Intraspecific spatial segregation on a green turtle foraging ground in the Florida Keys, USA

Abstract

Assessing the distribution, density, and abundance of organisms is essential for conservation and management of imperiled species. Simple counts of sampled individuals are often inadequate to make such estimates. This is especially true for highly mobile marine animals like green sea turtles (Chelonia mydas). We used distance sampling and density surface model techniques to generate estimates of green turtle abundance on foraging grounds at the Eastern Quicksands, located west of Key West, Florida, USA. From 2006 to 2018, we conducted 18 surveys of six standardized transect lines from which we estimated abundances, plotted spatial distributions, and identified spatial segregation of life stages using density surface models and null model analysis. The Eastern Quicksands represent one of the densest foraging aggregations of green turtles worldwide. Spatial segregation of Large Juvenile and Adult turtles was evident, which we hypothesize may be due to benthic habitat preferences and differing predator detection and avoidance strategies among the sea turtle life stages. Given the high green turtle densities in this foraging area, and recent increases in Florida green turtle nesting, combined with anthropogenic stressors to seagrass pastures, we foresee management concerns for long-term sustainability of seagrass at the Eastern Quicksands and recommend that this area be given Critical Habitat designation.

Data on Sea turtle relative abundance in nearshore waters adjacent to the Mississippi River delta, Gulf of Mexico, United States

“…Each transect was surveyed at approximately 15 km/hr during three non-consecutive survey days between the months of June and October in 2013. Transect and recording methods are described in Welsh and Mansfield [2] . We used two observers atop an elevated platform (eye-level = 4.5 m) on an 8.2 m survey vessel.…”

Fine-scale foraging segregation in a green turtle (Chelonia mydas) feeding ground in the Bijagós archipelago, Guinea Bissau

“…2005; Loṕez-Mendilaharsu et al, 2005;Welsh and Mansfield, 2022). Some authors suggested that size-specific vulnerability to sharks may be the root of this pattern, as they are the main natural predators of marine turtles and prefer to hunt them in shallows (Heithaus et al, 2006).…”

“…Juvenile animals, for example, can feed on sources not explored by adults or use habitats inaccessible to them, and vice versa (Werner and Gilliam, 1984;Ferreira et al, 2018). Intraspecific niche segregation is quite frequent among marine megafauna, and has been observed in most groups such as fish, birds, mammals, and reptiles (Breed et al, 2006;McClellan et al, 2010;Benjamins et al, 2015;Ferreira et al, 2018;de Lima et al, 2019;Louzao et al, 2019;Welsh and Mansfield, 2022).…”