Population Response of Giant Galápagos Tortoises to Feral Goat Removal

Published source details Marquez C., Gibbs J.P., Carrion V., Naranjo S. & Llerena A. (2013) Population Response of Giant Galápagos Tortoises to Feral Goat Removal. Restoration Ecology, 21, 181-185.
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This study is summarised as evidence for the following.

	Action	Category
	Remove or control invasive or problematic herbivores and seed eaters Action Link

Remove or control invasive or problematic herbivores and seed eaters

A controlled study in 1995–2005 on two islands in the Galápagos (Márquez et al. 2013) found that removing feral goats Capra hircus resulted in an increase in the percentage of juvenile giant tortoises Chelonoidis nigra vandenburghi, whereas the percentage of juvenile giant tortoises on an island with no goat removal remained stable. With goat removal, the percentage of tortoises captured that were juveniles was higher in the second phase of goat removal (2000–2005: 24% of tortoises were juveniles) compared to the first phase (1995–1999: 5% juveniles), whereas at two locations with no goat removal juvenile numbers remained constant (1995–1999: 3% and 1%; 2000–2005: 1% and 2%). With goat removal, a total of 669 tagged tortoises were recaptured over the course of the study, and with no goat removal, 103 tortoises were recaptured. Goat removal was carried out on one island in 1995–2005. A total of 62,868 goats were removed, with around 85% of those goats being removed in the initial phase (1995–1999). No goat control was carried out on the other island. On the goat removal island, tortoises were sampled along 2–8 km long transects (placed randomly in four altitudinal zones) for 11 years; twice a year from 1995–2000 and once a year from 2001–2005, and all tortoises were individually marked. The same monitoring approach was used at two locations on the island without goat removal.

(Summarised by: Maggie Watson, William Morgan)