Abstract
Globally, sea turtle research and conservation efforts are underway to identify important high-use areas where these imperiled individuals may be resident for weeks to months to years. In the southeastern Gulf of Mexico, recent telemetry studies highlighted post-nesting foraging sites for federally endangered green turtles (Chelonia mydas) around the Florida Keys. In order to delineate additional areas that may serve as inter-nesting, migratory, and foraging hotspots for reproductively active females nesting in peninsular southwest Florida, we satellite-tagged 14 green turtles that nested at two sites along the southeast Gulf of Mexico coastline between 2017 and 2019: Sanibel and Keewaydin Islands. Prior to this study, green turtles nesting in southwest Florida had not previously been tracked and their movements were unknown. We used switching state space modeling to show that an area off Cape Sable (Everglades), Florida Bay, and the Marquesas Keys are important foraging areas that support individuals that nest on southwest Florida mainland beaches. Turtles were tracked for 39–383 days, migrated for a mean of 4 days, and arrived at their respective foraging grounds in the months of July through September. Turtles remained resident in their respective foraging sites until tags failed, typically after several months, where they established mean home ranges (50% kernel density estimate) of 296 km2. Centroid locations for turtles at common foraging sites were 1.2–36.5 km apart. The area off southwest Florida Everglades appears to be a hotspot for these turtles during both inter-nesting and foraging; this location was also used by turtles that were previously satellite tagged in the Dry Tortugas after nesting. Further evaluation of this important habitat is warranted. Understanding where and when imperiled yet recovering green turtles forage and remain resident is key information for designing surveys of foraging resources and developing additional protection strategies intended to enhance population recovery trajectories.
Highlights
Green turtles (Chelonia mydas) are widely distributed, nesting circumglobally in temperate and tropical waters
The green turtle is listed as federally endangered under the United States Endangered Species Act (Endangered Species Act [ESA], 1973, as amended), green turtles nesting in the Gulf of Mexico appear to be increasing in abundance
Modest increases in green turtle nest counts have been reported on northwestern Gulf of Mexico beaches in Texas (Shaver et al, 2020) and nest counts for Florida green turtles have risen at an exponential rate [Chaloupka et al, 2008; Valdivia et al, 2019; Florida Fish and Wildlife Conservation Commission (FWC) unpublished data]
Summary
Green turtles (Chelonia mydas) are widely distributed, nesting circumglobally in temperate and tropical waters. A more recent assessment of global trends in green turtle nesting patterns indicated that four out of five regional management units (RMUs; Wallace et al, 2010) for the species are significantly increasing in abundance (Mazaris et al, 2017). Modest increases in green turtle nest counts have been reported on northwestern Gulf of Mexico beaches in Texas (Shaver et al, 2020) and nest counts for Florida green turtles have risen at an exponential rate [Chaloupka et al, 2008; Valdivia et al, 2019; Florida Fish and Wildlife Conservation Commission (FWC) unpublished data]. An exponential increase has been observed since 2013 and 841 green turtle nests were documented on the west coast of Florida in 2019 (FWC, unpublished data)
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