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Migrations Part 2: Fish can’t always go with flow

Chip Corsi fly fishing for trout on the Kootenai River upstream from Bonners Ferry, Idaho. (Rich Landers)
Chip Corsi fly fishing for trout on the Kootenai River upstream from Bonners Ferry, Idaho. (Rich Landers)

WILDLIFE WATCHING -- Yesterday, in the Idaho Fish and Game Department's 75th anniversary series of "reminders"  on wildlife topics, I featured the first of a three-part post on migrations -- Part 1:Mammals.

Today, we look at Part 2: Fish.

Mammals do it. Birds and fish do it. Even insects do it.

They migrate as part of their inborn strategy for survival, and the arrival of winter triggers a massive migration of all kinds of wildlife.

They may travel a thousand miles or a few feet. The distance is not what defines migration; it’s that animals move between habitats during the year to survive. They may move for many reasons – to find food, breed or raise their young. Migration is a tool they use when a habitat no longer meets their needs.

Migration patterns and routes are ancient and have been influenced by the natural features of the land, water and air. The same natural features that foster wildlife movement are also attractive to human activities. Roads bisect open spaces. Wind turbines pop up on ridgelines. Dams block rivers. Communication towers light up the night sky. Houses are built in key habitat. And human structures frequently become problems for migrating wildlife.


One of Idaho’s most dramatic wildlife migrations is its anadromous fish runs.

Salmon and steelhead travel from Idaho’s mountain streams to the ocean as juveniles, then return as adults to their home waters in Idaho to spawn. For sockeye and Chinook salmon this adds up to 1,800 river miles round trip.

Fish biologists have discovered that many other kinds of fish migrate as well, including bull trout, cutthroat and rainbow trout, suckers, to name a few. The three of the biggest obstacles to fish when they migrate are:

  • Culverts that allow a stream to flow under a road. They can become obstacles for fish passage if the water‘s energy lowers the downside river bed, creating an impassable barrier to fish going upstream. In other northwestern states, surveys have documented that the majority of road culverts may be partial or complete fish passage barriers.   
  • Unscreened water diversions that direct water into irrigation canals. They can also direct fish into the canals and onto farmers’ fields. This is called entrainment and in some instances can result in significant losses to native fish populations.
  • Dams installed for irrigation and power production. Many also block fish migrations.

Idaho Fish and Game works with private and public partners to reduce the impacts of these barriers for migrating fish. For water diversions, fish screens are installed to keep fish out of the canals. Problem culverts can be replaced with newer designs or replaced with bridges to allow fish passage.  

Although difficult and expensive, many dams can be retrofitted with fish ladders to allow safe passage of native fishes to spawning and rearing grounds. Some dams are too high for conventional fish ladders so alternative methods of providing passage must be explored like trapping and moving fish above the blockage.

Tomorrow, Part 3: Birds.


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Rich Landers
Rich Landers joined The Spokesman-Review in 1977. He is the Outdoors editor for the Sports Department writing and photographing stories about hiking, hunting, fishing, boating, conservation, nature and wildlife and related topics.

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