Jackson Birrell and Faculty Mentor: C. Riley Nelson, Department of Biology
Plecoptera (stoneflies) are important insects in aquatic ecosystems worldwide. They cover a wide
array of functional feeding groups and provide various ecosystem services (1). Stoneflies are
sensitive to reductions in water quality, allowing managers to use their presence or absence to
denote if a watershed is healthy or impaired. They are therefore known as bioindicators of stream
health (2). Plecoptera are also appreciated by fly fisherman throughout the world. Despite their
ecological, conservational and cultural importance, stoneflies are in decline. Their sensitivity to
anthropogenic disturbances including pollution, river damming, urbanization and climate change
make them particularly vulnerable and have lead to reductions in their diversity and distribution
in recent years (3,4). Several stonefly species have even gone extinct (5).
One species of stonefly, the giant salmonfly (Pteronarcys californica), is becoming regionally
extinct in multiple Utah streams. Despite being historically abundant in both the Logan and
Provo Rivers of Northern and Central Utah, they have already been extirpated from the Logan
(6) and are currently in decline in the Provo (7). We are concerned that these changes in
abundance and distribution in the Provo River are indications that the water quality and other
physical attributes such as armoring, flow regimes, etc. of the stream are changing. Furthermore,
the loss of Pteronarcys may put this ecosystem in further jeopardy for other species as well by
altering food web dynamics, nutrient availability or by causing trophic cascades (8,9). With this
in mind, we determined the current status of Pternoarcys californica on the Provo River by
quantifying their abundance and distribtution. Secondarily, we also documented the diversity of
all other stonefly species found in the stream.
We created a baseline for the abundance and distrubtuion of Pteronarucs californica in the Provo
River with which to compare our findings by compiling published data. We also used collections
from the BYU Monte L. Bean, anecdotal occurrence notes and unpublised raw data.
We sampled Plecoptera nymphs during two consecutive years in 2016 and 2017. When possible,
we took samples at sites where they had previously been collected. From April to May, 2016 we
sampled Plecoptera at regular intervals including 17 sites in the Lower Provo (Deer Creek Dam
to Utah Lake), 4 in the Middle (Jordanelle Dam to Deer Creek Reservoir), and 10 in the Upper
(Trial Lake to Jordanelle Reservoir). In 2017 we sampled from June until July and decreased our
sampling intensity to 6 sites on the Lower Provo, 2 sites on the Middle Provo and 4 sites on the
Upper Provo. During both years, we used a kick screen to collect all stoneflies from eight riffled
boulders at each site. We were able to sample across such a broad temporal scale because of
Pteronarcys californica have a four year lifecycle and are therefore always present in the stream.
In the lab, we identified all stoneflies to their lowest possible taxonomic unit, usually species but
sometimes genus, using two dichotomous keys (1, 10).
Historically, Pteronarcys californica was prevalent throughout the Provo River. In 1927,
Needham reported that giant salmonflies were more abundant in the lower reaches of the Provo
than on the Logan River, where over 50 individuals could be collected from under a single
boulder (11). Furthermore, studies indicate that in the 1970’s, thousands of Pteronarcys were
collected from the Lower Provo in a single year (12) and they were also abundant in the Upper
Provo (13). In a more quantitative study, Gaufin sampled at sites across the entire Provo River in
1947-1949. He found as many as 618 individuals at a single location on the Lower Provo, as well
as a total of 44 individuals on the Middle (14).
Throughout the 320 samples that we took during 2016 and 2017, we found a total of 17
Pteronarcys califorinca inidivduals. In general, they were more abundant upstream. We found
two individuals in the Lower Provo, zero in the Middle and 15 in the Upper. We found them at
six of the 30 collection sites, including two sites in the Lower Provo, zero in the Middle and four
in the Upper. We only found Pteronarcys at two of the 14 locations where they were collected
We also observed a trend of increased number of stonefly species upstream. We collected six
species from the Lower Provo, six from the Middle and 19 from the Upper. No Plecoptera were
found in heavily urbanized areas (sites 1-3).
Our results indicate that Pteronarcys californica is being extripated from the Provo River. Rather
than finding hundreds or thousands of individuals as others did in previous studies (11-14), we
found only 17 specimens in two years of collecting. This represents a sharp decline in their
abundances over the past century. Pteronarcys were also absent from the middle reaches of the
stream, indicating that they have undergone a decline in their distribtuion as well. Furthermore,
our results show that the water quality of the Lower Provo River is worse than in upper reaches.
We found less Pteronarcys and less stonefly species in the lower reaches where human
populations, agriculture and the number of dams are higher. Because stoneflies are indicators of
high water quality, this indicates a decrease in river health.
The loss of the giant salmonflies from the Provo River may have harmful ecological effects on
the watershed. They historically comprised a dominant portion of the biomass of the stream (14)
and were therefore an important food resource of fish and other organisms. They also fill a vital
role in nutrient cycling by shredding leaves (8). Without them, organsims in all trophic levels
could suffer. Unless water quality is imporved, Pternoarcys californica populations, as well as
the diversity and abundance of other native taxa, could decline further in the future.
Our data suggests that Pteronarcys californica are being extirpated from the Provo River and
that the Lower and Middle sections have experienced a decrease in water quality. We believe
that anthropogenic disturbances such as river damming, channelization, pollution, and climate
change are causing this shift. However, further research is needed to measure the combined
effects of these causes. We suggest that management of the Provo River watershed be improved
to mitigate the loss of Pteronarcys californica, protect other species, and conserve this
1. Merritt, R. W., K. W. Cummins, and M.B. Berg. 2008. An introduction to the aquatic
insects of North America. Kendall Hunt.
2. Barbour M. T., J. Gerritsen, B. D. Snyder, and J. B. Stribling. 1999. Rapid bioassessment
protocols for use in streams and wadeable rivers. USEPA, Washington.
3. Fochetti, R., and J. M. T. de Figueroa. 2006. Notes on diversity and conservation of the
European fauna of Plecoptera (Insecta). Journal of Natural History, 40(41-43), 2361-
4. Bojkova, J., K. Komprdova, T. Soldan, and S. Zahradkova. 2012. Species loss of
stoneflies (Plecoptera) in the Czech Republic during the 20th century. Freshwater
biology, 57(12), 2550-2567.
5. DeWalt, R. E., C. Favret, and D. W. Webb. 2005. Just how imperiled are aquatic insects?
A case study of stoneflies (Plecoptera) in Illinois. Annals of the Entomological Society of
America, 98(6), 941-950.
6. Vinson, M. 2008. A short history of Pteronarcys californica and Pteronarcella badia in the
Logan River, Cache County, Utah. University of Utah.
7. Nelson, C. Riley. 2015. Occurrence Notes. Unpublished raw data.
8. Short, Robert A., and Paul E. Maslin. “Processing of leaf litter by a stream detritivore:
effect on nutrient availability to collectors.” Ecology 58.4 (1977): 935-938.
9. Lecerf, Antoine, and John S. Richardson. “Assessing the functional importance of largebodied
invertebrates in experimental headwater streams.” Oikos 120.6 (2011): 950-960.
10. Baumann, R. W., A. R. Gaufin, and R. F. Surdick. 1977. The stoneflies (Plecoptera) of
the Rocky Mountains [USA]. Memoirs of the American Entomological Society (USA). no.
11. Needham, J. G., and R. O. Christenson. 1927. Economic insects in some streams of
northern Utah. Bulletin of Utah Agricultural Experiment Station, 201, 1-36.
12. Elder, J. A., and A. R. Gaufin. 1973. Notes on the occurrence and distribution of
Pteronarcys californica Newport (PLECOPTERA) within streams. The Great Basin
13. Richardson, J. W., and A. R. Gaufin. 1971. Food habits of some western stonefly
nymphs. Transactions of the American Entomological Society (1890-), 97(1), 91-121
14. Gaufin, Arden Rupert. “Production of bottom fauna in the Provo River, Utah.” (1951).