Spatial distribution of sea turtles on South Atlantic subtropical reefs

Abstract

Environmental conditions have a strong influence on sea turtle population dynamics. Sea turtles spend most of their lives in foraging areas; however, there is a lack of information on how oceanographic and biological parameters determine habitat use and density. Here, we estimated density of green turtles Chelonia mydas and hawksbill turtles Eretmochelys imbricata in a South Atlantic foraging area (Arraial do Cabo, Brazil). We also investigated the influence of environmental variables (wind fetch, temperature, depth, and visibility) and benthic composition on the distribution of turtles. Surveyed sites were split between a colder, more wave-exposed location (western), and a warmer, more sheltered location (eastern). To ensure that these mobile and sparsely distributed species were adequately surveyed, underwater visual censuses (timed transects) were conducted. Sea turtle densities were significantly different between warm/sheltered and cold/wave-exposed locations. C. mydas were almost 10 times more frequently sighted than E. imbricata. The local distribution of E. imbricata mirrored large-scale latitudinal patterns, where this tropical species is dominant on warmer reefs (similar to habitat conditions found at the eastern location). It was not possible to assess the environmental influence on E. imbricata sightings due to their low density. C. mydas were frequently sighted in the cold/exposed sites and negatively correlated with depth. Overall, the density of E. imbricata and C. mydas suggests that Arraial do Cabo is an important feeding ground in the western Atlantic Ocean. This study highlights that visual census can produce reliable density estimates of sea turtles in foraging areas.

Incorporating Geographical Scale and Multiple Environmental Factors to Delineate the Breeding Distribution of Sea Turtles

“…For example, sea turtles have been associated with nesting on wind-sheltered beaches at some sites [34][35][36] and wind-exposed beaches at other sites [37], with differences likely being linked to offshore (e.g., sandbanks versus reefs) and landward conditions (e.g., topography). Wind has been linked to the distribution of juvenile and adult turtles in subtropical regions [38] and the distribution of breeding sea turtles seeking optimal thermal conditions at suboptimal sites on the edge of the breeding range [30,39]. Thus, while temperature is typically used to predict the future distributions of sea turtles [32,40,41], the integration of other climatic factors might allow a more dynamic interpretation of the conditions required by a given species to enhance resilience, facilitating more informed policy decisions [12,42,43].…”

Synergistic use of UAV surveys, satellite tracking data, and mark‐recapture to estimate abundance of elusive species

“…Where multiple densities were recorded for one site, the mean density was calculated. Source data may be found in Appendix S1: Table S1 (numbers correspond to ID numbers listed in Table S1): (1) Key West, Florida; 1.8 turtles km −2 (Herren et al, 2018); (2) Rio Lagartos, Mexico; 34 turtles km −2 (Cuevas et al, 2007); (3) Doce Leguas, Cuba; 201 turtles km −2 (ROC, 2000); (4) Isle of Youth, Cuba; 59 turtles km −2 (ROC, 2000); (5) Playa Norte, Dominican Republic; 5.6 turtles km −2 (Leon & Diez, 1999); (6) Bahia de las Aguilas, Dominican Republic; 6.6 turtles km −2 (Leon & Diez, 1999); (7) Cabo Rojo, Dominican Republic; 8.2 turtles km −2 (Leon & Diez, 1999); (8) Los Frailes, Dominican Republic; 58.3 turtles km −2 (Leon & Diez, 1999); (9) Colita, Dominican Republic; 96.8 turtles km −2 (Leon & Diez, 1999); (10) Mona Reef, Puerto Rico; 24.1 turtles km −2 (Diez & van Dam, 2002); (11) Mona cliff wall, Puerto Rico; 28.6 turtles km −2 (Diez & van Dam, 2002); (12) Monita cliff wall, Puerto Rico; 120 turtles km −2 (Diez & van Dam, 2002); (13) Glover's Reef, Belize; 53 turtles km −2 (Strindberg et al, 2016); (14) Arraial do Cabo, Brazil; 1 × 10 −10 turtles km −2 (Mello‐Fonseca et al, 2021); (15) Mauritius; 0.49 turtles km −2 (Reyne et al, 2017); (16) Diego Garcia, Chagos Archipelago; 343 turtles km −2 (present study); (17) Cocos Keeling; 32.5 turtles km −2 (Whiting et al, 2014); (18) Heron Reef, Australia; 3.3 turtles km −2 (Limpus, 1992).…”

“…Despite the circum‐tropical distribution of hawksbill turtles (Mortimer & Donnelly, 2008), relatively few estimates of turtle density on their foraging grounds have been calculated, likely reflecting the inherent difficulties of obtaining these density estimates, but this is likely to change given the increased use of UAV surveys. For immature turtles, reported density estimates vary widely from <0.01 turtles km −2 in Brazil (Mello‐Fonseca et al, 2021) to 201 turtles km −2 in Cuba (ROC, 2000). This wide variation in density might reflect several factors, such as the proximity of large nesting populations that provide a source of juveniles, the varying suitability of different habitats, or the extent of long‐term protection.…”

Evidence of Leatherback Turtles (Dermochelys coriacea) in Brazilian subtropical coastal waters

“…The study area is located within a highly touristic marine protected area with a recently elaborated management plan lacking no-take zones. This region has great ecological and biogeographic importance, harboring tropical and subtropical species, including other species of sea turtles (Mello-Fonseca et al 2021).…”