Caretta caretta (South West Atlantic subpopulation)
|Scientific Name:||Caretta caretta (South West Atlantic subpopulation)|
See Caretta caretta
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Casale, P. & Marcovaldi, M.|
|Reviewer(s):||Wallace, B.P. & Pilcher, N.J.|
The South West Atlantic Loggerhead subpopulation breeds along the coasts of Brazil (Figure 2 in the Supplementary Material). This subpopulation is genetically distinct from other Loggerhead subpopulations (Bowen et al. 2005) supporting its designation as a single subpopulation, or regional management unit (Wallace et al. 2010), although it shows a further genetic substructure (Reis et al. 2010, Shamblin et al. 2014).
The available long-term series of nest counts (used as an index of population abundance) show an increase over the past three generations. Moreover, both geographic distribution and population size are relatively large. Therefore, the South West Atlantic Loggerhead subpopulation is considered Least Concern under current IUCN Red List criteria. This “Least Concern” status should be considered as entirely conservation-dependent, because the current population is the result of decades of intense conservation programs, especially at nesting sites (Marcovaldi and Chaloupka 2007) and the cessation of these programs would likely be followed by rapid population decline. In spite of this, 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 of 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) on 13 nesting sites showed a general positive trend, with one exception, relative to subpopulation size three generations ago (criterion A; Table 1 in the Supplementary Material). We also assessed the subpopulation under criteria B, C, and D but the South West Atlantic subpopulation did not qualify for a threatened category using any of these criteria.
No population viability analysis (criterion E) was available and the South West Atlantic 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 Habitats & 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 yrs or more—are obvious (see Seminoff and Shanker 2008 for a review). Abundance data from ~135 yrs 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 yrs; see Habitats & 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 (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 yrs.
For the South West Atlantic Loggerhead subpopulation, we included time series datasets of ≥10 yrs from 13 nesting sites in Brazil (Table 1 in the Supplementary Material). The total number of nests from these datasets was about 7,500 nests yr-1 in the most recent counts, while the total number of nests in the subpopulation, including beaches with <10 years of monitoring, was about 7,700 nests yr-1 (N. Marcovaldi pers. comm.). The contribution to the subpopulation by non-index beaches is thus <3%, and we consider the trends from the index beaches as representative of the trends across the entire subpopulation. We calculated annual and overall trends using past and present abundance estimates representing the annual average of five-year nest counts for each of the 13 index nesting sites within the subpopulation. We then calculated the overall subpopulation past-present trend. The most recent year for abundance data across all rookeries was 2013.
All except for one trend were positive and the overall trend for the South West Atlantic subpopulation was positive (+70%). The single one negative trend was for one site that accounted for only 7% of the entire subpopulation.
In conclusion, the South West Loggerhead subpopulation does not qualify for a threatened category under criterion A.
Since the subpopulation area is most of the Southwest Atlantic Ocean, the extent of occurrence (EOO) exceeds the threat 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 South West Atlantic is estimated as 711 km (N. Marcovaldi pers. comm.). Since the appropriate scale for AOO is a grid 2x2 km, the above linear measure was converted to 1,422 km². This value is below the Vulnerable category threshold for AOO (<2,000 km²); however the subpopulation did not meet any of the other subcriteria also required: number of locations is >10 and there is no evidence of continuing decline nor of extreme fluctuations. In conclusion, the subpopulation does not meet the requirements 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 = 7,700) (N. Marcovaldi pers. comm.) by the average value of four clutches per female (Marcovaldi and Chaloupka 2007) to obtain an average annual number of nesting females (1924). Next, we multiplied this value by the average remigration interval of two years (N. Marcovaldi pers. comm.), i.e. years between consecutive nesting seasons. The resulting total number of adult females, i.e. including nesting as well as non-nesting turtles, was 3,848. To derive from this the total number of adults, adult sex ratio is needed. Unfortunately this parameter is lacking for this subpopulation. In order to match the threshold for a threatened category (<10,000 adults) the female proportion should be higher than 38.5%, which is likely, although not known. Therefore, it is likely that the total number of adults is <10,000. However the subpopulation did not meet any of the other subcriteria also required, i.e. continuing decline, % of mature individuals in one subpopulation, and extreme fluctuations. In conclusion, the subpopulation does not meet the requirements for a threatened category under criterion C.
The number of mature individuals (see criterion C) and AOO value (see criterion B) exceeded the respective thresholds. 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. 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 South West Atlantic subpopulation breeds along the coast of Brazil (Marcovaldi and Chaloupka 2007) and its marine habitats extend throughout most of the South West Atlantic ocean (Barceló et al. 2013, González Carman et al. 2011, Marcovaldi et al. 2010, Prosdocimi et al. 2015, Sales et al. 2008, Vélez-Rubio et al. 2013, Wallace et al. 2010) (Figure 2 in the Supplementary Material).
Native:Argentina; Brazil; Uruguay
|FAO Marine Fishing Areas:|
Atlantic – southwest
|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): 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 (Fig. 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 South West Atlantic subpopulation breeds at least 15 nesting sites, with a total number of nests estimated at ca. 7,700 per year (M.A. Marcovaldi, pers. comm).
|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 1 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 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:||The South West Atlantic Loggerhead subpopulation was harvested for human consumption in the past, however this has now stopped.|
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:
While past threats to the South West Atlantic subpopulation, such as egg harvest for consumption and nesting beach destruction, have been successfully addressed by decades of conservation programs at nesting beaches (Marcovaldi and Chaloupka 2007), the current and probably increasing threat is represented by fishery bycatch (Pons et al. 2012, Sales et al. 2008, D. Monteiro, pers. comm., Vélez-Rubio et al. 2013).
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.
For the South West Atlantic subpopulation, intensive conservation actions have been implemented by several projects in the last decades at nesting beaches and foraging areas through promoting adequate legislation, social inclusion and environmental education in order to stop or reduce direct use, and destruction of nesting habitats (Marcovaldi et al. 2005, Marcovaldi and Chaloupka 2007). Initiatives to reduce incidental capture in fisheries are also performed intensively across the region (Domingo et al. 2006, González-Carman et al. 2012, Marcovaldi et al. 2002).
|Citation:||Casale, P. & Marcovaldi, M. 2015. Caretta caretta (South West Atlantic subpopulation). The IUCN Red List of Threatened Species 2015: e.T84191235A84191397.Downloaded on 21 October 2017.|
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