Green Turtles are highly susceptible to anthropogenic threats including bycatch, direct take and trade (legal and illegal), collision with marine vessels, habitat loss and degradation, pollution, disease and climate change.
Direct take of turtle meat, eggs, and parts has been the most important source of mortality for Green Turtles for centuries. Although this has declined in recent years, it remains a common practice in certain cultures in many parts of the world (Bräutigam and Eckert 2006, Humber et al. 2014, Senko and Burgher et al. 2022). A recent global analysis of all reported 'illegal exploitation'—i.e., the take or trade of turtles against established law in the locality where the take occurred— produced estimates of approximately 44,000 turtles/year over the past decade, most of which were Green Turtles (Senko and Burgher et al. 2022). This analysis also suggested a decline over time in the illegal take of turtles, although a review of legal turtle harvests (Humber et al. 2014) found that at that time at least 42 countries and territories permitted direct take of turtles, and the primary species used was Green Turtles (>80%).
Industrial and small-scale artisanal fisheries inflict severe impacts on sea turtles (Wallace et al. 2013a). In particular, small-scale fisheries occur primarily in developing nations with limited capacity and resources to obtain data, and where fisheries management is limited or non-existent, thus hindering comprehensive evaluations of the impacts of incidental capture of marine wildlife. Weak governance, poverty, and a lack of resources for local fisheries managers means that scant attention is devoted to assessing impacts of bycatch on sea turtles. Sea turtles get captured in coastal fishing gear most commonly in gillnets, longlines and trawl nets (Wallace et al. 2013a). Industrial-scale fisheries also incidentally capture Green Turtles and other sea turtle species; conservation resolutions approved by inter-governmental regional fisheries management organizations need to be adequately observed, enforced, and monitored over time to implement intended conservation benefits.
Climate change is known to influence migratory patterns and breeding success of sea turtles (Patricio et al. 2021), and a recent study in the Great Barrier Reef, Australia—home to the world's most abundant Green Turtle subpopulation—revealed feminization and highly skewed sex ratios attributed to impacts of climate change (Jensen et al. 2018). As long-lived reptiles with temperature-dependent sex determination, all marine turtles are vulnerable to change in climate, in particular the effect of rising temperatures on offspring sex ratios and lowered hatching or reduced hatchling fitness (Patricio et al. 2021). The increased incidence of hypothermic stunning, which killed thousands of Green Turtles in Texas during the winter of 2020–2021, is suggested to be linked to range shifts of foraging Green Turtles increasing their abundance in Texas inshore waters.
Habitat loss and degradation is a continuing threat for marine turtle populations both at sea from anthropogenic activities such as fisheries and through coastal development (Biddiscombe et al. 2020). The Intergovernmental Panel on Climate Change (IPCC) predicts that as sea levels rise in the next 100 years, coastlines will migrate landwards, and increased development of anthropogenic structures will further reduce beach availability for marine turtles (Biddiscombe et al. 2020). With coastal development comes light pollution and the impacts of artificial light at night include significantly decreased survival of hatchlings and disruption of nesting females (Biddiscombe et al. 2020). Plastic pollution degrades marine turtle habitat both at sea and on land and we have yet to understand the implications of ingestion of plastics on reproduction and longevity of marine turtles (Duncan et al. 2015).
Green Turtle Fibropapilloma (GTFP) disease is prevalent in many populations worldwide, and has been shown to be more prevalent in areas with lower water quality (Van Houtan et al. 2014), typically associated with coastal development. Although GTFP does not seem to be a current major threat, disease virulence may be enhanced with predicted climate change (Patricio et al. 2021).
Threats across the different regions are varied and more detail can be found in the regional subpopulation assessments. For more details about threats to Green Turtles globally, see Seminoff et al. 2015.
