| Summary: | In 2004, a population of dwarf longnose sucker was discovered co-existing with the normal form within the Elk River Watershed of south-eastern British Columbia. This thesis evaluated morphological, genetic and life history characteristics of this dwarf longnose sucker form to determine whether the dwarf morphotype warranted designation as an evolutionary significant unit and to determine any special habitat requirements. In addition to size, distinct morphological differences were indicated between Elk River Watershed dwarf and normal adult longnose sucker, with dwarf adults appearing to retain morphological features of juveniles and sharing morphological features with Salish sucker, which is a separate dwarf longnose sucker form that is considered endangered. Slight, but significant, genetic differences were indicated between Elk River Watershed dwarf and normal longnose sucker forms, and compared to Salish sucker, suggesting some basis for separate designation of the dwarf form. Dwarf longnose sucker are widespread in the Elk River Watershed, and most abundant in small, cool lentic water bodies that contained dense vegetative cover, potential oxycline fluctuation and/or limited fish species diversity. Dwarf adult longnose sucker showed some habitat preference differences compared to normal longnose sucker, with the findings suggesting that dwarf longnose sucker have adopted a more opportunistic life-history strategy than normal longnose sucker. It is postulated that an ontogenetic niche shift has allowed dwarf longnose sucker to more successfully exploit habitats experiencing periodic disturbances (e.g., hypoxia) that, in turn, has led to the occurrence of two longnose sucker morphotypes in the Elk River Watershed.
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