Influences of Fragmentation on Fluvial-specialist Black Bass Species
Abstract
North America's fluvial fish fauna are becoming increasingly imperiled, primarily by habitat degradation, non-native species invasions, and fragmentation. The present study was conducted to understand how these conservation threats have affected native, fluvial-specialist black bass (genus Micropterus) species that support popular sport fisheries and that can be used as umbrella species for the conservation of other aquatic organisms. Species distribution models illustrated that Shoal Bass (M. cataractae) were potentially distributed across up to 84% of the available stream length in their native basin, but that fragmentation by dams and large impoundments, as well as a potential asymmetric relationship with non-native congeners, has contributed to range loss. A range-wide genetic survey demonstrated that although the Shoal Bass has been described as potamodromous, appreciable population structure exists. Five distinct genetic clusters were recovered at the uppermost hierarchical level, each generally corresponding to natural isolating mechanisms (e.g., the Fall Line). Some substructure was detected within these clusters, which was likely related to recent fragmentation (i.e., impoundments) and variable recruitment. Finer-scale case studies of the conservation-genetic influences of impoundments and non-native congener fisheries revealed that impoundments generate propagule pressure that encourages invasion and introgression of non-native alleles into native black bass populations inhabiting upstream tributaries, but whether impoundments serve as barriers to gene flow for native populations was somewhat unclear. Quantifying local-scale population dynamics of Shoal Bass inhabiting three isolated tributaries of the upper Chattahoochee River basin revealed that these populations grew slower, lived longer, and experienced lower annual mortality than other studied populations, which may be adaptations to variable recruitment or lower over-winter survival of age-0 fish. The Big Creek population appears at risk of extirpation because of its isolated nature, low numbers of adults, and greater variation in recruitment. Overall, results provide novel insights into the factors influencing range loss, a framework for management units to conserve existing genetic diversity, a characterization of non-native invasion and hybridization in impoundment tributaries, and quantified population dynamics of several isolated Shoal Bass populations inhabiting the northern extent of the species' range.
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- OSU Dissertations [11222]