• Jithin Vijayan

Check Dams, Habitats and 'Cool' Tadpoles

In what kind of habitats do the ‘cool’ overwintering tadpoles live in Himalayan stream pools?

Do they change their habitat use patterns with the presence of check dams and across seasons? What are the implications of these changes, if any, when developing aquatic conservation plans?

Excited to share our new research article answering these questions!



Out today in the journal River Research and Applications of the International Society for River Science #Wiley


DOI: https://doi.org/10.1002/rra.4033


Before coming to the exciting results we found, let’s see what we already knew!

Understanding habitat requirements is important for developing conservation plans for any species. When coming to freshwaters - one of the most threatened ecosystems that often receive less attention in applied conservation management - this data is scarce and often difficult to collect.


Quantifying overwintering tadpoles and the features of their habitats - is often a challenging task in the field!; (A) quadrat sampling; (B) Boat survey during cold winter nights in pools that are difficult for wading; (C) measuring water depth and velocity in a natural pool


Flow modification to streams, such as check dams for water conservation and torrent control activities, are known to affect the stream communities by altering water depth, velocity, and substratum composition. (Mueller et al. 2011).


We have also shown recently that check dams can influence the behaviour and morphometric traits of overwintering tadpoles (Jithin et al. 2022)




But, studies on tadpole habitat use are limited, especially from modified habitats to answer our questions. This is when we know habitat constraints can lead to altered use of preferred habitat types, increasing competition, overexploitation and vulnerability to predation (Bunt et al. 2021).


When developing Habitat Suitability Criteria (HSC) curves, the biological component of habitat simulation models used in instream flow management, knowledge of seasonal and habitat type variation becomes important. This is because their applicability has been debated by issues with variation in preferences that occur through time and habitat availability (Dunbar et al. 2012).


Overwintering tadpoles feeding algae growing on the (A) logs in dammed pools; (B) check dam pools. Photo credits: V. Jithin



Overwintering tadpoles, spending the winter season by arresting their metamorphosis occurring in the montane streams of western Himalaya, and present in highly modified habitats by check dams are good models for answering our questions.


We wanted to know the influence of season and habitat modification on habitat use by overwintering tadpoles of Paa frogs (Nanorana spp.) and develop HSCs accordingly. For this, we looked at 2,435 tadpole occurrence points to see what kind of habitat they use in terms of water flow, depth, streambed substrate and hiding places. But we also needed to know what kind of habitat is available in the natural and modified (check dam) pools across the seasons.

In three natural and three check dam pools across winter and post-winter seasons, at every two-meter distance from the downstream, the observer waded or travelled in a toy boat across in a straight line and at every one-meter distance, recorded the kind of habitat available for the tadpoles. This means we captured a snapshot of the entire pool habitat available so that we can compare it with the kind of habitat tadpoles use.


Conceptual Illustration of the field sampling method and an image showing the condition of check dam after cleaning.

By comparing the habitat features available in the pools and those used by the tadpoles, we calculated the preference indices and subsequently developed habitat suitability curves.


🚨 What did we find?


➡️ Check dam and season can influence the water flow used by the overwintering tadpoles.

➡️ We found the influence of season on water depth used by the tadpoles.

➡️ Though natural pools did not show significant variation in habitat availability between seasons, modified pools clearly showed seasonal changes except in the case of instream cover.

➡️ Tadpoles mostly used intermediate depth (31-60 cm) and no flow areas in both pool types and seasons.

➡️ While the modified pool population mostly used humus substrate across seasons, tadpoles used leaf litter (winter) and gravel (post-winter) in natural pools.



To sum up: we show that it is important to incorporate seasonal and habitat type variations in hydrological modelling, for species occurring in anthropogenically modified habitats in highly seasonal environments (Theodoropoulos et al., 2018).

Based on the findings, we developed Habitat Suitability Curves (HSCs) for the overwintering tadpoles, which can be used for developing conservation plans in the Western Himalayan streams.



Previously, apart from fish and benthic invertebrates, HSCs have been developed for tadpoles of Rana boylii and Rana sierrae for generating habitat suitability indices for use in flow recommendations during hydropower relicensing.

The present study is the first one to develop HSCs for tadpoles in India.

Our HSC curves for depth across seasons suggest that 30-60 cm would be a suitable depth range for the tadpoles. The pool habitats in the study area should be maintained with this suitable range during the low flow season, especially during check dam construction and maintenance activities.


What are the implications of this study?

Since Himalayan streams are increasingly modified for water extraction, hydroelectric projects & recreation, the impact of these changes on aquatic habitat thus needs to be clearly understood for better management considering both people 👥 & aquatic life 🐟 needs.


END NOTE

This paper is from the last part of my MSc thesis 📒, from the Wildlife Institute of India, Dehradun. Financial and logistical support from @wii_india, @Uttkhand_Forest, @moefcc. Read the full paper to see what we found!


Access 🖱️the full paper here (read-only): https://onlinelibrary.wiley.com/share/author/EQCBTMZM4DNKCET34KJY?target=10.1002/rra.4033


Massive thanks to everyone who helped during my dissertation, especially Rishav Bhattarai, Sanul Kumar, Swati Nawani, Krishnendu Banerjee, Rawat family, and Devendar family for their assistance in the fieldwork. Many thanks to the anonymous reviewers who made constructive and encouraging comments which improved the manuscript quite a lot! Our team thanks Director, Dean, Research Coordinator, and M.Sc. Course Directors, WII for their support and encouragement during the study. We thank DFO, Mussoorie and RFO, Mussoorie WLS, for facilitating our research by providing fieldwork permits and logistical support.


Happy reading!

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