Natal Origin and Spatiotemporal Distribution of Leatherback Turtle (Dermochelys coriacea) Strandings at a Foraging Hotspot in Temperate Waters of the Southwest Atlantic Ocean

Abstract

Leatherback turtles migrate long distances between nesting beaches and distant foraging areas worldwide. This study analyzes the genetic diversity, life history stage, spatiotemporal distribution, and associated threats of a foraging aggregation in the Southwest Atlantic Ocean. A total of 242 leatherbacks stranded or bycaught by artisanal fisheries were recorded from 1997 to 2021 in Uruguay, with sizes ranging from 110.0 to 170.0 cm carapace lengths, indicating that the aggregation is composed of large juveniles and adults. Results of Bayesian mixed-stock analysis show that leatherbacks come primarily from the West African rookeries, based on mitochondrial DNA sequences obtained from 59 of the turtles representing seven haplotypes, including a novel one (Dc1.7). The main threat identified in the area is the fisheries bycatch but most of the carcasses observed were badly decomposed. There was significant seasonal and interannual variability in strandings that is likely associated with the availability of prey and the intensity of the fishing effort. Taken together, these findings reinforce the importance of these South American foraging areas for leatherbacks and the need to determine regional habitat use and migratory routes across the broader Atlantic region, in order to develop effective conservation measures to mitigate threats both at nesting beaches and foraging areas.

Sea turtle strandings in the temperate Southwest Atlantic: Analysis of drivers and potential causes

“…Once dead, small juvenile green turtles might be more vulnerable to scavenging and might therefore undergo a more rapid decomposition process than large loggerhead and leatherback turtles, thus reducing the chance of carcasses washing ashore. Indeed, the few green turtles observed in this study were severely decomposed in contrast to those found in Uruguay and southern Brazil, where living or freshly dead juvenile green turtles represent more than 50% of the strandings (Monteiro et al, 2016;Vélez-Rubio et al, 2013). Other possible explanations could be differences in turtle abundances (i.e., green turtles might be less abundant in the study area than the rest of the species) or a spatial segregation between green, loggerhead and leatherback turtles (although studies on the broad habitat use of these species suggest the opposite; López-Mendilaharsu et al, 2009;, 2016.…”

“…), thus plastic ingestion does not seem to be a plausible cause of mortality, neither directly (i.e., obstructions) nor indirectly (i.e., debilitation). On the other hand, there was no evidence of collision with vessels as observed in Uruguay (Vélez‐Rubio et al, 2023).…”

“…The green turtle (Chelonia mydas) is the most frequent species found stranded throughout the region, while loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) turtle reports increase towards the south. Olive ridley (Lepidochelys olivacea) and hawksbill (Eretmochelys imbricata) turtles are usually reported across Brazil, with sporadic reports in Uruguay and Argentina (de Farias et al, 2019;González Carman et al, 2011;Monteiro et al, 2016;Vélez-Rubio et al, 2013). The species are subject to interaction with fisheries and marine debris that lead to direct mortality or reduced seasonal reproductive output (Guimarães et al, 2021;López-Mendilaharsu et al, 2020;Marn et al, 2020).…”

“…In this study, we focus on the temperate SW Atlantic, where green (Chelonia mydas), loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) turtles forage seasonally from late austral spring to early fall (González Carman et al, 2011, 2016 Rubio et al, 2013). Fragmentary evidence suggests interaction and spatio-temporal overlap between turtle foraging areas and fishing trawling (González Carman et al, 2015;Prosdocimi et al, 2020), although causes of sea turtle mortality remain understudied compared with other foraging areas in the region and worldwide.…”