MACROHABITAT OF SONORA CHUB (GILA-DITAENIA) IN SYCAMORE CREEK, SANTA-CRUZ COUNTY, ARIZONA

Physical characteristics and persistence of macrohabitat used by diffe rent life stages of Sonora club (Gila ditaenia) were determined by rep eatedly measuring distinct reaches in Sycamore Creek, Santa Cruz Count y, Arizona, in 1990 and 1991. At the beginning of summer drought, habi tats occupied by adult Sonora club were deeper and larger than areas w ith only immature fish and unoccupied areas. The medians of maximum de pth were 47.0 cm (1990) and 39.7 cm (1991) for habitats with adults, 2 1.3 cm (1990) and 22.9 cm (1991) for habitats with only immature fish, and 14.6 cm (1990) and 19.7 cm (1991) for unoccupied areas. At the en d of summer drought, adults occupied habitats that were deeper and lar ger, and the percent decrease in area and depth was less than areas co ntaining only immature fish or no fish. The medians of percent decreas e in maximum depth were 13 % (1990) and 21 % (1991) for habitats with adults, 48 % (1990) and 41 % (1991) for habitats with only immature fi sh, and 42 % (1990) and 33 % (1991) for unoccupied areas. By the end o f summer drought, habitats with only immature fish were not physically different from unoccupied areas. Loss of total surface area was highe st in reaches that contained only immature fish or no fish (range = 36 % to 94%). Most Sonora chub lost from evaporating surface waters were immature fish. Ephemeral and unoccupied areas had higher percentages o f floating cover and coarser substrates than persistent, occupied area s.