|Scientific Name:||Chelonoidis hoodensis (Van Denburgh, 1907)|
Chelonoidis nigra ssp. hoodensis (Van Denburgh, 1907)
Geochelone elephantopus ssp. hoodensis (Van Denburgh, 1907)
Geochelone nigra ssp. hoodensis (Van Denburgh, 1907)
Testudo hoodensis Van Denburgh, 1907
|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. hoodensis as a full species, rather than retaining its previous subspecies ranking from earlier Red List assessments.|
|Red List Category & Criteria:||Critically Endangered A1bde ver 3.1|
|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. & Rhodin, A.G.J.|
The Española tortoise experienced a historical population collapse primarily caused by targeted exploitation, followed by habitat degradation resulting from introduced goats, within the three most recent generations (generation time 60 years), from an estimated historical population of 2,400 to 14 adults left on the island by the 1960s (a 99% reduction). All 14 adults (plus one male later found at the San Diego Zoo) were taken to the Tortoise Centre on Santa Cruz Island to begin a breeding program. The genetic diversity of the 15 tortoises is lower than that found in other Galápagos tortoise populations, suggesting that the Española population had been low for some time and had undergone a previous bottleneck. Following more than 30 years of repatriating juvenile tortoises, the population was estimated in 2007 at 770–864 tortoises, including both repatriates and their offspring (Gibbs et al. 2014), a ca 67% reduction from historical levels. The population is genetically depauperate, and the effective genetic population size of bottlenecked cohort is less than eight, with all of the tortoises on the island either F1 or F2 offspring of the 15 founders (Milinkovitch et al. 2003, 2007, 2013). In addition, not all of the genetic diversity found in the 15 founders is present in the F1 population. The population change over the past three generations amounts to a > 90% reduction in effective adult population, qualifying the species as Critically Endangered, CR A1bde. Chelonoidis hoodensis was assessed (at the subspecies level), as Critically Endangered D (population < 50 mature individuals) on the 1996 IUCN Red List. This assessment also incorporates contributions from the international workshop on Galápagos tortoises convened by the Galápagos National Park Directorate in July 2012.
|Previously published Red List assessments:|
Chelonoidis hoodensis occurs on Española Island [formerly Hood Island] in the Galápagos Islands of Ecuador. Española has a total surface area of 60.5 sq.km, of which 6 sq. km (10%) is currently occupied by tortoises and 24 sq.km (40%) could potentially sustain tortoises.
|Range Map:||Click here to open the map viewer and explore range.|
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 2,400 adults (J.P. Gibbs unpubl. data). By the 1960s, the total global population was known to be 15 mature adult animals, 12 females and three males (one was located at the San Diego Zoo and returned to Galápagos in 1977). An intensive conservation breeding and re-introduction program has subsequently increased the population: nearly 1,900 have been repatriated and of those approximately 50% survive (Gibbs et al. 2014). A total of 1,837 animals have been reintroduced to Española since 1975; reproduction by the reintroduced animals was first observed on the island in 1990 (Márquez et al. 1991). Most recent survey data (2010) estimate about 700 animals at Tunas/Caco in the central part of the island, and an additional 100 animals inland of Gardner Bay, about 800 in total. Given that about half of all repatriated animals survive, many have now reached reproductive age. Estimates for the current population vary from 11-20%comprised of in situ recruitment, thus repatriated animals make up 80-89% of the in situ population. The success of this program is also demonstrated by genetic analyses which indicate that while none of the tortoises sampled in 1994 had hatched on the island, of those tested in 2004 and 2007, 3% and 24% were in situ hatchlings , respectively (Milinkovitch et al. 2013). The recovery of this population despite its extremely low effective population size is probably due to Española tortoises having been subjected to population bottlenecks at different points in time prior to the arrival of humans in the Archipelago, rather than a single drastic reduction in recent times (Garrick et al. 2012). These declines may have been related to environmental fluctuations, which may have led to purging of deleterious recessive alleles improving the long-term survival prospects of the repatriated population (Milinkovitch et al. 2013). Nearly 400 juvenile Chelonoidis hoodensis have also been introduced to the island of Santa Fé [Barrington], previously inhabited by an undescribed extinct tortoise species.
|Current Population Trend:||Increasing|
|Habitat and Ecology:||Chelonoidis hoodensis is a saddlebacked tortoise adapted for browsing on cacti and other higher-growing vegetation in drier shrubland ecosystems. Based on first successful in situ reproduction, in 1990, of reintroduced animals born in captivity as early as 1971, age at first reproduction is approximately 20 years, and generation time is estimated at 60 years.|
|Generation Length (years):||60|
|Movement patterns:||Not a Migrant|
|Use and Trade:||Completely overexploited for human consumption in the 19th century. Log book records indicate a minimum of 1,698 tortoises were removed from Española [Hood] between 1831 and 1868 (Townsend 1925, Pritchard 1996).|
Historical overexploitation of tortoises for human consumption has been the most significant impact on the Española tortoise. Further impacts were suffered by the introduction of goats (which competed for food with tortoises and affected vegetation regeneration structure). Goats were eradicated from Española in 1978. Their long-term impact, along with the absence of giant tortoises, however, has resulted in dense thickets of woody vegetation at a level not evident for the last 500-1000 years, making it difficult for tortoises to disperse to all of their historical range (Gibbs et al. 2014). Española is a small island, with a small area suitable for tortoises, placing them at risk of weather catastrophes. The island is particularly susceptible to the effects of climate change. Española has a low cactus population density (a result of the long-term presence of goats), which impacts the tortoises, as Opuntia cactus is an important resource for tortoises. The risk of future goat, rat, or other (re-)introductions remains. A second population of Española tortoises is currently being established on Santa Fé Island, to replace the undescribed native species that went extinct in the mid-1800s and to recover the ecological functions once provided by giant tortoises there. The Española tortoise is the species genetically and morphologically closest to the original Santa Fé tortoise (Poulakakis et al. 2012). This second subpopulation of Chelonoidis hoodensis on Santa Fé will serve as an insurance colony for this species.
Legislation and regulation. Chelonoidis hoodensis 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 Española Island, and thus the entire native range of C. hoodensis, is protected as part of the Galápagos National Park. Continued efforts are needed to manage and monitor the recovery of the population in situ. Genetic research has demonstrated that the diversity of the repatriates could be increased through selected mating pairs/groups; new breeding groups were established in 2017 for this purpose. The genetic diversity among the 15 breeders is low (compared to other Galápagos tortoise species), i.e., the population has been inbred for a long time already and probably experienced repeated population fluctuations (Garrick et al. 2012; Milinkovitch et al. 2013). Effective genetic population size is 5-8 animals. Improved genetic management of P1 is needed. Goats were eradicated from Española in 1978. However, as a result of the goats and the concurrent absence of tortoises, there is need for habitat management (reducing dense thickets of woody vegetation and expanding the cactus population). Therefore, tortoise repatriations have been suspended for the next ten years. During that time, juvenile Española tortoises produced in the Tortoise Centre on Santa Cruz Island have been released onto Santa Fe Island, where tortoises (similar in morphology and genetics) went extinct in the mid-1800s. Not only does this restore a tortoise population on Santa Fé, it provides a back-up population of Española tortoises in case of some catastrophe on Española.
|Citation:||Cayot, L.J., Gibbs, J.P., Tapia, W. & Caccone, A. 2017. Chelonoidis hoodensis. The IUCN Red List of Threatened Species 2017: e.T9024A82777079.Downloaded on 24 September 2018.|
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