Caretta caretta (South Pacific subpopulation)
|Scientific Name:||Caretta caretta (South Pacific subpopulation)|
See Caretta caretta
|Red List Category & Criteria:||Critically Endangered A2b ver 3.1|
|Assessor(s):||Limpus, C. & Casale, P.|
|Reviewer(s):||Wallace, B.P. & Pilcher, N.J.|
The South Pacific Loggerhead subpopulation nests in eastern Australia and New Caledonia. Its marine habitats extend throughout the south Pacific, from Australia to south America (CMS 2014) (Figure 2 in the Supplementary Material). Genetic markers indicate that the South Pacific rookeries of Australia and New Caledonia represent a distinct subpopulation or regional management unit (Boyle et al. 2009, Fitzsimmons and Limpus 2014, Wallace et al. 2010).
The eastern Australia nesting population, which is more abundant than the New Caledonia nesting population, experienced a strong decline that qualifies for the category Critically Endangered according to IUCN Red List criterion A2b.
Application of criteria A2 is appropriate, as population reduction has been observed in the past where one cause of reduction was understood, reversible, and largely ceased while other significant causes of population decline are still operative, poorly understood and unmanaged. Based on criterion A2 this subpopulation suffered depletion relative to subpopulation size three generations ago ≥80%, although available data do not allow an exact estimation. Applicable subcriterion under criterion A2 is (b) an index of abundance appropriate to the taxon (counts of nesting females at nesting beaches. We also assessed the subpopulation under criteria B, C and D to the South Pacific subpopulation, but the subpopulation did not qualify for any threatened category under these criteria.
No population viability analysis (criterion E) was available and the South Pacific Loggerhead subpopulation assessment was conducted by applying criteria A, B, C and 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). In the South Pacific Loggerhead subpopulation (specifically in eastern Australia), population assessment also occurs at index foraging sites using tagging-recapture studies (see below).
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 & 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 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 years.
For the South Pacific Loggerhead subpopulation, the distribution of turtles nesting has been comprehensively surveyed in eastern Australian and New Caledonia. In eastern Australia, approximately 80% of the Loggerhead Turtle nesting has been concentrated at five major nesting beaches (Wreck Island, Woongarra Coast, Tryon Island, Erskine Island, Wreck Rock), each supporting hundreds of nesting females per year in the 1970s (Limpus and Limpus 2003b, Limpus 2008, Limpus et al. 2013). The remainder of the nesting population is dispersed at a large number of small nesting aggregations with 10s or <10 nesting females per year (Limpus 2008; unpublished data from Queensland Department of Environment and Heritage Protection (QDEHP), Queensland Turtle Conservation Project; Limpus et al. 2013). No nesting population in New Caledonia has been identified with more than tens of females nesting annually (WWF New Caledonia, unpublished data, 2006).
In New Caledonia, anecdotal information suggests a decline in the last decades, although it cannot be quantified (Limpus et al. 2006). In eastern Australia, long term counts of nesting females are available for seven index nesting sites: two index nesting beaches with total annual tagging census since the late 1960s to 2014 (Woongarra Coast, Heron Island) and four index nesting sites with mid-season tagging census from the 1970s to 2014 (Wreck Island, Lady Musgrave Island, Northwest Island and Wreck Rock beaches) and Tryon Island with mid-season tagging census counts in 1977 and 1996 (Limpus et al. 2013). These nesting sites are all located in Queensland, therefore the Queensland sites are considered to be the index sites for the whole South Pacific subpopulation (eastern Australia and New Caledonia). From the mid 1970s to 1999 a continuous and strong decline (86%) was observed (Limpus and Limpus 2003b): from approximately 3,500 nesting females per year to approximately 500 nesting females per year. Since 2001 the downward trend ceased and reversed (Limpus et al. 2013) with the annual nesting population increasing to approximately 700 nesting females per year by 2010 (unpublished data from QDEHP, Queensland Turtle Conservation Project). This was explained by the implementation of TEDs (Turtle Excluder Devices) in trawlers, and the mortality caused by this fishing gear was considered to be the main cause of the previous population decline (Limpus et al. 2013). Since 2010 to 2014 there has been a downward trend in nesting numbers recorded at the three major index nesting beaches (Woongarra Coast, Wreck Island and Wreck Rock) and a minor index nesting beach (Lady Musgrave Island) (unpublished data from QDEHP, Queensland Turtle Conservation Project). Hence the breeding population is now regarded as being in a new state of decline, with a population size less than it was in 2010, i.e., <700 nesting females per year, representing a decline >80% since the mid 1970s (3,500 nesting females per year).
This recent reduction in annual breeding numbers cannot be explained by any identified increase in adult mortality throughout the adult foraging range for this population. It is hypothesized that it is associated with a decline in recruitment of oceanic juveniles into the neritic foraging populations. At two index neritic foraging areas (the southern Great Barrier Reef and Moreton Bay), there has been a continuing decline in the proportion of loggerheads recorded that have recently recruited to coastal residency from the oceanic pelagic dispersal phase from at least the late 1980s to 2012 (Fig. 3 in the Supplementary Material) such that the occurrence of such recruits to coastal foraging are now uncommon in the foraging populations. This decline in recruitment to the foraging habitat is consistent with the results of the modelled mark-recapture data which indicate a failure in recruitment to coastal foraging. Given the 13 year lag between recruitment from oceanic pelagic foraging to commencement of breeding (Limpus and Limpus 2003a) further declines in the adult population in the decades to come can be expected as old age turtles die and adult recruitment declines.
Regarding the Southern GBR, Limpus et al. (2013) wrote: “Based on a tagging-recapture analysis of the loggerhead turtle population resident on the coral reefs of the southern GBR, (Chaloupka and Limpus 2001) identified that it declined at 3% per year during 1985 to the late 1990s. Because this decline occurred within a foraging population with very high, constant annual survivorship values and within a habitat with few anthropogenic impacts, they hypothesized that the decline was due to failure of recruitment from the post-hatchling oceanic dispersal phase. The decline in numbers of recently recruited immature C. caretta captured on these coral reef feeding areas of the southern Great Barrier Reef during the late 1990s (Limpus and Limpus 2003a) is consistent with this hypothesis.” Regarding Moreton Bay, the trend in population numbers for loggerhead turtle population that forages in Moreton Bay (Limpus et al. 1994) has been examined using a multi-state capture-mark-recapture modelling approach, examining the estimated number of adults, pubescent immatures and prepubescent immatures of both male and female during 1990-2008. This study shows a clearly declining foraging population across two decades (Fig. 4 in the Supplementary Material) even though adult and immature annual survivorship has remained high and constant across the study period (Chaloupka and Limpus, in prep).
The presumed decline in juvenile loggerhead recruitment from oceanic pelagic foraging to coastal benthic foraging can be due to the cumulative impact of current multiple threats causing reduced survivorship of hatchling and post-hatchling loggerhead turtles in the South Pacific. These threats include nesting habitat degradation inducing reduced hatchling survival and skewed sex ratios, predation on eggs and hatchlings by introduced predators, ingestion of plastic debris, and bycatch (see the Threats section for a detailed description of these threats).
In conclusion, the South Pacific Loggerhead subpopulation showed a strong decline >80% which is continuing nowadays and the causes of which have not ceased and are not completely understood. In such a context the subpopulation qualifies for a Critically Endangered category under criterion A2, and the applicable subcriterion is (b), an index of abundance appropriate to the taxon (counts of nesting females).
Since the subpopulation area includes a large marine area from Australia to South America, the extent of occurrence (EOO) exceeds the vulnerable threat category threshold (20,000 km²) for criterion B1. Regarding criterion B2, the area of occupancy (AOO) for sea turtles is identified by the nesting beach habitat, which represents the smallest habitat at a critical life stage. Since the appropriate scale for AOO is a grid 2x2 km, the AOO thresholds for the three threatened categories (10 km², 500 km² and 2,000 km²) correspond to 5, 250 and 1,000 km of linear coast, which is a more appropriate measure for sea turtles nesting beaches. Along the eastern Australian and New Caledoneian coasts the vast majority of nesting beaches are known but a few loggerhead may nest in others sites outside of eastern Australia and New Caledonia (Anonymous 2007, Limpus 2008). Respective to the above thresholds, probably the total length of the nesting beaches is approaching 1,000 km, but with about 80% of the eastern Australian nesting occurring on <30 km of beach at the five principle nesting locations. The total length of the seven index nesting sites of Queensland (see criterion A) is ~40 km.
Regarding the second subcriterion (number of locations, i.e., geographically or ecologically distinct areas in which a single threatening event can rapidly affect all individuals (IUCN 2014)), >50% of the current nesting population occurs on the mainland nesting beaches of eastern Australia where there is substantial but largely unquantified loss of eggs to predators and increasing impacts of coastal lighting on hatchling survival. Many nesting beaches are known that can be grouped in a number of major and minor rookeries along the eastern Australian and New Caledonian coasts (Anonymous 2007, Limpus 2008), however, grouping them in an exact number of locations as defined for this criterion is not easy.
Regarding the third subcriterion (continuing decline or of extreme fluctuations), although the subpopulation declined from the 1970s to the 2000s, and showed evidence of recovery during 2001-2010, the population is now again showing evidence of decline since 2010 (Limpus et al. 2013).
In conclusion, the South Pacific subpopulation does not unambiguously meet the requirements to qualify 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 number of adults in the subpopulation is not available. Therefore, the subpopulation cannot be assessed under criterion C.
To apply criterion D, the total number of adult females and males is needed. Although an estimation of the current total abundance of the subpopulation is not available, (Limpus and Limpus 2003b) indicate that the adult females breeding for the year represents less than 10% of the total adult population in the foraging ground. This subpopulation does not trigger the threshold for a threatened category (<1,000 adults) under Criterion D. Regarding Criterion D2, AOO exceeds the threshold for the Vulnerable category (<20 km²; see criterion B) and the large number of nesting locations do not trigger the threshold for the Vulnerable category (<5 locations), even though existing threats have been identified. In conclusion, the 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 the lack of standardized long-term data series of nesting activity (in New Caledonia) and the lack of an estimation of total abundance. However, as explained above (criterion A) this knowledge gap cannot affect the final assessment result under criterion A.
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 Pacific subpopulation breeds in eastern Australia (Queensland and New South Wales) and New Caledonia (Limpus 2008). Its marine habitats extend throughout the south Pacific Ocean form Australia to south America (CMS 2014, Hamann et al. 2013, Limpus 2008) (Figure 2 in the Supplementary Material).|
Native:Australia; Chile; Ecuador; Fiji; French Polynesia; New Caledonia; New Zealand; Niue; Papua New Guinea; Peru; Solomon Islands; Tokelau; Tonga
|FAO Marine Fishing Areas:|
Pacific – western central; Pacific – southwest; Pacific – southeast; 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): 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).|
The abundance of the South Pacific subpopulation has not been estimated, although the available data from index nesting sites indicate that the annual number of nesting females has been <700 in recent years (Limpus et al. 2013; unpublished data, QDEHP Queensland Turtle Conservation Project).
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||The distribution, habitat and ecology of loggerhead turtles in the South Pacific Ocean has been reviewed (CMS 2014; Limpus and Limpus 2003a,b; Limpus et al. 2013). The Loggerhead Turtle nests on island and mainland sandy beaches in tropical and temperate regions of eastern Australia and New Caledonia, between latitudes 19-32°S. 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). In the case of the South pacific Loggerhead Turtle population, this open ocean development occurs across the entire South Pacific Ocean. After approximately 16 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 approximately 29 years of age (Avens and Snover 2013, Limpus et al. 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 3.82 years for females (Limpus 2008) while males will have a shorter remigration interval (e.g., Hays et al. 2010, Wibbels et al. 1990). Adult males and females undertake breeding migrations of up to 2,600 km from their home foraging areas to their respective nesting beaches, traversing coastal and oceanic zones (Limpus et al. 2013, Plotkin 2003). The adult loggerhead turtles display high fidelity to their respective foraging and breeding areas. During non-breeding periods adults reside at coastal neritic feeding areas that coincide with juvenile developmental habitats (see above reviews).|
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 are harvested in the South Pacific region for human consumption of eggs, meat, and other 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) and Limpus (2008) as:
Regarding the South Pacific Loggerhead subpopulation, recent reviews (CMS 2014) expressed extreme concern regarding future recruitment to the adult breeding population for this subpopulation that is being driven by continuing unmanaged mortality at three separate phases in the early life of this population: impact of coastal lighting on hatchling dispersal and survivorship (Berry et al. 2013), ingestion of synthetic debris during post-hatchling dispersal in the east Australian Current (Boyle and Limpus 2008); bycatch mortality of large post-hatchlings in the long line fisheries of Peru and Chile (Alfaro-Shigueto et al. 2011).
The well identified threats to the South Pacific subpopulation are represented by oceanic fisheries through the whole south Pacific area including international waters, coastal fisheries in south America and Australia, predation on eggs in Australia (dogs, foxes, varanids) and New Caledonia (dogs), ingestion of anthropogenic debris (Boyle and Limpus 2008), and harvest by coastal communities in some south west Pacific countries. The direct take of loggerhead turtles and/or their eggs is negligible in eastern Australia but occurs at an unquantified level in New Caledonia. Excessive bycatch mortality in long line fisheries (Alfaro-Shigueto et al. 2011, Donoso and Dutton 2010, Mangel et al. 2011, Shigueto et al. 2006) throughout the South Pacific are wide spread and largely inadequately quantified for numbers caught and mortality rates. Additional threats are negative impacts of coastal lighting (disruption of ocean finding behaviour with resulting reduced survivorship of hatchlings and reduction in adult nesting populations at illuminated beaches), boat strikes, and entanglement in anthropogenic debris (Hamann et al. 2013, Limpus 2008, Limpus et al. 2013).
The quality of nesting habitat is deteriorating with the negative impacts of coastal lighting (disruption of ocean finding behaviour with resulting reduced survivorship of hatchlings and reduction in adult nesting populations at illuminated beaches) threatening breeding success at multiple mainland nesting beaches and at Heron Island. These impacts are largely unquantified but increasing (Berry et al. 2013, Kamrowski et al. 2012, Limpus et al. 2013), using satellite imagery of night illumination from the earth’s surface, have identified the Woongarra Coast as one of the two most light-polluted nesting areas along the Australian coast and hence posing a high risk to successful marine turtle breeding in the area. There are indications that the quality of the coastal foraging habitat of loggerhead turtles in the South Pacific is deteriorating in response to rising sea surface temperatures with resulting decline in annual breeding rates (Chaloupka et al. 2008). There are indications of reduction in habitat quality at the principal nesting location of the Woongarra Coast with rising summer temperatures resulting in hatchling sex ratio approaching 100% female and a reduction in hatching success in recent hot summers (Chu et al. 2008).
There is a variable and continual loss of eggs to introduced red fox and domestic dogs and in recent years native varanid lizards along the hundreds of kilometres of mainland nesting beaches in south Queensland which support more than half of the total annual nesting in Queensland. While not well documented, the level of predation has been reduced from the unsustainable losses of the 1970s and 1980s, Clutch losses are still in the low tens of percent of clutches being lost.
While ingestion of synthetic debris by coastal foraging loggerhead turtles occurs at only a low incidence, there is excessive ingestion of plastic debris and associated debilitation and death with small post hatchlings (>50% of examined small post-hatchlings) travelling south in the eastern Australian Current from the nesting beaches and out into the Pacific to the east of Australia (Boyle and Limpus 2008).
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 the Conservation of Migratory Species of Wild Animals (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.
Loggerheads are legally protected in Australia and specific protection and management regulations are in place in some nesting sites (restricted access, predators control) and at foraging habitats (Turtle Excluder Devices for trawlers) (Hamann et al. 2013, Limpus 2008).
The Convention on the Conservation of Migratory Species of Wild Animals (CMS) COP 11 passed a resolution endorsing the implementation of a Single Species Action Plan for the Loggerhead Turtle in the South Pacific (CMS 2014). This action plan has yet to be formally implemented.
|Citation:||Limpus, C. & Casale, P. 2015. Caretta caretta (South Pacific subpopulation). The IUCN Red List of Threatened Species 2015: e.T84156809A84156890.Downloaded on 18 September 2018.|
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