The Influence of Groundwater Fluctuations on the Distribution and Habitat Associations of Two Cyprinid Fishes in a Desert Spring Complex.

Authors: Mark Grover, Chris Crockett

Year: 2018

Abstract

Relationships between temporal variation in groundwater levels and the distribution and habitat use of two cyprinid fishes, Least Chub (Iotichthys phlegethontis) and Utah Chub (Gila atraria), were examined at a spring complex (Leland Harris Spring Complex) in the Snake Valley of the Great Basin, Utah, USA in which groundwater has been monitored since 2009. Seasonal declines in shallow groundwater were associated with protracted periods of high evapotranspiration during 2009-2017. Temporal changes in groundwater levels explained 97% of the variation in the mean values of surface water levels obtained from measurements taken over a three-year period at 47 monitoring points. Bathymetric data, combined with data from surface water monitoring, indicated that the volume of surface water present in springs and spring-fed ponds when groundwater levels were at their lowest was only 19% of the volume of water present during peak groundwater levels. Visual and minnow trap surveys indicated that Least Chub and Utah Chub were usually associated with relatively deep water, but migrated annually from deep springs to ponds, which were used as spawning and juvenile habitat, when groundwater and surface water levels were high, returning to core spring habitats as ponds receded during the late summer and early fall. Populations of both species became increasingly fragmented as groundwater and surface water levels declined. Least Chub and Utah Chub tended to use the same core habitats from one year to the next during the late summer and fall, and were positively associated at both the habitat and microhabitat level. The strong relationship between surface water and groundwater levels, and the dependence of Least Chub and Utah Chub on seasonal expansion of lentic habitats for reproduction, indicate that predicted reductions in groundwater levels resulting from proposed groundwater withdrawal projects would eliminate most of the spawning and juvenile habitat in the spring complex.