Divergence and hybridization in sea turtles: Inferences from genome data show evidence of ancient gene flow between species.

Reconstructing past events of hybridization and population size changes are required to understand speciation mechanisms and current patterns of genetic diversity, and ultimately contribute to species' conservation. Sea turtles are ancient species currently facing anthropogenic threats including climate change, fisheries, and illegal hunting. Five of the seven extant sea turtle species are known to currently hybridize, especially along the Brazilian coast where some populations can have ~32%-42% of hybrids. Although frequently observed today, it is not clear what role hybridization plays in the evolutionary diversification of this group of reptiles. In this study, we generated whole genome resequencing data of the five globally distributed sea turtle species to estimate a calibrated phylogeny and the population size dynamics, and to understand the role of hybridization in shaping the genomes of these ancient species. Our results reveal discordant species divergence dates between mitochondrial and nuclear genomes, with a high frequency of conflicting trees throughout the nuclear genome suggesting that some sea turtle species frequently hybridized in the past. The reconstruction of the species' demography showed a general decline in effective population sizes with no signs of recovery, except for the leatherback sea turtle. Furthermore, we discuss the influence of reference bias in our estimates. We show long-lasting ancestral gene flow events within Chelonioidea that continued for millions of years after initial divergence. Speciation with gene flow is a common pattern in marine species, and it raises questions whether current hybridization events should be considered as a part of these species' evolutionary history or a conservation issue.

Hydrogen isotope assimilation and discrimination in green turtles.

Although hydrogen isotopes (δ2H) are commonly used as tracers of animal movement, minimal research has investigated the use of δ2H as a proxy to quantify resource and habitat use. While carbon and nitrogen are ultimately derived from a single source (food), the proportion of hydrogen in consumer tissues originates from two distinct sources: body water and food. Before hydrogen isotopes can be effectively used as a resource and habitat tracer, we need estimates of (net) discrimination factors (Δ2HNet) that account for the physiologically mediated differences in the δ2H values of animal tissues relative to that of the food and water sources they use to synthesize tissues. Here, we estimated Δ2HNet in captive green turtles (Chelonia mydas) by measuring the δ2H values of tissues (epidermis and blood components) and dietary macromolecules collected in two controlled feeding experiments. Tissue δ2H and Δ2HNet values varied systematically among tissues, with epidermis having higher δ2H and Δ2HNet values than blood components, which mirrors patterns between keratinaceous tissues (feathers, hair) and blood in birds and mammals. Serum/plasma of adult female green turtles had significantly lower δ2H values compared with juveniles, likely due to increased lipid mobilization associated with reproduction. This is the first study to quantify Δ2HNet values in a marine ectotherm, and we anticipate that our results will further refine the use of δ2H analysis to better understand animal resource and habitat use in marine ecosystems, especially coastal areas fueled by a combination of marine (e.g. micro/macroalgae and seagrass) and terrestrial (e.g. mangroves) primary production.

Ecological regime shift drives declining growth rates of sea turtles throughout the West Atlantic.

Somatic growth is an integrated, individual-based response to environmental conditions, especially in ectotherms. Growth dynamics of large, mobile animals are particularly useful as bio-indicators of environmental change at regional scales. We assembled growth rate data from throughout the West Atlantic for green turtles, Chelonia mydas, which are long-lived, highly migratory, primarily herbivorous mega-consumers that may migrate over hundreds to thousands of kilometers. Our dataset, the largest ever compiled for sea turtles, has 9690 growth increments from 30 sites from Bermuda to Uruguay from 1973 to 2015. Using generalized additive mixed models, we evaluated covariates that could affect growth rates; body size, diet, and year have significant effects on growth. Growth increases in early years until 1999, then declines by 26% to 2015. The temporal (year) effect is of particular interest because two carnivorous species of sea turtles-hawksbills, Eretmochelys imbricata, and loggerheads, Caretta caretta-exhibited similar significant declines in growth rates starting in 1997 in the West Atlantic, based on previous studies. These synchronous declines in productivity among three sea turtle species across a trophic spectrum provide strong evidence that an ecological regime shift (ERS) in the Atlantic is driving growth dynamics. The ERS resulted from a synergy of the 1997/1998 El Niño Southern Oscillation (ENSO)-the strongest on record-combined with an unprecedented warming rate over the last two to three decades. Further support is provided by the strong correlations between annualized mean growth rates of green turtles and both sea surface temperatures (SST) in the West Atlantic for years of declining growth rates (r = -.94) and the Multivariate ENSO Index (MEI) for all years (r = .74). Granger-causality analysis also supports the latter finding. We discuss multiple stressors that could reinforce and prolong the effect of the ERS. This study demonstrates the importance of region-wide collaborations.

Biomarkers reveal sea turtles remained in oiled areas following the Deepwater Horizon oil spill.

Assessments of large-scale disasters, such as the Deepwater Horizon oil spill, are problematic because while measurements of post-disturbance conditions are common, measurements of pre-disturbance baselines are only rarely available. Without adequate observations of pre-disaster organismal and environmental conditions, it is impossible to assess the impact of such catastrophes on animal populations and ecological communities. Here, we use long-term biological tissue records to provide pre-disaster data for a vulnerable marine organism. Keratin samples from the carapace of loggerhead sea turtles record the foraging history for up to 18 years, allowing us to evaluate the effect of the oil spill on sea turtle foraging patterns. Samples were collected from 76 satellite-tracked adult loggerheads in 2011 and 2012, approximately one to two years after the spill. Of the 10 individuals that foraged in areas exposed to surface oil, none demonstrated significant changes in foraging patterns post spill. The observed long-term fidelity to foraging sites indicates that loggerheads in the northern Gulf of Mexico likely remained in established foraging sites, regardless of the introduction of oil and chemical dispersants. More research is needed to address potential long-term health consequences to turtles in this region. Mobile marine organisms present challenges for researchers to monitor effects of environmental disasters, both spatially and temporally. We demonstrate that biological tissues can reveal long-term histories of animal behavior and provide critical pre-disaster baselines following an anthropogenic disturbance or natural disaster.

Determining origin in a migratory marine vertebrate: a novel method to integrate stable isotopes and satellite tracking.

Stable isotope analysis is a useful tool to track animal movements in both terrestrial and marine environments. These intrinsic markers are assimilated through the diet and may exhibit spatial gradients as a result of biogeochemical processes at the base of the food web. In the marine environment, maps to predict the spatial distribution of stable isotopes are limited, and thus determining geographic origin has been reliant upon integrating satellite telemetry and stable isotope data. Migratory sea turtles regularly move between foraging and reproductive areas. Whereas most nesting populations can be easily accessed and regularly monitored, little is known about the demographic trends in foraging populations. The purpose of the present study was to examine migration patterns of loggerhead nesting aggregations in the Gulf of Mexico (GoM), where sea turtles have been historically understudied. Two methods of geographic assignment using stable isotope values in known-origin samples from satellite telemetry were compared: (1) a nominal approach through discriminant analysis and (2) a novel continuous-surface approach using bivariate carbon and nitrogen isoscapes (isotopic landscapes) developed for this study. Tissue samples for stable isotope analysis were obtained from 60 satellite-tracked individuals at five nesting beaches within the GoM. Both methodological approaches for assignment resulted in high accuracy of foraging area determination, though each has advantages and disadvantages. The nominal approach is more appropriate when defined boundaries are necessary, but up to 42% of the individuals could not be considered in this approach. All individuals can be included in the continuous-surface approach, and individual results can be aggregated to identify geographic hotspots of foraging area use, though the accuracy rate was lower than nominal assignment. The methodological validation provides a foundation for future sea turtle studies in the region to inexpensively determine geographic origin for large numbers of untracked individuals. Regular monitoring of sea turtle nesting aggregations with stable isotope sampling can be used to fill critical data gaps regarding habitat use and migration patterns. Probabilistic assignment to origin with isoscapes has not been previously used in the marine environment, but the methods presented here could also be applied to other migratory marine species.

Stable isotopic comparison between loggerhead sea turtle tissues.

RATIONALE: Stable isotope analysis has been used extensively to provide ecological information about diet and foraging location of many species. The difference in isotopic composition between animal tissue and its diet, or the diet-tissue discrimination factor, varies with tissue type. Therefore, direct comparisons between isotopic values of tissues are inaccurate without an appropriate conversion factor. We focus on the loggerhead sea turtle (Caretta caretta), for which a variety of tissues have been used to examine diet, habitat use, and migratory origin through stable isotope analysis. We calculated tissue-to-tissue conversions between two commonly sampled tissues. METHODS: Epidermis and scute (the keratin covering on the carapace) were sampled from 33 adult loggerheads nesting at two beaches in Florida (Casey Key and Canaveral National Seashore). Carbon and nitrogen stable isotope ratios were measured in the epidermis and the youngest portion of the scute tissue, which reflect the isotopic composition of the diet and habitat over similar time periods of the order of several months. RESULTS: Significant linear relationships were observed between the δ(13)C and δ(15)N values of these two tissues, indicating they can be converted reliably. CONCLUSIONS: Whereas both epidermis and scute samples are commonly sampled from nesting sea turtles to study trophic ecology and habitat use, the data from these studies have not been comparable without reliable tissue-to-tissue conversions. The equations provided here allow isotopic datasets using the two tissues to be combined in previously published and subsequent studies of sea turtle foraging ecology and migratory movement. In addition, we recommend that future isotopic comparisons between tissues of any organism utilize linear regressions to calculate tissue-to-tissue conversions.

Temporal consistency and individual specialization in resource use by green turtles in successive life stages.

Not all individuals in a population use the same subset of dietary and habitat resources. Patterns of individual specialization have been documented in an increasing number of organisms, but often without an associated time scale over which niche specialization was observed. We examined the patterns in individual resource use through time and in relation to the population with metrics of temporal consistency and degree of individual specialization. We used stable isotope analysis of carbon and nitrogen in successive subsections of scute tissue from the carapace to compare foraging patterns in three successive life stages of the green turtle (Chelonia mydas). Temporal consistency was measured as the mean within-individual variation in stable isotope values through time, whereas the degree of individual specialization was a ratio of the individual variation to that of the population. The distinction between these two parameters is important, as the metric of temporal consistency quantifies the regularity of individual resource use, and the degree of individual specialization indicates what proportion of the population niche an average individual uses. The scute record retains a chronological history of resource use and was estimated to represent a minimum 0.8 years in juveniles to a maximum of 6.5 years in adults. Both temporal consistency and individual specialization varied significantly among life stages. Adults were highly consistent in resource use through time and formed a generalist population with individual specialists maintaining long-term patterns in resource use. Oceanic and neritic juvenile life stages exhibited less temporal consistency in resource use with less individual specialization than adults. These observations are important when considering the ecological roles filled by green turtles in each life stage; also, individual differences in resource use may result in differential fitness consequences.

Holopelagic Sargassum aggregations provide warmer microhabitats for associated fauna.

Drifting aggregations of Sargassum algae provide critical habitat for endemic, endangered, and commercially important species. They may also provide favorable microclimates for associated fauna. To quantify thermal characteristics of holopelagic Sargassum aggregations, we evaluated thermal profiles of 50 aggregations in situ in the Sargasso Sea. Sea surface temperature (SST) in the center of aggregations was significantly higher than in nearby open water, and SST differential was independent of aggregation volume, area, and thickness. SST differential between aggregation edge and open water was smaller than those between aggregation center and aggregation edge and between aggregation center and open water. Water temperature was significantly higher inside and below aggregations compared to open water but did not vary inside aggregations with depth. Holopelagic Sargassum aggregations provide warmer microhabitats for associated fauna, which may benefit marine ectotherms, though temperature differentials were narrow (up to 0.7 °C) over the range of aggregation sizes we encountered (area 0.01-15 m2). We propose a hypothetical curve describing variation in SST differential with Sargassum aggregation size as a prediction for future studies to evaluate across temporal and geographic ranges. Our study provides a foundation for investigating the importance of thermal microhabitats in holopelagic Sargassum ecosystems.

Effects of gear modifications in a North Atlantic pelagic longline fishery: A multiyear study.

The threat of population declines caused by pelagic longline fisheries in the Atlantic has increased the concern to find strategies that minimize the bycatch and mortality of non-target marine animals. Gear modification, such as the use of circle hooks instead of conventional J-hooks, has been identified as an effective bycatch reduction strategy in different pelagic longline fisheries around the world. This study aimed to verify the effectiveness of the use of circle hooks by quantifying catch rates, relative size selectivity, and anatomical hooking position for the most common target species (swordfish, Xiphias gladius, and blue shark, Prionace glauca), and some bycatch species (loggerhead sea turtles, Caretta caretta, and shortfin mako, Isurus oxyrinchus) caught by the Azorean longline fishing fleet. The trial was conducted for five consecutive years (2000-2004) using eight different types of hooks. In general, the blue shark catches using circle hooks were significantly higher compared to J (Mustad 9/0). The circle hooks also showed high probabilities of catching juvenile blue sharks. Conversely, the circle hooks were efficient in reducing the loggerhead sea turtle bycatch and were related to fewer catches of small sea turtle individuals. The use of circle hooks was also associated with reduced swordfish catches compared to J (Mustad 9/0), and the effect of hook types on length at capture was only significant for Circle (L. & P. 18/0-CLP18) and Ringed Tuna (RT). No significant differences were observed comparing hook type to either catch rates or size selectivity for shortfin mako. Additionally, circle hooks were more likely to lodge in the mouth than in deeper anatomical positions, when compared to J (Mustad 9/0), for the four species analysed. The present study demonstrated that the use of circle hooks could mitigate the impact of the pelagic longline fisheries in the Azores by decreasing the bycatch of sea turtles and reducing animal injuries caused by deep hooking.

Intake and growth histories modulate bone morphology, microarchitecture, and mineralization in juvenile green turtles (Chelonia mydas).

Compensatory growth (CG) is accelerated growth that occurs when food availability increases after food restriction. This rapid growth may be associated with sublethal consequences. In this study, we investigated the effects of food restriction and subsequent realimentation and CG on bone structure in juvenile green turtles (Chelonia mydas). Turtles were fed ad libitum food for 12 weeks (AL), restricted food for 12 weeks (R), or restricted food for 5 weeks followed by ad libitum food for 7 weeks (R-AL). R-AL turtles demonstrated partial CG via enhanced food conversion efficiency (FCE) upon realimentation. After the 12th week, gross morphology (GM), microarchitecture, and mineralization of the right humerus of each turtle were analyzed. Many GM measurements (including proximal and maximal bone lengths, bone widths, and shaft thickness), most measurements of bone microarchitecture (excluding cortical and trabecular thickness and trabecular separation), and all mineralization measurements were labile in response to intake. We examined the possibility that changes in nutrient allocation to bone structure during realimentation facilitated CG in previously food-restricted turtles. Restoration of bone lengths was prioritized over restoration of bone widths during CG. Furthermore, restoration of trabecular number, connectivity density, and bone volume fraction was prioritized over restoration of cortical bone volume fraction. Finally, diaphyseal bone mineralization was partially restored, whereas no restoration of epiphyseal bone mineralization occurred during CG. Shifts in nutrient allocation away from certain bone attributes during food restriction that were not rectified when food availability increased probably provided an energy surplus that enhanced the conversion of food to growth and thus powered the CG response. Our study revealed how resource allocation to various bone attributes is prioritized as nutritional conditions change during development. These "priority rules" may have detrimental consequences later in life, indicating that conservation of green turtle foraging grounds should be given high priority.

Mitogenomic sequences better resolve stock structure of southern Greater Caribbean green turtle rookeries.

Analyses of mitochondrial control region polymorphisms have supported the presence of several demographically independent green turtle (Chelonia mydas) rookeries in the Greater Caribbean region. However, extensive sharing of common haplotypes based on 490-bp control region sequences confounds assessment of the scale of natal homing and population structure among regional rookeries. We screened the majority of the mitochondrial genomes of 20 green turtles carrying the common haplotype CM-A5 and representing the rookeries of Buck Island, St. Croix, United States Virgin Islands (USVI); Aves Island, Venezuela; Galibi, Suriname; and Tortuguero, Costa Rica. Five single-nucleotide polymorphisms (SNPs) were identified that subdivided CM-A5 among regions. Mitogenomic pairwise φ(ST) values of eastern Caribbean rookery comparisons were markedly lower than the respective pairwise F(ST) values. This discrepancy results from the presence of haplotypes representing two divergent lineages in each rookery, highlighting the importance of choosing the appropriate test statistic for addressing the study question. Haplotype frequency differentiation supports demographic independence of Aves Island and Suriname, emphasizing the need to recognize the smaller Aves rookery as a distinct management unit. Aves Island and Buck Island rookeries shared mitogenomic haplotypes; however, frequency divergence suggests that the Buck Island rookery is sufficiently demographically isolated to warrant management unit status for the USVI rookeries. Given that haplotype sharing among rookeries is common in marine turtles with cosmopolitan distributions, mitogenomic sequencing may enhance inferences of population structure and phylogeography, as well as improve the resolution of mixed stock analyses aimed at estimating natal origins of foraging turtles.

Individual specialists in a generalist population: results from a long-term stable isotope series.

Individual variation in resource use has often been ignored in ecological studies, but closer examination of individual patterns through time may reveal significant intrapopulation differences. Adult loggerhead sea turtles (Caretta caretta) are generalist carnivores with a wide geographical range, resulting in a broad isotopic niche. We microsampled scute, a persistent and continuously growing tissue, to examine long-term variation in resource use (up to 12 years) in 15 nesting loggerhead turtles. Using stable isotopes of nitrogen and carbon, we examined the resource use patterns (integration of diet, habitat and geographical location) and demonstrate that individual loggerheads are long-term specialists within a generalist population. We present our results in the context of a conceptual model comparing isotopic niches in specialist and generalist populations. Individual consistency may have important ecological, evolutionary and conservation consequences, such as the reduction of intraspecific competition.

Effect of repeated tissue sampling on growth rates of juvenile loggerhead turtles Caretta caretta.

We evaluated the effect of repeated tissue sampling on growth rates of juvenile loggerhead sea turtles Caretta caretta. Samples of blood, skin, and scute (keratinized epidermal layer covering the bony shell) were collected at 3 intervals over a 120 d period from 37 loggerheads; 8 control turtles were not sampled. No infections or scarring occurred at the sampling sites, and growth in mass of experimental and control turtles was not significantly different. The sampling regime did not affect the health or physiological status of the turtles.

Reference intervals and relationships between health status, carapace length, body mass, and water temperature and concentrations of plasma total protein and protein electrophoretogram fractions in Atlantic loggerhead sea turtles and green turtles.

OBJECTIVE: To determine reference intervals for concentrations of plasma total protein (TP) and electrophoretogram fractions (ELFs) for healthy, wild loggerhead sea turtles (Caretta caretta) and green turtles (Chelonia mydas) and to assess relationships between TP and ELF concentrations and health status, body size, body mass, and water temperature. DESIGN: Evaluation study. ANIMALS: 437 healthy and 35 ill Atlantic loggerhead sea turtles and 152 healthy and 3 ill Atlantic green turtles. PROCEDURES: Free-ranging turtles were captured from a nuclear power plant intake canal in southern Florida. Plasma samples were obtained from all turtles. Plasma TP and ELF concentrations were measured, and reference intervals were calculated. Wilcoxon rank-sum tests were used to compare TP and ELF values between healthy and ill loggerhead sea turtles. Spearman rank correlations were evaluated between concentrations of TP and ELFs and carapace length, body mass, and water temperature. RESULTS: Reference intervals for TP concentrations were 2.2 to 5.2 g/dL and 2.0 to 5.4 g/dL for loggerhead sea turtles and green turtles, respectively. Except for gamma-globulin, concentrations of ELFs were significantly higher in healthy than in ill loggerhead sea turtles. There was a positive correlation between TP, alpha-globulin, beta-globulin, and gamma-globulin concentrations and water temperature in loggerhead sea turtles and between only TP and alpha-globulin concentrations and water temperature in green turtles. CONCLUSIONS AND CLINICAL RELEVANCE: Reference intervals for concentrations of TP and ELFs for healthy, free-ranging loggerhead sea turtles and green turtles can be used in combination with other diagnostic tools to assess health status of sea turtles.

Use of a portable point-of-care (Vetscan VS2) biochemical analyzer for measuring plasma biochemical levels in free-living loggerhead sea turtles (Caretta caretta).

The agreement of plasma biochemical values between a portable point-of-care analyzer and a veterinary diagnostic laboratory in wild caught loggerhead sea turtles (Caretta caretta) was tested. Banked plasma samples from presumptively healthy turtles collected for an on-going project that involves health assessments of sea turtles from the southeast coast of Florida were used for this study. Plasma biochemical analytes evaluated included albumin, aspartate aminotransferase, calcium, creatinine kinase, glucose, potassium, sodium, phosphorus, total protein, bile acids, and uric acid. Paired plasma samples were run in duplicates and compared between a point-of-care analyzer and a veterinary diagnostic laboratory (VDL). Overall, the precision was greater as measured within the point-of-care analyzer than within the VDL analyzer; however, agreement between the two testing methods was poor. Correlation (r(i)) between the two analyzers was high for many of the analytes; however, the small P-value and high relative error led to the conclusion that the two analyzers were not equivalent. In addition, a comparison was made between the biochemical values obtained at the time of collection and after storage in an ultralow freezer for up to 2.5 yr. Plasma samples analyzed at the VDL, performed on different models of the same machine, were significantly lower after storage than those acquired near the time of collection. This difference was most likely because of sample degradation that occurred during storage. Whereas, statistically significant differences were observed within and between the analyzers, many of these differences may not be clinically significant. Even though this study has a few limitations, including a technical malfunction and the use of two different diagnostic laboratories, biochemical values for the given population are reported when using both a portable system and a diagnostic laboratory. Based on the findings of this study, the authors believe that point-of-care analyzers can provide valuable adjunctive diagnostics, especially in field situations.

Recovery of a large herbivore changes regulation of seagrass productivity in a naturally grazed Caribbean ecosystem.

What happens in meadows after populations of natural grazers rebound following centuries of low abundance? Many seagrass ecosystems are now experiencing this phenomenon with the recovery of green turtles (Chelonia mydas), large-bodied marine herbivores that feed on seagrasses. These seagrass ecosystems provide a rare opportunity to study ecosystem-wide shifts that result from a recovery of herbivores. We evaluate changes in regulation of seagrass productivity in a naturally grazed tropical ecosystem by (1) comparing Thalassia testudinum productivity in grazed and ungrazed areas and (2) evaluating potential regulating mechanisms of T. testudinum productivity. We established 129 green turtle exclusion cages in grazed and ungrazed areas to quantify T. testudinum growth (linear, area, mass, productivity : biomass [P:B]). In each exclosure, we recorded temperature, irradiance, water depth, nitrogen : phosphorus ratio (N:P) of blade tissue, grazing intensity before cage placement, and T. testudinum structural and nutrient characteristics. Thalassia testudinum exhibited compensatory growth in grazed areas via stimulated blade linear growth, blade area growth, and P:B across seasonal high and low growth periods and in shallow (3-4 m) and deep (9-10 m) seagrass meadows. Irradiance, depth, and N:P ratios had significant roles in regulating mass growth and P:B of T. testudinum in ungrazed areas. Depth was a significant regulating factor of mass growth and P:B in grazed areas; rates were higher and more variable in shallow meadows than in deep meadows. Grazing intensity was also a significant regulating factor for P:B, stimulating tissue turnover with increasing grazing pressure. This study provides important insights into how recovery of a large marine herbivore can result in dramatic, sustainable changes in the regulation of seagrass productivity. We also highlight the need for a historical perspective and use of appropriate indicators, including P:B and grazing intensity, when evaluating seagrass response to green turtle grazing as meadows are returned to a natural grazed state. In an age of green turtle recovery and global seagrass decline due to anthropogenic threats, a thorough understanding of green turtle-seagrass interactions at the ecosystem level is critical to ensure the restoration of seagrass ecosystems and continued recovery of green turtle populations.

Identifying patterns in foraging-area origins in breeding aggregations of migratory species: Loggerhead turtles in the Northwest Atlantic.

Population assessments conducted at reproductive sites of migratory species necessitate understanding the foraging-area origins of breeding individuals. Without this information, efforts to contextualize changes in breeding populations and develop effective management strategies are compromised. We used stable isotope analysis of tissue samples collected from loggerhead sea turtles (Caretta caretta) nesting at seven sites in the Northern Recovery Unit (NRU) of the eastern United States (North Carolina, South Carolina and Georgia) to assign females to three separate foraging areas in the Northwest Atlantic Ocean (NWA). We found that the majority of the females at NRU nesting sites (84.4%) use more northern foraging areas in the Mid-Atlantic Bight, while fewer females use more proximate foraging areas in the South Atlantic Bight (13.4%) and more southerly foraging areas in the Subtropical Northwest Atlantic (2.2%). We did not find significant latitudinal or temporal trends in the proportions of NRU females originating from different foraging areas. Combining these findings with previous data from stable isotope and satellite tracking studies across NWA nesting sites showed that variation in the proportion of adult loggerheads originating from different foraging areas is primarily related differences between recovery units: individuals in the NRU primarily use the Mid-Atlantic Bight foraging area, while individuals from the three Florida recovery units primarily use the Subtropical Northwest Atlantic and Eastern Gulf of Mexico foraging areas. Because each foraging area is associated with its own distinct ecological characteristics, environmental fluctuations and anthropogenic threats that affect the abundance and productivity of individuals at nesting sites, this information is critical for accurately evaluating population trends and developing effective region-specific management strategies.

Compensatory responses to food restriction in juvenile green turtles (Chelonia mydas).

The purpose of this study was to assess the compensatory responses to food restriction and subsequent increased food availability in juvenile green turtles (Chelonia mydas). Turtles were fed an ad libitum ration for 12 weeks (AL), a restricted ration for 12 weeks (R), or a restricted ration for 5 weeks and an ad libitum ration for 7 weeks (R-AL). Analysis of covariance was used to test the relationships between (1) growth and body size, (2) intake and body size, and (3) growth and intake for each of the three treatment groups. Body composition of turtles in each group was also evaluated at the beginning of the study and after weeks 5 and 12. After the switch to ad libitum feeding, R-AL turtles consumed comparable amounts of food and grew faster than AL turtles on a size-adjusted basis, but mean body sizes did not converge, although the overlap in their size ranges increased with time. The R-AL turtles also converted food to growth more efficiently and allocated proportionally more nutrients to protein accretion, thereby restoring body composition (except mineral content) to AL levels by the end of the study. Thus, accelerated size-specific growth without hyperphagia restored body condition but not size. These results indicate that (1) intake in juvenile green turtles is maximal when food is readily available and cannot be increased to compensate for a previous period of food limitation, (2) growth rates of ad libitum-fed turtles are only mildly plastic in response to past nutritional history, and (3) priority rules for nutrient allocation favor the attainment of an optimal condition rather than an optimal size. Nutritional setbacks experienced during the vulnerable juvenile stage could therefore have long-lasting consequences for wild turtles in terms of size-specific mortality risk, but these risks may be mitigated by the potential benefits of maintaining sufficient body stores.

Biochemical indices as correlates of recent growth in juvenile green turtles (Chelonia mydas).

Nucleic acid and protein concentrations and their ratios are increasingly used as correlates of nutritional condition and growth in marine species. However, their application in studies of reptile growth has not yet been validated. The green turtle (Chelonia mydas) is an endangered marine reptile for which assessing population health requires knowledge of demographic parameters such as individual growth rates. The purpose of this study was to evaluate a number of biochemical indices ([DNA], [RNA], RNA:DNA ratio, [protein], protein:DNA ratio, and RNA:protein ratio) in liver, heart, and blood as potential predictors of recent growth rate in juvenile green turtles under controlled feeding conditions. Intake of juvenile green turtles was manipulated over twelve weeks to obtain a range of growth rates. With the exception of [RNA](blood), [DNA](heart), and [protein]:[DNA](liver), all biochemical indices demonstrated significant linear relationships with growth rate during the last 1.5 weeks of the study. The best single predictors of recent growth were hepatic [RNA] and [RNA]:[protein], which explained 66% and 49%, respectively, of the variance in growth. Contrary to expectations, these two indices were negatively correlated with growth rate. To investigate the possibility that hepatic [RNA] was higher in slow-growing turtles because of elevated expression of antioxidant genes, we quantified glutathione peroxidase activity and total antioxidant potential. Both measures of antioxidant function were affected by intake and growth histories, but these effects did not explain our results for hepatic RNA and protein concentrations. We developed a model that predicted 68% of the variance in specific growth rate (SGR) with the equation SGR = -0.913(ln[RNA](liver)) + 17.689(Condition Index) + 4.316. In addition, our findings that [DNA] and [RNA]:[DNA] for blood were significantly correlated with SGR demonstrate the potential utility of minimally invasive tissue sampling that could facilitate instantaneous population monitoring.

Relative abundance of oceanic juvenile loggerhead sea turtles in relation to nest production at source rookeries: implications for recruitment dynamics.

After hatching, juveniles of most sea turtle species undertake long migrations across ocean basins and remain in oceanic habitats for several years. Assessing population abundance and demographic parameters during this oceanic stage is challenging. Two long-recognized deficiencies in population assessment are (i) reliance on trends in numbers of nests or reproductive females at nesting beaches and (ii) ignorance of factors regulating recruitment to the early oceanic stage. To address these critical gaps, we examined 15 years of standardized loggerhead sighting data collected opportunistically by fisheries observers in the Azores archipelago. From 2001 to 2015, 429 loggerheads were sighted during 67,922 km of survey effort. We used a model-based approach to evaluate the influence of environmental factors and present the first estimates of relative abundance of oceanic-stage juvenile sea turtles. During this period, relative abundance of loggerheads in the Azores tracked annual nest abundance at source rookeries in Florida when adjusted for a 3-year lag. This concurrence of abundance patterns indicates that recruitment to the oceanic stage is more dependent on nest abundance at source rookeries than on stochastic processes derived from short term climatic variability, as previously believed.