Plastic ingestion in giant tortoises as a novel anthropogenic impact for Galapagos wildlife

Abstract

The human population of Galapagos has rapidly increased in the last decades accelerating the anthropogenic pressures on the archipelago’s natural resources. The growing human footprint, including the associated inadequate management of waste, may lead to conservation conflicts. We conducted this study to determine to what extent giant tortoises were ingesting human waste in Santa Cruz Island, and which human-modified areas are most affected by this novel threat to environmental health. Additionally, we characterized the environmental debris available for tortoises to ingest and quantified tortoise abundance. We collected and processed a total of 6,629 tortoise feces along a gradient of anthropogenic disturbance based on human debris presence. We found 590 pieces of debris within human-modified areas (3.8 items/kg of feces) and only two pieces in the protected area (0.08 items/kg of feces). Plastic waste was the predominant garbage category we found into feces in the anthropic area (86.3%; n = 511), followed by cloth, metal, paper, synthetic rubber, construction materials, and glass. The composition of waste items found in the environment differed to the trash found within the feces, with plastics more abundant in tortoise feces than the environment. Tortoise abundance was higher in the protected area when compared to the human-modified, but proportion of tortoise’ recaptures was triple in the anthropic area than in the National Park. Additional tortoise health threats were observed during this study, including dog bite lesions, tortoise entanglement, and car accidents. Our results indicate that plastics are a frequent item in the diet of tortoises in anthropic areas of western Santa Cruz. More research is needed to understand the negative health impacts associated with plastics and other pollutants for Galapagos terrestrial species. We encourage local stakeholders to limit human-waste from entering the Galapagos environment to minimize threats to human and animal health.