After only one field season, HFF’s study of habitat use by adult rainbow trout has provided statistically meaningful descriptions of the role of aquatic plants (called macrophytes by biologists) in providing trout habitat in the Harriman State Park reach of the river.
Data collected by Grand Valley State University student Zach Kuzniar, with assistance from HFF staff and interns, showed that macrophyte coverage of the stream bottom increased from 26 percent in mid-June to 80 percent by late July. This increase was accompanied by increased oxygen production by the plants, providing trout with the highest oxygen concentrations on sunny afternoons during the middle of the summer when water temperatures were highest. Dense macrophyte growth slowed the river’s current, resulting in areas of low water velocity even when river flows were very high during irrigation season. This “ponding” effect also maintained higher water depths when river flows were reduced in late September.
The next step is to compare habitat characteristics measured during surveys with those observed at locations of radio-tagged trout to discover the particular small-scale features preferred by the fish.