Hidden Creek: Of Bull Trout, Floods and Logging

January 28, 2024

By Lorne Fitch

Bull trout, Alberta’s native fish, have swum the province’s waters since the last glaciation. With an almost magnetic fidelity, the fish have returned to spawn in Hidden Creek, an Oldman River tributary in southwestern Alberta, probably for thousands of years. Documentation of redds — small pits excavated in the stream bed by female fish to lay their eggs — first started in 1995 and went to 1998. Systematic monitoring resumed in 2008 and has continued annually. I have returned, in late September, for years now to find and count bull trout redds.

Recently I have waded the stream with some trepidation. Hidden Creek used to be the natal epicentre of bull trout spawning for the Oldman River watershed.

Logging over the winter of 2012/13 coupled with a major flood in the spring of 2013 dealt the stream, and bull trout, an almost mortal blow. Prior to the events of logging and a flood, the redd count hovered around 54 redds per year with a peak of 108. In 2013 post-flood redd numbers dropped slightly, from the average, to 41. From 2014 to 2019 the average dropped to less than 10 redds per year, an 80 percent reduction.

Bull trout females are the ultimate arbiters of whether a stream possesses the right stuff for spawning. Many must have voted, with their fins, to take a pass on Hidden Creek. Where else they went is a mystery since other streams lack consistent monitoring and are also significantly impacted by logging, roading, motorized recreation and random camping.

Something about the combination of flood and logging created a perfect storm of changes in Hidden Creek, to the detriment of bull trout spawning. Hidden Creek is not gauged, so the magnitude of the 2013 flood and its relation to other flood events is unknown. Even after major floods in 1995 (the largest on record to date in the watershed) and 2005 bull trout still swarmed to Hidden Creek, to take advantage of an abundance of groundwater, clean stream gravels and low water temperatures.

Following the 1995 flood there was rapid increase in numbers of redds and although redd counts were not done immediately following the 2005 flood, redd counts were very high three years following that event. The North Belly River and Blakiston Creek, both in Waterton Lakes National Park, showed a similar rise in spawning success following the 1995 flood. There is no similar pattern for spawning events after the 2005 flood for these streams.Comparing bull trout redd counts in Hidden Creek, the North Belly River, Blakiston Creek and Falls Creek (Ram River tributary), there seems to be no consistent and negative effect of major floods on spawning activity or on redd counts.

Flood impacts on trout might include factors such as flood timing, flood magnitude, duration of flooding and flood intensity. For fall
spawners like bull trout, many of the factors of a spring flood are of a lesser concern except as they affect the physical elements crucial for spawning success. A consistent observation from the years following the 2013 flood in Hidden Creek was the lack of suitably-sized gravels for spawning. It was apparent that these smaller gravels had been flushed out of the system, leaving behind only larger rocks and cobble, unsuitable for spawning. Very few of the traditional spawning sites had gravels left and only a limited number of these had evidence of spawning. It appeared that the few spawners left were chasing a limited gravel supply.

Erosion from naturally unstable stream banks coupled with overland flow from logging clearcuts and roads coated the stream substrate with sediment for several years following 2013. Even seven years out from 2013 there was still a sediment supply lingering in pools, where no sediment used to occur. It doesn’t take much sediment to start limiting spawning success — the literature suggests as little as ten per cent over natural background sediment levels has a discernible effect. Too much sediment likely dissuades a bull trout female from spawning. Even if she does, sediment interferes with the successful incubation of trout eggs laid in the gravels. The interstitial spaces between the gravels are clogged with sediment particles and this can smother the eggs, not allowing an exchange of
oxygen-rich water or the removal of metabolic wastes. Trout fry might be unable to extricate themselves from the sediment-impacted gravel. Bull trout are late bloomers, becoming sexually mature at about age five. If sediment levels inhibit successful reproduction, it sets the stage for fewer trout to mature and return, over time, to their natal stream. Year class failures echo through the entire watershed.

Although there is no discernible effect from flooding on spawning there may be a synergistic one resulting from logging. The effects of logging, especially clearcut harvests, are shown to change the hydrologic response of a watershed. Removal of the forest canopy, coupled with roads, skid trails and soil compaction from logging quickens the response time of snowmelt and rainfall runoff, sometimes by orders of magnitude. Basically, loggingresults in more water, delivered more quickly to a stream. This occurs with any level of forest harvest, but more so with large clearcuts. Flood peaks are elevated, and this intensifies the magnitude of a flood event.

This translates into more energy for erosion and more sediment flushed into streams. Since flows in Hidden Creek are not monitored it is difficult to determine to what degree logging increased natural flood flows. What was evident was the three tributary streams, that flow through cut blocks logged in the winter of 2012/2013, showed substantial new channel incisement, or downcutting. The logging road also intersected all of these streams.

Upstream of the logged area, three additional tributaries of somewhat equal size were inspected — none showed any evidence of recent channel incisement. This would seem to indicate that runoff from the logged areas was substantially enhanced, over non-logged areas, leading to greater erosion. Hidden Creek upstream of the logged areas did not have the same accumulations of sediment and it did not appear that gravel loss was as extreme as in downstream reaches. Unfortunately, the upper portion of Hidden Creek is mostly unavailable for spawning because a waterfall is a major obstruction.

It’s troubling that the tributary streams flowing through cut blocks showed only a perfunctory amount of erosion protection. Unlogged buffer zones were minimal, a few metres in width. Sediment controls, in the form of sediment fences, were either missing, or poorly installed and unmaintained. These were already overwhelmed by large amounts of sediment by the fall of 2013. Because of concerns over the logging of Hidden Creek, Forest Service staff apparently did regular winter inspections when logging was occurring, but there seemed to be little subsequent follow up to ensure erosion protection was in place and functioning. Self regulation was ineffective, as was agency oversight.

Conclusions are hard to draw without more empirical evidence, but it seems that logging exacerbated the flood flows of 2013, likely caused a substantial amount of erosion from newly logged cut blocks, and increased the amount of erosion of naturally unstable stream banks. This deposited a substantial amount of sediment in the lower reaches of Hidden Creek and scoured out much of the suitably-sized spawning gravels. To compound the problem, runofffrom an August 2013 rain storm turned Hidden Creek into a muddy soup. Other streams in the area, subject to the same weather event, remained clear indicating that logging had increased the erosion potential substantially in Hidden Creek.

Bull trout spawned in the autumn of 2013, creating forty-one redds. However, it is unknown whether that spawning effort produced new trout. If incubation was successful, that year class, following sexual maturity should have shown up in the numbers for 2018 and 2019. But they didn’t. Subsequent to 2013, redds counts dropped alarmingly, down to one redd in 2019. Redd counts in 2020 showed 34 redds, somewhat of aresurgence, but dropped to 19in 2022 and to fifteen in 2023.

This is far from the long-term average.

It shows the effects of logging can linger and a landscape can hum like an anvil long after the hammer of development has hit. When redd counts drop as dramatically as they have, it’s bad news. Signs of recovery occurred after six years. This is likely related to flushing of sediments from gravel by subsequent high-flow events and the recruitment of new gravels with normal bedload movement. It is easy to leap to a conclusion based on one year of higher redd counts but continued monitoring shows the blip of 2020 has not continued and there is no discernable sign of recovery.

One winter of logging has equated to at least six and probably 10 years of lost bull trout spawning and population recruitment for much of the Oldman watershed. For a species that is designated as Threatened, this is a near-mortal blow. It begs an essential question — can sensitive watersheds essential to the survival of trout species at risk be logged without serious impacts on those populations?

Whatever the forest service and the forest sector say, Hidden Creek provides an unequivocal answer.

Lorne Fitch is a Professional Biologist, a retired Fish and Wildlife Biologist and a former Adjunct Professor with the University of
Calgary.