The Case of the Missing Salmonflies

Updated: Jun 7

The West is full of so many famous waters that it's easy to overlook some of the smaller venues. Yet sometimes these local favorites offer great rewards to the anglers willing to indulge. One example is northern Utah’s Logan River. Diving down from southern Idaho through karst-canyonland into a Swiss inspired valley, most of the Logan runs cold and fast. It is home to the Bonneville cutthroat trout (brought back from the brink of extinction) and is a gem of a freestone river that is overshadowed by the meandering Snake to the North and the famous Green to the East. The Logan is most rewarding for hatch-matchers, so if you travel to the land of milk and honey, bring a well-stocked box; you don't want to miss a surprise green drake hatch as you're about to pack it in.

Most major western hatches can be targeted on the Logan to great effect. From early season BWOs, to skwalas, stoneflies, caddis, green drakes, quills, hoppers, and October caddis; all emerge in a relatively predictable fashion. Wrap it all up with the typical cutthroat’s proclivity to munch dry flies. But despite all the great hatches, there is one slot in the fly box that's missing these day...

A typical view on the Logan River during early-mid fall

Flashback to the early 20th century with a resurrected letter written by Frederick Jackson Turner (a frontiersman) to his wife bemoaning the difficulties of landing trout in the swift water of the Logan. He also describes to her a large, reddish "June-bug" the size of a grasshopper, whose presence is so noticeable that it distracts the trout from taking his own flies. What Turner was actually describing was the illustrious salmonfly — the angler’s king of the stoneflies. Known to emerge shortly after peak runoff in Spring, it’s no doubt Turner struggled landing trout in the swift, turbid water. This early letter highlights a golden age on the Logan when adult shucks of salmonflies accumulated in such densities that they looked like trash barges floating ashore. Not to mention the tall tales of the sizable Bonneville Cutthroat being caught in an age before intense harvesting, damming, and industrialization.

With the support of the local land grant university located at the mouth of the Logan Canyon, the river was well monitored. Interested naturalists sampled, studied, and unturned more stones in the Logan watershed. Consistent sampling confirmed the presence of salmonflies for forty years past Turner's letter, though the salmonflies likely thrived here for a long period. However, by the late 1960’s it appeared as though the abundance of salmonflies in the Logan River vanished into thin air. Could it have been the result of anthropogenic pollution? An overuse of dangerous herbicides or pesticides? Remember, this was around the time of Silent Spring, when impacts of pesticide use were just being understood. Yet, to this day, salmonflies have failed to reestablish, rebuking the theory of a one-time pollution event, unless the event has been subtly ongoing.

Plus, the largely undammed Logan River is known as a clean, cold-running stream that is highly capable of producing and sustaining robust trout populations; it is considered one of Utah's Blue Ribbon Fisheries. Even more strange, the parallel drainage south of the Logan, the Blacksmith Fork, still produces salmonflies. All this time, the Blacksmith Fork's salmonfly population has persisted. How could no salmonflies have reestablished in the Logan when dispersal sources were so close? Granted, salmonflies aren’t great fliers, but weather and wind have long distributed animals. If lizards were able to colonize South America from Africa by floating across the Atlantic ocean on driftwood, it seems likely that salmonflies might have wandered to the neighboring drainage.

In fact, I’ve personally seen salmonflies on Colorado’s Muddy Creek tailwater miles from the likely hatching source, the Colorado River. But what if too few were able to relocate back into the Logan? Would the results have been different if more insects had a better chance of reestablishing?

A beautiful Bonnie from my favorite stretch of the Logan

Cue salmonfly stocking. You heard me right; not rainbow trout stocking, but moving immature salmonfly nymphs from the nearby Blacksmith Fork to the Logan. The local university teamed up with Trout Unlimited starting in 2004 to attempt reintroduction. Along with the non-hatching reintroduction, adults were also relocated in several attempts. Though monitoring was able to track some signs of salmonfly presence by identified a few early-stage salmonfly nymphs, after three years no more salmonflies could be found, and future efforts dissolved.

Even more bizarre, a 2018 publication has documented declining populations in salmonflies in another Utah stream. South of Salt Lake City, the Provo River (most famous to anglers for its two tailwater sections) now concerns scientists with a dwindling population of salmonflies. Though no exact cause has been attributed to the decline, the authors provide a laundry list of potential causes for the decline: river damming, channelization, pollution (from nearby agricultural and urban areas), and increasing temperatures. Unfortunately, this list has been long-established and negatively affects many freshwater systems across the West, making it difficult to pinpoint the exact combination or manifestation of these variables impacting the Provo and possibly the Logan.

Side Note: Similar losses to salmonflies occurred on Colorado’s Arkansas River, where current stocking efforts are being met with the same lack of production as on the Logan. Though, in the Arkansas drainage, the loss of salmonflies is much more likely the result of poor water quality from heavy mining activities in the early 20th century.

Back to the Logan, without any specific sources of evidence, the best we can currently tell is that a local extinction (also known as extirpation) occurred. Some might argue that there are no signs for alarm as other populations exist elsewhere within this stonefly’s range, or that nature is inherently dynamic and local populations continuously rise and fall. However, from an evolutionary standpoint, substantial extirpation can still lead to a bottleneck in a species' genetic diversity (which can be thought of as a species' resiliency against extinction). Now consider that the global extinction rate has skyrocketed over the 20th century and that global temperatures have followed the same trend. In fact, many global trends have experienced accelerated growth since the industrial revolution.

Along with the Provo, scientists are now even concerned that the "holy" Madison River salmonflies might be losing an additional 28km of habitat (22% of suitable habitat on the Madison River) attributable to an increase in temperature from climate change.

So what happens if restocking salmonflies isn’t a feasible bailout strategy? What if rising stream temperatures desync their timing of the spring emergence? It's too early for widespread concern, but then again, we might look back to see that the writing was on the wall the whole time.


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  1. The Logan River Junebug.

  2. Needham, J. G. and R.O. Christenson. 1927. Economic Insects In Some Streams of Northern Utah. Logan, UT: Utah Agricultural Experiment Station Bulletin 201:1- 36.

  3. Hansen, B. P. An Environmental History of the Bear River Range. 1860-1910.

  4. Birrell, J. Nelson, R. 2018. Loss of the Giant Salmonfly Pteronarcys californica and changes in stonefly diversity in the Provo River, Utah (Plecoptera)

  5. Bear River Basin. Utah Division of Water Rights.

  6. Colorado aims to restore salmonfly for trout.

  7. Anderson, H. Albertson, L. Walters, D. 2019. Water temperature drives variability in salmonfly abundance, emergence timing, and body size. River Research and Applications.

  8. The Dawning of the Age of Anthropocene.