On the front line: integrated habitat mapping for olive ridley sea turtles in the southeast Atlantic

Abstract

Aim Knowledge and understanding of marine vertebrate spatial ecology are required to identify sources of threat and highlight areas for conservation. Olive ridley sea turtles Lepidochelys olivacea are in decline in some regions and data for the Eastern Atlantic are sparse. Here, we seek to describe observed, and potential, post-nesting habitats for this species in the southeast Atlantic. We contextualise these with fisheries catch data to identify areas of potential threat from fisheries interaction for this species.Location West coast of Africa, southeast Atlantic. MethodsWe tracked twenty-one female olive ridley turtles, from two nesting sites, between 2007 and 2010.We used ensemble ecological niche modelling, integrated with knowledge on the physical and biological oceanographic environment, to identify regions where environmental variables exist that may be critical in defining post-nesting habitats for this species. We further integrate fisheries catch data to contextualise potential threat from fisheries. ResultsWe describe key areas of observed, and potential, olive ridley turtle occurrence at sea, and reveal that there was considerable overlap of these conspecifics, from two distinct nesting regions, within the Angolan Exclusive Economic Zone (EEZ). With the inclusion of fisheries catch data for the region, we highlight areas that have the potential for conflict with fishing activities known to result in bycatch.Main conclusions This study demonstrates that it is imperative that marine conservation policy recognises the spatial extent of highly migratory species with expansive ranges. It also highlights that deficiencies exist in current knowledge of bycatch, both in gear specificity and in catch per unit effort. With integration of Vessel Monitoring System (VMS) data and those on fisheries catch, knowledge and understanding of bycatch may be improved and this will ultimately facilitate development of appropriate management strategies and long-term sustainability of fisheries and their supporting ecosystems.

Informing Marine Protected Area Designation and Management for Nesting Olive Ridley Sea Turtles Using Satellite Tracking

“…This intense habitat use allows for more targeted conservation measures . Some of the tracked females remained in the area for over a month before switching to the transiting phase and moving south, likely to known foraging grounds off the coast of Angola (Pikesley et al, 2013b). This is the first noted occurrence where olive ridley turtles almost exclusively used estuarine habitat during their internesting period.…”

“…Turtle P had location points within the internesting period that demonstrated an unexpected full behavioral switch from internesting to transiting then back to internesting. During the switch, the turtle remained in the Komo Estuary and later we saw the anticipated long-term behavioral switch to transiting along with a southward movement toward the foraging grounds (Pikesley et al, 2013b). Therefore, we included the short behavioral change in our internesting period analysis.…”

“…Protecting long-lived, highly migratory marine species is challenging since they encounter multiple threats across broad areas and in different life stages Maxwell et al, 2013;Lascelles et al, 2014), often requiring multi-faceted and multi-national conservation efforts (Blumenthal et al, 2006;Gore et al, 2008;Maxwell et al, 2011;Croxall et al, 2012;Pikesley et al, 2013b;Doherty et al, 2017). Several studies have used satellite telemetry to describe the horizontal movement data of large marine vertebrates Block et al, 2011;Hawkes et al, 2011;Hazen et al, 2012;Yurkowski et al, 2016;Citta et al, 2017;Vaudo et al, 2017) and to determine overlap with anthropogenic threats such as fisheries (seabirds: Suryan et al, 2007;Bugoni et al, 2009;Žydelis et al, 2011;sea turtles: da Silva et al, 2011;Witt et al, 2011;Revuelta et al, 2015; marine mammals: Geschke and Chilvers, 2010;Rosenbaum et al, 2014;sharks: Holmes et al, 2014), shipping (marine mammals: Mate et al, 1997;Schorr et al, 2009), and in-water habitat degradation (seabirds: Montevecchi et al, 2012;marine mammals: Johnson and Tyack, 2003;Rosenbaum et al, 2014).…”

Dispersal and dive patterns during the post-nesting migration of olive ridley turtles from French Guiana

“…In the Atlantic Ocean, the post-nesting movements of olive ridley turtles have only been investigated in the eastern population (Pikesley et al 2013), but data are lacking for the largest population nesting in French Guiana, whose conservation status is highly concerning (Kelle et al 2009, Wallace et al 2011, Plot et al 2012. Considering the high oceanographic dynamism along the coast of French Guiana (Frouin et al 1997, Fromard et al 2004) and the contrasting migration patterns of olive ridleys reported else-where (see above), one may predict a pronounced behavioral plasticity in the migration of olive ridley turtles after they have left their nesting site in French Guiana.…”

First report of an olive ridley (Lepidochelys olivacea) inside the Mediterranean Sea

“…The second possibility is of West African origin, which would result in a northward migration. Nevertheless, the movements involved are still not completely understood (Pikesley et al, 2013), although the south-north African route has already been described for green and loggerhead turtles (Carreras et al, 2011(Carreras et al, , 2014Clusa et al, 2014).…”