Continuing Volcanic Eruption Further Threatens Endangered Galapagos Tortoise
Howard L. Snell
Program Leader Associate Professor
Vertebrate Restoration Ecology Herpetology Curator
& Ecological Monitoring University of New Mexico
Charles Darwin Research Station Albuquerque, NM
Galapagos Ecuador
howard@fcdarwin.org.ec
1 October 1998
Continued Volcanic Eruption Threatens Galápagos Tortoises Already
Endangered by Introduced Species
A volcanic eruption on the southeastern slopes of Cerro Azul, Isla Isabela,
Galápagos, Ecuador has covered large areas of tortoise habitat with molten
lava. While volcanic eruptions are natural events, the potential impact of
this one exacerbates a series of anthropogenic effects that have severely
reduced the populations of two types of Galápagos tortoises. In the past
the crews of visiting whaling ships and residents of the Galápagos Islands
hunted tortoises to near extinction across most of Sierra Negra and large
portions of Cerro Azul, the two volcanoes of southern Isla Isabela.
For at least the last 100 years the populations have been unable to
naturally recover from those declines because successful reproduction was
severely curtailed. Introduced pigs and dogs prey upon the nests,
hatchlings, and young of the tortoises and a recently introduced ant
attacks hatchling tortoises as they emerge from their eggs. Due to the
combination of these effects the population of Geochelone elephantopus
vicina(1), the more typically shaped, "dome" tortoise, has been reduced to
fewer than 2,000 individuals. The other type of tortoise living in the
area, Geochelone e. guntheri(1), has a noticeably flatter shell than other
Galápagos tortoises and apparently numbers fewer than 100 individuals -
making it one of the most endangered of all Galápagos tortoises.
At midday on 15 September a radial fissure on the SE slope of Cerro Azul
erupted. The first lava flow from the eruption extended to the east before
turning southeast towards the coast. That flow ran through habitat of G.
e. vicina, the more numerous and widespread type of tortoise, but
apparently avoided nesting zones and densely inhabited regions. On 25
September the lava flow branched near its source, sending a new flow south
into the region called "Cinco Cerros." That flow is headed directly into
the area where the last G. e. guntheri remain and towards their only known
nesting area. During a flight over the region on 29 September the flow was
estimated to be 1.5 km from the nesting area, but its progress had slowed.
However, observations by ground crews at "Cinco Cerros" on 1 October
confirm that the eruption continues. As of 1 October one G. e. guntheri
and six G. e. vicina have been found burned by lava or fires associated
with it.
In response to this new threat, the Galápagos National Park Service and the
Charles Darwin Research Station have decided to incorporate 20 adults of G.
e. guntheri into their captive breeding and repatriation programs.
Previous efforts by those institutions to restore endangered populations of
Galápagos tortoises have been extremely successful and provide models for
this new project. With 12 to 14 females and six to eight males the project
can expect to produce 100 to 200 hatchling tortoises a year. Those young
tortoises will remain in captivity until they reach approximately five
years of age. Previous studies indicate that at five years they are large
enough to resist attack by feral animals and that at least 60% of them will
survive to reach reproductive maturity within another 10 to 15 years in the
wild. Successfully initiating this project will promote the recovery of
these endangered tortoises from the effects of the recent volcanic activity
and decades of depredations from introduced animals. It is not necessary
to include additional individuals of G. e. vicina in the programs for
several reasons. They are widely distributed on Cerro Azul, many more
remain in the wild, and they are already well represented in the captive
breeding and restoration program of the Galápagos National Park Service and
the Charles Darwin Research Station.
The most difficult part of placing 20 new tortoises into the program is
finding and moving them. Adults can weigh up to 500 pounds and can occur 7
km or more from the coast. The breeding center in Villamil is 50 km from
Cinco Cerros across incredibly rough terrain. It is necessary to use a
helicopter to move tortoises to the coast where they can be loaded into
boats and brought to Villamil.
Footnote:
(1)The taxonomy of Galápagos tortoises is disputed. In this document we
use names that reflect documented morphological differences and common use
for over 90 years. If you prefer using alternative nomenclature for
Galapagos tortoises, feel free. If you wish to debate the nomenclature
used here, please send your comments to tfritts@Compuserve.com. Tom is
possibly more interested in debating taxonomy than I.
Contacts for Further Information:
Charles Darwin Research Station - cdrs@fcdarwin.org.ec, howard@fcdarwin.org.ec
Galapagos National Park Service - png@ga.pro.ec or PNG@ECUA.NET.EC
Volcanic History of Cerro Azul: Terry Naumann (naumann@nevada.edu) and
Dennis Geist (dgeist@uidaho.edu)
Hotspot Monitoring System: Luke Flynn (flynn@kahana.pgd.hawaii.edu)
http://volcano1.pgd.hawaii.edu/goes/about.html - follow links
Howard L. Snell
Program Leader Associate Professor
Vertebrate Restoration Ecology Herpetology Curator
& Ecological Monitoring University of New Mexico
Charles Darwin Research Station Albuquerque, NM
Galapagos Ecuador
howard@fcdarwin.org.ec