Spatiotemporal patterns and environmental drivers of Loggerhead Sea Turtle (Caretta caretta) emergence and reproductive success on Loggerhead Key, Florida, USA

Populations of marine turtles are in decline worldwide and are protected by the US Endangered Species Act and by the Convention on International Trade in Endangered Species of Wild Fauna and Flora. An important component of wildlife conservation is consistent long-term monitoring of populations, but sea turtles are difficult to census except by counting the number of nests constructed by females on beaches throughout their range. Such a monitoring program has been in place in the state of Florida, USA, since the 1970s. Few studies of nesting sea turtles, however, have addressed the questions of the impact of benthic habitat on the density of sea turtle nests on adjacent beaches, or whether on- and offshore physical properties (e.g., sand coarseness and ground slope) affects hatching success. This study collected loggerhead sea turtle (Caretta caretta) crawl, nesting, and hatching data during the 2018 nesting season on the island of Loggerhead Key, located in Dry Tortugas National Park, Florida, USA. This study is the first of its type to attempt to correlate turtle crawl and nest site locations selected by nesting females with the physical properties of onshore and nearby offshore environments. After presenting a brief review of sea turtle biology, life cycle, ecological importance, threats to survival, and conservation status, we explore the monitoring program that has been in place in Florida for decades. By aggregating data collected since 2009 as part of the state monitoring program with our 2018 data, we found the trends of sea turtle emergences and total estimated number of eggs deposited at Loggerhead Key are increasing, while average clutch size is stable and comparable to other sub-populations in the Northwest Atlantic. Hatching success of successful nests from 2009 to 2018 was 74%. Spatial distribution of sea turtle emergences was not random; core areas for nesting and non-nesting emergences were clustered at the southwest end of the island and were related to both the sand grain type and benthic habitat directly offshore. Female sea turtles on Loggerhead Key nested more frequently at locations adjacent to relatively soft-bottom benthic habitats where beach sand was composed of medium-fine grains mixed with a small proportion of crushed shell particles. While many unmeasured co-variates may also play significant roles in this preference, these data provide a preliminary basis to prioritize areas of nesting beaches for protection and long-term monitoring