Loach Minnow & Spikedace mesohabitat use across space with varying abundances

Authors: Crosby Hedden, Brian Hickerson

Year: 2022

Abstract

Two fish species endemic to the Gila River basin, Spikedace, Meda fulgida and Loach Minnow, Tiaroga cobitis, are both thought to have strong habitat associations that restrict their potential distributions. Previous studies support the concept that Loach Minnow are riffle specialists, while research describing Spikedace habitat use varies. Our objective was to determine if mesohabitat associations are similar across stream reaches, and to observe if these patterns are consistent when local abundances change through time. We analyzed long-term monitoring data (2008-2021) from three stream reaches where populations of Spikedace and Loach Minnow previously existed or were translocated (Hot Springs Canyon, lower Blue River, middle Blue River). During the years covered by the dataset, Spikedace failed to establish a population in Hot Springs Canyon, began to establish a population in the middle Blue River, and established an extremely abundant population in the lower Blue River following translocation efforts. Translocations of Loach Minnow resulted in the establishment of a relatively small population in Hot Springs Canyon, and helped reestablish a robust population in the lower Blue River following impacts from the Bear Wallow Fire. The Loach Minnow population in the middle Blue River is a robust relict population that never received any translocations. We estimated relative abundance across three mesohabitat types (pool, riffle, run) for each year of monitoring. Each fish was captured in all three mesohabitats, although not evenly between them at all time. Loach Minnow relative abundance was significantly different among mesohabitat types, with relative abundance in riffle habitats being greater than in run or pool habitats at all reaches. No differences were observed in the relative abundance of Spikedace among habitats at any reach with the exception of the lower Blue River, where they utilized riffle and run habitats significantly more than pools. Further, we found a significant shift in Spikedace habitat use in the lower Blue River as abundances increased through time, where they utilized riffle and run habitats more following proliferation. Our results are consistent with previous studies in that Loach Minnow generally occupy riffle habitat while Spikedace habitat use appears to be less constrained by mesohabitat type at low relative abundances, and shifts to more specific mesohabitat types with increasing relative abundance.