Immature Green Turtles Research Articles

Fine scale geographic residence and annual primary production drive body condition of wild immature green turtles (Chelonia mydas) in Martinique Island (Lesser Antilles).

ABSTRACTThe change of animal biometrics (body mass and body size) can reveal important information about their living environment as well as determine the survival potential and reproductive success of individuals and thus the persistence of populations. However, weighing individuals like marine turtles in the field presents important logistical difficulties. In this context, estimating body mass (BM) based on body size is a crucial issue. Furthermore, the determinants of the variability of the parameters for this relationship can provide information about the quality of the environment and the manner in which individuals exploit the available resources. This is of particular importance in young individuals where growth quality might be a determinant of adult fitness. Our study aimed to validate the use of different body measurements to estimate BM, which can be difficult to obtain in the field, and explore the determinants of the relationship between BM and size in juvenile green turtles. Juvenile green turtles were caught, measured, and weighed over 6 years (2011–2012; 2015–2018) at six bays to the west of Martinique Island (Lesser Antilles). Using different datasets from this global database, we were able to show that the BM of individuals can be predicted from body measurements with an error of less than 2%. We built several datasets including different morphological and time-location information to test the accuracy of the mass prediction. We show a yearly and north–south pattern for the relationship between BM and body measurements. The year effect for the relationship of BM and size is strongly correlated with net primary production but not with sea surface temperature or cyclonic events. We also found that if the bay locations and year effects were removed from the analysis, the mass prediction degraded slightly but was still less than 3% on average. Further investigations of the feeding habitats in Martinique turtles are still needed to better understand these effects and to link them with geographic and oceanographic conditions.

Stable isotopes reveal dietary differences and site fidelity in juvenile green turtles foraging around São Tomé Island, West Central Africa

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 600:165-177 (2018) - DOI: https://doi.org/10.3354/meps12633 Stable isotopes reveal dietary differences and site fidelity in juvenile green turtles foraging around São Tomé Island, West Central Africa Joana M. Hancock1,2,3,*, Sara Vieira3, Victor Jimenez3, Jorge Carvalho Rio4, Rui Rebelo1 1cE3c - Centre for Ecology, Evolution and Environmental Changes, Faculty of Sciences, University of Lisbon, 1749-016 Lisbon, Portugal 2CIBIO - Research Centre in Biodiversity and Genetic Resources, University of Porto - Campus do Vairão, 4485-661 Vairão, Portugal 3Associação Programa Tatô - Sítio da Pedragosa, 8600-013 Barão de São João, Portugal 4MARAPA - Mar, Ambiente e Pesca Artesanal, CP 292 São Tomé, São Tomé e Príncipe *Corresponding author: joana.hancock@gmail.com ABSTRACT: Green sea turtles are common in West Central Africa, but little is known about the occurrence of immatures in foraging grounds in the Gulf of Guinea islands, known for their volcanic origin and narrow coastal fringes. This study presents results of in-water surveys in foraging grounds off São Tomé Island, in the São Tomé and Príncipe archipelago, providing the first available data on the size distribution of immature green sea turtles of different life-stage groups on these islands. Two sites offering distinct types of food sources were studied, and isotopic signatures of immature turtles hand-captured at each foraging site were used to infer (1) how long they were established at the foraging sites and (2) their diet preferences. Recruitment in the region was estimated to occur at a minimum size of 34 cm curved carapace length (CCL), and resident immature turtles ranged from 53 to 87 cm CCL. Immatures sampled at each site showed clear differences in isotopic signatures, suggesting that they establish specific home ranges related to the available diet items and use them for extended periods of at least several months. Macroalgae were as important as or more important than seagrasses for the turtles’ diets, and there was evidence that these individuals are not strictly herbivorous. Our study provides the first dataset for comparison with demographic data from other locations in West Africa, where current knowledge on green turtle foraging behavior is limited, and indicates that even oceanic islands that are geologically recent like São Tomé may provide important recruitment and development habitats for juvenile green turtles. KEY WORDS: Chelonia mydas · Settlement · Stable isotopes · Foraging ecology · Gulf of Guinea Full text in pdf format PreviousNextCite this article as: Hancock JM, Vieira S, Jimenez V, Carvalho Rio J, Rebelo R (2018) Stable isotopes reveal dietary differences and site fidelity in juvenile green turtles foraging around São Tomé Island, West Central Africa. Mar Ecol Prog Ser 600:165-177. https://doi.org/10.3354/meps12633 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 600. Online publication date: July 30, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Individual-level behavioral responses of immature green turtles to snorkeler disturbance.

Despite many positive benefits of ecotourism, increased human encounters with wildlife may have detrimental effects on wild animals. As charismatic megafauna, nesting and foraging sea turtles are increasingly the focus of ecotourism activities. The purpose of our study was to quantify the behavioral responses of immature green turtles (Chelonia mydas) to disturbance by snorkelers, and to investigate whether turtles have individual-level responses to snorkeler disturbance. Using a standardized disturbance stimulus in the field, we recorded turtle behaviors pre- and post-disturbance by snorkelers. Ninety percent of turtles disturbed by snorkeler (n=192) initiated their flights at distances of ≤3m. Using principal component analysis, we identified two distinct turtle personality types, 'bold' and 'timid', based upon 145 encounters of 19 individually identified turtles and five disturbance response variables. There was significant intra-individual repeatability in behavioral responses to disturbance, but bolder turtles had more behavioral plasticity and less consistent responses than more timid individuals. Bolder individuals with reduced evasion responses might be at a higher risk of shark predation, while more timid turtles might have greater energetic consequences due to non-lethal predator effects and repeated snorkeler disturbance. Over the longer term, a turtle population with a mix of bold and timid individuals may promote more resilient populations. We recommend that snorkelers maintain >3m distance from immature green turtles when snorkeling, and that ecotourism activities be temporally and spatially stratified. Further, turtle watching guidelines need to be communicated to both tour operators and independent snorkelers to reduce the disturbance of turtles.

Somatic growth rates of immature green turtles Chelonia mydas inhabiting the foraging ground Akumal Bay in the Mexican Caribbean Sea

Growth dynamics helps to elucidate demographic aspects, such as age at specific size and size at maturity or first reproduction, which are important for sea turtle management. The Mexican Caribbean Sea is an important feeding ground for green turtles, but demographic data for the turtles are lacking. Size-based growth rates of immature green turtles inhabiting a foraging ground at Akumal Bay (20°24′0″N and 87°19′16″W) were obtained by using a mixed longitudinal sampling design from historic mark–recapture data (2004–2014). Curved carapace length (CCL) of immature turtles at first capture ranged from 27.8–81.0cm and minimum size at recruitment was 27.8cm CCL. Recapture intervals ranged from 1 to 49months, 72% of the recaptures (n=172) occurred in less than a year and 90% before 1.5years. A monotonic size-specific growth function displays the maximum growth rate (6.25cmyr−1) at about 46–48cm CCL before starts declining steadily at >60cm CCL. Mean size presented a non-linear relationship with growth rates and year of capture had a negative linear effect over growth; the lowest annual mean growth rates were registered during 2009 and 2012. Based on GAM predictions an immature sea turtle recruited to the feeding ground (28cm CCL) would require between 13 and 14years to reach the average nesting size, supporting field observations. A negative linear relationship between annual mean growth rate and the relative estimated sea turtle abundance (p=0.001) suggests a density-dependent effect. The quantitative information presented will help understand life history patterns and provide a baseline to assess future dynamics of this green turtle population.

Genetic markers provide insight on origins of immature green turtles Chelonia mydas with biased sex ratios at foraging grounds in Sabah, Malaysia

An understanding of population dynamics is needed to assess the viability of migra- tory species. Monitoring of marine turtles at foraging grounds may detect changes in population trends that would take decades to be seen at nesting beaches. Mixed Stock Analysis using molec- ular markers provides a tool for estimating the origin of turtles sampled at foraging grounds. Here, we analysed mitochondrial DNA sequences of 90 immature green turtles at 2 foraging grounds in northwestern Sabah, Malaysia. We used data from 30 Indo-Pacific green turtle rookeries as the baseline for tracing the origin of turtles at the 2 foraging grounds. The inferred origins of turtles at the 2 locations were not different and indicated that the majority originated from 3 major popula- tions in Southeast Asia, the Turtle Islands of Sarawak in northwestern Borneo (29%), the Turtle Islands Heritage Protected Area (TIHPA) (28%) and Peninsular Malaysia (25%). Previous analy- ses indicated a 1:4 female-biased sex ratio at the foraging grounds, and based on our results, this largely reflects the use of unshaded beach hatcheries at some of the source rookeries for decades, which resulted in mostly female hatchlings. This result is supported by differences in the origins of male and female turtles. The result suggests a greater proportion of males originating from Peninsular Malaysia and fewer males originating from Sarawak and possibly the TIHPA com- pared to females. We discuss the implications of hatchery practices that influence sex ratios of hatchlings and recommend future research to improve the management of marine turtles in the region.

The spatio-temporal distribution and population structure of green turtles (Chelonia mydas) in New Zealand

ABSTRACTDespite being endangered internationally and protected nationally, little consideration has been given to the occurrence of green turtles (Chelonia mydas) in New Zealand. New Zealand lies on the southern boundary of the distributional range of green turtles in the southwestern Pacific, with individuals found within these waters historically considered to be occasional visitors or stragglers incidentally carried by ocean currents. However, the present work shows that green turtles are present year round in New Zealand’s northern waters (c. 34°–38° S). A review of sighting, stranding and incidental capture data collected between 1895 and 2013 illustrate New Zealand’s green turtle population comprises post-pelagic immature juveniles to large subadults. The female:male sex ratio of 1.7:1 is similar to those reported from warm temperate foraging grounds in eastern Australia. A subsample of new recruits indicates green turtles recruit to neritic habitats at approximately 40.8 cm curved carapace length. This study suggests that New Zealand’s neritic habitats constitute a transitional developmental ground for post-pelagic immature green turtles. We observed an exponential increase in the number of documented records over time, though whether this is due to increased numbers of turtles or increased reporting rates, or both, is unclear and warrants further investigation. More broadly, this work provides a baseline understanding of the ecology of green turtles at the edge of their range, providing opportunities to investigate regional niche modelling and connectivity of this highly mobile species, while also monitoring broad-scale effects of climate-induced environmental change.

Somatic Growth Rates of Green Turtles (Chelonia mydas) and Hawksbills (Eretmochelys imbricata) in the Galápagos Islands

Abstract Growth rates can be used as an indicator of overall turtle population health and provide a baseline against which to compare the quality of, or changes in, the conditions in foraging habitats. Previous studies of Green Turtles (Chelonia mydas) in the waters of the Galapagos Archipelago in the late 1970s revealed some of the slowest growth rates ever reported for immature Green Turtles. In this study, we evaluate whether growth rates have changed since the earlier study and the effects of color morph, body size, recapture interval, year, and site of capture on growth rates for Green Turtles at four key foraging grounds in the Galapagos Islands between 2003 and 2008. Results of this study confirm that somatic growth in Galapagos Green Turtles is very slow. In addition, somatic growth is significantly affected by morph, body size, and spatial variation. Mean growth rates generate implausibly long estimates of 133–200 yr for Galapagos Green Turtles to grow from 40-cm straight carapace length to sexua...

Random Mate Searching: Male Sea Turtle Targets Juvenile for Mating Behavior

Abstract Here, we report an incidental observation obtained by an animal-borne video logger of courtship behavior by an adult male green turtle (Chelonia mydas) directed toward an immature green turtle. Our result hypothesized that males may select a mating partner mainly using a visual cue based on size, but without high acuity, so that they can distinguish the size of mature females from that of immature turtles. Hence, male turtles may visualize the objects moving underwater that have the similar size to a mature female turtle as a mating partner, and consequently randomly attempt to court turtles including both immature and mature turtles.

Spatial and temporal variability of immature green turtle abundance and somatic growth in Puerto Rico

Understanding conservation needs relies on robust estimates of key population parameters, such as survival, abundance and somatic growth. We investigated the somatic growth and abundance dynamics of 2 aggregations of immature green turtles, at Tortuga Bay and Puerto Manglar (Culebra, Puerto Rico), throughout 15 yr of capture-mark-recaptures. We used nonlinear models to investigate the effects of carapace length, sampling year, growth interval and the pres- ence of fibropapillomas on growth rates, and used the size-specific growth rate function to esti- mate how long turtles remain at each bay. Abundances were estimated and compared with time- specific growth rate functions, to infer density-dependency effects on somatic growth rates, and trends in abundance were evaluated by fitting generalized linear models. We found foraging site specific growth rates and report the highest mean somatic growth rate for green turtles in the wild (6.1 ± 1.7 cm yr �1 , at Puerto Manglar). The size-specific growth rate function was monotonic at both sites, with growth rates declining continuously with increasing carapace length. We inferred minimum ages at maturity of 14 and 22 yr, for Puerto Manglar and Tortuga Bay turtles, respec- tively. Throughout the 15 yr of this study there was a positive trend in aggregation size at Puerto Manglar (mean annual increase of 10.9%), which was not observed at Tortuga Bay. Our study highlights the influence of geography and habitat quality on somatic growth rates, and delivers robust demographic estimates valuable for local and regional assessments of the conservation sta- tus of the green turtle.

Correction: Ethogram of Immature Green Turtles: Behavioral Strategies for Somatic Growth in Large Marine Herbivores

Correction: Ethogram of Immature Green Turtles: Behavioral Strategies for Somatic Growth in Large Marine Herbivores

Ethogram of Immature Green Turtles: Behavioral Strategies for Somatic Growth in Large Marine Herbivores

Animals are assumed to obtain/conserve energy effectively to maximise their fitness, which manifests itself in a variety of behavioral strategies. For marine animals, however, these behavioral strategies are generally unknown due to the lack of high-resolution monitoring techniques in marine habitats. As large marine herbivores, immature green turtles do not need to allocate energy to reproduction but are at risk of shark predation, although it is a rare occurrence. They are therefore assumed to select/use feeding and resting sites that maximise their fitness in terms of somatic growth, while avoiding predation. We investigated fine-scale behavioral patterns (feeding, resting and other behaviors), microhabitat use and time spent on each behavior for eight immature green turtles using data loggers including: depth, global positioning system, head acceleration, speed and video sensors. Immature green turtles at Iriomote Island, Japan, spent an average of 4.8 h feeding on seagrass each day, with two peaks, between 5∶00 and 9∶00, and between 17∶00 and 20∶00. This feeding pattern appeared to be restricted by gut capacity, and thus maximised energy acquisition. Meanwhile, most of the remaining time was spent resting at locations close to feeding grounds, which allowed turtles to conserve energy spent travelling and reduced the duration of periods exposed to predation. These behavioral patterns and time allocations allow immature green turtles to effectively obtain/conserve energy for growth, thus maximising their fitness.

Home range of immature green turtles tracked at an offshore tropical reef using automated passive acoustic technology

Seventeen immature green turtles Chelonia mydas were tracked concurrently by automated ultrasonic receivers at a coral reef off North-Eastern Australia (September–December 2010, 16.4°S, 145.6°E). The majority (n = 11) were tracked for the entire 100-day study, the remainder for 23–85 days. Detection data aggregated at 30-min intervals produced median 6.5–35 daily locations for individual turtles. Home range areas (95 % utilisation distribution) were ≤1 km2, \( {\bar{\text{x}}} \) ± SD = 0.74 km2 ± 0.159. To the best of our knowledge, these are the first home range estimates for C. mydas foraging at offshore tropical reefs. The findings are important for conservation in revealing near-continuous presence of the same individuals within a small geographic area. Time between detections was very short (median <3 min) demonstrating passive ultrasonic technology can track multiple turtles in a foraging environment with higher temporal resolution than typically achieved by satellite tracking.

Unintended backpackers: bio-fouling of the invasive gastropod Rapana venosa on the green turtle Chelonia mydas in the Río de la Plata Estuary, Uruguay

Here we report the first observations of the rapa whelk Rapana venosa massively bio-fouling immature green turtles Chelonia mydas. From November 2004 to July 2011, we examined 33 green turtles with rapa whelks attached to their carapaces in Uruguayan waters. The number of attached rapa whelks ranged from 1 to 49 individuals, representing up to 20 % of turtle weight. This previously unrecorded interaction may be of global importance to green turtles conservation because (a) immature green turtles from distant breeding populations utilize insular and coastal waters of the Rio de la Plata estuary and Atlantic coast of Uruguay as developmental and foraging habitats and (b) attached whelks may reduce green turtle fitness by reducing buoyancy, increasing drag, and causing severe injuries to the carapace.

Revisiting the ontogenetic shift paradigm: The case of juvenile green turtles in the SW Atlantic

The green turtle (Chelonia mydas) is a subcosmopolitan species found in tropical and temperate latitudes. The best knowledge on its behavior described an abrupt and irreversible ontogenetic shift that takes place early in life in some areas such as the Greater Caribbean and Australia. Young turtles move from oceanic to neritic habitats, from pelagic to benthic feeding and from an omnivorous to an herbivorous diet. However, whether this pattern applies elsewhere in the range of the species is not known. In the temperate waters of the South West (SW) Atlantic, preliminary evidence suggests that these juveniles would not comply with the tenets of an abrupt and irreversible ontogenetic shift as in tropical waters. We satellite tracked 9 neritic juveniles moving along the coast of Argentina, and applied a switching state-space model combined with kernel density estimation to identify preferential putative foraging areas and migratory routes. Results indicate that immature green turtles are not strictly herbivores or neritic in the temperate SW Atlantic. In summer and fall, juveniles foraged most of the time in estuarine areas without submerged macrophytes. In winter and spring, the turtles migrated north to warm coastal areas where macroalgae and seagrass are available. Concomitant to pelagic feeding, some turtles reached deep water areas where macrophytes are unlikely to occur. Adaptation to local conditions explains behavior better for the SW Atlantic than the abrupt and irreversible ontogenic shift described for warmer waters.

한국연안의 푸른바다거북(Chelonia mydas) 인공위성표지방류

To investigate the distribution and migrations of sea turtles occurring in Korean waters, an adult female green sea turtle Chelonia mydas was tagged with a satellite transmitter and released at Busan in October 2009. The confirmation was made for the first time that the released green sea turtle migrated back to Korea after visiting Jeju Island and Japan for approximately 9 months. The green sea turtle spent the winter in Jeju and Japan because of low water temperatures in the East Sea and South Sea during winter months, which were not suitable for turtle survival. Compared with an immature green sea turtle that was released at Jeju Island, the adult green showed a markedly different migration pattern, suggesting that juvenile and adult greens move differently because of their peculiar life cycle and their stage of maturity, in addition to responses to temperature changes. Additional satellite tracking with increased representation of species, sexes and sizes of turtles, and regions is required to gather information on the distribution and movements of sea turtles in Korean waters.

Survival probability of immature green turtles in two foraging grounds at Culebra, Puerto Rico

Inshore bays are key foraging grounds for immature green turtles Chelonia mydas. At these confined areas, capturemarkrecapture (CMR) programs generate valuable informa- tion that can be used to estimate vital rates, essential for the effective conservation of this endan- gered species. We compiled the CMR history profiles of 273 individuals from 13 yr of in-water sur- veys and employed the Cormack-Jolly-Seber model to estimate the survival probabilities of green turtles in 2 neritic bays at Culebra municipality, Puerto Rico. The CMR profiles were grouped into 2 size classes: juvenile and subadult. No adults were captured during the study. We found no sig- nificant differences in survival probability between the green turtles occupying each bay. We also assessed the survival probability of fibropapillomatosis (FP)-afflicted turtles versus FP-free turtles and found no significant differences among these groups. However, there was a significant differ- ence in survival between the 2 size classes. Juveniles showed a higher survival probability (0.8322, 95% CI = 0.7875 to 0.8690) than subadults (0.5290, 95% CI = 0.3851 to 0.6682). The low survival of subadults is potentially biased by the permanent emigration of some of these individu- als. Previous studies have shown that larger immatures leave shallow protected bays and occupy deeper open waters, sometimes associated with adults. Juveniles seem to be resident, and their survival rate can serve as a reference value for viability analysis. This is the first study on the survival of green turtles in the West Indies.

Population Structure and Growth of Immature Green Turtles at Mantanani, Sabah, Malaysia

In Southeast Asia, virtually all knowledge about sea turtle biology is derived via nesting beach studies. This study investigated life-stage parameters for a foraging population of immature Green Turtles Chelonia mydas off the coast of Borneo, Malaysia, to elucidate a significant portion of the at-sea life-stage component. Mark–recapture provided new data on localized movements between captures, growth, and residency period. Laparoscopic examination provided information on sex ratios and maturity. Turtles moved only an average of 380 m between recaptures and exhibited site-fidelity over several recaptures spanning up to two years. Size classes suggested all animals were juveniles and ranged from 38–80 cm CCL. Growth rates among recaptures averaged 3.6 cm yr−1. Laparoscopic examinations of the gonads confirmed that all individuals were immature, with a sex ratio of 1M ∶ 4F. These initial data on foraging C. mydas population structure and dynamics are of use for life-stage population models and turtle management and recovery planning.

한국 연안의 멸종위기 바다거북의 분포 및 좌초 현황

This paper reports the strandings of sea turtles on Korean shores monitored for the first time in 2008. A total of 19 sea turtles, consisting of 12 greens and 7 loggerheads, were recorded as stranded from the east coast to the south including Jeju Island. Reported strandings reached a peak in July and dominant area was Jeju Island. The curved carapace length of loggerhead sea turtles ranged 65-84.2cm and that of green sea turtles ranged 39.2-90cm, indicating most of them were immature to sub-adult. Out of 19 turtles, 11 were found dead with unknown reasons. Possible causes of death may include drawning by fishing gear, swallowing of marine debris, boat collision, and diseases. An immature green sea turtle tagged with a satellite transmitter spent winter near Jeju Island where it was released, suggesting that the Island provide immature greens a feeding ground. Considering thousands of sea turtles crawl on Japanese shores for nesting every year, the number of sea turtles reported in Korean waters was relatively small. Therefore, it is suggested that an appropriate monitoring system be necessary to protect and conserve endangered sea turtle species in Korean waters.

Diet selection by immature green turtles (Chelonia mydas) at Bahía Magdalena foraging ground in the Pacific Coast of the Baja California Peninsula, México

In order to determine if eastern Pacific green turtles(Chelonia mydas)exhibit feeding preferences samples of recently ingested food items were compared to the food resources available in the marine environment whereC. mydascongregates. Stomach samples were collected by conducting gastric lavage and, at the same time, vegetation transects were conducted during spring and winter. Green turtles in our study selectively consumed seaweeds, withCodium amplivesiculatumandGracialaria textoriias preferred species. Differences in the consumption of species were found across the two mentioned seasons and were consistent with changes in the availability of different algae species in the environment. Based on these results, it is recommended that sea turtle conservation plans along the Baja California Peninsula include Pacific coastal mangrove channels with a high diversity of algae species as priority areas for protection.

Annual variation in source contributions to a mixed stock: implications for quantifying connectivity

Connectivity among populations of highly migratory species is an area of active research and is often quantified with genetic markers. We determined mitochondrial DNA (mtDNA) sequences in 350 green turtles, Chelonia mydas, in 10 annual samples over a 12-year period from an aggregation of immature green turtles in the southern Bahamas. We found significant temporal structuring in haplotype frequencies among years for all turtles and for recruits. These significant differences were reflected in substantial variation in the relative contributions from different rookeries among years estimated by a Bayesian hierarchical model. Because this foraging aggregation has been the subject of a demographic study for over 30 years, we were able to determine that, among the three potential causes of temporal structuring-differential recruitment, mortality and emigration-recruitment accounts for most of this variation. We found that estimates of connectivity and genetic diversity in sea turtle populations are affected by the level of temporal variation reported here. More studies on the extent of temporal variation in composition of mixed stocks of other migratory species are needed to determine how this affects measures of connectivity.