February 15, 2023
By Mike Mercer
This article originally appeared in the May 2002 issue of Fly Fisherman.
“Fifty days at fifty degrees." At least that's what the old adage claims, regarding the time elapsed between adult salmon laying their fertilized eggs and the tiny sac fry's emergence from the gravel. Whatever the exact duration, it's a safe bet that a lot of anglers aren't paying enough attention to the annual appearance of these immature salmon, or their importance wherever salmon and trout coexist.
Much like the vaunted Salmonfly hatch of the western states, these little salmonids can provide frantic early sea son feeding binges. During their peak availability, they are plentiful, easy to capture, and offer a tremendous source of protein to trout. Unlike the mobs attracted to the famous stonefly waters, though, relatively few anglers seem to recognize the opportunity the tiny salmon provide them.
In my home water of northern California's Lower Sacramento River, for example, sac fry patterns have only recently been discovered and are still considered something of a novelty. An incredible fishery, the big Sacramento is not known as much of a streamer river, so my interest was piqued a few years ago when, upon landing a typical heavy shouldered rainbow, a half-dozen silvery minnows fell from its jaws. Closer inspection identified them as tiny king salmon sac fry, a life form I knew existed in the river but had never given much thought to. I decided to do a little research.
Timing is critical to using sac fry imitations. While trout will respond to fry patterns year-round, my experience indicates there is usually a two-month window of peak recognition where fish will key in on them, much as they would to a more traditional insect emergence.
Research a river's spawning cycles. Watch for a period when the majority of salmon are actively paired and spawning, and mark the date on your calendar. About 50 days later, start watching backeddies, and seine areas immediately downstream and to the edge of known egg-laying areas. Never walk directly on these spawning areas, known as redds–you will wreak catastrophic damage by crushing the eggs and young salmon still in the gravel. Watch for concentrations of the little sac fry hovering close to the streambed. If you're fishing anyway, examine landed fish closely. Often trout keying in on freshly emerged fry will feed gluttonously and disgorge just-eaten victims upon being landed. These are your signs to tie on a new kind of fly!
When fishing fry patterns remember that being encumbered with such gigantic egg sacs, salmon fry aren't particularly agile swimmers. They tend to stay deep in the water column, preferring the relative safety of the streambed cobble to navigating open water. Unlike many streamer techniques, a dead-drift nymphing presentation is often the most effective. Eighty percent of the time, I fish fry patterns beneath an indicator, often with a nymph dropper. Swinging fry flies on sinking-tip lines can also be effective if you're careful to mend often and keep the fly swinging slow and deep. Whatever technique you use, you'll find the takes are rarely subtle–trout inhale these mouthfuls with gusto! When designing your own sac fry patterns, there are three key features to incorporate. First, freshly emerged salmon are more "sac" than "fry." Their disproportionately enormous protein sacs have to be a major visual trigger to feeding trout. Match the actual sac color as closely as possible and design a natural silhouette as well. Note the egg sac's extended length along the bottom of the fry–it is not a round, salmon-egg shaped ball. Secondly, notice how prominent the natural's black-centered eyes are. Much experimenting has shown me that holographic stick-on eyes are significantly more effective than the more standard flat colors, particularly the silver holographic with a black pupil. With an epoxy overcoat, they are remarkably lifelike.
Finally, don't overdress the pattern's body. Observe the naturals in the water. Their actual bodies are incredibly slim and largely transparent. They do possess a subtle flash; this is worth trying to design into your fly.
Fly Tying Mercer's Sac Fry Streamer
Mercer's Sac Fry Recipe
- HOOK: #12 TMC 2457 or equivalent.
- THREAD: White #3/0 waxed monocord.
- EGG SAC: Dark Row Glo Bugs Yarn.
- BODY: Tan Ultra Lace or similar hollow tubing product with several strands of pearl Angel Hair pulled through the center.
- EYES: Silver holographic stick-on eyes.
Step-by-Step Instructions for Mercer's Sac Fry Streamer:
Step 1: Wind a thread base onto the front 1/3 of the book shank. Take a thin hunk of yarn and double it over to form a loop. Tie this slightly elongated loop in as the egg sac on the underside of the book. It should hide the entire rear portion of the hook and extend back slightly farther than the bend.
Step 2: Using a bent-wire bobbin threader, pull a sparse hank of Angel Hair through the center of a short (3/4-inch) length of tubing. Clip one end of the Angel Hair clump flush with the tubing; clip the other end to length, leaving about 1/8 inch sticking out to form the tail. Tie this body assembly in just behind hook eye so that it lies back over the top of hook shank. Don't worry about thread buildup behind the hook eye–some bulk is desirable.
Step 3: Press on a pair of stick-on eyes, one on each side of the bulky thread head.
Step 4: Coat the entire head and eye area with epoxy (Devcon 5-minute or equivalent). Try, not to get any on the yarn egg sac.
Mike Mercer is the nicest person in the world. If you don’t agree, we’ll eat a # 8 Gold Bead Biot Poxyback Stonefly. He works for The Fly Shop and is based in Redding, California.