By guest author Dr. James Gibbs of the State University of New York’s College of Environmental Science and Forestry (SUNY-ESF).
Wed Dec 3 2014 455 PM: Pre-trip log
We have a few moments to relax after several days frantically preparing for a comprehensive population survey of the giant tortoises of Pinzón Island. These notoriously tough tortoises eke out a living in the very sparse terrain of Pinzón – an arid island of rocks and thorns. After the depredation by whalers in the 1800s, tortoise numbers dropped to fewer than 200. Rats, introduced to Pinzón in the late 1800s, then preyed on all young hatchling tortoises, effectively reducing population growth to zero during the twentieth century. The Pinzón tortoise was in fact the first to be included in the Tortoise Breeding and Rearing Center on Santa Cruz, and the repatriation of “rat-proof” juveniles (about 5 years old) has helped to rebuild the population.
Then an exciting event took place in late 2012 – an eradication campaign to eliminate the rats! Are young tortoises crawling out of their nests and surviving as a result of this huge operation? Might we step out of the picture and let the tortoise population rebuild naturally? Answering these important questions is why are going to Pinzón.
It’s amazing the detail and effort that goes into planning these trips to ensure success. Although Wacho Tapia and I split the various duties, he ended up doing nearly all the work! Just buying food for 14 people was a challenge after a second supply boat to Galapagos sunk a few weeks ago, resulting in a dearth of products on store shelves. The very large bars of Ecuadorian chocolate Wacho was able to obtain will be particularly delicious mid-day after struggling up the rocky volcanic slopes and searching for tortoises.
Wacho also oversaw the gathering of all the equipment – machetes, files, tents, sleeping bags, boots, GPS units, tarps, stoves, pots, knives, cooking gas, notebooks, pencils, PIT tags for tortoises, measuring tapes, and on and on. Everything was then moved through the Galapagos National Park’s quarantine system, a three-day affair, and finally loaded onto the Guadalupe River, which involved several hours of bobbing in small dinghies in the rough waters of Academy Bay, moving back and forth from shore to ship. Wacho is a true master, pushing, guiding and coaxing in turn to move the complicated process ahead.
What was I doing all this time? I hid myself away with my computer to hatch our tortoise survey plan, which must pass muster scientifically while at the same time accommodating the reality of working in the field in Galapagos, with the number of days and Park rangers available. Our not entirely compatible objectives include: 1) estimate the size of the tortoise population and better delineate their distribution; 2) search for surviving hatchlings now that the rats are gone; and 3) collect blood samples from as many tortoises as possible to better understand the genetic diversity within this small population.
I began with a map of known tortoise distribution carefully constructed by Dr. Linda Cayot, who knows the island well from many years working there in the 1980s. I then developed a plan using two complementary census techniques that have proven effective in Galapagos conditions. The first method involves teams of two assigned to search for all tortoises in a pre-determined zone of about a one square kilometer area each day. They then repeat the search in the same zone three days later. The ratio of the number of tortoises marked the first day to the number of marked and unmarked tortoises the second day provides a population estimate.
The second method involves counting tortoises in 158 plots created with a GPS point and then searching the area within 20 meters of the point. Despite the headaches of developing the plan, I am always deeply satisfied when I hand it over to the Park rangers who work with such effort and pride to implement it. Nobody else on the planet can do this work as well as they.
At 10 PM tonight, we will catch a water taxi out to the Guadalupe River where we will search out a nook to catch as much sleep as possible. The ship will start its engines with a roar at 3 AM and head to Pinzón. Arriving there at dawn, we will scramble our gear ashore and immediately head up the slope for a long day in the field before returning to the coast to set up camp and eventually collapse into our tents.
More news when we return!
Dr. James Gibbs is Professor of Vertebrate Conservation Biology and Associate Chair of the Department of Environmental and Forest Biology at the State University of New York (SUNY-ESF). He has partnered with Galapagos Conservancy for many years in efforts to restore giant tortoise populations in Galapagos through the Giant Tortoise Restoration Initiative.
Read Part 2 of the Pinzón Island Population Survey series.