Abundance and detection correlates for Ash Meadows speckled dace across a heterogenous desert riverscape

Authors: Jacob Wolff, Michael Schwemm, Ambre Chaudoin, Michael Bower, Kevin Guadalupe, Joshuah Perkin

Year: 2024

Abstract

The Ash Meadows speckled dace Rhinichthys osculus nevadensis is a federally endangered minnow endemic to the Mojave Desert at Ash Meadows National Wildlife Refuge, Nevada. This subspecies was historically threatened by anthropogenic alterations such as groundwater pumping, agricultural redirection of spring outflows, non-native species introductions, and peat mining activities. Today, habitat restoration efforts to increase numbers are in place but require science-based evidence for guidance. Past surveys showed high abundances immediately after vegetation removal and channel restoration downstream of spring outflows. However, analyses that account for imperfect detection (i.e., capturing a dace when it is present) and responses to woody plant encroachment post-restoration are needed. This study identifies environmental correlates for dace abundance and detection. We distributed minnow traps across strong gradients of environmental variables hypothesized to correlate with abundance (i.e., water temperature, water velocity, canopy cover, channel area, and number of invasive crayfish). We used minnow traps to capture 244 and 314 dace in March and April of 2024, respectively, from Fairbanks, Jackrabbit, Tubbs, Bradford 1, and Bradford 2 springs, as well as a portion of the Kings Pool outflow. Preliminary results from N-mixture modelling suggest abundance correlated positively with canopy cover (i.e., more vegetation = more dace), water velocity, and channel area, while detection was negatively correlated with canopy cover (i.e., dace are less likely to be captured when vegetation is dense). These findings suggest natural vegetive cover (e.g., Coyote Willow, Ash trees) might benefit site abundances of dace despite reducing sampling efficiency. This presentation reports analyses from the first two of four sampling events.