Using Satellite Tracking to Optimize Protection of Long-Lived Marine Species: Olive Ridley Sea Turtle Conservation in Central Africa

Abstract

Tractable conservation measures for long-lived species require the intersection between protection of biologically relevant life history stages and a socioeconomically feasible setting. To protect breeding adults, we require knowledge of animal movements, how movement relates to political boundaries, and our confidence in spatial analyses of movement. We used satellite tracking and a switching state-space model to determine the internesting movements of olive ridley sea turtles (Lepidochelys olivacea) (n = 18) in Central Africa during two breeding seasons (2007-08, 2008-09). These movements were analyzed in relation to current park boundaries and a proposed transboundary park between Gabon and the Republic of Congo, both created to reduce unintentional bycatch of sea turtles in marine fisheries. We additionally determined confidence intervals surrounding home range calculations. Turtles remained largely within a 30 km radius from the original nesting site before departing for distant foraging grounds. Only 44.6 percent of high-density areas were found within the current park but the proposed transboundary park would incorporate 97.6 percent of high-density areas. Though tagged individuals originated in Gabon, turtles were found in Congolese waters during greater than half of the internesting period (53.7 percent), highlighting the need for international cooperation and offering scientific support for a proposed transboundary park. This is the first comprehensive study on the internesting movements of solitary nesting olive ridley sea turtles, and it suggests the opportunity for tractable conservation measures for female nesting olive ridleys at this and other solitary nesting sites around the world. We draw from our results a framework for cost-effective protection of long-lived species using satellite telemetry as a primary tool.

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

“…Satellite transmitters were attached to nesting females early in the nesting season to capture internesting movements (Maxwell et al, 2011). Olive ridley turtles at Pongara National Park nest between October and January, peaking in late October to early November (Metcalfe et al, 2015a).…”

“…SPLASH10-351C (Wildlife Computers, Redmond WA, USA) were deployed between 27th October and 31st October 2015 (n = 10). Attachment followed techniques described in Maxwell et al (2011), and did not start until the female began oviposition and care was taken not to disturb the nest during attachment. Transmitters were attached to the flattest portion of the two front most vertebral scutes of the carapace using either T308+ TM Epoxy (Powers Fastners, Brewster NY, USA) in 2012 and 2013 or Superbond 1:1 Expoxy Adhesive (FiberGlass Coatings, Inc. St. Petersburg FL, USA) in 2015.…”

“…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).…”

“…Olive ridley turtles (Lepidochelys olivacea), like other sea turtle species, lay multiple clutches of eggs in a nesting season (Plotkin, 2007;Maxwell et al, 2011). Therefore, they remain in the vicinity of nesting beaches for several weeks at a time (Whiting et al, 2007;Hamel et al, 2008;da Silva et al, 2011;Maxwell et al, 2011), termed the internesting period, during which they are susceptible to additional anthropogenic impacts (Pikesley et al, 2013a).…”

“…Therefore, they remain in the vicinity of nesting beaches for several weeks at a time (Whiting et al, 2007;Hamel et al, 2008;da Silva et al, 2011;Maxwell et al, 2011), termed the internesting period, during which they are susceptible to additional anthropogenic impacts (Pikesley et al, 2013a). This period also makes sea turtles ideal candidates for conservation measures because both sexes congregate in the same waters to breed and females typically return to the same beaches to nest multiple times in the same season (Van Buskirk and Crowder, 1994).…”