Coastal Cutthroat Trout as Sentinels of Lower Mainland Watershed ...

27progress in Oregon. In BC, a “top-down” approach was used with the first stageinvolving the sequencing of nuclear and mitochondrial DNA to define major cutthroatlineages within the province, leading to identification of ESUs for conservation as well asestimates of hydridization (Costello et al. 2002). On a larger scale in BC, coastalcutthroat trout of Georgia Basin are likely an extension of the Puget Sound ESU becausepopulations of the west coast of Vancouver Island show greater affinity to populations ofthe Queen Charlotte Islands (Costello pers. comm. 2005). Within these larger groups aregroupings of distinct populations, but discrete populations are thought to distributed atsmall spatial scales such as within large river reaches and tributaries of large rivers(Costello pers. comm. 2005).How much movement occurs between what may be discrete populations is not yet wellestablished in the published fisheries literature, especially in British Columbia. Residentfish above impassable barriers are generally isolated from downstream migratorypopulations aside from incidental movements or displacements downstream. Thus, themigratory form is likely to show phenotypic traits of the resident form, but unlikely visaversa. Slaney et al. (1997) suggested in a review of cutthroat stock status that someadjoining streams entering a large river or a marine bay or inlet may be a single stock, butthis is yet unconfirmed. Geographically, this suggestion is not dissimilar to coho salmonor steelhead originating from several tributaries within a watershed, which are typicallyconsidered a single breeding population. Within a geographic area, different life historytypes are documented to be more closely related to each other than those types from othergeographic areas (Johnston et al. 1999). This is similar to what has been documented insockeye and kokanee from the same drainages versus other drainages in British Columbia(Taylor et al. 1996).On a broad geographic scale over the entire range of coastal cutthroat, relative geneticdiversity measured by electrophoretic analysis is moderately high (22 %). In contrast,this diversity was relatively low (6 %) on a regional geographic basis (Williams et al.1997). In the Lower Fraser basin, relatively low genetic diversity was suggested from apreliminary study of five Lower Fraser tributaries. These included Dunville/Nevin,Young, Little Tamihi, Clayburn/Poignant, Hairsine/Steelhead, and Yorkson/MundayCreeks, located between the communities of Langley and Rosedale (Aquatic ResourcesLtd. and UBC Zoology 2002). Among all comparisons, about 5.5 % of the total geneticvariability was attributed to genetic differences among four populations, with the balanceattributed to genetic variation among individual trout within populations. Movements ofpit-tagged juvenile cutthroat occurred, but only for several meters downstream onaverage, except for two fish among two stream pairs within two systems (1-3 kmmovement). This relatively modest level of genetic variation attributable to differencesbetween populations was reported to be within the range of genetic variation of cutthroattrout associated with three other more extensively sampled geographic areas inWashington State (Aquatic Resources Ltd. and UBC Zoology 2002).Preservation of genetic traits that convey fitness advantages to regional coastal cutthroatpopulations is important, and thus regional fisheries management need support lifehistory profiling and genetic sampling, particularly of areas affected by fish culture