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Chelonoidis duncanensis 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Reptilia Testudines Testudinidae

Scientific Name: Chelonoidis duncanensis (Pritchard, 1996)
Common Name(s):
English Pinzón Giant Tortoise, Duncan Island Giant Tortoise
Spanish Tortuga Gigante de Pinzón
Synonym(s):
Chelonoidis nigra ssp. duncanensis (Pritchard, 1996)
Geochelone elephantopus ssp. ephippium (Günther, 1875)
Geochelone nigra ssp. duncanensis Pritchard, 1996
Geochelone nigra ssp. ephippium (Günther, 1875)
Testudo elephantopus ssp. ephippium (Günther, 1875)
Testudo ephippium Günther, 1875
Taxonomic Source(s): Fritz, U. and Havas, P. 2007. Checklist of chelonians of the world. Vertebrate Zoology 57(2): 149-368.
Taxonomic Notes: The previous Red List assessments for Galápagos tortoises treated the various allopatric island populations as subspecies of Chelonoidis nigra (now named Chelonoidis niger), as did several authors (Pritchard 1996, Caccone et al. 1999, Beheregaray et al. 2003, Fritz and Havas 2007,TTWG 2007, Rhodin et al. 2008). However, other authors have considered them as full species based on morphology (Bour 1980, Fritts 1983, Ernst and Barbour 1989) and the more recent consensus among researchers (Caccone et al. 2002; Russello et al. 2005, 2007; Poulakakis et al. 2008, 2012, 2015; Chiari et al. 2009) is to treat most as full species based on congruent patterns of mitochondrial and nuclear variation. This elevated species-level taxonomy has been largely accepted by TTWG (2009, 2014) and TEWG (2015) for most, but not all, phylogenetic lineages of Galápagos tortoises. This Red List assessment therefore now treats C. duncanensis as a full species, rather than retaining its previous subspecies ranking from earlier Red List assessments    

This species from Pinzón (Duncan Island) was included on IUCN Red Lists before 2007 under the name Geochelone nigra ssp. ephippium. However, this name was interpreted by Pritchard (1996) to actually refer to Chelonoidis abingdonii, the Pinta Giant Tortoise, and therefore was replaced by the name duncanensis Pritchard, 1996, a recommendation accepted by Fritz and Havas (2007) as well as TTWG (2007, 2014). While the name duncanensis is used here, as it has been on the Red List since 2007, a genetic analysis of the ephippium type specimen is planned, which will determine whether the name change is indeed warranted. Many researchers (e.g., Jensen et al. 2015), including most of the Assessors on this account, continue to use the name C. ephippium for the Pinzón Tortoise, and we await genetic analysis for a final determination as to the correct name to use.

Assessment Information [top]

Red List Category & Criteria: Vulnerable A1abde; D1+2 ver 3.1
Year Published: 2017
Date Assessed: 2015-04-22
Assessor(s): Cayot, L.J., Gibbs, J.P., Tapia, W. & Caccone, A.
Reviewer(s): Rhodin, A.G.J. & van Dijk, P.P.
Contributor(s): IUCN Galapagos Tortoises Red Listing Workshop, Galapagos National Park Directorate
Facilitator/Compiler(s): van Dijk, P.P.
Justification:

After collapse of the population in the 19th century due to targeted exploitation, mostly by whalers for food (Pritchard 1996), recruitment was prevented by predation of hatchlings by introduced Black Rats. The population has recently (last three decades) started to recover as a result of reintroduction of headstarted animals. A successful rat eradication campaign was carried out in December 2012, and the first in situ live hatchlings sighted in 2014. The historic effective population size has been estimated at around 850 adult individuals (Jensen and Russello unpubl. data); the census population on Pinzón in December 2014 was estimated at 486 animals of all age classes combined (~70% adult), with additional young animals held at the Galápagos National Park Directorate’s Tortoise Centre on Santa Cruz Island. Recent genetic analyses found that Pinzón tortoises maintain high levels of variation in situ despite their well-documented decline, although the effective population size (Ne) for this species is 50-60 (Garrick et al. 2015, Russello et al. unpubl. data). Generation time of the Pinzón Giant Tortoise is estimated at 60 years; while all of the native reproducing adults on Pinzón are well over 100 years of age, many of the head-started animals released between 1970–1990 are now reproducing. Thus within three past generations the population declined from its historic level of at least 900 to a low of 100–200 older adult animals in 1960, and has since increased to about 500 animals in the wild at present, of which not all are mature, representing a current population of mature adults at about half of historical levels, qualifying for Vulnerable A1abde. Genetic data show that founders of the captive population are a reasonably diverse and representative group, although the headstart cohorts are not representative of the wild population (Jensen et al. 2015). Future head-start activities should strive to collect eggs and hatchlings from all nesting zones  to ensure capturing the full extent and distribution of genetic variation. Notably, native reproduction is again underway as of December 2014 (Tapia et al. 2015). At fewer than 1,000 mature adults occupying a single subpopulation, the species also meets the criteria for Vulnerable D1. The size of Pinzón, and thus maximum extent of occurrence (EOO), is 18 sq. km., of which at most 9 sq. km. is occupied by suitable habitat (area of occupancy – AOO), qualifying for Vulnerable D2; with a range of less than 20 sq. km., the species will always qualify as Vulnerable D2 even if full historic population levels are restored. This assessment also incorporates contributions from the international workshop on Galápagos tortoises convened by the Galápagos National Park Directorate in July 2012. This species was previously listed on the Red List in 1996 as Chelonoidis nigra ssp. ephippium, and since 2007 as Chelonoidis nigra ssp. duncanensis, with a status assessment of Extinct in the Wild, a listing that was unfortunately inaccurate, as more than 100–200 wild individuals have always been known to persist on Pinzón

Previously published Red List assessments:

Geographic Range [top]

Range Description:Occurs only on the very small island of Pinzón (Duncan Island), Galápagos Islands, Ecuador. The size of Pinzón is 18 sq. km, of which at most 9 sq. km (50%) is suitable tortoise habitat (J.P. Gibbs unpubl. data).
Countries occurrence:
Native:
Ecuador (Galápagos)
Additional data:
Estimated area of occupancy (AOO) - km2:9
Number of Locations:1
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population: Based on an estimated average density of one tortoise per hectare of suitable habitat, the pre-human population size was estimated to have been about 900 adults (J.P. Gibbs unpubl. data). The population collapsed in the 19th century due to targeted exploitation by whalers (Pritchard 1996) and then threatened by further collecting for museums and exploitation by fishermen and potentially other mariners at the beginning of the 20th century. Potential recovery through recruitment during the 20th century was prevented by total predation of hatchlings by introduced Black Rats. The population only started to recover after the establishment of a conservation breeding program initiated in 1965 and re-introduction of head-started animals beginning in the 1970s. In the early 1970s, the population was estimated at 150-200 (MacFarland et al. 1974). The 2014 population on the island was estimated at 486 animals of all age classes combined; the 20 adults held in captivity were returned to Pinzón in 2015 and an additional 229 juveniles have been repatriated there since then. Genetic analyses have suggested that the repatriated tortoises do not capture the full complement of genetic diversity present in the native adults. Although the most recent study indicates that the repatriated tortoises are, in general, a good representation of the genetic diversity of the native adults, future collections of eggs/hatchlings will focus on all nesting zones  to ensure the highest overall genetic diversity of the captive reared tortoises released back to the wild (Jensen et al. 2015).
Current Population Trend:Increasing
Additional data:
Number of mature individuals:300-400, 340Continuing decline of mature individuals:No
Population severely fragmented:No
Continuing decline in subpopulations:No
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:Yes

Habitat and Ecology [top]

Habitat and Ecology:

Chelonoidis duncanensis is a saddlebacked tortoise, a morphological adaptation that increases the vertical range of foraging options, from grazing on herbaceous vegetation to browsing on shrubs and cactus; the Pinzón ecosystem is largely dry xeric brushland.

Systems:Terrestrial
Generation Length (years):60

Use and Trade [top]

Use and Trade: The population was heavily exploited by whalers in the 19th century who provisioned their ships with living tortoises (Pritchard 1996).

Threats [top]

Major Threat(s):

Previously threatened by offtake of live adults to provision whalers and others during the 19th century, followed by intensive collecting for museum specimens; in the 20th century, predation of all hatchlings by introduced Black Rats prevented population recovery until a program of head-starting (begun in 1965), followed by repatriation of the tortoises beginning in the  1970s. Rats, eradicated in 2012, still have an impact via their legacy of destructive activities, including potential effects on cactus regeneration from which it will take decades to recover. Major El Niño events (1982-83 and 1997-98) also had a major impact on cacti, causing the death of many.

Conservation Actions [top]

Conservation Actions:

Legislation and regulations: Chelonoidis duncanensis is protected under Ecuadorian national law. It has been included in Appendix I of CITES since 1975, prohibiting all forms of commercial international trade. All of Pinzón and thus the entire native range of C. duncanensis is protected as part of the Galápagos National Park. Following the extirpation of most of the adult population of this species by 19th century exploitation by whalers and the subsequent total depredation of hatchlings by introduced Black Rats in the 20th century, a captive breeding and headstart program was initiated on Santa Cruz Island in 1965 by the Charles Darwin Research Station, and is currently run by the Galápagos National Park Directorate. Gradual repatriation of headstarted tortoises has been successfully undertaken since the 1970s (Rhodin et al. 1983, Caporaso 1991, Cayot et al. 1994), and the population is recovering. In December 2012, a rat eradication campaign was successfully completed. The first tortoise hatchlings born in the wild were documented in December 2014 (Tapia et al. 2015). Rearing young in captivity will continue for some time while the population continues to grow.


Citation: Cayot, L.J., Gibbs, J.P., Tapia, W. & Caccone, A. 2017. Chelonoidis duncanensis. The IUCN Red List of Threatened Species 2017: e.T9021A3149054. . Downloaded on 13 December 2017.
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