Many consider the waters of the Bow River upstream of the Kananaskis Dam to be in a mostly natural state. But this notion is challenged in a report, Improving the Ecological Function of the Upper Bow River: Bow Lake to Kananaskis Dam. Authors Matt Blank and Tony Clevenger detail disappearing fish, growing water demand, and a changing climate as challenges in the Upper Bow River in this report, prepared for the Yellowstone to Yukon Conservation Initiative (Y2Y).

Although the Bow River is considered to have world-class fishing, two of its native fish species, the bull trout and the westslope cutthroat trout, are under threat and have largely been relegated to the extreme upper headwaters of the Bow rather than inhabiting their original range, which historically extended into the prairies. Bull trout has been ranked as “sensitive” by Alberta’s government — meaning it is known to be, or believed to be, particularly sensitive to human activities or natural events (Post and Johnston 2002). The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has been reviewing the species’ status since 1998.

The westslope cutthroat trout is considered “threatened”, which means the species “is likely to become endangered if nothing is done to reverse the factors leading to its extirpation or extinction” (COSEWIC 2009). The species is currently under consideration to be listed under the federal Species At Risk Act. Once listed, the provincial and federal governments must develop and implement a recovery plan for the species. See our fact sheet for more information about the westslope cutthroat trout.

The health of these two fish species indicates the health of the entire aquatic ecosystem of the upper Bow watershed.

Fish stocking and water-regulation activities, such as hydroelectric dam development, have affected more than 41.5% of the Bow River within the Banff National Park.The report finds that non-native fish species introductions and highway infrastructure are the main factors causing dwindling populations of the bull trout and the westslope cutthroat trout. Other factors include changes to aquatic habitat and river flow regimes, loss of connectivity between habitats needed for spawning and rearing, and over-harvesting of fish. The report points out that fish stocking and water-regulation activities, such as hydroelectric dam development, have affected more than 41.5% of the Bow River within the Banff National Park. Interbreeding with non-native fish is considered the greatest threat to the westslope.

Non-native fish

Like many introductions of non-native species – such as the possum in New Zealand, rabbits in Australia, or broom on Vancouver Island – the introduction of non-native species can have significant and unintended negative effects on the native ecosystem. Between 1901 and 1972, more than 17 million fish were introduced to the Bow River and its tributaries in the Banff National Park (BNP) to improve recreational fishing opportunities, according to the report. Ten non-native fish species, including rainbow trout, brown trout, brook trout, and lake trout, are now found within the BNP. Several of these non-native species effectively compete with native species for food sources and interbreed which dilutes their genetic purity.

In the Bow River system, both rainbow trout and brown trout were introduced. The rainbow trout, prized by anglers, interbreeds with westslope cutthroat trout. The brown trout competes with the westslope. As a result, pure populations of westslope are only found in the extreme upper waters of the Bow River system.

The report points out some surprising causes to reduced populations of these prized native species:

Road and rail infrastructure

Roads, such as the TransCanada, and rail infrastructure are extensive along the Bow River. These linear features channelize and cut off the river from natural connections with floodplains and groundwater. These features prevent sediment flow and debris – both of which are important for fish habitat – from reaching the river.

Road infrastructure can prevent fish movement between sections of the river and streams. Hanging culverts, where pipes that run beneath roads no longer follow and hang above the streambed, are one feature that disconnect river or stream sections. These types of disconnections can become more pronounced during low flow periods, such as late summer, early fall or winter, when low water depths make passage through culverts difficult.

Dams

Hydroelectric dams alter the natural flow pattern of the rivers and isolate portions of the river system. There are 13 dams on the Bow River system several of which are located in the upper stretches such as the Kananaskis Dam at Seebe, or the Spray Lakes Dam system near Canmore. For example, changing flow patterns from dam operations affects fish habitat. Dams also alter water temperature, changes to which fish are sensitive because their metabolisms have evolved to function optimally at certain temperature ranges. Dams also prevent upstream or downstream fish movement important for specific life stages, such as spawning, and from breeding with other fish populations.

Other factors

Pollution from wastewater treatment plants, from roads, and from urban development affect water quality and thus fish health and habitat. Overfishing has been a particular challenge for bull trout, which are aggressive and slow to grow and mature. Climate change is predicted to result in warmer water temperatures, alter the flow regime, and change aquatic productivity. These changes could make it easier for warm water fish to survive but much more difficult for cold water fish like the westslope and bull trout to survive.

Recommendations

The report makes a number of recommendations, including a full assessment of the distribution and genetic structure of the native and non-native species, development of climate change scenarios and possible impacts on native fish populations, assessment of transportation corridors impacts on connectivity and water quality, and identification of effects of winter water withdrawal on aquatic habitat. The report also recommends conducting a watershed integrity assessment to determine which areas of the upper Bow watershed need restoration or protection for fish health.

Sources

Blank, Matt and Tony Clevenger. 2008. Improving the Ecological Function of the Upper Bow River: Bow Lake to Kananaskis Dam. Yellowstone to Yukon Conservation Initiative, Canmore, Alberta, Technical Report #7, April 2009.

COSEWIC (Committee on the Status of Endangered Wildlife in Canada). 2009. Table 5. COSEWIC status categories. Accessed June 3, 2009.

Post, John R. and Fiona D. Johnston. 2002. Status of the Bull Trout (Salvelinus confluentus) in Alberta. Alberta Wildlife Status Report No. 39. Sustainable Reources Development and Alberta Conservation Association. P 37.