We began a study this spring that will help reveal what kind of habitat trout seek in the famed Ranch section of the Henry’s Fork. A thorough assessment of trout habitat at 180 random points in the Henry’s Fork between the upper Harriman State Park boundary and Osborne Bridge showed ideal water conditions during the first two weeks of the fishing season. It’s the first time a habitat assessment like this has been done on Harriman State Park.
Water temperature and dissolved oxygen concentration were nearly perfect for trout activity and growth. A daily pattern of increasing oxygen concentration throughout the morning and afternoon also showed that photosynthesis by aquatic plants was producing more oxygen than organisms were using, indicating a healthy aquatic ecosystem. Habitat conditions at the sample points will be measured again in August and September to investigate how conditions change throughout the season.
The assessment was part of the trout habitat-use study that began this spring. Forty adult rainbow trout were also radio-tagged and released between the upper Ranch boundary (the “log jam” as it’s known) and the cattle bridge below Osborne Bridge. Over the next month, we will relocate the radio-tagged trout. A cursory search for these fish showed that 80 percent of them were alive and well in the study reach several weeks after being released, a result of successful tagging methods. At each relocation point, we will compare the habitat being used by the tagged trout with the habitat nearby to see whether fish prefer certain conditions over others.
Contributed by Rob Van Kirk, HFF's Senior Scientist. To learn more about our research, email Rob.