Research Document - 2006/012
Towards the identification of Conservation Units in Atlantic salmon from Eastern Canada
By O’Reilly, P.
Abstract
Atlantic salmon (Salmo salar) is the only naturally occurring (non-introduced) representative of it's genus in Eastern Canada. During the freshwater phase of it's life cycle, the species once occupied most rivers and major streams along the Atlantic coasts of New Brunswick, Nova Scotia, Prince Edward Island, Quebec, and Newfoundland, and from the Maine-New Brunswick border in the south to Ungava Bay in the north. Within this extensive geographic distribution are several large regional zones that vary in terms of topographic relief, landforms, soils, water features, vegetation and climate. Riparian habitat also varies within these zones, with neighbouring rivers differing in terms of stream gradient, maximum distance to river mouth, bedrock type, pH, temperature, predators, and prey availability. Phenotypic differences have been identified among salmon from different general locations and between salmon from neighbouring rivers. In some instances, variation observed may reflect environmentally induced phenotypic plasticity, but in others, possible adaptations to local conditions. Overall, however, little is known about the existence and distribution of genetically based differences in life history and morphological traits among Atlantic salmon from Eastern Canada, and even less about the adaptive significance of such differences.
Analyses of neutral molecular genetic markers can help elucidate patterns and extent of genetic structuring, and provide insight into the amount of gene flow among salmon from different locations; this information is useful in assessing the potential for adaptive differences to accrue and can assist in identifying major ancestral lineages of Atlantic salmon. Although several published studies of neutral molecular genetic variation have been carried out that include populations of Atlantic salmon from Eastern Canada, most involve only one or two rivers from a few regions, and are of limited scope and utility in resolving biodiversity for conservation purposes. However, one broad-scale analysis of multiple allozyme loci has been completed, and fine-scale coverage of the Maritimes is also available for several classes of molecular genetic markers.
A number of methods have been developed to categorize within-species biodiversity for conservation purposes. Many of these involve similar approaches and utilize largely overlapping suites of information in delineating Conservation Units (CUs), defined here as "groups of individuals likely exhibiting unique adaptations that are largely reproductively isolated from other groups, and that may represent an important component of a species' biodiversity". In other instances, however, alternate methods employ different types of information, or use the same or similar information in different ways, possibly resulting in very different outcomes. Here, I make a case for testing candidate groupings against several divergent alternative methods in order to maximize the identification of biodiversity in Atlantic salmon from Eastern Canada.
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