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Historical and anthropogenic influences on genetic variation in bull trout (Salvelinus confluentus) in the Arrow Lakes, British Columbia Latham, Stephen J.

Abstract

This work investigates, within a watershed, (i) the distribution of an organism and its genetic variation and (ii) the mechanisms and consequences of anthropogenic influences on those distributions. I collected genetic data (at mitochondrial DNA and five nuclear microsatellite loci) for bull trout, Salvelinus confluentus, sampled from sites spanning approximately 260 km of the Columbia River, in Canada. Bull trout are recognized as a species of special conservation concern throughout almost all of their declining range. I performed analyses focussed on the conservation implications of management initiatives on resident and migratory life history forms. Large proportions of genetic variation were distributed among geographic locations. Populations were strongly genetically divided by waterfalls. Another obvious division occurred among mutually accessible habitats. I concluded that postglacial geological history was largely responsible for observed genetic divisions in both cases. Analyses further suggested that migratory behaviour (i.e., homing) and local selection against dispersers sustain this differentiation. Genetic diversity among bull trout populations is vulnerable to habitat degradation and to attempts to compensate for that degradation. Invasibility of exogenous allelic variation may be higher in resident populations than in migratory ones, but activities that reduce densities of bull trout (e.g., poaching, collection of broodstock) may promote recruitment of exogenous allelic variation in migratory populations. Despite anthropogenic impacts, substantial genetic variation still exists in the study area. Prioritizing populations and their habitats for conservation is difficult because they generally represent distinct evolutionary histories, as interpreted from allelic diversity and identity. Further, while allelic diversity in resident populations correlated positively with the presence of other fish species, rare alleles were more common in genetically depauperate populations. Consequently, intrapopulation diversity and uniqueness are traded-off intraspecifically, and habitats containing representative bull trout populations are unlikely to represent other biological diversity. Conservation of representative migratory populations is difficult also, as they are harvested in a mixed-population fishery. The fishery likely poses a greater risk to some populations than to others. Migratory bull trout are not panmictic in their feeding areas, however, and judicious use of no-harvest zones could protect susceptible populations with high value for conservation.

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