Creating a Home for Cutties in Cascade Creek
Guest blog by Nicole Sulewski and Dan Struthers
Cascade Creek Restoration Team
Parks Canada
Banff National Park
Small stream, big mission
Cascade Creek is nestled in the heart of Banff National Park, and features Cascade Ponds, a scenic day use area, and the Legacy Trail, a paved bike path that snakes past scenic mountain views from Canmore to Banff. Cascade Creek is also tucked between a hydropower dam, a highway, and a railroad. Its unique placement and history have led to various detrimental impacts, but also provide a unique opportunity for restoration, and returning native fishes to this special place, that can be readily enjoyed by park visitors.
Cascade Creek was once part of the Cascade River; historically, a home to native fishes, including threatened westslope cutthroat trout (WSCT). When the Minnewanka Dam was built in 1941 under the War Measures Act, flow to the lower 9-km of Cascade River (now named “Cascade Creek”) was reduced to nearly nothing. This drastic change in flow heavily impacted the aquatic ecosystem downstream. There was no longer enough flow to connect to the Bow River, drying up roughly halfway towards the Bow River, thus restricting access to fishes located in the Bow River. Because the flows were reduced, fine sediment started to build up, covering the gravel and cobble streambed, which native trout need to spawn in.
In past years, non-native brook trout colonized Cascade Creek, prior to damming, or from stocking practices post-damming, and thrived here due to the slow moving, silty waters. The combination of habitat loss, sedimentation, and competition with brook trout pushed out the native fishes, which rely on clean, cold, connected water. There were many barriers preventing restoration of the creek at that time. The fine sediment was nearly impossible to remove without higher flows, however, the flows could not easily be increased because the dam infrastructure and all road and railway crossings over the creek were not large enough to accommodate more water volume.
In 2013, nature intervened. There was a historic flood in Southern Alberta due to a prolonged rain event coinciding with the spring-melt season. During this flood, the spillway of the dam was opened, sending an unprecedented amount of water crashing down the Cascade Creek channel. This powerful torrent ripped the channel apart, leaving it far too wide for the small amount of remaining flow, and destroying necessary habitat features for fishes. Fortunately, the flood also took the fine sediment and undersized infrastructure with it.
While destructive to the stream channel, this was a catalyzing event for the restoration of Cascade Creek. After the flood, the undersized culverts were replaced with larger, fish-passable culverts. The dam infrastructure feeding the creek was upgraded to be able to release slightly higher flows. The increased flows and restoration efforts allowed the groundwater aquifer to recharge and restored connectivity to the Bow River.
Building a Home for the Cutties
The time was ripe for Parks Canada to begin working on restoring the stream channel with the goal of returning WSCT to Cascade Creek. The renowned stream restoration expert, Dr. Bob Newbury, was brought on to design a channel with riffle and pool habitat features that would work with a downscaled flow regime to create functional aquatic habitat for WSCT. An excavator was used to restore the channel to his design specifications. This involved modifying the channel dimensions, building riffles, and placing boulders; thus, creating habitat structure and protection from predators for WSCT. A total of three boulder runs and 14 riffle-pool sequences were constructed across a 4-km portion of Cascade Creek. A permanent fish barrier was installed at the downstream end of the creek to prevent recolonization of non-native fish found in the Bow River.
The “Home Inspection”
Before Parks Canada can reintroduce cutthroats back into Cascade Creek, we need to be confident that the ecosystem is suitable for maintaining a population in perpetuity. We conducted a variety of management actions and in-stream sampling to qualify whether this species could persist here, including:
- Eradication of the invasive brook trout population through electrofishing efforts between 2012 and 2016. We have continued electrofishing and conducted snorkel surveys to confirm the absence of non-native fishes in recent years (2019–2023).
- Monitoring of benthic invertebrates to assess the health of the creek, and to confirm that there will be sufficient food sources for WSCT, an insectivorous fish. We found that the stream has lots of the same invertebrates that are found in healthy streams in the park, and that there is plenty of food for WSCT of all ages.
- Water chemistry monitoring demonstrated that nearly all parameters are suitable, except for a few high phosphorus readings. We are still monitoring water quality to determine if this is a persistent issue, and what may be causing it.
- We have monitored the aquifer water levels in groundwater wells around the creek and compared them to the surface water dynamics in the creek. Results have shown that some areas of the creek consistently lose water to the groundwater aquifer, while other parts of the creek experience groundwater upwelling. The dynamics between surface water and groundwater in the system are intricately related.
- By monitoring stream temperature throughout Cascade Creek, we found that temperatures are suitable for WSCT by evaluating 1) “growing degree days” for juvenile rearing success, and 2) synchrony with the spawn timing window. These parameters are well within the range of temperatures that are necessary to support WSCT. The summer stream temperatures also appear to have some room to fluctuate to account for water temperature increases associated with climate change.
- Habitat complexity in Cascade Creek was assessed for the following parameters:
-substrate size: sufficient spawning gravel was found.
-canopy cover: canopy cover is currently quite low but is expected to increase over time as the riparian vegetation continues to establish after the 2013 flood.
-pool habitat: numerous pools are found along the length of Cascade Creek.
-instream cover features: sufficient habitat cover was found in the form of undercut banks, large woody debris, and boulders. - Riparian health was monitored in 2020 for a baseline evaluation post-flood and will be re-assessed in 5-year increments to track restoration progress over time. Riparian restoration, including manual and chemical removal of non-native vegetation, along with planting of native species is ongoing. We expect that through these efforts, riparian health will improve in the years to come.
- Sediment sampling and stream discharge measurements have been collected to inform sediment transport rates in the creek. This information will help with decision making for prescribing a flushing flow. Returning a flushing flow is crucial for removing fine sediment that can clog spawning substrate. Flushing fines is a long-term need. However, the base flows that we have now are sufficient to meet the needs of WSCT for the short-term, so we are planning to move forward with WSCT reintroduction while we continue working on the flow analysis. Having fish in the stream will help to indicate whether the flow manipulations are working as intended or adjust accordingly using an adaptive management approach (i.e., pull one lever, and see how WSCT respond).
Finding a Needle in a Haystack
The main challenge for Parks Canada to bring westslope cutthroat trout back to Cascade Creek was figuring out where to get them from. The donor WSCT stocks needed to be genetically pure, have an ancestral match to the Upper Bow River, and have enough genetic diversity to mitigate against negative genetic consequences. For example, there are many populations of WSCT in Banff National Park, however some of them have been stocked with fish from other regions, meaning they might not be as well adapted to the local ecosystems (i.e., cold, short-growing seasons compared to their southern geographic range). These stocked populations in the national park also tend to have low genetic diversity. And, WSCT hybridize with rainbow trout and other cutthroat subspecies, which has led to the loss of many genetically pure populations both in Banff National Park and beyond the park borders. We tested the genetics of numerous populations to make sure that our donor WSCT populations are genetically-pure WSCT with local adaptations to the upper Bow River basin. To test fish for genetics, a small tissue sample is taken from the anal fin and sent to a state-of-the-art trout genetics lab at the University of Montana. From this analysis, we landed on two populations that meet the genetic criteria: 1) Upper Stoney Creek and 2) Marvel Lake.
Recently, Parks Canada aquatic specialists also tested these two donor populations for high-risk pathogens to prevent transmitting diseases to new waterbodies, and to give translocated fish the highest chance of survival. To test for pathogens, lethal samples were required; taking 60 fish from a large population is the statistical gold standard to screen for pathogenic presence. Sub-adult individuals were taken from each population, and dissected for tissue samples, which were sent to the UPEI fish pathology lab for analysis. Both populations were found to be free from all concerning pathogens, including the whirling disease parasitic agent — Myxobolus cerabralis.
As both Stoney Creek and Marvel Lake are disease-free, genetically pure, and have local genetics to the upper Bow River basin, they are both deemed to be suitable for use as donor populations. As they both have relatively low genetic diversity, we plan to take fish from both populations to increase genetic diversity for the WSCT population in Cascade Creek.
The White Stork Approach: delivering baby cutties to a new home!
To bring cutties back to Cascade Creek, Parks Canada will be collecting gametes (eggs and milt) from fish in the source populations. The Agency is planning to do reintroduction over three years, taking gametes from the Marvel Lake population in the first and third year, and from the Stoney Creek population in the second year. The intent is to begin this work as early as May 2024. Gametes will be taken from approximately 50 individuals per year, and eggs and milt will be fertilized in the field. The fertilized eggs will then be transferred to an incubation trailer, where they will develop to the “eyed egg” stage. Then, the eggs will be placed in Remote Stream Incubator (RSI) units in Cascade Creek, where they will hatch out.
Once they have been reintroduced, the population will be monitored by Parks Canada aquatic specialists for several years to determine that their numbers are growing and surviving. After many long years, the cutties will finally have a new home in Cascade Creek!
So, how can you get involved with this native trout reintroduction project?
- Participate in Parks Canada’s volunteer riparian restoration projects aimed at improving the health and complexity of the riparian plant community along Cascade Creek.
- Participate in streamside garbage cleanup events to help keep this stream clean for cutthroat trout, and help reinforce the “leave no trace” approach for Banff National Park.
- Bring your families and friends to Cascade Creek in the summer months to observe this special place for yourselves. We encourage you to take a walk along Cascade Creek and keep an eye out for its newest inhabitants — the westslope cutthroat trout — soon to be reintroduced!
- To get involved, reach out to benevolebanff-banffvolunteer@pc.gc.ca to inquire about volunteer opportunities for this project.
And as always, to learn more about native trout in Alberta, visit www.albertanativetrout.com and Stories from the River.
