Friday, Sept , 2017
Watershed fragmentation takes a toll on fish
By Brett Winchel, TU
Brett Winchel holds a redband trout
ecognized as a distinct lineage, the Columbia River redband trout occupies only 45 percent of their historic range in the Pacific Northwest. Largely due to degradation and fragmentation of watersheds via land conversion, road construction, and natural resource development.
Most of these activities occur at lower elevations, forcing some populations of redband trout to occupy the less-impacted higher elevations within the watershed. The most abundant population of redband trout occurs in the McKenzie River. Here, redband trout are also known as the McKenzie redband, redside, or rainbows. The most imminent threat to redband trout is the stocking of hatchery rainbows within the McKenzie River. This can result in hybridization between the two subspecies, reducing their ability to thrive within the aquatic system. Other threats for the species include dams, irrigation diversions, and road culverts that create fish passage barriers. In lower elevations of their range, smallmouth bass and brown trout are displacing redbands by outcompeting them for resources as well as directly preying on them.
Similar in appearance to redband trout, steelhead are the anadromous form, as in they migrate to the ocean to forage and grow and then return to their natal streams to spawn. Steelhead are most threatened by warming water temperatures in many watersheds within their historic range. These warming waters can create thermal barriers during migration runs that put extra stress on the migrating steelhead. In addition to thermal barriers, physical barriers are another major threat. Due to the extensive migratory routes of many steelhead populations, they require connected watersheds. Hatchery stocking of steelhead poses another issue. Hatchery stocks can threaten the genetic integrity of wild steelhead populations and pose risks with hybridization between the two groups.
Coastal cutthroat trout
Coastal cutthroat are native to an extensive reach along the Pacific Coast, stretching all the way from California up into Washington, British Columbia and Alaska. The life history of this species can vary. Coastal cutthroat trout can remain as non-migratory resident freshwater fish, fluvial freshwater trout that migrate within a freshwater system, effluvial forms that migrate between lakes and tributary streams, and anadromous forms that migrate out to the ocean and back.
Instead of lengthy oceanic migrations, coastal cutthroat often utilize estuaries and other near shore environments before making their way back into their natal streams. Coastal cutthroat have been found to be more sensitive to warming water temperatures and are especially susceptible to the thermal barriers that are being found in some of their historic watersheds in the Pacific Northwest. Other issues for coastal cutthroat include poor forestry practices and poorly-designed and maintained roads that contribute to an increase in sediment loads in streams.
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