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Research: Beaver Dams Create Habitat Complexity Benefitting Juvenile Steelhead In John Day Tributary
Posted on Friday, September 28, 2018 (PST)

A recent study shows that beaver dams not only create more complex habitat for juvenile steelhead, but that the steelhead will actually move to different parts of that habitat during the day and night to feed and rest, as well as to find thermal refuge.

 

The study found that individual steelhead established more distinctive patterns of their use of the space within beaver impoundments on Bridge Creek, a tributary of Oregon’s John Day River, than they did in a separate run without the benefit of the beaver-created complex habitat.

 

The study published in the Canadian Journal of Fisheries and Aquatic Sciences is a sequel to another study on the impacts of beaver impoundments on water temperature published last year.

 

“In the temperature paper we demonstrated that beaver impoundments can also create thermal habitat complexity,” said Gus Wathen, fisheries scientist with Ecological Research in Bend, Ore. “This study demonstrates that fish can set up distinct and disparate movement patterns in highly complex habitat, allowing then to satisfy daily needs (food consumption, rest, digestion, predator avoidance, seeking thermal refuge, etc.) without having to search far, and expend a lot of energy to find microhabitat suitable for their specific need.”

 

The previous study (a ten-year study) was about the influence of beaver dams – some artificially added to the stream during the study – on stream water temperature. It found that the dams increase surface water storage and encourage cool groundwater flow. The results are a cooler stream at a time when typically high summer temperatures stress threatened juvenile steelhead (see CBB, June 2, 2017, “Partnering With Beavers: 10-Year Study Shows How Beaver Dams In Arid Streams Moderate Water Temps,” http://www.cbbulletin.com/439009.aspx). That study was published in the journal PLOS one May 17, 2017.

 

This latest study, “Beaver activity increases habitat complexity and spatial partitioning by steelhead trout,” was published online August 29, 2018 (http://www.nrcresearchpress.com/doi/abs/10.1139/cjfas-2018-0171#.W6qEr2hKjIU).

 

Wathen’s co-authors are Jacob Algeier, assistant professor in the Department of Ecology and Evolutionary Biology at the University of Michigan; Nicholaas Bouwes, fish ecologist, Ecological Research; Michael Pollock, research fish biologist, NOAA Fisheries’ Northwest Fisheries Science Center; Daniel Schindler, professor, School of Aquatic and Fisheries Sciences, University of Washington; and Chris Jordan, research fish biologist, Northwest Fisheries Science Center.

 

“Our study showed that within the beaver complex, individual fish established more distinctive patterns of spatial use of microhabitats than in the run,” the study says. “This pattern is reflected in increased specialization in activity and boldness behaviors, and variation in diel movement patterns of individuals in the beaver complex relative to those in the run where individuals showed less variation in their habitat selection strategies.”

 

In the run without beaver activity, the steelhead either established use patterns in deeper areas or they used other habitat “in seemingly random ways, presumably as if they are searching for quality microhabitat,” the study continues.

 

On the other hand, steelhead in beaver impoundments “display more specialized habitat use and movement patterns that changed through the day, presumably allowing individuals to fulfil daily needs (i.e., foraging, digestion, predator avoidance) in different physical space at different times,” the study says.

 

This additional movement within beaver impoundments can also result in higher densities of steelhead.

 

“More juvenile steelhead used the beaver complex for longer durations, compared to the run,” the study says. “From our fish capture surveys, we know that the density of juvenile steelhead was almost three times higher in the site impacted by beaver activity and, on average, these fish spent longer amounts of time within this habitat than in the more homogenous run.

 

“Therefore, we can conclude that availability of quality habitat constrains the degree to which fish can vary their daily habitat preference and that habitat heterogeneity allows variation in habitat selection over the diel cycle.”

 

Wathen said that “almost all stream dwelling fish in North America evolved with beaver and were accustomed, and maybe even dependent, on having them on the landscape. It wasn't until the fur trade came through and wiped out almost all beaver, that we developed this idealized notion of an unencumbered free flowing trout stream. Especially in environments where water is at a premium, like the arid ecosystems in the west, beaver are essential to ecosystem health.”

 

The “take home” for those charged with managing fish habitat, he said, is that complexity is a good thing.

 

“Stream restoration is big business across North America and I think a premium should be placed on creating habitat complexity in depth, water velocity, fish cover, and even thermally if it can be achieved.”

 

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