Summer habitat use by Sonora chub in Sycamore Creek, Santa Cruz County, Arizona

Abstract

The Sonora chub (Gila ditaenia) is a small minnow that is federally-listed as threatened. My research objectives were to quantify characteristics and persistence of macrohabitats used by this species through critical summer periods, and to quantify microhabitat selection in Sycamore Creek, Arizona. By the end of the summer drought, macrohabitats containing adults were deeper, larger and decreased less rapidly than areas with only immature fish or unoccupied areas. Loss of surface area was highest in inundated unoccupied areas and areas with only immature fish. Loss of Sonora chub from drying pools was highest in pools with immature fish. Ephemeral and unoccupied areas had higher percentages of floating algae and coarser substrates than persistent, occupied areas. General microhabitat characteristics selected by Sonora chub were areas with bedrock or fine substrates near cover and zero velocity. Microhabitat use usually differed among life stages, and availability and selection varied among pools.