Research

Research

 

Caretta Research Project has conducted nocturnal beach patrols on Wassaw National Wildlife Refuge since 1973. Patrols are designed to systematically count nesting events and intercept nesting turtles. By marking each individual, CRP amasses capture-mark-recapture (CMR) histories for each female, which over time provide the critical information needed to understand and manage this once depleted population.

CRP Biologists use this 46-year CMR database to estimate demographic rates, such as survival, recruitment and migration, and analyze long-term trends in the number of nests and nesting females on Wassaw Island. As one of the longest monitoring programs in the United States, data collected by CRP have proved invaluable for the development of long-term management plans for loggerhead turtles in the Northwest Atlantic Ocean.

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Long-term Trends

Loggerhead nests on Wassaw Island, 1973-2017

CRP has documented an 8-fold increase in the number of nests laid on Wassaw Island (see graph to the right). The dramatic increase in the number of nests starting in the mid-2000s corresponds with the initiation of rigorous egg protection procedures when the project began in the mid-1970s. Because loggerhead turtles take 30 years to reach sexual maturity, we have only recently witnessed the fruits of our labor.

Moreover, the implementation and enforcement of Turtle Excluder Devices (TEDs) in the shrimping industry beginning in the mid- to late-1990s has dramatically reduced the number of dead turtle strandings in the region. With fewer females drowning in shrimp trawlers, more females are migrating and re-migrating to Wassaw Island to lay their eggs each year.

The population trends seen on Wassaw Island are echoed across the entire Northwest Atlantic loggerhead population. Clearly, four decades of research, conservation, education and policy changes have provided the foundation for a now strong and recovering population.

Understanding Biases

CRP Biologist, Dr. Joe Pfaller, uses the dataset amassed by CRP to reveal how methodological biases effect our interpretations of demographic rates and population trends estimated from CMR data. Because CMR data are widely used in studies of sea turtles, as well as other threatened marine species, understanding biases associated with CMR data is critical for developing accurate management plans for many imperiled species.

In 2018, Joe published an influential paper in which he and his international co-authors found that biological interpretations of adult sea turtle survival rates are confounded by methodological biases. Important differences in survival rates between turtle species and regions (left two panels below) were masked by differences in methodologies among estimates (right four panels below). These results highlight the importance of evaluating sources statistical bias when interpreting patterns among similar demographic studies and directly inform efforts to identify research priorities for marine turtles globally.

Future studies will continue to harness the power of CRP's long-term dataset to help inform the methods and models by which researchers and managers develop accurate management plans for sea turtle populations around the world.

Figure from Scientific Reports publication showing the influence of different biological and methodological factors on adult sea turtle survival rates at a global scale.

Collaborations

Caretta Research Project's 46-year database and infrastructure on Wassaw Island are invaluable resources to science and management of sea turtles, leading to numerous collaborations with universities and conservation organizations:

University of Georgia - Since 2005, CRP has worked with Drs. Brian Shamblin and Joe Nairn of the Warnell School of Forestry and Natural Resources to elucidate important demographic information about loggerhead turtles using DNA collected from egg shells. Because freshly laid turtle eggs contain maternal DNA, scientiststs can identify which female laid a nest without seeing her. Dr. Shamblin now collects one egg from every loggerhead nest laid between North Florida and Maryland. These results have revealed new and exciting information on the nesting biology of our loggerheads, inclduing annual suvivorship, nest-site fidelity, clutch frequency and even parentage. We now know that Wassaw's loggerheads also use many other islands in Georgia, South Carolina and North Carolina.

University of Florida - Since 2003, CRP has worked with Drs. Karen Bjorndal and Alan Bolten, as well as a number of graduate students in the Archie Carr Center for Sea Turtle Research (ACCSTR), on a variety of interesting studies aimed to better understand the habitat-use patterns of loggerhead turtles in the North Atlantic Ocean. Most recently, CRP has collected tissue samples from individual turtles to be used in stable isotope analysis to determine where turtles spend their non-reproductive season away from Wassaw Island. These results show that Georgia's loggerheads actually spend most of their time in the Mid-Atlantic Bight between Cape Hatteras and Cape Cod. CRP and ACCSTR have also worked together to elucidate the roles that sea turtles play as predators in the open ocean and hosts to diverse array of hitchhiking epibiota.

Georgia Southern University - CRP has worked extensively with Dr. David Rostal and his graduate students on a variety of studies on the reproductive biology of loggerhead turtles. From nest-temperature data collected between 2000-2010 on Wassaw and Blackbeard islands, GSU student Anne Marie LeBlanc determined that the sex ratio of hatchlings produced was approximate 30% males, with some cooler years approaching 40% males. These results have important implications for the future of sea turtle populations in the face of global climate change. From data collected between 2008-2010, GSU student Ketan Patel discovered that nesting females use resource partitioning to decrease their egg size across the season without limiting yolk mass and ultimately hatchling size. Also from data collected in 2008-2010, GSU student Jake Lasala found the most loggerhead nests on Wassaw show multiple paternity, in which between 2-7 male turtles contribute genetically to each clutch of eggs. Jake also found that more fathers are likely to sire individual clutches at the beginning of the summer than at the end.

Armstrong Campus @ Georgia Southern University - CRP has worked with Dr. Kathryn Craven on studies investigating the potential causes of egg mortality in loggerhead nests, as well as influecnce that the mother turtle's cloacal secretions have on bacterial and fungal growth within the nest. Specifically, Dr. Craven collects unhatched eggs to culture and identify bacteria and fungi growing in the nests.  CRP has also helped Dr. Craven and her colleagues study the terrestrial invertbrate community that utilize turtle nests and the impact that ants have on emergence success. Dr. Craven is also the Faculty Advisor for the Terrapin Educational Research Program of Savannah (TERPS), a multi-institutional organization dedicated to the conservation of the Carolina diamondback terrapin in the Greater Savannah Region and the Georgia low country.

University of North Carolina, Chapel Hill - CRP has recently begun work with Dr. Ken Lohmann and two of his graduate students, Kayla Clark and John Haught, investigating hypotheses that seek to explain why sea turtles are attracted to and ultimately consume marine plastics. This work is ongoing, but the results should shed light on a globally important threat to sea turtle survival.