Green and hawksbill turtle abundance and population dynamics at foraging grounds in Bonaire, Caribbean Netherlands

Abstract

Green turtles Chelonia mydas and hawksbill turtles Eretmochelys imbricata are negatively impacted by natural and anthropogenic disturbances. Unknown numbers of turtles are killed annually in the coastal waters of Bonaire and Klein Bonaire, Caribbean Netherlands. We used N-mixture models, conventional distance sampling and the multiple Lincoln-Petersen method to estimate abundance from transect-count and net-capture surveys. Maximum likelihood and Bayesian generalised linear models were used to assess trends in annual abundance in 2003−2018, and a Bayesian state-space logistic model was developed to generate the posterior distributions of population parameters and make abundance predictions for 2019−2030. Mean ± SE annual abundance was 555 ± 149 green turtles (2.5 th and 97.5 th percentiles = 337, 943) and 70 ± 13 hawksbill turtles (49, 101), and there were no trends in western Bonaire and Klein Bonaire in 2003−2018. Mean annual abundance was 348 ± 135 green turtles (171, 731) and there was a positive trend inside Lac Bay, southeast Bonaire, 2003−2018. Green turtles have higher population growth rate and carrying capacity, and therefore can sustain higher human-induced mortality than hawksbill turtles. However, under low mortality rates (< 0.100), both species can fluctuate stably between the lower and upper limits of the carrying capacity. The methodology implemented can be adapted to estimate sea turtle abundance, monitor and model their population dynamics, and assess the negative impact of human-induced mortality in other Caribbean islands.

Seagrass ecosystem multifunctionality under the rise of a flagship marine megaherbivore

“…Seagrass meadows were mainly dominated by the native seagrass, Thalassia testudinum , and to a lesser extent Syringodium filiforme , as well as the invasive seagrass, Halophila stipulacea (Christianen et al, 2019 ) along with beds of the calcareous algae Halimeda spp. Today, Lac Bay's seagrass meadows are home to one of the largest green turtle foraging aggregations in the southern Caribbean (Debrot et al, 2012 ; Rivera‐Milán et al, 2019 ). The abundance of green turtles ( Chelonia mydas ) has been recovering in the leeward Dutch Caribbean islands in recent decades after past depletion due to overharvesting (Jackson, 1997 ).…”

“…Today, Lac Bay's seagrass meadows are home to one of the largest green turtle foraging aggregations in the southern Caribbean (Debrot et al, 2012;Rivera-Milán et al, 2019). The abundance of green turtles (Chelonia mydas) has been recovering in the leeward Dutch Caribbean islands in recent decades after past depletion due to overharvesting (Jackson, 1997).…”

Herbivores shape the seascape : Cascading effects of herbivores on the functioning of tropical seagrasses in a changing world

“…well as the invasive seagrass, Halophila stipulacea(Christianen et al 2019) along with beds of the calcareous algae Halimeda spp. Today, Lac Bay's seagrass meadows are home to one of the largest green turtle foraging aggregations in the southern Caribbean(Debrot et al 2012, Rivera-Milán et al 2019. The abundance of green turtles (Chelonia mydas) has been recovering in the leeward Dutch Caribbean islands in recent decades after past depletion due to overharvesting(Jackson 1997).…”

“…A diverse herbivore community can mitigate this effect (Chapter 2). Biotic resistance may even increase over time; for example on Bonaire, instead of turtles abandoning the invaded seagrass meadow, their population is increasing(Rivera-Milán et al 2019) together with an increase in green turtles eating invasive seagrass (pers. obs.).…”