Satellite Tracking of Post-nesting Green Sea Turtles (Chelonia mydas) From Ras Baridi, Red Sea

Introduction

The success of conservation efforts for animals that migrate between habitats when they reproduce (e.g., birds: Egevang et al., 2010; fish: Tamario et al., 2019; sea turtles: Russell et al., 2005) depends on understanding their population biology as well as the distribution of important habitats and the connections among these habitats in the context of threatening processes that may be encountered (Martin et al., 2007; Lascelles et al., 2014; Gajdzik et al., 2021). Because migrations for reproduction vary in length depending on the species and the distance between the habitats (Luschi, 2013; Lascelles et al., 2014; Dunn et al., 2019), the routes followed may cross international borders and, as a result, migrating animals may encounter different anthropogenic threats in different jurisdictions (López-Hoffman et al., 2017; Palacios-Abrantes et al., 2020; Gajdzik et al., 2021).

Specific details concerning the distribution and use of important habitats and the connecting migratory routes are needed on an appropriate scale so that regional ecosystem management options can be coordinated and tailored to reduce threatening processes (Rees et al., 2016; Lagabrielle et al., 2018; Hernandez-Avila et al., 2020; Gajdzik et al., 2021). This is particularly important in a marginal sea such as the Red Sea, wherein the majority of the coastal margin is managed by six countries (two other countries border the Gulf of Aqaba) (PERSGA, 2006). The Regional Organization for the Conservation of the Environment of the Red Sea and Gulf of Aden (PERSGA) has a prominent role in coordinating the protection of the marine and coastal environments in the region, including developing guidelines for conservation of living marine resources (e.g., Hariri et al., 2002; PERSGA, 2007). However, the existing marine protected areas in the Red Sea do not seem to provide the level of protective conservation management needed by very mobile and migratory species (i.e., dugong, turtles, and sharks, Rouphael et al., 2015). At least part of this situation stems from the lack of information concerning the migratory routes and habitats used by these marine species in the region (Gajdzik et al., 2021). Understanding the connectivity among important habitats (i.e., foraging areas, nesting sites) and the routes used to connect them is essential to development of effective conservation practices (Bolker et al., 2007; Dunn et al., 2019).

Adult marine turtles are bi-directional migratory iteroparous species that spend the majority of their time in their foraging areas where they live and periodically prepare for reproduction (Miller, 1997; Plotkin, 2003). Reproducing female sea turtles migrate to breeding areas and specific nesting beaches where they oviposit several clutches of eggs at intervals of about 2 weeks, and then return to their foraging areas (Meylan et al., 1990; Miller, 1997; Godley et al., 2008). Marine turtles show high fidelity to both their nesting and foraging areas (Limpus et al., 1992; Pilcher et al., 2020; Shimada et al., 2020). During their reproductive migrations green turtles (Chelonia mydas) may utilize coastal and open water corridors (Pendoley et al., 2014; Stokes et al., 2015; Mettler et al., 2019) and/or pass through the territorial waters of one or more nations (Blanco et al., 2012; Rees et al., 2012, 2018; Hart et al., 2018; Pilcher et al., 2021a,b). They may transit areas used for artisanal and/or commercial fishing (Gladstone, 2002; PERSGA, 2003, 2004, 2006, 2007). Although fishing is regulated in every country that borders the Red Sea, the impact of bycatch on the turtle populations is poorly defined (PERSGA, 2003; Mancini et al., 2015).

In recent years, satellite tracking of marine turtle movements between their nesting sites and foraging areas has elucidated much of the previously unknown biology and habitat use (Godley et al., 2002, 2008; Luschi et al., 2003; Blumenthal et al., 2006; Hart et al., 2013, 2017; Luschi and Casale, 2014; Pilcher et al., 2014, 2021a,b; Rees et al., 2016; Ferreira et al., 2020), including bi-directional movements (Limpus and Limpus, 2001; Pilcher et al., 2020). It is now well established that post-nesting turtles which used a particular nesting location return to several different foraging areas (Luschi et al., 1996; Bjorndal et al., 2005; Blumenthal et al., 2006; Bolker et al., 2007; Bradshaw et al., 2017; Shimada et al., 2020). Conversely, turtles foraging in one general habitat disperse to several different nesting locations (i.e., mixed stock) (Limpus et al., 1992; Dethmers et al., 2010; Carreras et al., 2011; Jensen et al., 2013; Read et al., 2015; Dutton et al., 2018). In combination with other methods (e.g., genetics), satellite tracking of marine turtles can be used to better define the uniqueness of nesting populations and shared use of habitat (Godley et al., 2010; Hart et al., 2012, 2020; Bourjea et al., 2015; Jensen et al., 2019). In addition, satellite tracking of marine species has contributed to identifying important foraging areas (Pilcher et al., 2014; Stokes et al., 2015, 2019), threatening processes (Hays et al., 2003; Hart et al., 2018), and helped with development of conservation and management options (Hays et al., 2014, 2019, 2021; Pendoley et al., 2014; Hays and Hawkes, 2018).

However, a better understanding of the migration patterns of marine species is necessary to support conservation efforts and to identify potential areas of threatening processes in the Red Sea (Gajdzik et al., 2021), particularly for species that are globally or regionally at risk. Of the five species of sea turtles that occur in the Red Sea, at least infrequently (Mancini et al., 2015), the green turtle (Chelonia mydas) and the hawksbill (Eretmochelys imbricata) are regularly observed. The loggerhead (Caretta caretta), the olive-ridley (Lepidochelys olivacea), and the leatherback (Dermochelys coriacea) are less commonly seen (Ross and Barwani, 1982; Frazier et al., 1987; Pilcher et al., 2006; PERSGA, 2010; Mancini et al., 2015; Miller, 2020). In the northern Indian Ocean region, the herbivorous green turtle (Bjorndal, 1997; Stokes et al., 2019; Esteban et al., 2020) is classified as Vulnerable (Mancini et al., 2019) and is listed in Appendix 1 of the Convention on International trade of Endangered Species (CITES, 2021).

Although the information concerning the routes used by green turtles as they migrate between nesting sites and foraging areas in the Arabian region is increasing (Pilcher et al., 2020, 2021a,b) much remains to be determined. Currently, little is known about the connectivity between nesting sites and foraging areas for green turtles (Mancini et al., 2015, 2018; Pilcher et al., 2021b) or about foraging area inclusion in existing Marine Protected Areas (MPAs) in the Red Sea because a relatively low number of green turtles have been tracked to foraging areas (Rouphael et al., 2015; Gajdzik et al., 2021). In 2010 satellite transmitters were used to identify the migratory pathways of four green turtles that had nested at Zabargad Island (off shore of Egypt) (Attum et al., 2014). This study provided evidence of the locations of foraging areas associated with nesting in the northern Red Sea (Attum et al., 2014). Recently, three green turtles were followed using satellite transmitters to foraging areas in the southern portion of the Red Sea from nesting areas located in Oman (Rees et al., 2012, 2018; Pilcher et al., 2021b). Although, the migrations to foraging areas by sea turtles that nest at sites in the northern Red Sea have received little attention (Attum et al., 2014; Mancini et al., 2015, 2018), their use of nesting sites and internesting habitat has recently been described in detail (Shimada et al., 2021a,b).

Surveys of the biology of green turtles nesting at Ras Baridi began in 1987 (Miller, 1989). In 1989 the National Center for Wildlife (NCW) [formerly the National Commission for Wildlife Conservation and Development] initiated detailed studies of multiple aspects of the nesting turtles, including their morphology and their nesting success (Al-Merghani et al., 2000; Pilcher and Al-Merghani, 2000; Al-Mansi et al., 2003; Al-Mansi, 2016). In addition to studies concerning the turtles, physical characteristics of the beach and environmental factors were studied to determine their impact on the hatching success of eggs (Al-Mansi et al., 1991; Pilcher, 1999; Tanabe et al., 2020). Jensen et al. (2019) defined a unique genetic allele from the green turtles nesting at Ras Baridi. Recently, an assessment of the nesting population and the use of internesting habitat in the vicinity of the Ras Baridi nesting beaches was described (Shimada et al., 2021a).

In late 2009 the NCW began a research program with the goal of identifying the migratory routes and the foraging areas used by green turtles nesting at Ras Baridi. Herein we present the results of satellite tracking of 16 post-nesting green turtles from Ras Baridi on the Red Sea Coast of the Kingdom of Saudi Arabia between 2009 to 2014.

Materials and Methods

Study Area

Ras Baridi (N 24° 16′ 24.33″; E 37° 37′35.30″) is located 60 km north of Yanbu on the eastern coast of Saudi Arabia, facing the north-central Red Sea (Figure 1) (for regional context see: Head, 1987; Tesfamichael and Pauly, 2016; Carvalho et al., 2019; Supplementary Material). Green turtles are the main species nesting at Ras Baridi, where the nesting season extends from August through November/December (Pilcher and Al-Merghani, 2000; Shimada et al., 2021b). An estimated 178 to 330 green turtles nest on the five well-developed pocket beaches (Shimada et al., 2021b; Figure 1). The beaches range from 50 to 1500 m long and are about 50 m wide. The other species that nests at Ras Baridi, at least infrequently, is the hawksbill (Eretmochelys imbricata) (Shimada et al., 2021b), which nests in low numbers throughout the region (Miller, 2020).