Fishing the Trico Hatch

First published in Sept. 2018
​Patches of mist hung over on the water on a late August morning as a bald eagle flew upstream on an unknown mission.  A doe and her nearly grown fawn stepped into the water to drink.  Small black duns began to rise from the water, accompanied by rise forms in a pool upstream.  I replaced my beadhead nymph with a #22 Trico dun, waded carefully to the tail of the pool, and began making short casts, silently willing the fly not to drag.  After several botched presentations, I finally found a trout gullible enough to take my fly, and, after a short fight an 11” brown was in my net.

I first encountered the Trico hatch nearly 20 years ago on the Rush and Kinnickinnic Rivers.  The idea of a river full of rising trout in the middle of the summer intrigued me, as did the challenge of enticing them with tiny imitations during the most pleasant, bug-free part of the day.  But a full-time job, a small child, and a love of sleep made it difficult to drive out from Minneapolis in time to hit an early-morning hatch, so I only fished it a few times. 
Fast forward to 2018.  The kid is grown up.  The job is history.  My circadian clock has been reset to Lark mode.  I decided this was the year to figure out the Trico hatch.  Between early July and early September, I have fished the Trico hatch a dozen times.  Not enough to claim status as an expert, but enough to gain a few insights and definitely enough to make me completely obsessed with them.  I thought I would share what I have learned with the TU Community in Western Wisconsin and Southeast Minnesota in the hope that some of this may be useful for other anglers.  I am also selfishly hoping that I might hear back from those of you who know more about Tricos than I.

​The Insect
Tricos inhabit trout streams from Maine to California, and are said to prefer alkaline spring creeks.  We have a boatload of these in the Driftless Area but the only streams I am aware of in Minnesota and Wisconsin that host a significant Trico hatch are the Whitewater, the Wisconsin Rush, and the Lower Kinni.  I would love to learn about more streams with Tricos, and I have to assume that at the very least, the tributaries of the above-mentioned streams host the hatch—something I intend to research next season.  I have not yet reached the level of obsession where I use a portable seine to check for insects, but I do look at spider webs to investigate the presence and quantity of the flies.  The first time I observed a Trico hatch this year was on July 5th.  The hatch started to taper off about August 25th, but as of September 3rd, there were still enough flies on the water for me to catch 7 fish in a little more than an hour.

The following article provides a good layman's overview of Trico biology and behavior: 
 http://www.troutnut.com/hatch/669/Mayfly-Tricorythodes-Tricos
The article points out that unlike most Mayflies, who take overnight to molt from duns into spinners, Tricos need only a few minutes to a few hours.  The male duns hatch at night, the females hatch early in the morning, and soon afterwards the mating swarms of spinners appear over the water.

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Season, Time and Temperature
Most of the sources I consulted stated that the best spinner falls occur on bright, sunny mornings where the overnight temperature dips into the mid 60s or lower.  The spinner fall is said to occur at daybreak, or when the air temperature hits 68 degrees, whichever comes later. My experience with the received wisdom has been mixed.  I can’t attest to whether the spinner fall occurs during or after a severe downpour, but I have seen it on muggy, overcast mornings, as well as bluebird mornings.  It does seem that air temperature plays a factor, as the spinner fall seemed to come earlier on warmer mornings.  The TroutNut article provides one explanation:  
“Trico action tends to be more intense during the heat of summer, when the flies must finish their business early before the hot sun dries them out. Later in the season their deadline is less strict and they become sporadically active through most of the morning.”
 
As summer progresses into autumn, the hatch and subsequent spinner fall occur later in the morning, until, by late August, you can fish the Trico until noon on cool mornings.  Civilized.  For what it is worth, the following table shows my hatch data from the 2018 season.  I did not distinguish between the Dun hatch and Spinner fall, but this should give a rough idea of when to be on the water.

Flies and Tactics
Although most sources emphasize the spinner fall, I had good success this season fishing a combination of dun and spinner.  I noticed that the rises during the first half of the hatch tend to be splashier as the trout go after active female duns trying to lift off from the water.  As the spinner fall arrives, the rise forms become quieter.  I generally start out with a #22 dun imitation.  Then, as the rises become more subtle, I add a #22-24 spinner dropper on 18” of 7x tippet.  Most of the fish hit the dropper, but I need the dun to see the strike!  If you are able to see a fish take a #24 Trico spinner from 20 feet away, call me.  I want to start taking the same vitamins as you.  I have heard of anglers having good success fishing emergers at the beginning of the hatch and drowned spinners at the end.  I have not tried this out yet:  another topic for future research.

Drag is the enemy. When fishing hatches of larger flies, I will often get one fish that jumps on a fly that is visibly dragging at the end of a float.  This happened to me just once this season on the Trico hatch, and it scared the heck out of me!  On the other hand, even “micro” drag, where the fly speed is almost imperceptibly different from the current, seems to put fish off, particularly with the spinner.  I find that a long (3-4’) tippet of 7x helps me to reduce drag.  At the start of the season I tried 6x—it just didn’t seem to let the fly float as naturally and I saw my hookups increase substantially when I switched to 7x.  Another key is short casts—I find a 20-25’ “pile cast” is the optimal length: it allows me to observe and control drag, and cast accurately into the feeding lane, while keeping me far enough away to avoid spooking fish.

​Where to fish
In my experience, there are certain pools and glides where fish tend to bunch up and feed heavily and others that look just as promising but have few fish.  Once I do find a spot that produces, it seems to be a good bet for the rest of the season.  Pools with a bit of riffle in them seem to be easier to fish—my theory is that the trout are not as sensitive to drag.  But I have not seen fish rising in “pocket water”—or what goes for pocket water here in the flat Midwest.  I do encourage you to prospect for fish.  I have several “go to” spots now, and in one of these spots the fish I catch are nearly always 12-13”, whereas the typical fish I catch in other spots are 9-11”.  My biggest fish this season was 14”, but I have seen larger fish feed on Tricos in weed-filled glides where micro-currents play havoc with drag, and the fish can break off 7x by burrowing into the weeds.  Another project for next season!