Movements, connectivity, and space use of immature green turtles within coastal habitats of the Culebra Archipelago, Puerto Rico: implications for conservation

Abstract

Juvenile green turtles occupy coastal marine habitats important for their ontogeny; however, the details of their movement, connectivity, and space use in these developmental habitats are still poorly understood. Given that these areas are often threatened by human disturbance, additional information on green turtle spatial ecology is needed to meet conservation endpoints for this endangered species. For this study, we used fixed passive acoustic telemetry to (1) describe movement patterns and connectivity of immature green turtles within, outside, and across 2 bays, Manglar and Tortuga bays, on Culebra and Culebrita islands, Puerto Rico; and (2) determine spatio-temporal drivers of the presence and absence of turtles within Manglar Bay. Network analysis used to quantify movement patterns showed that turtles in our study exhibited differential space use with little to no connectivity across the 2 bays. In addition, turtles exhibited high site fidelity, with larger turtles leaving on brief trips. We applied a presence−absence Bayesian binomial model on a subset of 9 turtles at an hourly temporal scale and showed that turtles within Manglar Bay occupied areas of lagoon and seagrass habitats at night and were rarely using areas of macroalgae habitat. The parameter estimates from the model enabled us to predict the space use of turtles across Manglar Bay, and the hourly probability distributions highlighted predictive diel movement patterns across the bay. Considering the importance of juvenile and subadult life stages for population viability, we recommend continued protection of these critical juvenile turtle developmental habitats to ensure recruitment into the adult life stage.

Space use and relative habitat selection for immature green turtles within a Caribbean marine protected area

“…Vulnerable to predation, such as from tiger sharks (Galeocerdo cuvier), immature green turtles must balance foraging opportunities and risk avoidance tactics [49]. Our results support previous findings that turtles forage in productive seagrass habitats and likely utilize physical structure, e.g., lagoon and reef-type structures, for protection [42,47,[50][51][52]. Furthermore, Casselberry et al [53] found acoustically tagged tiger sharks within BIRNM were more likely to inhabit depths > 10 m, at which point, relative habitat selection for turtles was very low (< 0.25).…”

“…Turtle MCPs and KDEs demonstrated space use was largely located directly south of the island and to the east and west, thus, space use did not perfectly match the predicted relative selection probabilities that were observed across a much broader spatial extent. This may be due to tagging effort being generally located south of the island where green turtle abundances were highest, thus, if immature green turtles exhibit small home ranges as demonstrated here and by Brill et al [54], Makowski et al [42], Griffin et al [47], and Chambault et al [55], we would expect tagged individuals to remain near their capture locations. Further, the RSF model could have been improved with additional covariates that capture additional environmental characteristics (e.g., fetch, wave energy, seagrass total area), ecological processes (e.g., density dependence, predator landscape metrics, [57]), and green turtle foraging strategies.…”

“…In addition, these areas are surrounded by less preferred, more exposed, and potentially more dangerous habitats (depths > 10 m), further suggesting constrained turtle space use. Similarly, immature green turtle space use on the neighboring island, Culebra Island, Puerto Rico (< 100 km), also remained in welldefined areas [47]. However, uncharacteristic of Buck Island, Culebra Island has larger protective embayments that immature turtles use almost entirely, even while suitable reef habitats exist directly adjacent to the bays.…”

“…Further, turtle core use areas, defined by 50% KDEs, within BIRNM were small (0.3 ± 0.0 km 2 ), similar to that reported by Makowski et al [42] (0.5 ± 0.4 km 2 ) and Chambault et al [55] (0.2 ± 0.3 km 2 ). When resource distributions (i.e., food and shelter) were tightly clustered, space use for immature green turtles was constrained [42,47,54]. Alternatively, when resources were dispersed, turtles have been shown to have a much larger distribution [56].…”

“…While this technology can be utilized to examine long-distance movements, the most prevalent and useful application for marine turtles is for the study of immature turtle space use within developmental grounds at a finer resolution. While this technology has proven to be valuable when providing insights on the immature turtle home range, space use, and behaviors [31,[42][43][44][45][46][47], there is still much to gain when it comes to understanding marine turtle ecology.…”