ABSTRACT: Abundance estimates corrected for changes in detection are needed to assess population trends. We used transect-count surveys and N-mixture models to estimate green turtle Chelonia mydas and hawksbill turtle Eretmochelys imbricata detection and total abundance at foraging grounds in Bonaire during 2003−2018, and we used these total abundance estimates to fit a Bayesian state–space logistic model and make abundance predictions for 2019−2030. During 2019−2022, we also recorded distance categories to estimate detection and total abundance using distance sampling and N-mixture models. In the present study, we focus on distance sampling to estimate observer detectability and total abundance, and to determine if total abundance increased, declined, or did not change during 2019−2022 and when compared with 2003−2018 estimates and 2019−2030 predictions. Detectability averaged 0.53 (SE = 0.02) for green turtles and 0.51 (SE = 0.06) for hawksbill turtles. Density (ind. km−2) and population size (individuals in the 4 km2 survey region) averaged 72.1 (SE = 17.3) and 288 (SE = 69) for green turtles and 21.8 (SE = 4.6) and 87 (SE = 18) for hawksbill turtles. Green turtle total abundance did not change during 2019−2022 (p > 0.05) but remained low when compared with 2003−2018 estimates and 2019−2030 predictions. Hawksbill turtle total abundance declined between 2020 and 2021 (z = 2.15, p = 0.03) and increased between 2021 and 2022 (z = −3.04, p = 0.002), but 2019−2022 estimates were similar to 2003−2018 estimates and 2019−2030 predictions. Our methodology can be used to monitor sea turtle populations at coastal foraging grounds in the Caribbean.
Seven species of turtles are present in a wide range of areas across the earth. The species that use
the beaches of Sint Maarten as nesting grounds are the Green sea turtle (Chelonia mydas),
Leatherback sea turtle (Dermochelys coriacea) and Hawksbill sea turtle (Eretmochelys imbricata).
Even with their protected status, populations are declining rapidly. This has a negative impact since
sea turtles have significant ecological, economic and social values. To prevent populations from
declining further, research is needed to create proper conservation strategies. This research focuses
on different factors that could hinder nesting activity and how they influence sea turtles on Sint
Maarten. These potential factors were researched in the literature and were determined to be
artificial lighting, dune scarps, coastal development, slope, distance from high tide line to beach line,
sargassum and human disturbances. Using a Spearman correlation test in SPSS, the correlation
between the presence of these factors and the total nesting activity that takes place was tested. The
test showed a moderate negative relation which was statistically significant
(rs = -.681, p = .044). This means that the number of factors that are present at each beach influence
the total nesting activity to some extent, but no strong correlation is present. These results indicate
that if more factors which could hinder the sea turtle nesting activity are present, less sea turtle
nesting activities take place on that beach on St. Maarten.
Ingestion of marine debris can have lethal and sublethal effects on sea turtles and other wildlife. Although researchers have reported on ingestion of anthropogenic debris by marine turtles and implied inci- dences of debris ingestion have increased over time, there has not been a global synthesis of the phenomenon since 1985. Thus, we analyzed 37 studies published from 1985 to 2012 that report on data collected from before 1900 through 2011. Specifically, we investigated whether ingestion prevalence has changed over time, what types of debris are most commonly ingested, the geographic distribution of debris ingestion by marine turtles relative to global debris distribution, and which species and life-history stages are most likely to ingest debris. The probability of green (Chelonia mydas) and leatherback turtles (Dermochelys coriacea) ingesting debris increased significantly over time, and plastic was the most commonly ingested debris. Turtles in nearly all regions studied ingest debris, but the probability of ingestion was not related to modeled debris densities. Furthermore, smaller, oceanic-stage turtles were more likely to ingest debris than coastal foragers, whereas carnivorous species were less likely to ingest debris than herbivores or gelatinovores. Our results indicate oceanic leatherback turtles and green turtles are at the greatest risk of both lethal and sublethal effects from ingested marine debris. To reduce this risk, anthropogenic debris must be managed at a global level.