Bull trout in the Lower Deschutes

In 2022 I caught more bull trout fishing the Warm Springs to Trout Creek stretch of the Lower D than I have in past years and heard similar accounts from other anglers. The fish have been bigger as well, 20″ was not unusual.

Bull trout were not the subject of a meeting I attended today with a number of fisheries biologists discussing the Lower D but I asked about them and thought I would share. Bull trout breed in modest but declining levels in Shitike Creek and the Warm Springs River. Shitike Creek meets the Lower D just northwest of the Highway 26 bridge and the Warm Springs River comes in at South Junction.

Another source of bull trout of is Lake Billy Chinook. Bull trout less than 10″ captured in the Selective Water Withdrawal tower are passed down to the Lower D and released near the Pelton Fish Trap. Bull trout captured in the Pelton Trap are not passed back up to LBC. As the graph shows, however, the number of bull trout transferred downstream is highly variable but has been consistently declining the past few years.

So, why are we catching more of them? It’s a mystery. My guess is that the small fish from the SWW over the past few years have flourished. Bull trout can live much longer than redband trout, sometimes over 10 years, and will continue to grow their entire lives given good habitat and abundant food, which is present in the Lower D. Going forward, the limiting factor is going to be spawning habitat. Bull trout need water around 45 degrees or colder for spawning. The Lower D is not that cold during spawning season and historical spawning tributaries like Shitike Creek and the Warm Springs River are warming due to global heating and loss of shade vegetation.

Another question you might ask is why are the numbers of bull trout caught at the SWW so variable? First, remember that the graph is not showing all bull trout captured at the SWW, only the number of fish less than 10″ and transported downstream. Nevertheless, it’s a pretty variable graph. There must be some correlation between weather, spawning success, and juvenile fish capture. I have not looked into that. Also, total bull trout abundance is closely tied to kokanee abundance, since bull trout mainly feed on kokanee. Kokanee populations throughout Oregon are known for wild boom bust cycles that fisheries biologists cannot fully explain. Sometimes you just have be comfortable with the unknown.