| Abstract/Description or Keywords |
During 2004-2007 we conducted redd surveys for bull trout in the Arrow Lakes Reservoir to identify which tributaries supported adfluvial populations, to assess adult abundance for the system as a whole, and to determine the relative contribution of individual streams. We identified two non-glacial streams (Caribou and MacDonald Creeks) that contain populations of the southern bull trout genotype in the ALR, and two non-glacial (Halfway River and Kuskanax Creek) and two large, glacial streams with multiple spawning tributaries (Illecillewaet and Incomappleaux Rivers) that support populations of the northern bull trout genotype. Under favourable flow conditions ALR tributaries are well suited to the redd survey method. Redds in glacial streams can also be counted if surveys are conducted later in the fall when glacial runoff subsides. During complete surveys of all study streams in 2006 and 2007, we counted 953 and 846 redds, respectively. These values are likely modest underestimates of the total number of bull trout redds in 2006 and 2007 for the ALR as a whole. In both glacial and non-glacial streams, redd densities were highest in upstream reaches below migration barriers, while lower reaches near the reservoir contained few or no redds. The two larger glacial systems contributed almost two-thirds of the total redd count in both 2006 and 2007. However, we observed the highest density of redds in relatively small, non-glacial streams, or tributaries to the larger glacial streams. Redd counts appear to be an effective tool for assessing bull trout spawner abundance in ALR tributaries. Annual surveys could provide a direct index of the population status of adfluvial bull trout stocks in the ALR. |
