Cayman Islands Sea Turtle Nesting Population Increases Over 22 Years of Monitoring

Abstract

Given differing trajectories of sea turtle populations worldwide, there is a need to assess and report long-term population trends and determine which conservation strategies are effective. In this study, we report on sea turtle nest monitoring in the Cayman Islands over a 22-year period. We found that green (Chelonia mydas) and loggerhead (Caretta caretta) nest numbers increased significantly across the three islands since monitoring began in 1998, but that hawksbill nest numbers remained low with a maximum of 13 nests recorded in a season. Comparing the first 5 years of nest numbers to the most recent 5 years, the greatest percentage increase in green turtle nests was in Grand Cayman from 82 to 1,005 nests (1,126%), whereas the greatest percentage increase for loggerhead turtle nests was in Little Cayman from 10 to 290 nests (3,800%). A captive breeding operation contributed to the increase in the Grand Cayman green turtle population, however, loggerhead turtles were never captive-bred, and these populations began to increase after a legal traditional turtle fishery became inactive in 2008. Although both species have shown significant signs of recovery, populations remain at a fragment of their historical level and are vulnerable to threats. Illegal harvesting occurs to this day, with multiple females taken from nesting beaches each year. For nests and hatchlings, threats include artificial lighting on nesting beaches, causing hatchlings to misorient away from the sea, and inundation of nests by seawater reducing hatch success. The impacts of lighting were found to increase over the monitoring period. Spatial data on nest distribution was used to identify critical nesting habitat for green and loggerhead turtles and is used by the Cayman Islands Department of Environment to facilitate remediation of threats related to beachside development and for targeted future management efforts.

The architecture of assisted colonisation in sea turtles: building new populations in a biodiversity crisis

“… The key events of the Cayman Islands green turtle populations are detailed, including their decline, the captive breeding, the reintroduction program and the recent recovery. The dashed white line represents the wild population showing the initial decline until its virtual extinction 24 and later increase 25 . The green dot on the dashed line represents the discovery of the first nests laid by wild females.…”

“…In this study, we show that assisted colonisation can establish sea turtle nesting populations and we also provide insight on factors related to feasibility and long-term viability. For sea turtles, important considerations for captive breeding include animal husbandry and welfare concerns, the potential for disease transfer through the release of animals from an intensive-rearing facility into the wild, high costs, and apparently low rates of recruitment of captive-bred individuals into wild nesting populations 25 . In this study, we showed the results from more than 25,000 yearling and hatchling turtles released in the 1980s 27 .…”

“…This sampling effort corresponded to 58% of the 552 nests reported during these nesting seasons and locations. Since regular nesting was not recorded in these islands prior to 1998 25 , these hatchlings can be considered to be the first generation after the foundation of the new wild population. For nests assigned to a sampled wild female (see results) we gathered information regarding nesting date and GPS location from the DOE database as well as the total number of hatched and unhatched eggs, following standard procedures 39 , and the presence of an embryo in the unhatched eggs, as checked visually.…”

“…The Cayman Islands green turtle ( Chelonia mydas ) reintroduction program offers a unique opportunity to study the process and consequences of assisted colonisations in sea turtles. The local green turtle nesting population was considered nearly extinct 24 but the number of nesting females has increased exponentially in Grand Cayman over the past 20 years 25 , partially as a result of the reintroduction program initiated in 1983 from the Cayman Turtle Farm (CTF) (now the Cayman Turtle Conservation and Education Centre Ltd.) 26 , 27 . This reintroduction was based on releasing captive-bred green turtles from the island of Grand Cayman where the CTF is based (Fig.…”

Widespread Use of Migratory Megafauna for Aquatic Wild Meat in the Tropics and Subtropics

“…Prolific historical commercial exploitation devastated the abundance of nesting turtles in the British Virgin Islands (Richardson et al, 2006), Jamaica (Amorocho et al, 2016), and the Cayman Islands (Fleming, 2001). While population recoveries have occurred in recent years, the abundance of nesting turtles remains a small fraction of what existed historically (Blumenthal et al, 2021). That the unregulated, historical, large-scale commercial harvest was demonstrably unsustainable is clear.…”