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

Tiffany M Dawson,Gianna Minton,Angela Formia,Francis Lambert,Kristian Metcalfe,Jacob Nzegoue,Philippe Du Plessis,Philip D Doherty,Sara M Maxwell,Emmanuel Chartrain,Brendan J Godley,Floriane Cardiec,Matthew J Witt,J Michael Fay,Dominic Tilley,Ivan Ndanga,François Boussamba,Georges Mba Asseko ,Pierre Didier Agamboué ,Guy‐Philippe Sounguet ,Jean Churley Manfoumbi ,Brice Didier Koumba Mabert ,Carmen Karen Kouerey Oliwina

doi:10.3389/fmars.2017.00312

Abstract

Understanding the horizontal and vertical habitat of olive ridley sea turtles (Lepidochelys olivacea), a threatened species, is critical for determining regions for protection and relevant gear modifications that may effectively reduce bycatch, the largest threat to this species. Satellite transmitters were used to determine the movement and dive behavior of 21 female olive ridley turtles tagged in Pongara National Park, Gabon during the 2012, 2013, and 2015 nesting seasons. A switching state-space model was used to filter the tracking data and categorize the internesting and post-nesting movements. Gridded utilization distribution (UD) home range analysis of tracking data revealed that the entire core habitat occurred in the Komo Estuary during the internesting period. Within the Komo Estuary, 58% of this core UD occurred in shipping lanes. Dive data from the 2015 tagging season revealed that during the internesting period, turtles spent the majority of their time resting on the estuary seabed. Approximately 20% of all dive time was spent on the bottom and all maximum dive depths corresponded to the depth of the seabed, indicating that bottom set gear during the internesting period may pose the greatest potential for fisheries interactions. National parks currently protect many of the nesting sites and the Gabon Bleu initiative has formally designated 10 new marine parks and a network of community and industrial fishing zones; this data was a layer used in determining the park and zone boundaries. Shared use of the estuary by fisheries, shipping, and olive ridley turtles creates a need for management measures to reduce interactions. Thus, the results from this study can further provide detailed information that can be used to support the development of evidence-based management plans.

Highlights

IntroductionProtecting long-lived, highly migratory marine species is challenging since they encounter multiple threats across broad areas and in different life stages (Witt et al, 2011; 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)
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). 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)
To examine estuary use and inform the process, we created zones similar to those being considered within the planning process and our results indicate that the area around the mouth of the estuary, Zone 2, is a critical area in need of conservation strategies and will be protected as a marine protected area under the newly established Nature Preservation Agency, and likely designated as an expansion of Pongara National Park

Summary

Introduction

Protecting long-lived, highly migratory marine species is challenging since they encounter multiple threats across broad areas and in different life stages (Witt et al, 2011; 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). 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) 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 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)

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Discussion

Conclusion