May 03, 2012
By Arlen Thomason
If your first thought upon seeing this image is of prehistoric monsters, you aren't too far off the mark. Nearly 250 million years ago this fellow's ancestors, bearing mugs not all that dissimilar, lumbered from the water and onto the land in much the same way as this salmonfly nymph did. The next step was the same, too—splitting open the nymphal encasement to free the winged adult inside. Sorry to say, the emerging adult then or now would be no more likely than this youngster to win a beauty contest. At least not if humans were judging. Fish, on the other hand, might have a different take on the matter.
Salmonflies in a Nutshell
Stonefly nymphs of the family Pteronarcyidae, genus Pteronarcys are among the largest in North America. The major Western species, P. californica, goes by the common name giant stonefly, or more widely, the salmonfly.
The salmonfly emergence on some rivers of the West is among the most famous and most anticipated hatches in the country. Who can resist scads of giant insects falling on the water, often greeted by large gaping trout mouths?
You might think that a two-inch nymph with a face like this would be among the fiercest predators prowling the river bottoms.
But you would be wrong. For all its size and fearsome appearance, a salmonfly nymph is more cud chewer than carnivore. Nothing makes it happier than grazing peacefully on algae and detrital fungi accumulated within the crannies of streambed cobble. Yet it has been reported to feed on juvenile insects on occasion, when opportunity arises and the unfortunate youngster fails to move out of the way.
Salmonfly nymphs generally spend two to three years in the water, depending on temperatures and food supply.
Their favorite places are brawling rivers with lots of medium to large rocks, serving not only as debris catchers and hiding places but also to churn lots of oxygen into the water. Stoneflies in the family Pteronarcyidae have the most complex gills of all stoneflies, sporting branched, feathery gills at the base of each leg, as well as on some abdominal segments. The only other stoneflies to have similar branched gills are the golden stoneflies, family Perlidae, though in that family gills are absent from the abdomen. Nevertheless, their gills apparently leave something to be desired when it comes to respiratory efficiency, since both groups prefer fast, well-oxygenated water.
Most cool Western streams with good water quality and sufficiently turbulent flow to provide aeration hold some salmonfly nymphs. But it is the largest such rivers that contain the greatest numbers. A special few of them, like Montana's Madison,
Idaho's Henry's Fork, and Oregon's Deschutes, support superhatches that are legendary.
Hatches begin in mid-April among many of the rivers west of the Cascades, and in May and June for most of those in the interior West. A couple of weeks before that, the big nymphs get itchy feet and start migrating toward shore.
Doing so exposes them to perilous currents and they often find themselves swept into the drift. A drifting salmonfly nymph is a sad sight. All it can do is curl into the fetal position and hope to touch down on a rock before it enters a trout's belly. Many don't make it.
The ones that do arrive safely at the shoreline need to choose their exit strategy carefully. Lots of big juicy nymphs emerging from the water are sure to attract attention from above as well as below. It is better to wait until most of the birds go to bed, and sight-hunting trout lose the advantage of good vision. So salmonfly nymphs lumber ashore at dusk and a little after, in the dark. They usually look for something close to climb on. Tall weeds will do, or the trunks of alders and cottonwoods. If they don't encounter such a perch nearby, they will sometimes crawl quite a distance to find one. Once they've gained some altitude and a vertical position, the molting process begins, and before long another salmonfly adult has entered the world. The morning light often finds it perched on a limb, overseeing its riverside domain, with thoughts of a mate on its mind.
Have you wondered where the name salmonfly comes from? If you look at one from below, the answer becomes apparent. Whereas the top of a P. californica adult is mostly brown, the bottom is a striking orange or salmon color. Though I've also read that the origin of the name may lie in the fact that these bugs hatch at the same time as salmon return to the rivers in the Pacific Northwest.
Over the next few days the principal salmonfly business is finding that perfect someone. On prolific bug waters that isn't difficult; there are so many close cohorts of the proper persuasion that bumping into Mr. or Ms. Right is a foregone conclusion. But in most places with average populations, the job requires a little more effort. It is here that the stonefly musical talents come into play. The male starts drumming his beat; a female answers with hers. Love found, they climb the willow altar together. Conjugal bliss is the conclusion, and before long the posterior end of the female's abdomen is flush with a mass of fertilized eggs.
If the weather is right—a warm sunny day, usually in the late afternoon—her wings whir into action and she helicopters out over the water, dropping her eggs as she goes. And so the cycle starts again. Unless, that is, an aeronautical accident—which occurs all too frequently—takes her prematurely onto the water's surface, where a hungry trout engulfs her, eggs and all.
Fishing a Salmonfly Hatch
My first significant encounter with a salmonfly hatch was in June 1996 on Montana's Madison River. I was spending that summer in Bozeman near Yellowstone Park, and was determined to fish all the famous and not-so-famous rivers in the land of fly-fishing legends. The storied salmonfly hatch was high on my list. Unfortunately, that was a spring with record runoff, and many of the area rivers were blown out well into the summer. The Yellowstone River flooded parts of Livingston and even washed out the renowned spring creeks nearby, which took several years to fully recover. That river didn't fall back into fishable shape until the end of July.
Though the water was a little higher than I would have liked, by the end of June the Madison was accessible to a careful wader. I had heard that the salmonfly hatch was happening, so I drove over one day to see for myself. And it was spectacular. Every bankside bush was covered with brown and orange bugs as big as 747s. I imagined this was what the biblical locust plagues must have looked like. It was hard to conceive that such large insects could be present in such huge numbers.
But I was puzzled. With so many bugs in the bushes, inevitably quite a few of them were falling into the water. I kept my eye on one after another as it struggled on the surface, expecting a malevolent swirl at any moment. But for the longest time, every drifting bug went unmolested. And my big imitating flies drew the same response.
About 5 or 6 P.M. most of the female salmonflies suddenly took to the air—by the thousands, in a cloud headed upstream. As I stood casting in the river, one after another of them flew clumsily into me, crawling up my arms, on my head, and under my shirt collar. There is nothing quite so creepy as a bunch of prickly salmonfly claws rasping down the back of your neck. It makes it difficult to concentrate on your casting, but somehow I managed.
Of course the number of bugs falling on the water was even greater than had crawled under my shirt, and finally a few fish were taking advantage. A big splash here, another one over there. Still, it was nothing like I expected. With so many steaks on the water, why weren't more fish chowing down? And what's worse, all the rises were to naturals; not a single one came to my flies.
Back at the fly shop, I related my exciting but frustrating experience to some sympathetic ears. "Yep," I was told, "that's nothing out of the ordinary."
It seems that by the time the salmonfly hatch reaches its peak in a particular section of the river, the trout have been gorging themselves on migrating nymphs and returning adults for two to three weeks. They're stuffed, and will only move occasionally to take anything from the surface.
The advice: as the hatch moves upstream over a several-week period, try to stay at its leading edge, where fish are just starting to see the activity.
"Go way upstream and try again tomorrow," the locals said—and then further advised, "don't just fish dry flies imitating adults; give some big, heavy dark nymphs a shot."
The next day found me upriver ten to fifteen miles, checking the banks for evidence of salmonflies. Here there were moderate numbers of nymphal shucks, indicating that the hatch had begun in this section, but just a few adults were evident on the shoreline. I tied on a big Clark's Stonefly and cast it along an undercut bank with overhanging bushes. It was immediately smacked by a nice fish, and several minutes later a pretty 15-inch brown trout was at my feet.
Despite the auspicious beginning, forty-five minutes and several dry-fly changes later, there had been no further action. So I went to Plan B. Off came the dry fly, and on went a heavily weighted Kaufmann's Stonefly nymph. That turned out to be the ticket. In another two hours of fishing, I caught eight or ten trout, up to 21 inches. These trout wanted their steaks all right, but they were more interested in deep dining than having a surface snack. It was important to dead-drift the nymph right along the bottom, letting the artificial tumble in the current the same way a hapless natural that had lost its grip on the bottom would do.
That's a lesson that I have never forgotten. Though I've since enjoyed excellent fishing during salmonfly hatches on a number of rivers, including Oregon's Deschutes, dry-fly action can be fickle. If you head to one of the famous Western rivers in search of the celebrated salmonfly hatch, with expectations of stupendous dry-fly action, there is a good chance you will be disappointed. You often have to time it just right for success on the surface. But nymph fishing can be another story. Rick Hafele and Dave Hughes wrote in The Complete Book of Western Hatches that they would rather be on a good salmonfly stream in the two weeks prior to the hatch than during it. I'm not sure I agree—because fishing the big dry flies is so much fun—but they are probably right that the odds of catching good numbers of big fish are improved.
Lest you get the wrong impression, I hasten to add that there is nothing more exciting than the spectacular mistake of a big fish exploding on a floating salmonfly imitation.
There is also nothing tentative about the take, and the sudden shock of the attack has caused many an angler to break off the fish with an overly enthusiastic reaction. (Use strong tippet, at least 3X, to help avoid that; trout eating salmonflies aren't leader shy.)
So for many of us it's worth taking the chance of a poor catching day just to have a shot at such an experience. And good days do come along; otherwise, you wouldn't hear all those stories about the fantastic salmonfly hatch. One good day like that can make up for a lot of near misses.
To improve the odds, especially on popular rivers with a heavily fished hatch, look for difficult-to-access places with deeper water right off the bank and an overhanging tree.
Big fish lie in such spots waiting for a clumsy salmonfly to lose its grip and tumble in. Cast a big fly—something like a size 4 to 8 Stimulator, Clark's Stone, or Sofa Pillow is a good choice—right under the tree.
This is not like fishing over a mayfly hatch, so you don't need to be very gentle about it when using a relatively light fly like these three. There is nothing delicate or graceful about a salmonfly hitting the water. Once there, it often struggles mightily but uselessly to make headway toward shore. From underwater, the view is of a lot of kicking and commotion.
Flies for the Salmonfly Hatch
Plenty of patterns have been developed to imitate both the nymphal and adult forms of salmonflies, and most of them work in various situations. Large, heavily weighted nymphs are appropriate for deep or swift water, whereas smaller and lighter patterns are better suited to more moderate flows. I'm fond of the dark Kaufmann Stone tied with black rubber legs, especially when fishing some of the Montana rivers in years with a heavy spring runoff. For dry flies, traditional ties or the newer foam-body stonefly imitations both have their places, depending on water conditions.
The popular Improved Sofa Pillow or the similar all-purpose Stimulator tied with an orange body take more than their share of fish when adult salmonflies are on the water.
Arlen Thomason is a molecular biologist in biomedical research. He lives with his wife Susie along Oregon's McKenzie River.