Arctic Grayling (Thymallus arcticus)
Habitat fragmentation in the Swan
The Swan River Arctic grayling population has decreased drastically because of habitat fragmentation and degradation from extensive road networks and high densities of stream crossings associated with industrial development in the watershed. Road density in the Swan River watershed is estimated to be between 1.10 and 1.21 km/km2.
From June 28 to July 31, 2015, the ACA assessed 218 stream crossings in the Swan River watershed, of which 195 crossings were previously assessed in 2002. A total of 66 (30%) crossings were dry, likely due to the historically low stream flows that occurred in 2015; 10 additional sites were ephemeral and non-fluvial. Of the remaining 142 fluvial sites, 131 crossings were impassable to fish; only 11 (8%) stream crossings permitted fish passage. Approximately 737 km of stream (25% of the total stream length in the Swan River watershed) have been fragmented due to damage or poorly installed crossing
structures, predominantly in low-order streams. (ACA 2015)
|Historic Adult Density (2018)||Current Adult Density (2018)|