Caretta caretta (Mediterranean subpopulation)
|Scientific Name:||Caretta caretta (Mediterranean subpopulation)|
See Caretta caretta
|Red List Category & Criteria:||Least Concern ver 3.1|
|Reviewer(s):||Wallace, B.P. & Pilcher, N.J.|
The Mediterranean Loggerhead subpopulation breeds along the coasts of the eastern Mediterranean basin (with just a few nests recorded in the western basin) and its marine habitats extend throughout the entire Mediterranean Sea (see Fig. 2 in Supplementary Information). Several genetic nesting stocks have been identified within this subpopulation (Carreras et al. 2007, Clusa et al. 2013, Garofalo et al. 2013), but metapopulation dynamics support its designation as a single subpopulation, or regional management unit (Wallace et al. 2010).
The available long-term series of nest counts (used as an index of population abundance; mostly from protected beaches) show an overall increase over the past three generations when all Loggerhead nesting sites in the Mediterranean are considered together. Moreover, both geographic distribution and population size are relatively large. Therefore, the Mediterranean Loggerhead subpopulation is considered Least Concern under current IUCN Red List criteria.
This “Least Concern” status should, however, be considered as entirely conservation-dependent, because the current population is the result of decades of intense conservation programs, especially at nesting sites (Casale and Margaritoulis 2010) and the cessation of these programs would be followed by a population decrease. However, due to the long maturation time of these animals and the available indexes of abundance (nest counts), the subpopulation would probably not qualify for a threatened category within five years after the cessation of conservation programs, as prescribed for triggering the Near Threatened category (IUCN 2014).
The analysis of time series datasets with ≥10 years of data of nesting activities (nest counts) at 16 nesting sites revealed different rookery trends within the Mediterranean Loggerhead subpopulation, but an overall subpopulation increase relative to subpopulation size three generations ago (criterion A2; Table 1 in the Supplementary Material). We also assessed the subpopulation under criteria B, C, and D to the Mediterranean subpopulation, but the extent of occurrence and area of occupancy exceeded the thresholds of criterion B, and this subpopulation did not trigger any threatened category of criteria C and D.
No population viability analysis (criterion E) was available and the Mediterranean Loggerhead subpopulation assessment was conducted by applying criteria A-D.
For marine turtles, annual counts of nesting females and their nesting activities (more often the latter) are the most frequently recorded and reported abundance metric across index monitoring sites, species, and geographic regions (National Research Council 2010).
To apply criterion A, three generations (or a minimum of ten years, whichever is longer) of abundance data are required (IUCN 2014). In the case of the Loggerhead, we conservatively estimate its generation time as 45 years (see the Habitat and Ecology section). For criteria A1-A2, data from three generations ago (~135 yrs) are necessary to estimate population declines beginning three generations ago up to the present (i.e., assessment) year. The challenges of this requirement on long-lived species like turtles—with generation lengths of 30 years or more—are obvious (see Seminoff and Shanker 2008 for a review). Abundance data from ~135 years ago are not available for Loggerheads anywhere in the world. Extrapolating backward using population trends based on current datasets was considered inappropriate because estimates produced would be biologically unrealistic and unsubstantiated, given what is currently known about sea turtle nesting densities on beaches and other factors (Mrosovsky 2003). In the absence of better information, we assumed that population abundance three generations ago (~135 years, one generation estimated 45 years; see the Habitat and Ecology section) was similar to the first observed abundance rather than to assume that the population has always been in a decline (or increase) of the same magnitude as in the current generation. A similar approach was used in the Red List assessment of another sea turtle, the Leatherback Turtle (Dermochelys coriacea) (Wallace et al. 2013) and of another long-lived, geographically widespread taxon, the African Elephant (Loxodonta africana) (Blanc 2008). Thus, to apply criterion A we assumed that the abundance at the beginning of an available time series dataset had not changed significantly in the preceding three generations, and therefore used the same abundance value in trend calculations. For the Loggerhead global and subpopulation assessments we only considered time series datasets of ≥10 years.
For the Mediterranean Loggerhead subpopulation, we included time series datasets of ≥10 years, from 16 rookeries in four countries (Greece, Turkey, Cyprus, Israel; Table 1 in the Supplementary Material), and we assumed that these index sites were representative of the overall population trend for the entire subpopulation. The total number of nests from these datasets was about 3,200 nests yr-1 in the most recent counts, while the total number of nests in the Mediterranean subpopulation is estimated as >7,200 nests yr-1 (Casale and Margaritoulis 2010). Since the datasets used in the analysis represent less than 50% of the whole subpopulation, the results should be regarded with caution, also because long-term monitored beaches likely benefited from long conservation programmes and protection status.
From one past and one recent abundance values (each representing the annual average of five year nest counts) we calculated annual and overall trends (past-present) for each index nesting sites within the subpopulation, and then we calculated the overall subpopulation past trend. The most recent year for available abundance data across all rookeries was 2013. Where time series ended prior to 2013, we estimated population sizes for each rookery through 2013 based on the population trend for existing years. Trends ranged from negative to positive across the different rookeries, with most negative trends observed in Greece (range: -1% to -6% per year decrease; Table 1 in the Supplementary Material). The overall trend for the Mediterranean population was positive (+7%) (Table 1 in the Supplementary Material). In conclusion, the Mediterranean Loggerhead subpopulation does not qualify for a threatened category under criterion A.
Since the subpopulation area is the entire Mediterranean Sea, the extent of occurrence (EOO) exceeds the threatened category threshold (20,000 km²). The area of occupancy (AOO) for sea turtles is identified with the nesting beach habitat, which represents the smallest habitat for a critic life stage. The total length of known Loggerhead nesting beaches in the Mediterranean is estimated as 1,490 km (Casale and Margaritoulis 2010, W. Fuller pers. comm., D. Margaritoulis pers. comm). Since the appropriate scale for AOO is a grid 2x2 km, the above linear measure was converted to 2,980 km². This value exceeds the threat category threshold (2,000 km²). It should be considered that this calculation assumes a linear aggregation of nesting beaches and therefore is the minimum theoretical value of this parameter, that is actually higher if beaches are many, separated and relatively short, which as in the Mediterranean case. The subpopulation does not meet any of the three options a, b, c: number of locations is >10, there is no evidence of continuing decline nor of extreme fluctuations. In conclusion, the subpopulation does not trigger any of the thresholds and options for a threatened category under criterion B.
To apply criterion C, we first calculated the number of mature individuals in the subpopulation, i.e., the total number of adult females and males. First, we divided the current average annual number of nests (n = 7,200) (Casale and Margaritoulis 2010) by the average number of clutches per female (1.9; Broderick et al. 2003) to obtain an average annual number of nesting females (3,789). Next, we multiplied this value by the average remigration interval, i.e., years between consecutive nesting seasons. As remigration interval we used 2.55, which is the average of three values available from the Mediterranean (Broderick et al. 2003, Hays et al. 2010, Ilgaz et al. 2007). The resulting total number of adult females (i.e., including nesting as well as non-nesting turtle) was 9,963. Finally, we divided this value by the average proportion of adult females on the total adults (0.45) calculated from the values available from three Mediterranean foraging grounds (Casale et al. 2014, Rees et al. 2013). This calculation provided an estimated mature adult population of 21,414 individuals, which exceeded all threat category thresholds for this parameter (<10,000 adults). The subpopulation did not meet any other parameter threshold: i.e., continuing decline, % of mature individuals in one subpopulation, and extreme fluctuations. In conclusion, the subpopulation does not trigger any of the thresholds and options for a threatened category under criterion C.
The number of mature individuals (see criterion C) and AOO value (see criterion B) exceeded the thresholds of 1,000 individuals and 20 km² respectively. In conclusion, the subpopulation does not trigger any of the thresholds and options for a threatened category under criterion D.
Sources of Uncertainty
Although monitoring of nesting activities by adult female sea turtles is the most common metric recorded and reported across sites and species, globally, there are several disadvantages to using it as a proxy for overall population dynamics, some methodological, some interpretive (National Research Council 2010). First, because nesting females are a very small proportion of a sea turtle population, using abundance of nesting females and their activities as proxies for overall population abundance and trends requires knowledge of other key demographic parameters (several mentioned below) to allow proper interpretation of cryptic trends in nesting abundance (National Research Council 2010). However, there remains great uncertainty about most of these fundamental demographic parameters for Loggerheads, including age at maturity, generation length, survivorship across life stages, adult and hatchling sex ratios, and conversion factors among reproductive parameters (clutch frequency, nesting success, remigration intervals, etc). These values can vary among subpopulations, further complicating the process of combining subpopulation abundance and trend estimates to obtain global population abundance and trend estimates, and contributing to the uncertainty in these estimates. Second, despite the prevalence of nesting abundance data for marine turtles, monitoring effort and methodologies can vary widely within and across study sites, complicating comparison of nesting count data across years within sites and across different sites as well as robust estimation of population size and trends. However, we have reduced this source of uncertainty by using in the analyses those data sets obtained though standardized monitoring. Furthermore, the 16 index nesting beaches used in this subpopulation assessment host less than 50% of the total estimated annual nests of the subpopulation. Therefore, it cannot be excluded that they are not representative of the nesting beaches as a whole and hence of the overall trend. For all of these reasons, the trends resulting from this assessment of the Mediterranean Loggerhead subpopulation should be used with caution. For further reading on sources of uncertainty in marine turtle Red List assessments, see Seminoff and Shanker (2008).
|Range Description:||The Loggerhead Turtle is globally distributed throughout the subtropical and temperate regions of the Mediterranean Sea and Pacific, Indian, and Atlantic Oceans (Wallace et al. 2010) (see Figure 1 in the Supplementary Information). The Mediterranean subpopulation breeds along the coasts of the eastern Mediterranean basin (with just a few individual nests recorded in the western basin) and its marine habitats extend throughout the entire Mediterranean Sea (Casale and Margaritoulis 2010).|
Native:Albania; Algeria; Croatia; Cyprus; Egypt; France; Greece; Israel; Italy; Lebanon; Libya; Malta; Montenegro; Morocco; Slovenia; Spain; Syrian Arab Republic; Tunisia; Turkey
|FAO Marine Fishing Areas:|
Mediterranean and Black Sea
|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. Regional management units are functionally equivalent to IUCN subpopulations, thus providing the appropriate demographic unit for Red List assessments. There are 10 Loggerhead RMUs (hereafter subpopulations): North West Atlantic Ocean, North East Atlantic Ocean, South West Atlantic Ocean, Mediterranean Sea, North East Indian Ocean, North West Indian Ocean, South East Indian Ocean, South West Indian Ocean, North Pacific Ocean, and South Pacific Ocean (see Figure 2 in the Supplementary Material). 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 Mediterranean subpopulation is fragmented into tens of rookeries, with a total of >7,200 nests estimated per year (Casale and Margaritoulis 2010).
|Current Population Trend:||Increasing|
|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). 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 kilometers (Plotkin 2003). During non-breeding periods adults reside at coastal neritic feeding areas that sometimes coincide with juvenile developmental habitats (Bolten and Witherington 2003).|
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).
|Generation Length (years):||45|
|Use and Trade:||Loggerhead Turtles and their eggs are taken for human use (i.e., consumption and commercial products).|
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 Mediterranean subpopulation are represented by fishery bycatch and nesting habitat degradation due to coastal development (Casale and Margaritoulis 2010).
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, 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). RFMO Recommendations are compulsory for their implementation by members, particularly within the Organizations leading with tuna fisheries. 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.
Almost all Mediterranean countries, including those with major nesting and foraging habitats for loggerheads, are signatories to international conventions for the conservation of species including sea turtles and have national laws for the protection of sea turtles, including fisheries agreements. For instance, the Bern Convention (Council of Europe) and European Union regulation (Habitats Directive), UNEP/MAP Action Plan for the Conservation of Marine Turtles in the Mediterranean Sea, several agreements and recommendations adopted by RFMOs such as ICCAT and the GFCM. Moreover, many countries have sea turtles conservation projects run by governmental bodies or NGOs. Special attention has been given to the protection of major nesting sites. For a detailed description of the conservation efforts see Casale and Margaritoulis (2010).
|Citation:||Casale, P. 2015. Caretta caretta (Mediterranean subpopulation). The IUCN Red List of Threatened Species 2015: e.T83644804A83646294.Downloaded on 23 November 2017.|
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