Walking a Fine Line: Miniature Distance Sampling Reveals Greater Abundance of Imperiled Conchos Pupfish in Marginal Habitats

Authors: Lindsey Elkins, Joshuah Perkin, Matthew Acre, Megan Bean, Sarah Robertson, Ryan Smith

Year: 2022

Abstract

Desert spring systems of the American southwest hold high local fish endemism and are ranked among the most threatened ecosystems in the world. The prioritization of conservation resources to protect species living within these arid landscapes requires knowledge of species abundance and distribution, but traditional survey methodologies can be challenging to apply in shallow ecosystems occupied by diminutive species. For example, the plight of desert-dwelling Conchos pupfish (Cyprinodon eximius) is representative of freshwater fishes the world over, including population extirpations caused by human poisoning of streams and reservoir construction, to the extent that the species was once considered extinct in the USA. We developed a novel application of miniature distance sampling to investigate spatiotemporal patterns in Conchos pupfish abundance and coupled this approach with species distribution modelling to guide conservation actions. Our multiscale approach included surveying abundances within 5-m transects (101-m), nested within three reaches (102-m) of the Devils River, USA (104-m), combined with species distribution modelling within stream segments (103-m) across the range of the species within the Río Grande basin, MEX and USA (105-m). Modelling revealed Conchos pupfish range correlated with low December precipitation and climate moisture index, but high herbaceous land cover and potential evapotranspiration rates. Within the Devils River, abundance was greatest, and most volatile, at the reach that experienced the greatest amount of drying, and among transects with minimal velocities and shallow depths. These results collectively highlight Conchos pupfish use of habitats on the margin between aquatic and terrestrial realms, where slight reductions in water availability could strongly affect the species. Our transferable framework provides conservation guidance by identifying (1) transect locations where fine scale protected areas might be delineated, (2) reaches where high abundances could be protected or used for repatriation, and (3) stream segments where future surveys might be conducted.