Population census of the Eastern Santa Cruz Giant Tortoise: Part 1

December 14, 2018

By Wacho Tapia, Director of the Giant Tortoise Restoration Initiative. Leer en español.

In the five years since I began leading the Giant Tortoise Restoration Initiative (GTRI) in Galapagos, I have organized and led many field expeditions — to Pinzón, San Cristóbal, Española, Santa Fe, and Wolf Volcano, one of the most difficult places in the Archipelago. But each time, I had the great advantage of knowing the area and the difficulties we would encounter.

Eastern Santa Cruz tortoise

An Eastern Santa Cruz tortoise in the arid zone

This time, however, I was organizing and directing a census of the Eastern Santa Cruz Giant Tortoise (Chelonoidis donfaustoi), the new species named in 2015. Based on our knowledge to date, the species is considered Critically Endangered. But it was essential that we determine the true status and range of the population to develop effective management measures for its long-term conservation. This expedition, however, was one of my greatest challenges.

I only knew a small portion of that section of the island, and like the census we carried out on San Cristóbal in 2016, this would be one of the biggest expeditions in the history of Galapagos conservation. In addition to covering known tortoise areas, we had to cover all areas we considered potential tortoise habitat — a total of 80 square kilometers of rugged terrain. And we would be working under adverse climatic conditions.

Hiking the area, we discovered that eastern Santa Cruz, much of which was little explored from a scientific point of view, is an extremely beautiful place. We were surprised, for example, to find lava flows (locally known as piedreros) running from an elevation of 120-130 m almost to the coast, so rough that not even tortoises can walk on them. And even in this period of drought, we found several matazarno trees (Psidia carthagenensis) in flower — very robust trees that have, due to their isolation, escaped illegal logging.

Tortoise nesting zone Eastern Santa Cruz Island

One of the tortoise nesting zones in the census area of Eastern Santa Cruz Island

In the more humid highlands, the landscape was completely different — green throughout, thanks to the constant garúa mists that had fallen during the last three months. But sadly, due to the invasion of introduced species and the presence of the agricultural zone, this part of the tortoises’ range is covered by elephant grass, blackberry, guava, and Cuban cedar. Although useful to humans, these species displace native species and are detrimental to the ecosystem.

Preparing for the census caused great stress. We’d been trying to complete it for a couple of years, but for a variety of reasons, it kept being postponed. To ensure that this year we would get it done, I started planning, in collaboration with the Galapagos National Park Directorate, in early 2018. To delineate the search blocks, I relied not only on the knowledge and expertise of park rangers and other experts, I also made several field trips to open trails.

Even so, when the day arrived to start the expedition, more unplanned issues arose. For example, the food was to be transported by mules, but to balance the weight, the folk loading the animals transferred products among the loads. The result? Each field team ended up without certain products — like oil and milk. The most serious lack in my group was coffee, which made for a miserable start to each day. I missed my coffee fix.

A tortoise digging a nest

An Eastern Santa Cruz tortoise digging a nest

We established 12 separate camps from the farms in the Agricultural Zone to the eastern coast of Santa Cruz. Each team of three was responsible for a defined search section (approximately 6.5 square kilometers), to ensure that we covered the total search area of 80 square kilometers. We’d rise in the dark, eat breakfast, and start out just as the sun rose, working until it set some 12 hours later — at which point our energy was depleted.

If possible, we returned to our camp for the night. Some nights, however, we were too far from camp and had to search for a nearby place with the fewest rocks to spread out our sleeping bags. If we were lucky, we’d find a small tunnel where we were more protected from the cold. We’d awake the next morning to the daily cry of ranger Marcelo Gavilanes: “Levantanse Bagotes” or “Get up you lazy bums.” After another breakfast in the dark, we’d begin another day searching for tortoises.

Marking a tortoise

A tortoise is marked for identification purposes during the census

With careful planning; the preparation of food, equipment, and water; a detailed field protocol; a long list of etceteras, and the expertise of the more than 50 park rangers, scientists, and porters who participated, we managed to complete the three weeks of intense but gratifying work. After successfully searching each section, we can now say, with complete certainty, that the range of the Eastern Santa Cruz tortoise covers an area not exceeding 40 square kilometers. Of course, there will always be a few individual tortoises that sporadically dare to explore outside those limits.

During the nearly three weeks of intense work, with 10 days focused on the tortoise area within the Galapagos National Park and the remaining days in the agricultural zone, we encountered 403 tortoises, marking each one with a microchip. Nearly 50% (190) of those encountered were juveniles, an excellent sign of a growing population. The final population estimate — based on our mark:recapture data — was 564 individuals.

Eastern Santa Cruz Tortoises

Eastern Santa Cruz Tortoises located and marked during the census

Completing this comprehensive population census only three years after the publication of the species description was made possible by financial support from the People’s Trust for Endangered Species and other donors to Galapagos Conservancy, and the enormous effort of park rangers and scientists. I wish to acknowledge and thank the entire team of professionals committed to tortoises and their conservation, and salute their ability to adapt to the adverse conditions we encountered — with enthusiasm and a smile on their faces.

Wacho TapiaWashington (Wacho) Tapia has served as the Galapagos-based Director of the Giant Tortoise Restoration Initiative since 2014. He coordinates and leads all GTRI fieldwork and plays a vital role in ecosystem conservation work in Galapagos. His work involves constant collaboration with the Galapagos National Park Directorate.

All photos © GTRI.



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