Logan River Salmonfly Disappearance

Reintroduction project summary in reverse chronological order

April and May 2007. More than 2,000 nymphs and 1,000 adults moved from the Blacksmith to the Logan River

Winter 2006/2007 - no nymphs located in the Logan River by USU entomology class.

April and May 2006. More than 2,000 nymphs and 600 adults moved from the Blacksmith to the Logan River.

Winter 2005/2006 - two nymphs collected from the Logan River at Woodcamp Campground. These were young of year nymphs, which means they hatched from eggs that were laid by the adults we transplanted in the spring of 2005.

June 15, 2005 - Evidence of adult emergence on the Logan River was found at the old highway cutoff upstream from Birch Glen. Several exuvia of Pteronarcys californica were collected at this site (see below).

May 28, 2005 - About 275 adult salmonflies were moved from the Blacksmith Fork to the Logan River at Woodcamp Campground. This group of adults was put at Woodcamp, rather then Preston Valley so that if we collect nymphs at this site in the future it will tells us that the adults that we released were able to successfully mate and lay their eggs. The BugLab collects aquatic invertebrates at this site each month, so if reproduction was successful we should know in about 6 months or so. We collected the eggs from 5 females and found that each female had about 350 eggs. The number of eggs carried by each female ranged from 97 to 588. Each egg is about 0.6 mm is size - see below.

May 20th - May 27th, 2005 - About 800 adult salmonflies were moved from the Blacksmith Fork to the Logan River and released at Preston Valley Campground.

April 23, 2005 - about 60 volunteers showed up at the Blacksmith Fork Bridge and over a couple hours we collected several thousand nymphs. We moved these nymphs to the Preston Valley Campground on the Logan River and released them. We then all celebrated with a barbecue and refreshments.

December 11, 2004 - several thousand nymphs moved from the Blacksmith Fork to the Logan RiverCache Anglers Trout Unlimited Chapter upcoming salmonfly transplant scheduled for April 23rd, 2005. Bring your waders, an insect collection net or screen if you have one and meet us at the mouth of the Blacksmith Fork Canyon at 10 AM. We will collect for an hour or so and then drive over to the Logan River where we will release the salmonflies in their new home.

Summer 2004 - The BugLab and Trout Unlimited meet to formulate a plan to reintroduce salmonflies to the Logan River. With the consent of the US Forest Service and the Utah Division of Wildlife Resources, we plan a four year project with two relocations each year.

Background - The salmonflies, Pteronarcys californica and Pteronarcella badia (Plecotpera: Pteronarcyidae) were once abundant in the Logan River. In a 1927 paper, James Needham wrote “Pteronarcys californica abounds in the clear waters of Logan River below 6000 feet. It is undoubtedly one of the most important insect species of the stream. Its greatest abundance seems to be in trash piles that gather against the upstream side of the larger rocks in midstream where it finds both food and shelter. Fifty or more well-grown nymphs could be taken on a screen by dislodging a single large stone" (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). In later pages of this publication he comments as well on the abundance of another species of salmonfly, Pteronarcella badia in the Logan River. The last reported collection of salmonflies on the Logan River was in 1966.

We at the BugLab first noticed that salmonflies were absent from the Logan River about 1994, but we did not know they had once been common until about 2000. It always seemed a bit strange to us that they were not in the Logan River as both species are very common in the Blacksmith Fork River - the Logan River’s largest tributary stream that drains the basin just to the south of the Logan River. For the last 5 years we have been on a quest to find these species in the Logan River and its tributaries and to summarize the history of collections for these two species in the Logan River and Cache Valley. We have attempted to locate all of the published papers and graduate student theses that report on collections of aquatic insects in the Logan River (Table 1). We have also reviewed the museum specimens both here at Utah State University and at Brigham Young University (Table 1).

Table 1. History of salmonfly collections in the Logan River, Cache County, Utah.

From the records we have collected to date it seems they disappeared from the Logan River sometime during the early to mid 1960s. The last collection record for salmonflies in the Logan River was by Nancy Erman (Professor Emeritus U.C. Davis). She reported collecting a few Pteronarcys in the Logan River at the Mendon Bridge on 7 September 1966 (Erman, N. A. 1968. Occurrence and distribution of invertebrates in lower Logan River. Master Thesis, Utah State University).

The cause of their demise has been a mystery. Possible, but somewhat unlikely, explanations we have thought of include a chemical spill, herbicide treatments for broad-scale sage brush eradication during the 1960s, and snow and ice melting chemicals used on Highway 89 that parallels much of the river. Salmonflies have been shown to be very sensitive to chemical pollutants. However, we have found no information on any of these events occuring in Logan Canyon. What is equally baffling is why they have not been able to recolonize the Logan River over the last 40 years if it was a one-time chemical spill that eradicated them. This suggests a continual source of pollution or something else that prevents their establishment. Salmonflies are not the best fliers, so dispersal would likely be slow, but after 40 years they should have made some inroads into the Logan River. They can be collected today in the Blacksmith Fork River just upstream of its confluence with the Logan River, so nymphs should be drifting down into the Logan River and we think that some of the adults would have flown up the Logan River during this time. We have never found any nymphs in the Logan River just upstream from the confluence with the Blacksmith Fork River. Over the last several years we have searched all of the streams in Cache Valley for salmonflies and have found them in the Little Bear River and Rock Creek - which are tributaries to the Blacksmith Fork River and in Sugar Creek and Mill Creek which are located north of the Logan River in the northern end of Cache Valley. Further south, they can also be found in the Ogden, Weber, and Provo Rivers.

As additional information is learned we will post it to this web site.