Oregon Department of Fish and Wildlife (ODFW) fish biologists in partnership with the Oregon Water Resources Department (OWRD) investigated how a suite of unusual conditions, including drought, better than average fall flows in recent years, and fish migrating out of Wickiup Reservoir, may have contributed to the death of about 450 trout on the Deschutes River near Bend last week.
The dead fish were found in a side channel of the river near Lava Island southwest of Bend. According to ODFW fish biologist Erik Moberly, the dead fish were reported last Thursday afternoon and on Friday morning volunteers and ODFW staff were able to rescue about 750 trout (a combination of redband rainbow and brown trout) and 500 sculpin that were still alive in a handful of water pools.
In addition to trout, about 1,220 mountain whitefish and a similar number of sculpin died when declining water levels left them stranded in the natural lava side channel, which normally has water only during higher flows. Redband rainbow trout are listed as a sensitive species by the state of Oregon. No other listed fish, including bull trout, were found.
All the dead fish were found within a ½ mile stretch of side channel.
Water levels in the Deschutes River normally decline this time of year as releases from Wickiup Reservoir are reduced by dam operators. Every year, the ramp down rate is conducted at a rate lower than the maximum ramp down rate set by the U.S. Forest Service Upper Deschutes Wild and Scenic River Management Plan, which was developed in collaboration with ODFW, OWRD, and irrigation districts.
Consistent with that plan, this year’s ramp down occurred at a slower rate than previous years. ODFW and OWRD will continue to investigate whether ramp down levels were a factor and if necessary, work with partners to make adjustments in the future. However, a slower ramp down rate is considered to be better for fish, leading water and fishery managers to look for other explanations why so many fish were stranded in the channel.
ODFW believes that two good years of water in 2011 and 2012, when the channel did not completely dry up, resulted in more fish in the side channel this year than would normally occur. In addition, there appears to be more fish in the river that emigrated from Wickiup reservoir, which was low this year due to drought conditions.
Logo courtesy Oregon Department of Fish and Wildlife