Green turtles ( Chelonia mydas) are large, hard-shelled sea turtles found across the world’s tropical and subtropical waters. They are unique among sea turtles for being primarily herbivorous, feeding mostly on seagrasses and algae, which gives their fat a greenish hue, hence their name. These reptiles play an ecological role in marine ecosystems by grazing on seagrass beds, preventing overgrowth and maintaining the health of these underwater habitats that serve as nurseries for many other species.
Global Population Status
The global population status of green turtles is complex, with varying trends across different regions. The International Union for Conservation of Nature (IUCN) classifies the species as Endangered globally, indicating a significant reduction in population numbers. Despite this overall classification, the status can differ for distinct population segments (DPSs) around the world.
The United States Endangered Species Act (ESA) lists 11 distinct population segments of green turtles, with three classified as endangered and eight as threatened. For example, the Central South Pacific, Central West Pacific, and Mediterranean DPSs are listed as endangered. In contrast, populations such as the Central North Pacific, North Atlantic, and South Atlantic DPSs are listed as threatened.
Some populations have shown signs of recovery due to conservation efforts. The North Atlantic population, particularly in Florida, has seen a substantial increase in nesting, with numbers rising from approximately 4,000 nests in the 1980s to over 230,000 in the 2010s. Similarly, the Hawaiian green turtle population has experienced an increase in nesting females, growing by 3-5% annually by 2015. However, other populations, like the one at Tortuguero in Costa Rica, which is the largest in the Caribbean, have recently shown a declining trend.
Challenges to Survival
Green turtle populations face numerous human-induced and environmental challenges. One significant threat is fisheries bycatch, where turtles become unintentionally entangled in various fishing gear like gillnets, longlines, and trawl nets, leading to injury, drowning, or death. An estimated 50,000 turtles are caught annually in shrimp nets, resulting in thousands of deaths.
Illegal harvesting of green turtles and their eggs also poses a threat. Historically, overharvesting for meat, fat, and eggs caused global declines. Despite legal protections in many countries, illegal collection of eggs and hunting of adult turtles persist in some regions. For instance, in the Indo-Australian archipelago, an estimated 100,000 green turtles are killed each year.
Habitat loss and degradation further imperil green turtles. Coastal development, including the construction of seawalls and resorts, directly destroys or disturbs nesting beaches. Seagrass beds, which are feeding grounds for these herbivores, are also at risk from pollution and sedimentation caused by onshore development.
Climate change presents additional challenges. Rising sea levels and increased storm intensity erode nesting beaches and can inundate nests, washing away eggs. Warmer sand temperatures on nesting beaches can skew the sex ratio of hatchlings, as sea turtle sex is temperature-dependent. Temperatures above 29.1 degrees Celsius tend to produce females, potentially leading to an imbalance with a scarcity of males in future populations.
Plastic pollution and disease also contribute to population declines. Green turtles can mistake plastic bags and other debris for food, leading to internal blockages, malnutrition, or starvation. Furthermore, pollution can weaken their immune systems, making them more susceptible to diseases like fibropapillomatosis (FP). This debilitating disease, associated with a herpesvirus, causes tumor growths on the turtles’ soft tissues and internal organs, impairing their ability to see, swim, and feed, often with lethal outcomes.
Efforts to Protect Green Turtles
Numerous conservation strategies and initiatives are underway to protect green turtle populations worldwide, involving a combination of legal frameworks, habitat protection, and community engagement. International agreements like Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) prohibit international trade of green turtles, while the Inter-American Convention (IAC) provides a legal framework for countries in the Americas and Caribbean to conserve sea turtles and their habitats.
The establishment of marine protected areas (MPAs) is a conservation tool. These designated ocean areas restrict human activities like fishing, providing safe foraging and nesting habitats. Studies show that 35% of the world’s green turtles are found within these protected zones. Networks of MPAs, such as the RAMPAO in West Africa, are proving effective in safeguarding green turtle habitats, although protecting migratory corridors outside these areas remains a challenge.
Efforts to reduce fisheries bycatch include the mandatory use of Turtle Excluder Devices (TEDs) in trawl nets. These devices allow turtles and other large marine animals to escape while retaining the target catch. TEDs have proven effective, with NOAA Fisheries testing showing they are 97% effective at preventing sea turtle capture in shrimp trawl nets.
Community involvement and public awareness campaigns also play a role in conservation. Organizations work with local communities to reduce illegal harvesting by developing alternative livelihoods and promoting the value of sea turtles through ecotourism. Public awareness campaigns educate individuals on the threats facing turtles and encourage responsible practices, such as reducing plastic consumption and participating in beach cleanups.
Rehabilitation centers, like The Turtle Hospital in Florida, rescue and treat sick or injured turtles, including those affected by fibropapillomatosis or fishing line entanglements, before releasing them back into the wild. These centers also contribute to research and public education, offering insights into turtle health and behavior.