Can farmland watercourses provide habitat for native fish?

Fall view of Willamette Valley in Northern Polk County. Image credit, Rvannatta.Looking back 150 years ago, the active floodplains of western Oregon contained a dense, braided network of meandering side channels.  These streams remained dry half of the year but flooded seasonally providing important habitat for numerous freshwater fish. Today, this complex system no longer exists.

Thanks to modern human ingenuity, channels have been straightened, wetlands filled, dikes constructed, and ditches developed. These actions greatly reduced the natural floodplain and left behind intermittent watercourses (ditches and altered channels) used largely for agricultural purposes. Scientists have generally considered these agricultural areas biologically barren, supporting few if any fish species.

However, a new study has found that fish, mostly native species, actually do find their way into these watercourses during the critical winter months for refuge and spawning habitat.

The team of researchers from Oregon State University and the Natural Resource Conservation Service, set out to answer four questions regarding the private agricultural land of the Upper Willamette River:

(1) Are there fish present in the watercourses?

(2) What are the distributions of native vs. exotic fish?

(3) Are the areas used as spawning and/or nursery habitats?

(4) What are the environmental factors affecting fish abundance?

Each month from December 2002 to May 2003, the team sampled fish in 5 sub-basins with minnow traps and a backpack electrofishing unit.  In May 2003, they measured 17 habitat characteristics including distance to perennial flow, nutrient concentrations, and % land covered in grass.

The results of the study showed that fish utilize the intermittent streams and ditches as habitat during the winter and early spring months. Out of the 1,526 fish captured in the study, 99% of them were native comprising 10 different  species. This included the federally listed upper Willamette chinook salmon (Oncorhynchus tshawytscha) and upper Willamette steelhead (Oncorhynchus mykiss), though they were less common.

A large proportion of the fish studied also used the areas as spawning and nursery habitat. This particular finding was indicated by the presence of recently hatched fish that would never haven been able to swim upstream at such an early stage in life. In their statistical analysis of habitat characteristics, the researchers discovered that species richness was directly correlated to % forest cover and velocity and inversely related to conductivity.

Now that we know seasonal watercourses on private agricultural land provide habitat and refuge for native fish species, it gives further support for conservation and restoration of these areas. The study authors conclude:

"These agricultural watercourses are appropriate for the conservation practices such as wetland restoration, stream habitat improvement, the creation of fish passages and riparian buffers, and others that contribute to conservation of native aquatic species in managed landscapes. With funds available through the U.S. Department of Agriculture and other sources, farmers could be compensated for contributing to the long-termprotection of native fish species and their winter habitats"

--Reviewed by Evyan Borgnis

Source:	Transactions of American Fisheries Society
Title:	Fish use of intermittent watercourses draining agricultural lands in the upper Willamette River Valley, Oregon
Authors:	a) Randall Colvin, Guillermo Giannico, Judith Li, b) Kathryn Boyer, a) William Gerth
	a) Oregon State University, Corvallis, Oregon b) Natural Resource Conservation Service, Portland, Oregon