Crane Prairie Reservoir was built in 1922 as an irrigation reservoir; the water is held back by the first of many dams on the Deschutes River. Crane is a favorite for anglers in the Central Oregon Cascades targeting large, hard fighting “Cranebows”. These native rainbow trout are either wild, spawning in the Upper Deschutes above the reservoir, or hatchery-raised from originally wild stock. Only triploid (sterile) hatchery fish are now released into the reservoir, eliminating the potential for breeding with wild fish.
Like most fisheries, Crane Prairie has seen ups and downs. In the early 2000’s, fishing was excellent, with abundant Cranebows, which were frequently deep, wide fish over 20 inches in length. Fishing started to change, however, around 2015. Since that time, ODFW angler creel surveys, trapping, netting, and anecdotal reports show that while Cranebows remain abundant, they are smaller. A big fish is now in the 16” to 18” range, a decline in size that has continued to the present.
The cause of this is speculative, but Brett Hodgson, ODFW Deschutes District Fish Biologist, believes it is due to dramatic growth in the brown bullhead catfish population. Bullheads are an invasive species that were illegally introduced into Crane Prairie sometime in the 1980s. These fish would occasionally be found in nets and traps over the years but became commonly captured in large numbers starting around 2015.
To get an idea of bullhead population density, in 2019 ODFW moved nets that had been used for tui chub trapping in East and Paulina Lakes to Crane Prairie for 3 weeks. Over that time, nets were commonly filled with bullheads. In total, over 5,000 pounds of catfish up to 14 inches long were removed from the lake.
It is likely that bullheads are competing with other fish, including Cranebows, for food. Clearly, limited food supply will stunt fish growth. It is also believed that the bass population in Crane Prairie is rapidly growing which would have a similar impact on trout growth.
This begs the question, why are brown bullhead catfish, and possibly bass, populations significantly increasing? No one knows for certain, but about the same time these population booms began, Crane Prairie started being managed to benefit the Oregon Spotted Frog, an endangered species. The OSF breeds near the shoreline of lakes and the edges of rivers. To be successful, it requires stable water levels while eggs are developing. Working with the US Fish & Wildlife Service in the middle of the last decade, irrigators started managing releases from the reservoir to maintain a stable reservoir level during OSF breeding season and to limit fluctuations at other times.
Prior to this management regime, Crane Prairie would see more dramatic changes in water levels. The hypothesis is that those changes would suppress catfish and bass populations, while a steadier water body has allowed them to explode. While it appears we can see the impact on trout, it is not clear what the impact has been on OSF. It would be reasonable, however, to assume that OSF are an attractive food source for bullheads and bass.
What should or can be done about this is an interesting question. Bullhead and bass are both invasive species in the Upper Deschutes and ideally would be removed. Unfortunately, doing so in Crane Prairie would be exceptionally difficult. Poisoning the lake is not possible due to the presence of OSF as well as the fact that there is a river flowing in and out of the reservoir.
For years, East and Paulina Lakes have suffered a similar problem with tui chub. The solution in these lakes has been an intensive program of netting these fish, particularly during spawning season when they bunch up in shallower water. It is a costly and labor intensive effort, but it has been effective in increasing the size and health of trout. Tui chub have not been eliminated, but they have been controlled and trout fishing has improved.
No such program is currently planned for Crane Prairie. ODFW does not have the manpower or funding for the sustained trapping program that would be necessary for long term effectiveness. US Fish & Wildlife has not announced plans to protect OSF from predation by catfish or bass. Perhaps the irrigators should fund this effort as part of the Habitat Conservation Plan. At a minimum, the impacts of these invasive species deserve serious study and a plan for their control.
Does anyone know how to catch catfish on a fly? It could be an unusual tournament.