Apr 24

Amongst the black lava rocks that line the wave-lashed edges of the Galapagos Islands, the world’s only sea-going lizard can be found.  Amblyrhynchus cristatus, the marine iguana, is a remarkable and well-known endemic reptile of the Galapagos Archipelago.  Though widespread and highly abundant on certain islands, small, declining and genetically distinct populations on other islands are causing concern for conservationists.  One population in particular, found at the very tip of the easternmost island of San Cristobal has garnered attention not only for its critically small size, but also for being highly distinctive in genetic terms.  This ‘Punta Pitt population’, named after its location, is so genetically distinct that we are investigating whether it deserves recognition as a new species or sub-species.

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A marine iguana at Isla Lobos, San Cristobal Island. Larger males, like this one, swim and dive to forage on sub-tidal algae, whereas smaller individuals graze along the intertidal zone

 Since 2012 we have travelled to San Cristobal each year to collect information and new samples that will teach us more about Punta Pitt iguanas.  Before we started, iguanas on San Cristobal were known from only two colonies which seem not to interbreed with one another.  We began in 2012 by sailing around the island and sampling iguanas wherever we encountered them.  We found and sampled many new colonies, all on the west coast.  The entire eastern side of the island, wild and wave-battered, sadly eluded us.

Processing samples in the field at La Galapaguera, where Punta Pitt type iguanas are found

Processing samples in the field at La Galapaguera, where Punta Pitt type iguanas are found

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Weighing a young iguana at Islotte Pitt

In 2013 we returned to San Cristobal, this time to take a closer look at Punta Pitt and investigate the threat posed by feral cats, known to eat marine iguana hatchlings.  We camped at a remote beach for seven weeks.  During this time we fitted four feral cats with GPS-enabled radio collars and followed their movements.  We also collected measurements, samples and photographs of marine iguanas in order to investigate both physical and genetic differences between iguanas on the island.  Though we were only three people at the camp, we were certainly not lonely; the resident mocking birds, as curious as they are comical, watched our every move.  Constant vigilance was needed to prevent the legion of local hermit crabs from stealing all manner of things, and most evenings provided a cascade of newly hatched green turtles on the dunes, making their way down to the sea.

The resident mocking bird, who assumed ownership of all our things at camp (especially any unguarded porridge)

The resident mocking bird, who assumed ownership of all our things at camp (especially any unguarded porridge)

Frigate birds oversee the dish washing at camp

Frigate birds oversee the dish washing at camp

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The finches give our packing boxes a close inspection

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Newly hatched green turtles begin their journey down the dunes to the sea at Salinas beach

We are now in the midst of the final field-season of my PhD.  This season will be shorter, and we intend to find a way to sample the East coast.  This will involve searching for safe landing sites with an experienced fisherman, and a lot of walking along lava rocks.  If we are successful, we will have surveyed and sampled almost the whole island.  Back in Germany, we are working hard to analyse the morphological and genetic data that will tell us whether or not Punta Pitt iguanas are a new species.  In any case, the information we have gathered here in San Cristobal will be a valuable contribution to assessing the conservation status of marine iguanas on this island, where their population is the smallest of any of the Galapagos Islands.

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Punta Pitt type iguanas on the headland at Playa Cafe, the white cross is a temporary mark which indicates a sampled iguana

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Amy MacLeod is in the final year of her PhD at the Technische Universität Braunschweig in Germany. You can contact her by email at ms.amymacleod@gmail.com

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