07. Deaths of overwintering Nanorana spp. tadpoles due to desiccation during check dam maintenance in a western Himalayan stream, India

Abstract

affected by drought, although many amphibians exhibit plasticity in the duration of tadpole development, in response to drought conditions, with trade-offs such as reduced body condition, survival etc. (Cayuela et al., 2016; Yeung, 2021). Droughts may be induced by human activity such as when check dams are drained for maintenance purposes. Check dams are important civil engineering structures built for soil conservation, groundwater recharging and water extraction, and are very common in Indian streams (Agoramoorthy et al., 2008). Here, we report the first observations of the deaths of overwintering tadpoles of two species of Nanorana during check dam maintenance. It is known that check dams have negative impacts on stream channel morphology (Fortugno et al., 2017), water quality, velocity, and substrate fineness (Kang & Kazama, 2012), cause loss of larval microhabitat (Thomas et al., 2019), and influence the breeding ecology of frogs (Lind et al., 1996). However the influence of check dam maintenance has been little documented. Our observations concern two dicroglossid frog species. The small paa frog Nanorana minica (Dubois, 1975) that is associated with montane subtropical forests and streams distributed in Nepal, Uttarakhand and Himachal Pradesh at 1000–2400 m a.s.l. (Ohler et al., 2004; Bhattarai et al., 2020; Frost, 2021). It is listed as Vulnerable on the IUCN Red List and major conservation threats are waterway management and loss of habitat through forest clearance (Ohler et al., 2004). The other species is the Himalaya paa frog Nanorana vicina (Dubois, 1976) that is distributed in the Himalayan front of India, north-central Pakistan from Kashmir, Himachal Pradesh to Punjab, and Uttarakhand ranging from 2000–3000 m a.s.l. and is associated with montane streams, springs, fountains and other running water within open forest and grassland habitats (Ohler & Dutta, 2004; Frost 2021). Apart from morphological descriptions and other natural history records, little is known of the larval ecology of either species (Das & Dutta, 2007; Sircar, 2010; Banerjee et al., 2020; Gill et al., 2020; Jithin, 2021). Jithin (2021) reported overwintering tadpoles of N. minica and N. vicina from the western Himalaya, India. The overwintering tadpoles feed on periphyton growing on check dam walls, bedrocks, boulders, cobbles, leaf litter surface, submerged logs in the pool; humus and animal carcasses; the check dam pools also offer a temperature gradient (Boix-Fayos et al., 2007: Banerjee et al., 2020; Jithin, 2021). We recorded tadpole mortality at two check dam maintenance events along the Dhobhighat (Ringali Gad) stream, flowing through the Mussoorie Wildlife Sanctuary. This second-order stream flows through private resorts,