Bull Run

Science: Bull Run Cutthroats

Bull Run Cutthroats: Learning Lessons From a Special Trout

By Terry Otto

 The Bull Run watershed is a rain-catching basin on the west flank of Mt Hood.  The municipal water source for Portland, Oregon, and closed to the public since 1895, this remarkably beautiful and wild

Bull Run
Photo Credit DSaiget

sub-alpine protected habitat is home to a population of native coastal cutthroat trout.  The isolation of Bull Run cutthroats(Oncorhynchus clarkii clarkii) has allowed biologists to study trout behavior without interference from the angling public.  It’s a rare opportunity.

Bull Run Lake, at the very top of the watershed, is the center for these studies.  Yearly redd counts in the small tributaries monitor the health of the spawning population, while other studies have shed light on the behaviors of trout that spawn on the gravel shoals within the lake.

Lake Spawning Bull Run Cutthroats

Shoal spawning is a rare occurrence in trout populations, and even in this lake many of the trout still choose to spawn in the tiny tributaries instead of the lake itself.

Bull Run
Photo Credit Terry Otto

As a biological technician for the Forest Service, I was part of the team that engaged in the shoal-spawning studies of Bull Run Cutthroats.  It was an eye-opening experience, enhanced by the wildness of the Bull Run itself.  Travel to the lake was often difficult, and involved the use of motor vehicles, snow machines, and even foot power at times.  All the while we were surrounded by astounding natural beauty, and un-bashful wildlife. Black bears, deer, elk, and even cougar could be glimpsed as we went about our tasks.  Deep snows and the 5 to 10 degree Celsius temperatures in the lake forced us to take special precautions as we performed our work.  But even with the hardships, it was an unforgettable and rewarding experience.

And then there are the Bull Run cutthroats.  We floated over them for hours at a time, observing their annual effort to foster future generations.  They faced formidable odds.  The lake is extremely oligotrophic, which means it’s deep, unfertile, and cold.  Food is scarce, and the growing season short.  Fish grow very slowly in these conditions, but left alone and un-fished, Bull Run cutthroats reach sizes of 18 inches or more.

Big, aggressive bucks, sporting bright spawning colors, roamed the flats ceaselessly, looking for ripening hens, and picking fights with other bucks. The constant activity could be exhausting at times.

Cutthroats and Cannibalism  

In this nutrient-poor environment the cutthroats often resort to cannibalism.  We watched as the hens laid their eggs in the gravel nests, only to have most of them devoured by the surrounding spawners before the exhausted female could bury them.  Even the female’s spawning partner took part in the carnage.

It was a shock to witness this brutal side of nature.  To observe a male devouring the eggs that would carry his genetics into the future is rare, but Bull Run cutthroats can’t afford to refuse such a substantive meal.  Surprisingly, studies confirmed that these shoal-spawned redds produced good numbers of young, in spite of the carnage.

On-going studies continue to surprise scientist regarding these special trout, and it’s a testament to the abilities of these native fish that they adapt and survive in such a restrictive, hostile environment. What has been witnessed and documented concerning this population gives hope to scientists and fishermen alike that native fish can overcome severe obstacles, and even thrive.

Bull Run cutthroats are survivors, and will hopefully give life to this unique lake at the top of the world for generations to come.  And they will continue to provide biologists with unique insights into the lives of high-country trout.

Special note: Trespassing in the Bull Run can incur fines of up to $4,000.


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