A Tortoise Bone from the California Gold Rush, and its Link to Long-Term Tortoise Conservation in Galapagos
By Cyler Conrad, Archaeologist at Los Alamos National Laboratory, and Laura Pagès Barceló, Educator at the Bosque Ecosystem Monitoring Program
In 2013, the remains of a Galapagos giant tortoise were recovered during the analysis of archaeological materials excavated in downtown San Francisco; the bones were mixed in with refuse deposits dating to the early 1850s, during the California Gold Rush. At the time, I (Cyler) was assigned the task of identifying the animal bones, as part of my work for the Cultural Resource Management firm, Archeo-Tec, in Oakland, CA. The identification of a Galapagos tortoise from a Gold Rush-era archaeological assemblage was a surprise! Why and how did Galapagos tortoise bones end up in downtown San Francisco, in a refuse deposit from the mid 19th century, well over 3,300 miles from its home?
My search for answers led me to historical archives, maritime journals, archaeological assemblages, and eventually to a collaboration with Laura at the University of New Mexico. Inevitably, as our search expanded, so did the questions we hoped to answer.
Galapagos tortoises are one of the most iconic animals in the world. For the past 500 years, explorers, pirates, whalers, merchants, and scientists have interacted with these reptiles, with both positive and negative outcomes. During the bulk of this time, tortoise populations were in continual decline due to exploitation for food by passing maritime and merchant vessels. The seafarers, remarkably successful in terms of the number of tortoises taken, distributed them throughout a broad geographic range around the world. During the California Gold Rush (~1850s), historic documents indicate that tortoises were carried from Galapagos by migrants moving to northern California – to San Francisco, Sacramento, and many other cities, towns, and mining camps. The gold mining population was hungry and tortoises provided a new source of food.
The discovery of a Gold Rush-era Galapagos tortoise bone provided a unique opportunity. Bones include information embedded in their organic and inorganic matrix that helps identify the type of diet and habitat the organism lived on during its lifetime. The tortoise humerus discovered in San Francisco dates to the 1850s, providing an exciting snapshot of mid-19th century tortoise dietary ecology in the Galapagos. This inspired to begin a project, along with our colleagues, to identify what types of foods tortoises had consumed during this period and how it compared to dietary changes over the next 100 years as the Islands went through major changes. For example, we expected tortoise dietary changes to be impacted by the introduction of invasive species, like goats, pigs, or cattle – animals that would overgraze and out-compete tortoises for food.
Along with our colleagues, including Marie Labonte and Brian M. Kemp at the University of Oklahoma, Patrick Campbell at the London Natural History Museum, Addison Wynn at the Smithsonian Institution, National Museum of Natural History, David Kizirian at the American Museum of Natural History, Lauren Scheinberg at the California Academy of Sciences, and Emily Lena Jones at the University of New Mexico, we sampled tortoises collected during the 19th and 20th centuries from nine different islands to understand long-term tortoise dietary ecology. We tested carbon, nitrogen, hydrogen, and oxygen stable isotopes in bone collagen, bone apatite, keratin, and skin to determine diets from several dozen individual tortoises.
Our results indicate that there are differences in the types of diets eaten by tortoises on specific islands in Galapagos. This result matches modern and historical tortoise biological surveys, which suggest that these reptiles consume a large diversity of foods on an annual basis. For some islands, tortoises appear to eat cacti and other types of vegetation that are typically called CAM or C4 plants, based on their photosynthetic pathway. Tortoises feeding mainly on this vegetation type show more positive carbon stable isotope values. On other islands, where tortoises appear to eat more C3 plants, like forbs, shrubs, or leaves from trees, their carbon stable isotope values are more negative. In general, tortoises tend to feed on a wide range of food sources irrespective/independent of island and/or taxon.
As we continue our research and learn more about the specific diets that tortoises consumed through time, we expect that this tortoise dietary history will provide useful information to better understand the impact of the anthropogenic changes that occurred historically and continue to occur in Galapagos. We are excited to work alongside the Galapagos Conservancy to help broaden our dataset to include information on tortoise diets from biological surveys and records. The Giant Tortoise Restoration Initiative team is working hard to conserve, restore, and, in some cases, rewild tortoise populations throughout the Archipelago. We hope our stable isotope project will provide a dataset to help understand what types of foods tortoises ate in the past and how the tortoise diet has changed and where it remains similar to the past. Finally, we hope this information will provide a valuable contribution in the ongoing effort to restore native Galapagos vegetation and tortoise habitats in the future.
Cyler Conrad received his PhD in anthropology (archaeology) at the University of New Mexico, Albuquerque, NM, USA in 2018.
He is interested in understanding human-environment interactions in the past using archaeological and geochemical analyses.
Laura Pagès Barceló received her MS in biology at the University of New Mexico, Albuquerque, NM, USA in 2018.
She is interested in animal physioecology with an emphasis on sea turtle ecology and conservation.
Image credits: Newspaper transcript courtesy of the California Digital Newspaper Collection, Center for Bibliographic Studies and Research, University of California, Riverside. All other photos courtesy of the author.