Caretta caretta (North East Atlantic subpopulation)
|Scientific Name:||Caretta caretta (North East Atlantic subpopulation)|
See Caretta caretta
|Red List Category & Criteria:||Endangered B2ab(iii) ver 3.1|
|Assessor(s):||Casale, P. & Marco, A.|
|Reviewer(s):||Wallace, B.P. & Pilcher, N.J.|
The North-East Atlantic Loggerhead subpopulation nests in the Cabo Verde Archipelago, with just a few nests recorded in Mauritania and Guinea. Its marine habitats extend throughout a large marine area off the coast of north-west Africa as far as coastal areas of Sierra Leone and the western part of the Mediterranean (Hawkes et al. 2006, Monzon-Arguello et al. 2010).
This subpopulation has been identified as a separate genetic stock from other Loggerhead stocks (Monzon-Arguello et al. 2010), including several small genetically diverse nesting groups (Stiebens et al. 2013), considered as a single subpopulation, or regional management unit (Wallace et al. 2010) with the need of local management (Stiebens et al. 2013).
The available data indicate that the Cabo Verde Archipelago is by far the main rookery for this subpopulation. Few or not well quantified nests have been reported from Mauritania and Guinea, although genetic data are not available from these locations to assess whether they belong to the same subpopulation. We assumed, for the purposes of this assessment and given the relative proximity of these sites, that all these rookeries belong to the same subpopulation. The area of occupancy (AOO) (based on nesting habitat) is relatively small and the number of locations is small as well. The main rookery at Cabo Verde is subject to a continuing anthropogenic pressure causing a continuing decline in habitat area, extent and quality. Under these circumstances the subpopulation qualifies for the category Endangered according to IUCN Red List criterion B2 subcriteria (a) and (b).
This subpopulation meets the thresholds for the Endangered category of the subcriteria B2ab(iii): specifically a small AOO (<500 km²), few locations (<5) and continuing decline in habitat area, extent and quality. The subpopulation also qualifies for the Vulnerable category under criterion D2, as it occurs in a small number of locations with a plausible threat that could drive the subpopulation to CR in short time.
Criterion A could not be applied due to the lack of time series datasets with ≥10 years of data representative of the subpopulation nesting activity. Criterion C was applied but the subpopulation exceeded the threshold of number of adults for all threatened categories.
No population viability analysis (Criterion E) was available and the North-East Atlantic Loggerhead subpopulation assessment was conducted by applying criteria A-D.
Historic information suggests a strong reduction of the subpopulation (Marco et al. 2012). However, this information cannot be easily converted into indices of abundance to be compared with current abundance.
For the Loggerhead global and subpopulation assessments we only considered time series datasets (nest counts) of ≥10 yrs. Unfortunately, such datasets were not available for the North East Atlantic subpopulation. First, nesting activity was monitored for a relatively long period only in few of the beaches in Cabo Verde and these beaches cannot be considered as representative of the whole nesting ground of Cabo Verde because they have been protected by specific conservation programmes (A. Marco, pers. comm.). Second, it cannot be assumed that the monitoring method was uniform and the different years comparable. For these reasons, criterion A could not be applied to this subpopulation.
Since the subpopulation area includes a large marine area from north-west Africa to the western Mediterranean, the extent of occurrence (EOO) exceeds the threat category threshold (20,000 km²) for criterion B1. Regarding criterion B2, the area of occupancy (AOO) for sea turtles is identified with the nesting beach habitat, which represents the smallest habitat for a critical life stage. The total length of known Loggerhead nesting beaches in the Cabo Verde Archipelago is 212 km (A. Marco, pers. comm.). Since the appropriate scale for AOO is a grid 2x2 km, the above linear measure is converted to 424 km². However, in insular contexts the linear approximation may not be the best representation of a grid 2x2 km, therefore we also directly counted the number of 2x2 km cells including all the nesting beaches of the Cabo Verde archipelago, resulting in 98 cells, equivalent to 392 km². Given the uncertain and anecdotal nature of the nesting activity in Mauritania and Guinea (Fretey 2001) we assume that the total AOO for the North East Atlantic is <500 km², which triggers the threshold for the Endangered category.
The number of locations of the subpopulation is probably one (Cabo Verde) and maximum three, if Mauritania and Guinea are considered. Therefore, the maximum number of locations is <5, which triggers the threshold for the Endangered category. Finally, there is evidence of continuing decline in habitat area, extent, and quality. The heavy sand extraction activity and tourism development caused a dramatic reduction of the number of beaches suitable for sea turtle nesting and the quality of the remaining beaches (Loureiro 2008). Based on AOO, number of locations and decline in habitat area, extent and quality, the subpopulation qualifies for the Endangered category under criterion B2ab(iii).
To apply criterion C, the total number of adult females and males is needed. The nesting female population in Cabo Verde has recently been estimated at 8,900 (Marco et al. 2012). The adult sex ratio is unknown, however it would have to be extremely skewed (females >89%) in order to meet the threshold of 10,000 adults for a threatened category. Therefore, it is likely that the number of adults is above 10,000 and the subpopulation does not meet criterion C.
The number of mature individuals (see above, criterion C) exceeds the thresholds for threatened categories. However, the subpopulation is restricted to a few locations (<5) and is subject to a threat that could drive it to CR in a short time. Threats are represented by the reduction of area and quality of nesting habitats (see above, criterion B) and by the killing for meat consumption of a high proportion of females (5-36%) of the females nesting in a year (Marco et al. 2012). These threats occur in the single country hosting the majority or totality of the subpopulation (Cabo Verde), and have therefore common causes and common management by the same national regulations. Under these circumstances the subpopulations qualifies for the Vulnerable category under criterion D2.
Sources of Uncertainty
The most important source of uncertainty for the assessment of this subpopulation is the limited information about nesting activity along the coasts of north-west Africa. However, in spite of the general progress in sea turtle knowledge in the west Africa, data on Loggerheads remain limited, which is possibly an indication of a real low level of nesting activity by this species on the mainland shores. More information about nesting levels and genetic characteristics of west Africa rookeries may improve future assessments of the North East Atlantic subpopulation, as well as an estimation of adult sex ratio.
For further reading on sources of uncertainty in marine turtle Red List assessments, see Seminoff and Shanker (2008).
|Range Description:||The Loggerhead Turtle has a worldwide distribution in subtropical to temperate regions of the Mediterranean Sea and Pacific, Indian, and Atlantic Oceans (Wallace et al. 2010) (Figure 1 in the Supplementary Material). The North-East Atlantic subpopulation breeds in the Cabo Verde archipelago (Marco et al. 2012) and along the north-west Africa coast (Fretey 2001) and its marine habitats extend throughout a large marine area off the coast of north-west Africa as far as coastal areas of Sierra Leone and the western part of the Mediterranean (Hawkes et al. 2006, Monzon-Arguello et al. 2010).|
Native:Cape Verde; Guinea; Mauritania; Sierra Leone
|FAO Marine Fishing Areas:|
Atlantic – eastern central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Loggerheads are a single species globally comprising 10 biologically described regional management units (RMUs; Wallace et al. 2010), which describe biologically and geographically explicit population segments by integrating information from nesting sites, mitochondrial and nuclear DNA studies, movements and habitat use by all life stages. RMUs are functionally equivalent to IUCN subpopulations, thus providing the appropriate demographic unit for Red List assessments. There are 10 Loggerhead RMUs (hereafter subpopulations): Northwest Atlantic Ocean, Northeast Atlantic Ocean, Southwest Atlantic Ocean, Mediterranean Sea, Northeast Indian Ocean, Northwest Indian Ocean, Southeast Indian Ocean, Southwest Indian Ocean, North Pacific Ocean, and South Pacific Ocean. Multiple genetic stocks have been defined according to geographically disparate nesting areas around the world and are included within RMU delineations (Wallace et al. 2010) (shapefiles can be viewed and downloaded at: http://seamap.env.duke.edu/swot).|
The North-East Atlantic subpopulation is relatively abundant, with an estimated 10,000-20,000 nests per year and 8,900 adult females (Marco et al. 2012). The subpopulation includes genetically different nesting groups (Stiebens et al. 2013).
|Current Population Trend:||Unknown|
|Habitat and Ecology:||The Loggerhead Turtle nests on insular and mainland sandy beaches throughout the temperate and subtropical regions. Like most sea turtles, Loggerhead Turtles are highly migratory and use a wide range of broadly separated localities and habitats during their lifetimes (Bolten and Witherington 2003). Upon leaving the nesting beach, hatchlings begin an oceanic phase, perhaps floating passively in major current systems (gyres) that serve as open-ocean developmental grounds (Bolten and Witherington 2003). After 4-19 years in the oceanic zone, Loggerheads recruit to neritic developmental areas rich in benthic prey or epipelagic prey where they forage and grow until maturity at 10-39 years (Avens and Snover 2013). However, in some subpopulations, like the North East Atlantic, a part of adults continue to forage in the oceanic zone (Eder et al. 2012, Hawkes et al. 2006). Upon attaining sexual maturity Loggerhead Turtles undertake breeding migrations between foraging grounds and nesting areas at remigration intervals of one to several years with a mean of 2.5-3 years for females (Schroeder et al. 2003) while males would have a shorter remigration interval (e.g., Hays et al. 2010, Wibbels et al. 1990). Migrations are carried out by both males and females and may traverse oceanic zones spanning hundreds to thousands of kilometres (Plotkin 2003). During non-breeding periods adults usually reside at coastal neritic feeding areas that sometimes coincide with juvenile developmental habitats (Bolten and Witherington 2003). However, in some cases, like the North East Atlantic subpopulation, females reside in the oceanic zone (Eder et al. 2012). |
The IUCN Red List Criteria define generation length to be the average age of parents in a population, i.e., older than the age at maturity and younger than the oldest mature individual, and care should be taken to avoid underestimation (IUCN 2014). Although different subpopulations may have different generation length, since this information is limited we adopted the same value for all the subpopulations, taking care to avoid underestimation as recommended by IUCN (2014).
Loggerheads attain maturity at 10-39 years (Avens and Snover 2013), and we considered here 30 years to be equal or greater than the average age at maturity. Data on reproductive longevity in Loggerheads are limited, but are becoming available with increasing numbers of intensively monitored, long-term projects on protected beaches. Tagging studies have documented reproductive histories up to 28 years in the North Western Atlantic Ocean (Mote Marine Laboratory, unpubl. data), up to 18 years in the South Western Indian Ocean (Nel et al. 2013), up to 32 years in the South Western Atlantic Ocean (Projeto Tamar unpubl. data), and up to 37 years in the South Western Pacific Ocean, where females nesting for 20-25 years are common (C. Limpus, pers. comm). We considered 15 years to be equal or greater than the average reproductive longevity. Therefore, we considered here 45 years to be equal or greater than the average generation length, therefore avoiding underestimation as recommended by IUCN (IUCN Standards and Petitions Subcommittee 2014).
|Continuing decline in area, extent and/or quality of habitat:||Yes|
|Generation Length (years):||45|
|Use and Trade:||In the North East Atlantic, a high proportion of females are killed for meat consumption.|
Threats to Loggerheads vary in time and space, and in relative impact to populations. Threat categories affecting marine turtles, including Loggerheads, were described by Wallace et al. (2011) as:
The main threats to the North East Atlantic subpopulation are represented by the reduction of area and quality of nesting habitats (Loureiro 2008) and by the killing for meat consumption of a high proportion (5-36%) of the females nesting in a year (Dutra and Koenen 2014, Marco et al. 2012). Fishery bycatch is also emerging as an important issue (Melo and Melo 2013). Some non-anthropogenic threats, like embryonic mortality by tidal flooding, predation and fungi are reason of concern (Abella Pérez 2010, Sarmiento-Ramírez et al. 2014).
Loggerhead Turtles are afforded legislative protection under a number of treaties and laws (Wold 2002). Annex II of the SPAW Protocol to the Cartagena Convention (a protocol concerning specially protected areas and wildlife); Appendix I of CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora); and Appendices I and II of the Convention on Migratory Species (CMS). A partial list of the International Instruments that benefit Loggerhead Turtles includes the Inter-American Convention for the Protection and Conservation of Sea Turtles, the Memorandum of Understanding on the Conservation and Management of Marine Turtles and their Habitats of the Indian Ocean and South-East Asia (IOSEA), the Memorandum of Understanding on ASEAN Sea Turtle Conservation and Protection, the Memorandum of Agreement on the Turtle Islands Heritage Protected Area (TIHPA), and the Memorandum of Understanding Concerning Conservation Measures for Marine Turtles of the Atlantic Coast of Africa.
As a result of these designations and agreements, many of the intentional impacts directed at sea turtles have been lessened: harvest of eggs and adults has been slowed at several nesting areas through nesting beach conservation efforts and an increasing number of community-based initiatives are in place to slow the take of turtles in foraging areas. In regard to incidental take, the implementation of Turtle Excluder Devices has proved to be beneficial in some areas, primarily in the United States and South and Central America (National Research Council 1990). Guidelines are available to reduce sea turtle mortality in fishing operations in coastal and high seas fisheries (FAO 2009). However, despite these advances, human impacts continue throughout the world. The lack of effective monitoring in pelagic and near-shore fisheries operations still allows substantial direct and indirect mortality, and the uncontrolled development of coastal and marine habitats threatens to destroy the supporting ecosystems of long-lived Loggerhead Turtles.
The main conservation actions for to the North East Atlantic subpopulation have been conducted in the last decade and are represented by awareness programs, beach patrolling, beach protection and promotion of regulations aimed to reduce turtle killing for meat consumption (Dutra and Koenen 2014; Marco et al. 2012).
|Citation:||Casale, P. & Marco, A. 2015. Caretta caretta (North East Atlantic subpopulation). The IUCN Red List of Threatened Species 2015: e.T83776383A83776554.Downloaded on 21 April 2018.|
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