Stream Crossing Inventories in The Swan and Notikewin River Watersheds of Northwestern Alberta
John P. Tchir and Paul J. Hvenegaard
Aquatic habitat fragmentation, degradation and encroachment are important results of access infrastructure on lotic habitats and can limit the distribution, abundance and subsequent viability of fish stocks. During 2002, the effects of road crossings on fish habitat quality and connectivity in two Northern Alberta watersheds (Notikewin River watershed (NRW), Swan River watershed (SRW)) were examined. Stream crossings were identified through spatial analysis. Culvert crossings were quantitatively assessed for habitat fragmentation and qualitatively for sediment contributions. Culvert crossings (61% NRW, 74% SRW) failed to provide connectivity of potential fish habitat. Fragmentation was highest in the SRW with approximately 20% of the stream network fragmented as compared to 9.5% in the NRW. Culverts were inadequately sized to respective stream channels causing habitat loss due to encroachment in both watersheds. A large proportion of culverts surveyed (NRW 17%, SRW 18%) contributed moderate levels of silt to respective watercourses. The frequency of culverts rated as contributing high amounts of sediment was highest in the SRW (19%) compared to the NRW (3%). In the SRW, proportionately more bridges were rated as having high levels of silt deposition (NRW 8%, SRW 36%). Habitat fragmentation and silt deposition caused by culvert crossings found in these watersheds suggest stream-crossing practices and monitoring need to be significantly improved to conserve Arctic grayling (Thymallus arcticus) and other lotic sport fish species in Northern Alberta.