Trends in Sea Turtle Nesting in Florida
Three species of sea turtle nest routinely on Florida’s beaches: the loggerhead turtle (Caretta caretta), the green turtle (Chelonia mydas) and the leatherback turtle (Dermochelys coriacea). FWRI coordinates monitoring of sea turtle nesting activity in Florida through two separate and complementary programs: the Statewide Nesting Beach Survey (SNBS) program and the Index Nesting Beach Survey (INBS) program. The SNBS was initiated in 1979; its purpose is to document the total distribution, seasonality, and abundance of sea turtle nesting in Florida. The SNBS program encompasses nearly all sandy beaches in the State (228 beach sites for a total of 1,351 km in 2021) that are monitored daily for a minimum of four months per year. Since 1989, the Index Nesting Beach Survey (INBS) has been carried out on a subset of SNBS beaches with the purpose of measuring trends in the number of nests. The index survey uses standardized data-collection criteria including consistent effort by location, fixed dates, and specialized annual training of beach surveyors. As of 2016, 36 beaches participate in the INBS program, representing 445 km of coastline.
FWRI coordinates sea turtle nesting data collection through a network of trained surveyors, including federal, state and local government agency personnel; members of conservation organizations; university researchers; and private citizens. Overall, approximately 3,000 individuals are involved in an outstanding citizen science effort to document sea turtle nesting activity and hatchling production statewide. What follows is a species-by-species overview of sea turtle nesting trends in Florida.
Florida hosts the greatest number of nesting loggerheads in the world with an annual average of 103,342 clutches (2018-2022). The loggerheads that nest in Florida represent three Recovery Units and seven genetically distinct Management Units (MU). Loggerhead nest counts on Florida’s index beaches have varied greatly since 1989 revealing a complex trend with wide fluctuations that corresponded to decreasing and increasing trends during short intervals and an overall stable (unchanging) trend over the entire period monitored so far. Researchers do not yet understand fully what drives fluctuations in annual clutch counts and whether the observed pattern is part of a long-term cycle. Because sea turtles come ashore to lay their eggs and nests are easily counted, these counts are commonly used as an index of abundance and population trends. However, nest counts do not provide a direct index of adult female population abundance because females typically lay more than one clutch per season, and most do not reproduce every year. FWRI Researchers recently attempted to investigate the likelihood that observed fluctuations of nests represented inter-annual changes of the adult female population by accounting for uncertainty in reproductive rate parameters. When researchers accounted for uncertainty in both clutch frequency (number of clutches laid in a season) and remigration interval (number of years between reproductive seasons), they found evidence for an increasing trend in female abundance only for two small MUs (Central-west and Northeast Florida). Researchers found no evidence of an increasing or a declining trend in the most abundant MUs (Central-east and Southeast FL, which account for about 82% of all loggerhead nests in Florida) or for all loggerheads that nest in Florida. Despite extensive conservation efforts and protections for loggerheads in Florida and the wider USA, researchers did not find evidence of a strong population recovery. FWRI researchers recommend maintaining a high level of protection, addressing persistent anthropogenic (human-caused) threats, continuing collection of rigorous nest-count data, and monitoring reproductive parameters to better link nest counts to adult female population abundance. Results from this study demonstrates the need for caution in using nest counts as a direct proxy for adult female population status, as it may lead to unsupported conclusions potentially detrimental to conservation.
The Florida green turtle nesting aggregation is of rising regional importance with an annual average of 30,785 clutches (2018-2022). Florida green turtle nest counts have increased eightyfold since standardized nest counts began in 1989 – a trend that differs dramatically from that of the loggerheads that nest on the same beaches. Nesting green turtles tend to follow a two-year reproductive cycle and, typically, there are wide year-to-year fluctuations in the number of nests recorded. Green turtles set record high nest-counts in 2011, 2013, 2015, 2017 and 2019. The last three years (2020-2022) did not follow the typical two-year cycle but were intermediate years. Changes in the typical two-year cycle have been documented in the past as well (e.g., 2003-2004 and 2010-2011) and are not cause of concern. Nest counts may resume the two-year high and low cycle as observed in the past or their pattern may change in the future. More years of standardized nest counts are needed to assess this.
The Florida leatherback nesting aggregation is part of the Northwest Atlantic (NWA) Regional management Unit (RMU). This RMU was recently reclassified as Endangered on the global RedList of Threatened Species because of the observed decline especially in French Guyana. Florida is the only state in the continental U.S. where leatherback turtles regularly nest and 1,389 clutches have been laid annually in the last five years (2018-2022). Like nest counts for green turtles, leatherback nest counts have been increasing over the period of monitoring. However, while green turtle nest numbers on Florida’s index beaches continue to rise, leatherback nest numbers reached a peak in 2014 followed by a steep decline (2015-2017) and a promising rebound (2018-2022). Florida hosts only a few hundred leatherback nests annually and these turtles can lay as many as 11 clutches during a nesting season. Thus, fluctuations in nest counts may be the result of a small change in number of females. More years of standardized nest counts are needed to understand whether the fluctuations are natural or warrant concern.
Nest counts are collected during early morning surveys designed to detect signs left by sea turtles that emerged the previous night. Trained surveyors use visible characteristics of tracks and nests to distinguish species (loggerhead, green turtle, leatherback turtles) and to distinguish nests from abandoned nesting attempts.
The INBS and SNBS are two of the core programs in the FWRI sea turtle program. The work is funded by proceeds from the sale of Florida’s Sea Turtle License Plates and from a recurring grant from the U.S. Fish and Wildlife Service.
Sea turtles are protected species under the Endangered Species Act and international law (e.g., CITES – Convention on International Trade in Endangered Species of Wild Fauna and Flora). Sea turtles are highly migratory animals that are difficult to study. Nesting data are much easier to collect and are routinely used to assess recovery of the species and the effectiveness of recovery actions (e.g., see the USFWS and NOAA Loggerhead Recovery Plan). Nest numbers are also one of the key parameters currently used by the IUCN (International Union for Conservation of Nature) Red List Assessment. Sea turtle nesting data, in particular SNBS data, are also used routinely by state and federal management to determine take, to determine when and whether a project can take place (e.g., sand placement on a beach, any type of construction on nesting habitat), and to mitigate and minimize take (e.g., oil spill response).
The next exciting challenge for the FWRI nesting program is the development of an FWC nesting web-based application that allows collection of real time data (crawl-level data) and associated nest fate data. An FWC sea turtle nesting app will increase tremendously the resolution of the data FWC receives and the capability to address in a timelier manner threats (e.g. respond to active predation, ability to detect issues during nesting season and not after the fact, ability to accurately assess number of nests potentially impacted by storms, ability to provide better data to HSC permitting staff and other entities (e.g. USACE). This next step will only be successful if embraced by our extensive network of permit holders and volunteers.