Faculty Research at Morehead State University


Declining Status of Two Species of the Macrhybopsis aestivalis Complex (Teleostei: Cyprinidae) in the Arkansas River Basin and Related Effects of Reservoirs as Barriers to Dispersal

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From 1991 to 1997, we made 323 seine collections at 187 sites to determine the distributional status of two species of the Macrhybopsis aestivalis complex, M. tetra- nema (Gilbert) and M. hyostoma (Gilbert), in the Arkansas River Basin. A total of 545 M. hyostoma and 112 M. tetranema were taken in 39 collecting visits to 30 sites. Our survey indicated that the endemic M. tetranema has been extirpated from about 90% of its historic range, whereas the more widespread M. hyostoma has been extirpated from about 55% of its former range in the basin. Approximate year of extirpation for six populations of M. hyostoma in major stream segments was significantly correlated with year-of-completion for reservoirs that would have prevented recolonization from existing populations. This is consistent with the hypothesis that extirpations resulted from disruption of previously existing source/sink relationships among populations. No such correlation was detected for extirpations of seven populations of M. tetranema. This result would be expected from the metapopulation model in which the now-extirpated populations of M. tetranema were self-sustaining except during unusually harsh conditions (e.g., droughts). This factor apparently explains recolonization of the Cimarron River by M. hyostoma subsequent to extirpation of both species of Macrhybopsis from this river. The recolonization was delayed by about 25 years, apparently because of reservoir habitat between the Cimarron River and the other major stream draining into the reservoir, the upper Arkansas River, where there was a persistent population of the species.