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Determining the diet and trophic status of endangered species can provide insights into their key habitats and predator-prey relationships, both essential for conservation. Integrating dietary information from live-captured and dead-stranded turtles from the same area can also shed light on their ecological diversity. Here, diet intake and prey diversity are determined for juvenile green turtles Chelonia mydas from a mixed stock foraging aggregation in the Southwestern Atlantic Ocean (SWAO) using stable carbon (δ13C) and nitrogen (δ15N) isotope analysis. Skin samples were collected from 117 live-captured (LC) turtles and 66 dead-stranded (DS) individuals along the Paraná coast, southern Brazil. Bayesian isotope ellipse space was determined using the program SIBER. A larger isotopic niche space was found among DS turtles, probably because it included long-term resident turtles and recently settled individuals, the latter of which presented low δ15N values compared to larger putative local turtles. The Bayesian stable isotope mixing model MixSIAR was used to determine dietary contributions, using isotopic values of putative prey. MixSIAR results indicated invertebrates and macroalgae as primary prey groups, showing the omnivorous strategy of green turtles in the SWAO. Moreover, many of the smallest DS turtles had δ15N values suggestive of seagrass consumption, which may reflect individual- and/or life-stage-based diet variability. These findings underscore the value of integrating stranding monitoring protocols with research on live green turtles to evaluate habitat use and diet intake assembled in a neritic foraging area. The data also further knowledge about green turtle foraging ecology and are relevant for species and habitat conservation throughout the SWAO.

Green turtles Chelonia mydas are listed as Endangered on the IUCN Red List, yet in the South Pacific few conservation-relevant data are available for the species, especially relating to foraging and habitat use. Here, in situ observations and stable isotope analysis (δ13C and δ15N) were used to evaluate green turtle diet and recruitment patterns at Yadua Island and Makogai Island, Fiji. Juvenile green turtles (N = 110) were hand-captured, measured, and sampled. Stable isotope analysis was performed on skin samples and on putative prey items. ‘Resident’ turtles versus ‘recent recruits’ were classified based on their bulk skin tissue isotope values, which were compared with stable isotope values of local prey items and analyzed via cluster analysis. Green turtle diet composition was estimated using MixSIAR, a Bayesian mixing model. Recent recruits were characterized by ‘low δ13C/high δ15N’ values and ranged in curved carapace length (CCL) from 25.5 to 60.0 cm (mean ± SD = 48.5 ± 5.7 cm). Recruitment mostly occurred in summer. Green turtles identified as ‘residents’ had CCLs ranging from 43.5 to 89.0 cm (mean ± SD = 57.4 ± 9.0 cm) and were characterized by ‘high δ13C/low δ15N’ values; mixing model results indicate they fed primarily on invertebrates (40%), fishes (31%), and marine plants (29%). This study confirms the value of seagrass pastures as both an essential habitat and a primary food source for green turtles, and can serve as a baseline for evaluations of natural and anthropogenic changes in local green turtle aggregations.

Trophic position and niche width are fundamental components of a species’ ecology, reflecting resource use, and influencing key demographic parameters such as somatic growth, maturation, and survival. Concepts about a species’ trophic niche space have important implications for local management and habitat protection, and can shed light about resilience to changing climate for species occurring over broad spatial scales. For elusive marine animals such as sea turtles, trophic niche is challenging to study, and researchers often rely on other metrics, such as isotopic niche, as a proxy. Here, stable isotope analysis (δ13C and δ15N values) was conducted on bulk skin tissue of 718 green turtles (Chelonia mydas) distributed among 16 foraging areas in the eastern Pacific from the USA to Chile, a range spanning ~10,000 km. Compound‐specific nitrogen isotope analysis of amino acids (CSIA‐AA) was applied to 21 turtles among seven sites. Isotopic niche space was determined via Bayesian ellipse area (BEA) and convex hull area (CHA) analyses of bulk isotope values, which were also used along with amino acid δ15N values to determine trophic position (TP). Substantial variability in bulk tissue δ13C and δ15N values was found within and among sites, and amino acid δ15N values confirmed this was largely due to spatial differences in baseline nitrogen isotopic compositions, but also to a lesser extent from TP differences among the green turtle foraging populations. Isotope niche space varied among sites, influenced by the diversity of prey types and relative input of terrestrial‐ vs. marine‐derived nutrients; BEAs were the most suitable measurement of isotopic niche space due to the larger influence of outlying values with the CHA approach. Amino acid isotope‐derived TP estimates that accounted for local habitat conditions (e.g., mixed seagrass/macroalgae diet) performed the best among several approaches; TP ranged from 2.3 to 3.6, which indicates an omnivorous diet for most populations. In addition to providing additional spatial resolution for δ13C and δ15N isoscapes in the eastern Pacific, especially in coastal habitats, this study further establishes CSIA‐AA as an effective tool to study the trophic ecology of sea turtles across a variety of food webs and habitats.

East Pacific (EP) green turtles (Chelonia mydas) have undergone substantial population recovery over the last two decades owing to holistic protection at nesting beaches and foraging areas. At the northern end of their range in southern California United States, green turtles have been seen in more areas and in greater numbers since 2014 than before as a result. A resident population of green turtles has established near La Jolla Shores (LJS), a protected site with daily marine tourism (e.g., kayakers, snorkelers, divers). To study this local aggregation, innovative and non-invasive methods were required because the traditional capture-recapture methods were infeasible due to public relations sensitivities. Green turtle habituation to humans at this site has created a unique opportunity for citizen-based science using underwater photography to document turtles and their surroundings. We obtained 309 usable photographs of local green turtles from members of the dive/snorkel community in LJS. Photos were taken from April 2016 to June 2019. Images were processed in Hotspotter—a patterned species instance recognition software—to identify seven individuals, five of which were consistently photographed throughout that period. These images helped infer minimum residency duration (MRD), seasonal differences in algal coverage on the carapace, habitat association, behavioral patterns, and diet. Mean MRD was 424 days (SE = 131 days, calculated from entire population, n = 7), during which turtles were active in 82.8% of the photographs; the remainder of the photographs depicted foraging (14.9%) or resting behavior (2.3%). Green turtles were seen foraging in water temperatures as low as 15.8°C, the lowest recorded temperature for foraging green turtles documented in literature. Additional opportunistic observational platforms were used to look at trends of increasing green turtle abundance in southern California since 2015 that supported the arrival of a new aggregation of green turtles in LJS. Our use of citizen-sourced photographs confirms the presence of a resident aggregation of green turtles in LJS. Existence of green turtles and other protected species in highly populated areas provide excellent opportunities to educate beachgoers and seafarers about conservation of these species. This study also highlights the value of citizen-based science in areas where traditional research techniques are ill-suited.

Compound specific nitrogen isotope analysis of amino acids (AA CSIA) has been used to study the trophic ecology of many marine organisms because of its ability to characterize the δ15N value at the base of a food web while simultaneously providing trophic position information from a single tissue sample of a consumer. Although application of this method is becoming more widely used in trophic studies, critical assumptions such as amino acid designation and trophic discrimination factors remain unresolved for many taxa and tissue types. In this study, we used captive green turtles (Chelonia mydas) in a controlled feeding study to determine and evaluate individual amino acid isotope fractionation patterns and trophic discrimination factors (TDFs) for skin and plasma. Our data build on findings from previous studies that show that the traditional paradigm of using glutamic acid and phenylalanine as trophic and source amino acids, respectively, for trophic position estimation is consistent for green turtles; we also provide evidence to support the potential utility of other combinations of amino acids for trophic position calculations. Green turtle TDFs for glutamic acid and phenylalanine were 4.0 ± 0.5 ‰ and 6.6 ± 0.7 ‰ for skin and plasma, respectively. We found serine to have the largest Δδ15N (turtle-diet discrimination) value of all amino acids in both skin and plasma, while lysine Δδ15N values were consistent for use as a source amino acid in skin and plasma tissue. We evaluated our TDFs by estimating trophic position of four sea turtle species using previously published amino acid isotope data. These results indicate that for green turtles, the traditional use of glutamic acid and phenylalanine along with a combination of trophic amino acids paired with lysine can provide robust trophic position estimates. Moreover, we highlight the taxa and tissue-specific nature of amino acid nitrogen isotope fractionation patterns in green turtle tissues and underscore that well-approximated TDFs can refine trophic position estimates for sea turtles.

Aquatic pollution is known to reduce biodiversity and disrupt wildlife populations. Mercury (Hg) pollution is pervasive worldwide, contributing to the degradation of ecosystems, and causing deleterious effects to exposed organisms and populations. Batoids have a life history linked to the benthic substrate of coastal areas and occupy upper trophic levels. These combined with large bodies, long lifespan, and slow growth rates contributes to increased uptake and accumulation of Hg. However, mechanisms governing these associations are not well understood. Using multiple biogeochemical tracers (δ13C, δ15N and total Hg), we describe trophic interactions of three sympatric batoid species inhabiting an urbanized estuary and identify diet sources that contribute to Hg accumulation and trophic position among these mesopredators. We also use the Bat-ray (Myliobatis californica) as a model species, to compare diet composition, trophic position, and isotopic niche between two populations in two Californian bays. Trophic plasticity in M. californica was characterized by isotopic niche, diet proportions, and trophic position estimates using Bayesian statistics. We found diet and local contamination background strongly associated with Hg accumulation, and Hg levels that exceed EPA water quality criterion (

Stage durations are integral to wildlife population models that can inform manage- ment, as they influence age at maturation and stage-specific survival rates. To refine oceanic stage duration estimates for western North Atlantic loggerhead sea turtles Caretta caretta, skele- tochronological analysis was conducted on humeri collected in the Azores islands and along the US Atlantic coast. Complementary skeletal growth increment-specific stable isotope analysis was also performed for a sub-set of the humeri, to identify the skeletal growth mark associated with the shift from oceanic to neritic habitat through stable nitrogen isotope (δ 15 N) values and the presence of turtles in inshore waters. Although the transitional growth mark in this sub-sample corresponded to a range of sizes similar to those described in previous studies, mean size at recruitment (55.3 cm straightline carapace length (SCL)) for these turtles was larger than previously estimated. Similarly, while the range of ages at recruitment—corresponding both with the transitional growth mark and those yielded by fitting smoothing splines to SCL-at-age data—overlapped almost fully with earlier estimates, the mean age estimate (12.4 yr) differed from previous studies. Validated back-calculation of somatic growth rates from skeletal growth marks yielded means and ranges that encompassed those of previous loggerhead growth studies in this geographic area. General- ized additive models and generalized additive mixed models used to assess the potential influence of discrete and continuous covariates on back-calculated growth rates spanning 1984 to 2009 indi- cated significant effects of age, SCL, calendar year, and δ 15 N, but none for sex or location.

Collecting tissue samples from sea tur- tles for stable isotope analysis often occurs at remote field sites. For blood tissue, samples are treated with an anticoagulant that allows for later separation of plasma from cellular components. However, the effect of this technique on stable isotope values of sea turtle blood has not been established. We measured the effects of 3 widely used anticoagulants, acid citrate dextrose (ACD), sodium heparin (SH) and ethylenediaminetetraacetic acid (EDTA), on stable carbon (! 13 C) and stable nitrogen (! 15 N) values in whole blood, red blood cells, and blood plasma of 11 green turtles Chelonia mydas captured in San Diego Bay, California, USA. Vials containing each of the 3 blood preservatives as well as a vial containing no additive (i.e. control vial) were filled in random order. Blood in the no-additive vial was immediately sepa- rated into fractions (e.g. red blood cells, plasma) via centrifugation, whereas blood collected in the treat- ment vials was chilled and then centrifuged 48 h after collection. We found that, relative to the con- trols, ACD-preserved whole blood and blood plasma were 13 C enriched, EDTA-treated red blood cells and plasma were 15 N de pleted, and SH-treated whole blood was 15 N en riched. Because SH was the only anticoagulant with no measured effect on blood plasma and red blood cells — the most commonly studied blood fractions for sea turtle stable isotope studies — we recommend its exclusive use as a blood anticoagulant for field studies where prompt centri - fugation is not possible.

article i nfo The green turtle, Chelonia mydas, is a circumglobal species that is susceptible to overexploitation as a food resource,incidentalmortality in fisheries, andcoastalforaginghabitatdegradation,all of whichhavecontributed to its listing as Endangered on the IUCN Red List. Efforts to recover regional green turtle populations have been hampered bya lackof information ontheir biology. In particular,temporalpatternsof diet intake and habitat use inneriticforagingareasarenotwellunderstood.Historicalparadigmssuggestthatadultgreenturtlesareobligate herbivores with diets consisting of seagrasses and/or marine algae. However, these insights are largely based on conventional diet analysis techniques that only yield snapshots of recently consumed foods. Stable isotope analysis has been used to determine contributions of various potential food resources to a consumer's diet, and this approach is commonly applied to identify diet composition and long-term trophic relationships of a species. In this study, we measured the stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope values of 86 green turtles and