Turtle populations continue to face unpredictable challenges from climate change, according to a joint study between researchers from Deakin University and the National Oceanic and Atmospheric Administration (NOAA), published today in Nature Reviews Biodiversity.
Once severely impacted by overhunting and habitat loss, sea turtles have made a significant comeback due to conservation efforts and legal protections.
'Sea turtles are a beacon of marine conservation success, with many nesting populations showing remarkable recoveries,' said Deakin Distinguished Professor and Chair in Marine Science Graeme Hays.
The comprehensive study reviews the global status of the seven sea turtle species, detailing findings of a worldwide increase in sea turtle populations, including the discovery that more turtles are nesting on beaches that have implemented stronger protective measures.
Efforts such as reducing artificial lighting, which previously disoriented hatchlings, and the adoption of turtle-safe fishing practices, have contributed to these positive trends. In some areas, hunting sea turtles has decreased as awareness and conservation ethics have evolved.
Despite significant progress, challenges remain.
Pacific leatherback turtles, for example, continue to decline due to their arduous migrations across the Pacific Ocean. Climate change poses an ongoing threat, but scientists believe that conservation measures have strengthened sea turtles' resilience.
'When I think of sea turtles, resilience is the first word that comes to mind', said Dr Jeffrey Seminoff, from the NOAA Fisheries' Southwest Science Centre in California, USA. They are vulnerable to environmental changes but thrive when given the opportunity.'
The increasing sea turtle numbers also reflect shifting public values.
Younger generations view turtles less as a resource for consumption and more as valuable components of a healthy marine ecosystem. In some regions, former poachers now serve as eco-tour guides, helping tourists witness nesting turtles.
Historically, sea turtles were so abundant in the Caribbean that they frequently bumped into ships at night. However, overhunting rapidly reduced their numbers, with estimates suggesting a 95% decline from the original population of 19-33 million green sea turtles in the Caribbean.
Global declines occurred due to market-driven hunting, fishing net entanglement, and the loss of nesting habitats. However, increased legal protections and conservation initiatives have helped monitor and safeguard nesting sites.
Scientists analysed nesting records and other data to assess global sea turtle populations. The review revealed predominantly positive trends across species and regions. For instance, a 2017 analysis of 299 annual abundance time series found that population increases were three times more frequent than decreases.
An updated 2024 analysis showed even more promising results, with increases occurring six times more often than declines.
Four out of five regional green sea turtle populations are growing, with significant increases in loggerhead nesting sites. On Sal Island in Cape Verde, loggerhead nests surged from approximately 500 in 2008 to 35,000 in 2020.
Although data on species such as hawksbill, olive ridley, Kemp's ridley, and flatback turtles is limited, most available records indicate population growth. Many of these species remain protected under U.S. and international endangered species regulations.
Rising temperatures threaten sea turtle populations by skewing sex ratios toward females. However, emerging research indicates adaptive responses, such as loggerhead turtles in the Mediterranean shifting nesting sites to cooler areas. This behavioural shift could help maintain a balanced sex ratio and mitigate climate change effects.
Dr Seminoff emphasized that when harmful human activities are curtailed, species can recover and thrive.
Looking ahead, scientists have outlined key priorities for sea turtle conservation, including:
- Promoting climate resilience
- Reducing bycatch and illegal hunting
- Understanding and mitigating pollution impacts, particularly plastics
- Ensuring sufficient foraging habitats, such as seagrass meadows
Deakin's Professor Hays praised the efforts of individuals worldwide who have contributed to the resurgence of sea turtles.
'This success story demonstrates that humanity has the ability to reverse biodiversity loss when we commit to concerted conservation efforts,' he said.
