A novel approach to estimate the distribution, density and at-sea risks of a centrally-placed mobile marine vertebrate

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Formulating management strategies for mobile marine species is challenging, as knowledge is required of distribution, density, and overlap with putative threats. As a step towards assimilating knowledge, ecological niche models may identify likely suitable habitats for species, but lack the ability to enumerate species densities. Traditionally, this has been catered for by sightings-based distance sampling methods that may have practical and logistical limitations. Here we describe a novel method to estimate at-sea distribution and densities of a marine vertebrate, using historic aerial surveys of Gabonese leatherback turtle (Dermochelys coriacea) nesting beaches and satellite telemetry data of females at sea. We contextualise modelled patterns of distribution with putative threat layers of boat traffic, including fishing vessels and large ship movements, using Vessel Monitoring System (VMS) and Automatic Identification System (AIS) data. We identify key at-sea areas in which protection for inter-nesting leatherback turtles could be considered within the coastal zone of Gabonese Exclusive Economic Zone (EEZ). Our approach offers a holistic technique that merges multiple datasets and methodologies to build a deeper and insightful knowledge base with which to manage known activities at sea. As such, the methodologies presented in this study could be applied to other species of sea turtles for cumulative assessments; and with adaptation, may have utility in defining critical habitats for other central-place foragers such as pinnipeds, or sea bird species. Although our analysis focuses on a single species, we suggest that putative threats identified within this study (fisheries, seismic activity, general shipping) likely apply to other mobile marine vertebrates of conservation concern within Gabonese and central African coastal waters, such as olive ridley sea turtles (Lepidochelys olivacea), humpback dolphins (Sousa teuszii) and humpback whales (Megaptera novaeangliae).We thank the following for support and funding: CARPE (Central African Regional Program for the Environment, Darwin Initiative, EAZA ShellShock Campaign, Gabon Sea Turtle Partnership with funding from the Marine Turtle Conservation Fund (United States Fish and Wildlife Service, U.S. Department of the Interior), Harvest Energy, Large Pelagics Research Centre at the University of Massachusetts (Boston), NERC, Vaalco Energy and the Wildlife Conservation Society. We are sincerely grateful to the field teams and logistics staff who assisted in the aerial and ground surveys and with field-site assistance. BJG and MJW receive funding from the Natural Environment Research Council (NE/J012319/1), the European Union and the Darwin Initiative

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

This is the final version. Available from Frontiers Media via the DOI in this record. 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

Mismatches in Scale Between Highly Mobile Marine Megafauna and Marine Protected Areas

Marine protected areas (MPAs), particularly large MPAs, are increasing in number and size around the globe in part to facilitate the conservation of marine megafauna under the assumption that large-scale MPAs better align with vagile life histories; however, this alignment is not well established. Using a global tracking dataset from 36 species across five taxa, chosen to reflect the span of home range size in highly mobile marine megafauna, we show most MPAs are too small to encompass complete home ranges of most species. Based on size alone, 40% of existing MPAs could encompass the home ranges of the smallest ranged species, while only \u3c 1% of existing MPAs could encompass those of the largest ranged species. Further, where home ranges and MPAs overlapped in real geographic space, MPAs encompassed \u3c 5% of core areas used by all species. Despite most home ranges of mobile marine megafauna being much larger than existing MPAs, we demonstrate how benefits from MPAs are still likely to accrue by targeting seasonal aggregations and critical life history stages and through other management techniques

Mismatches in Scale Between Highly Mobile Marine Megafauna and Marine Protected Areas

Marine protected areas (MPAs), particularly large MPAs, are increasing in number and size around the globe in part to facilitate the conservation of marine megafauna under the assumption that large-scale MPAs better align with vagile life histories; however, this alignment is not well established. Using a global tracking dataset from 36 species across five taxa, chosen to reflect the span of home range size in highly mobile marine megafauna, we show most MPAs are too small to encompass complete home ranges of most species. Based on size alone, 40% of existing MPAs could encompass the home ranges of the smallest ranged species, while only \u3c 1% of existing MPAs could encompass those of the largest ranged species. Further, where home ranges and MPAs overlapped in real geographic space, MPAs encompassed \u3c 5% of core areas used by all species. Despite most home ranges of mobile marine megafauna being much larger than existing MPAs, we demonstrate how benefits from MPAs are still likely to accrue by targeting seasonal aggregations and critical life history stages and through other management techniques

Sea turtles and survivability in demersal trawl fisheries: Do comatose olive ridley sea turtles survive post-release?

Abstract Incidental capture of air-breathing species in fishing gear is a major source of mortality for many threatened populations. Even when individuals are discarded alive, they may not survive due to direct injury, or due to more cryptic internal physiological injury such as decompression sickness. Post-release mortality, however, can be difficult to determine. In this pilot study, we deployed survivorship pop-up archival tags (sPAT) (n = 3) for an air-breathing species, the olive ridley sea turtle (Lepidochelys olivacea), one of the first studies to do so. We found that at least two of the three turtles survived after being captured in demersal fish trawl nets and being resuscitated from a comatose state following standard UN Food and Agriculture Organization guidelines. One turtle died; however, the absence of a change in light level but continued diving activity suggested that the turtle was likely predated. Whether capture contributed to the turtle’s susceptibility to predation post-release is unknown, and average tow duration during this fishing trip was similar in duration to that of a turtle that survived (1.5 h). The two surviving turtles displayed normal horizontal and vertical movements based on previous tagging studies. This study suggests that resuscitation techniques may be effective; however, additional study is necessary to increase sample sizes, and to determine the severity of decompression sickness across different levels of activity and in other fishing gears. This will result in better population mortality estimates, as well as highlight techniques to increase post-release survivorship

A first estimate of sea turtle bycatch in the industrial trawling fishery of Gabon

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Gabon hosts nesting grounds for several sea turtle species, including the world’s largest rookery for the leatherback turtle (Dermochelys coriacea), Africa’s largest rookery for the olive ridley turtle (Lepidochelys olivacea) and smaller aggregations of the hawksbill turtle (Eretmochelys imbricata) and green turtle (Chelonia mydas). To assess the level of incidental captures of turtles by the Gabonese trawl fishery, an onboard observer program was conducted in the period 2012–2013. A total of 143 turtles were captured by 15 trawlers during 271 fishing days. The olive ridley turtle was the main species captured (80% of bycaught turtles), with mostly adult-sized individuals. The remaining 20% included green turtles, hawksbill turtles, leatherback turtles and undetermined species. Bycatch per unit of effort (BPUE) of olive ridley turtles varied greatly depending on the period of the year (range of means: 0.261–2.270). Dead and comatose turtles were 6.2 and 24.6% respectively (n = 65). By applying the available fishing effort to two BPUE scenarios (excluding or considering a seasonal peak), the total annual number of captures was estimated as ranging between 1026 (CI 95% 746–1343) and 2581 (CI 95% 1641–3788) olive ridley turtles, with a mortality ranging from 63 (CI 95% 13–135) to 794 (CI 95% 415–1282) turtles per year depending on the scenario and on the fate of comatose turtles. Such a potential mortality may be reason for concern for the local breeding population of olive ridley turtles and recommendations in terms of possible conservation measures and further research are given.Funding for the observer program and training was provided by the Government of Gabon, the Marine Turtle Conservation Fund (Fish and Wildlife Service, US Department of the Interior), NOAA (US Department of Commerce, Division of International Affairs), UK Darwin Initiative (Department for Environment Food and Rural Affairs), and the World Wide Fund for Nature

Fulfilling global marine commitments; lessons learned from Gabon

As part of the Post-2020 Biodiversity Framework, nations are assessing progress over the past decade in addressing the underlying drivers that influence direct pressures on biodiversity and formulating new policies and strategies for the decade to come. For marine conservation, global marine protected area (MPA) coverage is still falling short of the 10% target set in 2010. Here we show that while this reflects a lack of progress in many low- and middle-income countries, a few of these nations have met or exceeded international commitments. To provide an in-depth explanation of how this was achieved in Gabon, we summarize the lessons learnt by our consortium of policy makers and practitioners who helped implement a comprehensive and ecologically representative network of 20 MPAs. We show the importance of creating a national framework, building long-term stakeholder support, and focusing on research that guides implementation and policy; and outline a four-step approach that countries and donors could use as an example to help meet international commitments. By responding to calls to share lessons learned to inform future Convention on Biological Diversity targets, we show how Gabon's experiences could inform change elsewhere