Current distributional status of the critically endangered Valcheta Frog: Implications for conservation

Abstract

The Valcheta Frog, Pleurodema somuncurense (Cei, 1969), is a critically endangered species endemic from Somuncura plateau, Patagonia, Argentina. Although this frog is facing several human-related threats, the available information about its population status and trends is scarce. In order to update the range of the species, from 2013 to 2015, we conducted exhaustive surveys in all its geographical distribution, including sites never explored in the past. In 2014, we estimated occupancy and probability of detection with a three-visit survey in 40 sites of headwaters of Valcheta stream. Frogs were present in 58% of sites, and the probability of detection was high. We increased the known range of Valcheta Frog in 160%, by adding new sites occupied by the species. However, the status of the species remains of great concern, since its total range barely reaches 4 square kilometres.

Status and population dynamics of the Critically Endangered Valcheta frog Pleurodema somuncurense on the Patagonian Somuncura Plateau

“…Although exhaustive surveys were conducted between 2013 and 2017, no more individuals were recorded after the dam was constructed. The small size of the known habitat area and the high detectability of this frog (Velasco et al 2016) make the non-detection of individuals at El Destacamento un likely, and thus, we agree with the local population extinction hypothesis. Although a reintroduction program is currently underway to re cover the local population of El Desta camento, we decided not to consider this population as extant until the reestablishment is effectively confirmed.…”

“…In the case of El Ariete, the last record of individuals was in 1969 (Cei 1969b). After more than a decade of searching (Diminich 2006), we found only 1 isolated individual at this site in February 2015 (Velasco et al 2016). However, no more individuals were recorded during the following 3 yr, even after applying a high survey effort (Velasco 2018).…”

“…Although the factual causes of the absence of individuals in this population are difficult to establish, it is likely that they are associated with anthropogenic disturbance. The dam constructed in El Destacamento in 2009 not only caused the stagnation of water but also promoted con siderable pres-sure on the native vegetation by the livestock (Arellano et al 2017b), negatively affecting the stream habitats (Velasco et al 2016). Although exhaustive surveys were conducted between 2013 and 2017, no more individuals were recorded after the dam was constructed.…”

“…1). All currently known populations of the Valcheta frog Pleurodema somuncurense inhabit this stream (Velasco et al 2016).…”

“…The Valcheta frog is a micro-endemic species restricted to the hot headwaters of the Valcheta stream in the Somuncura Plateau. This frog faces a combination of threats, including habitat degradation (Chebez & Diminich 2008, Velasco et al 2016, direct predation by the invasive rainbow trout Onchorynchus mykiss (Úbeda & Grigera 2007, Basso et al 2012, Velasco et al 2018, potential trophic resource competition with the introduced characid fish Cheirodon interruptus (Velasco et al 2018) and infection by the chytrid fungus Batrachochytrium dendrobatidis (Arellano et al 2017a). All these threats are negatively affecting the Valcheta frog by promoting the isolation and decline of local populations, with at least 2 cases of local extinctions in recent decades (Velasco et al 2016).…”