Captive breeding can prove to be a useful conservation approach in restoring populations of diminished wild animals. After the death of “Lonesome George” in 2012, the Galapagos now has a real conservation success story to tell of a closely related tortoise. The Hood Island tortoise once dwindled to a population of just 15 individuals, but now thanks to a five decade captive breeding program the wild population has reached approximately 2,100 individuals. Listed as critically endangered, this species is of high importance on its native home, the island of Española. The tortoise has been described as an ecosystem engineer which means it has a large impact on regulation and alteration of the Española ecosystem.
The major threats that faced this species were exploitation and habitat damage done by feral goats, introduced to the island in the 1800s. The goats fed extensively on the prickly pear cactus, an important source of food, water and shelter for the tortoises. In the 1970s conservationists stepped in to save the tortoise by culling and finally eradicating the goat from Española in the 1990s. As a safeguard, the last 15 individuals were taken into captivity. An intensive effort from the captive breeding program has seen the release of over 1,500 individuals to date. In 2007, 50% of the individuals released in 1975 were still alive. Today, the fecundity rates of the population are considered sufficient to ensure population persistence without human intervention.
Reaching a self-sustaining population is a major milestone in the conservation of this species. However, despite the success of the captive breeding programme the tortoises range remains restricted. This is due to a legacy of environmental damage left by the goats where woody plants replaced the important cactuses. The woody plants restrict cactus growth and the movement of tortoises. This prevents the tortoise from dispersing the cactus seeds creating a vicious cycle. The population growth of the tortoises has recently begun to slow and without more cactuses it is unlikely the population will grow beyond the current 2100 individuals. Predictions estimate a reduction in woody plant density of 50% would increase the tortoises’ carrying capacity by 52%. Captive breeding has undoubtedly helped bring this species back from the brink of extinction, highlighting its importance in endangered species conservation. This is especially true when regular reintroductions to the wild are implemented. However, of equal importance is the restoration of natural habitat, necessary for maintenance of large populations.