Local Habitat Conditions Can Safeguard Trout
Against Forest Harvest and Climate Change
Local variability in environmental conditions may play a key role
in understanding emerging responses of populations to land use
and climate change, but its influence has been overlooked. Local
habitat conditions can be managed and, hence, managers have
the potential to safeguard the local persistence of populations.
Combining field experiments and models offers key information
on the role of local habitat conditions to trout, helping to ensure
their long-term conservation in streams of the Pacific Northwest.
Jason Dunham, U.S. Geological Survey, Forest Rangeland Ecosystem Science Center
Our experimental design approximated conditions experienced by coastal cutthroat trout during low-flow conditions
in small streams in western Oregon, USA. Here, we conducted a realistically-scaled experiment in a semi-natural
setting using coastal cutthroat trout where available food, space, and other potentially confounding covariates
associated with cover were held constant, such as water depth, turbidity, and velocity. We conducted a manipulative
experiment using outdoor streams at the Oregon Hatchery Research Center (http://www.dfw.state.or.us/fish/OHRC/).
|• Local variability among streams—like water depth and available habitat—mediate the effects of forest harvest and climate change on trout. Climate change affects trout by triggering early emergence, reducing numbers of older trout, and increasing numbers of younger trout.
• In contrast, forest harvest produces fewer and less consistent responses across trout populations and, even, in some cases, reduces or counters the effects of climate change alone through increased summer flow.
• Instream cover improves trout survival by providing a place to hide from avian predators. Trout survive better in places with greater shade, suggesting that shade is important in cases where instream cover is limited, especially during seasonal low flow.
• Trout are restricted by available habitat during seasonal low flow and streams with deeper pools have higher trout biomass highlighting the importance of local habitat conditions. Hence, pools play a key role to trout populations, particularly with future projections of stream drying across portions of their range.
|• Although Coastal Cutthroat Trout are declining, they continue to occupy headwater streams precluding them from being listed with an elevated conservation status federally. Managers need information about local habitat conditions that allow trout to persist in headwater streams and may help increase survival and biomass throughout their range.
• Habitat variability is the key to protecting trout into the future because habitat diversity decouples the effect of land use and climate change on trout. Management plans may encourage a mix of conditions changing through time to diversify population responses.
• Seasonal low flow represents a biological crunch time for trout. Increasing pools in streams will improve their biomass by both increasing their survival and body size.
• Availability of instream cover increase trout survival by mediating the effect of predation by birds. Conservation strategies for trout should consider management tactics that maintain or improve stream habitat of instream cover in areas of high natural predation or in areas of recent forest harvest when shade is reduced.
Penaluna, B.E., H.V. Andersen, and J.B. Dunham. 2021. Nowhere to hide: the importance of cover selection to stream-living trout. Ecology of Freshwater Fish 30(2):256–269. https://doi.org/10.1111/eff.12581
Penaluna, B.E., J.B. Dunham, and D.L.G. Noakes. 2016. Instream cover and shade mediate avian predation on trout in semi-natural streams. Ecology of Freshwater Fish 25(3): 405-411. https://doi.org/10.1111/eff.12221
Penaluna, B.E., J.B. Dunham, S.F. Railsback, I. Arismendi, S. Johnson, R.E. Bilby, M. Safeeq, and A.E. Skaugset. 2015. Local variability mediates vulnerability of trout populations to land use and climate change. PLoS ONE 10(8): e0135334.
Penaluna, B.E., S.F. Railsback, J.B. Dunham, S. Johnson, R.E. Bilby, and A.E. Skaugset. 2015. The role of environmental regimes and the geophysical template to stream-living trout. Canadian Journal of Fisheries and Aquatic Sciences 72: 893–901.