Results of an Eradication Program on the Ecological Relationships of Fishes in Leon Creek, Texas

Abstract

The fishes of Leon Creek are an assemblage of opportunists with a wide spectrum of feeding habits. The relative abundance of various taxa changed following a rotenone treatment designed to reduce genetic contamination of an endemic (Cyprinodon bovinus) by an introduced exotic (C. variegatus). Except for green sunfish, each fish (and a Gambusia hybrid swarm) was reestablished and is predicted to resume its role in the ecosystem in the near future. The introduction of Cyprinodon variegatus (sheepshead minnow) into Leon Creek and its subsequent hybridization with and extensive genetic contamination of Cyprinodon bovinus (Leon Springs pupfish) resulted in the recommendation for efforts to eradicate the exotic genetic material by rotenone treatment (Kennedy 1977; Echelle et al., ms). Our participation emphasized a study of the impact of the program on the other fishes inhabiting Leon Creek. Much of the literature on this creek has been devoted to Cyprinodon bovinus, a fish with its range restricted to Leon Creek. The first report on fishes in Leon Creek (actually Leon Springs approximately 22 kilometers northwest of the extant population) was of the 1851 samples by J. H. Clark, who obtained Cyprinodon bovinus and Gambusia nobilis (Girard 1859). Subsequent collections at Leon Springs contain other fishes that are likely to have been stocked. Minckley and Arnold (1969) alluded to a bovinus-like Cyprinodon that had been collected from downstream Leon Creek, but the first published reports of other fishes were by Hubbs and Echelle (1972), Echelle and Miller (1974), and Kennedy (1977), who report Cyprinus carpio (carp), Gambusia geiseri (largespring gambusia), Gambusia nobilis (Pecos gambusia), Gambusia affinis (mosquitofish), Lucania parva (rainwater killifish), Fundulus kansae (plains killifish), and Lepomis cyanellus (green sunfish) as