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Ecology and conservation of green turtles in Guinea-Bissau

  • MARE – Marine and Environmental Sciences Centre, ISPA / University of Exeter
102 Testudo Vol. 9 No. 3
Ecology and conservation of green turtles in
Ana R. Patrício1,2*, Castro Barbosa3, Paulo Catry1 and Aissa Regalla3
1MARE – Marine and Environmental Sciences Centre, ISPA – Instituto
Universitário de Ciências Psicológicas, Socias e da Vida, Lisbon, 1149 –
041, Lisboa, Portugal
2Centre for Ecology and Conservation, University of Exeter, Cornwall
Campus, Penryn TR10 9FE, UK
3Instituto da Biodiversidade e das Áreas Protegidas, Dr. Alfredo Simão
da Silva (IBAP), CP70, Bissau, Guiné-Bissau
*Corresponding author: Ana R. Patricio, email:
Green turtle, a great traveller
Green turtles (Chelonia mydas) are a highly migratory species, establishing
connectivity between distant areas (Scott et al. 2014a). They venture into
their first great migration as soon as they emerge from their nests at sandy
beaches and crawl into the sea, where they associate with prevalent currents
to disperse into the open ocean (Putman et al. 2010; Scott et al. 2014b).
During this oceanic period, they can travel several thousand kilometres, living
an epipelagic life-style, which can last 3-5 years (Reich et al. 2007). After
this stage, juvenile turtles recruit to shallow coastal foraging areas, where
they may remain resident until adulthood, or travel between nearby feeding
grounds (Bolten et al. 2003).
During the dispersal stage of green turtles, in the first years of life, animals
from various populations mix with the help of ocean currents (Patrício et al.
2017). As a result, in coastal feeding areas, it is common to have aggregations
composed of animals from several nesting beaches (mixed stocks; Bolker et
al. 2007). It is essential to know the origin of these animals, to understand
the threats to which they are subjected throughout their life cycle, and to
establish collaborations between countries that share this resource. Through
genetic characterisation of individual turtles, it is possible to compare mixed-
stock foraging aggregations with nesting populations, to estimate their
rookery origin.
Finally, as adults, they perform cyclic breeding migrations, every two to
five years on average (Seminoff et al. 2015), between nesting beaches and
neritic foraging grounds, covering hundreds to thousands of kilometres each
time (Scott et al. 2014a). For such a vagrant animal as the green turtle, the
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effective conservation of populations depends highly on understanding the
links established between the different areas occupied throughout their life
cycle, so that the full-range of threats can be identified and addressed.
Conservation challenges
After centuries of overexploitation for the consumption of meat, eggs, oil
and soup (Rieser 2012), the green turtle has been recovering in most of its
distribution range, thanks to decades of conservation efforts (Mazaris et al.
2017). However, this species is now facing several different anthropogenic-
induced threats, with bycatch (Wallace et al. 2010), plastic pollution (Wilcox
et al. 2018; Duncan et al. 2019) and coastal development (Biddiscombe et al.
2020) having the greatest impact. Green turtles are also highly vulnerable to
upcoming climate change (Varela et al. 2018; Patrício et al. 2021) and these
pressures can act synergistically, further enhancing negative impacts.
The conservation challenges are ever greater, as the aforementioned threats
are ubiquitous in our seas and coastal habitats, and even more so because
the source/s of some threats are impossible to pinpoint (e.g. plastic pollution
or climate change). Ensuring the protection of a range of suitable habitats
to allow populations to thrive and adapt is, thus, a priority for population
continuity. However, to define which areas are key to protect we must first
understand the spatial distribution of populations and the connectivity they
establish, through dispersal and migration, between breeding and foraging
sites. This is particularly urgent for areas that are poorly known, due to
limited research in the past, such as West Africa.
Major population of green turtles in West Africa
West Africa is a region of global importance for green turtles, hosting one
of the largest populations globally (SWOT 2011; Patrício et al. 2019). The
core breeding rookery for this population is located at Poilão Island, in the
southeast limit of the Bijagós Archipelago, Guinea-Bissau (Catry et al. 2009;
Barbosa et al. 2018), where an average of 27,251 clutches are laid annually
(2013-2017; Broderick & Patrício 2019). Lower numbers of nesting occur
on several other islands of the archipelago and on the northern continental
coast of Guinea-Bissau (Catry et al. 2002). There is also nesting in other
countries of the region, but in much lower numbers (~10 to ~100 nests/year;
Agyekumhene et al. 2017).
Foraging aggregations are also known to occur across the Bijagós (Barbosa
pers. comm.), with an important developmental area around the islands of
Unhocomo and Unhocomozinho (Catry et al. 2010), which has yet to be
genetically characterized. Important green turtle foraging areas are also
known at Cabo Verde (Marco et al. 2011; Monzón-Argüello et al. 2010),
at the National Park of the Banc d’Arguin (PNBA), in Mauritania (Cardona
© British Chelonia Group + Ana R. Patrício,
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104 Testudo Vol. 9 No. 3
et al. 2009; Godley et al. 2010), around the Bijol Islands, in The Gambia
(Hawkes et al. 2008) and in Guinea (Fretey et al. 2008). Additionally, bycatch
data support the presence of foraging green turtles in other countries of the
region (e.g. Ghana, Togo and Benin; Agyekumhene et al. 2017).
Potentially, several of the foraging aggregations in West Africa are linked
to the major rookery of the Bijagós, yet there is a paucity of tracking and of
genetic data to confirm this hypothesis. The exception is the connectivity with
the PNBA, which was confirmed through satellite tracking of post-breeding
females from Poilão Island (Godley et al. 2010). However, the sample size for
this study was limited (n = 4) and a more recent work suggests the existence
of plasticity in foraging strategies for this population (Patrício et al. 2019),
possibly associated with multiple post-breeding destinations.
Study aims
Considering the challenges intrinsic in the conservation of migratory species,
and the knowledge gaps in the study region, we set out to understand the
spatial distribution of green turtles nesting at Poilão Island, and the connectivity
between juvenile green turtles from the Bijagós and Atlantic rookeries.
Specifically, we use 1) genetic analyses to assess the origin of the juvenile
green turtles foraging in the Bijagós archipelago, and 2) satellite telemetry
to investigate the inter-nesting spatial distribution, the post-breeding
migrations and the foraging habitat use by green turtles that nest at Poilão
Island. Ultimately, our results will provide the scientific basis to inform marine
spatial planning and other conservation measures in the region, aimed at
protecting this resource.
Study site
The Bijagós is a deltaic archipelago west of the mainland coast of Guinea-Bissau.
It comprises 88 islands and islets and covers an area of 10,000km2. Only 21 of
the islands are permanently inhabited, with a human population of ca. 25,000,
mostly from the Bijagó ethnic group (Campredon & Catry 2016). Some of the
uninhabited islands are considered sacred and only accessed during religious
and social ceremonies. These traditional restrictions have contributed to the
protection of the archipelago's remarkable biodiversity, which includes several
other charismatic species besides the green turtle, notably the West African
manatee (Trichechus senegalensis), the Atlantic humpback dolphin (Sousa
teuszii) and the ‘marine’ hippopotamus (Hippopotamus amphibious). A large
part of the islands is surrounded by mangroves and extensive mudflats, which
provide shelter and developmental areas for many species of fish, molluscs,
and crustaceans, and feeding grounds for wintering shorebirds. In addition
to the green turtle, three other species of sea turtle nest on the beaches
of the archipelago: the olive ridley (Lepidochelys olivacea), leatherback
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(Dermochelys coriacea), and hawksbill (Eretmochelys imbricata). Loggerhead
turtles (Caretta caretta) are present in the surrounding waters, but do not
nest in Guinea-Bissau. This rich biodiversity led to the establishment of three
marine protected areas (MPAs) within the archipelago, and to the designation
of the Bijagós-Bolama Biosphere Reserve by UNESCO in 1996.
It is within one of the archipelago’s MPAs, the João Vieira-Poilão Marine
National Park (PNMJVP in its Portuguese acronym), in the southeast limit of
the Bijagós, at Poilão Island, that the main green turtle rookery is located
(Fig. 1a). Poilão (N 10.87°, W 15.72°) is a low-lying small island, with an area
Fig. 1. Upper, right to left: location of the Bijagós Archipelago in West Africa and zoomed
map of the Bijagós Archipelago showing the location of the study sites; a. Poilão Island and
b. Unhocomo and Unhocomozinho Islands (U&U). Dashed line shows limits of the João-Vieira
Poilão National Marine Park (PNMJVP). Lower, right to left: a. Outer limits and delineation of
the no-take zone (central zone) of the PNMJVP, and islands within the MPA, including Poilão
(yellow diamond); b. Unhocomo and Unhocomozinho Islands (U&U) and in-water capture
locations (yellow diamonds).
© British Chelonia Group + Ana R. Patrício,
Castro Barbosa, Paulo Catry and Aissa Regalla 2021
106 Testudo Vol. 9 No. 3
of 43ha, covered by undisturbed tropical forest, and surrounded by a rocky
subtidal zone. It has a tropical climate, with the rainy season between May
and November, peaking in August, coinciding with the peak of the nesting
Besides Poilão, this MPA has three other islands – João Vieira, Cavalos
and Meio – and three islets – Cabras, Águias and Baixo de Gaivotas. After
Poilão, most nesting occurs on Cavalos (2,507 nests in 2016), followed by
Meio (2,063 nests in 2016) and João Vieira (596 nests in 2011; Barbosa et al.
2018). Although there is marked interannual variability in nesting numbers,
the relationship of nesting abundance (absolute number of nests) among
these islands has been consistent over the years. Nesting density (nests per
square metere) is very high at Cabras Islet, but nesting abundance has yet to
be quantified there. The other two islets are submersed during high tide and
thus not suitable for nesting.
The main green turtle feeding and developmental grounds in the Bijagós
are located at the westernmost limit of the archipelago, in the shallow waters
surrounding the islands of Unhocomo and Unhocomozinho (N 11.31º, W
16.40º; Fig. 1b). These feeding grounds are characterized by areas of rocky
seabed covered with algae (Caulerpa sp., Sargassum sp. and Dictyota sp.),
adjacent to mangroves (Rhizophora sp.) and sandy areas, with low-density
seagrass patches (Halodule sp.) and sparse rocks covered in algae. The sea
surface temperature average is 27.3°C (ranging from 25.1°C to 29.5°C).
To assess the connectivity of green turtles from the Bijagós, we collected
biopsy samples from juvenile green turtles foraging around Unhocomo and
Unhocomozinho and deployed satellite tags on females found nesting at
Poilão Island. We also continued the standard monitoring of nesting activities
and report the nesting number estimates for the last 15 years.
Monitoring of nesting activities
Since 2007, IBAP has used a standard protocol to monitor the nesting activities
of green turtles at Poilão. Because the island is, for its most part, surrounded
by intertidal rocks which are exposed at low tide (Fig. 2), the turtles must wait
for high tide to access the beach to nest. It is therefore around the peak of
the night high tide that IBAP patrols the 2km beach to assess the number of
nesting females. In the early morning, there is an additional survey to count
tracks from the previous night, and to count the number of turtles that are
stranded on the intertidal rocks. These turtles usually rest in intertidal pools,
where they can keep their body temperatures within tolerable limits before
returning to the sea with the high tide.
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Monitoring is conducted annually from August to November, to encompass
the nesting distribution. Because nesting density at Poilão is too high to allow
counting all the nests, we estimate the number of clutches laid per season
by multiplying the number of nesting female emergences by 0.813, to adjust
for nesting success in Poilão (Catry et al. 2009).
Genetic assessment
We collected biopsy samples from the epidermis of juvenile green turtles found
foraging at Unhocomo and Unhocomozinho for genetic analysis. The number
of biopsy samples collected was minimal without jeopardising statistically
valid results, and the sampling techniques chosen have been refined over the
years of practice to minimise impact on animals (e.g. reduced handling time,
reduced size of samples). All procedures used are widely applied in the field
of sea turtle research and were carried out by trained personnel following
recommended guidelines (NMFS-SFC, 2008) in order to reduce stress to the
animals and ensure their welfare.
To capture turtles, we used an entanglement net (800m long, 20cm mesh
size) which was deployed from a pirogue operated by Bijagós fishers. Water
depth varied from 4-1m. Each net set lasted one hour, and we swam the
length of the net throughout this period to look for entangled turtles (i.e.
three people started at equidistant points along the net and kept swimming
to ensure that turtles were released from the net as fast as possible). Most
turtles did not get entangled; instead, they would swim along the net trying
to find a way out, and were captured by hand. Once captured, we brought
the turtles to a logistic vessel anchored next to the net.
Once at the logistic vessel, we measured the curved carapace length (CCL)
using a flexible metric tape to the closest millimetre for each individual and
tagged both front flippers with uniquely numbered, self-piercing Inconel tags
(©National Band & Co). We used sterile biopsy punches (6mm diameter) to
Fig. 2. Left: Poilão Island, in the Bijagós Archipelago, Guinea-Bissau, with intertidal rocks
exposed due to low tide. Right: green turtles waiting for high tide to return to the sea.
Photos by IBAP (left) and Rita Patricio (right).
© British Chelonia Group + Ana R. Patrício,
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108 Testudo Vol. 9 No. 3
collect skin samples from the right shoulder, after disinfecting the area with
a diluted povidone-iodine solution. We used single-use surgical gloves and
biopsy punches for each new sample. Samples were stored in 96% ethanol,
inside 2ml Eppendorf tubes uniquely labelled.
We will extract the DNA of samples and amplify specific regions of the
mitochondrial DNA (i.e. ~860bp fragment from control region and short
tandem repeats; Shamblin et al. 2012; Tikochinski et al. 2018), used in sea
turtle population genetic assessments and shown to improve resolution
of connectivity studies (Shamblin et al. 2012; Tikochinski et al. 2018). We
will then compare the haplotypes found in the Bijagós with haplotypes
throughout Atlantic green turtle rookeries, to estimate the contribution of
each putative source to this foraging aggregation.
Satellite tracking
During the 2018 to 2020 nesting seasons at Poilão Island, we deployed
45 satellite tags on nesting females (Fig. 3) to study their movements. We
also applied flipper tags and passive integrated transponders (PIT) tags to
each turtle. To deploy the satellite transmitters, we waited for the turtles to
start laying their eggs and then executed the attachment procedure within
20 minutes, while the turtle continued to lay. First, we sanded the second
vertebral scute where the tag was to be attached and cleaned it with acetone.
Then we applied a base of fibreglass and fast-dry epoxy (®Devcon-5min
Epoxy) and allowed it to dry for five minutes. A ‘cushion’ for the tag was then
made with magic metal (®Loctite) before we pressed the tag gently on top
of the fibreglass base and allowed ten minutes for it to dry further. For the
last step, we applied again fibreglass with epoxy around the tag to secure
it, and allowed five minutes for the second fibreglass and epoxy application
to dry. All turtles continued with their nesting activity throughout the tag
application, successfully laid their eggs, and covered and camouflaged the
nest; therefore, we are confident that the procedure did not disturb them.
Preliminary results
This population shows high inter-annual variability in nesting numbers (Fig.
4), and the year 2020 was a record year, with over 60,000 clutches estimated
at Poilão Island alone (Fig. 4). This variability in nesting numbers across years is
common among sea turtle populations, particularly among green turtles, and
it is potentially linked to the availability of food resources at foraging areas, in
addition to the natural reproductive cycle of breeding females (Broderick et al.
2001). The very high number of clutches in 2020 reinforces the importance
of this population for the maintenance of foraging aggregations across the
West Africa region, and potentially, the Atlantic.
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Testudo Vol. 9 No. 3 109
At Unhocomo and Unhocomozinho we captured a total of 103 green turtles,
of which 99 were immatures, ranging from recruit (i.e. a turtle that recently
moved from oceanic to neritic waters) to subadult sizes (CCL: 35-79cm; Fig. 5),
indicating that this is mainly a developmental site. We also caught four adults,
two females and two males (CCL: 87.5-97.0cm). The genetic assessment
at Unhocomo and Unhocomozinho will allow us to estimate the origin of
this foraging aggregation, and estimate the connectivity between Atlantic
nesting beaches and this juvenile developmental area, further highlighting the
importance of the Bijagós Archipelago for Atlantic green turtles.
Thanks to satellite tracking technology, we have obtained daily movements
of green turtles from this large population and have some very interesting
findings. The spatial distribution during the inter-nesting intervals will be key
to understanding whether the current limits of the PNMJVP ensure adequate
protection to turtles during the nesting season. Tracking data from their post-
nesting migrations will allow us to understand the connectivity established
between Poilão and foraging grounds along West Africa. We have found
that this population feeds in coastal areas in Guinea-Bissau, Senegal, The
Gambia and Mauritania. Knowledge of the spatial distribution of this
Fig. 3. Green turtle with ®Wildlife Computers Spot tag, at Poilão Island, Guinea-Bissau.
Photo by Rita Patricio.
© British Chelonia Group + Ana R. Patrício,
Castro Barbosa, Paulo Catry and Aissa Regalla 2021
110 Testudo Vol. 9 No. 3
Fig. 4. Estimated number of green turtle clutches at Poilão Island, in the Bijagós Archipelago,
Fig. 5. Size-classes of green turtles found foraging at the water surrounding the islands of
Unhocomo and Unhocomozinho, in the Bijagós Archipelago, Guinea-Bissau. Dark blue: recruits
(i.e., turtles that have recently moved from oceanic to neritic waters); light blue: resident
juveniles; yellow: subadults; orange: adults.
© British Chelonia Group + Ana R. Patrício,
Castro Barbosa, Paulo Catry and Aissa Regalla 2021
Testudo Vol. 9 No. 3 111
population outside the breeding period will allow us to understand the range
of threats that this population may be exposed to, including identifying
areas of conflict with fishing activities. Ultimately, these results should help
establish collaborations among sea turtle conservation projects within the
region, and potentially help define areas in need of protection.
This work is conducted through a partnership between the MARE – ISPA,
Instituto Universitário and the Instituto da Biodiversidade e das Áreas
Protegidas Dr. Alfredo Simão da Silva (IBAP), and it is funded by the MAVA
Foundation and the Regional Partnership for Coastal and Marine Conservation
(PRCM), through the projects ‘Consolidation of sea turtle conservation at the
Bijagós Archipelago, Guinea-Bissau’ and ‘Survie des Tortues Marines’, with
additional support from the Rufford Foundation and the British Chelonia
Group, to whom we are deeply thankful. Research permits for this work
were obtained from national and local authorities in Guinea-Bissau, namely
the Instituto da Biodiversidade e das Áreas Protegidas, Dr. Alfredo Simão da
Silva (IBAP), which was also involved in fieldwork and in all outputs related
to this research. Fieldwork was also conducted with the collaboration of
members from local communities of the Bijagós, particularly from the islands
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Climate change is a threat to marine turtles that is expected to affect all their life stages. To guide future research, we conducted a review of the most recent literature on this topic, highlighting knowledge gains and research gaps since a similar previous review in 2009. We suggest a number of research priorities for an improved understanding of how climate change may impact marine turtles, including: improved estimates of primary sex ratios, assessments of the implications of female-biased sex ratios and reduced male production, assessments on the variability in upper thermal limits of clutches, models of beach sediment movement under sea level rise, and assessments of impacts on foraging grounds. Lastly, we suggest that it is not yet possible to recommend manipulating aspects of turtle nesting ecology as the evidence-base with which to understand the results of such interventions is not robust enough, but that strategies for mitigation of stressors should be helpful, providing they consider the synergistic effects of climate change and other anthropogenic-induced threats to marine turtles, and focus on increasing resilience.
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The Intergovernmental Panel on Climate Change predicts that sea levels will rise by up to 0.82 m in the next 100 years. In natural systems, coastlines would migrate landwards, but because most of the world’s human population occupies the coast, anthropogenic structures (such as sea walls or buildings) have been constructed to defend the shore and prevent loss of property. This can result in a net reduction in beach area, a phenomenon known as “coastal squeeze”, which will reduce beach availability for species such as marine turtles. As of yet, no global assessment of potential future coastal squeeze risk at marine turtle nesting beaches has been conducted. We used Google Earth satellite imagery to enumerate the proportion of beaches over the global nesting range of marine turtles that are backed by hard anthropogenic coastal development (HACD). Mediterranean and North American nesting beaches had the most HACD, while the Australian and African beaches had the least. Loggerhead and Kemp’s ridley turtle nesting beaches had the most HACD, and flatback and green turtles the least. Future management approaches should prioritise the conservation of beaches with low HACD to mitigate future coastal squeeze.
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Chelonia mydas (South Atlantic subpopulation) IUCN Red List assessment: The analysis of time series datasets with ≥10 years of data (nest counts) at ten nesting sites revealed different rookery trends within the region, but an overall subpopulation increase relative to subpopulation size three generations ago. This assessment only uses breeding females as an indicator of population and as such we urge caution. The rise in many populations presented here is a result of decades of positive action and a reduction of some threats. This species remains conservation dependent and we strongly recommend that conservation actions that have proved successful are continued.
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Understanding the drivers of key interactions between marine vertebrates and plastic pollution is now considered a research priority. Sea turtles are primarily visual predators, with the ability to discriminate according to colour and shape; therefore these factors play a role in feeding choices. Classification methodologies of ingested plastic currently do not record these variables, however here, refined protocols allow us to test the hypothesis that plastic is selectively ingested when it resembles the food items of green turtles (Chelonia mydas). Turtles in the eastern Mediterranean displayed strong diet-related selectivity towards certain types (sheet and threadlike), colours (black, clear and green) and shapes (linear items strongly preferred) of plastic when compared to the environmental baseline of plastic beach debris. There was a significant negative relationship between size of turtle (curved carapace length) and number/mass of plastic pieces ingested, which may be explained through naivety and/or ontogenetic shifts in diet. Further investigation in other species and sites are needed to more fully ascertain the role of selectivity in plastic ingestion in this marine vertebrate group.
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Few studies have looked into climate change resilience of populations of wild animals. We use a model higher vertebrate, the green sea turtle, as its life history is fundamentally affected by climatic conditions, including temperature‐dependent sex determination and obligate use of beaches subject to sea level rise (SLR). We use empirical data from a globally important population in West Africa to assess resistance to climate change within a quantitative framework. We project 200 years of primary sex ratios (1900–2100) and create a digital elevation model of the nesting beach to estimate impacts of projected SLR. Primary sex ratio is currently almost balanced, with 52% of hatchlings produced being female. Under IPCC models, we predict: (a) an increase in the proportion of females by 2100 to 76%–93%, but cooler temperatures, both at the end of the nesting season and in shaded areas, will guarantee male hatchling production; (b) IPCC SLR scenarios will lead to 33.4%–43.0% loss of the current nesting area; (c) climate change will contribute to population growth through population feminization, with 32%–64% more nesting females expected by 2120; (d) as incubation temperatures approach lethal levels, however, the population will cease growing and start to decline. Taken together with other factors (degree of foraging plasticity, rookery size and trajectory, and prevailing threats), this nesting population should resist climate change until 2100, and the availability of spatial and temporal microrefugia indicates potential for resilience to predicted impacts, through the evolution of nest site selection or changes in nesting phenology. This represents the most comprehensive assessment to date of climate change resilience of a marine reptile using the most up‐to‐date IPCC models, appraising the impacts of temperature and SLR, integrated with additional ecological and demographic parameters. We suggest this as a framework for other populations, species and taxa.
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Climate change associated sea level rise (SLR) is expected to have profound impacts on coastal areas, affecting many species including sea turtles which depend on these habitats for egg incubation. Being able to accurately model beach topography using digital terrain models (DTMs) is therefore crucial to project SLR impacts and develop effective conservation strategies. Traditional survey methods are typically low‐cost with low accuracy or high‐cost with high accuracy. We present a novel combination of drone‐based photogrammetry and a low‐cost and portable real‐time kinematic (RTK) GPS to create DTMs which are highly accurate (<10 cm error) and visually realistic. This methodology is ideal for surveying coastal sites, can be broadly applied to other species and habitats, and is a relevant tool in supporting the development of Specially Protected Areas. Here we applied this method as a case‐study to project three SLR scenarios (0.48, 0.63 and 1.20 m) and assess the future vulnerability and viability of a key nesting habitat for sympatric loggerhead (Caretta caretta) and green turtle (Chelonia mydas) at a key rookery in the Mediterranean. We combined the DTM with 5 years of nest survey data describing location and clutch depth, to identify (1) regions with highest nest densities, (2) nest elevation by species and beach, and (3) estimated proportion of nests inundated under each SLR scenario. On average, green turtles nested at higher elevations than loggerheads (1.8 m vs. 1.32 m, respectively). However, because green turtles dig deeper nests than loggerheads (0.76 m vs. 0.50 m, respectively), these were at similar risk of inundation. For a SLR of 1.2 m, we estimated a loss of 67.3% for loggerhead turtle nests and 59.1% for green turtle nests. Existing natural and artificial barriers may affect the ability of these nesting habitats to remain suitable for nesting through beach migration. This article is protected by copyright. All rights reserved.
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Plastic in the marine environment is a growing environmental issue. Sea turtles are at significant risk of ingesting plastic debris at all stages of their lifecycle with potentially lethal consequences. We tested the relationship between the amount of plastic a turtle has ingested and the likelihood of death, treating animals that died of known causes unrelated to plastic ingestion as a statistical control group. We utilized two datasets; one based on necropsies of 246 sea turtles and a second using 706 records extracted from a national strandings database. Animals dying of known causes unrelated to plastic ingestion had less plastic in their gut than those that died of either indeterminate causes or due to plastic ingestion directly (e.g. via gut impaction and perforation). We found a 50% probability of mortality once an animal had 14 pieces of plastic in its gut. Our results provide the critical link between recent estimates of plastic ingestion and the population effects of this environmental threat.
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We document a tendency for published estimates of population size in sea turtles to be increasing rather than decreasing across the globe. To examine the population status of the seven species of sea turtle globally, we obtained 299 time series of annual nesting abundance with a total of 4417 annual estimates. The time series ranged in length from 6 to 47 years (mean, 16.2 years). When levels of abundance were summed within regional management units (RMUs) for each species, there were upward trends in 12 RMUs versus downward trends in 5 RMUs. This prevalence of more upward than downward trends was also evident in the individual time series, where we found 95 significant increases in abundance and 35 significant decreases. Adding to this encouraging news for sea turtle conservation, we show that even small sea turtle populations have the capacity to recover, that is, Allee effects appear unimportant. Positive trends in abundance are likely linked to the effective protection of eggs and nesting females, as well as reduced bycatch. However, conservation concerns remain, such as the decline in leatherback turtles in the Eastern and Western Pacific. Furthermore, we also show that, often, time series are too short to identify trends in abundance. Our findings highlight the importance of continued conservation and monitoring efforts that underpin this global conservation success story.
1.-The assessment of the composition and dynamics of endangered populations is crucial for management and conservation, and appropriate genetic markers are critical. 2.-The genetic structuring of the Mediterranean green turtle (Chelonia mydas) populations and the origin of the stranded animals found along the Israeli coast was investigated using new highly polymorphic short tandem repeat (STR) markers. 3.-The structuring of nesting populations was studied using pairwise genetic distances and a principal coordinates analysis (PCoA). 4.-The contribution of the different nesting populations to the stranded sample was assessed by using a mixed‐stock analysis. 5.-A clear population genetic structure, not detected before, has been revealed. The four nesting populations are genetically well differentiated, and thus should be considered as different management units. The populations from Turkey and Israel showed higher resemblance, despite residing at opposite ends of the Mediterranean distribution. The Turkish nesting population is the main source of the stranded turtles sampled along the Israeli shore, confirming that individuals from this population migrate from north to south along the eastern shore of the Mediterranean, as previously shown by telemetry studies. 6.-The use of a highly polymorphic haplotyping method enabled the detection of a clear genetic structuring of the green turtle populations in the eastern Mediterranean Sea that was not revealed in previous studies, demonstrating the importance of marker selection in population genetics. 7.-The analysis of the genetic composition of the stranded turtles allowed us to investigate the migration patterns from nesting to foraging areas, supporting previous satellite‐tracking and stable‐isotope results. 8.-These results will help to delineate conservation management units for the species in the Mediterranean, and reveal connectivity among beaches and mixed aggregations.