Research and Monitoring of Bonaire's Sea Turtles: 2017 Technical Report

Sea Turtle Conservation Bonaire (STCB) has been protecting sea turtles on Bonaire since 1991, so this year represents the 26th Anniversary of our organization. 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, and we regularly track sub-adult and post-breeding migrations 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. In 2017, Scientific Advisor Dr. Frank Rivera-Milán analyzed in-water transect counts, net captures, and nesting data that STCB has collected over the years. In cooperation with STCB, Rivera-Milán will produce scientific publications in the coming years, as well as review STCB’s methodology for netting (net captures), in-water surveys (transect counts) and nesting. 

During the 2017 season, we recorded 78 nests at our index beach on Klein Bonaire. A total of 61 hawksbill and 17 loggerhead nests and suspected nests were documented on “No Name Beach”. On the beaches on Bonaire and Klein Bonaire combined, we observed three sea turtle species (hawksbills, loggerheads and green turtles) crawling 228 times, which included a total of 128 confirmed or suspected nests. 21 green turtle nests were recorded in northeastern Bonaire. Hawksbills and loggerheads mainly nested on Klein Bonaire and the beaches of southern Bonaire. That said, three loggerhead and three hawksbill nests were recorded in northeastern Bonaire. The nesting period on Bonaire in 2017 ran from April to December with the highest number of nests laid between mid-June and mid-September. 

Estimates of clutch size and hatch success suggest that around 12,155 turtles hatched from nests on Klein Bonaire and Bonaire in 2017, including approximately 7,988 hawksbills, 2,033 loggerheads, and 2,134 green turtles. Sea turtle nesting activities across Klein Bonaire and Bonaire have been increasing since monitoring began in 2002. 

During in-water snorkel surveys, we counted and, when possible, captured green turtles and hawksbills in all regions sampled, including Klein Bonaire, along the west coast of Bonaire, and near the reef bordering Lac. Netting in Lac was conducted in three weekly sessions across the year. 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 occurrence of fibropapillomatosis (FP) among green turtles captured in nets at Lac declined considerably in 2017, continuing the downwards trend observed in 2015. This year only 5.5% of green turtles captured in and around Lac had visible FP tumors. 

STCB co-authored an important research paper in 2017: “Ecological regime shift drives declining growth rates of sea turtles throughout the West Atlantic” together with researchers led by Karen A. Bjorndal.

During 2017, there were 35 sea turtle hotline incidents reported, 32 of which were directly related to turtles in trouble; one involved the general public harassing sea turtles; and one call was related to poaching. The fishing industry and associated by-catch, one of the biggest threats Caribbean-wide, was implicated in approximately 23% of the turtles in trouble. A total of nine incidents were related to a large mass of seaweed sargassum that drifted inside the Lagoen and Sorobon area at the end of December. In the open ocean, these floating mats are extremely diverse, providing important habitat for over 250 species of fish and invertebrates, many of which are not found anywhere else. Young sea turtles often spend their tender years finding refuge and a plentiful food supply in these floating seaweed mats. However, when it enters coastal areas and starts rotting, it can cause mortality. Unfortunately, climate change has brought warmer temperatures, which increases algal growth rates, and possibly stronger currents/shifting currents, which combined with more and more land-based nutrients flowing into our oceans, are thought to be the reason why we are seeing more and more massive ‘strandings’ of these floating seaweed mats.