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

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.

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

“…The mean maximum dive depths for these instrumented turtles (Fig. 2) are similar to dive depths recorded for turtles in other parts of the world (Australia, [38,39]; French Guiana, [40]), as well as from previous studies in this region on nesting female turtles [37], suggesting potentially 'normal' dive behavior of turtles post-release, though we caution that the tags did not collect the full dive profile data to allow us to fully assess behavior, and that Turtle B's tag collected only 3 days of data before death and subsequent release. We additionally caution that there may be a greater risk for decompression sickness when capture occurs at greater depths, or in other regions of the world where water temperatures are colder.…”

“…The greatest straight-line distance was 270 km south in 30 days (Turtle A; Table 1), but distance per day was as low as 0.9 km/d for Turtle C which appeared to remain in the vicinity where capture occurred near the mouth of the Komo Estuary. The Komo Estuary is adjacent to a known nesting site, and some olive ridley turtles nesting there are known to remain resident in the area for the months following nesting [37]. The nesting season occurs from September through March with a peak in November [32], and this turtle was recorded in the area in the area in July and August, further suggesting this may be a resident foraging ground during other parts of the year.…”

Using Cumulative Impact Mapping to Prioritize Marine Conservation Efforts in Equatorial Guinea

“…These results are not particularly surprising as Equatorial Guinea hosts an important fisheries sector (Belhabib et al, 2016), as well as offshore petrochemical infrastructure and shipping, that are largely concentrated on the continental shelf. Similar trends are also evident in neighboring countries like Gabon and the Republic of Congo, where continental shelf waters are subject to more persistent pressure from human activities such as shipping and fisheries than offshore waters (Dawson et al, 2017;Metcalfe et al, 2018;Pikesley et al, 2018).…”

“…For leatherback and olive ridley sea turtles, location data were derived from platform transmitter terminals (PTT) attached to nesting females in Gabon (olive ridley: n = 60 individuals; leatherback: n = 37 individuals); attachment and tag details provided in previously published studies (Witt et al, 2008(Witt et al, , 2011Maxwell et al, 2011;Pikesley et al, 2013;Dawson et al, 2017). Satellite telemetry data were collected using the Argos satellite system (CLS, 2016) and downloaded with the Satellite Tracking and Analysis Tool [STAT; Coyne and Godley (2005)].…”

Route Fidelity during Marine Megafauna Migration

“…Empirical approaches, such as animal telemetry, can be used to develop and assess data-based models of animal movement, with the strongest models creating opportunities to inform conservation and management decision making with respect to both space and time. At a fundamental level, telemetry studies remain uniquely powerful ways to inform marine conservation through databased demonstrations of when and where marine megafauna are located across vast expanses of open-ocean (Shillinger et al, 2008;Gredzens et al, 2014;Maxwell et al, 2016;Dawson et al, 2017). Technological advances in animal telemetry, combined with advances in remote sensing (e.g., Figures S3-S8), have created unprecedented opportunities to retrospectively extract and analyse the geophysical and oceanographic conditions experienced by individual migrants during long-distance migration.…”