Tag: trout

 

Lorne Fitch, P. Biol.

Some years ago I attended an American Fisheries Society conference. It was three days of dense descriptions of fisheries research. At the finish I was numb at both ends. It ended, as most do, with a banquet and an after dinner speaker. Did I mention alcohol?

After we were stuffed and somewhat medicated the speaker invited us to close our eyes. I thought, “This is my fondest wish.” We were asked to imagine ourselves under sail in 1778 off the coast of Hawaii.  It felt strangely comforting to do so.

“Imagine,” the speaker said, that a shout comes down from the crow’s nest, “I can see the tops of trees.” Then, “I can see big canoes, with outriggers, made from big trees, being paddled out to us.” His voice then rose in volume, shocking us out of our somnambulant state. “Where did the trees come from?” he asked.

Our reverie was over, it was time to reengage our brains. The speaker was James Furnish, then the Deputy Chief of the US Forest Service. He pointed out the logs used to build those dugout canoes were from rivers of the Pacific Northwest, like the Columbia. In flood time they had been washed out of rivers and had floated across the ocean to the Hawaiian islands. In the present age this is unlikely to occur because logging, dams, agriculture and urban development has dried up the supply of logs.

Furnish, once he had our attention, went on to give us an engaging, entertaining talk on large woody debris and its function in stream dynamics and fish habitat. It opened my eyes. With that new knowledge I started to look at wood with new eyes, appreciative ones. An observation of the Oldman reservoir one day, as the dam operator was dragging logs out of the entrance to the spillway, started me thinking. 

At that time we were doing regular flights of the Oldman River, downstream of the dam, to inventory angler numbers. To the angler count was added the number of large logs that could be seen from the air. What became clear was that large logs were mostly missing from the river as far downstream as Ft. Macleod. 

Since part of the fisheries mitigation program for the Oldman reservoir had a downstream component, I pointed out that lack of instream wood would seriously impact improvement of fish habitat. That’s when I was told the budget for fisheries mitigation had been spent and once spent, mitigation had been achieved. Instead of taking logs out of the reservoir and refloating them downstream, they were burnt.

At about the same time the Habitat Branch of Fish and Wildlife was either directing mitigation to repair things like pipeline crossings or attempting to improve fish habitat conditions on small streams. What worked and tended to linger were log walls to slow bank erosion, logs pinned perpendicular to the channel to form plunge pools and root wads building log jams.

Dr. Kim Green reaffirmed, with elegantly simple explanations for the intimate connection between forests and fish, the role of large woody debris. This knowledge on the complex nature of rivers comes from her own research in Columbia River watersheds and from the substantial research undertaken in  Pacific Northwest systems. 

If a trout population is to persist, it must replace itself. All trout species require gravel of an optimal size in which the females excavate depressions, called redds, where eggs are deposited. These gravels are constantly on the move during high water, driven by greater water velocities. Logs, especially those that array themselves perpendicular to the flow, slow water and trap gravels.

Logs of all sorts and sizes add to channel roughness, decreasing water velocity and creating areas of slower moving water, including pools, where fish can rest. The differences in water velocities between a channel with wood and one without can be measured in orders of magnitude. Slowing water down, with obstructions, forces an exchange between surface and subsurface flows. Water directed downward into the substrate is stored longer, emerges cooler in the summer and warmer in the winter, delighting trout.

Often the overhead cover created by a log jam or a tree that wedges itself along a streambank provides trout escape from predation and predators such as anglers, whose lures and flies adorn the logs. That same woody material also armours a bank from erosion, decreasing the addition of sediment. It also creates shade, reducing the sun’s influence on water temperatures.

Streams and rivers of the Eastern Slopes are relatively infertile. Wood, bark, needles and leaves are the essential building blocks of stream productivity. Trout don’t eat wood directly but, like us requiring an intermediary like an herbivore, benefit from those critters that do process wood, such as aquatic invertebrates.

When a tree falls in a stream the dynamics and complexity of the system are enhanced. Benefits to fish ramp up considerably. What happens when trees don’t  fall into a stream? The distribution and abundance of trout decline and they may disappear. This is particularly troublesome if those trout are native species and are categorized as species at risk, which almost all are.

I’ve spent many hours in helicopters flying watersheds of the Eastern Slopes. From the air one of the things that jumps out is fallen trees and log jams in stream and river channels, or on the floodplains. Occasionally, in isolated reaches, it looks as if a lumber yard has been parachuted into the stream valley. But mostly, there is little wood observed in these stream channels. 

Jim Rennie, an avid angler, observes there are many reaches of southern Alberta waters that lack “holding” habitat, without the structure and complexity to attract and hold trout. This was confirmed in a research study of the upper Oldman watershed, using aerial photographs from 1983 as the base. There was an overall reduction in large woody debris volume and orientation, as well a significant decrease in functional wood in reaches of North Racehorse Creek, the upper Livingstone River and the upper Oldman River. All these watersheds have an extensive logging footprint.

Why aren’t trees falling into the streams and rivers of the Eastern Slopes? Again, Dr. Green’s observations from several studies in the Eastern Slopes are illuminating. Basically she points out that, “there has been an increase in the frequency of flood disturbance related to logging.” Climate change is a driver, but the footprint of logging may exacerbate snowmelt and rainfall events. Flooding is now more frequent plus the floods are of a greater magnitude and severity (several 100-year floods in less that 20 years).

Ironically, flooding is key to the recruitment of trees to stream channels. Flood flows pick up downed trees and topple others from the floodplain, depositing them into the channel. Narrow or no buffer zones from logging means there is less wood available to be added to the channels. More and bigger floods flush wood out of headwater streams and rivers.

 Dr. Green has described one big flood in the Oldman watershed (1995), exacerbated by the logging footprint, that lofted much woody material far up on the floodplain where it remains inaccessible from floods of lesser size. There it sits, rotting away, instead of residing in the channel where it can persist for a century or longer.

Wood in streams is on a conveyer belt, from the slopes to the floodplain, to the channel and on downstream. Some of it hangs on through floods, relatively permanent, but much slowly migrates downstream. For the stream system to retain its dynamics and complexity, wood needs to be constantly added. If, at any time, that pathway of wood is interrupted, the stream can down cut during a flood, incising its channel deeper into the floodplain. Then, wood may not intersect with the water.

With about a century of logging behind us and fifty years of them as intensive, industrial-strength, clear-cut logging I’m not sure we have many, or any unimpacted watersheds left in the Forest Reserves that can form an image and a benchmark of what they were like before intensive logging.

My colleague, Dr. Michael Sullivan, describes some isolated rivers in the National Parks with amounts of large woody debris resembling the jumbled game of Pick-up sticks. Bull trout, in trouble beyond the park border, are plentiful and big in these wild watersheds. This reminds me of Aldo Leopold reflecting on a journey in a pristine place: “It is here I first realized…that all my life I had seen only sick land…here was a biota still in perfect aboriginal health.”

For recovery of native trout we must first acknowledge something has gone missing from their waters. Wood, in its various forms and sizes has in many watersheds. There are four pillars of trout habitat—clean water, cold water, complex habitat and connected habitats. Wood adds to, perhaps is essential for habitat complexity. Wood scarcity is like musical chairs, the children’s game of elimination where there are less chairs than kids. It’s no different for trout, whether the music stops or not.

James Furnish ended his banquet address with some advice. “ Large woody debris is as important to a stream as is the water. That wood has to come from somewhere, so protect that somewhere [the watershed]. Protect the best. Restore the rest. Native fish will appreciate those efforts.” Furnish is now retired, and has written a memoir that speaks to forest management working in concert with nature. 

As a follow up to Furnish’s advice two fundamental things are required. First is to dial down the footprint of clear-cut logging. The evidence is abundant an expanding logging footprint exacerbates flooding (and drought). Second, until the watersheds have restored some dynamic equilibrium from logging we need to add wood to our streams to resurrect their complexity and allow recovery of native trout. 

Trout need more trees in the water. Imagine where putting wood back might take us in recovery efforts for our present beleaguered native trout.

March 2024

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