Federally endangered Yaqui chubs Gila purpurea are restricted to the Rio San Bernardino, a small headwater tributary of the vast Rio Yaqui basin of Sonora, Mexico, and Arizona, United States. The species faced almost certain extirpation in the United States during the late 1960s when its remaining habitats went dry. Just prior to that event in 1969, individuals were successfully transplanted into nearby Leslie Creek. Captive propagation was later used to produce fish to re-establish populations in its native range after habitats were reclaimed and protected. We present the history of conservation efforts which include numerous transfers of differing numbers of fish between captive and 'wild' stocks. We examined the effects of these recovery efforts on the genetic and phenotypic structure of populations. Genetic and morphological differentiation were respectively assessed using allozyme electrophoresis and principal components analysis. Considerable genetic stability was indicated, with observed variations attributable to documented or inferred changes in population sizes. Morphology also remained uniform, both temporally and spatially, with no evidence of changes attributable to recovery manipulations or ecophenotypic responses to novel environments. Yaqui chubs exhibit high fecundity and quickly establish large effective population sizes, life history characteristics which likely account for the minimal effects of population manipulations.
