Migrating fish get help in uphill battle

Round culverts create an almost impossible passage for freshwater fish moving upstream because of the speed of the water rushing through the drains

By Environmental News Network staff

Who hasn't heard about the monumental migrations of salmon and steelhead? Unimpeded, they can swim hundreds of miles for the single-minded purpose of procreation.

Freshwater fish also migrate, but not nearly as far. Small fish such as minnows and darters move about; so do bass and trout. In terms of scale though, these smaller fish move a long way and need to find the right habitat as the seasons change. But like salmon and steelhead of the Northwest, they run headlong into barriers.

Huge dams without fish ladders are obvious barriers to migrating fish. But that culvert you drive over on your way to work could keep fish from reaching necessary habitat, too. Culverts on small streams often block fish from reaching upstream areas.

A culvert may have water in it and it may not look like an obstacle for fish, but the flows may be too shallow or too swift for them to swim through. The culvert could be too long. And typically, flows are uniformly fast throughout the culvert, so fish have nowhere to rest and are washed downstream. Round culverts make fish passage nearly impossible.

On the downstream end, concentrated flows often erode the stream bed and scour pools, making a small waterfall too large for fish to jump over.

When fish populations become disjointed, inbreeding can occur. Isolated fish may not be able to reach all the habitat necessary to fulfill their requirements. The number of fish could be depressed and the general health weakened.

To remedy such a situation in southeastern Oklahoma, the U.S. Fish and Wildlife Service's Oklahoma Fishery Resources Office and Tulsa Ecological Services Office partnered with John Hancock Natural Resource Group to open up miles of stream on commercially forested land. A box culvert with the bottom on the natural stream grade replaced a round culvert.

The box culvert eventually filled with natural materials and allowed fish to pass easily through it

Two species of fish are immediate beneficiaries: the federally threatened leopard darter and the Ouachita-strain smallmouth bass. Both occur in the Little River watershed. The Ouachita smallmouth is a fairly recent discovery, a form of smallmouth bass unique to that part of Oklahoma and Arkansas. Removing the barrier has connected habitat crucial for these unique fish.

"It's not uncommon for Little River headwater creeks to stop flowing in the heat of summer; culverts become barriers to fish seeking out habitat at lower flow," said Brent Bristow, U.S. Fish & Wildlife Service biologist. "With the barriers gone, darters and bass can once again reach habitat they really need seasonally."

Spawning is one such season. According to Paul Balkenbush, stream fish biologist for the Oklahoma Department of Wildlife Conservation, improved culvert designs allow native smallmouth to reach necessary habitat at high flows. That helps assure a good mix of genetics and a robust fish population.

Finding spawning habitat may not be the only need to move about. In small streams, fish find refuge in deep pools to ride out the winter. Getting to the same pools may mean the difference of surviving a summer when flows drop and temperatures climb. Without the access to necessary habitat, fish populations may suffer. Mobility is everything.

The service's Arizona Fishery Resources Office is similarly engaged. The East Fork White River is important habitat for two fish, both federally listed as threatened: the loach minnow and Apache trout, an important sport fish.

But a low-head dam that delivered irrigation water also blocked fish movement. The White Mountain Apache Tribe and Arizona Fishery Resources Office redesigned the dam to continue delivering irrigation water. Flows are now concentrated midstream over a natural bottom that easily passes fish.

"Many small, in-stream structures look innocuous," said Lynn Starnes, the service's assistant regional director for fisheries in the Southwest region. "But even small structures if not properly placed can have big consequences on fish populations. The Service is committed to ... connect fish habitat to improve conditions for fishing and conserve imperiled species."

Copyright 2000, Environmental News Network, All Rights Reserved

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