BackgroundResolving threats to widely distributed marine megafauna requires definition of the geographic distributions of both the threats as well as the population unit(s) of interest. In turn, because individual threats can operate on varying spatial scales, their impacts can affect different segments of a population of the same species. Therefore, integration of multiple tools and techniques — including site-based monitoring, genetic analyses, mark-recapture studies and telemetry — can facilitate robust definitions of population segments at multiple biological and spatial scales to address different management and research challenges.Methodology/Principal FindingsTo address these issues for marine turtles, we collated all available studies on marine turtle biogeography, including nesting sites, population abundances and trends, population genetics, and satellite telemetry. We georeferenced this information to generate separate layers for nesting sites, genetic stocks, and core distributions of population segments of all marine turtle species. We then spatially integrated this information from fine- to coarse-spatial scales to develop nested envelope models, or Regional Management Units (RMUs), for marine turtles globally.Conclusions/SignificanceThe RMU framework is a solution to the challenge of how to organize marine turtles into units of protection above the level of nesting populations, but below the level of species, within regional entities that might be on independent evolutionary trajectories. Among many potential applications, RMUs provide a framework for identifying data gaps, assessing high diversity areas for multiple species and genetic stocks, and evaluating conservation status of marine turtles. Furthermore, RMUs allow for identification of geographic barriers to gene flow, and can provide valuable guidance to marine spatial planning initiatives that integrate spatial distributions of protected species and human activities. In addition, the RMU framework — including maps and supporting metadata — will be an iterative, user-driven tool made publicly available in an online application for comments, improvements, download and analysis.

Where conservation resources are limited and conservation targets are diverse, robust yet flexible priority-setting frameworks are vital. Priority-setting is especially important for geographically widespread species with distinct populations subject to multiple threats that operate on different spatial and temporal scales. Marine turtles are widely distributed and exhibit intra-specific variations in population sizes and trends, as well as reproduction and morphology. However, current global extinction risk assessment frameworks do not assess conservation status of spatially and biologically distinct marine turtle Regional Management Units (RMUs), and thus do not capture variations in population trends, impacts of threats, or necessary conservation actions across individual populations. To address this issue, we developed a new assessment framework that allowed us to evaluate, compare and organize marine turtle RMUs according to status and threats criteria. Because conservation priorities can vary widely (i.e. from avoiding imminent extinction to maintaining long-term monitoring efforts) we developed a “conservation priorities portfolio” system using categories of paired risk and threats scores for all RMUs (n = 58). We performed these assessments and rankings globally, by species, by ocean basin, and by recognized geopolitical bodies to identify patterns in risk, threats, and data gaps at different scales. This process resulted in characterization of risk and threats to all marine turtle RMUs, including identification of the world's 11 most endangered marine turtle RMUs based on highest risk and threats scores. This system also highlighted important gaps in available information that is crucial for accurate conservation assessments. Overall, this priority-setting framework can provide guidance for research and conservation priorities at multiple relevant scales, and should serve as a model for conservation status assessments and priority-setting for widespread, long-lived taxa.

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A method of estimating natural sex ratios of hatchlings of species with temperature-dependent sexual differentiation from data on incubation durations is described. The method was applied to loggerhead turtles (Caretta caretta) nesting in Brazil. Data on incubation durations were collected from 11 nesting beaches monitored for up to six seasons. It was estimated that 82.5% of the loggerhead hatchlings produced were female. The strongly female-biased sex ratio in Brazil is similar to that found. previously for loggerheads using beaches in the eastern U.S.A. This suggests that a female-biased hatchling sex ratio may be a feature of loggerhead populations.RCsumC : On trouvera ici la description d'une mCthode d'estimation des rapports m2les : femelles i partir de donnCes sur la durCe de l'incubation chez des tortues nConates appartenant i des espkces i differentiation sexuelle dCterminCe par la tempkrature. La methode a Ct C utilisCe chez des Caouanes (Caretta caretta) du BrCsil. La durCe de l'incubation a Ct C mesurCe dans les nids de tortues sur 11 plages de reproduction ob les donnCes ont Ct C relevCes pendant plusieurs saisons, parfois jusqu'i six. Nos estimations ont rCvClC que 82,5% des tortues i 1'Cclosion Ctaient des femelles. Ce rapport m2les : femelles trks faible mesurC au BrCsil est semblable i celui qui a Ct6 enregistre sur des plages de reproduction de cette tortue dans 1'Est des ~t a t s -~n i s .Ce nombre dCmesurC de femelles chez les tortues fraichement Ccloses est donc probablement une caractkristique des populations de caouanes. [Traduit par la RCdaction]

We studied inter-and postnesting movements in the major loggerhead Caretta caretta nesting population in Brazil. Ten breeding females were satellite-tracked from nesting grounds in the state of Bahia, northeastern Brazil, for up to 1284 d. Eight females stayed in the nesting area after deployment, showing fidelity between internesting home ranges and nesting locations, even at a local scale. During postnesting movements, all of the turtles migrated to the northern coast of Brazil to individual foraging areas on the continental shelf. Distances between nesting and foraging areas reached up to 2400 km, and migration lasted from 28 to 47 d. Five females were tracked during subsequent breeding migrations to the nesting area at different remigration intervals of 2 or 3 yr. Females were also tracked during a second postnesting migration back to foraging areas, and these showed strong fidelity to foraging grounds. Movements to and from foraging grounds occurred along the shelf, clearly delineating a migratory corridor. The northern coast of Brazil, specifically the coast of the state of Ceará, is an important foraging ground for loggerheads nesting along the northern coast of Bahia.

The loggerhead turtle Caretta caretta is one of the large and long-lived species that comprise the charismatic marine megafauna. The loggerhead is considered endangered, especially in the Pacific Ocean, where there have been substantial declines in all the major nesting populations. On the other hand, some loggerhead nesting populations in the northwest Atlantic are apparently increasing, but the conservation status of loggerheads in the Atlantic-Mediterranean is not well known. Here we report on a long-term and geographically extensive study of the nesting abundance of the Brazilian loggerhead genetic stock resident in south Atlantic waters. We show that there has been a substantial long-term increase in nesting abundance of this once depleted Atlantic stock following the cessation of egg and turtle harvesting in the 1980s. We estimated that the 2003/2004 austral summer nesting season in Brazil encompassed more than 4800 loggerhead nests or >1200 nesters or > 0.57 million eggs. National conservation efforts have contributed significantly to the improving status of the Brazilian loggerhead stock since the mid-1980s, but there are emerging threats such as incidental capture in coastal and pelagic fisheries that might limit any further recovery. Moreover, we found that the Brazilian nesting population is probably one of the largest remaining loggerhead nesting populations in the world. Hence, continued protection of the Brazilian loggerhead stock is of paramount importance for the global conservation of this species.

Testing theories of dispersal is challenging in highly migratory species. In sea turtles, population size, geographic distance, natal homing, and ocean currents are hypothesized to affect dispersal. Little is known, however, about these mechanisms in sea turtles foraging along the South American coast. Green sea turtles feeding at Ubatuba (UB, n = 114) and Almofala (AF, n = 117), Brazil, were sequenced at the mitochondrial DNA (mtDNA) control region (486 bp) and genotyped at 7 microsatellite loci to test dispersal hypotheses. Fifteen mtDNA haplotypes were revealed, including a previously undescribed sequence, and the average observed heterozygosity (H(o)) was 76.4%. Overall short-term temporal differences were not detected, and differentiation was less pronounced in microsatellite than in mtDNA analyses. Mitochondrial results reveal significant differentiation between the Brazilian feeding grounds and most other Atlantic groups, whereas microsatellites uncover similarities to some of the geographically closest populations. Ubatuba and Almofala are mixed stocks, drawn primarily from Ascension, with lesser contributions from Surinam/Aves and Trindade. Costa Rica is also a significant source of individuals feeding at AF. The results are consistent with a model of juvenile natal homing impacted by other factors. Effective protection of turtles foraging along the extensive Brazilian coast may enhance breeding populations thousands of kilometers away.

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.