Spring Spawn

May 5, 2020

Spring is in the air, and for rivers this means an impending spring runoff.

Every year spring runoff, along with stream temperatures, signals the seasonal spawning migration of both native westslope and non-native rainbow trout. These environmental triggers tell adult fish it’s time to return to their natal streams, near where they were born and spent their early life, to reproduce, or spawn in fisheries language.

As rivers swell and stream temperatures approach 10 degrees Celcius, spring-spawning fish congregate at the mouths of healthy tributaries in big numbers. High water allows cutthroat to migrate into the small, headwater streams, in search of ideal spawning grounds.  Often, a fish will swim more than 100 miles, over the course of several weeks, to reach the perfect spot.

The qualifications for a productive spawning stream are exacting. Spawning adults are searching for deposits of specifically sized gravel, not too big, but not too small.  Gravel must large enough to provide protective pore spaces where fish eggs can shelter and develop, but small enough for a fish to move. During spawning, female fish expend tremendous amounts of energy to excavate a nursery, called a redd, for their eggs.  Using the strength of their own body, female fish pile layers of gravel, eggs, and more gravel.  Fast flowing, clean, and cold water must move through these redds to remove flush out waste and disease, and deliver essential oxygen to the developing eggs and young fish.

As cutthroat migrate between the river and its tributaries for spawning, they have to navigate through man-made obstructions, like impassable culverts, misleading irrigation diversions, and even segments of creeks that dry up seasonally due to dewatering. CFC’s on-the-ground restoration program has financed and constructed numerous projects specifically designed to improve fish passage and benefit spring spawning trout, like native westslope cutthroats.

Fish passage culvert projects, often on US Forest Service land, allow spring migrating trout to reach key spawning areas in headwaters.  These culvert pipes have “stair-step” fish ladders built in to slow the water and allow trout and other fish to move upstream. Fish screens on irrigation ditches prevent trout from being caught in ditches, where they become easy prey for herons, raccoons, and other predators, or become stranded as ditches dry up in late summer. Instream flow projects involve buying or leasing irrigation water keeping it in the creek to aid cutthroat trout migration in the spring.

The CFC is working on fish passage projects with our partners in the Upper Clark Fork, on cutthroat spawning tributaries like Cottonwood-Baggs Creek, Dry Cottonwood Creek, and Boulder Creek. Today we are starting work with FWP to improve the potential for cutthroat spawning runs in Miller Creek, just outside Missoula.








Here are some ways that you, your friends, and family, can explore the amazing natural phenomena of spring spawning:

1) Join us for a live happy hour on Facebook! We’ll be live and cutting loose with CFC technical advisor and Professor of Aquatic Ecology, Dr. Lisa Eby,  UM graduate students Andrew Lahr and Troy Smith, and CFC’s Restoration Director Will McDowell on Thursday, May 7th at 4:30 pm.

2) Thanks to Trout Unlimited and Montana Fish Wildlife and Parks, you can also dive into the spawning migration virtually, following individual westslope cutthroat as they stage and spawn up Rock Creek in Granite County.

Follow tagged cutthroat live on the Race-up Rock Creek website. The interactive dashboard lets you choose a favorite fish to follow, explore all past locations, and keep updated on how many miles your fish has moved.  Who will migrate the farthest? To make it interesting…. I’m putting 10$ in on Big Phil.

The project is a joint venture between Trout Unlimited and Montana Fish, Wildlife and Parks to learn more about how trout use the habitat in Rock Creek. Trout are tagged and then adopted through a donation, which is used to fund future work.


3) Follow us on social media all week as we share information about the spring spawn! 


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