When do Trout Spawn? – Colorado Spawning Summary

“Don’t walk through that area!” yells a guide as he warns another angler about a spawning area on the Eagle River. Every spring and fall, the various fish species begin their annual rituals of spawning.  As an angler, it’s our duty to understand the spawn is a fundamental step in the future of the ecosystem. It’s in our best interest to know exactly what, where, and when takes place. Below you will find some pertinent information in regards to trout spawning in Colorado.

Trout Redd – Photo Steve Parker

When do Trout Spawn?

Spawning is directly related to water temperatures, as eggs need enough oxygen in the water to hatch. River conditions vary year to year and place to place but here is a general idea of how it all happens here in Colorado. Rainbow and Cutthroat Trout spawn every spring (anywhere from February to May). The magic temperatures range is at least 42 to 44 °F (6 to 7 °C). While the Brown and Brook trout spawn in autumn (usually from September to December) when water temperatures drop back into the ideal range. Rocky Mountain Whitefish spawn in late fall-early winter (typically October-December). The variety of suckerfish species in Colorado typically spawn late spring into mid-summer.

A small vibrant trout Redd Photo: Steve Parker

How do Trout Spawn?

When the spawning occurs, the female fish will search out shallow, gravel river bottom often near or below tributaries or even in the tributaries. The females begin the process by sculpting the nests called Redds. They clear the area of silt, sediments, etc to give the eggs a safe and oxygenated resting area.

The male trout begin the ritual by dressing up in their vibrant colors you often see most prominent with fall brown trout. They begin the mating by fiercely fighting and fending off other males to find a female of their liking. The males use their teeth and kypes to aggressively fight other males. Kypes are developed pre-spawn as it is a sex characteristic that develops at the distal tip of the lower jaw. Once the male pairs up with a female the male proceeds to defend that Redd whole heartily from anything that poses a threat.

The female will deposit the eggs onto the Redd and the male will fertilize them. The hen then covers the eggs for them to mature over the course of the next few months. A female can lay anywhere from 200 to 8,000 eggs depending on the size of the fish and external conditions. Of those eggs very few mature to become adults.

Unlike salmon who die after spawning, trout can spawn multiple times throughout their life. The process is typically the most stressful and enduring part of a trout’s lifecycle.

Photo: Steve Parker

“Don’t Tread the Redd”

During the spring in fall, it is important to be on the lookout for these trout nests called Redds. It’s our duty to be mindful of where we are wading as well as where your dogs and nonfishing friends are walking. When you see a Redd it is usually a good indication that there are more in the vicinity as well. If you do hang around you may even be able to see the magic happen, it is a sight I recommend every angler to see at least once. Also, be sure to be up to date on all regulations, certain areas of rivers close due to spawning.

Rocky Mountain Whitefish and Suckers Spawning Specifics

Rocky Mountain Whitefish

Whitefish spawning happens in the late fall-early winter (typically October-December) on local water. Whitefish don’t build redds like trout instead the mountain whitefish congregate in large schools in streams to broadcast their adhesive eggs over gravel bars in tributary streams. The eggs develop over winter and then hatch in March.

Flannelmouth Sucker caught on the Roaring Fork River

The variety of different sucker fish in the rivers also spawns in this way. The time of year of the sucker spawns varies on the stretch of river and species of sucker fish. But, for the most part, it seems the suckerfish spawn in warmer water temperatures. “Flannelmouth sucker typically spawn in the Upper Colorado River basin between April and June.” (McAda 1977, McAda and Wydoski 1980, Snyder and Muth 1990, Tyus and Karp 1990). “The Mountain Sucker spawn occurs sometime during late spring or summer, between May and mid-August, at water temperatures between 11 and 19 °C (52 and 66 °F) (Belica and Nibbelink 2006).”

Guide Tip: It is common for larger trout specifically rainbows to congregate behind these schools of whitefish or suckers. When you encounter the whitefish or sucker spawn look for rainbows feeding on the eggs, and target them with egg fly patterns.

Should you fish to a spawning trout?

This seems like an obvious question for many trout anglers but for any bass, saltwater, or other species anglers out there, when a fish is spawning it is typically a green light to catch a trophy. Or maybe the only time the fish is available to target. But, in the trout world, the general consensus would disagree to targetting spawning fish. 

A spawning trout is typically very vulnerable, trout are a fragile species. The spawning takes place in a very shallow visible area, spawning fish are more aggressive than ever, and will charge at anything that moves into the spawning bed. So is there sport in that? Not much at all, but many (not all) anglers don’t understand that this might be unethical, so it’s in our best interest to educate others. 

The Opposition:

In many river systems, we depend on this annual event for our trout to repopulate. Disturbing this process poses a threat to the success of this spawn. One opposition to this debate is fishing to spawners is not related to sport but conservation. “Is the species that is spawning native or an important part of that specific river and ecosystem or is it actually negatively impacting the ecosystem?” For example, should a nonnative rainbow trout be spawning in an area where other native Colorado River Cutthroat Trout are trying to spawn? This is a question that can be answered by our wildlife managers. They manage our waters in the best interest of conservation measures.

We always do need to look to them to educate, inform and enforce the public and the anglers about this conservation impacts. So next time you see a wildlife manager during spawning months, be sure to ask them what is going on in the river and what you should be on the lookout for.  Just something to think about every time you do see fish spawning. 

Guide Takeaways from Spawning

  • Know how to identify a Redd, ask your fishing buddies when you think you see one or ask your guide to point one out.
  • Know how to identify a spawning fish, look for indications in males, like kypes, colors, and wounds. In females large bellies, worn down tails, etc. When handling these fish use extra caution and care.
  • During spawning months typically both male and females don’t have a protective slime layer or only partially. Use proper handling techniques to keep the fish wet and make sure if you do handle the fish that your hands are wet.
  • Minimize your wading in rivers, instead keep your boots on the bank or in a boat. A small rock being dislodged can destroy fertilized eggs.
  • For the opportunist angler, during the spawning months, egg patterns are more effective. Familiarize yourself with the different species that are spawning in the rivers and the colors of their eggs. *This does not mean to fish an egg on a spawning bed but rather just as you would on your nymph rig in a deep pool.*

Be sure to check out Vail Valley Angler’s guide Mike Salomone’s article about Spawning Awareness here.

As anglers, it’s in our best interest to understand the trout life cycle and work with our wildlife managers to educate, inform, and protect our ecosystems from degradation.

Patrick Perry, Content Contributor, and Former Guide @patperry

Cover Photo from Steve Parker