Caretta caretta (North Pacific subpopulation)
|Scientific Name:||Caretta caretta (North Pacific subpopulation)|
See Caretta caretta
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Casale, P. & Matsuzawa, Y.|
|Reviewer(s):||Wallace, B.P. & Pilcher, N.J.|
The North Pacific Loggerhead subpopulation nests along the coasts of Japan (see Figure 2 in the Supplementary Material). This subpopulation has been identified as one genetic stock different from other Loggerhead stocks (Boyle et al. 2009) supporting 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) shows an increase over the past three generations. Moreover, both geographic distribution and population size are relatively large. Therefore, the North Pacific 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 increase comes as a result of decades of intense conservation programs, especially at nesting sites (Matsuzawa 2006) and the cessation of these programs would likely make the population decrease rapidly. 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 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 35 nesting sites showed a general positive trend relative to subpopulation size three generations ago (criterion A2; Table 1 in the Supplementary Material). We also assessed the subpopulation under criterion B, C, and D but the North Pacific subpopulation did not qualify for a threatened category in any of these criteria.
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 estimated its generation time as 45 years (see the Habitat and Ecology section). For criteria A1-A2, data from three generations ago (~135 years) 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 (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 Pacific Loggerhead subpopulation, we included time series datasets of 10-41 years from 35 nesting beaches in Japan (see Table 1 in the Supporting Material), comprising >90% of the total number of nests of the subpopulation. The total number of nests from these datasets was about 8,400 nests yr-1 in the most recent counts (average of five years), while the total number of nests in the subpopulation, including beaches with <10 years of monitoring (62 nesting beaches in total), was about 9,050 nests yr-1 in the most recent years (average of years 2009-2013; Sea Turtle Association of Japan, unpubl. data; Yakushima Umigame-Kan 2011a; Yakushima Umigame-Kan 2011b, 2012, 2013, 2014). 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. Trends ranged from negative to positive across the different nesting beaches. The overall trend for the North Pacific Loggerhead subpopulation was positive (+169%).
In addition to the above analysis based on nest counts, we also analysed track counts. Tracks of females emerging on the beach are a poorer population index because they include both emergences which result in a nest and those which do not, but in some nesting beaches track counts started before nest counts and therefore they may provide trends over a longer time period (24-60 years). Such track data from 14 nesting beach are coherent with nest data and show a positive overall trend from the past to present time (+259%; Table 2). However, we used the most conservative value from nest counts (+169% see above) as reflective of the actual trends.
In conclusion, the North Pacific Loggerhead subpopulation does not qualify for a threatened category under criterion A.
Since the subpopulation area includes a large marine area from Viet Nam to north America, 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. The total length of known loggerhead nesting beaches in Japan (ca. 300) is at least 1,635 km linear extent (Sea Turtle Association of Japan, unpubl. data; Yakushima Umigame-Kan 2011b). Since the appropriate scale for AOO is a grid 2x2 km, the above linear measure was converted to 3,270 km², which exceeds the vulnerable category threshold (2,000 km²). Regarding the number of locations (the term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals (IUCN 2014)), the number and geographical distribution of nesting beaches make the identification and quantification of locations difficult, but the number of locations should be probably considered as >10, so exceeding the threshold for a threatened category. Moreover, the subpopulation did not meet any of the other subcriteria also required: there is no evidence of continuing decline (see criterion A) nor of extreme fluctuations. In conclusion, the subpopulation does not meet the requirements for a threatened category under criterion B.
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 (average of years 2009-2013: 9,053 nests yr-1; Sea Turtle Association of Japan, unpubl. data; Yakushima Umigame-Kan 2011a; Yakushima Umigame-Kan 2011b, 2012, 2013, 2014). 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 seasons are 2.7 years and three nests per female respectively (Conant et al. 2009). 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. According to the above values the adult females alone would be about 8,100. Although the adult sex ratio is unknown, it would have to be extremely skewed (females >81%) in order to meet the threshold of <10,000 adults for a threatened category. Moreover, the subpopulation does not meet any other parameter threshold, i.e., continuing decline, % of mature individuals in one subpopulation, or extreme fluctuations. In conclusion, the North Pacific Loggerhead subpopulation does not qualify for a threatened category under criterion C.
The number of mature individuals (see criterion C) and AOO value (see criterion B) exceed the respective 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.
A recent population viability analysis (PVA) estimated at 6% the probability that the subpopulation declines at 50% of the recent abundance levels within the next 100 years (Van Houtan 2011), therefore the probability of extinction is <10% (the threshold for a threatened category) and the subpopulation does not qualify for a threatened category under criterion E.
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) (see Figure 1 in the Supplementary Material). The North-Pacific subpopulation breeds along the coasts of Japan and its marine habitats extend throughout most of the north Pacific Ocean (Kobayashi et al. 2008, Kobayashi et al. 2011, Wallace et al. 2010) (see Figure 2 in the Supplementary Material).|
Native:China; Japan; Korea, Republic of; Malaysia; Mexico; Philippines; United States; Viet Nam
|FAO Marine Fishing Areas:|
Pacific – western central; Pacific – northwest; Pacific – 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. 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 (see 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 North Pacific subpopulation breeds at least at 62 nesting sites, with a total number of nests estimated at ca. 9,050 nests yr-1 (average of years 2009-2013; Sea Turtle Association of Japan, unpubl. data; Yakushima Umigame-Kan 2011a; Yakushima Umigame-Kan 2011b, 2012, 2013, 2014).
|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 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 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 North Pacific subpopulation are represented by fisheries through the whole geographical range, including pelagic fisheries in international waters, and coastal fisheries in Japan, in the North-East China Sea and in Baja California (Kamezaki et al. 2003, Peckham et al. 2007, Peckham et al. 2008, Seminoff et al. 2014). Egg predation by Raccoons (Nyctereutes procyonoides) and Weasels (Mustela itatsi) occurs but has not been quantified. Egg poaching occurred in the past but has nearly disappeared in recent times thanks to conservation programs (Kamezaki et al. 2003).
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 Pacific subpopulation, conservation actions began in Japan in the 1950s with conservation at some nesting beaches (Matsuzawa 2006). In the 1970s conservation actions had a significant progress in beach protection and awareness campaigns to reduce egg poaching, which eventually ceased. Legal protection of the species was then established. Besides these actions focused on nesting sites, other conservation actions aimed to mitigate incidental bycatch in the high-sea drift fishery (moratorium in the top of 1990’s), the pelagic longline and coastal small scale fisheries have been successfully implemented or are in development (e.g., Gilman et al. 2007, Ishihara et al. 2011, Peckham et al. 2007, Peckham et al. 2008).
In 2012, a record level of loggerhead turtle strandings occurred in Baja California Sur (representing a 600 percent increase over the annual average) which prompted the U.S. to identify Mexico for bycatch of protected living marine resources (i.e., Loggerhead Turtles) pursuant to the High Seas Driftnet Fishing Moratorium Protection Act under the Magnuson Stevens Reauthorization Act (National Marine Fisheries Service 2013).
|Citation:||Casale, P. & Matsuzawa, Y. 2015. Caretta caretta (North Pacific subpopulation). The IUCN Red List of Threatened Species 2015: e.T83652278A83652322.Downloaded on 19 September 2018.|
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