High in the Venezuelan mountains, a vibrant jewel of amphibian biodiversity teeters on the brink of extinction: the black and yellow Rancho Grande Harlequin Toad (Atelopus cruciger).
This beautiful toad, once common across the northern mountains of Venezuela, now clings precariously to existence. Photo by Jaime Culebras (Photo Wildlife Tours).
Across Central and South America, harlequin toads of the genus Atelopus are facing a dire crisis. Out of 100 species, 83% are listed as globally threatened by the IUCN Red List, and 40% are Possibly Extinct. Habitat loss from human activities, the introduction of predatory fish like rainbow trout, and the devastating chytridiomycosis disease have decimated their populations. In Venezuela, the situation is particularly severe, with the Rancho Grande Harlequin Toad being the only one of the nine Atelopus species of the country with stable, albeit small, populations.
Despite these grim facts, there is a beacon of hope. The Atelopus Survival Initiative (ASI), launched in 2021, brings together researchers, conservationists, NGOs, zoos, governments, and local communities from more than 15 countries in a collaborative effort to save harlequin toads. In Venezuela, Centro para la Reproducción e Investigación para Arlequines (CRIA) leads the conservation actions for Atelopus cruciger.
Over the past few decades, the habitat of the Rancho Grande Harlequin Toad has shrunk dramatically, from 17,000 to just 80 square kilometers. Once widespread and abundant, today less than 400 reproductive individuals are estimated to persist in the wild, fragmented into two isolated subpopulations. This led to its classification in 2019 as Critically Endangered in the IUCN Red List.
ASI members Margarita Lampo (left) and Onil Ballestas (right) have been working tirelessly to save the Rancho Grande Harlequin Toad from extinction. Photo by Jaime Culebras (Photo Wildlife Tours).
CRIA and Center for Ecology at Instituto Venezolano de Investigaciones Científicas members and collaborators have monitored the toad population since 2005, establishing one of the longest ongoing studies of amphibian populations. Capture-recapture studies and visual counts suggested a relatively stable population size of 50-150 breeding individuals over the past two decades. Notably, despite chytridiomycosis infection, the Rancho Grande Harlequin Toad exhibits a degree of resilience, with birth and reproduction rates exceeding disease-induced mortality. This resilience likely stems from the relatively pristine environment of the remaining populations.
Drawing on extensive experience, CRIA is working with local and international partners on a multi-pronged approach. This combines scientific research, captive breeding programs, and community outreach to combat the threat of extinction.
Scientific research is crucial for understanding the toad's current conservation status and developing effective strategies. Captive breeding colonies serve as backup populations, akin to a Noah's Ark, to secure the species' survival and provide individuals for future reintroduction programs. Additionally, these colonies serve as an awareness-raising tool for visitors, especially children. Field surveys monitor existing populations and identify suitable areas for reintroduction programs.
The activities involve searching for lost populations in historic locations. Photo by Javier Mesa.
Recent expeditions led by CRIA revisited nine historical habitats of the Rancho Grande Harlequin Toad, meticulously searching for signs of its presence for more than 90 hours, covering around 30 km along seven rivers. Despite extensive exploration efforts, no evidence of additional populations was found. However, the team documented several pristine areas with ideal environmental conditions for reintroduction. These sites boast clean water, healthy forests, and minimal human disturbance.
The team also revisited the current known population to monitor its health and population parameters. Current estimates suggest an adult population of 34-162 individuals, indicating relative stability over the past two decades. The presence of juveniles further confirms ongoing breeding within this subpopulation.
The ex-situ component of the project has also yielded promising results. Employing advanced reproductive techniques, the captive breeding center has successfully bred hundreds of tadpoles and juveniles. This allowed for reintroduction trials, releasing around 200 tadpoles into carefully selected habitats. These tadpoles will be monitored over the coming months to assess their adaptation to the new environment, and a release of juveniles is planned for 2025.
Tadpoles were successfully raised from the captive breeding program. Photo by Jaime Culebras (Photo Wildlife Tours).
In addition to fieldwork, educational initiatives play a vital role in raising awareness and fostering a sense of stewardship among local communities. Workshops and interactive sessions held at local schools and at the Leslie Paint Zoo disseminate crucial information about the Rancho Grande Harlequin Toad and inspire a commitment to biodiversity conservation among the younger generation.
Creating environmental awareness among children and visitors to captive breeding centers is also an important component of the conservation project. Photo by Jaime Culebras (Photo Wildlife Tours).
Ultimately, this multifaceted approach, supported by funding from ASI, Indianapolis Zoo, and Amphibian Ark, represents a beacon of hope for the Rancho Grande Harlequin Toad. Through collective action and unwavering dedication, a glimmer of hope persists for the survival of this extraordinary amphibian species.
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