Baseline Inventory of Sport Fish in the Edson River 2011
Jason Blackburn, Brad Hurkett, Troy Furukawa, and Mike Rodtka
We collected baseline data on the distribution and abundance of sport fish in the Edson River. The objectives are to enable future assessment of the fish community following restoration activities planned in the study area, with the ultimate goal of facilitating recovery of Arctic grayling and Athabasca rainbow trout. We stratified the Edson River based on riparian health scores reported in a 2010 aerial videography assessment and then electrofished 28 reaches (~27 km) using a cataraft electrofisher.
The most abundant and widely distributed sport fish was mountain whitefish (Prosopium williamsoni) (n=237), followed by rainbow trout (Oncorhynchus mykiss) (n=30) and Arctic grayling (Thymallus arcticus) (n=27). Non-sport species, white sucker (Catostomus commersoni) and longnose sucker (Catostomus catostomus), dominated the catch in terms of biomass at 44%, followed by mountain whitefish at 28%, Arctic grayling at 9% and rainbow trout at 8%. Total biomass of sport fish species and nonsport fish species was nearly identical.
Total fish biomass decreased with decreasing riparian health and sport fish biomass was generally higher at sites associated with healthy riparian areas (good and fair–good), than at sites with unhealthy riparian areas (fair, poor–fair and poor). In contrast, biomass of non-sport fish showed little difference between good, fair–good, fair and poor–fair ranked sites, only decreasing at sites ranked as poor.
Using Spearman rank correlation analysis we explored relationships between riparian health, fish habitat, stream profile, and fish abundance metrics to determine their utility for future monitoring. Total fish cover calculated from littoral area plots along the stream margins had little correlation to fish relative abundance, biomass or species richness. Conversely, bank stability was correlated to fish relative abundance species richness, and riparian health, thereby serving as a potential useful indicator of both riparian and fish community health.
Width-to-depth ratio was correlated to fish biomass, relative abundance, and species richness variables, and also strongly correlated to bank stability. This suggests greatest species richness and fish abundance occurred at wide, shallow reaches, with stable banks.
Total fish biomass and sport fish biomass tended to increase with dominant substrate size, whereas non-sport fish biomass varied little among coarser substrate types, declining only where substrates were finest.
Substrate type at healthy riparian areas (>50% of the riparian area was ranked good), was dominated by cobbles and boulders. The substrate of unhealthy riparian areas (<50% of the riparian area was ranked good) was dominated by fines and sand.