Juvenile Loggerhead Turtles Research Articles

The contribution of fish to the diet of loggerhead sea turtles in the western Mediterranean revisited

Early juvenile loggerhead turtles (Caretta caretta) rely on gelatinous zooplankton, whereas individuals larger than 40 cm curved carapace length are adapted to crush hard-shelled invertebrates. Nevertheless, fish were reported to be the staple food of loggerhead turtles in the western Mediterranean 30 years ago. Here, the temporal consistency of such a fish-based diet of loggerhead turtles is assessed through gut content analysis and stable isotope analysis of samples from the Mediterranean coast of Spain spanning three decades. The gut contents of 134 juvenile loggerhead turtles (curved carapace length range: 27–71 cm) from three different periods (1991, 1999–2008 and 2010–2017) were analyzed, as well as a subsample of the same turtles (n = 10 in each period) for both bulk and compound-specific stable isotope ratios (CSIA-AA). Gut content analysis revealed a decline in the frequency of occurrence and numerical abundance of fish and an increasing contribution of gastropods and bivalves throughout time, although pelagic tunicates were always the most frequently observed prey. The δ15Nbulk of turtle bone also dropped throughout the study period, but the values of the stable isotope ratio of N in phenylalanine (δ15NPhe) indicated that 52.5% of that variability was due to a baseline shift over time. Accordingly, the trophic position estimated from CSIA-AA did not follow the decreasing pattern of δ15Nbulk, but fluctuated throughout time. The overall evidence indicates that fish consumption by loggerhead turtles in the study region declined through time, but the trophic position of loggerhead turtles did not change simultaneously. This is probably because low trophic prey such pelagic tunicates and filter-feeding bivalves and suspension-feeding gastropods were the bulk of the diet during the whole study period and fish played a minor role, even when their frequency of occurrence peaked. Past levels of high fish consumption might be due to high levels of fishery discards, currently declining because of the recent reduction of the fishing fleet.

Identifying the foraging grounds of the new loggerhead turtle nesters in the western Mediterranean

Abstract The western Mediterranean Sea has traditionally served as a primary foraging ground for juvenile loggerhead turtles from three distinct regional management units: the North‐western Atlantic, the Mediterranean and Cape Verde. Nesting activities were sporadic. Recently, nesting activity on the beaches of eastern Spain has increased, due to warmer sand and water temperatures during the summer months. The study has integrated stable isotope analysis of carbon (C), nitrogen (N) and sulphur (S) with satellite telemetry to identify the foraging grounds of these new colonizers nesting on Spanish beaches. Results indicate that the majority of these adult females forage oceanically in the Algerian Basin, with a few exhibiting distinct stable isotope signals, tentatively associated with foraging in shallow coastal areas in the central Mediterranean Sea. The dominance of oceanic foragers in this new population is noteworthy, given the Algerian Basin's oligotrophic nature. This contrasts with the prevalence of neritic foraging in adult females nesting in the central and eastern Mediterranean Sea. The use of the Algerian Basin as a foraging ground for adult loggerhead turtles exposes them to bycatch from drifting longlines. The authorities should refrain from increasing bluefin quotas imposed on longliners in the Algerian Basin unless the fishery avoids using squid as bait and agrees to deploy hooks deeper than 25 m to reduce loggerhead turtle bycatch.

Basin-wide estimates of loggerhead turtle abundance in the Mediterranean Sea derived from line transect surveys

Loggerhead turtles are a globally vulnerable species of marine turtle. Broad-scale patterns of distribution and abundance can provide regional managers a tool to effectively conserve and manage this species at basin and sub-basin scales. In this study, combined aerial and shipboard line transect survey data collected between 2003 and 2018 were used to estimate distribution and abundance throughout the Mediterranean Sea. Approximately 230,000 linear kilometers of survey effort, from seven different surveying organizations were incorporated into a generalized additive model to relate loggerhead density on survey segments to environmental conditions. Two spatial density models estimating loggerhead density, abundance, and distribution were generated – one a long-term annual average covering 2003-2018 and another covering the summer of 2018, when a basin-wide aerial survey, the Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and Contiguous Atlantic Area Survey Initiative, was performed. Both models were adjusted for availability bias using dive data from loggerhead turtles tagged with time depth recorders. Mean abundance for the long-term average model was estimated as 1,201,845 (CV=0.22). The summer 2018 abundance estimate was 789,244 turtles and covered a smaller area than the long-term average. These estimates represent the first basin-wide estimates of abundance for loggerhead turtles in the Mediterranean not based on demographic models. Both models predicted similar distributions, with higher abundance predicted in the northern Adriatic Sea, central Mediterranean basin, Tyrrhenian Sea, and south of the Balearic Islands. Lower densities were predicted in the eastern Mediterranean Sea and the Aegean Sea. The highest density areas generally did not coincide with previously established adult loggerhead turtle foraging areas, which are typically neritic, indicating the models are predominantly predicting oceanic distributions, where most of the survey effort occurred. Juvenile loggerhead turtles are predominantly oceanic and comprise most of the population, but care must be taken when using these models as they may not accurately predict distribution of neritic foraging areas, where subadult and adult loggerheads can often be found. Despite this limitation, these models represent a major step forward for conservation planning and understanding basin-wide distribution and abundance patterns of this species.

Movement Patterns of Juvenile Loggerhead Turtles (Caretta caretta L. 1758) and Green Turtles (Chelonia mydas L. 1758) Hatched in Captivity and Released in the Korean Waters.

Simple SummaryDespite the continuous observation and drift of globally endangered sea turtles in Korean waters, relevant research and protection policies are deficient. To restore sea turtle populations near Korea, the Ministry of Oceans and Fisheries, Republic of Korea, has been hatching and rearing sea turtles in captivity and releasing juveniles into the sea. We satellite-tracked juvenile loggerhead and green turtles to confirm their movement patterns and adaptability in the wild. The tracked sea turtles used sea currents for movement, and the tracking duration and movement patterns differed according to their body size. In addition, while the loggerhead turtles moved to the Northeast East Sea, the green turtles tended to move west or southwest from the release point. By considering the release time and location, according to the growth level and species, the adaptability of artificially hatched and reared turtles to natural habitats is expected to be high.With most sea turtle populations declining, activities to conserve their habitat and nesting grounds and restore their populations are being implemented worldwide. To preserve the Northwestern Pacific populations, the National Marine Biodiversity Institute of Korea has been releasing artificially propagated sea turtles, but whether these individuals join the wild population remains unknown. The present study aimed to determine the movement patterns of artificially propagated juvenile loggerhead (Caretta caretta) and green (Chelonia mydas) turtles fitted with satellite transmitters on their carapaces and released in the waters of Jeju or Yeosu, Republic of Korea, between August 2018 and April 2022. Loggerheads traveled northward to the East Sea, whereas green turtles moved west or southwest. Two 36-month-old and two 48-month-old loggerheads moved toward their potential nursery grounds and toward their feeding grounds, respectively. Three green turtles with a curved carapace length (CCL) of <40 cm moved toward their nursery or feeding grounds, while three individuals (CCL > 45 cm) moved toward their inshore foraging areas. The travel paths were closely related to the direction of local sea currents. Our results implied that releasing artificially propagated sea turtles, considering their age and CCL, can positively contribute to the conservation of Northwestern Pacific populations.

Comparison Between Effects of Four Crystalloid Solutions on Acid-Base and Electrolyte Abnormalities in Stranded Juvenile Loggerhead Sea Turtles (Caretta caretta).

Dehydration, electrolyte abnormalities, and acid-base alterations are common findings in stranded sea turtles. Fluid therapy is essential for reestablishment of homeostasis. The aim of this study was to compare the efficacy and effects on acid-base and electrolyte status of four different crystalloids (0.9% NaCl solution, 0.9% NaCl and lactated Ringer's solutions 1:1 ratio, Plasmalyte, and Jarchow's solution) in 63 stranded juvenile loggerhead turtles (Caretta caretta). Crystalloid fluids were administered intracoelomically on the day of admission for a duration of three consecutive days at a rate of 20 mL/kg/day through the inguinal fossa. Blood samples were collected at three timepoints: on admission, 24 h after discontinuing fluid therapy and prior to release. Samples were analyzed using a portable electronic blood analyzer for pH, pCO2, pO2, bicarbonate, lactate, sodium, potassium, chloride, glucose, and BUN concentration. Thirty-four loggerhead turtles (53.9%) had some type of acid-base alteration at the time of admission. The combination of 0.9% NaCl and lactated Ringer's solutions resulted in the highest percentage of improved/resolved acid-base and electrolyte abnormalities (33.4 % more animals with normal acid-base status compared to the admission time) compared to Jarchow's solution, which was the least effective (15.8% decrease in the number of animals with normal acid-base status compared to the admission time). This study constitutes the second controlled study of fluid therapy in sea turtles, and corroborates the recommendation made previously on the use of 0.9% NaCl + lactated Ringer solution to resolve mild to moderate acid-base alterations in juvenile loggerhead turtles. In addition, convalescent acid-base, electrolyte and plasma biochemical reference intervals are also provided as a standard profile for sea turtle rehabilitation centers.

Testing a Novel Aggregated Methodology to Assess Hydrodynamic Impacts on a High-Resolution Marine Turtle Trajectory

We designed a novel aggregated methodology to infer the impact of ocean motions on the movements of satellite-tracked marine turtles adopting available oceanographic observations and validated products of a numerical oceanographic forecasting system. The method was tested on an 11-months trajectory of a juvenile loggerhead turtle (LT) wandering in the Tyrrhenian Sea (Mediterranean Sea) that was reconstructed with a high-resolution GPS tracking system. The application of ad-hoc designed metrics revealed that the turtle’s route shape, ground speed and periodicities of its explained variance mimic the inertial motions of the sea, showing that this methodology is able to reveal important details on the relation between turtle movements and oceanographic features. Inertial motions were also identified in the observed trajectory of a surface drifting buoy sampling the Tyrrhenian Sea in a common period. At each sampling point of the turtle trajectory, the sea current eddy kinetic energy (EKE) and a Sea Current Impact index were computed from a validated set of high-resolution ocean modeling products and their analysis showed the relevant effects of the highly variable local sea currents mechanical action. Specifically, the metric we adopted revealed that the turtle trajectory was favorably impacted by the encountered sea current advection for about 70% of its length. The presented oceanographic techniques in conjunction with high-resolution tracking system provide a practicable approach to study marine turtle movements, leading the way to discover further insights on turtle behavior in the ocean.

Predation of satellite-tagged juvenile loggerhead turtles Caretta caretta in the Northwest Atlantic Ocean

We present evidence of predator interactions with 8 juvenile loggerhead sea turtles Caretta caretta equipped with pop-up satellite archival transmitting tags (PSATs) following incidental capture in the Northwest Atlantic. Ingestion of PSATs occurred up to 5 mo after tagging and was identified by an abrupt change in depth distribution, a stabilization and/or increase in ambient temperature and a marked drop in light levels to near zero, with cessation of diel light level cycling. In some cases, following expulsion from the digestive tract of predators, positively buoyant PSATs descended to the sea floor or beyond the programmed release depth threshold (1800 m), indicating that they remained tethered to the indigestible carapaces of turtles and that the entire turtle was originally consumed. PSAT data, combined with the sudden termination of satellite uplinks from 2 loggerheads also equipped with platform transmitting terminals, provided additional evidence of whole-turtle predation. PSAT data indicated that both endothermic and ectothermic sharks ingested tags. Based on PSAT-logged temperature data, dive patterns and geographic distribution, the following shark species were considered as candidate predators: white, porbeagle, shortfin mako, tiger and blue. This study represents the first analysis of data collected by loggerhead turtle PSATs inside predators. The results expand the list of shark species known to prey on large juvenile loggerheads and point to the importance of acknowledging predation as an important source of mortality for loggerhead turtles in the Northwest Atlantic Ocean.

Movements of loggerhead sea turtles (Caretta caretta) in the Gulf of California: integrating satellite telemetry and remotely sensed environmental variables

AbstractThe loggerhead turtle (Caretta caretta) is a circumglobal species and is listed as vulnerable globally. The North Pacific population nests in Japan and migrates to the Central North Pacific and Pacific coast of North America to feed. In the Mexican Pacific, records of loggerhead presence are largely restricted to the Gulf of Ulloa along the Baja California Peninsula, where very high fisheries by-catch mortality has been reported. Records of loggerhead turtles within the Sea of Cortez also known as the Gulf of California (GC) exist; however, their ecology in this region is poorly understood. We used satellite tracking and an environmental variable analysis (chlorophyll-a(Chl-a) and sea surface temperature (SST)) to determine movements and habitat use of five juvenile loggerhead turtles ranging in straight carapace length from 62.7–68.3 cm (mean: 66.7 ± 2.3 cm). Satellite tracking durations ranged from 73–293 days (mean: 149 ± 62.5 days), transmissions per turtle from 14–1006 (mean: 462 ± 379.5 transmissions) and total travel distance from 1237–5222 km (mean: 3118 ± 1490.7 km). We used travel rate analyses to identify five foraging areas in the GC, which occurred mainly in waters from 10–80 m deep, with mean Chl-aconcentrations ranging from 0.28–13.14 mg m−3and SST ranging from 27.8–34.4°C. This is the first study to describe loggerhead movements in the Gulf of California and our data suggest that loggerhead foraging movements are performed in areas with eutrophic levels of Chl-a.

Movement patterns of large juvenile loggerhead turtles in the Mediterranean Sea: Ontogenetic space use in a small ocean basin.

Mechanisms that determine how, where, and when ontogenetic habitat shifts occur are mostly unknown in wild populations. Differences in size and environmental characteristics of ontogenetic habitats can lead to differences in movement patterns, behavior, habitat use, and spatial distributions across individuals of the same species. Knowledge of juvenile loggerhead turtles' dispersal, movements, and habitat use is largely unknown, especially in the Mediterranean Sea. Satellite relay data loggers were used to monitor movements, diving behavior, and water temperature of eleven large juvenile loggerhead turtles (Caretta caretta) deliberately caught in an oceanic habitat in the Mediterranean Sea. Hidden Markov models were used over 4,430 spatial locations to quantify the different activities performed by each individual: transit, low‐, and high‐intensity diving. Model results were then analyzed in relation to water temperature, bathymetry, and distance to the coast. The hidden Markov model differentiated between bouts of area‐restricted search as low‐ and high‐intensity diving, and transit movements. The turtles foraged in deep oceanic waters within 60 km from the coast as well as above 140 km from the coast. They used an average area of 194,802 km2, where most individuals used the deepest part of the Southern Tyrrhenian Sea with the highest seamounts, while only two switched to neritic foraging showing plasticity in foraging strategies among turtles of similar age classes. The foraging distribution of large juvenile loggerhead turtles, including some which were of the minimum size of adults, in the Tyrrhenian Sea is mainly concentrated in a relatively small oceanic area with predictable mesoscale oceanographic features, despite the proximity of suitable neritic foraging habitats. Our study highlights the importance of collecting high‐resolution data about species distribution and behavior across different spatio‐temporal scales and life stages for implementing conservation and dynamic ocean management actions.

Delineating foraging grounds of a loggerhead turtle population through satellite tracking of juveniles

Abstract Tracking of juvenile sea turtles is a research priority to inform the protection of relevant habitats and ensure sustainable rates of recruitment into adult populations. Based on satellite tracking, mixed stock analysis, and mark–recapture studies, Drini Bay in the South Adriatic Sea, Central Mediterranean, has been confirmed as an important foraging site used by loggerhead turtles from all major rookeries in the Mediterranean subpopulation. Three juvenile loggerhead turtles (Caretta caretta) from Drini Bay were tracked for 763, 364, and 211 days respectively. All turtles exhibited different movement patterns. The two smaller turtles ranged widely beyond the bay. One of these (69.5 cm curved‐carapace length; CCL) used the coldest region of the Mediterranean during the first winter of tracking where mean weekly temperatures dipped below 12°C but moved southwards to warmer waters during the second winter. In comparison, the other (66 cm CCL) individual moved south to winter in warmer waters from the outset. Both individuals returned to Drini Bay during summer, demonstrating fidelity to the study site. The third turtle, which was larger (76 cm CCL), remained in Drini Bay for the duration of tracking. These results support the findings of other mark–recapture studies at Drini Bay, which have suggested that the foraging site is being used in a transient way by immature turtles. All three turtles preferentially used the shallow waters (&lt;30 m) in the south of Drini Bay. The study demonstrates a high degree of overlap between the habitat use of the three tracked turtles and that of adult turtles tracked from nesting sites, and although based on a small sample size, contributes to a growing knowledge base regarding the wider habitat use of the Mediterranean loggerhead population.

Foraging ecology of Mediterranean juvenile loggerhead turtles: insights from C and N stable isotope ratios

Bycatch is one of the key threats to juvenile marine turtles in the Mediterranean Sea. As fishing methods are regional or habitat specific, the susceptibility of marine turtles may differ according to inter- and intra-population variations in foraging ecology. An understanding of these variations is necessary to assess bycatch susceptibility and to implement region-specific management. To determine if foraging ecology differs with region, sex, and size of juvenile loggerhead turtles (Caretta caretta), stable isotope analysis of carbon and nitrogen was performed on 171 juveniles from a range of foraging regions across the central and eastern Mediterranean Sea. Isotope ratios differed with geographical region, likely due to baseline variations in δ13C and δ15N values. The absence of sex-specific differences suggests that within an area, all comparably sized animals likely exploit similar foraging strategies, and therefore, their susceptibility to fisheries threats will likely be similar. The isotope ratios of juveniles occupying the North East Adriatic and North Levantine basin increased with size, potentially due to increased consumption of more prey items at higher trophic levels from a more neritic source. Isotope ratios of juveniles with access to both neritic and oceanic habitats did not differ with size which is consistent with them consuming prey items from both habitats interchangeably. With foraging habitats exploited differently among size classes in a population, the susceptibility to fisheries interactions will likely differ with size; therefore, region-specific management approaches will be needed.

Swirling in the ocean: Immature loggerhead turtles seasonally target old anticyclonic eddies at the fringe of the North Atlantic gyre

In a highly heterogeneous open ocean, swirling oceanographic structures such as eddies drive ocean productivity and aggregate many predators, including oceanic sea turtles. During early life, juvenile loggerhead turtles can spend more than a decade feeding on gelatinous zooplankton in the open ocean, but the way they use mesoscale eddies is still poorly understood. Here, we investigated the relationships between (1) the distribution and (2) the diving behaviour of immature loggerhead turtles of the North-East Atlantic and mesoscale eddies. For this purpose, 28 turtles were satellite tracked from the Azores archipelago. Using the Residence Time (RT) analysis as a proxy to identify high-use areas, the tracks and dive data of the turtles as well as drifter trajectories were analysed in relation to eddy characteristics, which include eddy radius, amplitude, type (cyclonic vs. anticyclonic), lifetime and region (inner core, outer core, periphery). The turtles dispersed widely using many distinct high-use areas. Although there were always more cyclones than anticyclones over the study region, the individuals seasonally associated more with the inner cores of old anticyclonic eddies, likely due to the higher productivity of decaying anticyclones. The comparison between passive drifters and turtles’ movements showed an active swimming behaviour from the turtles rather than a passive advection through currents. Three dive types were identified, and the one associated with the highest RT was characterized by dives of medium duration and depths in the inner cores of eddies. This study is the first to highlight strong affinities of oceanic loggerhead turtles for old anticyclonic eddies around the Azores, suggesting a greater complexity of these warm-core eddies that appear to be much more productive than cyclones.

High resting metabolic rates with low thermal dependence induce active dives in overwintering Pacific juvenile loggerhead turtles.

The metabolic rate and activity of sea turtles generally decreases with decreasing seasonal ambient temperature. Juvenile loggerhead turtles in the Mediterranean Sea made prolonged inactive dives (>400 min), indicating a state of dormancy during the cold winter period. However, seasonal differences in dive duration were not detected in juvenile loggerheads in the western North Pacific, even though the ambient water temperature changed by more than 10°C. Thus, metabolic states might differ among populations, explaining differences in the diving behaviour of juveniles during winter. Here, we tested the hypothesis that the active overwintering behaviour of juvenile loggerheads in the western North Pacific is driven by a high resting metabolic rate (RMR) with low thermal dependence. The RMR of juveniles in the western North Pacific (N=13) was 1.4-5.7 times higher (Q10=1.8) than that of juveniles in the Mediterranean Sea (Q10=5.4). To validate the high RMR values in the western North Pacific, the difference between core body temperature and ambient water temperature (ΔTb) was estimated from measured RMR and was compared with measured ΔTb The measured and estimated ΔTb matched each other. In addition, most of the dives conducted by the turtles in the western North Pacific were within the calculated aerobic dive limit (cADL) expected from the measured metabolic rate. Our results indicate that high RMR with low thermal dependence induces active diving during the overwintering periods of juvenile loggerheads in the western North Pacific, supporting the suggestion that metabolic states differ among populations.

Ketoprofen pharmacokinetics of R- and S-isomers in juvenile loggerhead sea turtles (Caretta caretta) after single intravenous and single- and multidose intramuscular administration.

Ketoprofen is a nonsteroidal anti-inflammatory and analgesic agent that nonselectively inhibits cyclooxygenase, with both COX-1 and COX-2 inhibition. Recent studies on COX receptor expression in reptiles suggest that nonselective COX inhibitors may be more appropriate than more selective inhibitors in some reptiles, but few pharmacokinetic studies are available. The goal of this study was to determine single- and multidose (three consecutive days) pharmacokinetics of racemic ketoprofen administered intravenously and intramuscularly at 2mg/kg in healthy juvenile loggerhead turtles (Caretta caretta). The S-isomer is the predominant isomer in loggerhead sea turtles, similar to most mammals, despite administration of a 50:50 racemic mixture. Multidose ketoprofen administration demonstrated no bioaccumulation; therefore, once-daily dosing will not require dose adjustment over time. S-isomer pharmacokinetic parameters determined in this study were Cmax of 10.1μg/ml by IM injection, C0 of 13.4 μg/ml by IV injection, AUC of 44.7 or 69.4μg*hr/ml by IM or IV injection, respectively, and T½ of 2.8 or 3.6hr by IM or IV injection, respectively. Total ketoprofen plasma concentrations were maintained for at least 12hr above concentrations determined to be effective for rats and humans. A dose of 2mg/kg either IM or IV every 24hr is likely appropriate for loggerhead turtles.

New findings about the spatial and temporal use of the Eastern Atlantic Ocean by large juvenile loggerhead turtles

AbstractAimsEffective conservation of threatened or endangered species requires a robust understanding of their spatio‐temporal distribution. Although a huge amount is known about the movements of Atlantic adult sea turtles, much less is known about juvenile turtles, and much of the life history model is therefore inferred. We set out to describe the spatio‐temporal distribution of juvenile loggerheads turtles found around the Canary Islands.LocationEastern North Atlantic Ocean.MethodsBetween 1999 and 2012, we satellite‐tracked 24 healthy large juvenile loggerhead turtles (mean straight carapace length = 47.4 cm, range = 34.6–54.5 cm) captured in the waters around the Canary Islands. We describe their regional distribution, identify high‐use areas and create a model for habitat suitability using minimum convex polygons, density rasters and ensemble ecological niche modelling, integrated with physical and biological environmental data.ResultsTurtles used a huge oceanic area (2.5 million km2) with particularly high usage around the Canary Islands, Spain, Portugal, Morocco and Western Sahara. In spring and summer, turtles generally moved further north towards the Iberian Peninsula. Ecological niche modelling identified sea surface temperature as the most important contributory variable to the habitat models. We also recorded three juvenile turtles making westward migrations away from the eastern Atlantic Ocean, presumably back towards their original natal beaches near sexual maturity.Main conclusionsThe results of the present study provide insight into a significant knowledge gap on the spatio‐temporal distribution of large juvenile loggerhead turtles in the eastern Atlantic Ocean. The data highlight that turtles occupy a vast open oceanic area, which hampers the ability of static conservation approaches to afford effective protection. However, ensemble ecological niche modelling highlights key suitable habitat for juvenile loggerhead turtles, which could be used in dynamic conservation protection.

Inferring long-term foraging trends of individual juvenile loggerhead sea turtles using stable isotopes

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 537:265-276 (2015) - DOI: https://doi.org/10.3354/meps11452 Inferring long-term foraging trends of individual juvenile loggerhead sea turtles using stable isotopes April Goodman Hall1,*, Larisa Avens1, Joanne Braun McNeill1, Bryan Wallace2,3, Lisa R. Goshe1 1National Marine Fisheries Service, Southeast Fisheries Science Center, Beaufort Laboratory, Beaufort, NC 28516, USA 2Stratus Consulting, Boulder, CO 80302, USA 3Nicholas School of the Environment, Duke University, Beaufort, NC 28516, USA *Corresponding author: april.goodman@noaa.gov ABSTRACT: Individual variation in diet composition has important evolutionary, ecological, and conservation implications. However, few studies of marine turtles have examined long-term foraging behavior of individuals. Using stable carbon (δ13C) and nitrogen (δ15N) isotope values from blood plasma, we examined long-term variation in resource use of 27 juvenile loggerhead turtles Caretta caretta captured multiple times in North Carolina between 2001 and 2010. Seven turtles displayed a marked increase in δ15N values consistent with a shift from oceanic to neritic habitat. These turtles, which we designated as ‘recruits’, had initial straightline carapace lengths (SCL) and δ15N values at first sampling that were significantly lower (p = 0.007 and p < 0.0001, respectively) than the remaining 20 ‘resident’ turtles. For the resident group, the influence of SCL on δ13C (p = 0.02) and δ15N (p = 0.05) values was significant. Individual effects on δ13C values were also significant (p < 0.001), indicating that foraging patterns vary among individuals; however, individual effects were not significant for δ15N (p = 0.07). Stable isotope niche width calculations suggested that residents were consistent in resource selection over time, and individuals were specialized in resource use relative to the population. Also, the resident population was more specialized than generalized in resource use, and stable isotope mixing (MixSIAR) model results suggest their diet is largely comprised of horseshoe crabs Limulus polyphemus. These findings improve understanding of the foraging ecology of juvenile loggerhead turtles, and highlight the importance of examining the long-term diet composition of individuals. KEY WORDS: Caretta caretta · Individual specialization · Niche width · Resource use · Stable isotopes Full text in pdf format PreviousNextCite this article as: Goodman Hall A, Avens L, Braun McNeill J, Wallace B, Goshe LR (2015) Inferring long-term foraging trends of individual juvenile loggerhead sea turtles using stable isotopes. Mar Ecol Prog Ser 537:265-276. https://doi.org/10.3354/meps11452 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 537. Online publication date: October 14, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Summer migration to temperate foraging habitats and active winter diving of juvenile loggerhead turtles Caretta caretta in the western North Pacific

Endangered loggerhead turtles (Caretta caretta) are highly migratory marine reptiles that spend extended maturation periods at sea. Although an understanding of the biology and ecology of juveniles is essential for effective conservation of this species, such information is still limited, especially for the North Pacific population. The first quantitative bycatch survey in northern Japan revealed that the Sanriku coastal area served as an important summer foraging habitat for large juvenile loggerhead turtles in the western North Pacific. To examine their year-round distribution and diving behaviour, we deployed satellite-relayed data loggers on six turtles (mean SCLn–t ± SD = 69.2 ± 9.2 cm, range = 58.3–82.5 cm). While turtles predominantly utilize the Sanriku coastal area and surrounding oceanic waters during summer, all turtles spent most of their time travelling in oceanic waters (>200 m) several kilometres east of Japan and sometimes in association with the Kuroshio Extension Current during winter. Although water temperature experienced by turtles significantly decreased during winter, they predominantly stayed in water >15 °C. There was no strong seasonal pattern in diving behaviour, and daily average dive duration was 20.9 ± 11.6 min regardless of summer or winter. In addition, turtles sporadically performed deep dives, including the deepest dive (>340 m) ever recorded for this species, during winter. These results suggest that juveniles remained active and possibly foraging in oceanic habitats throughout the winter rather than adopting the quiescent overwintering strategy (i.e. undertaking prolonged dives lasting >300 min) previously reported in adult females.

Correction: “Going with the Flow” or Not: Evidence of Positive Rheotaxis in Oceanic Juvenile Loggerhead Turtles (Caretta caretta) in the South Pacific Ocean Using Satellite Tags and Ocean Circulation Data

Correction: “Going with the Flow” or Not: Evidence of Positive Rheotaxis in Oceanic Juvenile Loggerhead Turtles (Caretta caretta) in the South Pacific Ocean Using Satellite Tags and Ocean Circulation Data

"Going with the flow" or not: evidence of positive rheotaxis in oceanic juvenile loggerhead turtles (Caretta caretta) in the South Pacific Ocean Using Satellite Tags and Ocean Circulation Data.

The movement of juvenile loggerhead turtles (n = 42) out-fitted with satellite tags and released in oceanic waters off New Caledonia was examined and compared with ocean circulation data. Merging of the daily turtle movement data with drifter buoy movements, OSCAR (Ocean Surface Current Analyses - Real time) circulation data, and three different vertical strata (0–5 m, 0–40 m, 0–100 m) of HYCOM (HYbrid Coordinate Ocean Model) circulation data indicated the turtles were swimming against the prevailing current in a statistically significant pattern. This was not an artifact of prevailing directions of current and swimming, nor was it an artifact of frictional slippage. Generalized additive modeling was used to decompose the pattern of swimming into spatial and temporal components. The findings are indicative of a positive rheotaxis whereby an organism is able to detect the current flow and orient itself to swim into the current flow direction or otherwise slow down its movement. Potential mechanisms for the means and adaptive significance of rheotaxis in oceanic juvenile loggerhead turtles are discussed.

The spatial ecology of juvenile loggerhead turtles (Caretta caretta) in the Indian Ocean sheds light on the “lost years” mystery

While our understanding of the early oceanic developmental stage of sea turtles has improved markedly over recent decades, the spatial context for this life history stage remains unknown for Indian Ocean loggerhead turtle populations. To address this gap in our knowledge, 18 juvenile loggerheads were satellite tracked from Reunion Island (21.2°S, 55.3°E) between 2007 and 2011. Nine turtles swam north toward Oman (20.5°N, 58.8°E), where one of the world’s largest rookeries of loggerheads is located. Three individuals traveled south toward South Africa and Madagascar, countries that also host loggerhead nesting grounds. Fourteen of the transmitters relayed diving profiles. A dichotomy between diurnal and nocturnal diving behavior was observed with a larger number of shorter dives occurring during the day. Diving behavior also differed according to movement behavior as individuals spent more time in subsurface waters (between 10 and 20 m) during transit phases. The study provides an understanding of the oceanic movement behavior of juvenile loggerheads in the Indian Ocean that suggests the existence of an atypical trans-equatorial developmental cycle for the species at the ocean basin scale in the Indian Ocean. These results address a significant gap in the understanding of loggerhead oceanic movements and may help with the conservation of the species.