Retrospective Evaluation of the Effects of Human Disturbance and Goldfish Introduction on Endangered Pahrump Poolfish

Abstract

Life history data for Pahrump poolfish (Empetrichthys latos latos) collected from 1937 to 1975 were organized and analyzed to improve our understanding of changes caused by human habitat disruption and introduced goldfish (Carassius auratus) at Manse Spring, Nevada. Pahrump poolfish twice demonstrated their ability to recover numerically from a population crash. The first crash followed a November 1961 introduction of a few goldfish and sub- sequent removal of vegetation by local ranch children intent on turning Manse Spring into a swimming hole. The sec- ond crash followed another major habitat disturbance resulting from an unsuccessful attempt to eradicate goldfish in July 1967. Each crash (1962-1963 and 1967-1968) reduced the poolfish population to fewer than 50 adults and was fol- lowed by a population recovery to more than 1000. Following the first habitat disruption, changes in poolfish population structure and poolfish diet were observed. These changes caused an increased mortality rate, resulting in disappearance or decline in relative abundance of larger poolfish size classes with a commensurate reduction in production of mature eggs by the population. We detected no additional changes in life history characteristics that could be associated with the second population crash and recovery. We concluded that removal of vegetation in the summer of 1962 and the more extreme habitat disruption and fish handling in June-July 1967 were human-induced pulse disturbances resulting in poolfish population crashes. We also concluded that the changes in poolfish life history characteristics resulted princi- pally from press disturbances attributable to goldfish.