The document summarizes a study on the influence of salmon recolonization on riparian communities in the Cedar River in Washington state. After a century without salmon due to a dam, a fish ladder was installed in 2003, allowing salmon to return. The study hypothesizes that increasing salmon biomass inputs would increase the density and diversity of aquatic insects, spider prey, and riparian spiders. Field studies found significant correlations between salmon biomass and increased aquatic insect density, spider prey density, and spider diversity with distance from the dam. The results suggest salmon influence both aquatic and riparian food webs through emergent aquatic insects.

1. The Influence of Salmon Recolonization on Riparian
Communities in the Cedar River, Washington, USA
Abstract ID: 68156; Paper ID: B21D-0480
Jessie A. Moravek1, Hannah L. Clipp2, and Peter M. Kiffney2
1) Northwestern University, Evanston, IL; 2) NOAA Northwest Fisheries Science Center, Seattle, WA
INTRODUCTION / HYPOTHESIS
v
River obstructions that cut salmon off from freshwater spawning grounds reduce
salmon populations and also influence aquatic and riparian ecosystems. Upstream
salmon migration transports marine-derived nutrients into freshwater
environments, which provides an energy-rich food source for aquatic and riparian
food webs. Although many studies focus on the role of salmon in aquatic food
webs, connections between salmon and riparian systems are not well defined. The
2003 installation of a fish ladder in the Cedar River, WA, has allowed salmon to
recolonize the river after a century of absence, and provides a valuable opportunity
to study the effects of salmon on riparian environments.
Hypothesis: Salmon biomass inputs will influence the density and diversity of
aquatic insects, spider prey, and riparian spiders in the Cedar River ecosystem.
Cedar River, WA
 30km southeast of Seattle;
provides drinking water to
1.4 million people
 1901 construction of the
Landsburg Dam prevented
salmon migration for over
a century
 Fish ladder installed in
2003; re-opened the upper
river to Chinook and
Coho salmon.
METHODS
BACKGROUND
SALMON DISTRIBUTION
The relationship is described with the exponential
decay equation y = a-bx, where x is distance from
dam, a is the curve fit parameter for salmon
inputs at 0km, and b is a curve fit parameter that
describes the loss of salmon upstream.
(Kiffney, Peter. Unpublished data. 2015.)
Field Methods
 Salmon: Estimated salmon biomass input
(kg/m2) from salmon carcasses
 Aquatic Insects: Surveyed aquatic insects
in 0.1 m2 quadrats (4 per reach)
 Spider Prey: Collected and identified prey
in spider webs within ten meter transects
(2-4 replicates per reach)
 Spiders: Surveyed and identified spiders
and webs within one meter of water along
ten-meter transects (2-4 per reach)
Data Analysis
 SW diversity, richness, density
 Regression analysis: p < 0.05
AQUATIC - RIPARIAN EXCHANGE
ACKNOWLEDGEMENTS
Thank you to Peter Kiffney, Tom Good, and
Hannah Clipp for field and lab assistance.
This work was funded by the NOAA Hollings
Scholarship Program
CONCLUSION
Photo by Jason Hall
Cedar River Food Web
• Data supports hypothesis that salmon inputs are
significantly correlated with aquatic insect density,
spider prey density, and spider diversity.
• Relationships may also be influenced by physical
factors (stream gradient, water temperature, etc.) or
other food web components (riparian vegetation, etc.)
• Results motivate further investigation of trophic
interactions using stable isotopes.
Jessie Moravek: jessiemoravek2016@u.northwestern.edu
Photo: J.Hall
Salmon influence many aspects of aquatic and riparian food webs. Dark arrows
represent connections between aquatic and riparian systems, and light arrows
represent connections within systems. This study focuses on stream invertebrates,
emergence, and spiders.
(Baxter, C., K. Fausch, and W. Saunders. 2005. Tangled webs: reciprocal flows of invertebrate prey link streams and
riparian zones. Freshwater Biology 50(2):201-220).
y = 0.042(-0.203x)
R2 = 0.90
Linear regressions illustrate significant correlations between taxa. (a) Aquatic
Insect density increased with salmon biomass input, p = 0.01 and R2 = 0.60. (b)
Spider prey density increased with aquatic insect density, p = 0.04 and R2 = 0.59.
(c) Spider diversity decreased with salmon biomass input, p = 0.02 and R2 = 0.69.
Distance from the dam (km)
0 5 10 15 20
Salmonbiomassinput(kg/m
2
)
0.000
0.005
0.010
0.015
0.020
0.025
0.030
y = 0.042(-0.203x)
R2 = 0.90
The process of salmon
recolonization creates a gradient
of salmon biomass input that
decreases with distance from
the dam. The gradient allows us
to compare habitat factors with
different levels of salmon inputs.
Salmon Biomass Input vs.
Distance from Dam
Photo: J.Hall
(a)
(b)
(c)