Weathering the storm: Improving the availability and stability of artificial shelters for hellbender salamanders

Abstract

Artificial shelters show considerable promise as tools for studying imperiled hellbender salamanders. Their full utility has not yet been fully reached in practice, however, because during initial trials shelters often became blocked by sediment or dislodged during high stream discharge events. To determine whether these challenges could be overcome, we deployed 438 artificial shelters of two different designs across 10 stream reaches and three rivers in the upper Tennessee River Drainage in 2013–2018. We recorded shelter entrance availability during surveys, and recorded which shelters became dislodged following high discharge events. We evaluated two hypotheses: (a) shelter availability was driven by shelter placement and maintenance frequency and (b) shelter stability was driven by shelter design and shelter placement. Shelters were available 78.6% of the time on average (range = 0–100%), and 88.6% (388 of 438) of shelters were stable across all high discharge events. Shelter availability was maximized by clearing sediment from shelter entrances at least once every 40 days (more often in impaired reaches with high siltation) and after large storm events, situating the shelter within 1 m of ≥5 boulders, and orienting shelters such that their entrances do not face directly downstream. Shelter stability with our initial shelter design was 77.5% (169 of 218), but approached 100% (219 of 220) for heavier (~40 kg vs. ~25 kg) shelters with recessed lids, and in reaches with abundant large boulders. Our findings demonstrate that with an improved design and careful placement, artificial shelters can serve as valuable tools for monitoring hellbenders in reaches with modest siltation.

Factors influencing the availability of artificial hellbender (Cryptobranchus alleganiensis) shelters in North Carolina, USA

“…Sediment blockage of shelter entrances was the most common reason for shelters being deemed unavailable in our study (96% of all unavailable occasions attributed to sediment blockage), similar to findings from Virginia (81% of unavailable occasions attributed to sediment blockage, Bodinof Jachowski et al 2020). Shelter dislodgement during our study was relatively rare (18% of unavailable occasions), which is also consistent with studies from southwestern Virginia (Bodinof Jachowski et al 2020, Button et al 2020 a ). Placing shelters in areas of the channel with greater relative flow velocities (i.e., the thalweg, which in our case was approximately mid–stream) increased shelter availability.…”

“…Shelter availability (71%) in our study is comparable to the average rate in southwestern Virginia (78.6%, Button et al 2020 a ), which was maximized in conditions that hinder sediment buildup. Sediment blockage of shelter entrances was the most common reason for shelters being deemed unavailable in our study (96% of all unavailable occasions attributed to sediment blockage), similar to findings from Virginia (81% of unavailable occasions attributed to sediment blockage, Bodinof Jachowski et al 2020).…”

“…The modified hydrodynamic design is a teardrop shape with an open bottom to allow access to natural substrate (Diaz 2020). We recessed the lid for all three designs to reduce lid loss and shelter dislodgment during high flows (Button et al 2020 a ).…”

“…Later work showed that increasing shelter weight, adding a recessed lid design, careful fine scale positioning of shelters at installation (i.e. selecting the angle of the tunnel entrance relative to the current), and frequent maintenance could nearly eliminate the risk of shelter dislodgement (Button et al 2020 a ).…”

Understanding landowner decisions regarding access to private land for conservation research

“…Upon making contact with a landowner, we asked if they would be willing to participate in one of two research projects. If the creek on their property was suitable for supporting hellbender populations, we asked the landowners if they would be interested in allowing scientists to install underwater concrete shelters (as in Button et al, 2020) for hellbenders on their property as part of a research project. If their property was not suitable for hellbenders, we asked landowners if they would be interested in participating in a citizen science project where they would collect water quality data to inform research on hellbenders.…”