Caretta caretta (North West Indian Ocean subpopulation)
|Scientific Name:||Caretta caretta (North West Indian Ocean subpopulation)|
|Species Authority:||(Linnaeus, 1758)|
See Caretta caretta
|Red List Category & Criteria:||Critically Endangered A4b ver 3.1|
|Reviewer(s):||Wallace, B.P. & Pilcher, N.J.|
The Northwest Indian Loggerhead subpopulation nests in Oman and Yemen. Its marine habitats extend from the Gulf of Aden to the Arabian Gulf (Figure 2 in the Supplementary Material). Genetic markers indicate that the North West Indian Ocean Loggerhead subpopulation represents a distinct subpopulation or regional management unit (Shamblin et al. 2014, Wallace et al. 2010).
The Masirah island stock, which probably represents over 90% of the subpopulation, has experienced a massive decline that is projected to increase in magnitude in the future, which qualifies for the category Critically Endangered according to IUCN Red List criterion A4, subcriterion (b).
Application of criterion A4 is appropriate, as population reduction has been projected across a time period including both the past and the future and where the causes of reduction may not have ceased, may not be understood, and may not be reversible. Based on criterion A4 this subpopulation will suffer a depletion >80% relative to subpopulation size three generations ago. The applicable subcriterion under criterion A4 is (b) an index of abundance appropriate to the taxon (counts of tracks).
The subpopulation also qualifies for the Endangered category under criterion A2b. We also assessed the subpopulation under criteria B, C and D to the North West Indian Ocean Loggerhead subpopulation, which did not qualify for a threatened category under these criteria.
No population viability analysis (Criterion E) was available and the North West Indian Ocean 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 Habitats and Ecology section below). 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 Habitats and Ecology section below) 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 years.
For the North West Indian Ocean subpopulation, track counts have been collected in a standardized way at an index beach which is considered as representative of the overall nesting activity of the subpopulation (Tucker et al. 2013, Witherington et al. in press). From one past and one recent abundance values (each representing the annual average of five year track counts) we calculated annual and overall trends (past-present) for this index nesting site, and then we calculated the overall subpopulation past trend. The oldest data collected are from the period 1985-1990 and were compared to recent data (2009-2013) reflecting a dramatic past-present decline of 71% (Table 1 in the Supplementary Material). Another dataset from a past period (1977-1986) is probably methodologically comparable and reports an average value over 10 years of 596 tracks per day (Ross 1998, J.P. Ross, pers. comm). This value would provide a past-present decline of 68%.
Several threats are known for this subpopulation, including bycatch in fisheries, egg predation, and coastal development (Hamann et al. 2013), although quantification of the impact to the subpopulation is not available. No or limited management has been implemented (Hamann et al. 2013) to address these threats, therefore it is likely that these threats have not ceased. Hence, such a situation fits criterion A2 (the causes of reduction may not have ceased or may not be understood or may not be reversible). Since the inferred reduction was >50%, also supported by the additional set of past data, the North West Indian Ocean subpopulation qualifies for the Endangered category under criterion A2, and the applicable subcriterion is (b) an index of abundance appropriate to the taxon (counts of tracks).
We also evaluated this subpopulation against Criterion A4, using the same overall scheme as described above. Criterion A4 permits for analysis of population trend during a “moving window” of time (i.e., over three generations), but where the time window must include the past, present, and future. Furthermore, multiple time frames are to be examined, and the maximum decline calculated for a given time frame is to be compared to the thresholds (IUCN 2014). Therefore, we made the same assumption about the earliest available historical abundance being equivalent to the population abundance for generations past, and estimated future population abundance in 2028, 2043, and 2058 (i.e., at 15, 30 and 45 years since 2013, considered as the present time) which all fall within the next generation (i.e., 45 years). These future projections assume that the derived population trend will continue without deviation during the next generation. Implicit in this assumption is that no changes to degree of threats or conservation efforts impacting rookeries, subpopulations, or the global population will occur during that time. Given the existing threats to this subpopulation, and the fact that no or limited management exists to reduce these threats (Hamann et al. 2013), this is a reasonable assumption in the absence of better information. Projecting the past decline (criterion A2) forward, this subpopulation would decline of 92% at year 2043, and the maximum decline estimated (IUCN 2014) would be 96% at year 2058 (Table 2 in the Supplementary Material). This projected reduction exceeds 80%, which is also supported by the additional set of past data (Ross, 1988, J.P. Ross, pers. comm.). Consequently, the Northwest Indian Loggerhead subpopulation qualifies for the Critically Endangered category under criterion A4, and the applicable subcriterion is (b) an index of abundance appropriate to the taxon (counts of tracks).
Since the subpopulation area includes a large marine area, from the Gulf of Aden to the Arabian Gulf (Hamann et al. 2013, Rees et al. 2010) 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 critic life stage. In addition to the main nesting area in Masirah island, nesting is documented on at least 178 beaches in Oman and also in Socotra island, Yemen (Baldwin et al. 2003). Although only a limited number of clutches are laid at these sites, such a diffuse nesting makes it difficult to assess the exact AOO. Regarding the other three subcriteria, while a continuous decline can be reasonably assumed (see criterion A), there are no data to assess possible extreme fluctuations and the identification and quantification of locations, as defined for this criterion (IUCN 2011), is difficult for the same reasons mentioned above. In conclusion, the subpopulation does not meet the requirements for a threatened category under criterion B1 and cannot be assessed under criterion B2 because of data deficiency.
To apply criterion C, the total number of adult females and males is needed. Unfortunately, an estimation of the current total abundance of the subpopulation is not available and the only available information is represented by approximate annual nest counts of 70,000 (see the Population section below). 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. The available estimations for remigration interval and nests per females per season are 2.6-3 years (Hamann et al. 2013) and 5.5 nests per female (Tucker et al. 2013) respectively. The proportion of females is not available and without it only the number of adult females can be tentatively estimated with the following formula: adults = nests * nests per female-1 * remigration interval. If mid values of the above ranges are considered (2.8 years and 5.5 nests per female), the adult females alone would be >35,000, thus well above the threshold of 10,000 adults of both sexes required for qualifying for a threatened category. Therefore, although some other subcriteria could be met, like an estimated continued decline >10% or >90% individuals in one ‘subpopulation’ of the subpopulation (if Masirah island is so defined), the North West Indian Ocean subpopulation does not meet the requirements for a threatened category under criterion C.
To apply criterion D, the total number of adult females and males is needed. The same arguments reported for criterion C apply for criterion D1 which would require <1,000 adults to qualify for a threatened category. Regarding criterion D2, AOO and number of locations, although uncertain, are probably above the thresholds (typically <20 km² and ≤ 5 locations, respectively) required to qualify for a threatened category (see criterion B).
In conclusion, the North West Indian Ocean subpopulation does not meet the requirements for a threatened category under criterion D.
Sources of Uncertainty
The most important source of uncertainty for the assessment of this subpopulation is that it is based on only one index site and the lack of an estimation of total abundance. 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 West Indian Loggerhead subpopulation breeds in Oman and Yemen (Baldwin et al. 2003). Its marine habitats extend from the Gulf of Aden to the Arabian Gulf (Al Mohanna and Meakins 2000, Hamann et al. 2013, Rees et al. 2010) (Figure 2 in the Supplementary Material).|
Native:Bahrain; Djibouti; Eritrea; Iran, Islamic Republic of; Kuwait; Oman; Pakistan; Qatar; United Arab Emirates; Yemen
|FAO Marine Fishing Areas:|
Indian Ocean – western
|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 (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).|
Population abundance estimates are not available for the North West Indian Ocean Loggerhead subpopulation. The only available index of population abundance is represented by nest counts. The average annual nest counts in the period 2010-2014 at Masirah island, Oman, was 64,561 nests (Tucker et al. 2013, Witherington et al. in press), while about 5,000 nests per year are estimated in other nesting sites in Oman and 50-100 females are estimated to nest annually in Socotra island, Yemen (NMFS NOAA USFWS 2011). These data suggest that Masirah island hosts over 90% of the nests of this subpopulation. Based on the figures above, we consider here a total abundance of 70,000 nests per year for the entire subpopulation. If a conversion factor of 5.5 nests per female per year (Tucker et al. 2013, Witherington et al. in press) is considered, about 13,000 females would nest annually in this subpopulation.
|Current Population Trend:||Decreasing|
|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 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:||Loggerhead Turtle eggs are harvested in this region 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 North West Indian Ocean Loggerhead subpopulation are represented by fisheries, egg predation, and coastal development (Hamann et al. 2013), although quantification of the impact to the subpopulation is not available.
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 North West Indian Ocean Loggerhead subpopulation, some management or protection is limited to Masirah island nesting grounds (Hamann et al. 2013).
|Citation:||Casale, P. 2015. Caretta caretta (North West Indian Ocean subpopulation). The IUCN Red List of Threatened Species 2015: e.T84127873A84127992.Downloaded on 22 August 2017.|
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