek, Great Inagua from 1978 through 2001, and Conception Creek, Conception Island from 1989 through 2001—to generate estimates of annual survival proba- bilities. We employ a joint analysis of live-recapture and dead-recovery data (Burnham model) to generate estimates of true survival and permanent emigration probabilities for the Union Creek sam- pling population. Because fewer dead-recovery data were available for the Conception Creek sam- pling population, we used a Cormack-Jolly-Seber modeling approach to estimate an apparent annual survival probability of 0.680, which confounds mortality and permanent emigration. Our best esti- mate of true annual survival probability for Union Creek green turtles, protected from human- induced mortality, is 0.891. High survival probabilities in immature stages are necessary for species such as sea turtles with long lifespans and late sexual maturity to maintain stable populations. After green turtles emigrated from Union Creek, annual survival probability declined to 0.761 as the tur- tles were no longer protected from human-induced mortality, demonstrating the negative effect of this mortality on the future of green turtle populations in the Caribbean. This study reports the first application of the joint analysis of live-recapture and dead-recovery data to sea turtle populations and demonstrates the advantages of this modeling approach.

Assessing humoral and cell-mediated immune response in Hawaiian green turtles, Chelonia mydas

Seven immature green turtles, Chelonia mydas, captured from Kaneohe Bay on the island of Oahu were used to evaluate methods for assessing their immune response. Two turtles each were immunized intramuscularly with egg white lysozyme (EWL) in Freund’s complete adjuvant, Gerbu, or ISA-70; a seventh turtle was immunized with saline only and served as a control. Humoral immune response was measured with an indirect enzyme linked immunosorbent assay (ELISA). Cell-mediated immune response was measured using in vitro cell proliferation assays (CPA) using whole blood or peripheral blood mononuclear cells (PBM) cultured with concanavalin A (ConA), phytohaemagglutinin (PHA), or soluble egg EWL antigen. All turtles, except for one immunized with Gerbu and the control, produced a detectable humoral immune response by 6 weeks which persisted for at least 14 weeks after a single immunization. All turtles produced an anamnestic humoral immune response after secondary immunization. Antigen specific cell-mediated immune response in PBM was seen in all turtles either after primary or secondary immunization, but it was not as consistent as humoral immune response; antigen specific cell-mediated immune response in whole blood was rarely seen. Mononuclear cells had significantly higher stimulation indices than whole blood regardless of adjuvant, however, results with whole blood had lower variability. Both Gerbu and ISA-70 appeared to potentiate the cell-mediated immune response when PBM or whole blood were cultured with PHA. This is the first time cell proliferation assays have been compared between whole blood and PBM for reptiles. This is also the first demonstration of antigen specific cell-mediated response in reptiles. Cell proliferation assays allowed us to evaluate the cell-mediated immune response of green turtles. However, CPA may be less reliable than ELISA for detecting antigen specific immune response. Either of the three adjuvants appears suitable to safely elicit a detectable immune response in green turtles.

GREEN TURTLE SOMATIC GROWTH MODEL: EVIDENCE FOR DENSITY DEPENDENCE

The green turtle, Chelonia mydas, is a circumglobal species and a primary herbivore in marine ecosystems. Overexploitation as a food resource for human populations has resulted in drastic declines or extinction of green turtle populations in the Greater Caribbean. Attempts to manage the remaining populations on a sustainable basis are hampered by insufficient knowledge of demographic parameters. In particular, compensatory responses resulting from density-dependent effects have not been evaluated for any sea turtle population and thus have not been explicitly included in any population models. Growth rates of immature green turtles were measured during an 18-yr study in Union Creek, a wildlife reserve in the southern Bahamas. We have evaluated the growth data for both straight carapace length (SCL) and body mass with nonparametric regression models that had one response variable (absolute growth rate) and five potential covariates: sex, site, year, mean size, and recapture interval. The SCL model of size-specific growth rates was a good fit to the data and accounted for 59% of the variance. The body-mass model was not a good fit to the data, accounting for only 26% of the variance. In the SCL model, sex, site, year, and mean size all had significant effects, whereas recapture interval did not. We used results of the SCL model to evaluate a density-dependent effect on somatic growth rates. Over the 18 yr of our study, relative population density underwent a sixfold increase followed by a threefold decrease in Union Creek as a result of natural immigration and emigration. Three lines of evidence support a density-dependent effect. First, there is a significant inverse correlation between population density and mean annual growth rate. Second, the condition index (mass/(SCL)3) of green turtles in Union Creek is positively correlated with mean annual growth rates and was negatively correlated with population density, indicating that the green turtles were nutrient limited during periods of low growth and high population densities. Third, the population in Union Creek fluctuated around carrying capacity during our study and thus was at levels likely to experience density-dependent effects that could be measured. We estimate the carrying capacity of pastures of the seagrass Thalassia testudinum, the major diet plant of the green turtle, as a range from 122 to 4439 kg green turtles/ha or 16–586 million 50-kg green turtles in the Caribbean. Because green turtle populations are probably regulated by food limitation under natural conditions, carrying capacity can serve as a baseline to estimate changes in green turtle populations in the Caribbean since pre-Columbian times and to set a goal for recovery for these depleted populations. Finally, we compare the growth functions for green turtle populations in the Atlantic and Pacific oceans. Not only does the form of the size-specific growth functions differ between the two regions (monotonic declining in the Atlantic and nonmonotonic in the Pacific), but also small juvenile green turtles in the Atlantic have substantially higher growth rates than those in the Pacific. Research is needed to evaluate the causes of these differences, but our results indicate that demographic parameters between ocean basins should only be extrapolated with great caution.

Diet selection by immature green turtles, Chelonia mydas, in subtropical Moreton Bay, south-east Queensland

Diet selection by immature green turtles (Chelonia mydas) in Flathead Gutter, Moreton Bay, was determined by examining food ingested in relation to food availability (measured as vegetation composition and abundance within the feeding site). Food composition was sampled by oesophageal lavage. Turtles were repeatedly located over a 10-week period by means of sonic telemetry and visual identification. The number of resightings indicated that these turtles remained within their feeding grounds for at least short periods of time. Immature green turtles fed on both seagrass and algal species. However, most fed selectively on algae, primarily Gracilaria sp. Food items consumed frequently by these turtles were analysed for total nitrogen, gross energy and neutral detergent fibre levels. There was a negative correlation between fibre level and the preferred food species, where the more frequently selected species had lower levels of fibre. The preferred species also had higher nitrogen levels

Digesta composition and retention times in wild immature green turtles, Chelonia mydas: a preliminary investigation.

Digesta retention time (DRT) of particulate matter (the calculated time for elimination of 50% of marker beads) and food intake levels were measured in three wild immature green turtles, Chelonia mydas, by using inert plastic markers. DRTs were long, ranging from 156 to 325 h (6.5–13.5 days).

Simulated hibernation of sea turtles in the laboratory: I. Feeding, breathing frequency, blood pH, and blood gases

Captive immature green (Chelonia mydas) and Kemp's ridley (Lepidochelys kempi) sea turtles were examined to determine if a hibernation-like state could be induced under controlled conditions. Both species demonstrated that they are able to acclimate to cold temperatures behaviorally. However, the two species appeared to respond differently to decreasing temperature. Whereas the green turtles tolerated the onset of cold water temperatures by reducing swimming activity, the ridleys became very agitated and active as they were exposed to temperatures below 20 degrees C. Nevertheless, both species displayed semi-dormant behavior at temperatures below 15 degrees C, coming to the surface to breathe periodically at intervals of up to three hours. At low temperatures, venous blood pO2 and pCO2 decreased, whereas venous blood pH increased. Feeding also decreased as either species was exposed to cold temperature: greens (at 15 degrees C) and ridleys (at 20 degrees C) decreased food consumption to 50% of control levels, and ceased feeding below 15 degrees C. Thus, these species tolerated temperature drops and the associated hypophagia. They did not exhibit cold-stunning behavior, as has been observed in wild sea turtles exposed to rapid temperature drops, or prolonged periods of hibernation-like dormancy, as has been proposed for wild sea turtles during cold winter months.

Body Temperatures and Winter Feeding in Immature Green Turtles, Chelonia mydas, in Moreton Bay, Southeastern Queensland

Body temperatures of immature Clenonia mydas does not deviate significantly from water temperature in the range of 15-22.7 degrees C. Additionally, there was no correlation between Tb and body mass, indicating that larger turtles in the sampled range of sizes (9.2 - 39.5 kg) were not gaining a thermal advantage over smaller individuals.

Estimation of Green Turtle (Chelonia mydas) Growth Rates from Length-Frequency Analysis

Length-frequency analysis (using the computer program MULTIFAN) was used to estimate growth rates and number of age classes in a population of immature green turtles (Chelonia mydas) at Great Inagua in the southern Bahamas. Results from MULTIFAN were compared with growth rates estimated from nonlinear regression analysis on capture-recapture data and with calculated growth rates for 5-cm carapace length increments for the same population of green turtles. MULTIFAN underestimated growth rates of the smaller green turtles but yielded a better estimate of asymptotic size than did the nonlinear regression analysis. Estimates generated by MULTIFAN and by nonlinear regression analysis for the number of years it takes a green turtle at Great Inagua to grow from 30 to 70 cm carapace length fell within the 95% confidence limits of the calculated growth data from capture-recapture data. When the number of length-frequency samples was reduced sequentially from 10 years to two years, MULTIFAN was successful in estimating the number of age classes in the population for each of the nine sample sets. Length-frequency analysis shows promise as a method to rapidly estimate the number of year classes in a population of immature sea turtles and to estimate von Bertalanffy growth parameters.

Growth Rates of Wild Immature Green Turtles in the Galapagos Islands, Ecuador

Despite a deluge of publications on growth in immature captive green turtles, particularly hatchlings (e.g., Harrisson, 1955; Caldwell, 1962; Lebeau and Lebrun, 1976; Garnett, 1980), or growth after release of captive-reared green turtles (e.g., Kowarsky and Capelle, 1979; Ehrhardt and Witham, 1992), growth rates of wild green turtles under completely natural conditions have received surprisingly little attention. The earliest results are those of Schmidt (1916) for wild green turtles in the U.S. Virgin Islands (then the Danish West Indies). Since then, data on growth rates of immature green turtles in the wild have been published for Bermuda (Burnett-Herkes et al., 1984), Australia (Limpus and Walter, 1980), Hawaii (Balazs, 1982), Florida (Mendonca, 1981; Wershoven and Wershoven, 1992), Bahamas (Bjorndal and Bolten, 1988), the U.S. Virgin Islands (Boulon and Frazer, 1990), and Puerto Rico (Collazo et al., 1992). This paper provides data on the growth rates of wild immature green turtles tagged in the Galapagos Islands between 1975 and 1980.

Sex Ratio and Sex-Specific Growth Rates of Immature Green Turtles, Chelonia mydas, in the Southern Bahamas

Sex Ratio and Sex-Specific Growth Rates of Immature Green Turtles, Chelonia mydas, in the Southern Bahamas

On the whereabout of immature sea turtles (Caretta carettaandChelonia mydas) in the eastern Mediterranean

Abstract Numbers and spatial distribution of dead sea turtles washed ashore in Turkey indicate that immature Green Turtles (Chelonia mydas) stay more or less around their birth place and later reproduction grounds, whereas Loggerhead Turtles (Caretta caretta) apparently dismigrate to a much greater extent.

Growth Rates of Immature Green Turtles, Chelonia mydas, on Feeding Grounds in the Southern Bahamas

Growth in carapace length, carapace width, plastron length and body mass was measured in 149 growth increments for 122 green turtles, Chelonia mydas, at Great Inagua, Rahamas. Initial carapace length of the 149 growth increments ranged from 28.3-75.5 cm. Absolute growth rates for all linear parameters decreased with increasing size, but no significant difference in absolute growth rates for body mass was noted over the size range measured. Equations were developed to convert carapace length or plastron length to mass so that growth in mass could be modeled from data for either linear parameter. Three sizespecific growth models-Von Bertalanffy, Gompertz and logistic-were tested for goodness of fit. The Von Bertalanffy model had the best fit for seven body size parameters. With increasing size, there was a significant negative allometric relationship between carapace width and carapace length, but the relationship between plastron length and carapace length was isometric. Growth rates were compared with those of other green turtle populations. In our study area, green turtles grow more slowly than hawksbills, Eretmochelys imbricata, or loggerheads, Caretta caretta, of similar size.

Movements and Feeding Ecology of Immature Green Turtles (Chelonia mydas) in a Florida Lagoon

The seasonal and diel movements of 14 green turtles (Chelonia mydas) in Mosquito Lagoon, Florida were monitored using sonic telemetry. The feeding ecology of this population was also studied using dissection and stomach flushing techniques. Immature green turtles made random, long distance movements (x = 8.2 km/day) and occupied deeper waters (x = 1.6 m), apparently not feeding, when water temperatures ranged from 11-18 C; at water temperatures above 25 C they adopted a home range. Turtles were active at temperatures up to 34 C. No diel pattern was evident during winter months, but a definite bimodal pattern was evident at high water temperatures, with green turtles feeding on grass flats in midmorning and midafternoon and moving into deeper waters during the midday hours. Home range area was significantly correlated with body weight but the center of grazing activity was not. Seagrasses made up 88% of the turtles' diet throughout the year.

A study of appetite, digestion and growth in juvenile green turtle ( Chelonia mydas L.) fed on artificial diets

One-year-old immature green turtles (500–900 g) were kept at 25°C in recirculating seawater. When deprived of food for 108 h and then offered floating trout pellets, they consumed a satiation meal ( S g) described by the equation S = 0.025 W 0.96 where W is wet body weight in g. When food was offered at different deprivation times after satiation, maximum meals were taken after 60–72 h and corresponded to 2.5% body weight. Longer deprivation (108 h) led to reduced intake of 1.9–2% body weight. Gastric emptying was measured using X-radiography or chromic oxide to label the faeces. Complete stomach emptying required 110 ± 11 h S.D. and maximum appetite occurred when the stomach was estimated to be 80–95% empty. The average time for a meal to be voided from the alimentary tract was 176 ± 16 h S.D. Diets containing 40–50% protein and 4.2–5 kcal/gram were assimilated with apparent efficiencies of 76 ± 6% S.D. and 86 ± 6% for energy and protein nitrogen, respectively. A preliminary estimate for an energy budget for these animals based on a 23 day growth period accounted for 90% of the daily food intake as: 100 I⋍39M + 32E where known daily intake ( I calories) is compared with measures or estimates of metabolic rate ( M), growth ( G) and excreted wastes ( E). Although this balance is similar to that of herbivorous fish, the turtle has slower feeding and digestion rates than its teleost counterparts.