Variation in reproductive output of marine turtles

Most marine turtle species are non-annual breeders and show variation in both the number of eggs laid per clutch and the number of clutches laid in a season. Large levels of inter-annual variation in the number of nesting females have been well documented in green turtle nesting populations and may be linked to environmental conditions. Other species of marine turtle exhibit less variation in nesting numbers. This inter-specific difference is thought to be linked to trophic status. To examine whether individual reproductive output is more variable in the herbivorous green turtle (Chelonia mydas Linneaeus 1758) than the carnivorous loggerhead (Caretta caretta Linneaeus 1758), we examined the nesting of both species in Cyprus over nine seasons. Green turtles showed slower annual growth rates (0.11 cm year⁻¹ curved carapace length (CCL) and 0.27 cm year⁻¹ curved carapace width (CCW)) than loggerhead turtles (0.36 cm year⁻¹ CCL, 0.51 cm year⁻¹ CCW). CCL was highly correlated to mean clutch size in both green (R²=0.51) and loggerhead turtles (R²=0.61) and maximal clutch size of green turtles (R²=0.58). Larger females did not lay a greater number of clutches or have a shorter remigration interval than smaller females of either species. On average, the size of green turtle clutches increased and that of loggerhead turtles decreased as the season progressed. Individual green turtles, however, produced more eggs per clutch through the season to a maximum in the third or fourth clutch. In loggerhead turtles, clutches 1-4 were very similar in size but the fifth clutch was 38% smaller than the first. No individuals of either species were recorded laying more than five clutches. Green turtles may not be able to achieve their maximum reproductive output with respect to clutch size throughout the season, whereas only loggerhead turtles laying five clutches (n=5) appear to become resource depleted. Green turtles nesting in years when large numbers of nests were recorded laid a greater number of clutches than females nesting in years with lower levels of nesting.     

Monitoring and conservation of critically reduced marine turtle nesting populations: lessons from the Cayman Islands

Historically, nesting marine turtles were abundant in the Cayman Islands and were an integral part of the economy and culture. Today, nesting of loggerhead turtle Caretta caretta and green turtles Chelonia mydas takes place at very low levels. Hawksbill Eretmochelys imbricata nesting has not been recorded since 1999. We overview highly detailed monitoring data gathered over a 6-year period allowing insight into the magnitude and spatial and temporal patterns of marine turtle nesting, cost-effectiveness of monitoring such reduced populations, impacts of development on reproductive success and current threats to the recovery of the population. Nesting is diffuse and widely distributed for both nesting species on Grand and Little Cayman. Modelled nesting detection profiles for Grand Cayman show that in order to maintain data resolution, most sandy coastline must be surveyed throughout each season. However, in Little Cayman it may be possible to reduce effort. Legal take of adults and illegal take of eggs may be significantly impacting the remaining population. Surprisingly, we observed no significant correlation between density of coastal development and clutch density, adult emergence success or hatching success for either species. A significant relationship exists however, between density of coastal development and incidence of misorientation events in loggerhead hatchlings but not in green turtle hatchlings. Effective protection of known nesting habitat and the elimination of exploitation of remaining adults and eggs within the population are critical to its recovery.     

Molecular resolution of marine turtle stock composition in fishery bycatch: a case study in the Mediterranean

Based on an extensive sampling regime from both nesting populations and bycatch, frequency analyses of mitochondrial (mt) DNA control region haplotypes in the Mediterranean were used to assess the genetic structure and stock composition of the loggerhead sea turtle, Caretta caretta, in different marine fisheries. The analyses show the following. (i) In drifting longline fisheries working in Mediterranean pelagic habitats 53–55% of turtles caught originated from the Mediterranean stock; (ii) In bottom-trawl fisheries all turtle bycatch is derived from this regional stock; (iii) This regional stock contribution to fishery bycatch suggests that the population size of the Mediterranean loggerhead nesting population is significantly larger than previously thought. This is consistent with a recent holistic estimate based on the discovery of a large rookery in Libya. (iv) Present impact of fishery-related mortality on the Mediterranean nesting population is probably incompatible with its long-term conservation. Sea turtle conservation regulations are urgently needed for the Mediterranean fisheries. (v) The significant divergence of mtDNA haplotype frequencies of the Turkish loggerhead colonies define this nesting population as a particularly important management unit. Large immature and adult stages from this management unit seem to be harvested predominantly by Egyptian fisheries. (vi) Combined with other data, our findings suggest that all the nesting populations in the Mediterranean should be considered as management units sharing immature pelagic habitats throughout the Mediterranean (and possibly the eastern Atlantic), with distinct and more localized benthic feeding habitats in the eastern basin used by large immatures and adults. (vii) Between the strict oceanic pelagic and the benthic stages, immature turtles appear to live through an intermediate neritic stage, in which they switch between pelagic and benthic foods.     

Natural beaches confer fitness benefits to nesting marine turtles

Coastal ecosystems provide vital linkages between aquatic and terrestrial habitats and thus support extremely high levels of biodiversity. However, coastlines also contain the highest densities of human development anywhere on the planet and are favoured destinations for tourists, creating a situation where the potential for negative effects on coastal species is extremely high. I gathered data on marine turtle reproductive output from the literature to determine whether coastal development negatively influences offspring production. Female loggerhead (Caretta caretta) and green turtles (Chelonia mydas) nesting on natural beaches (as opposed to beaches with permanent development) produce significantly more hatchling turtles per nest; all else being equal, females that successfully produce more offspring will have higher fitness than conspecifics producing fewer offspring. Thus, female marine turtles nesting on natural beaches probably have higher fitness than turtles nesting on developed beaches. Consequently, populations nesting on natural beaches may be able to recover more quickly from the historic population declines that have plagued marine turtles, and some species may recover more quickly than others.     

Relationship between tropical cyclones and the distribution of sea turtle nesting grounds

Aim This study examines the relationship between the distribution of existing sea turtle nesting sites and historical patterns of tropical cyclone events to investigate whether cyclones influence the current distribution of sea turtle nesting sites. The results, together with information on predicted cyclone activity and other key environmental variables, will help in the identification and prediction of future nesting sites for sea turtles as changes to the coastal environment continue. Location Queensland, Australia. Methods We used data on the nesting distribution of seven populations of four species of sea turtles [green (Chelonia mydas), flatback (Natator depressus), hawksbill (Eretmochelys imbricata) and loggerhead (Caretta caretta)] from the eastern Queensland coast, and tropical cyclone track data from 1969 to 2007 to explore the relationship between (1) sea turtle nesting phenology and cyclone season, and (2) sea turtle nesting sites and cyclone distribution. Furthermore, using two green turtle populations as a case study, we investigated the relationship between cyclone disturbance and sea turtle reproductive output, nesting site and season. Bootstrapping was used to explore if current sea turtle nesting sites are located in areas with lower or higher cyclone frequency than areas where turtles are currently not nesting. Results All populations of sea turtles studied here were disturbed by cyclone activity during the study period. The exposure (frequency) of tropical cyclones that crossed each nesting site varied greatly among and within the various sea turtle populations. This was mainly a result of the spatial distribution of each population’s nesting sites. Bootstrapping indicated that nesting sites generally have experienced lower cyclone activity than other areas that are available for nesting. Main conclusions Tropical cyclones might have been sufficiently detrimental to sea turtle hatching success on the eastern Queensland coast that through a natural selection process turtles in this region are now nesting in areas with lower cyclone activity. Therefore, it is important that future studies that predict climate or range shifts for sea turtle nesting distributions consider future cyclone activity as one of the variables in their model.     

Regional management units for marine turtles: a novel framework for prioritizing conservation and research across multiple scales

Background

Resolving 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 Findings

To 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/Significance

The 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.     

Bioko: critically important nesting habitat for sea turtles of West Africa

We evaluate the conservation status and threats faced by sea turtle nesting populations at Bioko Island, Equatorial Guinea (Central Africa). Beaches were monitored to obtain a detailed sea turtle nest census and, where possible, tagging of adult females was undertaken. Four sea turtle species were found nesting in the area: the green turtle (Chelonia mydas), the leatherback (Dermochelys coriacea), the olive ridley (Lepidochelys olivacea) and the hawksbill (Eretmochelys imbricata); with the former two species nesting in regionally important numbers. Nesting activity was concentrated between November and February, with a peak in December–January. Tagging and recapture of green turtles in two consecutive seasons suggested an estimated 560 (interquartile range: 420–1,681) and 414 (interquartile range: 190–1,255) nesting females in the area, respectively. Estimated numbers of nesting leatherbacks ranged from 123 to 215 and 243 to 293 in the first and second season, respectively. The other two species were less abundant (olive ridley: 19–29 and 28–43; hawksbill: 4–10 and 2 turtles). Data were compared with more recent surveys in the area and contextualised with information on human related threats. Despite the size of nesting stocks, ongoing permitted and illegal take of adult turtles at the nesting site constitutes a serious threat for these breeding aggregations. Additionally, tag returns from throughout the Gulf of Guinea suggest that the level of take in regional fisheries may also be a major threat.     

Predicted distributions and abundances of the sea turtle ‘lost years’ in the western North Atlantic Ocean

Oceanic dispersal characterizes the early juvenile life-stages of numerous marine species of conservation concern. This early stage may be a ‘critical period’ for many species, playing an overriding role in population dynamics. Often, relatively little information is available on their distribution during this period, limiting the effectiveness of efforts to understand environmental and anthropogenic impacts on these species. Here we present a simple model to predict annual variation in the distribution and abundance of oceanic-stage juvenile sea turtles based on species’ reproductive output, movement and mortality. We simulated dispersal of 25 cohorts (1993–2017) of oceanic-stage juveniles by tracking the movements of virtual hatchling sea turtles released in a hindcast ocean circulation model. We then used estimates of annual hatchling production from Kemp's ridley Lepidochelys kempii (n = 3), green Chelonia mydas (n = 8) and loggerhead Caretta caretta (n = 5) nesting areas in the northwestern Atlantic (inclusive of the Gulf of Mexico, Caribbean Sea and eastern seaboard of the U.S.) and their stage-specific mortality rates to weight dispersal predictions. The model's predictions indicate spatial heterogeneity in turtle distribution across their marine range, identify locations of increasing turtle abundance (notably along the U.S. coast), and provide valuable context for temporal variation in the stranding of young sea turtles across the Gulf of Mexico. Further effort to collect demographic, distribution and behavioral data that refine, complement and extend the utility of this modeling approach for sea turtles and other dispersive marine taxa is warranted. Finally, generating these spatially-explicit predictions of turtle abundance required extensive international collaboration among scientists; our findings indicate that continued conservation of these sea turtle populations and the management of the numerous anthropogenic activities that operate in the northwestern Atlantic Ocean will require similar international coordination.     

Trophic status drives interannual variability in nesting numbers of marine turtles.

Large annual fluctuations are seen in breeding numbers in many populations of non-annual breeders. We examined the interannual variation in nesting numbers of populations of green (Chelonia mydas) (n = 16 populations), loggerhead (Caretta caretta) (n = 10 populations), leatherback (Dermochelys coriacea) (n = 9 populations) and hawksbill turtles (Eretmochelys imbricata) (n = 10 populations). Interannual variation was greatest in the green turtle. When comparing green and loggerhead turtles nesting in Cyprus we found that green turtles were more likely to change the interval between laying seasons and showed greater variation in the number of clutches laid in a season. We suggest that these differences are driven by the varying trophic statuses of the different species. Green turtles are herbivorous, feeding on sea grasses and macro-algae, and this primary production will be more tightly coupled with prevailing environmental conditions than the carnivorous diet of the loggerhead turtle.     

GLOBAL PHYLOGEOGRAPHY OF THE LOGGERHEAD TURTLE (CARETTA CARETTA) AS INDICATED BY MITOCHONDRIAL DNA HAPLOTYPES

Restriction-site analyses of mitochondrial DNA (mtDNA) from the loggerhead sea turtle (Caretta caretta) reveal substantial phylogeographic structure among major nesting populations in the Atlantic, Indian, and Pacific oceans and the Mediterranean sea. Based on 176 samples from eight nesting populations, most breeding colonies were distinguished from other assayed nesting locations by diagnostic and often fixed restriction-site differences, indicating a strong propensity for natal homing by nesting females. Phylogenetic analyses revealed two distinctive matrilines in the loggerhead turtle that differ by a mean estimated sequence divergence p = 0.009, a value similar in magnitude to the deepest intraspecific mtDNA node (p = 0.007) reported in a global survey of the green sea turtle Chelonia mydas. In contrast to the green turtle, where a fundamental phylogenetic split distinguished turtles in the Atlantic Ocean and the Mediterranean Sea from those in the Indian and Pacific oceans, genotypes representing the two primary loggerhead mtDNA lineages were observed in both Atlantic–Mediterranean and Indian-Pacific samples. We attribute this aspect of phylogeographic structure in Caretta caretta to recent interoceanic gene flow, probably mediated by the ability of this temperate-adapted species to utilize habitats around southern Africa. These results demonstrate how differences in the ecology and geographic ranges of marine turtle species can influence their comparative global population structures.     

Impacts of a geotextile container dune core on marine turtle nesting in Juno Beach,Florida, United States

Hard armoring technologies (e.g. rock revetments and seawalls), which are installed to protect homes from beach erosion, can diminish the aesthetics and amenity of the beach. Over time, these structures cause beach narrowing and often prevent marine turtle access to nesting habitat altogether. An alternative armoring technology, known as geotextile dune core systems (or geocores), has been developed and implemented to protect inland infrastructure from beach erosion, yet there remains an absence of research on possible effects on marine turtles. In this study, we examined the impacts of a geocore installed on Juno Beach, Florida, United States in February 2014 on loggerhead (Caretta caretta) and green turtle (Chelonia mydas) nesting success, hatching success, and emergence success. A before‐after‐control‐impact paired series design evaluated the difference in nesting success per week for the impact and control sites 4 years before (2010–2013) and 4 years after (2014–2017) the installation of the geocore. Neither loggerhead nor green turtle nesting success was significantly different after the installation of the geocore; however, when analyzing loggerhead crawls that came to within 5 m of the geotextile bags, nesting success decreased. Neither hatching nor emergence success was significantly different after the installation of the geocore for either species. Our results suggest that geocores may minimally affect loggerhead and green turtles and provide a suitable restoration technique for homeowners facing beach erosion.     

Contextualising the Last Survivors: Population Structure of Marine Turtles in the Dominican Republic

Nesting by three species of marine turtles persists in the Dominican Republic, despite historic threats and long-term population decline. We conducted a genetic survey of marine turtles in the Dominican Republic in order to link them with other rookeries around the Caribbean. We sequenced a 740_bp fragment of the control region of the mitochondrial DNA of 92 samples from three marine turtle species [hawksbill (n = 48), green (n = 2) and leatherback (n = 42)], and incorporated published data from other nesting populations and foraging grounds. The leatherback turtle (Dermochelys coriacea) in the Dominican Republic appeared to be isolated from Awala-Yalimapo, Cayenne, Trinidad and St. Croix but connected with other Caribbean populations. Two distinct nesting populations of hawksbill turtles (Eremochelys imbricata) were detected in the Dominican Republic and exhibited interesting patterns of connectivity with other nesting sites and juvenile and adult male foraging aggregations. The green sea turtle (Chelonia mydas) has almost been extirpated from the Dominican Republic and limited inference could be made from our samples. Finally, results were compared with Lagrangian drifting buoys and published Lagrangian virtual particles that travelled through the Dominican Republic and Caribbean waters. Conservation implications of sink-source effects or genetic isolation derived from these complex inter-connections are discussed for each species and population.     

Stormy oceans are associated with declines in sea turtle hatching

Many sea turtle populations are below 10% of their pre-Columbian numbers [1-4]. Though historic and systematic over-exploitation is the principal cause of these declines, sea turtles face similar threats today. Adults and juveniles are actively hunted and commercial fisheries catch them incidentally. Nesting suffers from beach development, egg poaching and the poaching of nesting females. Accompanying these familiar hazards is the largely unknown consequences of recent climate change. Here we report monitoring surveys from the Dry Tortugas National Park (DTNP, 24.64N 82.86W), Florida, and show that hurricanes and other storm events are an additional and increasing threat to loggerhead turtle (Caretta caretta) and green sea turtle (Chelonia mydas) nesting. Both species are listed by the US Endangered Species Act and the IUCN considers them 'endangered'.     

Global conservation priorities for marine turtles

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.     

Sea turtle species vary in their susceptibility to tropical cyclones

Severe climatic events affect all species, but there is little quantitative knowledge of how sympatric species react to such situations. We compared the reproductive seasonality of sea turtles that nest sympatrically with their vulnerability to tropical cyclones (in this study, “tropical cyclone” refers to tropical storms and hurricanes), which are increasing in severity due to changes in global climate. Storm surges significantly decreased reproductive output by lowering the number of nests that hatched and the number of hatchlings that emerged from nests, but the severity of this effect varied by species. Leatherback turtles (Dermochelys coriacea) began nesting earliest and most offspring hatched before the tropical cyclone season arrived, resulting in little negative effect. Loggerhead turtles (Caretta caretta) nested intermediately, and only nests laid late in the season were inundated with seawater during storm surges. Green turtles (Chelonia mydas) nested last, and their entire nesting season occurred during the tropical cyclone season; this resulted in a majority (79%) of green turtle nests incubating in September, when tropical cyclones are most likely to occur. Since this timing overlaps considerably with the tropical cyclone season, the developing eggs and nests are extremely vulnerable to storm surges. Increases in the severity of tropical cyclones may cause green turtle nesting success to worsen in the future. However, published literature suggests that loggerhead turtles are nesting earlier in the season and shortening their nesting seasons in response to increasing sea surface temperatures caused by global climate change. This may cause loggerhead reproductive success to improve in the future because more nests will hatch before the onset of tropical cyclones. Our data clearly indicate that sympatric species using the same resources are affected differently by tropical cyclones due to slight variations in the seasonal timing of nesting, a key life history process.     

Biochemical Indices and Life Traits of Loggerhead Turtles (Caretta caretta) from Cape Verde Islands

The loggerhead turtle (Caretta caretta) is an endangered marine reptile for whom assessing population health requires knowledge of demographic parameters such as individual growth rate. In Cape Verde, as within several populations, adult female loggerhead sea turtles show a size-related behavioral and trophic dichotomy. While smaller females are associated with oceanic habitats, larger females tend to feed in neritic habitats, which is reflected in their physiological condition and in their offspring. The ratio of RNA/DNA provides a measure of cellular protein synthesis capacity, which varies depending on changes in environmental conditions such as temperature and food availability. The purpose of this study was to evaluate the combined use of morphometric data and biochemical indices as predictors of the physiological condition of the females of distinct sizes and hatchlings during their nesting season and how temperature may influence the physiological condition on the offspring. Here we employed biochemical indices based on nucleic acid derived indices (standardized RNA/DNA ratio-sRD, RNA concentration and DNA concentration) in skin tissue as a potential predictor of recent growth rate in nesting females and hatchling loggerhead turtles. Our major findings were that the physiological condition of all nesting females (sRD) decreased during the nesting season, but that females associated with neritic habitats had a higher physiological condition than females associated with oceanic habitats. In addition, the amount of time required for a hatchling to right itself was negatively correlated with its physiological condition (sRD) and shaded nests produced hatchlings with lower sRD. Overall, our results showed that nucleic acid concentrations and ratios of RNA to DNA are an important tool as potential biomarkers of recent growth in marine turtles. Hence, as biochemical indices of instantaneous growth are likely temperature-, size- and age-dependent, the utility and validation of these indices on marine turtles stocks deserves further study.     

Population genetics and phylogeography of sea turtles

The seven species of sea turtles occupy a diversity of niches, and have a history tracing back over 100 million years, yet all share basic life-history features, including exceptional navigation skills and periodic migrations from feeding to breeding habitats. Here, we review the biogeographic, behavioural, and ecological factors that shape the distribution of genetic diversity in sea turtles. Natal homing, wherein turtles return to their region of origin for mating and nesting, has been demonstrated with mtDNA sequences. These maternally inherited markers show strong population structure among nesting colonies while nuclear loci reveal a contrasting pattern of male-mediated gene flow, a phenomenon termed 'complex population structure'. Mixed-stock analyses indicate that multiple nesting colonies can contribute to feeding aggregates, such that exploitation of turtles in these habitats can reduce breeding populations across the region. The mtDNA data also demonstrate migrations across entire ocean basins, some of the longest movements of marine vertebrates. Multiple paternity occurs at reported rates of 0-100%, and can vary by as much as 9-100% within species. Hybridization in almost every combination among members of the Cheloniidae has been documented but the frequency and ultimate ramifications of hybridization are not clear. The global phylogeography of sea turtles reveals a gradient based on habitat preference and thermal regime. The cold-tolerant leatherback turtle (Dermochelys coriacea) shows no evolutionary partitions between Indo-Pacific and Atlantic populations, while the tropical green (Chelonia mydas), hawksbill (Eretmochelys imbricata), and ridleys (Lepidochelys olivacea vs. L. kempi) have ancient separations between oceans. Ridleys and loggerhead (Caretta caretta) also show more recent colonization between ocean basins, probably mediated by warm-water gyres that occasionally traverse the frigid upwelling zone in southern Africa. These rare events may be sufficient to prevent allopatric speciation under contemporary geographic and climatic conditions. Genetic studies have advanced our understanding of marine turtle biology and evolution, but significant gaps persist and provide challenges for the next generation of sea turtle geneticists.     

Temporal changes in artificial light exposure of marine turtle nesting areas

Artificial light at night poses a significant threat to multiple taxa across the globe. In coastal regions, artificial lighting close to marine turtle nesting beaches is disruptive to their breeding success. Prioritizing effective management of light pollution requires an understanding of how the light exposure of nesting areas changes over time in response to changing temporal and spatial distributions of coastal development. We analyzed multitemporal, satellite night‐light data, in combination with linear mixed model analysis, to determine broadscale changes in artificial light exposure at Australian marine turtle nesting areas between 1993 and 2010. We found seven marine turtle management units (MU), from five species, have experienced significant increases in light exposure over time, with flatback turtles nesting in east Australia experiencing the fastest increases. The remaining 12 MUs showed no significant change in light exposure. Unchanging MUs included those previously identified as having high exposure to light pollution (located in western Australia and southern Queensland), indicating that turtles in these areas have been potentially exposed to high light levels since at least the early nineties. At a finer geographic scale (within‐MU), nine MUs contained nesting areas with significant increases in light exposure. These nesting areas predominantly occurred close to heavily industrialized coastal areas, thus emphasizing the importance of rigorous light management in industry. Within all MUs, nesting areas existed where light levels were extremely low and/or had not significantly increased since 1993. With continued coastal development, nesting females may shift to these darker/unchanging ‘buffer’ areas in the future. This is valuable information that informs our understanding of the capacity and resilience of marine turtles faced with coastal development: an understanding that is essential for effective marine turtle conservation.     

Accounting for Imperfect Detection Is Critical for Inferring Marine Turtle Nesting Population Trends

Assessments of population trends based on time-series counts of individuals are complicated by imperfect detection, which can lead to serious misinterpretations of data. Population trends of threatened marine turtles worldwide are usually based on counts of nests or nesting females. We analyze 39 years of nest-count, female-count, and capture-mark-recapture (CMR) data for nesting loggerhead turtles (Caretta caretta) on Wassaw Island, Georgia, USA. Annual counts of nests and females, not corrected for imperfect detection, yield significant, positive trends in abundance. However, multistate open robust design modeling of CMR data that accounts for changes in imperfect detection reveals that the annual abundance of nesting females has remained essentially constant over the 39-year period. The dichotomy could result from improvements in surveys or increased within-season nest-site fidelity in females, either of which would increase detection probability. For the first time in a marine turtle population, we compare results of population trend analyses that do and do not account for imperfect detection and demonstrate the potential for erroneous conclusions. Past assessments of marine turtle population trends based exclusively on count data should be interpreted with caution and re-evaluated when possible. These concerns apply equally to population assessments of all species with imperfect detection.     

Long-term trends in abundance of green sea turtles (Chelonia mydas) assessed by non-lethal capture rates in a coastal fishery

Sea turtle populations underwent severe decline in historical times, mainly through harvesting eggs and adults on nesting beaches. With the reduction of this threat in many areas, coupled with other conservation actions, some populations have demonstrated encouraging recovery, although remaining below their previous levels and undergone additional modern threats such as incidental capture in fisheries and pollution. Trends in sea turtle populations have usually been assessed through monitoring of females or nests on nesting beaches. Here we present data from a 22-year monitoring period for a juvenile green sea turtle Chelonia mydas mixed-stock in southeastern Brazil that were incidentally captured in passive non-lethal pound nets. A total of 3639 green turtles were captured in 5323 fishing days.pound⁻¹ with mortality rate of 2%. Captures occurred in all months, but bycatch rates, excluding recapture events, were higher in September and October, probably due to the recruitment of turtles migrating from southern areas, as well as recruits from the oceanic zone. Capture rates increased by 9.2% per year in the period from 1995 to 2016, in line with increasing source populations, particularly the main source contributor at Ascension Island, but also Trindade Island (Brazil) and Aves Island (Venezuela). Mean Curved Carapace Length of green turtles was higher during austral summer/early autumn and decreased markedly in May, probably due to the small-sized individuals that recruited to the study site. We show that the incidental capture of sea turtles in non-lethal fisheries, such as Brazilian pound nets, could also provide data on trends of populations nesting in distant places, and can contribute to the assessment of population status of sea turtles within Regional Management Units throughout the Atlantic Ocean.