Caretta caretta (North East Indian Ocean subpopulation)
|Scientific Name:||Caretta caretta (North East Indian Ocean subpopulation)|
|Species Authority:||(Linnaeus, 1758)|
See Caretta caretta
|Red List Category & Criteria:||Critically Endangered D ver 3.1|
|Reviewer(s):||Wallace, B.P. & Pilcher, N.J.|
The North East Indian Ocean subpopulation of Loggerhead Turtle nests in Sri Lanka. Its marine habitats are assumed to extend throughout a large marine area in the Bay of Bengal and possibly beyond (Fig. 2 in the Supplementary Material). Genetic data are not available and this subpopulation, or regional management unit, was defined on the basis of the geographic distance from other areas (Wallace et al. 2010).
The available data indicate a low number of nests and consequently a low number of adults (<50). This makes the North East Indian Ocean subpopulation qualify Critically Endangered according to IUCN Red List criterion D.
Very little is known about this subpopulation and this scarce information, compared to other sea turtle species in the same area, suggests a very low abundance of this subpopulation reflected by the information on low numbers of nests per year. Hence, it is reasonable to apply Criterion D to the plausible number of adults (<50), and consequently the subpopulation qualifies as Critically Endangered. This subpopulation also meets the thresholds for the Endangered category under criterion B2a,b(iii) and specifically a small area of occupancy (AOO) (45 km²; threshold <500 km²), few locations (one; threshold <5), and continuing decline in habitat area. The lack of other information prevents evaluation of criteria A, C and E.
Although the scarce information about this subpopulation generates uncertainty, this uncertainty is not so high to categorize this subpopulation as Data Deficient. The Data Deficient category can be applied only to subpopulations for which both Least Concern and Critically Endangered are plausible categories (IUCN 2014). This is clearly not the case for the North-East Indian subpopulation for which a Least Concern category is unrealistic under criteria B and D, even hypothesizing large information gaps. Specifically, a number of adults >1,000 (criterion D) is unrealistic, as well as an AOO >2,000 km² or number of locations >10 (criterion B2).
For the Loggerhead Turtle global and subpopulation assessments we only considered time series datasets (nest counts) of ≥10 yr. Unfortunately, such datasets were not available for the North East Indian Ocean subpopulation. For this reason, criterion A could not be applied to this subpopulation.
Since the subpopulation area includes the large marine area of the Bay of Bengal, the extent of occurrence (EOO) exceeds the threat category threshold (20,000 km²) for criterion B1. Regarding criterion B2, the 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 North East Indian Ocean Loggerhead nesting beaches in Sri Lanka is 22.5 km (Kapurusinghe 2006) Since the appropriate scale for AOO is a grid 2x2 km, the above linear measure is converted to 45 km², which triggers the threshold for the Endangered category (<500 km²). The number of locations of the subpopulation is one (Sri Lanka) (i.e. <5), which triggers the threshold for the Critically Endangered category. Finally, there is evidence of continuing decline in habitat area, extent, and quality. The heavy sand extraction activity and erosion caused a dramatic reduction of the habitat suitable for sea turtle nesting (de Silva 2006, Kapurusinghe 2006). Based on AOO, number of locations, and decline in habitat area, the subpopulation qualifies for the Endangered category under criterion B2ab(iii).
No data are available to trigger some of the subcriteria required, such as continuing decline and extreme fluctuations of the subpopulation. Therefore, although the number of mature individuals (see criterion D) meets the thresholds for all the threatened categories, the subpopulation does not meet criterion C, partly because of lack of data.
To apply criterion D, the total number of adult females and males is needed. The number of annual nests in Sri Lanka is probably <25 (T. Kapurusinghe, pers. comm).
The number of adults can be derived from the number of nests per year with the following formula: adults = nests * nests per female-1 * remigration interval * female proportion-1.
Unfortunately, number of nests per female, remigration interval and female proportion are not available for this subpopulation. However, if nests per females = remigration interval and sex ratio = 0.5 then adults = nests*2. In most Loggerhead subpopulations the number of nests per females is greater than the remigration interval (Conant et al. 2009, Hamann et al. 2013) and the female proportion is >0.5 (Wibbels 2003), and as a consequence in most Loggerhead subpopulations the number of adults < nests*2. If we assume that also the Northeast Indian subpopulation follows this common relationship, than the number of adults would be <50. Since the IUCN Red List Categories and Criteria recommend to ‘adopt a precautionary but realistic attitude’, i.e. a low risk tolerance (IUCN 2014), we believe it is appropriate to consider as the most realistic scenario that the number of adults is < 50 and this would also represent a precautionary approach.
Under this scenario, a number of adults <50 meets the threshold for the Critically Endangered category under criterion D.
No population viability analysis was available for this subpopulation.
Sources of Uncertainty
The main source of uncertainty for this subpopulation assessment is represented by the nest counts, both because of limited monitoring and because nests reported as Loggerhead nests might actually be nests of Lepidochelys olivacea. 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) (Fig. 1 in the Supplementary Material). |
The North East Indian Ocean subpopulation breeds in Sri Lanka (Kapurusinghe 2006). Although nesting has been reported from Myanmar too (Thorbjarnarson et al. 2000), this represents a problem of misidentification with another species, the Olive Ridley Turtle (Lepidochelys olivacea). This problem was already highlighted in the original report (Thorbjarnarson et al. 2000). More recently (in 2012, C. Limpus, pers. comm.) there was consensus among the numerous fisheries officers and academics involved in turtle conservation/monitoring that the turtles nesting in Myanmar are not Loggerheads but Olive Ridleys and no Loggerhead hatchlings were found in museum collections. Such wrong identifications are probably due to the fact that at the beginning of the 20th century the Olive Ridley Turtle was considered a subspecies of Caretta caretta (Dodd 1988, Marquez 1990). There is an unconfirmed report in Bangladesh, but it was probably an Olive Ridley for the similarities of the two species (Rashid and Islam 2006) and for the reasons above. Therefore, the breeding area is here considered limited to Sri Lanka. The marine habitats are assumed to extend throughout at least the Bay of Bengal.
|FAO Marine Fishing Areas:|
Indian Ocean – eastern
|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 (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).|
Very little information exists about the North East Indian Ocean subpopulation. It seems to be very small. Annual nests in Sri Lanka are probably <25 (T. Kapusuringhe, pers. comm).
|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). 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).|
However, none of these parameters have been quantified specifically for North East Indian Ocean loggerhead subpopulation.
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:||It is assumed that this species is harvested in the North East Indian Ocean region for its eggs and meat.|
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 Indian Ocean subpopulation have not been specifically assessed, although Wallace et al. (2011) has categorized this subpopulation as highly threatened. However, it can be assumed that they are the same of other sea turtle species occurring in the same area, i.e., egg and meat consumption, and habitat degradation (de Silva 2006, Kapurusinghe 2006).
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.
There no specific conservation actions for to the North-East Indian subpopulation, however legislation and actions contrasting in particular sea turtle egg poaching (de Silva 2006, Kapurusinghe 2006) are probably benefiting Loggerhead Turtles too.
|Citation:||Casale, P. 2015. Caretta caretta (North East Indian Ocean subpopulation). The IUCN Red List of Threatened Species 2015: e.T84126444A84126520.Downloaded on 22 August 2017.|
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