Researchers Find Nesting Female Sea Turtles Are Getting Smaller

In 2021, researchers at UCF’s Marine Turtle Research Group (MTRG) analyzed the size of nesting female green and loggerhead sea turtles from the extensive data that they had collected in Archie Carr National Wildlife Refuge from 1982 through 2019. Their findings (see “Long-term trends in marine turtle size at maturity at an important Atlantic rookery”) indicated a “significant decrease” in the size of mature females of both species. Their research also found that the growth rate of juvenile greens started declining in the late 1990’s, and adult loggerhead female size has gotten smaller since the mid-2000’s. The researchers attributed this phenomenon to three factors: “changes in population demographics, habitat quality, and behavioral reactions to these changes.”

What impact could this have? Smaller females usually lay a fewer number of eggs per clutch. So, fewer hatchlings could result in a decrease in population numbers. With sea turtles facing so many threats (e.g., ocean pollution, climate change, entanglement in fishing gear, coastal development, etc.), any reduction in their populations is concerning.

Subsequent studies conducted in other nesting habitats in the world also show that nesting female sea turtles are getting smaller. Research done in Cabo Verde (off the west coast of Africa) discovered smaller nesting loggerheads, but also found that the numbers of loggerhead nests increased significantly from 2008 to 2020. Additionally, a research study conducted in the Seychelles, (off Africa’s east coast) also found a decrease in the size of mature female greens, but from 1996 to 2016, they discovered an increase in the number of nesting females so that the total number of eggs actually increased. From their findings, they concluded that for the green sea turtle population at the Aldabra Atoll in the Seychelles, the smaller clutches produced by the smaller nesting females did not impact the overall number of eggs because more females were nesting.

• Cabo Verde – “Changes in mean body size in an expanding population of a threatened species”
• Seychelles – “Long-term changes in adult size of green turtles at Aldabra Atoll and implications for clutch size, sexual dimorphism and growth rates”

Editor’s Note: One of the authors of the study done in the Seychelles is Dr. Cheryl L. Sanchez who was the guest speaker at the STPS August Membership Meeting. To read a summary of her presentation, please see page 16 of the STPS Fall 2024 “Turtle Times” Newsletter.

A 2023 article titled “Are Sea Turtles Getting Smaller?” in The State of the World’s Sea Turtles (SWOT) points out that increased nesting has not been observed at every location where smaller mature female sea turtles have been documented. So, they conclude that multiple factors may be at play in these different populations and their nesting habitats, and additional research is needed so that the appropriate conservation steps can be taken to avoid any future decline in sea turtle populations.