Small foraging grounds, large population significance: adult- and male-rich aggregations of green turtles in Senegal

Green turtles ( Chelonia mydas ) undertake long-distance migrations between breeding and foraging grounds, yet foraging areas remain far less studied. West Africa is a biodiversity-rich region of global importance for green turtles, hosting one of the three largest Atlantic nesting rookeries, on Poilão Island, Guinea-Bissau, as well as major coastal foraging aggregations for which data are limited. Using a recent integrative approach, we combine nesting, satellite tracking and in-water capture data to estimate the abundance, demographic structure, and spatial distribution of green turtles in Senegal. Tracking analyses reveal that green turtles do not use the entire Senegalese coast, but instead concentrate in two small areas — Saloum Delta and Joal — that coincide with existing marine protected areas. We estimate that 12,589–14,010 green turtles forage in these sites, resulting in an exceptionally high spatial concentration. Turtles foraging in Senegal (~ 300–400 km north of the main rookery in Poilão) had a mean curved carapace length of 89.1 ± 14.3 cm and were significantly larger than those foraging in Mauritania, 1,000 km north of Poilão. The adult sex ratio was male-rich, with 1 male:1.54 females (vs. 1:3.75 reported for Mauritania), supporting emerging evidence that males forage closer to breeding grounds. This study provides the first in-water assessment of green turtles in Senegal and demonstrates how small foraging grounds can support large aggregations with distinct demographic structure, reinforcing the value of in-water studies for understanding spatial population structure in marine megafauna.