Brook Trout and Beaver Dams

Vandermark Creek is a trout stream feeding the upper Genesee River in western New York. I have fished the headwater section of the creek occasionally over a period of many years, particularly for native brook trout in the area of the Vandermark State Forest. The upper creek is surrounded by a mix of woodland and aging fields and has remained basically stable for as long as I have known it. Over the past 10 years, however, I’ve seen a marked decline in its brook trout numbers, and I have a theory as to why.

I don’t know when beaver came to be employed at the state forest, but the rodent engineers are there, and they’re rocking the ecology of the woods. So what, you may be thinking. Aren’t there bigger threats to native trout today, say hydro-fracking, silt accumulation, global warming, etcetera? Why worry about a mammal that’s evolved with brook trout over the eons? Granted, the eastern char has a lot to be concerned about today, but let’s not disregard the beaver.

Castor canadensis may have evolved naturally with brook trout on a multitude of eastern streams, but remember, the trout’s current range is a mere fraction of what it was in pre-colonial days, and the presence of expanding beaver colonies on a single brook trout water can have a major impact, especially if poor land use by our own two-legged species has already minimized the number of fish.

My introduction to Vandermark Creek came long ago, during my Alfred University days in the 1970s. Since then I’ve never caught more than two trout at a single outing there, and I’ve never fished downstream for the brown trout that are stocked on a minimal basis every year. The creek has never seemed all that good for fishing, though I did manage to land a nice 11-inch brookie on the stream about five years ago. My last two outings at the creek were unsuccessful, and on a recent winter morning I inspected the low, clear waters and saw little more than beaver dams, silt, and large quantities of chubs.

As the value of beaver fur has lessened over the past few decades, minimizing trapper interest, beaver populations have surged in many rural areas. The Avery Report, a study published in 1992, collected data from the impact of beaver colonies on trout streams in Wisconsin. The report had studied fish and mammal numbers before and after the removal of beaver dams on trout streams. After looking at streams for six years following the removal of beaver dams, the Avery Report concluded that brook trout numbers rose and that water temperatures cooled. Stream turbidity was reduced; gravel beds were again exposed, allowing the spawning process. The flow rate of streams increased; the depth of water and the channel widths decreased. Unfortunately, across the study area in the 1980s, summer air temperatures were higher than normal, thus the water temperatures of the streams were cooler by a mere 2 degrees Celsius. Considering the potential effect of global warming on native trout stream waters, conclusions from the studies of dam removal do not sound encouraging. As one report suggested, “air temperature is the most important element in controlling trout habitat.”

I saw many little beaver dams in various conditions along the creek, and though I briefly fantasized that the beavers could be discouraged and the beaver dams removed by hand, I also realized I’d need an army of assistance and I wasn’t even comfortable with the idea of messing around with nature, as unbalanced as it seemed in this location. It would be nice to see the sediment cleared away and to know that oxygen levels would be increased, but it would also be nice to see the whole human world living together in peace and harmony. It wasn’t going to happen any time soon.

It’s a different story in our western states. For example, beaver ponds in the Rocky Mountains often have an opposite effect on trout. The ponds allow herbaceous plants to grow, eventually adding to the food supply. But here we’re talking about water temperatures rising from the 40s into the 50s under harsh conditions, rather than rising from the 50s or 60s into the 70s or beyond. Western ponds tend to have short life spans for fishing opportunities, but some of the fastest brook trout fishing I ever experienced was on the beaver ponds of the Colorado Rockies.

I asked Scott Cornett, fisheries biologist for the Department of Environmental Conservation in western New York, to weigh in on the subject of beaver ponds on eastern trout streams, and Cornett replied, in part: “Most of our streams have become marginal temperature-wise for brookies due to our poor land use practices, and the beaver ponds just push them over the edge.” He went on to say that new beaver ponds occasionally allow good brook trout fishing, but they quickly become silted in. As beavers rapidly consume the nearby wood supply, the waters warm up to allow, at best, the spread of brown trout in the watershed.

I don’t know what can be done about the problem, if anything, other than encouraging good land use practices. I’d like to hear about your own experiences with brook trout at the beaver ponds, or your thoughts about the interesting rodent and the colorful char.