Sandy Point National Wildlife Refuge (United States Virgin Islands)

From 2004 - 2007, the beach at Sandy Point National Wildlife Refuge (St. Croix,
USVI) experienced low summer erosion, which allowed native pioneer vegetation to
spread seaward and invade leatherback-nesting areas. The encroachment of vegetation
reduced nest survival. Here I describe the results of an experimental assessment of
vegetation control methods and of the effects of native vegetation on leatherback
hatching and emergence success. I tested four treatments: (i) naturally vegetated, (ii)
herbicide treated vegetation, (iii) mechanically removed above ground vegetation, and
(iv) non-vegetated (control) plots. Nests were relocated into each of the plot types then
left to incubate naturally. Hatching and emergence success was reduced when vegetation
was present. Vegetation was not adequately controlled by any of the methods tested. The
results identify future research needs for the development of appropriate management to
control the native vegetation and enhance leatherback nest productivity.

The tropical fire ant, Solenopsis geminata is a New World species with a wide native
range including South America as well as several Caribbean islands. The red imported
fire ant, Solenopsis invicta is native to parts of South America. Both species are known
for preying on sea turtles’ eggs and hatchlings. The objectives of this thesis research
were to conduct follow-up and baseline ant species distribution surveys on four sea turtle
nesting beaches in St. Croix, U. S. Virgin Islands. Tuna baits were set out at beaches;
specimens were collected, frozen, preserved then identified. Results show that there was
a significant change in the fire ants’ distribution at Sandy Point National Wildlife Refuge
(SPNWR) while none were found at Jack Bay. Fire ants were also present on the other
two baseline surveyed nesting beaches. The displacement of S. geminata by S. invicta
was observed at SPNWR, which also was presumed by previous surveys.

Sex determination in leatherback sea turtles is directed primarily by the temperatures a
clutch experiences during the middle third of development. Warmer temperatures tend to produce females will cooler temperatures yield males. Nest temperatures can vary
spatially and temporally. During the 2010 and 2011 nesting seasons, this study estimated the hatchling sex ratio of leatherback sea turtles on Sandy Point National Wildlife Refuge (SPNWR), St. Croix, U.S. Virgin Islands. I measured sand temperatures from May- August and across the spatial range of leatherback nesting habitat. I spatially interpolated those temperatures to create maps that predicted temperatures for all nests incubating on SPWNR. Nest temperatures were also directly measured and compared with predicted nest temperatures to validate the prediction model. Sexes of dead-in-nest hatchlings and full term embryos were used to confirm the sex-temperature response. The model showed that microclimatic variation likely impacts the production of both sexes on SPNWR.