CORVALLIS, Ore. – A newly published study by researchers at Oregon State University has found that farmers’ fields that are seasonally inundated with floodwaters play a role not only in creating a sanctuary for fish during high-velocity water, but in providing access to high-energy foods and even places for breeding.
Even more important, the researchers say, is that these “intermittent watercourses” are dominated by native fishes whose behavior may have evolved to take advantage of such conditions.
“Floods have always been a dynamic part of the system, much the same way that snow is for elk in Yellowstone,” said Guillermo Giannico, a freshwater fish ecologist at Oregon State University and one of the authors of the study. “Over time, animals will adapt to get the most out of their habitat. We have found that native fish have adjusted their behavior to use these floodplains, mostly in agricultural lands, to great benefit.”
Results of the study were just published in the journal, Transactions of the American Fisheries Society. Funding for the research was provided by the U.S. Department of Agriculture, the Oregon Seed Council, and the Natural Resources Conservation Service (NCRS).
In their paper, Giannico and co-authors Randall Colvin, Judith Li and William Gerth of OSU, and Kathryn Boyer from NCRS, call for the promotion of agricultural conservation practices that benefit stream species and maintain aquatic biodiversity in floodplain habitats. Although much of the complex channels of streams and rivers in Oregon’s Willamette Valley have been lost to development, Giannico says, those remaining in these agricultural lands are of benefit to native fishes.
“When looking at the situation you have to start with the observation that grass seed and other farmers are producing crops with perhaps fewer effects on fish than we formerly thought because we are finding several native fish species when we look for them, even though these areas are naturally dry for half of the year,” said Giannico, who is an associate professor in OSU’s Department of Fisheries and Wildlife.
“Some of the linkages between permanent water sources and agricultural fields have disappeared and we’re working with farmers to help them understand how these processes work and to identify ways to conserve what is there,” he added. “Many want to help, as long as we don’t undercut their bottom line.”
The research team studied five sub-basins in the Willamette River drainage – the Luckiamute River, Mary’s River and Long Tom River on the west side of the valley, and the Calapooia River and Muddy Creek on the east side. These sub-basins include the high-elevation Cascade Mountains, the hills of the Coast Range, and the floor of the Willamette Valley, where most of the flooding would occur.
They discovered 13 different fish species using agricultural fields from December through May, and only three of those species were exotic, or non-native. Even more surprising to researchers was the sheer number of native versus exotic individuals. Of the 1,526 fish they captured, almost 99 percent were natives.
The most common were redside shiners (534 individuals) and threespine sticklebacks (347 fish), which were found at nearly three-fourths of the sampling sites. They also found tiny Chinook salmon and cutthroat trout, as well as speckled dace, largescale suckers and northern pikeminnows, which are native to the valley.
Though the public may be unfamiliar with many of the native species, Giannico said, they all have value to the unique ecosystem.
“The fish that are caught in the Northwest for sport or commercial reasons do not thrive in isolation,” he pointed out. “All of these species are part of an interconnected food web. Some are prey for salmon and steelhead; others compete with them for resources and habitat. Most consume insects and other invertebrates that are surprisingly diverse and abundant in the waters, grasses and shrubs of the floodplain.”
The OSU researchers say understanding how natural systems operate is tremendously complex and though it may be difficult to understand the value of a sculpin or dace from a human perspective, all species fill a niche.
“As the old saying goes, you can remove a bolt from an airplane and it probably will still fly, but if you keep removing bolts, you don’t know what will happen when the next one is gone,” Giannico said.
The OSU researchers point out in their article that agricultural fields are not created equally in terms of providing ideal habitat. Those that have drainage ditches that are deep and “torpedo-like” tend to funnel water too rapidly to streams and rivers, thus shortening the “wet season.” Deep manmade ditches also are more likely to disconnect floodwaters from historic floodplains.
Shallower ditches that meander through slightly wooded areas, or have a riparian buffer of shrubs separating the channel from the fields are preferred by a much larger number of fish species, Giannico pointed out.
“When people settled into the valley, they apparently were not comfortable with the uneven network of native channels and instead crafted a symmetrical system of ditches that they moved to the edge of the fields,” he said. “This may have helped maintain the fields, but it was at the cost of ideal fish habitat.
“Now we’re working with farmers to see if we can have the best of both worlds – a system that allows farmers to maintain productive fields while at the same time encouraging optimum habitat for aquatic species.”