Climate change is a threat to marine turtles that is expected to affect all of their life stages. To guide future research, we conducted a review of the most recent literature on this topic, ...highlighting knowledge gains and research gaps since a similar previous review in 2009. Most research has been focussed on the terrestrial life history phase, where expected impacts will range from habitat loss and decreased reproductive success to feminization of populations, but changes in reproductive periodicity, shifts in latitudinal ranges, and changes in foraging success are all expected in the marine life history phase. Models have been proposed to improve estimates of primary sex ratios, while technological advances promise a better understanding of how climate can influence different life stages and habitats. We suggest a number of research priorities for an improved understanding of how climate change may impact marine turtles, including: improved estimates of primary sex ratios, assessments of the implications of female-biased sex ratios and reduced male production, assessments of the variability in upper thermal limits of clutches, models of beach sediment movement under sea level rise, and assessments of impacts on foraging grounds. Lastly, we suggest that it is not yet possible to recommend manipulating aspects of turtle nesting ecology, as the evidence base with which to understand the results of such interventions is not robust enough, but that strategies for mitigation of stressors should be helpful, providing they consider the synergistic effects of climate change and other anthropogenic-induced threats to marine turtles, and focus on increasing resilience.
Linking foraging and breeding habitats is key to the understanding of behaviour, ecology and demography of migratory species. Establishing such connections has long been hampered by the logistical ...problems of following individuals between foraging and breeding areas, especially in the marine realm. We used variation in nitrogen stable isotope patterns between 2 foraging regions of loggerhead sea turtlesCaretta carettadetermined from samples of satellite-tracked individuals to assign untracked turtles to a foraging region. We sought to enhance determination of the relative importance of geographically separated foraging regions and to investigate the relationship between fitness correlates and inferred migratory strategies. Of 18 turtles followed by satellite tracking from Zakynthos (Greece), 10 moved north to foraging areas in the Adriatic Sea and the Gulf of Amvrakikos and 8 moved south to foraging areas off the coast of North Africa. Of 51 untracked individuals sampled for stable isotope analysis, we considered the stable isotope signature of 47 to qualify for assignment to foraging areas in the north (n = 22) and south (n = 25). Females foraging north were significantly larger (curved carapace length), and the former group laid larger clutches (even after correction for body length) than turtles foraging south, a fact that can be interpreted as a carry-over effect. Combining satellite tracking with stable isotope signatures in marine turtles opens new perspectives into how forensic tracking methodologies may be used to scale up knowledge from electronic tracking of a limited number of individuals to sample sizes that are more meaningful from a population perspective.
Despite the obvious power and advantages of the Argos system to track animals by satellite, the data generated are difficult for many biologists to exploit. A broad range of skills is required to ...efficiently download, collate, filter and interpret Argos data. Integration of animal movements with other physical (e.g. remote sensing imagery) and anthropogenic (e.g. fishery distributions) datasets presents additional technical and computing challenges. The Satellite Tracking and Analysis Tool (STAT) is a freely available system designed for biologists who work on animal tracking; it includes a set of standardized tools and techniques for data management, analysis, and integration with environmental data. STAT logs in to the Argos computer network each day and downloads all available locations and associated data for each user. These data are parsed and stored in a relational database and automatically backed up to an offsite location. A number of data filtering options are available, including setting maximum speed, time or distance between consecutive points, Argos location class, and turning angle. A variety of environmental data layers, including bathymetry, sea surface temperature, sea surface height, ocean currents and chlorophyll, can be sampled for all locations in the STAT database and can be downloaded and incorporated into tracking maps and animations. STAT also facilitates collaboration and the sharing of animal tracking information with the wider public and funding organizations. We hope that STAT will act as a catalytic foundation, fostering collaboration among users of satellite telemetry, and ensuring maximum value from these studies.
Global climate change is expected to have major impacts on biodiversity. Sea turtles have temperature-dependent sex determination, and many populations produce highly femalebiased offspring sex ...ratios, a skew likely to increase further with global warming. We estimated the primary sex ratio at one of the world’s largest green turtle Chelonia mydas rookeries in Guinea-Bissau, West Africa, and explored its resilience to climate change. In 2013 and 2014, we deployed data loggers recording nest (n = 101) and sand (n = 30) temperatures, and identified hatchling sex by histological examination of gonads. A logistic curve was fitted to the data to allow predictions of sex ratio across habitats and through the nesting season. The population-specific pivotal temperature was 29.4°C, with both sexes produced within incubation temperatures from 27.6 to 31.4°C: the transitional range of temperatures (TRT). Primary sex ratio changed from maleto female-biased across relatively small temporal and spatial scales. Overall it was marginally female-biased, but we estimated an exceptionally high male hatchling production of 47.7% (95% CI: 36.7–58.3%) and 44.5% (95% CI: 33.8–55.4%) in 2013 and 2014, respectively. Both the temporal and spatial variation in incubation conditions and the wide range of the TRT suggest resilience and potential for adaptation to climate change if the present nesting habitat remains unchanged. These findings underline the importance of assessing site-specific parameters to understand populations’ responses to climate change, particularly with regard to identifying rookeries with high male hatchling production that may be key for the future conservation of sea turtles under projected global warming scenarios.
Green turtles
Chelonia mydas
have been subject to high levels of anthropogenic exploitation, with harvesting at their nesting sites especially pronounced throughout the late 19
th
and early 20
th
...centuries, leading to worldwide declines. Due to their delayed sexual maturity, long-term protection and monitoring is crucial to allow and accurately demonstrate population recovery. Subsequent to their exploitation, Aldabra Atoll (Republic of Seychelles) has offered the longest continuous protection for nesting green turtles anywhere in the Western Indian Ocean, beginning in 1968. Here, we document the continuing recovery of that population by estimating clutch production within 12 mo nesting seasons over 50 yr of monitoring. An estimated mean of 15297 clutches were laid annually between December 2014 and November 2019. This represents an increase of 173% since Aldabra’s intensive monitoring programme was initiated in 1980, and 410- 665% since 1968. Clutch number increases were recorded at all but 1 of 6 monitored beach groups around the atoll but were most pronounced at Settlement Beach, where exploitation of nesting females was historically most intense. Seasonality data since 2000 showed a year-round nesting season, with elevated activity in April-June peaking on average in May, and a potential shift to later in the year over time. This study highlights the considerable contribution of Aldabra Atoll to regional green turtle numbers and the benefit of long-term protection and monitoring at what can be considered a global reference site for this species.
Growing evidence suggests that anthropogenic litter, particularly plastic, represents a highly pervasive and persistent threat to global marine ecosystems. Multinational research is progressing to ...characterise its sources, distribution and abundance so that interventions aimed at reducing future inputs and clearing extant litter can be developed. Citizen science projects, whereby members of the public gather information, offer a low-cost method of collecting large volumes of data with considerable temporal and spatial coverage. Furthermore, such projects raise awareness of environmental issues and can lead to positive changes in behaviours and attitudes. We present data collected over a decade (2005–2014 inclusive) by Marine Conservation Society (MCS) volunteers during beach litter surveys carried along the British coastline, with the aim of increasing knowledge on the composition, spatial distribution and temporal trends of coastal debris. Unlike many citizen science projects, the MCS beach litter survey programme gathers information on the number of volunteers, duration of surveys and distances covered. This comprehensive information provides an opportunity to standardise data for variation in sampling effort among surveys, enhancing the value of outputs and robustness of findings. We found that plastic is the main constituent of anthropogenic litter on British beaches and the majority of traceable items originate from land-based sources, such as public littering. We identify the coast of the Western English Channel and Celtic Sea as experiencing the highest relative litter levels. Increasing trends over the 10-year time period were detected for a number of individual item categories, yet no statistically significant change in total (effort-corrected) litter was detected. We discuss the limitations of the dataset and make recommendations for future work. The study demonstrates the value of citizen science data in providing insights that would otherwise not be possible due to logistical and financial constraints of running government-funded sampling programmes on such large scales.
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•Plastic is the main constituent of marine anthropogenic litter on British beaches.•The majority of traceable items originate from land, specifically public littering.•Clear differences in regional litter abundance were detected.•Significant increases in some individual litter items, spanning a decade, were identified.•Citizen science programmes are an effective tool for monitoring marine anthropogenic litter.
Although published literature regarding the 5 species of marine turtle found along the continental African east coast has grown substantially over the last decades, a comprehensive synthesis of their ...status and ecology is lacking. Using a mixed methods approach, which combined an exhaustive literature review and expert elicitation, we assessed the distribution and magnitude of nesting, foraging areas, connectivity, and anthropogenic threats for these species in Somalia, Kenya, Tanzania, Mozambique, and South Africa. A complex pattern of nesting sites, foraging areas, and migration pathways emerged that identified areas of high importance in all 5 countries, although significant data gaps remain, especially for Somalia. Illegal take, bycatch, and loss of foraging and nesting habitat were identified as the most serious anthropogenic threats. Although these threats are broadly similar along most of the coast, robust data that enable quantification of the impacts are scarce. Experts identified regional strengths and opportunities, as well as impediments to turtle conservation. Topics such as legislation and enforcement, collaboration, local stakeholders, and funding are discussed, and future directions suggested. Given the projected growth in human population along the continental African east coast and expected accompanying development, anthropogenic pressures on turtle populations are set to increase. Stronger regional collaboration and coordination within conservation and research efforts are needed if current and future challenges are to be tackled effectively.
River cetaceans are particularly vulnerable to anthropogenic impacts due to their constrained ranges in freshwater systems of China, South Asia, and South America. We undertook an exhaustive review ...of 280 peer-reviewed papers and grey literature reports (1998-2020) to examine the current status of knowledge regarding these cetaceans and their conservation. We aimed to better understand the scale of threats they face, and to identify and propose priority future efforts to better conserve these species. We found that the species have been studied with varying frequency and that most of the research on threats has focused on habitat degradation and fragmentation (43%, mainly driven by dams and extractive activities such as sand mining and deforestation), and fishery interactions (39%, in the form of bycatch and direct take). These threats occur across all species, but more information is needed, primarily on quantifying the population impacts as a basis for designing mitigation measures. Other threats identified include pollution, vessel collisions, traditional use, and poorly managed tourism. Emerging methods such as environmental DNA and unmanned aerial vehicles are described for studying these species. Promising conservation interventions include cetacean-specific protected areas, natural
ex situ
protection, community-led conservation, and education programmes. However, transnational political will is required for a step change towards broad-scale protection in freshwater environments. In addition, we propose increasing capacity building, developing management plans, working closely with fishing communities, enhancing public awareness, expanding regional collaborations, and diversifying funding.
Biologging data have provided important insights into the biology of marine mammals, sea turtles, birds, fish, and some invertebrates. These techniques have primarily targeted adult organisms. As a ...result, the early life histories of many marine species are still poorly understood. Technological advances have enabled attachment of smaller tags to young animals, although equipment limitations, access to and capture/handling of animals, and equipment and data recovery pose additional challenges to researchers. In this Theme Section, we highlight novel uses of biologging data on juvenile animals, including reviews of tagging efforts on multiple life-history stages and the integration of oceanographic data in tagging efforts.
The northwestern Indian Ocean hosts globally crucial marine biodiversity, which is relatively understudied. There has, however, been significant research and conservation effort focused on marine ...turtles across the region in recent decades. We undertook an exhaustive review of 251 relevant publications to extract and collate the current information concerning marine turtles. To ensure completeness, we received input on a preliminary draft from a large group of experts who have worked extensively in the region. Data presented here are from all 13 countries with significant coastlines in the region (Bahrain, Djibouti, Egypt, Eritrea, Iran, Kuwait, Oman, Qatar, Saudi Arabia, Somalia, Sudan, United Arab Emirates, and Yemen) on occurrence, nesting biology, morphology, foraging areas, population status, threats, and relevant national legislation and international conservation strategies. The experts independently provided details on what they felt were the (1) most significant threats to marine turtles, (2) most critical knowledge gaps for marine turtle ecology, (3) impediments to practical conservation, and (4) essential strengths and opportunities in the region.
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