Research and Monitoring of Bonaire’s Sea Turtles: 2015 Technical Report

Sea Turtle Conservation Bonaire (STCB) was formed in 1991 in order to protect the island’s marine turtle populations. In 2002 we standardized our research and monitoring efforts, following the appointment of a Scientific Officer. Annually we monitor our nesting beaches around Bonaire, conduct intensive in-water netting and snorkel surveys (capture-mark- recapture), and track post-breeding migration using satellite telemetry. These techniques provide us with a better understanding of Bonaire sea turtles’ breeding success, abundance, health, growth rates, migratory paths and distant feeding grounds, residency duration, habitat quality, and threats.

During the 2015 season, we recorded 56 nests at our index beach on Klein Bonaire. Total hawksbill (46) and loggerhead (10) nests documented there were once again similar to numbers observed during recent years. Across Bonaire and Klein Bonaire, we observed three sea turtle species crawling 233 times, which includes 77 confirmed or suspected nests. Eight green turtle nests were recorded in northeastern Bonaire with a further five green turtle nests on Klein Bonaire. Hawksbills and loggerheads exclusively nested on Klein Bonaire and the beaches of southern Bonaire. Total nesting activities peaked from mid-June through to mid-September, with nests being laid between April and the end of December 2015.

We continue to be concerned about false crawls (unsuccessful nesting attempts) for both hawksbills and loggerheads as we again documented a much higher number of false crawls in 2015 than in 2013 when our concerns first developed. This phenomenon may result from a small number of individuals which were inefficient nesters (i.e., false crawled multiple times before successfully laying a nest), disturbance to turtles during nesting, and/or indicate deterioration in the quality of particular nesting sites, perhaps due to factors such as presence of an invasive vegetation species on our index beach. Estimates of clutch size and hatch success suggest that nearly 8,170 sea turtles hatched on the beaches of Bonaire and Klein Bonaire during 2015, including some 5,170 hawksbills, 1,700 loggerheads and 1,300 green turtles.

During in-water snorkel surveys, we observed and captured green turtles and hawksbills in all regions sampled, including Klein Bonaire, along the west coast of Bonaire, and near the reef bordering Lac. This year netting in Lac was conducted in four weekly sessions across the year, as a result of research in 2014 that suggested this may be a more effective sampling strategy. The aggregation of green turtles near Lac remains much larger than sites along the west coast, and greens captured there were bigger than conspecifics elsewhere, perhaps a result of the composition and high densities of sea grasses in Lac.

The total prevalence of fibropapillomatosis (FP) among green turtles captured in nets at Lac and Lagoen marginally declined in 2015 for the first time in five years, although there were still nearly a third of captures in the nets observed to have external tumors present (30%). The highest incidence was at Lagoen where six of the seven green turtles captured in the net there were observed with external FP tumors.

During 2015 STCB began the fieldwork component of a five-year research program in partnership with a research team funded by the Dutch National Research Organization (NWO) to study connectivity among sea turtles between the Dutch Caribbean Islands. As part of this research, satellite tags were fixed to four sub-adult green turtles; 19 nests were equipped with temperature loggers; and a long term experiment was set up in Lac Cai to learn more about turtle grazing and seagrass productivity there.

There were 27 sea turtle hotline stranding incidents reported during 2015, involving 35 individual sea turtles. Once again, one of the biggest threats Caribbean-wide to sea turtles was the fishing industry and associated by-catch. There were two turtles in trouble in separate incidents requiring rehabilitation early in 2015, including an olive ridley sea turtle which was successfully returned to the wild post rehabilitation. 

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