Course:CONS200/2023WT2/Successes, challenges and the future of the reintroduction of Galapagos tortoises

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Map of the Galapagos Islands. Located in the Pacific Ocean, approximately 1,000 km from continental Ecuador and is composed of 127 islands.

Off the Eastern coast of Ecuador lies the chain of Galapagos Islands, which became the Galapagos National Park in 1959[1]. The exploitation of the turtles for food and oil in the 18th and 19th centuries, the continuous poaching, and the introduction of non-native species to the Galapagos Islands have induced the giant tortoise population decline and caused extinction on certain islands[1]. Due to this, the Galapagos Island Conservancy was established in 1985, and its long-term goals are to restore tortoise populations to their previous numbers and distributions on all the islands[1]. Starting in May of 2010, the Galapagos Conservancy released sterilized adult tortoises to act as ‘ecosystem engineers’, following the period of vegetative destruction by goats on the island[1]. The first 400 young tortoises have already been released onto the island, and releases are set to continue for the next 5-10 years[1]. However, these successes have not come without challenges. Captive breeding, invasive species, introduced diseases, and de-extinction are just a few to name[2]. The future of the Galapagos Islands remains variable, as we continue to reintroduce the Galapagos tortoises and preserve the ecology of the islands.

Galapagos Giant Tortoise

Importance of the Galapagos Tortoises & Their Interactions

The Galapagos giant tortoises are referred to as ecosystem engineers, meaning that they have a significant role to play in biodiversity and landscape-level heterogeneity[3]. They manipulate the abundance and distribution of other living organisms through direct effects of their diet (herbivory), disturbance and seed dispersal of the plant community[3]. Galapagos giant tortoises rely on cacti for food, shelter, and source of water[3]. In return, they help disperse the seeds of cactus. Therefore, the cactus and Galapagos giant tortoises have a symbiotic relationship that brings mutual benefits to both species.

On the Galápagos Islands where the population of large native herbivores is reduced, the islands are discovered to have severe issues of woody plant encroachment that are caused by the invasive feral goats and other livestock that overgraze and reduce the local grass density[4]. As a result, the population of woody plants increases and changes the competitive balance between woody shrubs and grasses in favour of the shrubs[4]. The loss of native grass species can ultimately result in land degradation and soil erosion[4].

With the reintroduction of the Galapagos giant tortoises on the Galápagos Islands, researchers found that these giant tortoises, acting as ecological replacement herbivores, can lead to board-scale changes in plant communities by significantly reversing the woody plant encroachment[4]. The woody shrubs are a source of giant tortoises' diet. By eating the woody plants, the giant tortoises help reduce the density and reproduction of these plants. They also utilize their bodies to mechanically wear off the root tissues of the adult woody trees, which eventually leads to the large mortality of the woody plant community, creating space for the grass species to grow and thrive and eventually restore the normal ecosystem function of the Galapagos islands[4].

Despite their important roles in ecosystem balance and health, the Galapagos tortoises are also known for their endemism on the island. Even though they were once found on most of the continents of the world,  the unlimited exploitation of Galapagos species in the past centuries by pirates, whalers, and fur sealers for their meat and shells, which were further processed into food and oil that lights the lamp, had led to massive extinction in many continents [5]. Today, the Galapagos tortoises are one of the two groups (the other one living on Aldabra Atoll in the Indian Ocean) of giant tortoises in the world, with a population of approximately 20000 to 25000 on the islands[5]. The reintroduction of the Galapagos tortoises and the continuing conservation of giant tortoise species have not only helped to restore the health and function of the ecosystem on the Galapagos Islands but also highlighted the importance of humans living in a harmonious relationship with nature and different unique species, especially with species like Galapagos tortoises that are critically endangered.

Factors Behind Extinction

The disappearance and decline of the Galapagos Island giant tortoises have been caused by many factors, many of them due to various human activities. Tortoise populations on three of the islands have become fully extinct in historical times, their extinction being caused by the predation of humans, as the tortoises have no natural predators themselves[6]. In the past, damaging actions from whalers, buccaneers, and fur sealers have been a great cause to the extinction of the giant tortoises on some islands.

Among the 15 recognized species of giant tortoises, the IUCN Red List categorizes six as Critically Endangered, three as Endangered, and two as Extinct[1]. The 18th and 19th centuries saw the extinction of several species on the Galapagos Islands, including giant tortoises and endemic rice rats, largely due to human exploitation for food and oils by buccaneers and whalers[1]. Tortoises were sourced for their fresh meat, which was advantageous for people on a ship because these animals can survive with a lack of food and water for several months[7]. They were also used for their oil, beneficial for lamps. Despite their benefits in the past, this exploitation resulted in a loss of 100,000 to 200,000 tortoises[7].

Apart from human actions, the threat of invasive species also contribute to the main causes of the decline and partial extinction of the Galapagos Islands tortoises.The introduction rats, goats, and pigs have caused major destruction to the giant tortoises, as these animals are not native and do not belong in the Galapagos ecosystem. The non-native animal species like rats, pigs and ants prey on tortoise eggs while dogs target the adult tortoises. These species also compete with the tortoises for food[7]. Other species, like goats, cattles, donkeys, and invasive plant species degrade and destroy tortoise habitats[1]. These species often contain a high proportion of endemic taxa which have contributed to the number of wildlife that became endangered[8]. Lastly, other species such as cattle, goats, and horses trample tortoise nests degrade the vegetation in their habitats[7]. The giant tortoises are affected by the barriers to the migration routes, woody plants being their main issue for migration[4]. Also, there could be possible heath concerns for the tortoises due to their close proximity with other farm animals[7]. Eradication initiatives have successfully eliminated these menacing species; nevertheless, ongoing monitoring is imperative since passing ships can reintroduce these species and even introduce new ones to the Galapagos Islands[9]. Despite these efforts, tortoise populations dwindled dramatically from an estimated 250,000 individuals to between 8,000 and 14,000 individuals by the 1970s[2].

While there are other contributing factors to the extinction of giant tortoises, human activities, such as poaching and tourism, and the threat of invasive species have remained the primary focus. The other factors include the overexploitation of the tortoises for meat and oil, agricultural habitat clearance, and the introduction of invasive animals to the islands. As mentioned before, humans and their natural ancestors have been the main predators for the Galapagos Islands tortoises[6].

Ongoing Challenges of Restoration Efforts

Reintroducing the Galapagos Island Tortoise has proven to be a difficult task. Over the years, human activities, invasive species, predation, and poaching have been significant issues.

Historically, human activities were the cause of invasive species becoming present on the island, either for meat supply or by accident through other means[2]. Invasive species such as goats, rats, donkeys, and cattle compete for food with the native tortoises on the island and are a threat to their survival[1]. The invasive species affect the survival of eggs and hatchlings because they prey on young tortoise nests[1]. For example, the black rats that were introduced in the 1800's will prey on the eggs and baby tortoises in the nests, decreasing the survival rates of the hatchlings[1]. This predation gives no chance for the slow-growing tortoises to reproduce[1].

Furthermore, invasive species have altered the vegetation complex of the island, hurting the native tortoise populations by disrupting their eating patterns and changing their habitat[2]. Goats have been a main issue, as they trample the tortoise's food sources and create erosion on the slopes they walk on[2]. Even worse is the fact that the goats destroy a critical resource on the island: the Opuntia cactus, a vital plant that provides food, shade, and water for the tortoises[2]. This severity of degradation varies across the islands, depending on the number of invasive species present, the current environmental conditions, and the topography of each island[2].

Since restoration efforts began in 1994, tortoise cohorts have still been declining, even as restoration efforts have continued[3]. Scientists are finding that resources are becoming limiting and island populations may be reaching carrying capacity[3]. This is often due to their high population density in certain areas of the islands, a result of the invasive species impacts[3]. Specifically, tortoises tend to prefer areas with a high density of cacti and low density of woody plants, areas that are becoming scarce on the islands[3]. Their movements are restricted to small island areas because woody plants block their paths for movement and reduce cacti availability through competition of light and water[3]. To compete against these plants would require significant human intervention, possibly by removing the woody plants or somehow incorporating more cacti into the tortoise environment[3].

On top of past challenges, the Illegal Wildlife Trade (IWT) remains a continuous threat to the Galapagos giant tortoises[10]. Due to their exploration for food and oil sources during the 18th and 19th centuries they have downsized to about 10% of their previous historical numbers[10]. Despite being protected under CITES and the Galapagos National Park laws, smuggling and poaching still exist due to their population scarcity, making them highly valuable on the black market [10]. With only 15 recognized species and two of them already extinct, the lack of funding to conserve this species is highly concerning[10].

The conservation of the Galapagos giant tortoises consists of many discourses, as the concept of 'conservation' reflects many perspectives of the intrinsic values nature's intrinsic value on the Galapagos Islands[11]. However, even though nature is valuable to humans does not always mean effective conservation strategies and actions are in place[11]. Conservation requires large financial investments and support, and funding is often lacking because habitat restoration demands an extensive amount of work and money[11]. In addition, local interests prioritize support towards using ecosystems for tourism and food over conserving it[11]. With over 200,000 visitors per year on the islands, economics increasingly dominate the discourse about the Galapagos ecosystem, creating a more economic based ecosystem rather than environmentally based[11]. To also conserve this valuable ecosystem, invasive species control, law enforcement, and community management are just a few factors needed for the Galapagos Island tortoises to thrive[11]. Controlling invasive species is high on the list of things to help the islands, along with strengthening the local government[11]. To ensure the survival of the giant tortoises and protect the island's biodiversity, we must effectively manage the threats they face in their isolated and complex ecosystem so that they will be able to keep reproducing and prosper in our future[11].

Successes in Monitoring & Management

Recent data shows that the Galapagos giant tortoises captive breeding programs established in 1965[12] and the reintroduction projects established in 2010[12] are on track to meet their goals of restoring tortoise populations to their current numbers and distribution[1]. Since the reintroduction project began in 2010, tortoise populations are now secure and at a very low risk of extinction[3]. In 2017, approximately half of the reintroduced tortoises were still alive and fertility rates were high enough to stabilize the population[3]. An important factor which allowed for tortoise populations to recover was the completion of Project Isabela[13]. Project Isabela began in 1997 and was the largest ecosystem restoration project ever conducted in a protected area[13]. The primary goal of this project was the removal of several introduced invasive species (like goats, rats, and pigs) that threatened the survival of giant tortoises and native plant communities within the islands[12]. Additionally, the project has also been successful in eliminating introduced rat species, which has allowed for a greater survival rate of tortoise hatchlings[13].

A major success from Project Isabela was the complete removal of introduced goats from three islands, Northern Isabela, Santiago, and Pinta[12]. In total, the project cost nearly $12 million and involved arial and ground hunting by rangers and trained snipers[12]. By 2006, Project Isabela achieved its goals and successfully eradicated all 183,000 goats. After the invasive goats were removed, native plants began to regrow, which allowed for endemic animal populations to return to their natural habitats[12].

Another success story resulting from restoration efforts is the reintroduction of giant tortoises on Santa Fe Island. Santa Fe Island is a small, relatively flat and uninhabited island at the center of the Galapagos[14]. It is one of the oldest volcanoes, with rock formations below the surface of the water that date back 3.9 million years[14]. Prior to the Giant Tortoise restoration project, tortoises were not present on the island; but, accounts from fisherman and whalers suggest that giant tortoises were once native to the island[1]. Genetic analyses of the bone fragments collected from the island suggest that the Santa Fe tortoise was a unique taxon, endemic to Santa Fe that went extinct in the mid-1800s[14].

Beginning in 2015, sterilized tortoises were reintroduced to Santa Fe Island to act as ecosystem engineers[1]. The endemic Santa Fe species went extinct long before the reintroduction project began, so Española tortoise—determined to be the most closely related to the Santa Fe species—were reintroduced[1]. The first group of 201 juvenile tortoises ranging in age from 5-8 years old was released in the interior of the island and additional cohorts of juvenile tortoises were released every year following[1]. Surveys and monitoring of the reintroduced population shows almost a 100% survival rate and dispersal of individuals to nearly all parts of the Island[1]. The Santa Fe tortoises are a very important success for the Galapagos Island Project and continue to motivate further conservation efforts on the Islands.

Management challenges still exist in the efforts to return tortoise populations to the high densities that they once had on the islands[3]. Currently, tortoise populations only occupy a small area of the Galapagos Islands and much of their habitat has been degraded by past disturbances; like invasive species and human activities, which ultimately limits the growth of tortoise populations. A recommendation to improve the long-term viability of the species would be to increase restoration of tortoise habitat such that the species can colonize larger areas within the islands[3]. For example, the removal of woody plants and shrubs could facilitate tortoise movement and allow for certain cactus species to reestablish, which is an important food source for tortoises[3]. However, the labor-intensive process of removing woody plants and the remoteness of the Galapagos Islands present logistical and economical concerns regarding this restoration strategy.

Future of Continued Conservation

The Galapagos Island tortoises have faced intense decline due to years of exploitation, poaching, predation, and habitat destruction, ultimately linked to anthropogenic influence. The endemic Giant tortoises reached extinction on three islands and populations reached critical levels on seven of the islands[1]. The restoration project to return tortoises to their historic range and abundance began with the establishment of the Galapagos National Park in 1959[1]. Captive breeding and release initiatives began in 1965, leading to the Galapagos Island Conservancy forming in 1985[1]. In 2010, the ongoing project began releasing sterilized tortoises to act as ecosystem engineers in order to restore the native vegetation destroyed by invasive species[1]. The hope is to use the sterilized tortoises to reduce invasive woody shrubs on the landscape, in order to make it suitable habitat to maintain large tortoise populations and to someday release the captively bred tortoises to their historic range[4]. However, this goal does not come without challenges.

As we look into the future, there is still work that must be done, not only to maintain the current successes within the Galapagos Islands but to also meet the long term goals of the Galapagos Island Conservancy. Since the discovery of the Galapagos Islands in the 1500s, humans have undeniably played the largest role in the decline of giant tortoises, as they brought with them many plants and animals, hunted tortoises for meat, and transformed the landscape so much that it became unsuitable for tortoises[12]. Although a key to conservation is to reduce human influence on the islands, the Galapagos Islands are becoming one of the most popular travel destinations, with more than a quarter-million people visiting every year[12]. Successes have been observed in terms of mitigating the effects of introduced species on the ecosystem; however, currently the number of introduced species still exceeds the number of native species[12]. Illegal hunting of the endangered giant tortoises also threatens the recovering populations[10]. Illegal hunting has become a significant threat because the current populations are found near the coast, which increases their vulnerability to poachers[10]. Similarly, illegal fishing within the Galapagos National Park further draws humans to the islands and depletes the ecosystem[12].

Another factor that plays a significant role in affecting the living condition of Galapagos tortoises is climate change. The El Nino phenomenon causes significant increase in the precipitation over the island, which would destroy the roots of the Opuntia cacti and in turn affect the Galapagos tortoises as they rely on cacti for food and shelter[15]. As the climate becomes warmer, the intensity and frequency of El Nino phenomenon could possibly increase, making the living condition harsher for the Galapagos tortoises and other species on the island[15] Therefore, the future conservation projects on Galapagos Islands must consider the impacts that climate change is likely to have on this region. 

In conclusion, if giant tortoises are to return to their historical distribution and abundance within islands, continued restoration of habitat, more investigation into the impacts of climate change, management of invasive species and mitigation of human activity must be prioritized[3]. The continued efforts to restore suitable habitat will allow tortoises to migrate further inland, away from poachers. Anthropogenic influence must also be strongly limited and monitored, such that invasive species do not continue to be introduced and natural habitat can return to its natural state. Finally, conservation efforts should continue in order to further remove invasive species in order to restore the equilibrium between native and introduced species[12].

References

  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 "Giant Tortoise Restoration in the Galápagos Islands". Galapagos Conservancy. 2022. Retrieved March 4, 2024.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Searcy, Christopher A. (2020). Gibbs, James P.; Cayot, Linda J.; Tapia Aguilera, Washington (eds.). Galapagos giant tortoises. Biodiversity of World: Conservation from Genes to Landscapes. Elsevier Inc. pp. 511–518. ISBN 978-0-12-817554-5.
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 Gibbs, James P; Hunter, Elizabeth A; Shoemaker, Kevin T; Tapia, Washington H; Caycot, Linda J (October 28, 2014). "Demographic Outcomes and Ecosystem Implications of Giant Tortoise Reintroduction to Española Island, Galapagos". Plos one. 10.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 Hunter, Elizabeth A.; Gibbs, James P. (March 2014). "Densities of Ecological Replacement Herbivores Required to Restore Plant Communities: A Case Study of Giant Tortoises on Pinta Island, Galapagos". Restoration Ecology. 22: 248–256.
  5. ↑ 5.0 5.1 "Biodiversity". Galapagos Conservancy. April 10, 2024. Retrieved April 10, 2024.
  6. ↑ 6.0 6.1 "Galapagos Tortoise". Wikipedia. Retrieved April 14, 2024.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 "Galapagos Giant Tortoise". Galapagos Conservation Trust. Retrieved April 14th, 2024. Check date values in: |access-date= (help)
  8. ↑ Ellis-Soto, Diego; Blake, Stephen; Soultan, Alaaeldin; Guezou, Anne; Cabrera, Fredy; Lotters, Stefan (2017 Jul 20). "Plant species dispersed by Galapagos tortoises surf the wave of habitat suitability under anthropogenic climate change". PLoS One. 12(7) – via National Library of Medicine. Check date values in: |date= (help)
  9. ↑ "Galapagos Giant Tortoises". International Fund for Animal Welfare. 2023. Retrieved April 14, 2024.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 Quinzin, M. C.; Bishop, A. P.; Miller, J. M.; Poulakakis, N.; Tapia, W.; Torres‐Rojo, F.; Sevilla, C.; Caccone, A. (2023). "Galapagos giant tortoise trafficking case demonstrates the utility and applications of long-term comprehensive genetic monitoring". Animal Conservation. 26: 826–838.
  11. ↑ 11.0 11.1 11.2 11.3 11.4 11.5 11.6 11.7 Benitez-Capistros, Francisco; Hugé, Jean; Dahdouh-Guebas, Farid; Koedam, Nico (March 2016). "Exploring conservation discourses in the Galapagos Islands: A case study of the Galapagos giant tortoises". Ambio. 45: 706–724. doi:https://doi.org/10.1007/s13280-016-0774-9 Check |doi= value (help).
  12. ↑ 12.00 12.01 12.02 12.03 12.04 12.05 12.06 12.07 12.08 12.09 12.10 Moore, Randy (2021). "Project Isabela". Galapagos: an encyclopedia of geography, history, and culture. 1.
  13. ↑ 13.0 13.1 13.2 Tapia, Washington; Gibbs, James P; Rueda, Danny; Carrion, Jorge; Villalba, Fredy; Malaga, Jeffreys; Quezada, Galo; Lara, Daniel; Cayot, Linda J (2016). "Giant Tortoise Restoration Initiative: Beyond rescue to full recovery" (PDF). Galapagos Report 2015-2016: 173–180.
  14. ↑ 14.0 14.1 14.2 Galapagos Conservancy. "Santa Fe Island".
  15. ↑ 15.0 15.1 Ona, Irma; Carlo, Giuseppe (2011). "Adapting to Climate Change in the Galápagos Islands" (PDF). World Wildlife Fund. World Wildlife Fund, Conservation International. Retrieved April 14, 2024.


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