Lower Deschutes Fish Update

Rod French, ODFW’s Mid-Columbia District Fish Biologist, presented at last week’s Fisheries Workshop.  This annual presentation by ODFW has been largely unchanged for years, which is excellent news.  Trout have been surveyed in the lower Deschutes since the 1970s and there have been no observed negative impacts on them from the operation of the Selective Water Withdrawal tower in Lake Billy Chinook.  If anything, trout are larger and more abundant now, which is to be expected given the more natural temperature profile of the river.  Below are a lot more details, or take a look at Rod’s presentation.

Trout size, abundance, age distribution, and health all look excellent.  If anything, there are more, larger fish.  It is true that black spot disease has become more prevalent (it’s actually a parasite, not a disease), but there is no evidence that it is having a negative impact on the fish.  It is also important to note that black spot disease reports are increasing in other Oregon rivers as well.  Angler creel surveys continue to show that Deschutes trout catch rates are high, on par with other “blue ribbon” rivers in the western US.

Bass continue to be detected in the summer months, mostly in the lower 12 miles of the river, as they seasonally migrate in from the Columbia where there is a very large population.  There is no evidence of spawning or juvenile bass in the Deschutes.

Wild steelhead and chinook returns as observed at Sherars Falls are “extremely depressed”.  Last year’s estimate is a total of 1,605 wild steelhead.  Adult hatchery fish numbers are also way down.  Drought and poor ocean conditions are believed to be the culprit.  Drought warms rivers and reduces spawning and rearing habitat.  A hot Pacific has lead to the breakdown of the food web in some areas.

It is important to understand that up until around 2010 the predominant steelhead fishery on the lower Deschutes was out of basin hatchery strays, fish that were raised in hatcheries on other rivers but who came up the Deschutes.  It is estimated that as many as 25,000 out of basin strays would enter the Deschutes, representing over 70% of all steelhead caught on the lower 43 miles of the Deschutes.  Last year out of basin strays dropped to 457.  This decline has to do with changes in smolt and river management in the Columbia basin (see note below).  These management changes coincided with the operation of the SWW leading many to falsely blame the SWW for the decline in steelhead catch rate.

Deschutes hatchery steelhead returns have traditionally averaged between 3,000 and 5,000 fish but were down to 2,140 last year.  The prediction is for similar returns this coming season.

Similarly, wild chinook returns are well below normal as are hatchery returns.  Only 247 wild spring chinook returned in 2018.  Spring chinook are near the end of the 2019 run and hatchery managers do not believe that they will get enough brood stock to reach next year’s production target.

Note: In an attempt to increase survival, for many years Columbia basin smolts were barged down past the last dam before they were released.  Having not made the journey themselves, these fish were poorly imprinted and would wander up many rivers, including the Deschutes, as they attempted to find their way.  Barging was stopped about a decade ago and spill was increased in Columbia River dams during migration season in order to facilitate smolt survival.