Logging Predicted to Extirpate Bull Trout

Forecasts indicate that bull trout will become extirpated from many portions of Alberta's Kakwa watershed within the next 20 years. Results from scientific modelling predict that harvesting timber from 35 percent of a subbasin will eliminate bull trout in 24 to 43 percent of the stream reaches they now occupy.

The loss of trout will be most pronounced where the fish currently exist at moderate and high densities.

The modelling was based on surveys which detected bull trout in 75 of 172 stream reaches in the Kakwa watershed near the BC - Alberta border. Subbasins containing bull trout on average had 5 percent of the area harvested and 0.11 km of roads per square kilometre. Drainages lacking bull trout averaged three times more harvesting and 2.5 times greater road density.

Other environmental factors also affect the presence and quantities of bull trout in Kakwa streams. They mainly inhabit third and fourth-order streams, from 2 to 8 m wide, and at elevations between 950 and 1600 m. The trout also require a scarcity of fine sediments, a condition that logging and road building can alter.